JPH0810811B2 - Structure of piezoelectric resonator for overtone oscillation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a piezoelectric resonator, in particular, a piezoelectric for overtone oscillation that enables oscillation at a desired overtone frequency without requiring a special oscillation circuit. It relates to the structure of a resonator.

(Prior Art) In recent years, in various electronic devices such as communication devices, the demands for higher frequency and ultra-miniaturization have become more severe. In addition to the use of overtone vibration of piezoelectric resonators such as resonators, surface acoustic wave (SAW) resonators have been widely used.

However, the former generally extracts the desired output through an LC tuning circuit that is tuned to the desired overtone frequency, or inserts an LC tuning circuit in a part of the oscillator circuit so that the negative resistance of the circuit causes the desired overtone. They are designed to be sufficiently large only in the frequency domain, and all of them have a defect that they require a coil and are extremely inconvenient in promoting the IC of the oscillation circuit.

On the other hand, as is well known, the oscillation frequency of the SAW resonator is uniquely determined by the material of the piezoelectric substrate and the pitch of the interdigital transducer (IDT) electrodes formed on the surface of the piezoelectric substrate, so that the resonator itself can be downsized. Although there is no problem in the circuit as described above, it has a defect that it is far inferior to the AT cut crystal unit in terms of frequency-temperature characteristics.

By the way, in the past, in the field of manufacturing crystal oscillators, etc., when the crystal substrate of the oscillator is made smaller due to the demand for miniaturization of the oscillator, the aspect ratio of the crystal substrate and the dimensional ratio of the side to the substrate thickness are specified. It is known that when the value reaches the value of the above range, it often oscillates with third-order or fifth-order overtone vibration, and there has been a problem how to suppress such a phenomenon.

Therefore, a patent application has been filed by the Siemens company in West Germany for the idea of using this phenomenon to obtain a crystal unit for overtone oscillation (Japanese Patent Publication No. 58-29890).

However, according to the invention of the above patent application, it is unavoidable to make the size of the quartz substrate extremely smaller than the size of the excitation electrode, and the influence of the supporting strain around the quartz substrate affects the excitation part, so that the frequency-temperature There are problems such as unstable characteristics, variations in resonance frequency before and after thermal cycle, and large changes in resonance frequency with time. It was not applicable to oscillators that require high frequency stability.

In order to solve all the defects of the conventional resonator as described above, the present inventor has already proposed in Japanese Patent Application No. 60-77065 that the vibration energy of overtone vibration of a desired order or more is applied to the excitation electrode at the center of the piezoelectric substrate. While confining, the vibration energy of the lower-order overtone vibration including the fundamental wave vibration is leaked, and the leaked energy is arranged in the outer periphery of the excitation electrode with a required gap (the above-mentioned application). (Hereinafter, referred to as “vibration energy absorption section”) and converted into heat to be consumed and the impedance for the desired order overtone vibration and that for lower order overtone vibration including the fundamental wave. It has been clarified that a sufficient head drop can be provided between the two to cause oscillation due to the overtone vibration of the desired order.

Further, the inventor of the present application has found that the above-mentioned idea is the lowest symmetry (S
o) Not only the use of mode vibration, but also higher-order symmetry (S ₁ , S ₂ ,
...) mode and asymmetric _{(a 0, a 1, a} 2, was disclosed that is expandable applicable to the use of the vibration of ...) mode (see Japanese Patent Application No. Sho 61-9756).

Therefore, when the above-mentioned resonator is used, in order to adapt it to all kinds of oscillation circuits, considering that the absolute value of the load resistance on the oscillation circuit side is larger on the low frequency side, the fundamental vibration is included. Since it is necessary to sufficiently absorb the vibration energy of the lower-order overtone vibration, it is necessary to provide the vibration energy propagation region of the above-mentioned unnecessary vibration on the outer peripheral portion of the resonator piezoelectric substrate, and the portion is a simple point or line. It was already known that the shape had to be a region having a certain area with almost no effect, but since it was unclear how to set the cutoff frequency of the region, at the beginning of manufacturing Since the unnecessary vibration energy propagation region is formed with the electrode film thickness corresponding to the excitation electrode in consideration of easiness, there is a problem that a sufficient satisfactory unnecessary vibration suppressing effect may not be obtained.

With respect to this problem, the inventor of the present application clarified experimentally how much the cutoff frequency of the unnecessary vibration energy propagation region should be set in the original application for the divisional application.

On the other hand, the present situation is that the structure of the piezoelectric resonator for overtone oscillation as described above is not considered sufficiently for practical use.

(Object of the Invention) The present invention has been made in view of the above-mentioned structural problems in the piezoelectric resonator for overtone oscillation. It is intended to provide an overtone piezoelectric resonator having a structure capable of sufficiently exhibiting the characteristics.

(Outline of the Invention) In order to achieve the above-mentioned object, an overtone piezoelectric resonator according to the present invention separates a required gap (vibration energy propagating portion) from an excitation electrode forming a vibration energy confining portion having a cutoff frequency f _1. Then, at least the sub-electrode that constitutes the unnecessary vibration energy propagation part having the cut-off frequency f ₃ (where f ₃ <f ₁ ) extends from both sides of the excitation electrode to the vicinity of the outer edge of the piezoelectric substrate, and the excitation electrode and the sub-electrode are provided. One of the electrodes is connected to the front and back of the piezoelectric substrate by a conductive pattern.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.

Prior to describing the embodiments to facilitate understanding of the present invention, an overtone oscillation resonator to which the present invention should be applied will be briefly described with reference to FIG.

In FIG. 2 (a), electrodes 2 and 2'having a diameter of 2a are attached to both sides of the central portion of the piezoelectric substrate 1 having a thickness H, and the cutoff frequency of the portion is changed.
₂ between the cut-off frequency ₂ becomes part of the surrounding allowed drops ₁ - ₁ comprising providing a cut-off frequency difference the electrodes 2, 2 'attachment confinement vibration energy unit, the non-electrode portions 3, 3' vibration of the The sub-electrodes 4 and 4'are provided at appropriate positions on the outer periphery of the energy propagation section.
Provide an unnecessary vibration energy propagation area with cutoff frequency f ₃ (f ₃ ≈f ₁ <f ₂ ) attached.

Considering the case where this resonator is used as, for example, a resonator for fifth-order overtone oscillation, the vibration energy confinement ratio of the fundamental wave (first-order) and third-order overtone vibration is reduced to 7
If the next overtone is set to be large, the equivalent resistance for the fifth or higher-order overtone vibration in which the vibration energy is confined is larger as the overtone order is higher.

On the other hand, the vibration energy of the fundamental wave and the third overtone vibration leaks toward the outer peripheral edge of the piezoelectric substrate 1 and the sub electrodes 4,
Since the unnecessary vibration energy propagation region to which 4'is adhered propagates in a so-called propagation mode without loss and is consumed through the supporting portion on the outer peripheral edge of the resonator, the impedance for these vibrations becomes extremely high and the fifth order overtone is eventually obtained. A resonator for oscillation is obtained.

In order to obtain the above characteristics, the vibration energy confinement rate T ₅ of the _fifth overtone vibration is first set to about 80% as shown in FIG. From this figure, T ₅ = 80%
Confinement factor in Is approximately 0.53, but the above confinement factor Since n, H, ₂ and a are the conditions, it can be easily calculated how much value ₁ should be selected. ₁ Sadamare if cutoff frequency difference ₂ - ₁ is the resonator as shown in the from electrode deposition amount that satisfies this by an amount directly related to the so-called plate back is already known (a) to easily produce be able to.

However, as described above, the cut-off frequency f ₁ of the vibration energy confinement part to which the excitation electrodes 2 and 2'are attached and the sub-electrode 4,
Cutoff frequency f ₃ of unwanted vibration energy propagation part with 4'attached
When the values of and are almost equal, according to the experimental result disclosed by the inventor of the above-mentioned Japanese Patent Application No. 60-77065, the diameter is 7 mm.
50MH at 3rd overtone using AT cut quartz substrate
In a resonator intended to oscillate z,
The CI value for the next overtone vibration is 150 Ω and 52 Ω, respectively, with the end of the unwanted vibration energy propagating portion simply held by a clip and an alternating electric field is applied, and 280 Ω and 52 Ω, respectively, with the clip portion further fixed with a conductive adhesive. It is about 53Ω, which is sufficient to prove the theory of the piezoelectric resonator for overtone oscillation, but in practice there is a shortage in the CI value, which may cause oscillation at an undesired frequency depending on the characteristics of the oscillation circuit. I didn't say no.

Therefore, in order to solve this problem, the inventor of the present application has a cut-off frequency f ₁ of a vibration energy confining portion having a planar shape as shown in FIG. 3 and attached with excitation electrodes 2 and 2'and sub-electrodes 4 extending on both sides thereof. , 4'are attached to the cut-off frequency f _{3 of} the unnecessary vibration energy propagation region, that is, the electrode film thickness ratio is changed in several steps, and as a result of the experiment, the CI of the fundamental wave vibration and the third-order overtone vibration are It has been found that there is a difference in the difference in value as shown in FIG.

According to the present invention, as a result, that is, the cut-off frequency f ₃ of the unnecessary vibration energy propagation region to which the sub-electrodes 4 and 4 ′ are attached is set to the excitation electrodes 2 and 2 ′.
In the piezoelectric resonator for overtone oscillation in which the cut-off frequency f ₁ of the attached vibration energy confinement portion is lowered, preferably significantly reduced, as shown in FIG. 2'and one of the sub-electrodes 4,4 'constituting the unnecessary vibration energy propagation region are connected to the conductive patterns 5,5' on the front and back of the piezoelectric substrate 1, respectively.

The resonator having such a structure can hold the resonator and energize the excitation electrodes 2 and 2'by connecting to the lead wire at the outer peripheral edge of the piezoelectric substrate 1 where the sub electrodes 4 and 4'are present. It is needless to say that the above-mentioned application disclosed in Japanese Patent Application No. 60-77065 mentioned above can be carried out simultaneously, and since the connecting point between the lead wire and the resonator is generally fixed by a conductive adhesive or the like. As is clear from the experimental results by the inventor, it is possible to sufficiently consume the unnecessary vibration energy and increase the CI value thereof.

According to the present invention, as shown in FIG. 5 (a), the piezoelectric substrates in the unnecessary vibration energy propagation region to which the sub-electrodes 4 and 4'are attached are made thick to obtain a sufficient reduction amount of the cutoff frequency of the portion. A conductor is vapor-deposited on the excitation electrode 2, as shown in FIG.
It will be apparent that the same can be applied to the case where the thickness of the piezoelectric substrate of the vibration energy confining portion to which 2'is attached is reduced by etching or the like to intend oscillation with higher overtone vibration.

(Effect of the Invention) Since the overtone oscillation piezoelectric resonator according to the present invention has the structure as described above, a slight modification is required to increase the deposition amount in the unnecessary vibration energy propagation region compared to other portions. Except for the need, not only can a general piezoelectric resonator be manufactured in exactly the same way, but its mechanical fixing and energization of the excitation electrode can be performed at the same time, and moreover, the consumption of vibration energy of the vibration which is not desired to be oscillated can be sufficiently consumed. Therefore, there is a remarkable effect in supplying a resonator capable of stable overtone oscillation without increasing the manufacturing cost.

[Brief description of drawings]

1 (a) and 1 (b) are a plan view and an AA sectional view showing an embodiment of an overtone piezoelectric resonator according to the present invention, and FIGS. 2 (a) to 2 (c) are related to the present invention. FIG. 4 is a diagram illustrating the principle of such an overtone piezoelectric resonator, FIG. 3 is a diagram showing parameters of the resonator used in the experiment for determining the thickness of the sub-electrode, and FIG.
FIG. 5 is a diagram showing the experimental results showing the relationship of the CI drop between the fundamental wave vibration and the third-order overtone vibration with respect to the film thickness ratio between the auxiliary electrode and the excitation electrode. FIGS. 5 (a) and 5 (b) relate to the present invention. It is sectional drawing which shows the other Example of an overtone piezoelectric resonator. 1 ... Piezoelectric substrate, 2, 2 '... Excitation electrode (vibration energy confinement part), 3, 3' ... Non-electrode part (vibration energy propagation part), 4, 4 '... Sub electrode (unnecessary vibration energy propagation) Area), 5 ... Conductive pattern

Claims (1)

[Claims] _{1. A} cut-off frequency f _{1 is provided on the} front and back of the piezoelectric substrate at the center of the piezoelectric substrate.
The excitation electrode forming the vibration energy confinement part has a cutoff frequency f ₂ (where f ₁ <
f ₂ ) further comprises a vibration energy propagating portion, which is an outer periphery of the vibration energy propagating portion and extends from at least both sides of the vibration energy confining portion to near the outer edges of the front and back surfaces of the piezoelectric substrate,
Cutoff frequency f ₃ for propagating the vibration energy of overtone vibration of a lower order than the overtone vibration of the desired order of oscillation including oscillation of the fundamental wave that leaks in a large amount outside the region surrounded by the vibration energy propagating portion in the propagation mode (Where f ₃ <f ₁ ) is provided with a sub-electrode that constitutes an unnecessary vibration energy propagation region, and one of the excitation electrode and the sub-electrode is connected by a conductive pattern on the front and back of the piezoelectric substrate, respectively. Structure of piezoelectric resonator for overtone oscillation.