KR900000077B1 - Piezo electric device - Google Patents

Abstract

The three terminal piezoelectric filter has a square piezoelectric substrate with a first and a second side, having a ring electrode deposited on the above-mentioned first side and a center electrode deposited around within the ring electrode. The center electrode has at least one arm extending along the direction of diagonal line of substrate and a ground electrode is deposited on the second side of the substrate. And also the substrate can be of paralleogram.

Description

Piezoelectric element

1a, b and c are schematic views of a three-terminal piezoelectric filter element according to the prior art.

FIG. 2 is a circuit diagram of a filter using the three-terminal piezoelectric filter element of FIGS. 1A-1C.

3a, b and c are schematic views of a two-terminal piezoelectric resonator element which is fast in the prior art.

4 is a circuit diagram of a ladder filter using a two-terminal piezoelectric resonance element.

5 is a graph showing impedance characteristics of a rectangular piezoelectric element.

6A-B are diagrams showing charge distribution of rectangular piezoelectric elements for dominant vibration and various spurious vibrations.

7a, b and c are top, bottom, and cross-sectional views of a three-terminal piezoelectric filter element according to a first embodiment of the present invention.

8, 9, 10, 11, and 12 are plan views showing different modifications of the three-terminal piezoelectric filter element of FIG. 7A.

Figures 13a, b and c are partial views showing different shapes of the arm tips.

14 is a circuit diagram of an IF filter for an AM radio receiver using the piezoelectric filter element of the present invention.

FIG. 15 is a circuit diagram similar to FIG. 14 but further using a transformer.

FIG. 16 is the same as that of FIG. 15, but uses a coupling capacitor with a piezoelectric filter element of the prior art.

17 is a graph showing the frequency characteristics of the IF filter of FIG.

FIG. 18 is a graph showing the spurious characteristics of the IF filter of FIG.

19 is a graph showing the frequency characteristics of the IF filter of FIG.

20 is a graph showing the spurious characteristics of the IF filter of FIG.

21 is a graph showing the frequency characteristics of the IF filter of FIG.

22 is a graph showing the spurious characteristics of the IF filter of FIG.

23a, b and c are top, bottom and sectional views of a two-terminal piezoelectric resonator device according to a second embodiment of the present invention.

FIG. 24 is a government plane diagram showing a modification of the second implementation. FIG.

* Explanation of symbols for main parts of the drawings

1 piezoelectric plate 2 ring electrode

4 ground electrode 5 filter element

13: center electrode 55, 56: resonator device

62: rim 65: first electrode

67: piezoelectric plate 69: second electrode

A piezoelectric element such as a three-terminal piezoelectric filter element used in an intermediate frequency (IF) filter for an AM lion receiver of the present invention or a two-terminal piezoelectric resonator element used in a ladder filter or an oscillator.

A three-terminal piezoelectric filter element 5 is shown in Figs. 1A-1C, which includes a rectangular piezoelectric plate 1, a ring electrode 2, a center electrode 3, and a ground electrode 4. The ring electrode 2 and the center electrode 3 are deposited on one side of the piezoelectric plate and the ground electrode 4 is deposited on the other side thereof.

When a three-terminal piezoelectric filter element is used for the IF filter of an AM radio receiver, two or more filter elements 5 are in series with the coupling capacitor Co inserted in the data transmission line in the manner shown in FIG. Connected. In Fig. 2, the data transmission signal D is connected between the center electrodes, but it can be connected between the ring electrodes or between the center and the ring electrodes. The capacitor Co inserted in the data transmission line is provided to reduce the coupling effect.

In view of minimizing the size of the IF filter, it is preferable to eliminate the coupling capacitor Co, which is normally externally provided to the chip element containing other circuit elements. However, the coupling effect will not be reduced to the required level when the coupling capacitor Co is removed to directly connect the central electric cable. In this case the coupling effect is reduced by reducing the electrostatic capacitance between the center electrode 3 and the ground electrode 4 and also by reducing the conversion effect between the electrical signal and the mechanical motion of the filter element. However, other problems arise, such that when the center electrode is greatly reduced at large, unwanted spurious vibrations are produced in the frequency ranges of x3, x5, and x7 of the filtering frequency.

Therefore, in the prior art, the IF filter of the above-described type without the coupling capacitor Co has not been practically used.

An example of a two-terminal piezoelectric resonator element 55 is shown in Figs. 3A-3C, which includes a rectangular piezoelectric plate 57, a first electrode 58 and a second electrode 59. The first electrode 58 and the second electrode 59 are deposited on opposite surfaces of the piezoelectric plate. The size of the first electrode 58 is smaller than the size of the second electrode 59 to reduce the electrostatic capacitance. In use, at least one serially connected two-terminal piezoelectric resonator 55 and at least one parallel-connected two-terminal piezoelectric resonator 56 are outputted with input terminals 51 and 52 in the manner shown in FIG. The terminals 53 and 54 are connected to form a ladder filter. However, the problem as described above occurs when the unwanted spurious vibration is calculated in the frequency ranges of 1.5, 3, 5, and 7 of the resonance frequency when the first electrode is reduced in size.

The present invention has been developed in view of substantially solving the above-mentioned drawbacks and its typical object is to provide an improved piezoelectric element such as a three-terminal piezoelectric filter element or a two-terminal piezoelectric resonator element which has a small electrostatic capacitance and reduces spurious vibration. will be.

It is a further object of the present invention to provide an improved piezoelectric element of the type described above which can be easily manufactured. In achieving these and other objects, a three-terminal piezoelectric filter element according to one preferred embodiment of the present invention is a quadrilateral piezoelectric plate having first and second surfaces, a ring electrode deposited on a first surface around the piezoelectric plate, and a ring. It has a center electrode deposited on a first side of one portion within the electrode and a ground electrode deposited on a second side of the piezoelectric plate. The central electrode has at least one arm extending along at least one diagonal of the piezoelectric plate.

According to another embodiment of the present invention, a two-terminal piezoelectric resonator element includes a quadrilateral piezoelectric plate having first and second surfaces, a first electrode deposited on the first surface, and a second electrode deposited on the second surface of the piezoelectric plate. Have The first electrode is formed by a ring portion provided around the piezoelectric plate and a central portion having at least one arm of the piezoelectric plate.

These and other objects and aspects of the invention will appear from the following description taken in connection with the preferred practice thereof with reference to the accompanying drawings.

Prior to the description of the present invention, spurious vibrations will be described with reference to FIGS. 5 and 6A-6L.

In order to investigate the spurious vibration, the impedance characteristics of the piezoelectric element test model having a size of 4.9 x 4.9 x 0.5 (mm) with electrodes completely deposited on opposite flat surfaces are detected. The material used for the piezoelectric element test model is the same as that shown in Fig. 1a or 3a or any of the elements used in the present invention. The impedance characteristics as detected are shown in FIG. 5, where peak VIIa represents the change in impedance of the frequency for the required or dominant manner of vibration, while the other peaks VIIa-VIIl are spurious system vibrations. Indicates the change in impedance of the frequency for.

The obtained impedance characteristics are compared with the impedance characteristics obtained by the computer simulation of the same model through the finite element method and find that the impedance characteristics obtained by the computer simulation are very similar to those obtained through the actual test. Using a computer further, charge distributions for different vibration frequencies are obtained.

In Fig. 6a, the charge distribution of the dominant mode of vibration is shown. The rectangle indicated by the dotted line indicates the shape of the piezoelectric element, and the area enclosed by the solid line indicates the distribution of electric charge such as the (-) charge observed at one moment. At the next moment, ie after half a cycle, the area enclosed by the solid line is filled with a positive charge.

FIG. 6B shows the charge distribution of the first spurious method of vibration corresponding to the peak ＂b＂ indicated in FIG. Similarly, FIGS. 6C-6L show a spurious charge distribution of vibrations corresponding to the peaks ＂c＂-＂＂ shown in FIG. As shown in FIG. 5, the spurious vibrations produced at peaks ＂c＂, ＂g＂, ＂h＂ and ＂i＂ are very weak with very small amplitudes and they can be ignored. The piezoelectric element according to the present invention has a spurious oscillation in the manner described below, in particular peaks ＂b＂, ＂e＂, ＂f＂, with charge distributions indicated in degrees 6b, 6e, 6f, 6j, 6k and 6l, respectively. It is arranged to suppress or eliminate the spurious vibrations calculated in ＂j＂, k ＂and＂ l ＂.

7A, 7B and 7C, a three-terminal piezoelectric filter element 11 according to the first embodiment of the present invention is shown. The three-terminal piezoelectric filter element 11 has a four-sided piezoelectric plate 1 such as a rectangular shape having an opposing flat surface. The ground electrode 4 is entirely deposited on one of the flat surfaces of the plate 1, and the ring electrode 2 and the center electrode 13 are deposited on the other flat surface. A ring electrode 2 is provided in the ring of the other flat surface, and a central electrode 13 is provided in the area surrounded by the ring electrode 2. According to the first embodiment, the ring electrode 2 has four arms (a1), (a2), (a3) and (a4) extending from the center of the piezoelectric plate along the diagonals (d1) and (d2) in the shape of X. It is easily changed by changing the width of. Spurious vibrations are suppressed by the method described below.

The spurious oscillation of the peak ＂d 를 has the charge distribution shown in Figure 6d, where the positive charge is centered and the negative charge lies at four corners. When the center electrode 13 is applied, the arms a1-a4 are bridged to the negative and positive charge regions, thereby balancing the charge accumulated in these regions, invalidating the distribution shown in FIG. . Thus spurious vibrations are eliminated or suppressed. In a similar manner, the arms shown in Figs. 6e, 6f, 6j, 6k, and 6l by the arms extending inwardly, suppress the spurious vibrations.

Again, when two arm structures are to be used, any two of the four arms are provided to be arranged in a straight or V shape. By way of example the arms a2 and a4 are provided in FIG. 10 but instead the arms a1 and a3 may be provided. Instead, arms a1 and a2 or arms a2 and a3 may be provided.

Furthermore, according to the present invention, the end of each arm indicated as an awl may be round as shown in FIG. 13A, or may be provided as a cutting edge which forms two to provide a right corner as shown in FIG.

These corners may be rounded as in FIG. 13C. Furthermore, although not shown, a cutout or protrusion may be formed on each arm.

Again, the arm may be curved as long as the arm generally extends in the diagonal direction.

The two piezoelectric filter elements of FIGS. 7A-7C are connected to the AM radio receiving IF filter in the manner shown in FIG. 14 to obtain frequency characteristics, spurious characteristics and various filter data. In the test operation, signals having frequencies of 445-465 KHz and 0-10 KHz are inputted from the standard signal generator 21 to the first stage piezoelectric filter element 11a and the signal output from the second stage piezoelectric filter element 11b is a high frequency voltmeter. It is detected by (22). In the circuit of Fig. 14, the circuit element has the following specification.

R _g + R ₁ = R ₂ = 3000Ω

C ₁ = 50 pF

In the detected result, FIG. 17 shows frequency characteristics, FIG. 18 shows spurious characteristics, and various filter data are shown in Table 1 below.

TABLE 1

Referring to Fig. 15, another IF filter is displayed, which further has a transformer T1 connected to the input side of the first stage piezoelectric filter element 11a. In the circuit of Fig. 15, the circuit element has the following specification.

R11 = 300Ω R12 = 2KΩ

C10 = 7pF C11 = 50pF

The same test operation was performed for the circuit of FIG. 15, and in the detected result, FIG. 19 shows frequency characteristics, FIG. 20 shows spurious characteristics, and various filter data are shown in Table 2 below.

TABLE 2

Referring to FIG. 16, a circuit similar to FIG. 15 is shown for comparison purposes. Instead of the piezoelectric filter elements 11a and 11b, piezoelectric filter elements 5a and 5b as shown in Figs. 1a-1c are provided with the coupling capacitor Co.

The same test operation is performed for the circuit of FIG. 16, and in the detected results, FIG. 21 shows frequency characteristics, FIG. 22 shows spurious characteristics, and various filter data are shown in Table 3 below.

TABLE 3

According to the test results, the IF filter (FIG. 15) using the piezoelectric filter element according to the present invention has a similar operation characteristic to that of the IF filter (FIG. 16) used in the piezoelectric filter element of the prior art. In fact, the IF filter (FIG. 15) according to the present invention exhibited better spurious suppression than the IF filter (FIG. 16) of the prior art.

By way of example, when Tables 2 and 3 are compared, it is understood that the IF filter (FIG. 15) according to the present invention suppresses spurious vibrations which add about 8 dB in the frequency range 0-3 MHz than the IF filter (FIG. 16) of the prior art. .

The peak of the attenuation in the frequency domain on the center frequency fo is also about 58 dB for the IF filter (FIG. 15) according to the invention, while the same is about 48 dB for the IF filter of the prior art.

Therefore, it can be said that the IF filter (FIG. 15) according to the present invention suppresses the spurious vibration of thickness of about 10 dB more in the frequency range 5.5-7 KHz than the IF filter (FIG. 16) of the prior art. It should be noted that the piezoelectric filter elements 5a and 5b and the piezoelectric filter elements 11a and 11b have different thicknesses. It is understood that the suppression of the thickness spurious vibrations contributes strongly to the surface charges caused by the thickness vibrations so that the small size of the central electrode causes a reduction in driving efficiency. Referring to FIGS. 23A, 23B and 23C, a two-terminal piezoelectric resonator element 61 according to a second embodiment of the present invention is shown. The two-terminal resonator element 61 has a four-sided piezoelectric plate 67 such as a rectangle having opposing flat surfaces 67a and 67b. The first electrode 65 is deposited on one flat surface 67a and the second electrode 69 is deposited on the other flat surface 67b.

The first electrode 65 has four arms a1, a2, a3, and a4 extending from four corners along the diagonal lines d1 and d2 so as to form a cross in the ring portion. 67a) by a ring portion 62 extending in a rectangular shape.

The second electrode 69 is entirely deposited on the flat surface 67b. When the first electrode 65 is arranged in the manner shown in FIG. 23a, the first electrode 65 is reduced in comparison with that shown in FIG. 1a and thus the electrostatic capacitance is reduced. The electrostatic capacitance can be easily changed by changing the width of each of the arms a1, a2, a3 and a4. By the arms a1, a2, a3 and a4, the spurious vibration is suppressed in the manner described above. The two-terminal piezoelectric resonator element according to the second embodiment is changed in various ways. By way of example, the number of arms a1-a4 is equal to the two arms d2 and d4 as shown in FIG. 24 as long as the arms generally extend along the diagonals d1 and / or d2. At least better than four. The piezoelectric resonator element can also be arranged in parallel quadrilateral as in the modification of the first embodiment.

When the piezoelectric resonator element of the present invention is used in a ladder filter, at least one of the two-terminal piezoelectric resonator elements connected in series must be the two-terminal piezoelectric resonator element of the present invention shown in Figs. 23A-23C, and the two stages connected in series. The piezoelectric resonator element may be according to the prior art as shown in FIGS. 3A-3C.

Two-terminal piezoelectric resonator elements connected in parallel should be according to the prior art.

When the ladder filter is arranged in the manner described above, the spurious vibration is suppressed and at the same time the ladder filter can be arranged in a compact size as described below.

In view of the reduction in the size of the ladder filter (FIG. 4), the number of piezoelectric resonator elements should be reduced, and at the same time the size of each resonator element should be reduced, but the required filter characteristics should not be lost.

For this purpose, it is necessary to increase the electrostatic capacitance ratio of the resonators connected in series to the resonators 56 connected in parallel. This is due to the decay of the number, which is the shape of the filter characteristic, but large, but improved by using the resonators 55 and 56 having a mechanical quality factor Qm. In order to increase the electrostatic capacitance ratio of the resonators 55 and 56, the flow rate of the piezoelectric element 55 should be reduced, and at the same time the thickness of the piezoelectric element 55 should be made thick. Moreover, the dielectric constant of the piezoelectric element 56 should be increased and at the same time the thickness of the element 56 should be made thin. However, if the piezoelectric element 55 is made thick, the size of the ladder filter may not be reduced to the required size. Again, when the piezoelectric element 56 is made thin, the piezoelectric element is easily broken. However, by using the resonator element of the present invention, the electrostatic capacitance can be easily controlled by changing the width of the arms a1-a4 without changing the thickness of the resonator element or the required filter characteristics.

While the present invention has been fully described with reference to some preferred embodiments, many modifications and variations thereof will appear to those trained in the art, and therefore the scope of the invention is not limited by the details of the preferred embodiments described above, but the It will be limited only by the item of the claim.

Claims (17)

The three-terminal piezoelectric filter element has a quadrilateral piezoelectric plate 1 having first and second surfaces, a ring electrode 2 deposited on the first surface around the piezoelectric plate, and the first surface at a portion in the ring electrode. And a central electrode 13 having at least one arm extending along the at least one diagonal of the piezoelectric plate, wherein the ground electrode 4 is deposited on the second surface of the piezoelectric plate. 3-terminal piezoelectric filter element. The three-terminal piezoelectric filter element according to claim 1, wherein the piezoelectric plate (1) is rectangular. 3. The three-terminal piezoelectric filter element according to claim 1, wherein the piezoelectric plate (1) is in parallel four deformation. 3. The terminal according to claim 1, wherein the center electrode 13 has four arms a1, a2, a3, a4 extending from the center of the piezoelectric plate in the shape of X along the diagonal of the piezoelectric plate. Piezoelectric filter element. 3. The three-terminal piezoelectric element according to claim 1, wherein the center electrode 13 has three arms (for example, a1 and a2 a4) extending from the center of the piezoelectric plate in the shape of T along the diagonal of the piezoelectric plate. Filter element. The three-terminal piezoelectric filter element according to claim 1, wherein the image center electrode (13) has two arms (for example, a2 and a4) extending from the center of the piezoelectric plate along the diagonal of the piezoelectric plate. The three-terminal piezoelectric filter element according to claim 1, wherein the arm has an awl at its end. The three-terminal piezoelectric filter element according to claim 1, wherein the arm has a rounded shape. The three-terminal piezoelectric filter element according to claim 1, wherein the arm is formed by two right corners thereof. The filter has at least first and second three-terminal piezoelectric filter elements 11a and 11b, each having a quadrilateral piezoelectric plate 1 having first and second surfaces, and the first periphery of the quadrilateral plate. The center electrode 13 has a ring electrode 2 deposited on a surface and a central electrode 13 deposited on a first surface at a portion in the ring electrode, the center electrode having at least one arm extending along at least one diagonal line of the piezoelectric plate. A ground electrode 4 is deposited on the second surface of the piezoelectric plate and connected to the ground, and an input line is connected to one of the center electrode 13 and the ring electrode 2 of the first three-terminal piezoelectric filter element. The data transmission line is either one of the center electrode 13 and the ring electrode 2 of the second three-terminal piezoelectric filter element and the other of the center electrode 13 and the ring electrode 2 of the first three-terminal piezoelectric filter element. Connected between one and the output line is connected to the other of the center electrode 13 and the ring electrode 2 of the second three-terminal piezoelectric filter element Featured filter. The two-terminal piezoelectric resonator element has a quadrilateral piezoelectric plate 67 having first and second surfaces and a first electrode 65 deposited on the first surface, and the first electrode includes a ring portion provided around the piezoelectric plate. 62) and a central portion having at least one arm (a1, a2, a3, a4) extending along at least one diagonal of the piezoelectric plate, wherein the second electrode 69 is the second surface of the piezoelectric plate. A two-terminal piezoelectric resonator element, characterized in that deposited on. 12. The two-terminal piezoelectric resonator element according to claim 11, wherein the piezoelectric plate is rectangular. 12. The two-terminal piezoelectric resonator element according to claim 11, wherein the piezoelectric plate (67) is in a parallel quadrilateral shape. 12. The two-terminal piezoelectric resonator device according to claim 11, wherein the center electrode has four arms a1, a2, a3, a4 extending from the center of the piezoelectric plate in the shape of X along the diagonal line of the piezoelectric plate. . 12. The two-terminal piezoelectric resonator device according to claim 11, wherein the central electrode has three arms (for example, a1, a2, a4) extending from the center of the piezoelectric plate in the form of T along the diagonal of the piezoelectric plate. . 12. The two-terminal piezoelectric resonator device according to claim 11, wherein the center electrode has two arms (for example, a2 and a4) extending from the center of the piezoelectric plate along the diagonal of the piezoelectric plate. A two-terminal piezoelectric resonator element 56 in which a ladder filter has at least one series-connected two-terminal piezoelectric resonator element 55 and at least one parallel-connected two-terminal piezoelectric resonator element 56; The element 55 has a quadrilateral piezoelectric plate 67 having first and second surfaces and a first electrode 65 deposited on the first surface, the first electrode having a ring portion 62 provided around the piezoelectric plate. And a central portion having at least one arm (a1, a2, a3, a4) extending along at least one diagonal of the piezoelectric plate, and the second electrode 69 is deposited on the second surface of the piezoelectric plate. A two-terminal piezoelectric resonator element, characterized in that.

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