JPH05102786A - Piezoelectric vibrator - Google Patents

Abstract

PURPOSE:To surely warrant stable suppression effect by making a main electrode and a sub electrode mismatching and connecting a damping impedance to the sub electrode. CONSTITUTION:A main electrode 1 and a sub electrode 2 are arranged separately on a front side of a piezoelectric plate 4 and a common electrode is disposed on a rear side opposite to the main electrode and the sub electrode 2 on the front side. When the electrode widths W1, W2 differ and both the electrodes 1, 2 are adjusted to a substrate resonance frequency, the thickness of the sub electrode 2 is made thicker than the thickness of the main electrode 1. When an oscillation circuit is formed by connecting the piezoelectric vibrators, the fundamental frequency component of an oscillation amplifier section is efficiently consumed by a damping impedance 5 connecting from the main electrode 1 to the sub electrode 2 and the oscillation at the fundamental frequency is efficiently suppressed, Since the thickness of the sub electrode 2 differs from the thickness of the main electrode 1, a ternary overtone frequency is delivered to the sub electrode 2 and oscillated excellently without consumption and attenuation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric vibrator in which a pair of main electrodes are provided on the front and back surfaces of a piezoelectric plate, and in particular, a predetermined overtone resonance frequency is frequency-selectively suppressed and a desired overtone is obtained. The present invention relates to a piezoelectric vibrator in which a sub-electrode that allows frequency-selective oscillation of a resonance frequency is provided and a damping impedance is connected.

[0002]

2. Description of the Related Art When a small-sized piezoelectric oscillator circuit that oscillates at a desired overtone resonance frequency is formed by using a chip-type semiconductor element, a chip-type inductor is provided in an oscillation circuit formed by the small-sized piezoelectric vibrator and the chip-type semiconductor element. In general, the difficulty of high-order overtone oscillation of a piezoelectric vibrator is solved by inserting a tuning tank circuit of a capacitor and a capacitor so as to have a frequency selection characteristic. However, in a small oscillation circuit, the volume occupied by the tuning tank circuit becomes relatively large,
The tuning tank circuit has been one of the components to be removed because not only the frequency adjustment is required but also the stability of the oscillation frequency may be significantly impaired by the temperature fluctuation. As a high-order overtone piezoelectric vibrator for the purpose of solving this problem, the following two means are already known.

The first means is disclosed in JP-A-61-236208.
No. 62-168409 and 62-169508.
No. 62-169509, No. 62-169510, and the like. When the vibration displacement distribution of the piezoelectric vibrating plate is confined in the excitation electrode, the higher the vibration order becomes, the more the confinement range becomes. Uses the peculiar effect of the energy confinement phenomenon of being concentrated by the excitation electrode. At this time, if the sub-electrodes are spaced apart from each other in the vicinity of the excitation electrodes, the vibration energy is mechanically-electrically converted and extracted as electric energy on the sub-electrodes, as the resonance vibration has a lower order. If the vibration energy is consumed by short-circuiting the sub-electrodes, it is possible to selectively attenuate and suppress low-order overtone vibrations, especially fundamental vibrations, thereby providing a high-order overtone piezoelectric vibrator. ..

The second means is Japanese Patent Application No. 62-230108.
The piezoelectric diaphragm is mechanically held by merely disposing the main electrode asymmetrically on the surface of the piezoelectric diaphragm without disposing the characteristic sub-electrode by the first means. The vibration energy of low-order vibration is mechanically and acoustically transmitted to the tool to be absorbed and dissipated. It is based on almost the same principle as the first means, and is intended to provide, for example, a third-order overtone piezoelectric vibrator in which fundamental wave resonance vibration is suppressed.

In the first means, since the sub-electrode and the main electrode can be arranged on the surface of the piezoelectric plate at the same time, it is possible to set parameters which require control such as arrangement, thickness and shape relatively easily. It was considered an advantageous measure. Since the electromechanical coupling coefficient indicating the electromechanical conversion efficiency is about 50% even in the case of PZT, the energy conversion efficiency proportional to the square of this coupling coefficient is about 25%. However,
Since the mechanical-acoustic matching between both electrodes is not considered at all, the mismatch loss is large, and the electrical matching is not considered for the load, so it can be said that the extracted energy is efficiently consumed. It is difficult to control the vibration energy of the main electrode by only a few percent. Piezoelectric plate with a particularly low electromechanical coupling coefficient, eg electromechanical coupling coefficient 10%
In the crystal plate and the like, it is almost impossible to expect any effect by this resonance vibration suppressing means. Actually, the suppression effect by the first means is insufficient and the operation is unstable, and it has not yet been widely used. The second means is to directly transmit the vibration energy mechanically and acoustically to the cage without converting it electrically, so that the energy is dissipated.
It is considered that it is easy to use and exhibits practically effective effects as compared with the first means. However, in order to realize various vibrators, it is necessary to conduct an experiment by confirming the optimum external dimensions and electrode arrangement of the piezoelectric diaphragm, which is probably an empirical procedure. It was not necessarily appropriate as a teaching principle, and there was a strong demand for establishment of a rational overtone oscillator design method. In addition, the second means has many problems to be solved, such as the higher the resonance frequency becomes, the more difficult it is to realize, and the second means has not yet been widely used.

[0006]

In order to establish an effective and rational design method for realizing a piezoelectric vibrator that reliably and stably oscillates a desired higher resonance frequency, the following basic problems are solved. There was a need. Conventionally, the vibration energy of low-order resonance vibration is extracted by utilizing the mechanical-acoustic coupling that naturally exists between the main electrode and the sub-electrode or between the main electrode and the cage, but regarding acoustic matching, No consideration at all. That is, since a mismatched acoustic coupling between two electrodes physically separated or between the electrode and the holder is simply used, a part of the vibration energy to be suppressed is extracted. However, the vibration energy extracted in this mismatched state is consumed or dissipated in the same electrical or mechanoacoustic mismatched state due to electrode short circuit or mechanical holding. Is. Eventually, only a small part of the vibrational energy to be suppressed can be suppressed. In other words, in order to realize a stable and reliable high-order resonance frequency overtone piezoelectric vibrator, the main and sub electrodes are mechanically acoustically matched at the resonance frequency to be suppressed, and the most efficient and reliable It is necessary to extract the vibration energy of the main electrode so that the extracted energy is consumed to the maximum extent possible, and at the desired resonance frequency for oscillation purpose, the vibration energy of the main electrode is converted to the auxiliary electrode as much as possible. An acoustic mismatch between the electrodes must be maintained to prevent extraction.

The present invention has been made in view of this problem, and at the resonance frequency to be suppressed, the main electrode and the sub-electrode form a pass band type acoustic coupling filter to efficiently select the vibration energy of the main electrode in a frequency selective manner. In order not to suppress the oscillation frequency by extracting it to the auxiliary electrode and consuming it at the same time as the damping impedance that is connected to or disposed in the auxiliary electrode, and by making the main electrode and the auxiliary electrode in a mismatched state at the desired oscillation frequency. It is an object of the present invention to provide a piezoelectric vibrator for high-order overtone, which is characterized by setting a constituent parameter of an electrode. The present invention utilizes the following two phenomena to solve this problem.

[0008]

First, the phenomenon that the resonance frequency of an electrode is lower than the resonance frequency (cutoff frequency) of the piezoelectric plate when the electrodes are arranged on the front and back plate surfaces of the piezoelectric plate is utilized. The amount of frequency decrease depends not only on the thickness of the electrode but also on the shape and size. Therefore, even if electrodes with the same thickness and the same electrode material are arranged, the actual (apparent) frequency decrease will occur if the electrode shape is smaller. It is known that the amount is small.
FIG. 5 shows this relationship. That is, with respect to the true frequency back amount Rt which depends only on the thickness of the electrode material when the electrodes are arranged on the entire front and back plate surfaces of the piezoelectric plate, the apparent frequency back amount in consideration of the shape and size of the electrode. It is well known that a nonlinear frequency back amount relationship is established between the quantities Rq. It is known that the relationship between the two frequency back amounts and the electrode shape changes with the overtone order, and the difference decreases as the order rises. The present invention has been made by utilizing this relationship. That is, to explain with reference to the example of FIGS. 1 and 2 which is an embodiment of the present invention, the electrode width and the electrode thickness of the two electrodes are the main electrode 1 (W1, H1) and the sub electrode 2 (W, respectively).
2, H2), W1> W2, and the fundamental wave resonance frequency f1m of the main electrode 1 is adjusted to match the fundamental wave resonance frequency of the auxiliary electrode, and the relationship of H1 <H2 is established. Since the overtone vibration is generally confined by the electrode periphery as compared with the fundamental wave vibration, the apparent frequency back amount Rq becomes less dependent on the electrode shape as the overtone vibration order rises.
That is, since the frequency difference between the true frequency back amount and the apparent frequency back amount becomes small, the overtone resonance frequency f3s of the auxiliary electrode 2 becomes lower than the overtone resonance frequency f3m of the main electrode 1, so that f3m> The frequency relationship of f3s is obtained, and as a result, both frequencies do not match (FIG. 3).

Secondly, a phenomenon that a simple integral multiple (odd multiple) relationship is not established between overtone resonance frequencies including the fundamental wave of the piezoelectric diaphragm is used. This relationship is expressed by a frequency relational expression derived from the piezoelectric vibration basic equation, and is well known empirically. This relationship will be described by taking the thickness longitudinal vibration of a piezoelectric ceramic polarized in the direction perpendicular to the plate surface as an example. As a matter of course, the same relational expression holds in the thickness shear vibration of the piezoelectric plate polarized in the direction parallel to the plate surface or in the thickness vibration system of other piezoelectric materials. In an infinite ceramics piezoelectric plate with a thickness of 2h, the resonance frequency function formula of the thickness longitudinal vibration is expressed as a tangent function transcendental equation including the electromechanical coupling coefficient term (K26) as shown in Formula 1, and therefore the root of this relational expression is It is obtained as the intersection of the curve and the straight line in FIG. Therefore, unless the electromechanical coupling coefficient (K26) is 0, the resonance angular frequency coefficient (ηn)
h (n = 1, 3, 5 ...., ηn = ωn / c, ωn: n
It is easily understood that a simple integer (odd number) multiple relationship does not hold between the following overtone angular frequency, c: speed of sound in the medium.

The present invention is constructed by utilizing these two phenomena. The main electrode and the sub-electrode pair similar to a monolithic filter are spaced on the front and back plate surfaces of the piezoelectric plate to suppress the main electrode. The electrodes should be separated by an appropriate distance so that both electrodes form a band-pass acoustic coupling filter at the desired resonance frequency, and the resonance frequencies of the two electrodes do not match at the desired resonance frequency, resulting in an acoustic mismatch. Set a different shape and size, adjust the frequency of the sub-electrode to the resonance frequency to be suppressed by the main electrode, and connect or arrange the damping impedance to the sub-electrode to set the specified resonance vibration of the main electrode to the frequency. It is intended to realize a piezoelectric vibrator that selectively suppresses and can oscillate a desired resonance vibration in a frequency-selective manner.

[0011]

1 and 2 show an embodiment of the present invention. 1 shows a piezoelectric plate structure of a piezoelectric vibrator for the purpose of suppressing a fundamental wave resonance frequency f1m of a main electrode 1 and selectively oscillating a third overtone resonance frequency f3m. A main electrode 1 and a sub-electrode 2 are separated from each other on the front surface of the piezoelectric plate 4, and a common electrode 3 is disposed on the back surface so as to face the main electrode 1 and the sub-electrode 2 on the front surface. If the electrode widths W1 and W2 are different, if the two electrodes 1 and 2 are adjusted to the fundamental wave resonance frequency f1m, the sub electrode 2
Can be made thicker than the thickness H1 of the main electrode 1. Then, at the fundamental wave frequency f1m of the main electrode 1, both electrodes 1 and 2 can form a passband type acoustic coupling filter, but since the shape dimensions of both electrodes are different, it is not always good at the resonance frequency f1a of obliquely symmetric vibration. A pass band cannot be formed and a distorted transmission characteristic as shown in FIG. 3 is exhibited. When the piezoelectric vibrator is connected to form the oscillation circuit shown in FIG. 3, for example, the fundamental wave frequency f1 in the oscillation amplification unit 6 is increased.
Since the frequency component of m is efficiently transmitted to the damping impedance 5 (matching impedance Z) connected from the main electrode 1 to the sub electrode 2 and consumed, the fundamental frequency f
Oscillation of 1 m is effectively suppressed. Connecting the matching impedance Z to the sub-electrode 2 generally corresponds to impedance matching at the output end of the bandpass filter, and the component of the fundamental frequency f1m to be suppressed has a small loss and high damping impedance 5 of the sub-electrode 2. It is transmitted to and consumed. The electrode thickness H2 of the sub-electrode 2 is the main electrode 1
The desired third-overtone frequency f3m of the main electrode and the third-overtone frequency f3s of the auxiliary electrode 2 do not match and do not match because the thickness is different from the thickness H1 of the third electrode. Good oscillation can be performed without being transmitted to the electrode 2 and being consumed and being attenuated. In this example,
Since the dimension L0 in the length direction of the electrode shape is designed to be equal, the dimension in the width direction is set to W1 ≠ W2. Here, the dimension in the width direction may be made equal and the dimension in the length direction may be different, or both dimensions may be different. When the two dimensions are different, the oblique symmetry that normally occurs in a two-electrode configuration is used. Vibration can be suppressed more effectively. The distance G0 between both electrodes is designed in consideration of the amount of attenuation of the fundamental resonance frequency f1m to be suppressed and the influence on the desired third-order overtone resonance frequency f3m.
When 0 is set to a large value, the pass band is narrowed to correspond to an increase in the insertion loss amount of the filter, and the suppression effect is attenuated. Therefore, the suppression effect of the fundamental wave frequency f1m and the effect on the desired resonance frequency f3m are reduced. It must be decided in consideration of both. However, in any case, the monolithic filter design method can be applied as it is, which is very convenient. In FIG. 3, the transmission characteristic shows a transmission characteristic in which loss is greatly distorted at the resonance frequency f1a of obliquely symmetric vibration, but this is a rather preferable characteristic. This is because if the overtone resonance frequency of the obliquely symmetric vibration similarly appears at the desired overtone resonance frequency, it may coincide with the desired oscillation frequency and suppress it. Undesired vibration modes such as must be suppressed. The damping impedance 5 is not limited to a small surface mount type resistor, and a resistance film formed by a carbon film or a metal film may be formed between both electrodes. The impedance of the reactance component such as a capacitor may be connected or arranged in parallel to the resistance component. The damping impedance 5 and the sub-electrode 2 can be connected to each other by wiring, which is electrically led out from the piezoelectric vibrator. The common electrode 3 may face the respective main electrodes and sub-electrodes, and may be independently provided with the same pattern as both electrodes. If a resistance material film is used for the sub-electrodes, it is possible to omit adding damping impedance, but it is necessary to adjust the resistance value or the like after the arrangement. In the present embodiment, the resonance vibration to be suppressed is a specific harmonic resonance vibration, but spurious vibrations due to unnecessary vibration modes can be suppressed in exactly the same manner. In this case, in general, the change in the unwanted vibration mode due to the temperature is very large as compared with the main vibration, so that the acoustic coupling is likely to become sparse during the temperature change, and it is not appropriate to set a wide operating temperature range for the purpose. When the present invention is applied to a crystal resonator, the electromechanical coupling coefficient is extremely small, so that the crystal resonator can function extremely effectively as compared with the conventional example.

FIG. 7 shows another embodiment of the present invention. In the embodiment shown in FIG. 1, since the main electrode 1 and the sub electrode 2 have a similar structure to the monolithic filter, the resonance frequency f1a of obliquely symmetric vibration may still be exhibited. If the shapes of the main electrode and the sub-electrode are made asymmetric, a certain suppression effect can be expected. However, in order to further increase the suppression effect, if two sub-electrodes 7 and 8 are provided at both ends of the main electrode 9, resonance vibration will occur. The induced charge on the sub-electrode is attenuated on both sides, so that it is effectively suppressed. It is more effective if the sub-electrodes are connected in common, and in the vicinity of the desired overtone resonance frequency,
It is very convenient because there is no fear that an overtone resonance frequency of obliquely symmetric vibration will occur. When the resonance frequencies to be suppressed of the sub-electrodes 7 and 8 are set to be different, the shapes of the electrodes are different, so that the frequencies can be adjusted independently, and then the damping impedances 9 and 10 may be connected. For example, it is possible to oscillate the overtone resonance frequency of a desired order, such as suppressing the fundamental wave and the third overtone and selectively oscillating only the fifth overtone. In this case, since the sub-electrodes 7 and 8 are set to have different shapes and sizes from each other, the effect of suppressing the oblique symmetric vibration is maintained as it is due to the different shapes and the effect of canceling the induced charges. Therefore, compared with the embodiment of FIG. 1, the suppressing effect is generally remarkable, the influence on the desired oscillation frequency is large, and it is necessary to increase the distance between the electrodes somewhat. Other operations and characteristics are almost the same as those in the embodiment of FIG.

FIG. 8 shows another embodiment of the present invention. Each sub-electrode 11, 12, 13, 14 forms a band-pass type acoustic coupling filter at the overtone resonance frequency to be suppressed independently of the main electrode 16 and does not match at the desired overtone resonance frequency. The shape size and thickness of each sub-electrode are set. Main electrode 1 and each sub-electrode 1
The distances 1, 12, 13, 14 are set in consideration of the degree of suppression of the overtone resonance frequency to be suppressed and the degree of influence on the desired overtone resonance frequency, as in the case of each of the above embodiments. Is. According to the configuration of the embodiment shown in FIG. 8, for example, when a seventh-order overtone piezoelectric vibrator is to be obtained, the fundamental wave, the third-order, the fifth-order, and the ninth-order overtone resonance frequencies are suppressed. The parameters of the main electrode 1 and each sub electrode may be designed. This design is a little complicated, requiring twice the computational procedure for the propagation in the width direction and twice for the propagation in the length direction, which are almost equal to those of the monolithic filter.

[0014]

By adopting the constitution of the present invention, the machine-
Even in the case of a piezoelectric plate such as a crystal plate having a poor electrical conversion efficiency, it is possible to selectively extract and suppress the resonance vibration of the frequency that should be efficiently suppressed for the first time by the extraction means by the mechanical-acoustic matching of the predetermined vibration energy. It is now possible to reasonably and accurately design the resonance frequency to be suppressed. In particular, by providing or connecting a damping impedance to the sub-electrode in order to adopt an effective impedance matching means similar to that of a monolithic filter, it is possible to ensure a more reliable and stable suppression effect than in the past. became. Another effect of the present invention is that the occurrence of obliquely symmetric vibration can be considerably suppressed by the asymmetrical configuration of the main electrode and the sub electrode, but it is also effectively suppressed by separating the sub electrodes at both ends of the main electrode to cancel the charge. I can do it. Furthermore, up to four overtone resonance frequencies can be independently suppressed, and a reliable and stable overtone piezoelectric oscillator for oscillation of the third or higher higher tone resonance frequencies is provided. For the first time, the realization of oscillators became possible. In particular, it is of great significance to be able to provide a piezoelectric vibrator capable of particularly oscillating a higher-order resonance frequency of the fifth order or higher, which has been difficult in the past. The present invention is
It is effective not only for realizing a high-order overtone oscillator, but also as a means for removing spurious due to a specific unwanted vibration mode. In this case, the configuration, function, and effect are similar to those described above, except that the resonance frequency of the sub-electrode is adjusted to match the frequency of the unwanted vibration mode of the main electrode to be suppressed.

[Brief description of drawings]

FIG. 1 is a perspective view of a piezoelectric plate of a piezoelectric vibrator showing an embodiment of the present invention.

2 is a cross-sectional view of the piezoelectric plate of the embodiment of the present invention shown in FIG.

FIG. 3 is an oscillation circuit diagram in which the piezoelectric vibrator of the present invention is connected.

FIG. 4 is a transmission characteristic diagram showing the piezoelectric vibrator of the embodiment of the present invention in FIG. 1 in the oscillation circuit in FIG.

FIG. 5 is a graph showing the relationship between the true frequency back amount Rt and the apparent frequency back amount Rq when the electrode width dimension W0 of the piezoelectric plate is used as a parameter.

FIG. 6 is a graph illustrating the relationship between resonance frequencies of the piezoelectric ceramic plate.

FIG. 7 is a perspective view of a piezoelectric plate showing another embodiment of the present invention.

FIG. 8 is a plan view of a piezoelectric plate showing another embodiment of the present invention.

[Explanation of symbols]

1 Main Electrode 2,7,8,11,12,13,14 Sub-electrode 3 Common Electrode 4 Piezoelectric Plate 6 Oscillation Amplifier 5,14,15,16,17 Damping Impedance 1 ', 3'Extraction Electrode

Claims (1)

[Claims] 1. A piezoelectric vibrator in which main electrodes are arranged facing each other on the front and back plate surfaces of a piezoelectric plate and electrically led to the outside, and the main electrodes are separated from the main electrodes and face the front and back surfaces of the piezoelectric plate. At least one sub-electrode is provided, and at the resonance frequency of the main electrode to be suppressed, the main electrode and the sub-electrode form a band-pass type acoustic coupling filter for damping the resonance frequency to be suppressed. And, in order to make the acoustic coupling between the main electrode and the sub-electrode mismatch by making the resonance frequency of the main electrode different from the resonance frequency of the sub-electrode, an appropriate distance between the main electrode and the sub-electrode is provided. Damping impedances that are set to different shapes and dimensions, and the resonance frequency of the sub-electrode is adjusted to the resonance frequency of the main electrode to be suppressed, so that the sub-electrode has a damping impedance substantially equal to the load impedance of the acoustic coupling filter. A piezoelectric vibrator characterized by being connected.