JPH0354895B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vibrator and a piezoelectric filter that utilize bending vibration of a single piezoelectric element. In particular, interdigitated electrodes are formed parallel to one side on a single square piezoelectric plate, making it easy to support. It relates to something that uses saddle-shaped bending vibration.

Conventionally, vibrators that utilize the bending vibration of piezoelectric materials
It is used in audio frequency acoustics such as telephone receivers, speakers, buzzers, microphones, and pickups, vibration sensors, transducers for airborne ultrasound, and resonators and filter elements in frequency bands of several hundred kilohertz or less.

As a typical example of a bending vibrator, one having a bimorph structure in which two piezoelectric plates or a piezoelectric plate and a metal plate are bonded together with an adhesive is known. However, due to the presence of an adhesive layer in this bimorph structure, variations in resonance frequency and Q (quality factor)
This is undesirable as it causes a decrease in

On the other hand, as a piezoelectric single bending vibrator without adhesive,
A configuration in which multiple strip electrodes provided on the surface of a piezoelectric ceramic are alternately polarized and driven with alternating current has been proposed, for example, by Tanaka (``Barium titanate and its applications'', published by Ohmsha, 1965, p. 117) and Konno et al. Proceedings of the Acoustical Society of Japan, October 1970, Paper No. 3-4-17, p. 405)
It is stated by. Although these configurations mainly utilize the piezoelectric longitudinal effect, they have rarely been used until now because the capacitance ratio cannot be reduced.

In contrast, Shimizu et al., among the inventors, proposed a normal bimorph resonator that utilizes the piezoelectric transverse effect by providing interdigital electrodes (comb-shaped electrodes) on the surface of a piezoelectric ceramic plate in parallel to the direction of expansion/contraction strain. Patent application No. 57-56313 concerning a single piezoelectric bending vibrator with a small capacitance ratio comparable to , and a single mode bending vibration piezoelectric filter
(Japanese Patent Application Laid-Open No. 173912/1982).

As a result of further research, the inventors of the present invention have developed a single piezoelectric bending vibrator and a piezoelectric filter that do not rely on a bonded structure, which are easier to support than those of the patent application No. 57-56313, and have a much smaller spurious response. It is an object of the present invention to provide a single piezoelectric bending vibrator and a three-terminal or four-terminal bending vibration piezoelectric filter.

In the present invention, a plurality of electrodes are provided on at least one side of a square piezoelectric plate in parallel with a side, the plurality of electrodes are connected every other to form an interdigital electrode, and a direct current is applied to the interdigital electrode. A saddle shape in which a voltage is applied to polarize the piezoelectric plate, and plane-perpendicular bending vibrations of opposite phases occur on two center lines parallel to the sides of the square piezoelectric plate, and the two diagonal lines are vibration nodal lines. This is a single piezoelectric bending vibrator characterized in that the vibration mode is excited and detected by the interdigital electrodes.

The present invention further provides a filter using such a piezoelectric vibrator.

According to the present invention, by using a square piezoelectric plate and making use of not only the piezoelectric transverse effect but also the piezoelectric longitudinal effect, it is possible to generate a saddle that cannot be driven with a normal bimorph vibrator. A unique bending vibrator and filter that can excite shaped bending vibrations, are easy to support, and have extremely low spurious resonance responses are obtained.

The operating principle of the present invention will be explained.

FIG. 1 shows the basic structure of a bending vibrator according to the present invention, in which interdigital electrodes 2 and 3 are configured to be parallel to one side of a square piezoelectric plate 1, and these electrodes are arranged on the periphery of every other electrode. is connected to the extraction electrode. Then, a voltage is applied between the interdigital electrodes 2 and 3 to polarize the electrodes in a direction perpendicular to the length direction of the electrodes.

If this structure is driven by applying an AC voltage to 2 and 3, the driving force of the piezoelectric transverse effect and the piezoelectric longitudinal effect will be added, and the two center lines as shown in Fig. 2 will be applied. Surface perpendicular bending vibrations with opposite phases occur on A-B and CD, and two diagonal lines M-
A saddle-shaped vibration mode with vibration node lines M' and N-N' is excited. That is, when the end of one center line AB is displaced upward in the plane, the end of the other center line CD is displaced downward in the plane. Such a vibration mode is difficult to excite using a normal bimorph structure.

The resonance frequency and vibration mode of the piezoelectric vibrator according to the present invention were calculated using the finite element method.

Figure 3 a is a two-dimensional representation of the distribution of displacement μ _z in the surface-perpendicular direction (Z direction) in the 1/4 area of the piezoelectric plate (for example, the area surrounded by 0AMD in Figure 2). . The length of the diagonal line represents the size of u _z . From this figure, we can see that the displacement becomes larger as you get closer to the center line 0-A (or 0-D) along the side from the nodal line 0-M, and on the center line, the closer you get to the side from the center, the larger the displacement becomes. , △0AM and △0MD indicate that the displacements in the area are in opposite phases.

Figure b similarly shows the displacements u _x and u _y in the x and y directions on the surface of the plate for the 1/4 area.For convenience, only the changes in the contour are shown, and the displacement is 10 times larger than in figure a. The figure is enlarged to . u _x and u _y are equal in size and in opposite phase on the top and bottom surfaces of the plate.

As is clear from FIGS. 3a and 3b, in the piezoelectric bending vibrator according to the present invention, the vibration displacement in the x and y directions is extremely small, and it is clear that the bending vibration mainly vibrates in the thickness direction of the piezoelectric plate. It is.

As described above, the strain distribution on the surface of the square piezoelectric plate was calculated in order to find the electrode shape for effectively exciting the vibration mode of the saddle-shaped bending vibration according to the present invention. Figure 4 shows the distribution of principal distortion values in the 1/4 area, and the arrows indicate the magnitude and direction of distortion. Each stretching strain S _xx in the x and y directions,
This shows that S _yy is large and the shear strain S _xy in the xy plane is small. From the strain distribution in FIG. 4, it can be seen that the interdigital electrodes should be arranged parallel to one side. That is, the stretching strain in the direction parallel to the electrode finger due to the piezoelectric transverse effect and the stretching strain in the direction perpendicular to the electrode finger due to the piezoelectric longitudinal effect occur in opposite phases, and both of them cause the excitation of the saddle-shaped vibration mode. It will work additively with respect to

From FIG. 3a and FIG. 4, the four corners M of the vibrator,
At points M', N, and N', the displacement u _z and strains S _xx and S _yy are both zero, so even if these four corners are held down, the influence on this mode is small, and it is convenient to support them.

In order to determine the shape and size of the active region of the interdigital electrodes for efficiently exciting the saddle-shaped bending vibration mode in the present invention, the following calculations were performed.

As clarified in the above-mentioned Japanese Patent Application No. 57-56313, in the case of utilizing the piezoelectric transverse effect, when the ratio a/p of the electrode width a and the electrode period p is 0.5, the capacitance ratio is the minimum, and the piezoelectric When using the longitudinal effect, the smaller a/p is, the smaller the capacity ratio becomes.If a/p is set to 0.3,
The capacity ratio in the case of using the horizontal effect is approximately 1/2 of that in the case of using the vertical effect. Therefore, the effective distortion of the symmetric saddle mode, which is directly linked to the piezoelectric transverse effect and the piezoelectric longitudinal effect |
The distribution of S _xx |+|S _yy /√2| was calculated. The results are shown in FIG. In the figure, the maximum value at the center 0 is set as 10, and is expressed as an isovalue line. (however,
The direction of the electrode fingers of the interdigital electrodes is parallel to the x direction. ) Based on the above results, we fabricated a bending vibrator. A square piezoelectric ceramic plate with a side of 10 mm and a thickness of 0.5 mm (lead zirconate titanate manufactured by Tohoku Metal Industry Co., Ltd.)
N6 material), p=0.5mm, a/p 0.2, 0.3,
0.5, and the capacitance ratio γ and admittance characteristics were measured by forming interdigital electrodes on both sides with the outline of the active region approximately aligned with the contour line 4 in FIG. 5 so that the active region was as wide as possible. The results are shown in FIG. The resonance frequency of the main vibration is 14.9KHz, and the capacitance ratio γ
This shows that a fairly small oscillator with a value of 11 to 12.5 can be obtained. Also, when a/p is 0.2, the spurious response is very small, but when a/p is 0.3 and 0.5
The larger the value, the more the spurious response appears. In particular, the spurious response of a mode whose nodal lines are two diagonal lines, similar to the nodal line of the main vibration, as shown in FIG. 7, is large. Therefore, the following calculations were performed to suppress these spurious signals.

The capacitance ratio γ is proportional to the electrode area (area of the active region) A, and inversely proportional to the square of the integration of the mode strain S within the active region, that is, γ=k
Since it is expressed as A/(∫ _A SdA) ² (k: constant), the active area (area is A) for the capacitance ratio γ ₀ when the entire surface is electroded (the total area A ₀ of the plate is the active area) is The ratio γ/γ ₀ of the capacitance ratio γ when changed can be expressed by the following equation.

γ/γ ₀ = A (∫ _A0 SdA) ² /A ₀ (∫ _A SdA) ²
...(1) Equation (1) in the mode of main vibration and spurious response (mode shown in Fig. 7) when l shown in Fig. 8 is changed so as to symmetrically change the active area of the interdigital electrode. The value was calculated. The results are shown in FIG. 9, and it can be seen that in order to simultaneously suppress the spurious response of the mode shown in FIG. 7, it is sufficient to set l/l ₀ =0.42. Figures 10a and 10b show experimental results to prove this. Figure a shows the case where interdigital electrodes are provided as close to the full surface electrode as possible (l/l ₀ ≒ 0.8), and figure b shows l/l.
This figure shows the input admittance characteristics when the electrodes are formed so that l ₀ =0.42. l/
It was experimentally confirmed that when l ₀ =0.42, spurious responses are significantly suppressed. The capacitance ratio γ of the main vibration is approximately 17, which is when the entire surface is electroded (γ = 11.5).
It is 1.5 times that of , which agrees well with the calculation results shown in Figure 9.

The above has been explained using the embodiment of the vibrator according to the present invention, but by forming interdigital electrodes parallel to one side on a square piezoelectric plate, the piezoelectric transverse effect and the piezoelectric longitudinal effect are additively utilized. We have demonstrated that it is possible to obtain a single piezoelectric bending vibrator that has a small capacitance ratio comparable to that of conventional bimorph vibrators, has no adhesive layer, is easy to support, and has low spurious responses.

Next, a piezoelectric filter, which is another aspect of the present invention, will be explained.

By applying the above bending vibrator, a three-terminal or four-terminal single mode filter is constructed.

The piezoelectric filter according to the present invention has two types of interdigital electrodes formed parallel to one side of a square piezoelectric plate, and a signal is input from one electrode to excite bending vibration, which is then transmitted to the other electrode as an electric signal. It is converted into and extracted.

A specific example thereof is shown in FIG. 11 and subsequent figures.

In Fig. 11, interdigital electrodes are formed on one side of the piezoelectric plate 1, one electrode is divided into two electrodes 4 and 6 at the center, one for input and the other for output. This is a three-terminal (or four-terminal) filter with electrode 5 as a common electrode. Figure b is the same as figure a.
The cross section is shown at AB, and symbols 7 and 8 are input and output terminals connected to the electrodes 4 and 6.
Symbol 9 is a lead-out electrode for connecting the common electrode to the ground electrode.

In FIG. 12, electrodes similar to those in FIG. 11 are formed on both sides of a piezoelectric plate 1 so that the front and back sides face each other.
Reference numerals 7 and 8 are input and output terminals connected to the opposing electrodes 4 and 6 on the front and back sides, respectively, and 9 is a common terminal connected to the electrodes 5 on the front and back sides.

In FIGS. 11 and 12, the interdigital electrodes are divided into two at the center to serve as input and output electrodes.
FIGS. 13 and 14 show an example in which the way the electrodes are divided is changed so that input electrodes and output electrodes are alternately arranged in a complicated shape. Figure 13 shows the case where the electrode is divided into three parts, and the electrode 4,
4' is an input terminal, 6, 6' and 7, 7' are output terminals (6 and 7 are connected), and 5, 5' are common terminals. In FIG. 14, the common electrodes 5, 5' are shaped like a meander line (zigzag line), and input electrodes 4, 4' and output electrodes 6, 6' are arranged on both sides of the common electrodes 5, 5'. With this kind of electrode arrangement,
Spurious responses caused by dividing the electrodes in FIGS. 11 and 12 into two are suppressed, and the characteristics are improved.

FIG. 15 shows an example of filter characteristics when a single mode three-terminal filter is constructed using the electrodes shown in FIG. 13.

The structure of the piezoelectric filter of the present invention has been described above. According to the present invention, a filter with relatively low frequency and low loss can be realized with relatively small dimensions, and there is no adhesive layer like a bimorph resonator. Therefore, variations in characteristics are reduced, and furthermore, since it takes a saddle-shaped vibration mode, the two diagonal lines become vibration nodal lines, making it extremely easy to support. Also,
Spurious resonance responses are suppressed up to high frequency ranges, making it possible to provide high-quality piezoelectric filters.

In addition, conventional techniques such as screen printing coating of silver powder, sputtering method, and vapor deposition method are sufficient for forming the electrodes in the present invention, and since electrodes of arbitrary shapes can be easily produced by photoetching method, the main method is It is possible to determine the active region of the interdigital electrodes according to the strain distribution that strongly excites vibrations and suppresses spurious responses.

In addition, with the single mode filter obtained by the present invention, a filter with high selectivity can be easily obtained by directly connecting multiple filters with the same characteristics in cascade without using a coupling capacitance or the like. Naturally, these are also included in the present invention.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the basic structure of the bending vibrator according to the present invention, FIG. 2 is a diagram explaining the vibration mode of the bending vibrator shown in FIG. 1, and FIG. A diagram showing the distribution of displacement in the direction perpendicular to the surface in a plane. Figure 3b is a diagram showing the amount of displacement in the x and y directions on the surface of the plate in the 1/4 area, and Figure 4 is a diagram showing the displacement in the x and y directions in the 1/4 area. Figure 5 is a diagram showing the distribution of effective strain in the symmetric saddle mode, Figure 6 is the admittance of the flexural oscillator when changing the electrode width a and the electrode period p. 7 is a diagram showing the vibration mode, FIG. 8 is a diagram showing the active region of the interdigital electrode, FIG. 9 is a diagram showing the relationship between the active region and the capacitance ratio, and FIG. 10a, b is
FIG. 11 is a diagram showing the admittance characteristics of different active regions, and FIG. 11 is a diagram showing an example of a piezoelectric filter. FIG. 11 is a plan view, FIG.
Figures 1 to 14 are diagrams showing other different embodiments of the piezoelectric filter, in which figure a is a plan view, figure b is a sectional view, and figure 1 is a cross-sectional view.
FIG. 5 is a diagram showing filter characteristics of a three-terminal filter using the electrode configuration of FIG. 13. 1... Piezoelectric ceramic plate, 2, 3... Interdigital electrodes,
4, 4'... Input terminal, 5, 5'... Common terminal,
6, 6', 7, 7'...Output terminals.

Claims (1)

[Claims] 1. A plurality of electrodes are provided on at least one side of a square piezoelectric plate in parallel with one side, and the plurality of electrodes are connected every other to form an interdigital electrode, and the interdigital electrode A DC voltage is applied to the electrodes to polarize the piezoelectric plate, and plane-perpendicular bending vibrations with opposite phases occur on two center lines parallel to the sides of the square piezoelectric plate, with the two diagonal lines serving as vibration nodal lines. A single piezoelectric bending vibrator characterized in that a saddle-shaped vibration mode is excited and detected by the interdigital electrodes. 2 Scope of Claims In the piezoelectric single bending vibrator according to claim 1, the shape of the interdigital electrodes is
1. A single piezoelectric bending vibrator, characterized in that it is formed in accordance with the strain distribution of the vibrator so as to strongly excite the saddle-shaped bending vibration mode of the main vibration, while suppressing the excitation of the spurious mode. 3 Form interdigital electrodes with electrode fingers parallel to one side on at least one side of a square piezoelectric plate, apply DC voltage to the interdigital electrodes to polarize the piezoelectric plate, and polarize the piezoelectric plate. In a single piezoelectric bending vibrator that utilizes a saddle-shaped vibration mode in which plane-perpendicular bending vibrations occur in opposite phases on two center lines and two diagonal lines serve as vibration nodal lines, the interdigital electrodes are excited to vibrate. It is divided into two parts, one for use and one for detection.
A piezoelectric filter characterized by forming a terminal or four-terminal filter. 4. Scope of Claims In the piezoelectric filter according to claim 3, the shape of the interdigital electrodes is such that the vibrator is configured to strongly excite the saddle-shaped bending vibration mode of the main vibration, while suppressing the excitation of the spurious mode. A piezoelectric filter characterized in that it is formed to match the strain distribution of.