JP2016001160A - Vibration type angular velocity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure durability by suppressing deterioration of a piezoelectric thin film or a piezoelectric material in a vibrator.SOLUTION: A protection film 8 is formed so as to cover an exposed part of a piezoelectric film 6b for driving or a piezoelectric film 7b for detection constituted of an oxide piezoelectric film which are provided at least on a driving element 6 or a detection element 7. Hereby, desorption of oxygen from the piezoelectric film 6b for driving or a piezoelectric film 7b for detection can be suppressed. Therefor, durability of a vibration type angular velocity sensor can be secured.

Description

  The present invention relates to a piezoelectric vibration type angular velocity sensor.

  Conventionally, a vibration type angular velocity sensor is known. In the vibration type angular velocity sensor, when an angular velocity is applied in a state where the vibrator is driven to vibrate, the vibrator is deformed according to the applied angular velocity, so that the deformation of the vibrator is detected by a detection element. The applied angular velocity is detected. In order to improve the sensitivity of such a vibration type angular velocity sensor, it is effective to increase the Q value which is a dimensionless number representing the state of vibration in the vibrator. For this reason, for example, Patent Document 1 proposes a structure in which a high value is obtained as the Q value of the vibrator by vacuum-sealing the vibrator. In addition to vacuum sealing, there is a structure in which the Q value of the vibrator is increased by low-pressure sealing that seals in a state lower than atmospheric pressure.

JP 2005-172690 A

  In the vibration type angular velocity sensor configured as described above, a piezoelectric thin film or a block-like piezoelectric element is used as a detection element for detecting deformation of the vibrator according to the applied angular velocity or a drive element for driving and vibrating the vibrator. A piezoelectric type composed of a body may be used.

  However, an oxide piezoelectric body such as lead zirconate titanate (PZT) used as a piezoelectric thin film or piezoelectric body causes oxygen loss in a low oxygen state, that is, in a vacuum sealed state or a low pressure sealed state. For this reason, the function as a piezoelectric thin film or a piezoelectric member is deteriorated, and the durability of the vibration type angular velocity sensor cannot be ensured.

Further, as a sealing method in the vibration type angular velocity sensor, there is a gas sealing with a gas such as He or N _2. However, in a low oxygen state that does not contain oxygen, oxygen is also released. In addition, there is a method in which gas sealing is a mixed sealing in which O ₂ is added to He and oxygen is included in the gas so that oxygen escape from the oxide piezoelectric body and the piezoelectric thin film is suppressed. Oxygen escape cannot be suppressed by vacuum sealing or low pressure sealing for increasing the value.

  An object of the present invention is to provide a piezoelectric vibration type angular velocity sensor capable of suppressing deterioration of a piezoelectric thin film or a piezoelectric body in a vibrator and ensuring durability.

  In order to achieve the above object, according to the first aspect of the present invention, the arm portions (2, 3) that are driven to vibrate, the drive element (6) that drives and vibrates the arm portions, and the angular velocity applied during the drive vibration. A vibrator (1) having a detection element (7) for taking out the deformation caused by the electric signal as an electric signal, and the vibrator is sealed by a vacuum seal or a low-pressure seal that is at a lower pressure than atmospheric pressure. A type angular velocity sensor, wherein either the driving element or the detection element is composed of a piezoelectric element including an oxide piezoelectric film (6b, 7b) or a block-shaped oxide piezoelectric body (10), Furthermore, it is characterized by having a protective film (8) covering the surface of the oxide piezoelectric film or the oxide piezoelectric body.

  Thus, since the protective film which covers the surface of an oxide piezoelectric film or an oxide piezoelectric material is provided, it becomes possible to suppress the detachment | desorption of oxygen from these. Therefore, it is possible to ensure the durability of the vibration type angular velocity sensor.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows an example of a corresponding relationship with the specific means as described in embodiment mentioned later.

1 is a perspective view of a tuning-fork type vibration angular velocity sensor according to a first embodiment of the present invention. It is II-II 'sectional drawing of FIG. It is sectional drawing which showed the mode of detachment | desorption of oxygen. It is the molecular structure figure which showed the mode of the detachment | desorption of oxygen. It is a perspective view of the tuning fork type vibration type angular velocity sensor concerning a 2nd embodiment of the present invention. It is VI-VI 'sectional drawing of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
In the present embodiment, as a piezoelectric vibration type angular velocity sensor, a driving element and a detection element configured by using a piezoelectric thin film with respect to a tuning fork type angular velocity sensor will be described as an example. Hereinafter, with reference to FIGS. 1-4, the detail of the vibration type angular velocity sensor concerning this embodiment is demonstrated.

  As shown in FIG. 1, the vibratory angular velocity sensor includes a vibrator 1. The vibrator 1 is formed in a tuning fork shape by a pair of substantially prismatic arm portions 2 and 3 whose longitudinal direction is one direction and a connecting portion 4 that connects one end of each arm portion 2 and 3. Among these, at the center position on the opposite side to the arm portions 2 and 3, it is supported by the support portion 5 having the constricted portion 5 a. The external shape of such a block-shaped structure is configured by patterning the base material 10 made of a semiconductor material such as silicon by etching, for example.

  Hereinafter, as shown by xyz orthogonal coordinates in FIG. 1, the arrangement direction of the arm portions 2 and 3 is orthogonal to the x axis, and the longitudinal direction of the arm portions 2 and 3 is orthogonal to both the y axis, the x axis, and the y axis. The direction will be described using the z axis.

  The vibrator 1 is fixed to a substrate or the like (not shown) in a portion of the support portion 5 on the side opposite to the constricted portion 5a, and is connected to the connecting portion 4 and the arm portions 2, 3 from the constricted portion 5a. Is in a floating state released from the substrate.

  Although not shown, a drive element 6 and a detection element 7 each having a piezoelectric thin film are provided at a connection portion of each arm portion 2 and 3 of the vibrator 1 with the connection portion 4.

  As shown in FIG. 2, the driving element 6 is configured by laminating a lower layer electrode 6a, a driving piezoelectric film 6b, and an upper layer electrode 6c on the surface of a base material 10 forming the outer shape of the vibrator 1. ing. The drive element 6 is formed at a connection location of the arm portions 2 and 3 with the connection portion 4 so that the arm portions 2 and 3 can be driven to vibrate. To a position extending from the inside to the connecting portion 4. As shown in FIG. 1, the lower layer electrode 6a and the upper layer electrode 6c are connected to a pad or GND for applying a driving voltage (not shown) through the wiring portions 6d and 6e drawn out through the connecting portion 4 and the support portion 5, respectively. It is connected to the pad for connection. The driving piezoelectric film 6b is composed of an oxide piezoelectric film containing oxygen, for example, a PZT film.

  In such a configuration, by generating a potential difference between the lower layer electrode 6a and the upper layer electrode 6c, the driving piezoelectric film 6b sandwiched therebetween is displaced, and the arm portions 2 and 3 are forcibly vibrated. Thus, the arm portions 2 and 3 are driven to vibrate along the x-axis direction. For example, the driving piezoelectric film 6b of one driving element 6 of the arm portions 2 and 3 is displaced by compressive stress, and the driving piezoelectric film 6b of the other driving element 6 is displaced by tensile stress. By repeatedly applying such a voltage to each driving element 6, the tuning fork type arm portions 2 and 3 are vibrated so as to open and close in the x-axis direction.

  As shown in FIG. 2, the detection element 7 is configured by laminating a lower layer electrode 7a, a detection piezoelectric film 7b, and an upper layer electrode 7c on the surface of a base material 10 forming the outer shape of the vibrator 1. ing. The detection element 7 is formed at a connection portion of the arm portions 2 and 3 with the connection portion 4 so as to detect vibration of the arm portions 2 and 3 generated based on application of angular velocity. The arm portions 2 and 3 extend to a position extending into the connecting portion 4. As shown in FIG. 1, the lower layer electrode 7a and the upper layer electrode 7c are connected to a detection signal output pad (not shown) through wiring portions 7d and 7e drawn out through the connecting portion 4 and the support portion 5. Yes. The detection piezoelectric film 7b is composed of an oxide piezoelectric film containing oxygen, for example, a PZT film.

  In such a configuration, when the arm portions 2 and 3 are displaced as the angular velocity is applied, the detection piezoelectric film 7b is deformed accordingly. Thereby, for example, an electric signal (current value in the case of constant voltage driving, current value in the case of constant current driving) between the lower layer electrode 7a and the upper layer electrode 7c changes, and this is used as a detection signal indicating the angular velocity. The signal is output to the outside through a detection signal output pad (not shown). Specifically, as described above, when a driving voltage is applied to the driving element 6, the arm portions 2 and 3 are driven to vibrate. When an angular velocity around the z axis is applied under this driving vibration, the arm portions 2 and 3 vibrate in the y axis direction due to the Coriolis force. The vibration state of the vibration is detected as a detection vibration, and the applied angular velocity is detected based on the state of the detection vibration.

  Further, as shown in FIG. 2, a protective film 8 is formed so as to cover the drive element 6 and the detection element 7 in the vibrator 1 having the drive element 6 and the detection element 7 configured as described above. . The protective film 8 is for suppressing oxygen escape from the driving piezoelectric film 6b and the detecting piezoelectric film 7b made of an oxide piezoelectric film. At least the driving piezoelectric film in the driving element 6 and the detecting element 7 is used. 6b and the exposed piezoelectric film 7b are formed so as to cover the exposed portion. In FIG. 1, the protective film 8 is omitted for easy understanding of the drawing, but actually, the protective film 8 is formed so as to cover the drive element 6 and the detection element 7.

For example, as shown in FIG. 3, in the structure in which the lower layer electrode 6a, the driving piezoelectric film 6b, and the upper layer electrode 6c are stacked, the driving piezoelectric film 6b is exposed from between the lower layer electrode 6a and the upper layer electrode 6c at the outer edge. Become. If this portion is not covered with the protective film 8, as shown in FIGS. 3 and 4, oxygen is emitted from an oxide piezoelectric film, for example, a PZT film containing Pb, Zr, Ti, O ₃ , at a high temperature. As a result, the function of the driving piezoelectric film 6b deteriorates, and the durability of the vibration type angular velocity sensor cannot be ensured. In FIG. 3, the drive element 6 is taken as an example, but the same can be said for the detection element 7.

  However, by covering the drive element 6 and the detection element 7 with the protective film 8 as in the present embodiment, desorption of oxygen from the drive piezoelectric film 6b and the detection piezoelectric film 7b can be suppressed, and these piezoelectric films As a result, it is possible to suppress deterioration of the function. This makes it possible to ensure the durability of the vibration type angular velocity sensor.

The protective film 8 may be made of a material that can suppress the desorption of oxygen from the driving piezoelectric film 6b and the detection piezoelectric film 7b. For example, the protective film 8 may be formed of an insulating oxide such as an LP-TEOS film made of Si (OC ₂ H ₅ ) _{4 or} ALD-Al ₂ O ₃ formed by an ALD (atomic layer deposition) method. it can. Further, the protective film 8 can be formed of insulating nitride instead of insulating oxide, or the protective film 8 can be formed of nitride piezoelectric film not containing oxygen. For example, AlN or ScAlN can be used as the nitride piezoelectric film.

  Further, the protective film 8 covers the exposed portions of the driving piezoelectric film 6b and the detecting piezoelectric film 7b from the upper layer electrodes 6c and 7c, that is, from one surface opposite to the driving piezoelectric film 6b and the detecting piezoelectric film 7b. Although formed, it may be arranged between the upper layer electrodes 6c and 7c and the driving piezoelectric film 6b or the detecting piezoelectric film 7b. In particular, when the protective film 8 is composed of a nitride piezoelectric film, the protective film 8 itself can function as a piezoelectric film. In that case, the design based on the two types of piezoelectric characteristics is possible by the driving piezoelectric film 6b and the detecting piezoelectric film 7b formed of the oxide piezoelectric film and the protective film 8 formed of the nitride piezoelectric film.

  Note that the protective film 8 does not necessarily have to be formed of a single layer film made of one kind of material, and may be made of a laminated film of a plurality of kinds of materials.

  As described above, the vibration type angular velocity sensor according to the present embodiment is configured. Although the vibration type angular velocity sensor configured as described above is not illustrated, a cap member is bonded to a substrate supporting the vibrator 1 or the vibrator 1 is accommodated in a case. Thus, the vibrator 1 is structured to be vacuum sealed or low pressure sealed.

  Thus, in the structure in which the vibrator 1 is vacuum-sealed or low-pressure sealed, since it is in a low oxygen state, the driving piezoelectric film 6b and the detecting piezoelectric film 7b made of an oxide piezoelectric film are used. Desorption of oxygen can occur. However, since the protective film 8 is formed so as to cover at least the exposed portions of the driving piezoelectric film 6b and the detecting piezoelectric film 7b, it is possible to suppress the desorption of oxygen from these. Therefore, it is possible to ensure the durability of the vibration type angular velocity sensor.

(Second Embodiment)
A second embodiment of the present invention will be described. In the present embodiment, the base material 10 of the vibrator 1 is changed with respect to the first embodiment, and the other parts are the same as those in the first embodiment. Therefore, only different portions from the first embodiment will be described. To do.

  In the vibration type angular velocity sensor of this embodiment shown in FIG. 5, the block-shaped base material 10 in the vibrator 1 is made of an oxide piezoelectric material such as PZT instead of a semiconductor material. That is, the arm parts 2 and 3, the connection part 4, and the support part 5 are comprised with the block-shaped piezoelectric material.

  The drive element 6 is disposed between the first electrode 6f and the second electrode 6g among the first electrode 6f and the second electrode 6g and the base material 10 which are disposed separately on the surfaces of the arm portions 2 and 3. It is composed of parts. As shown in FIG. 5, the first electrode 6f and the second electrode 6g are pads for applying a driving voltage (not shown) through the wiring portions 6h and 6i drawn through the connecting portion 4 and the support portion 5. It is connected to the pad for GND connection.

  The detection element 7 is also arranged between the first electrode 7f and the second electrode 7g among the first electrode 7f and the second electrode 7g and the base material 10 which are arranged separately on the surfaces of the arm portions 2 and 3. It is composed of parts. As shown in FIG. 5, the first electrode 7 f and the second electrode 7 g are connected to a detection signal output pad (not shown) through the wiring portions 7 h and 7 i drawn through the connecting portion 4 and the support portion 5. Has been.

  The vibrator 1 configured as described above is covered with the protective film 8 so that the base material 10 is not exposed. In this embodiment, as shown in FIG. 6, the protective film 8 is formed on the surface of the base material 10, that is, the base material 10, the first and second electrodes 6f, 6g, 7f, 7g and the wiring portions 6h, 6i, 7h, 7i. The entire surface of the base material 10 is covered. However, since it is sufficient that the surface of the base material 10 is not exposed, the protective film 8 is disposed on the first and second electrodes 6f, 6g, 7f, 7g and the wiring portions 6h, 6i, 7h, 7i. You may do it.

  Note that the block-like structure constituting the vibrator 1 can also be formed by patterning the base material 10 made of a piezoelectric material by etching or the like.

  In the vibrator 1 configured as described above, each of the arm portions 2 in which the base material 10 is formed of an oxide piezoelectric body by applying a driving voltage between the first electrode 6f and the second electrode 6g, The angular velocity can be detected by driving and vibrating 3. Thus, even if the base material 10 of the vibrator 1 is formed of an oxide piezoelectric body, if the base material 10 is not exposed by being covered with the protective film 8, the base material 10 Desorption of oxygen from water can be suppressed. This makes it possible to ensure the durability of the vibration type angular velocity sensor.

(Other embodiments)
The present invention is not limited to the embodiment described above, and can be appropriately changed within the scope described in the claims.

  For example, in the above embodiment, a piezoelectric fork type angular velocity sensor has been described by taking a tuning fork type as an example, but is not limited to a tuning fork type. That is, as long as at least one of the drive element and the detection element of the vibrator 1 uses a piezoelectric thin film or a block-like piezoelectric body, the present invention is applied to vibration type angular velocity sensors having other structures. be able to. For example, detection beams extending in one direction and drive beams corresponding to arm portions arranged on both sides of the detection beams are connected via a connecting portion, and the connecting portion is supported by a support portion fixed to the substrate. The present invention can also be applied to a tripod tuning fork type vibration type angular velocity sensor.

  In the first embodiment, the protective film 8 is formed so as to cover the piezoelectric films 6b and 7b included in the drive element 6 and the detection element 7, and in the second embodiment, the protective film 8 is configured by an oxide piezoelectric body. The base material 10 was covered with the protective film 8. In each of these embodiments, the protective film 8 is made of a material different from the oxide piezoelectric film or the oxide piezoelectric body included in the drive element 6 and the detection element 7. On the other hand, the protective film 8 can be made of the same material as the oxide piezoelectric film or the oxide piezoelectric body included in the drive element 6 and the detection element 7. For example, the surface of each piezoelectric film 6b, 7b included in the drive element 6 or the detection element 7 or the surface of the base material 10 made of an oxide piezoelectric material is made amorphous by ion implantation. Thereby, since the detachment of oxygen is suppressed in the amorphized portion, the protective film 8 can be constituted by the amorphous layer.

  Moreover, in each said embodiment, although the drive element 6 and the detection element 7 were comprised separately, these can also be comprised by one element. For example, in the configuration of the first embodiment, in the structure in which the lower layer electrode, the piezoelectric film, and the upper layer electrode are stacked, the arm portions 2 and 3 are connected by applying a driving voltage between the lower layer electrode and the upper layer electrode. Drive vibration can be performed. Further, when the arm portions 2 and 3 are deformed by the Coriolis force, the piezoelectric film is deformed accordingly, so that it can be taken out as an electric signal between the lower layer electrode and the upper layer electrode. Therefore, it is also possible to serve as the drive element 6 and the detection element 7 with one element.

  In each of the above embodiments, both the drive element 6 and the detection element 7 are composed of piezoelectric elements, but only one of them may be used.

DESCRIPTION OF SYMBOLS 1 Vibrator 2, 3 Arm part 4 Connection part 5 Support part 6 Drive element 7 Detection element 8 Protective film 10 Base material

Claims (9)

An arm portion (2, 3) that is driven to vibrate, a drive element (6) that drives and vibrates the arm portion, and a detection element (7) that extracts deformation caused by the angular velocity applied during the drive vibration as an electric signal. A vibratory angular velocity sensor comprising: a vibrator (1) having a vibrator; and the vibrator is sealed by a vacuum seal or a low-pressure seal that is at a lower pressure than atmospheric pressure,
One of the drive element and the detection element is composed of a piezoelectric element including an oxide piezoelectric film (6b, 7b) or a block-shaped oxide piezoelectric body (10),
The vibration type angular velocity sensor further comprises a protective film (8) covering the surface of the oxide piezoelectric film or the oxide piezoelectric body.   The vibration type angular velocity sensor according to claim 1, wherein the protective film is made of an insulating oxide. The vibration type angular velocity sensor according to claim 2, wherein the insulating oxide is LP-TEOS or ALD-Al ₂ O ₃ .   The vibration type angular velocity sensor according to claim 1, wherein the protective film is an insulating nitride.   The vibration type angular velocity sensor according to claim 1, wherein the protective film is a nitride piezoelectric film.   6. The vibration type angular velocity sensor according to claim 5, wherein the insulating nitride is AlN or ScAlN.   2. The vibration type angular velocity sensor according to claim 1, wherein the protective film is configured by an amorphous layer obtained by amorphizing a surface of the oxide piezoelectric film or the oxide piezoelectric body.   The vibrator is formed using a semiconductor material as a base material, and the driving element or the detection element includes a lower electrode (6a, 7a), an oxide piezoelectric film (6b, 7b) and an upper layer on the base material. The vibration type angular velocity sensor according to any one of claims 1 to 7, wherein the electrode (6c, 7c) is laminated.   The vibrator is formed by using the oxide piezoelectric body as a base material, and the driving element or the detection element includes a first electrode (6f, 7f) and a second electrode (6g) spaced apart from each other on the base material. 7g), the vibration type angular velocity sensor according to any one of claims 1 to 7.

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