JP2001027648A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor with high sensitivity, where a piezo- electric device with an excellent packaging used, a high resistance is not mounted on a substrate, and an output voltage to a constant acceleration does not drop until a low frequency area. SOLUTION: A plurality of rectangle piezo-electric crystal layers 41, 42, 43 laminated constitute a vibration part of a piezo-electric device 101. Then, the piezo-electric crystal layers 41, 43 are polarized, and then electrodes are formed on both faces of the layers 41, 43. The electrodes are extended to a connection part and a holding part retaining the vibration part, and are connected to end face electrodes 31, 32, 33 formed on side face of an acceleration sensor. Impedance formed by the piezo-electric layers 41, 43 and the electrodes of the both faces are mutually and electrically connected in parallel. The vibration part vibrates in a vibration space formed by a vibration resin sheet 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an acceleration sensor used for measuring acceleration, detecting vibration, and the like. More specifically, the present invention relates to a small and high-performance acceleration sensor.

[0002]

2. Description of the Related Art In recent years, electronic devices have become smaller, and portable electronic devices such as notebook computers have become widespread. In order to secure and improve the reliability of these electronic devices against impact, there is an increasing demand for high-performance acceleration (shock) sensors that are compact and surface mountable.

For example, if an impact is applied during a writing operation to a high-density hard disk, a head position shift occurs. As a result, there is a possibility that a data write error or damage to the head may occur. Therefore, it is necessary to detect the impact applied to the hard disk, stop the write operation, and retract the head to a safe position.

Further, there is an increasing demand for detecting acceleration for an acceleration sensor for detecting an impact of an airbag device for protecting a passenger from an impact at the time of a collision of an automobile, a suspension control, and the like.

[0005] These acceleration sensors are required to be further reduced in size and weight.

By the way, piezoelectric ceramics can be used as an acceleration sensor because, when a force proportional to acceleration is applied to the piezoelectric ceramics, distortion occurs inside the piezoelectric ceramics, and electric charges are generated on both sides of the piezoelectric ceramics.

FIG. 46 is a view for explaining a conventional piezoelectric acceleration sensor. FIG. 46 (A) is a plan view of a piezoelectric element 150 used for the acceleration sensor, and FIG. 46 (B) is a schematic configuration of the acceleration sensor. FIG. The acceleration sensor has a structure in which a plate-shaped or disk-shaped piezoelectric element 150 and a metal plate 54 are stacked and bonded. Piezoelectric element 1
Reference numeral 50 denotes an electrode 51 and 52 formed on the upper surface of the piezoelectric ceramic and an electrode 53 formed on the lower surface. The electrode 52 is used as a driving electrode during self-diagnosis, and the electrode 51 is used as a detecting electrode. When the laminate of the piezoelectric element 150 and the metal plate 54 is fixed to the support 55 and flexes and vibrates in the vertical direction, charges are generated at the output electrodes.

FIG. 47 shows a general signal processing circuit of a piezoelectric acceleration sensor. Acceleration sensor 56 for measuring acceleration
Uses a source follower circuit using a field effect transistor (hereinafter, FET). In this source follower circuit, the impedance conversion efficiency is large, and the gain of the circuit is almost 0 dB.

In the circuit of FIG. 47, the output frequency range on the low frequency side is the capacitance C11 of the acceleration sensor 56.
And a cut-off frequency determined from a time constant (1 / ωs) of a high-pass filter including a resistor Rh connected in parallel with the acceleration sensor 56. Then, the cutoff frequency fhc of the high-pass filter is obtained by the following [Equation 1].

[0010]

Fhc = 1 / ωs = 1 / (2π · C11 · Rh)

In general, the capacitance of a piezoelectric acceleration sensor depends on its shape. A piezoelectric sensor manufactured using piezoelectric ceramics has a capacitance of several hundred pF. When a chip resistor generally used as the resistor Rh is used as the gate Rh, the resistance is about 1 M to 10 MΩ. Therefore, in the case of a piezoelectric sensor using piezoelectric ceramic, the cutoff frequency is generally about several hundred Hz.

As described above, the lower limit of the measurable frequency of the piezoelectric acceleration sensor is determined by the capacitance of the acceleration sensor and the resistance value connected thereto, and the output decreases on the low frequency side.

Next, the principle of the self-diagnosis will be described below with reference to FIG. A self-diagnosis pulse from a transmitter is applied to the piezoelectric element 150 to the drive electrode 52 for self-diagnosis.
The piezoelectric element vibrates by the self-diagnosis pulse, and the vibration causes the acceleration sensor to vibrate. At that time, a charge corresponding to the magnitude of the vibration is generated in the detection electrode 51,
It is converted to a voltage by a signal processing circuit. If the voltage detected as a result of the vibration generated by the self-diagnosis pulse is different from a predetermined value, the signal processing circuit is configured to diagnose that the acceleration sensor is abnormal and take measures when the abnormality is abnormal. As described above, a function of performing a self-diagnosis of a failure of the acceleration sensor can be added.

[0014]

When an acceleration sensor using a piezoelectric ceramic is used for safety devices such as airbags or to improve riding comfort on rough roads, a characteristic required for low-frequency acceleration detection is as follows. That is, high sensitivity, small pyroelectric effect, and self-diagnosis can be performed.

In general, when the same piezoelectric ceramic is used, the sensitivity is inversely proportional to the thickness of the piezoelectric element. Therefore, in order to increase the sensitivity, the thickness of the piezoelectric element must be reduced as much as possible.

However, the production of thin metal plates and piezoelectric ceramics requires sophisticated techniques and process control.
In addition, when the metal plate and the piezoelectric ceramic are bonded with an adhesive, unevenness in the thickness of the adhesive may cause instability of the output voltage at the time of acceleration detection or cracking of the piezoelectric ceramic due to stress on a specific portion of the piezoelectric ceramic. And so on. In addition, breakage of the piezoelectric ceramic occurs when a temperature is applied due to the difference in linear expansion coefficient between the metal plate and the piezoelectric ceramic. Therefore,
There is a limit to thin piezoceramics, 80 to 10
It is up to about 0 μm.

Further, when the signal processing circuit of the above-mentioned piezoelectric acceleration sensor is used, as described above, there is a problem that the output voltage is reduced for acceleration having a frequency lower than the cutoff frequency.

That is, even when the acceleration of the same magnitude is applied to the acceleration sensor, only a lower voltage is output from the signal processing circuit when the acceleration is a low-frequency acceleration than when the acceleration is a high-frequency acceleration. When such a piezoelectric acceleration sensor and a signal processing circuit are used for a device that detects acceleration or impact at a certain level or more, it is preferable that the sensitivity be less dependent on frequency. For example, in the airbag device, the airbag is set to operate when a certain or more impact is applied. In the case where the signal processing circuit of the impact detection device is the above-described circuit, if the operation is set based on the impact having a frequency higher than the cutoff frequency, the low-frequency impact cannot be detected. On the other hand, if it is set to operate based on the shock at a frequency lower than the cutoff frequency, the airbag is activated by detecting even a small shock that does not need to operate for high frequency shocks There is a problem of letting them do it.

On the other hand, there is a method of reducing the cutoff frequency fhc by increasing the resistance Rh connected in parallel with the acceleration sensor and obtaining a constant output up to a low frequency. However, resistors exceeding 10 MΩ are quite expensive and impractical.

Further, there is a problem that a high resistance cannot be substantially obtained unless special attention is paid to a leakage current between wirings of a mounting board. A member such as a guard ring for preventing leakage current must be provided at the connection terminal of the resistor to the substrate. There is a problem that the leakage current between the wirings of the substrate changes due to a change in environment such as humidity, and the resistance value is apparently reduced.

The signal processing circuit shown in FIG. 47 can be easily formed into an integrated circuit, but it is very difficult to incorporate a resistor Rh having a high resistance of 10 MΩ or more into the integrated circuit with current semiconductor technology. It is. Therefore, in addition to the acceleration sensor and the integrated circuit for signal processing, it is necessary to prepare and mount a high resistance separately, but this increases the number of mounted components, increases the mounting area, and reduces the size of impact detection devices and other devices. Hinders

On the other hand, there is a measure to increase the capacitance C11 of the acceleration sensor. When the material is the same, the capacitance of the piezoelectric acceleration sensor becomes larger as the thickness of the piezoelectric body becomes smaller, and becomes larger as the area becomes larger. However, when the thickness of the piezoelectric body is reduced, in addition to the above-described problems, there is a problem that the mechanical strength is reduced and the piezoelectric body is easily broken, and it is difficult to handle in a process. In addition, when the area is increased, miniaturization becomes difficult. Furthermore, since the shape of the piezoelectric body determines the resonance frequency closely related to the measurement frequency band, there is a problem that the shape of the piezoelectric sensor cannot be easily changed.

Further, when an oscillation pulse is given to the driving electrode by a transmitter for self-diagnosis and the vibration is detected by the vibration detecting electrode by driving at a low frequency, the vibration detecting electrode is used as described above. Is small because the capacitance of the piezoelectric element of the vibration detecting electrode portion is small. Since the vibration detection electrode is not provided on the entire surface of the piezoelectric element, the capacitance is further lower than the capacitance of the entire piezoelectric element. Further, the amount of electric charge generated in the vibration detection electrode also decreases according to the area.

If the output voltage of the vibration detection at a low frequency decreases during the self-diagnosis, the accuracy of the self-diagnosis at a low frequency decreases. Therefore, there is a problem that self-diagnosis cannot be performed accurately in all frequency bands.

In order to perform self-diagnosis, if the electrodes are divided and one is a vibration detecting electrode and the other is a driving electrode, two means such as a wire ring are required for extracting a signal from the electrode. However, there is a problem that the structure becomes complicated and the miniaturization is hindered.

In addition, an acceleration sensor for detecting acceleration by vibration of a piezoelectric body must have a portion for holding the piezoelectric element, and this holding portion allows the detection electrode and the drive electrode to be taken out of the device and to be packaged. However, there is a problem that the sensitivity varies due to the variation of the holding position due to the assembly and bonding for the above.

The present invention has been made in view of the above-mentioned various conventional problems, and the output voltage can be reduced to a low frequency range with a constant acceleration without mounting a high resistance on a substrate. It has high sensitivity without having to do it, has flat output voltage frequency characteristics, can perform self-diagnosis accurately over a wide frequency range, and is easy to assemble for packaging.
It is an object of the present invention to provide a small acceleration sensor with less sensitivity variation.

[0028]

The present invention has the following configuration to achieve the above object.

That is, the acceleration sensor of the present invention has a piezoelectric element formed by stacking a plurality of piezoelectric layers, and the piezoelectric element includes a vibrating section in which a plurality of rectangular piezoelectric layers are stacked; A connecting portion connected to one side of the vibrating portion to hold the vibrating portion; and a holding portion formed integrally with the connecting portion, wherein the vibration of at least two or more piezoelectric layers among the piezoelectric layers is performed. The portion constituting the portion is polarized, electrodes are formed on the upper and lower surfaces of the vibrating portion in the direction of lamination of the polarized piezoelectric layers, and the upper and lower electrodes and the piezoelectric layer between them are formed. Impedances are electrically connected in parallel to each other, the electrodes on the upper and lower surfaces are continuously formed on at least a part of the connection portion and the holding portion, and the electrical connection between the electrode and the outside is the holding portion. Through the electrodes formed in The features.

According to such a configuration, a high capacitance is maintained, a high sensitivity is maintained even at a low frequency, and a self-diagnosis in a low frequency region is also performed accurately without using an electrical connection means such as a wiring. By providing a vibrating part, a connecting part, and a holding part on the piezoelectric element, and holding the piezoelectric element with the holding part, a vibration space can be secured, packaging is easy, and a small acceleration sensor with no variation due to holding is provided. Can be provided.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(First Embodiment) FIG. 1 is an external perspective view of a piezoelectric element used in an acceleration sensor according to a first embodiment of the present invention. The piezoelectric element 101 includes a layer 41, a layer 42, a layer 43
Are laminated.

FIG. 2 shows the piezoelectric element 101 of FIG.
It is a figure showing the name of each part used in the following explanation. The hatched portion in FIG. 2A corresponds to the vibrating section 1 and FIG.
The portion hatched in FIG. 2 is referred to as the connection portion 2, and the portion hatched in FIG.

As shown in FIGS. 1 and 2, the piezoelectric element 101
Has a holding portion 3 having a rectangular planar shape and an opening at the center in the shape of a square, and a vibrating portion 1 having a rectangular planar shape disposed in the opening of the holding portion 3. One short side of the vibrating part 1 is
The holding section 3 is connected to one short side (connection section 2) in a cantilever state. The vibrating unit 1 is disposed substantially at the center of the piezoelectric element 101, vibrates vertically in a space formed in a vertical direction (stacking direction) described later, and functions as a sensor. The connecting portion 2 holds the vibrating portion 1 in a cantilever state and also has a role of drawing out an electrode in the vibrating portion 1 to the holding portion 3 (details will be described later). The connection part 2 forms a part of the holding part 3 and both are integrally formed. The holding section 3 is a section for fixing the piezoelectric element 101 to other components of the acceleration sensor.

FIG. 3 is an exploded perspective view showing the configuration of the acceleration sensor according to the present embodiment. The acceleration sensor of the present embodiment is configured by laminating a resin sheet 5 and an alumina substrate 4 on both sides of a piezoelectric element 101, respectively. The resin sheet 5 has a rectangular planar shape and an opening in the center in a “b” shape, and the planar shape is the holding portion 3 of the piezoelectric element 101.
, And are stacked on the holding unit 3. On the outer surface of the alumina substrate 4, external electrodes 21, 22, 23 are formed of a silver-palladium alloy. By laminating the alumina substrate 4 via the resin sheet 5 having an opening,
Vibration spaces are secured above and below the vibrating part 1 of the piezoelectric element 101.

Each of the layers 41, 42 and 43 of the piezoelectric element 101 is made of a sheet-like ceramic mainly composed of lead zirconate titanate. The thickness of each layer is from 10 μm to 80
About μm (particularly 50 μm) is suitable. It is manufactured by laminating and firing a sheet-shaped ceramic green sheet. For this reason, each layer can be made thinner as compared with the case where a piezoelectric ceramic plate is bonded, and the capacitance of each layer increases.

On the upper surface of the layer 41, two electrodes 11a and 12a are formed separately. Both are divided by a margin portion parallel to the long side direction of the rectangular vibrating portion 1 and provided in parallel to the long side direction of the vibrating portion 1 (that is, substantially perpendicular to the connection portion 2). Although not shown in the drawing, the electrode 13a is provided between the layer 41 and the layer 42, the electrode 11b and the electrode 12b are provided between the layer 42 and the layer 43, and the electrode 13a is provided on the bottom of the layer 43.
b are formed respectively.

FIG. 4 shows the electrode 11 of the piezoelectric element 101 of FIG.
It is sectional drawing in the lamination direction in XX 'line parallel to the long side direction which passes a part. FIG. 5 is a plan view showing the shape of each electrode. FIG. 5A shows an electrode 11a formed on the layer 41,
12B, FIG. 5B shows an electrode 13a formed between the layer 41 and the layer 42, and FIG.
FIG. 5 shows electrodes 11b and 12b formed between
(D) shows the electrode 13b formed on the lower surface of the layer 43.

The electrode 11 formed between the layers 42 and 43
b and 12b are electrodes 11a and 1 provided on the surface of the layer 41.
The shape is almost the same as 2a. The electrode 13a and the electrode 1
3b is also formed in substantially the same shape. Electrodes 13a, 13b
Are electrodes 11a and 12a and electrodes 11b and 12b, respectively.
Is formed over the entire surface of the vibrating portion so as to face the vibration portion.

The electrodes 11a, 11b, 12a, 12b
The piezoelectric element 101 is formed up to the end on the connection portion 2 side (the left side in FIG. 5), and as a result, is exposed on the outer peripheral side surface of the piezoelectric element 101. On the other hand, the electrodes 13a and 13b
1 is formed up to the end opposite to the connection portion 2 (right side in FIG. 5), and as a result, is exposed on the outer peripheral side surface of the piezoelectric element 101. In addition, the electrodes 13a and 13b are not formed up to the end on the connection portion 2 side (the left side in FIG. 5) of the piezoelectric element 101, and are slightly receded from the end. This is to prevent a short circuit with the end electrodes 31 and 32 described later.

Each of these electrodes can be formed of, for example, a silver-palladium alloy, and preferably has a thickness of about 0.1 μm to 5 μm.

The layers 41 and 43 are polarized, and the directions of polarization 40 are opposite to each other as shown in FIG. Layer 4
2 is not polarized.

FIG. 6 is a sectional view of the acceleration sensor according to the present embodiment in the stacking direction. As described with reference to FIG. 3, the resin sheets 5 are stacked above and below the holding unit 3 of the piezoelectric element 101,
Further, the alumina substrate 4 on which the external electrodes 21, 22, 23 are formed is laminated. End face electrodes 31, 32, and 33 formed by sputtering are formed on the end faces in the longitudinal direction. The end face electrode 31 is connected to the electrodes 11a and 11b exposed on the outer peripheral side of the piezoelectric element 101 and the external electrode 21, and the end face electrode 32 is connected to the electrodes 12a and 12b exposed on the outer peripheral side of the piezoelectric element 101 and the external electrode 22. The end electrode 33 is connected to the electrodes 13 a and 13 b exposed on the outer peripheral side surface of the piezoelectric element 101 and the external electrode 23. As a result, the electric charge generated by the acceleration can be taken out to the external electrodes 21, 22, 23 on the alumina substrate 4, and can be taken out of the acceleration sensor.

By connecting the electrodes as described above, the layers 41 and 43 are all electrically connected in parallel. Therefore, the capacitance of the entire piezoelectric element is a value obtained by adding the capacitance of each layer. Since the layers are superimposed, each layer can be formed as a thin layer while maintaining a predetermined strength as a whole. Therefore, the capacitance of each layer can be increased. Moreover, since the total capacitance is a value obtained by adding the capacitances of the respective layers, it is possible to obtain a larger capacitance than a single-layer piezoelectric element having the same thickness and area. In other words, the same capacitance can be realized by a piezoelectric element having a small area.

Since the rectangular vibration part 1 is fixed to the connection part 2 in a cantilever state, it is necessary to mount the acceleration sensor so that the main surface of the vibration part 1 is orthogonal to the direction of the acceleration to be detected. There is. That is, when detecting acceleration in a direction parallel to the board on which the acceleration sensor is mounted, the acceleration sensor (piezoelectric element) must be arranged substantially vertically on the mounting board. That is, the electrode surface of the piezoelectric element 101 must be substantially perpendicular to the mounting substrate. In the case of a rectangular piezoelectric element, even if the piezoelectric element is mounted vertically, the height of the acceleration sensor does not increase, so that a small acceleration sensor can be realized.

FIG. 7 is a schematic sectional view in the stacking direction showing the principle of operation of the acceleration sensor. When the acceleration 60 is applied in the vertical direction in FIG. 7, the vibrating portion of the piezoelectric element 101 performs flexural vibration as shown in FIG. At this time, the layers 41, 42, 43
Of the two layers 41 and 43 on the surface side, one is elongated and the other is shrunk so as to shrink. In the state shown in FIG. 7, the layer 41 expands and the layer 43 contracts, and the distortion causes electric charges.
Since the polarization directions 40 of the layers 41 and 43 are opposite, charges of the same polarity are obtained at the electrodes 11a and 12a and the electrodes 11b and 12b, and charges of the same polarity are obtained at the electrodes 13a and 13b. Further, since the electrodes are connected in parallel as described above, the charges generated in the layers 41 and 43 are added, and a large amount of charges can be obtained.

Although the front and back surfaces of the piezoelectric element are greatly distorted, in this embodiment, the sensitivity can be increased because the polarized piezoelectric layer is provided there.

FIG. 8 is a block diagram of an acceleration detecting device when the self-diagnosis function of the acceleration sensor according to the present embodiment is performed. At the time of self-diagnosis, the electrodes 12a and 12b are used as driving electrodes, and the electrodes 11a and 11b are used as vibration detecting electrodes. The external electrode 22 is connected to a drive circuit 6a for driving a vibration for self-diagnosis. A drive AC voltage is generated from the drive circuit 6a,
The voltage is applied to electrodes 12a and 12b and electrodes 13a and 13b, which are driving electrodes of the piezoelectric element. This AC voltage causes layer 4
1. An electric field is generated inside the layer 43. Although the electric field is applied in the same direction, the polarization direction is different, so that distortion is generated in the opposite direction, and the entire piezoelectric element performs flexural vibration. As described above, electric charges are generated by this vibration, and this is detected by the electrodes 11a and 11b and the electrodes 13a and 13b, which are the electrodes for detecting vibration. The detected charges are input to the impedance conversion circuit 6b through the external electrodes 21 and 23. The impedance conversion circuit 6b is generally configured using an FET or the like as shown in FIG. This impedance conversion circuit 6
The output voltage from b is the acceleration detection circuit / abnormality detection circuit 6
c, where it is determined whether there is any abnormality in the piezoelectric element. In general, the abnormality detection circuit 6c includes a high-pass filter, a low-pass filter, a smoothing circuit, a comparator, and the like. The abnormality diagnosis is performed by determining whether a voltage that matches a predetermined value is output from the impedance conversion circuit 6b with respect to the AC voltage input from the drive circuit 6a. When there is an abnormality in the piezoelectric element, the abnormality detection circuit 6c issues an instruction to perform a process at the time of abnormality.

Since the driving electrodes 12a and 12b are laminated, each layer is thin and the electric field is large, a large amplitude flexural vibration can be obtained only by inputting a small amplitude AC voltage from the driving circuit 6a. The accuracy of the self-diagnosis is improved.

The vibration detecting electrodes 11a and 11b are also laminated, so that the capacitance can be increased.
The vibration induced by the drive circuit 6a can be detected with high sensitivity up to a low frequency region without using a high resistance for the impedance conversion circuit 6b, and highly accurate self-diagnosis can be performed in a wide frequency range.

Even during normal acceleration detection, since the piezoelectric element 101 is formed by stacking thin layers and connecting the layers in parallel, the capacitance of the entire piezoelectric element increases. In addition, each layer serving as a detection element can be thinned without impairing the mechanical strength of the entire piezoelectric element. Therefore, a sufficiently high sensitivity can be obtained even at a low-frequency acceleration,
It can be measured without using high resistance.

At the time of normal acceleration detection, the driving electrode 12
A higher sensitivity can be obtained by using both the electrodes a and 12b and the electrodes 11a and 11b for vibration detection as electrodes for acceleration detection and connecting them to the impedance conversion circuit 6b.

Although the layer 42 is not polarized, by providing this layer, the strength of the entire piezoelectric element can be maintained even if the layers 41 and 43 are extremely thin. The layer 42 also has the effect of increasing the capacitance.

The self-diagnosis circuit and the impedance conversion circuit are not limited to those shown in FIGS.

The polarization direction 40 of the layers 41 and 43 is not limited to the illustrated direction, but may be any direction as long as they are opposite to each other.

The electrodes 11a and 11b may be used as driving electrodes, and the electrodes 12a and 12b may be used as vibration detecting electrodes.

The layers 41, 42 and 43 are not limited to those containing lead zirconate titanate as a main component, but may be those containing lead titanate, lead zirconate, lead lanthanate or the like as a main component. Although the thicknesses of the layers do not all need to be the same, it is preferable that the layers 41 and 43 have substantially the same thickness. Layer 42 may be thicker than the other layers, in which case
Contributes to improved impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, and 13b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate thereof, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

The number of layers of the piezoelectric element 101 is not limited to three, and the number of layers may be further increased. In this case, electrodes may be connected every other layer at the end face or the like.

In the above example, the vibration space of the vibrating section 1 is secured by laminating the resin sheets 5, but the means for securing the vibration space is not limited to this. For example, without laminating the resin sheet 5, a concave portion having a predetermined depth may be formed in a region on the surface of the substrate 4 on the side of the piezoelectric element 101 which is not opposed to the holding portion 3 so that the vibrating portion 1 can vibrate. .

As described above, it is possible to have high capacitance, maintain high sensitivity even at a low frequency, and perform a self-diagnosis at a low frequency range with high accuracy without using an electrical connection means such as wiring. By providing a vibrating part, a connecting part, and a holding part on the piezoelectric element, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging is easy, and a small acceleration sensor without variation due to holding can be realized. .

(Embodiment 2) FIG. 9 is a sectional view in the stacking direction of a piezoelectric element used for an acceleration sensor according to Embodiment 2 of the present invention.

The piezoelectric element 102 of the present embodiment has the layers 41, 42, 43 similar to the piezoelectric element 101 of the first embodiment.
Are laminated, and their external shape is almost the same as that of the piezoelectric element 101 shown in FIG. Piezoelectric element 1 of the present embodiment
Also in 02, a rectangular vibrating part is held in a cantilever state in the opening of the holding part whose central part is opened in a “B” shape. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

In the piezoelectric element 102 of the present embodiment, the layer 41
The layer 43 is polarized, but the polarization direction 40 is the same as in the first embodiment.

FIG. 10 is a plan view showing the shape of each electrode. FIG. 10A shows an electrode 11a formed on the layer 41,
10B shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 10C shows an electrode 13b formed between the layer 42 and the layer 43, and FIG. (D)
Indicates electrodes 11b and 12b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

Electrodes 11a, 11b, 12a, 12b, 1
Although the shapes of 3a and 13b are the same as those of the first embodiment, the locations where the electrodes are formed are different from those of the first embodiment. That is, in this embodiment, the electrode 1 is provided between the layer 42 and the layer 43.
3b, and electrodes 11b and 12b are formed on the lower surface of the layer 43.

The assembly of the sensor is the same as that of the first embodiment shown in FIG.

As in the first embodiment, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. The electrode 33 is the electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

Although the polarization direction 40 of the layer 41 and the layer 43 is the same, the electrodes on the front and back of the layer 43 are opposite to those of the first embodiment.
a and electric charges of the same polarity are obtained on the electrodes 11b and 12b,
In addition, charges of the same polarity are obtained on the electrodes 13a and 13b. As a result, the acceleration can be detected.

In the case of self-diagnosis, the electrodes 11a, 11a
8 can be performed in the same manner as in FIG. 8, where b is a vibration detecting electrode and the electrodes 12a and 12b are driving electrodes. The electrodes 11a and 11b are used as driving electrodes, and the electrodes 12a and 12b are
b may be a vibration detection electrode.

Embodiment 1 also takes out electric charges from the electrodes.
Can be performed in the same manner.

The polarization direction 40 of the layers 41 and 43 is not limited to the illustrated direction, but may be the same as each other.

The layers 41, 42, and 43 are not limited to those containing lead zirconate titanate as a main component, but may contain lead titanate, lead zirconate, lead lanthanate, or the like as a main component. Although the thicknesses of the layers do not all need to be the same, it is preferable that the layers 41 and 43 have substantially the same thickness. Layer 42 may be thicker than the other layers, in which case
Contributes to improved impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, and 13b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate thereof, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

The number of layers of the piezoelectric element 102 is not limited to three, and the number of layers may be further increased. In this case, electrodes may be connected every other layer at the end face or the like.

In the above example, the resin sheet 5 is laminated to secure the vibration space of the vibration section 1, but the means for securing the vibration space is not limited to this. For example, without laminating the resin sheet 5, a concave portion having a predetermined depth may be formed in a region of the surface of the substrate 4 on the side of the piezoelectric element 102 which is not opposed to the holding portion 3 so that the vibrating portion 1 can vibrate. .

As described above, it is possible to have high capacitance, maintain high sensitivity even at a low frequency, and perform a self-diagnosis at a low frequency range with high accuracy without using an electrical connection means such as wiring. By providing the piezoelectric element with a vibrating part, a connecting part, and a holding part, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging can be easily performed, and a small acceleration sensor without variation due to holding can be realized.

(Embodiment 3) FIG. 11 is a sectional view in the stacking direction of a piezoelectric element used for an acceleration sensor according to Embodiment 3 of the present invention.

The piezoelectric element 103 according to the present embodiment has the layers 41, 42, 43 similar to the piezoelectric element 101 according to the first embodiment.
Are laminated, and their external shape is almost the same as that of the piezoelectric element 101 shown in FIG. Piezoelectric element 1 of the present embodiment
Also in 03, a rectangular vibrating part is held in a cantilever state in the opening of the holding part whose central part is opened in a “B” shape. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

In the piezoelectric element 103 of the present embodiment, the layer 41
And the layer 43 are polarized, and the polarization direction 40 is the opposite direction as in the first embodiment.

FIG. 12 is a plan view showing the shape of each electrode. FIG. 12A shows an electrode 11a formed on the layer 41,
12B, FIG. 12B shows an electrode 13a formed between the layer 41 and the layer 42, and FIG. 12C shows electrodes 11b and 12b formed between the layer 42 and the layer 43; FIG.
2 (D) shows the electrode 13b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

The electrodes 11a and 11b are formed in a region closer to the connecting portion 2 from a substantially central portion in the longitudinal direction of the vibrating portion 1 and
a and 12b are connected from the substantially central portion in the longitudinal direction of the vibrating portion 1 to the connecting portion 2
Are formed in a region on the opposite side (closer to the tip of the cantilever). The electrodes 11a and 11b are formed up to the end of the piezoelectric element 103 on the connection portion 2 side (the left side in FIG. 12), and as a result, are exposed on the outer peripheral side surface of the piezoelectric element 103. Similarly, the electrodes 12a and 12b are drawn out to the end on the connection portion 2 side (left side in FIG. 12) of the piezoelectric element 103 in the long side direction of the vibrating portion 1, and as a result, are exposed on the outer peripheral side surface of the piezoelectric element 103. ing. The electrodes 13 a and 13 b have the same shape as that of the first embodiment, and
The side (the left side in FIG. 12) is not formed up to the end, but is formed slightly receding from the end.

The assembling of the sensor is the same as that of the first embodiment shown in FIG.

As in the first embodiment, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. The electrode 33 is the electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The polarization direction 40 of the layer 41 and the layer 43 is opposite to each other, and the lamination order and connection method of each electrode are the same as in the first embodiment.
Charges of the same polarity are obtained on the electrodes a and 12a and the electrodes 11b and 12b, and charges of the same polarity are obtained on the electrodes 13a and 13b. As a result, the acceleration can be detected.

In the case of self-diagnosis, the electrodes 11a, 11
8 can be performed in the same manner as in FIG. 8, where b is a vibration detecting electrode and the electrodes 12a and 12b are driving electrodes.

Embodiment 1 also takes out electric charges from the electrodes.
Can be performed in the same manner.

The direction of polarization 40 of the layers 41 and 43 is not limited to the direction shown in FIG.

FIG. 13 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the second embodiment of the present invention.

The piezoelectric element 104 shown in FIG.
Like the piezoelectric element 103, the layers 41, 42, and 43 are laminated, and the external shape thereof is the same as that of the piezoelectric element 10 shown in FIG.
It is almost the same as 1. Also in the piezoelectric element 104 of the present example, in the opening of the holding portion whose central portion is opened in the shape of “b”,
The rectangular vibrating part is held in a cantilever state. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

Although the layers 41 and 43 of the piezoelectric element 104 are polarized, the polarization direction 40 is the same as that of the piezoelectric element 103.

FIG. 14 is a plan view showing the shape of each electrode. FIG. 14A shows an electrode 11a formed on the layer 41,
14B shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 14C shows an electrode 13b formed between the layer 42 and the layer 43, and FIG. (D)
Indicates electrodes 11b and 12b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

Electrodes 11a, 11b, 12a, 12b, 1
Although the shapes of 3a and 13b are the same as those of the piezoelectric element 103, the locations of the electrodes are different from those of the piezoelectric element 103.
That is, in the piezoelectric element 104 of this example, the layers 42 and 43
The electrode 13b is formed between
b and 12b are formed.

The assembling of the sensor is the same as that of the piezoelectric element 103.

Similarly to the piezoelectric element 103, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. 33 to electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

Although the polarization direction 40 of the layer 41 and the layer 43 is the same, the electrodes on the front and back of the layer 43 are opposite to those of the piezoelectric element 103. Therefore, when the vibrating portion undergoes flexural vibration, the electrodes 11a, 1
Electric charges of the same polarity are obtained at 2a and the electrodes 11b and 12b, and electric charges of the same polarity are obtained at the electrodes 13a and 13b. As a result, the acceleration can be detected.

The self-diagnosis function and the extraction of charges from the electrodes are the same as in the case of the piezoelectric element 103.

Note that the direction of polarization 40 of the layers 41 and 43 is not limited to the direction shown in FIG.

In the piezoelectric elements 103 and 104, each layer 4
1, 42 and 43 are not limited to those containing lead zirconate titanate as a main component, but lead titanate, lead zirconate,
A material containing lead lanthanate or the like as a main component may be used. Although the thicknesses of the layers do not all need to be the same, it is preferable that the layers 41 and 43 have substantially the same thickness. The layer 42 may be thicker than the other layers, in which case it contributes to improved impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, and 13b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate thereof, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element are
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

Note that the number of layers of the piezoelectric elements 103 and 104 is not limited to three, and the number of layers may be further increased. In such a case, electrodes may be connected every other layer at an end face or the like.

In the above example, the resin sheet 5 is laminated to secure the vibration space of the vibration section 1, but the means for securing the vibration space is not limited to this. For example, without laminating the resin sheet 5, a concave portion having a predetermined depth is formed in a region of the surface of the substrate 4 on the side of the piezoelectric elements 103 and 104 that does not face the holding portion 3 so that the vibrating portion 1 can vibrate. Is also good.

As described above, it is possible to maintain a high capacitance, maintain a high sensitivity even at a low frequency, and perform a self-diagnosis at a low frequency range with high accuracy without using an electrical connection means such as wiring. By providing the piezoelectric element with a vibrating part, a connecting part, and a holding part, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging can be easily performed, and a small acceleration sensor without variation due to holding can be realized.

(Embodiment 4) FIG. 15 is an external perspective view of a piezoelectric element used for an acceleration sensor according to Embodiment 4 of the present invention. The piezoelectric element 105 includes a layer 41, a layer 42, a layer 4
3 are laminated.

FIG. 16 is a diagram showing names of respective parts used in the following description of the piezoelectric element 105 of FIG. In FIG. 16 (A), the hatched portion is the vibrating portion 1, and in FIG. 16 (B), the hatched portion is the connecting portion 2, and FIG.
The portions hatched in (C) are referred to as holding portions 3 respectively.

As shown in FIGS. 15 and 16, the piezoelectric element 10
Reference numeral 5 denotes a holding section 3 having two rectangular openings having a rectangular shape in plan view, and a vibrating section 1 having a rectangular flat shape disposed in each opening of the holding section 3. One short side of the vibrating portion 1 is connected in a cantilever manner to a bridge portion (connecting portion 2) between two openings of the holding portion 3. The two vibrating parts 1
It is arranged substantially at the center of the piezoelectric element 105 and vibrates up and down in a space formed in a vertical direction (stacking direction) described later, and functions as a sensor. The connecting portion 2 holds the vibrating portion 1 on both sides in a cantilever state, and
It also has a role of pulling out the inner electrode to the holding section 3 (details will be described later). The connection part 2 forms a part of the holding part 3 and both are integrally formed. The holding section 3 is a section for fixing the piezoelectric element 105 to other components of the acceleration sensor.

FIG. 17 is an exploded perspective view showing the configuration of the acceleration sensor according to the present embodiment. The acceleration sensor of the present embodiment is configured by laminating a resin sheet 5 and an alumina substrate 4 on both sides of a piezoelectric element 105, respectively. The resin sheet 5 has two rectangular openings in a rectangular shape when viewed in plan.
The planar shape is substantially the same as the holding portion 3 of the piezoelectric element 105, and is stacked on the holding portion 3. On the outer surface of the alumina substrate 4, external electrodes 21, 22, 23 are formed of a silver-palladium alloy. By laminating the alumina substrate 4 via the resin sheet 5 having an opening, a vibration space is secured above and below the vibration part 1 of the piezoelectric element 105.

Each of the layers 41, 42 and 43 of the piezoelectric element 105 is made of a sheet-like ceramic mainly composed of lead zirconate titanate. The thickness of each layer is from 10 μm to 80
About μm (particularly 50 μm) is suitable. It is manufactured by laminating and firing a sheet-shaped ceramic green sheet. For this reason, each layer can be made thinner as compared with the case where a piezoelectric ceramic plate is bonded, and the capacitance of each layer increases.

On the upper surface of the layer 41, two electrodes 11a and 12a are formed separately. Both are divided by a margin portion parallel to the long side direction of the piezoelectric element, and continuously extend in parallel with the long side direction (ie, substantially orthogonal to the connection portion 2) over the two vibrating portions 1 and the connection portion 2 therebetween. So). Although not shown in the figure, the electrode 13a is formed between the layers 41 and 42, the electrodes 11b and 12b are formed between the layers 42 and 43, and the electrode 13b is formed on the bottom surface of the layer 43.

FIG. 18 is a sectional view taken along the line XX ′ parallel to the long side direction passing through the electrode 11a of the piezoelectric element 105 in FIG. FIG. 19 is a plan view showing the shape of each electrode. FIG. 19A shows the electrodes 11a and 12a formed on the layer 41, and FIG.
19 (C) shows the electrodes 11b and 12b formed between the layers 42 and 43, and FIG. 19 (D) shows the electrodes formed on the lower surface of the layer 43. 13
b.

Electrode 11 formed between layers 42 and 43
b and 12b are electrodes 11a and 1 provided on the surface of the layer 41.
The shape is almost the same as 2a. The electrode 13a and the electrode 1
3b is also formed in substantially the same shape. Electrodes 13a, 13b
Are electrodes 11a and 12a and electrodes 11b and 12b, respectively.
Is formed over the entire surface of both the vibrating portion and the connecting portion so as to face.

The electrodes 11a, 11b, 12a, 12b are
One side of the holding unit via the connection 2 of the piezoelectric element 105 (FIG. 1)
9 is formed on the left side (short side on the left side), and as a result, is exposed on the outer peripheral side surface of the piezoelectric element 105. On the other hand, the electrode 13
a and 13b are formed up to the end of the other side (short side on the right side in FIG. 19) of the holding part via the connection part 2 of the piezoelectric element 105, and as a result, are exposed to the outer peripheral side surface of the piezoelectric element 105. I have.

Each of these electrodes can be formed of, for example, a silver-palladium alloy, and preferably has a thickness of about 0.1 μm to 5 μm.

The layers 41 and 43 are polarized.
As shown in FIG. 7, the directions of polarization 40 are opposite to each other. Layer 42 is not polarized.

Similarly to the first embodiment, end face electrodes 31 and 32 are formed on opposing outer peripheral side faces, electrodes 11 a and 11 b and external electrode 21 are connected to each other by end face electrode 31, and electrode 12 a is formed by end face electrode 32. , 12b and the external electrode 22 are interconnected, and the electrodes 13a, 13
b and the external electrodes 23 are mutually connected. As a result, layer 4
1 and the layer 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

By connecting the electrodes as described above, the layers 41 and 43 are all electrically connected in parallel. Therefore, the capacitance of the entire piezoelectric element is a value obtained by adding the capacitance of each layer. Since the layers are superimposed, each layer can be formed as a thin layer while maintaining a predetermined strength as a whole. Therefore, the capacitance of each layer can be increased. Moreover, since the total capacitance is a value obtained by adding the capacitances of the respective layers, it is possible to obtain a larger capacitance than a single-layer piezoelectric element having the same thickness and area. In other words, the same capacitance can be realized by a piezoelectric element having a small area.

The polarization directions of the layers 41 and 43 are opposite to each other, and the connection method of the electrodes is the same as that of the first embodiment.
Due to the flexural vibration of the vibrating section 1, charges of the same polarity are obtained on the electrodes 11a and 12a and the electrodes 11b and 12b, and charges of the same polarity are obtained on the electrodes 13a and 13b. As a result, the acceleration can be detected.

In the case of self-diagnosis, the electrodes 11a, 11a
8 can be performed in the same manner as in FIG. 8, where b is a vibration detecting electrode and the electrodes 12a and 12b are driving electrodes. The electrodes 11a and 11b are used as driving electrodes, and the electrodes 12a and 12b are
b may be a vibration detection electrode.

Embodiment 1 also takes out electric charges from the electrodes.
Can be performed in the same manner.

The direction of polarization 40 of the layers 41 and 43 is not limited to the direction shown in FIG.

FIG. 20 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the fourth embodiment of the present invention.

The piezoelectric element 106 shown in FIG.
Similarly to the piezoelectric element 105, the layers 41, 42, and 43 are laminated, and the external shape thereof is the piezoelectric element 1 shown in FIG.
It is almost the same as 05. Piezoelectric element 106 of the present embodiment
In this case, a rectangular vibrating portion is held in a cantilever state in each of the openings of the holding portion having two “b” -shaped openings. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

Although the layers 41 and 43 of the piezoelectric element 106 are polarized, the polarization direction 40 thereof is the same as that of the piezoelectric element 105.

FIG. 21 is a plan view showing the shape of each electrode. FIG. 21A shows an electrode 11a formed on the layer 41,
FIG. 21B shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 21C shows an electrode 13b formed between the layer 42 and the layer 43, and FIG. (D)
Indicates electrodes 11b and 12b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

Electrodes 11a, 11b, 12a, 12b, 1
Although the shapes of 3a and 13b are the same as those of the piezoelectric element 105, the locations where the electrodes are formed are different from those of the piezoelectric element 105.
That is, in the piezoelectric element 106 of this example, the layers 42 and 43
The electrode 13b is formed between
b and 12b are formed.

The assembling of the sensor is the same as that of the piezoelectric element 105.

Similarly to the piezoelectric element 105, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. 33 to electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

Although the polarization direction 40 of the layer 41 and the layer 43 is the same, the electrodes on the front and back of the layer 43 are opposite to those of the piezoelectric element 105. Therefore, when the vibrating portion flexes and vibrates, the electrodes 11a, 1
Electric charges of the same polarity are obtained at 2a and the electrodes 11b and 12b, and electric charges of the same polarity are obtained at the electrodes 13a and 13b. As a result, the acceleration can be detected.

The self-diagnosis function and the extraction of charges from the electrodes are the same as those of the piezoelectric element 105.

The polarization direction 40 of the layers 41 and 43 is not limited to the direction shown in FIG. 21, but may be the same as each other.

In the piezoelectric elements 105 and 106, each layer 4
1, 42 and 43 are not limited to those containing lead zirconate titanate as a main component, but lead titanate, lead zirconate,
A material containing lead lanthanate or the like as a main component may be used. Although the thicknesses of the layers do not all need to be the same, it is preferable that the layers 41 and 43 have substantially the same thickness. The layer 42 may be thicker than the other layers, in which case it contributes to improved impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, and 13b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate thereof, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element are
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

Note that the number of layers of the piezoelectric elements 105 and 106 is not limited to three, and the number of layers may be further increased. In such a case, electrodes may be connected every other layer at an end face or the like.

In the above example, the resin sheet 5 is laminated to secure the vibration space of the vibrating section 1, but the means for securing the vibration space is not limited to this. For example, without laminating the resin sheet 5, a concave portion having a predetermined depth is formed in a region of the surface of the substrate 4 on the side of the piezoelectric elements 105 and 106 that does not face the holding portion 3 so that the vibrating portion 1 can vibrate. Is also good.

As described above, it is possible to have a high capacitance, maintain a high sensitivity even at a low frequency, and accurately perform a self-diagnosis in a low frequency region without using an electrical connection means such as a wiring. By providing the piezoelectric element with a vibrating part, a connecting part, and a holding part, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging can be easily performed, and a small acceleration sensor without variation due to holding can be realized.

(Embodiment 5) FIG. 22 is a sectional view in the stacking direction of a piezoelectric element used in an acceleration sensor according to Embodiment 5 of the present invention.

The piezoelectric element 107 according to the present embodiment has the layers 41, 42, 43 similar to the piezoelectric element 105 according to the fourth embodiment.
Are laminated, and their external shape is almost the same as the piezoelectric element 105 shown in FIG. 15 except for the electrode shape. Also in the piezoelectric element 107 of the present embodiment, a rectangular vibrating portion is held in a cantilever manner in each opening of the holding portion having two “b” -shaped openings. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

In the piezoelectric element 107 of the present embodiment, the layer 41
And the layer 43 are polarized, and the polarization direction 40 is the opposite direction as in the piezoelectric element 105 of the fourth embodiment.

FIG. 23 is a plan view showing the shape of each electrode. FIG. 23A shows an electrode 11a formed on the layer 41,
FIG. 23B shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 23C shows electrodes 11b and 12b formed between the layer 42 and the layer 43, FIG.
3 (D) shows the electrode 13b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

The electrodes 11a and 11b are provided on one vibrating portion side.
The electrodes 12a and 12b are formed on the other vibrating portion side so as to be insulated so as not to enter the other vibrating portion. The electrodes 11a and 11b are connected to one side of the connection 2 (FIG. 2).
3 and the electrodes 12a and 12b are connected to one side (the left side of FIG. 23) of the holding portion 3 of the piezoelectric element 107 via the other side of the connection portion 2 (the lower side of FIG. 23). (Short side) is formed, and as a result, it is exposed on the outer peripheral side surface of the piezoelectric element 107. The electrodes 13a and 13b have the same shape as that of the fourth embodiment, and the other side (short side on the right side in FIG. 23) of the holding section via the connection section 2 of the piezoelectric element 107.
, And as a result, is exposed on the outer peripheral side surface of the piezoelectric element 107.

The assembly of the sensor is the same as that of the fourth embodiment shown in FIG.

As in the fourth embodiment, the electrodes 11a and 11b are connected to the external electrode 21 by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. The electrode 33 is the electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The polarization directions 40 of the layers 41 and 43 are opposite to each other, and the lamination order and connection method of each electrode are the same as those of the piezoelectric element 105 of the fourth embodiment. 11a, 12a and the electrodes 11b, 12b have the same polarity, and the electrodes 13a, 13b
And a charge of the same polarity is obtained. As a result, the acceleration can be detected.

In the case of self-diagnosis, the electrodes 11a, 11
8 can be performed in the same manner as in FIG. 8, where b is a vibration detecting electrode and the electrodes 12a and 12b are driving electrodes. The electrodes 11a and 11b are used as driving electrodes, and the electrodes 12a and 12b are
b may be a vibration detection electrode.

Embodiment 4 also takes out electric charges from the electrodes.
Can be performed in the same manner.

The polarization direction 40 of the layers 41 and 43 is not limited to the direction shown in FIG.

FIG. 24 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the fifth embodiment of the present invention.

The piezoelectric element 108 shown in FIG.
Like the piezoelectric element 107, the layers 41, 42, and 43 are laminated, and the appearance is almost the same as the piezoelectric element 105 shown in FIG. 15 except for the electrode shape. Also in the piezoelectric element 108 of this example, a rectangular vibrating part is held in a cantilever state in each of the openings of the holding part having two “b” -shaped openings. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

Although the layers 41 and 43 of the piezoelectric element 108 are polarized, the polarization direction 40 thereof is the same as that of the piezoelectric element 107.

FIG. 25 is a plan view showing the shape of each electrode. FIG. 25A shows an electrode 11a formed on the layer 41,
FIG. 25 (B) shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 25 (C) shows an electrode 13b formed between the layer 42 and the layer 43, and FIG. (D)
Indicates electrodes 11b and 12b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

Electrodes 11a, 11b, 12a, 12b, 1
The shapes of 3a and 13b are the same as those of the piezoelectric element 107, but the positions where the electrodes are formed are different from those of the piezoelectric element 107.
That is, in the piezoelectric element 108 of this example, the layers 42 and 43
The electrode 13b is formed between
b and 12b are formed.

The assembling of the sensor is the same as that of the piezoelectric element 107.

Similarly to the piezoelectric element 107, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. 33 to electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The polarization direction 40 of the layer 41 is the same as that of the layer 43. However, since the electrodes on the front and back of the layer 43 are opposite to the piezoelectric element 107, the electrodes 11a, 1
Electric charges of the same polarity are obtained at 2a and the electrodes 11b and 12b, and electric charges of the same polarity are obtained at the electrodes 13a and 13b. As a result, the acceleration can be detected.

The self-diagnosis function and the extraction of charges from the electrodes are the same as in the case of the piezoelectric element 107.

The polarization direction 40 of the layers 41 and 43 is not limited to the direction shown in FIG. 24, but may be the same as each other.

In each of the piezoelectric elements 107 and 108, each layer 4
1, 42 and 43 are not limited to those containing lead zirconate titanate as a main component, but lead titanate, lead zirconate,
A material containing lead lanthanate or the like as a main component may be used. Although the thicknesses of the layers do not all need to be the same, it is preferable that the layers 41 and 43 have substantially the same thickness. The layer 42 may be thicker than the other layers, in which case it contributes to improved impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, and 13b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate thereof, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

Note that the number of layers of the piezoelectric elements 107 and 108 is not limited to three, and the number of layers may be further increased. In this case, electrodes may be connected every other layer at an end face or the like.

In the above example, the resin sheet 5 is laminated to secure the vibration space of the vibration section 1, but the means for securing the vibration space is not limited to this. For example, a concave portion having a predetermined depth is formed in a region not facing the holding portion 3 on the surface of the substrate 4 on the side of the piezoelectric elements 107 and 108 without laminating the resin sheet 5 so that the vibrating portion 1 can vibrate. Is also good.

As described above, it is possible to maintain a high capacitance, maintain a high sensitivity even at a low frequency, and accurately perform a self-diagnosis in a low frequency region without using an electrical connection means such as wiring. By providing the piezoelectric element with a vibrating part, a connecting part, and a holding part, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging can be easily performed, and a small acceleration sensor without variation due to holding can be realized.

(Embodiment 6) FIG. 26 is an external perspective view of a piezoelectric element used for an acceleration sensor according to Embodiment 6 of the present invention. FIG. 27 shows the piezoelectric element 109 of FIG.
FIG. 5 is a cross-sectional view in the stacking direction along line XX ′ parallel to the long side direction of FIG.

The piezoelectric element 109 according to the present embodiment has the layers 41, 42, 43 similar to the piezoelectric element 105 according to the fourth embodiment.
Are laminated, and their external shape is almost the same as the piezoelectric element 105 shown in FIG. 15 except for the electrode shape. Also in the piezoelectric element 109 of the present embodiment, a rectangular vibrating portion is held in a cantilever state in each opening of the holding portion having two “b” -shaped openings. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

In the piezoelectric element 109 of the present embodiment, the layer 41
And the layer 43 are polarized, and the polarization direction 40 is the opposite direction as in the piezoelectric element 105 of the fourth embodiment.

FIG. 28 is a plan view showing the shape of each electrode. FIG. 28A shows an electrode 11a formed on the layer 41,
FIG. 28B shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 28C shows electrodes 11b and 12b formed between the layer 42 and the layer 43, FIG.
8 (D) shows the electrode 13b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

The electrodes 11a and 11b are formed in the vicinity of the connecting portion between the two vibrating portions 1 having a cantilever structure, and the electrodes 12a and 12b are formed at the distal end portions of the two vibrating portions 1 having a cantilever structure. You. The electrodes 11a and 11b are connected to one side (upper side in FIG. 28) of the connection portion 2 and to the electrodes 12a and 12b.
Extends on the other side (lower side in FIG. 28) of the connection section 2 along the peripheral side of the vibrating section 1, and in each case, one side of the holding section 3 of the piezoelectric element 109 (short side on the left side in FIG. 28) , And as a result, is exposed on the outer peripheral side surface of the piezoelectric element 107. The electrodes 13a and 13b have the same shape as that of the fourth embodiment, and are formed up to the end of the other side (short side on the right side in FIG. 28) of the holding section via the connection section 2 of the piezoelectric element 109.
As a result, the piezoelectric element 107 is exposed on the outer peripheral side surface.

The assembly of the sensor is the same as that of the fourth embodiment shown in FIG.

Similarly to the fourth embodiment, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. The electrode 33 is the electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The polarization directions 40 of the layers 41 and 43 are opposite to each other, and the order of lamination and connection method of each electrode are the same as those of the piezoelectric element 105 of the fourth embodiment. 11a, 12a and the electrodes 11b, 12b have the same polarity, and the electrodes 13a, 13b
And a charge of the same polarity is obtained. As a result, the acceleration can be detected.

In the case of self-diagnosis, the electrodes 11a, 11a
8 can be performed in the same manner as in FIG. 8, where b is a vibration detecting electrode and the electrodes 12a and 12b are driving electrodes.

Embodiment 4 also takes out electric charges from the electrodes.
Can be performed in the same manner.

The directions 40 of polarization of the layers 41 and 43 are not limited to the directions shown in FIG.

FIG. 29 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the sixth embodiment of the present invention.

The piezoelectric element 110 shown in FIG.
26, the layers 41, 42, and 43 are laminated, and the external shape of the piezoelectric element 109 shown in FIG.
09 is almost the same. Also in the piezoelectric element 110 of the present example, the rectangular vibrating portion is held in a cantilever state in each opening of the holding portion having two “b” -shaped openings. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

Although the layers 41 and 43 of the piezoelectric element 110 are polarized, the polarization direction 40 thereof is the same as that of the piezoelectric element 109.

FIG. 30 is a plan view showing the shape of each electrode. FIG. 30A shows an electrode 11a formed on the layer 41,
30B shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 30C shows an electrode 13b formed between the layer 42 and the layer 43, and FIG. (D)
Indicates electrodes 11b and 12b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

Electrodes 11a, 11b, 12a, 12b, 1
Although the shapes of 3a and 13b are the same as those of the piezoelectric element 109, the locations where the electrodes are formed are different from those of the piezoelectric element 109.
That is, in the piezoelectric element 110 of this example, the layers 42 and 43
The electrode 13b is formed between
b and 12b are formed.

The assembly of the sensor is the same as that of the piezoelectric element 109.

Similarly to the piezoelectric element 109, the electrodes 11a and 11b are connected to the external electrode 21 by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. 33 to electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The polarization directions 40 of the layer 41 and the layer 43 are the same, but since the electrodes on the front and back of the layer 43 are opposite to the piezoelectric element 109, the electrodes 11a, 1
Electric charges of the same polarity are obtained at 2a and the electrodes 11b and 12b, and electric charges of the same polarity are obtained at the electrodes 13a and 13b. As a result, the acceleration can be detected.

The self-diagnosis function and the extraction of charges from the electrodes are the same as in the case of the piezoelectric element 109.

The direction 40 of polarization of the layers 41 and 43 is not limited to the direction shown in FIG.

In the piezoelectric elements 109 and 110, each layer 4
1, 42 and 43 are not limited to those containing lead zirconate titanate as a main component, but lead titanate, lead zirconate,
A material containing lead lanthanate or the like as a main component may be used. Although the thicknesses of the layers do not all need to be the same, it is preferable that the layers 41 and 43 have substantially the same thickness. The layer 42 may be thicker than the other layers, in which case it contributes to improved impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, and 13b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate thereof, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

Note that the number of layers of the piezoelectric elements 109 and 110 is not limited to three, and the number of layers may be further increased. In such a case, electrodes may be connected every other layer at an end face or the like.

In the above example, the resin sheet 5 is laminated to secure the vibration space of the vibration section 1, but the means for securing the vibration space is not limited to this. For example, a concave portion having a predetermined depth is formed in a region of the surface of the substrate 4 on the side of the piezoelectric elements 109 and 110 that does not face the holding portion 3 without laminating the resin sheet 5 so that the vibrating portion 1 can vibrate. Is also good.

As described above, it is possible to maintain high sensitivity even at a low frequency and to perform self-diagnosis in a low-frequency region with high accuracy without using an electrical connection means such as wiring. By providing the piezoelectric element with a vibrating part, a connecting part, and a holding part, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging can be easily performed, and a small acceleration sensor without variation due to holding can be realized.

(Embodiment 7) FIG. 31 is an external perspective view of a piezoelectric element used in an acceleration sensor according to Embodiment 7 of the present invention. FIG. 32 shows the piezoelectric element 111 of FIG.
FIG. 5 is a cross-sectional view in the stacking direction along line XX ′ parallel to the long side direction of FIG.

The piezoelectric element 111 according to the present embodiment has the layers 41, 42, 43 similar to the piezoelectric element 109 according to the sixth embodiment.
Are laminated, and their external shape is almost the same as the piezoelectric element 109 shown in FIG. 26 except for the electrode shape. Also in the piezoelectric element 111 of the present embodiment, a rectangular vibrating portion is held in a cantilever state in each opening of the holding portion having two “U” -shaped openings. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

In the piezoelectric element 111 of the present embodiment, the layer 41
And the layer 43 are polarized, and the polarization direction 40 is the opposite direction as in the piezoelectric element 109 of the sixth embodiment.

FIG. 33 is a plan view showing the shape of each electrode. FIG. 33A shows an electrode 11a formed on the layer 41,
FIG. 33 (B) shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 33 (C) shows electrodes 11b and 12b formed between the layer 42 and the layer 43, FIG.
3 (D) shows the electrode 13b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

The electrodes 11a and 11b are formed in the vicinity of the connection between the two vibrating portions 1 having a cantilever structure, and the electrodes 12a and 12b are formed insulated closer to the tip of the vibrating portion 1 than the electrodes 11a and 11b. You. Two vibrating parts 1 of cantilever structure
No electrode is formed at the tip of the device, and the capacitance, sensitivity, and self-diagnosis sensitivity can be adjusted by adjusting the arrangement and size of the region where the electrode is not formed. The electrodes 11a and 11b are connected to one side of the connection portion 2 (FIG. 3).
3, and the electrodes 12 a and 12 b extend to the other side (the lower side in FIG. 33) of the connection part 2 along the peripheral side of the vibrating part 1. Holder 3
Is formed up to the end of one side (the short side on the left side in FIG. 33), and as a result, is exposed on the outer peripheral side surface of the piezoelectric element 111. The electrodes 13a and 13b have the same shape as that of the fourth embodiment, and are formed up to the end of the other side (short side on the right side in FIG. 33) of the holding section via the connection section 2 of the piezoelectric element 111. As a result, the piezoelectric element 111 is exposed on the outer peripheral side surface.

The assembly of the sensor is the same as that of the fourth embodiment shown in FIG.

As in the fourth embodiment, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. The electrode 33 is the electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The polarization directions 40 of the layers 41 and 43 are opposite to each other, and the order of lamination and connection method of each electrode are the same as those of the piezoelectric element 105 of the fourth embodiment. 11a, 12a and the electrodes 11b, 12b have the same polarity, and the electrodes 13a, 13b
And a charge of the same polarity is obtained. As a result, the acceleration can be detected.

When performing a self-diagnosis, the electrodes 11a, 11a
8 can be performed in the same manner as in FIG. 8, where b is a vibration detecting electrode and the electrodes 12a and 12b are driving electrodes.

Embodiment 4 also takes out charges from the electrodes.
Can be performed in the same manner.

The direction of polarization 40 of the layers 41 and 43 is not limited to the direction shown in FIG.

FIG. 34 is a cross-sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the seventh embodiment of the present invention.

The piezoelectric element 112 shown in FIG.
Like the piezoelectric element 111, the layers 41, 42, and 43 are laminated, and the external shape thereof is the piezoelectric element 1 shown in FIG.
It is almost the same as 111. Also in the piezoelectric element 112 of this example, a rectangular vibrating portion is held in a cantilever state in each of the openings of the holding portion having two “b” -shaped openings.
Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

Although the layers 41 and 43 of the piezoelectric element 112 are polarized, the polarization direction 40 thereof is the same as that of the piezoelectric element 111.

FIG. 35 is a plan view showing the shape of each electrode. FIG. 35A shows an electrode 11a formed on the layer 41,
FIG. 35 (B) shows an electrode 13a formed between the layer 41 and the layer 42, FIG. 35 (C) shows an electrode 13b formed between the layer 42 and the layer 43, and FIG. (D)
Indicates electrodes 11b and 12b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

Electrodes 11a, 11b, 12a, 12b, 1
Although the shapes of 3a and 13b are the same as those of the piezoelectric element 111, the locations of the electrodes are different from those of the piezoelectric element 111.
That is, in the piezoelectric element 112 of this example, the layers 42 and 43
The electrode 13b is formed between
b and 12b are formed.

The assembly of the sensor is the same as that of the piezoelectric element 111.

Similarly to the piezoelectric element 111, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. 33 to electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The polarization directions 40 of the layer 41 and the layer 43 are the same, but since the electrodes on the front and back of the layer 43 are opposite to the piezoelectric element 111, the electrodes 11a, 1
Electric charges of the same polarity are obtained at 2a and the electrodes 11b and 12b, and electric charges of the same polarity are obtained at the electrodes 13a and 13b. As a result, the acceleration can be detected.

The self-diagnosis function and the extraction of charges from the electrodes are the same as in the case of the piezoelectric element 111.

The directions 40 of polarization of the layers 41 and 43 are not limited to the directions shown in FIG. 34, but may be the same as each other.

In the piezoelectric elements 111 and 112, each layer 4
1, 42 and 43 are not limited to those containing lead zirconate titanate as a main component, but lead titanate, lead zirconate,
A material containing lead lanthanate or the like as a main component may be used. Although the thicknesses of the layers do not all need to be the same, it is preferable that the layers 41 and 43 have substantially the same thickness. The layer 42 may be thicker than the other layers, in which case it contributes to improved impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, and 13b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate thereof, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

Note that the number of layers of the piezoelectric elements 111 and 112 is not limited to three, and the number of layers may be further increased. In this case, electrodes may be connected every other layer at an end face or the like.

In the above example, the resin sheet 5 is laminated to secure the vibration space of the vibration section 1, but the means for securing the vibration space is not limited to this. For example, a concave portion having a predetermined depth is formed in a region of the surface of the substrate 4 on the side of the piezoelectric elements 111 and 112 that does not face the holding portion 3 so that the vibrating portion 1 can vibrate without laminating the resin sheet 5. Is also good.

As described above, it is possible to have high capacitance, maintain high sensitivity even at a low frequency, and accurately perform self-diagnosis in a low-frequency region without using electrical connection means such as wiring. By providing the piezoelectric element with a vibrating part, a connecting part, and a holding part, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging can be easily performed, and a small acceleration sensor without variation due to holding can be realized.

In the present embodiment, a region where no electrode is formed is provided at the tip of the vibrating section 1, but the position where the region is formed is not limited to this. For example, the electrodes 11a,
It may be provided between the electrode 11B and the electrodes 12a and 12b (that is, the area of the margin portion for distinguishing both electrodes is increased).

Further, the region where such an electrode is not formed can be similarly formed on the piezoelectric element 103 of the third embodiment, and the same effect can be obtained.

(Eighth Embodiment) FIG. 36 is an external perspective view of a piezoelectric element used in an acceleration sensor according to an eighth embodiment of the present invention. FIG. 37 shows the piezoelectric element 113 of FIG.
FIG. 5 is a cross-sectional view in the stacking direction along line XX ′ parallel to the long side direction of FIG.

The piezoelectric element 113 according to the present embodiment includes the layers 41, 42, and 43 similarly to the piezoelectric element 111 according to the seventh embodiment.
Are laminated, and the external shape is almost the same as the piezoelectric element 111 shown in FIG. 31 except for the electrode shape. Also in the piezoelectric element 113 of the present embodiment, a rectangular vibrating portion is held in a cantilever state in each opening of the holding portion having two “U” -shaped openings. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

In the piezoelectric element 113 of the present embodiment, the layer 41
And the layer 43 are polarized, and the polarization direction 40 is the opposite direction as in the piezoelectric element 111 of the seventh embodiment.

FIG. 38 is a plan view showing the shape of each electrode. FIG. 38A shows an electrode 11a formed on the layer 41,
12A and 14A are shown, and FIG.
38C shows an electrode 13a formed between the layers 42 and 43. FIG.
4D, and FIG. 38D shows the electrode 13b formed on the lower surface of the layer 43. Each electrode can be formed using silver palladium.

The electrodes 11a and 11b are near the connecting portion of the two vibrating portions 1 having the cantilever structure, the electrodes 12a and 12b are at the distal end portions of the two vibrating portions 1 having the cantilever structure, and the electrodes 14a and 1b.
4b is formed insulated between the electrodes 11a and 12a and between the electrodes 11b and 12b, respectively. Electrode 11
a and 11b are connected via one side (upper side in FIG. 38) of the connecting portion 2 and the electrodes 12a and 12b are connected along the peripheral side of the vibrating portion 1 to the other side (refer to FIG. The lower part of FIG.
8 is formed to the end of the left side (short side on the left side), and as a result, is exposed on the outer peripheral side surface of the piezoelectric element 113. Electrodes 14a, 1
Reference numeral 4b denotes a dummy electrode, and the capacitance, sensitivity and self-diagnosis sensitivity can be adjusted by adjusting the arrangement and size of the dummy electrodes 14a and 14b. Electrodes 13a, 1
3b has the same shape as that of the seventh embodiment, and is formed up to the end of the other side (short side on the right side in FIG. 38) of the holding section via the connection section 2 of the piezoelectric element 113. It is exposed on the outer peripheral side surface of the element 113.

The assembling of the sensor is the same as that of the fourth embodiment shown in FIG.

Similarly to the fourth embodiment, the electrodes 11a and 11b are connected to the external electrode 21 by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. The electrode 33 is the electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

The polarization direction 40 of the layer 41 and the layer 43 is opposite, and the order of lamination and connection method of each electrode are the same as those of the piezoelectric element 105 of the fourth embodiment. Electric charges of the same polarity are obtained on the electrode 11a and the electrode 11b. As a result, the acceleration can be detected.

In the case of self-diagnosis, the electrodes 11a, 11a
8 can be performed in the same manner as in FIG. 8, where b is a vibration detecting electrode and the electrodes 12a and 12b are driving electrodes.

Embodiment 4 also takes out electric charges from the electrodes.
Can be performed in the same manner.

The direction of polarization 40 of the layers 41 and 43 is not limited to the direction shown in FIG.

FIG. 39 is a sectional view in the stacking direction of a piezoelectric element having another configuration used in the acceleration sensor according to the eighth embodiment of the present invention.

The piezoelectric element 114 shown in FIG.
36, the layers 41, 42, and 43 are laminated, and the appearance of the piezoelectric element 113 shown in FIG.
13 is almost the same. Also in the piezoelectric element 114 of this example, a rectangular vibrating part is held in a cantilever state in each opening of the holding part having two “b” -shaped openings. Each of the layers 41, 42, and 43 can be manufactured using ceramics containing lead zirconate as a main component.

Although the layers 41 and 43 of the piezoelectric element 114 are polarized, the polarization direction 40 thereof is the same as that of the piezoelectric element 113.

FIG. 40 is a plan view showing the shape of each electrode. FIG. 40A shows an electrode 11a formed on the layer 41,
12A and 14A are shown, and FIG.
FIG. 40C shows an electrode 13b formed between the layer 42 and the layer 43, and FIG.
0 (D) indicates the electrodes 11b and 12 formed on the lower surface of the layer 43.
b and 14b are shown. Each electrode can be formed using silver palladium.

The electrodes 11a, 11b, 12a, 12b, 1
The shape of 3a, 13b, 14a, 14b is
Are similar to those of the piezoelectric element 1
13 is different. That is, in the piezoelectric element 112 of this example, the electrode 13b is formed between the layer 42 and the layer 43,
The electrodes 11b, 12b and 14b are formed on the lower surface of the substrate.

The assembly of the sensor is similar to that of the piezoelectric element 113.

Similarly to the piezoelectric element 113, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. 33 to electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41 and 43 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

Although the polarization direction 40 of the layer 41 and the layer 43 is the same, the electrodes on the front and back of the layer 43 are opposite to the piezoelectric element 113.
Electric charges of the same polarity are obtained at 1b and the electrodes 11b and 12b, and electric charges of the same polarity are obtained at the electrodes 13a and 13b. As a result, the acceleration can be detected.

The self-diagnosis function and the extraction of charges from the electrodes are the same as in the case of the piezoelectric element 113.

The direction of polarization 40 of the layers 41 and 43 is not limited to the direction shown in FIG.

In the piezoelectric elements 113 and 114, each layer 4
1, 42 and 43 are not limited to those containing lead zirconate titanate as a main component, but lead titanate, lead zirconate,
A material containing lead lanthanate or the like as a main component may be used. Although the thicknesses of the layers do not all need to be the same, it is preferable that the layers 41 and 43 have substantially the same thickness. The layer 42 may be thicker than the other layers, in which case it contributes to improved impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, 13b, 14a, and 14b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate of these, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

The number of layers of the piezoelectric elements 113 and 114 is not limited to three, and the number of layers may be further increased as in the ninth embodiment described below.
The electrodes may be connected at the end face or the like every other layer.

In the above example, the resin sheet 5 is laminated to secure the vibration space of the vibrating section 1, but the means for securing the vibration space is not limited to this. For example, a concave portion having a predetermined depth is formed in a region of the surface of the substrate 4 on the side of the piezoelectric elements 113 and 114 that does not face the holding portion 3 so that the vibrating portion 1 can vibrate without laminating the resin sheet 5. Is also good.

As described above, it is possible to have high capacitance, maintain high sensitivity even at a low frequency, and perform a self-diagnosis at a low frequency range with high accuracy without using an electrical connection means such as wiring. By providing the piezoelectric element with a vibrating part, a connecting part, and a holding part, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging can be easily performed, and a small acceleration sensor without variation due to holding can be realized.

The dummy electrode described in the present embodiment can be formed in the same manner on the piezoelectric element 103 of the third embodiment, and the same effect can be obtained.

(Embodiment 9) FIG. 41 is an external perspective view of a piezoelectric element used in an acceleration sensor according to Embodiment 9 of the present invention. FIG. 42 shows the piezoelectric element 115 of FIG.
FIG. 5 is a cross-sectional view in the stacking direction along line XX ′ parallel to the long side direction of FIG.

The piezoelectric element 115 according to the present embodiment
1, 42, 43, 44, and 45, and the appearance of the piezoelectric element 1 shown in FIG.
13 is almost the same. Piezoelectric element 115 of the present embodiment
In this case, a rectangular vibrating portion is held in a cantilever state in each of the openings of the holding portion having two “b” -shaped openings. Each of the layers 41, 42, 43, 44, and 45 can be manufactured using ceramics containing lead zirconate as a main component.

In the piezoelectric element 115 of the present embodiment, the layer 4
1, 42, 44 and 45 are polarized, and the polarization direction 40 thereof is such that the layers 41 and 44 are upward and the layers 42 and 45 are downward.

FIG. 43 is a plan view showing the shape of each electrode. FIG. 43A shows an electrode 11a formed on the layer 41,
12A and 14A are shown, and FIG.
FIG. 43 (C) shows the electrodes 11a, 12a, 1 formed between the layers 42 and 43. FIG.
FIG. 43 (D) shows the electrode 13b formed between the layer 43 and the layer 44, and FIG.
43 show the electrodes 11b, 12b and 14b formed between the electrodes 5, and FIG.
b. Each electrode can be formed using silver palladium.

The electrodes 11a, 11b, 12a, 12b, 1
The shapes of 3a, 13b, 14a, and 14b are the same as those of the piezoelectric element 113 of the eighth embodiment. That is, the electrode 1
1a and 11b are near the connecting portion of the two vibrating portions 1 of the cantilever structure, the electrodes 12a and 12b are at the tip of the two vibrating portions 1 of the cantilever structure, and the electrodes 14a and 14b are the electrodes 11a and 12a, respectively. And between the electrodes 11b and 12b. The electrodes 11a and 11b are connected to one side (upper side in FIG. 43) of the connecting portion 2 and the electrodes 12a and 12b are connected to the connecting portion 2 along the periphery of the vibrating portion 1.
43 is extended to the other side (the lower side in FIG. 43), and both are formed up to the end of one side (the short side on the left side in FIG. 43) of the holding portion 3 of the piezoelectric element 115. It is exposed on the outer peripheral side. The electrodes 14a and 14b are dummy electrodes, and the capacitance, sensitivity, and self-diagnosis sensitivity can be adjusted by adjusting the arrangement and size of the dummy electrodes 14a and 14b. The electrodes 13a and 13b are
Fifteen connection portions 2 are formed up to the end of the other side (the short side on the right side in FIG. 43) of the holding portion.
15 is exposed on the outer peripheral side surface.

The assembly of the sensor has the same configuration as that of the fourth embodiment shown in FIG.

As in the fourth embodiment, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. The electrode 33 is the electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41, 42, 44, and 45 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

Since the polarization directions of the layers 41 and 44 and the layers 42 and 45 are opposite to each other, when the vibrating portion performs flexural vibration, electric charges of the same polarity are obtained at the electrodes 11a and 12a and the electrodes 11b and 12b. Charges of the same polarity are obtained on the electrodes 13a and 13b. As a result, the acceleration can be detected.

In the case of self-diagnosis, the electrodes 11a, 11a
8 can be performed in the same manner as in FIG. 8, where b is a vibration detecting electrode and the electrodes 12a and 12b are driving electrodes.

Embodiment 4 also takes out electric charges from the electrodes.
Can be performed in the same manner.

The direction of polarization 40 of the layers 41, 42, 44 and 45 is not limited to the direction shown in FIG. 42, and the layers 41 and 42, the layers 44 and 45, and the layers 41 and 45 respectively The directions may be opposite to each other.

FIG. 44 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the ninth embodiment of the present invention.

The piezoelectric element 116 shown in FIG.
Layer 41, 42, 43, 4
4, 45 are laminated, and the external shape is almost the same as the piezoelectric element 115 shown in FIG. Also in the piezoelectric element 116 of the present example, a rectangular vibrating portion is held in a cantilever state in each of the openings of the holding portion having two “b” -shaped openings. Each of the layers 41, 42, 43, 44, and 45 can be manufactured using ceramics containing lead zirconate as a main component.

The layers 41, 42, 44, 4 of the piezoelectric element 116
5 is polarized, but its polarization direction 40 is different from that of the piezoelectric element 115. That is, layers 41 and 45 are polarized upward, and layers 42 and 44 are polarized downward.

FIG. 45 is a plan view showing the shape of each electrode. FIG. 45A shows an electrode 11a formed on the layer 41,
12A and 14A are shown, and FIG.
45C shows an electrode 13a formed between the layers 42 and 43. FIG.
FIG. 45D shows the electrodes 11b, 12b, and 14b formed between the layer 43 and the layer 44, and FIG.
(E) shows the electrode 13b formed between the layer 44 and the layer 45, and FIG. 45 (F) shows the electrode 1b formed on the lower surface of the layer 45.
1b, 12b and 14b are shown. Each electrode can be formed using silver palladium.

Electrodes 11a, 11b, 12a, 12b, 1
The shape of 3a, 13b, 14a, 14b is
Are similar to those of the piezoelectric element 1
15 is different. That is, in the piezoelectric element 116 of this example, the electrodes 11b, 12b, and 14b are provided between the layers 43 and 44.
Is formed, and the electrode 13b is formed between the layer 44 and the layer 45.
The electrodes 11b, 12b, and 14b are formed on the lower surface of the layer 45.

The assembly of the sensor is the same as that of the piezoelectric element 115.

Similarly to the piezoelectric element 115, the electrodes 11a and 11b and the external electrode 21 are connected to each other by the end face electrode 31, and the electrodes 12a and 12b and the external electrode 22 are connected to each other by the end face electrode 32. 33 to electrode 13
a, 13b and the external electrodes 23 are mutually connected. As a result, the layers 41, 42, 44, and 45 are connected in parallel, and the capacitance is the sum of the capacitances of the respective layers, so that a large capacitance can be obtained.

As described above, when the vibrating portion performs flexural vibration, electric charges of the same polarity are obtained on the electrodes 11a and 11b and the electrodes 11b and 12b, and electric charges of the same polarity are obtained on the electrodes 13a and 13b. As a result, the acceleration can be detected.

The self-diagnosis function and the extraction of charges from the electrodes are the same as in the case of the piezoelectric element 115.

The direction of polarization 40 of the layers 41, 42, 44, and 45 is not limited to the direction shown in FIG. 44. The layers 41 and 45 have the same direction, and the layers 41 and 42 and the layer 44 have the same direction. And the layer 45 may be opposite to each other.

In each of the piezoelectric elements 115 and 116,
1, 42, 43, 44, and 45 are not limited to those containing lead zirconate titanate as a main component, and may be those containing lead titanate, lead zirconate, lead lanthanate, or the like as a main component. The thicknesses of the layers need not all be the same,
Preferably, 1, 42, 44, 45 have approximately the same thickness. The layer 43 may be thicker than other layers, in which case it contributes to an improvement in impact resistance.

The electrodes 11a, 11b, 12a, 12
b, 13a, 13b, 14a, and 14b are not limited to silver palladium, but may be gold, chromium, nickel, copper, or the like, or a laminate of these, or an alloy thereof.

The material of the substrate 4 is not limited to alumina, but may be a resin or the like.

Electrodes 21 and 2 formed on alumina substrate 4
The materials 2 and 23 are not limited to silver palladium, but may be a reflowable material such as silver-solder or silver brazing.

The end electrodes 31, 32, 33 of the piezoelectric element
The electrode is not limited to sputtering, and may be formed of a resin-curable electrode paste.

In the above example, the vibration space of the vibrating portion 1 is secured by laminating the resin sheets 5, but the means for securing the vibration space is not limited to this. For example, without laminating the resin sheet 5, a concave portion having a predetermined depth is formed in a region of the surface of the substrate 4 on the side of the piezoelectric elements 115 and 116 that does not face the holding portion 3 so that the vibrating portion 1 can vibrate. Is also good.

As described above, it is possible to have high capacitance, maintain high sensitivity even at a low frequency, and accurately perform self-diagnosis in a low-frequency region without using electrical connection means such as wiring. By providing the piezoelectric element with a vibrating part, a connecting part, and a holding part, and holding the piezoelectric element with the holding part, a vibration space can be secured, a packaging can be easily performed, and a small acceleration sensor without variation due to holding can be realized.

[0295]

As described above, according to the present invention, a high capacitance can be obtained, a high sensitivity can be maintained even at a low frequency, and a high sensitivity can be maintained in a low frequency region without using an electrical connection means such as wiring. Self-diagnosis can be performed with high accuracy, and a vibration space, a connection portion, and a holding portion are provided on the piezoelectric element, and the holding of the piezoelectric element enables the securing of a vibration space, easy packaging, and variations due to holding. It is possible to provide a small acceleration sensor without the need.

[Brief description of the drawings]

FIG. 1 is an external perspective view of a piezoelectric element used for an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of each part of the piezoelectric element of FIG.

FIG. 3 is an exploded perspective view showing a configuration of the acceleration sensor according to the first embodiment of the present invention.

4 is a cross-sectional view of the piezoelectric element of FIG. 1 taken along line XX ′ in the stacking direction.

FIG. 5 is a plan view showing the shape of each electrode of the piezoelectric element of FIG.

FIG. 6 is a cross-sectional view in the stacking direction of the acceleration sensor according to the first embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view in the stacking direction showing the operation principle of the acceleration sensor according to the first embodiment of the present invention.

FIG. 8 is a block diagram of signal processing at the time of self-diagnosis of the acceleration sensor according to the first embodiment of the present invention;

FIG. 9 is a sectional view in the stacking direction of a piezoelectric element used in the acceleration sensor according to the second embodiment of the present invention.

FIG. 10 is a plan view showing the shape of each electrode of the piezoelectric element of FIG.

FIG. 11 is a sectional view in the stacking direction of a piezoelectric element used for an acceleration sensor according to a third embodiment of the present invention.

FIG. 12 is a plan view showing the shape of each electrode of the piezoelectric element of FIG.

FIG. 13 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the third embodiment of the present invention.

FIG. 14 is a plan view showing the shape of each electrode of the piezoelectric element of FIG.

FIG. 15 is an external perspective view of a piezoelectric element used in the acceleration sensor according to the fourth embodiment of the present invention.

16 is an explanatory diagram of each part of the piezoelectric element of FIG.

FIG. 17 is an exploded perspective view showing a configuration of an acceleration sensor according to a fourth embodiment of the present invention.

18 is a cross-sectional view of the piezoelectric element of FIG. 15 taken along line XX ′ in the stacking direction.

19 is a plan view showing the shape of each electrode of the piezoelectric element of FIG.

FIG. 20 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the fourth embodiment of the present invention.

21 is a plan view showing the shape of each electrode of the piezoelectric element of FIG.

FIG. 22 is a sectional view in the stacking direction of a piezoelectric element used in the acceleration sensor according to the fifth embodiment of the present invention.

FIG. 23 is a plan view showing the shape of each electrode of the piezoelectric element of FIG. 22.

FIG. 24 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the fifth embodiment of the present invention.

FIG. 25 is a plan view showing the shape of each electrode of the piezoelectric element of FIG. 24;

FIG. 26 is an external perspective view of a piezoelectric element used in the acceleration sensor according to the sixth embodiment of the present invention.

FIG. 27 is a cross-sectional view of the piezoelectric element of FIG. 26 taken along line XX ′ in the stacking direction.

FIG. 28 is a plan view showing the shape of each electrode of the piezoelectric element of FIG. 26;

FIG. 29 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the sixth embodiment of the present invention.

30 is a plan view showing the shape of each electrode of the piezoelectric element in FIG. 29.

FIG. 31 is an external perspective view of a piezoelectric element used for an acceleration sensor according to a seventh embodiment of the present invention.

FIG. 32 is a cross-sectional view of the piezoelectric element of FIG. 31 taken along line XX ′ in the stacking direction.

FIG. 33 is a plan view showing the shape of each electrode of the piezoelectric element of FIG. 31.

FIG. 34 is a sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the seventh embodiment of the present invention.

FIG. 35 is a plan view showing the shape of each electrode of the piezoelectric element in FIG. 34.

FIG. 36 is an external perspective view of a piezoelectric element used in the acceleration sensor according to the eighth embodiment of the present invention.

FIG. 37 is a cross-sectional view of the piezoelectric element of FIG. 36 taken along line XX ′.

FIG. 38 is a plan view showing the shape of each electrode of the piezoelectric element of FIG. 36.

FIG. 39 is a cross-sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the eighth embodiment of the present invention.

40 is a plan view showing the shape of each electrode of the piezoelectric element in FIG. 39.

FIG. 41 is an external perspective view of a piezoelectric element used in the acceleration sensor according to the ninth embodiment of the present invention.

42 is a cross-sectional view of the piezoelectric element of FIG. 41 taken along line XX ′ in the lamination direction.

FIG. 43 is a plan view showing the shape of each electrode of the piezoelectric element in FIG. 41.

FIG. 44 is a cross-sectional view in the stacking direction of a piezoelectric element having another configuration used for the acceleration sensor according to the ninth embodiment of the present invention.

FIG. 45 is a plan view showing the shape of each electrode of the piezoelectric element of FIG. 44.

46A and 46B are views for explaining a conventional acceleration sensor, FIG. 46A is a plan view of a piezoelectric element used for the acceleration sensor, and FIG. 46B is a schematic diagram showing a schematic configuration of the acceleration sensor. is there.

FIG. 47 is a diagram showing a general signal processing circuit used for an acceleration sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Vibration part 2 Connection part 3 Holding part 4 Alumina substrate 5 Resin sheet 6a Drive circuit 6b Impedance conversion circuit 6c Acceleration detection circuit / abnormality detection circuit 11, 12, 13, 14 Electrode 21, 22, 23 External electrode 31, 32, 33 End electrode 40 Polarization direction 41, 42, 43, 44, 45 Layer 51, 52, 53 Electrode 54 Metal plate 55 Support 56 Acceleration sensor 60 Acceleration 101, 102, 103, 104, 105, 106, 1
07, 108, 109, 110, 111, 112, 11
3,114,115,116,150 Piezoelectric element

Continuing on the front page (72) Inventor Shuichiro Yamaguchi 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Reference) 2G064 BD18

Claims (15)

[Claims] 1. A piezoelectric element comprising a plurality of piezoelectric layers laminated, wherein the piezoelectric element is connected to a vibrating section in which a plurality of rectangular piezoelectric layers are laminated, and to one side of the vibrating section. A connecting portion for holding the vibrating portion, and a holding portion formed integrally with the connecting portion, wherein at least two or more piezoelectric layers of the piezoelectric layers constitute the vibrating portion. Electrodes are formed on upper and lower surfaces of the vibrating portion in the direction of lamination of the polarized piezoelectric layers, and impedances formed by the electrodes on the upper and lower surfaces and the piezoelectric layers between them are electrically connected to each other. The electrodes on the upper and lower surfaces are connected in parallel, and the electrodes on the upper and lower surfaces are also formed continuously on at least a part of the connection part and the holding part. The electrical connection between the electrodes and the outside is performed by the electrodes formed on the holding part. Acceleration sensor, which is performed through 2. The polarized piezoelectric layer is disposed at least on both upper and lower outermost layers of the vibrating section.
2. The acceleration sensor according to 1. 3. The piezoelectric layer is laminated with five or more layers, and at least portions of the upper and lower outermost layers and layers adjacent to the both outermost layers that constitute the vibrating portion are polarized,
The acceleration sensor according to claim 1, wherein a polarization direction of the outermost layer is opposite to a polarization direction of an adjacent layer. 4. The acceleration sensor according to claim 2, wherein the polarization directions of the outermost piezoelectric layers are opposite to each other. 5. The acceleration sensor according to claim 2, wherein the polarization directions of the two outermost piezoelectric layers are the same. 6. The acceleration sensor according to claim 1, wherein the connection section holds one short side of the vibration section. 7. The acceleration sensor according to claim 1, wherein the vibration section is held on both sides of the connection section. 8. The acceleration sensor according to claim 1, wherein at least one of the electrodes formed on the upper and lower surfaces of the piezoelectric layer in the vibrating portion is divided into two. 9. The acceleration sensor according to claim 8, wherein one of the two divided electrodes is used as a drive electrode during self-diagnosis, and the other is used as a vibration detection electrode during self-diagnosis. 10. The two divided electrodes are formed so as to be substantially orthogonal to the connection part, one of the electrodes is used as a driving electrode at the time of self-diagnosis, and the other electrode is used for vibration detection at the time of self-diagnosis. The acceleration sensor according to claim 8, which is used as an electrode for use. 11. One of the two divided electrodes is formed near the connection part of the vibrating part, and the other is formed on the opposite side of the connection part from the connection part, and is formed near the connection part. 9. The acceleration sensor according to claim 8, wherein the electrode is used as a vibration detection electrode during self-diagnosis, and the other electrode is used as a driving electrode during self-diagnosis. 12. An electrode is formed on the upper and lower surfaces of the piezoelectric layer common to the vibrating portions on both sides, and at least one of the electrodes formed on the upper and lower surfaces is disposed within the other vibrating portion. 8. The electrode is divided so as not to penetrate, and one of the divided electrodes is used as a drive electrode during self-diagnosis, and the other electrode is used as a vibration detection electrode during self-diagnosis. 2. The acceleration sensor according to 1. 13. The acceleration sensor according to claim 11, further comprising a region where no electrode is formed on the connection portion side and / or the non-connection portion side of the electrode used as the driving electrode. 14. The acceleration sensor according to claim 11, further comprising a dummy electrode that is not connected to the electrode used as the vibration detection electrode and the driving electrode. 15. The acceleration sensor according to claim 1, wherein the piezoelectric element is held by the holding portion such that the vibrating portion can vibrate in a direction in which the piezoelectric layers are stacked.