JP2000124764A - Strip-shaped piezoelectric resonator for frequency filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the band width of a piezoelectric resonator with its simple constitution when the resonator is used to a frequency filter by polarizing the resonator over its front face and in its thickness direction, providing the electrodes on the main surfaces of both sides of the resonator, excluding the electrodes on both sides and at both end of the resonator to form an inactive part at the using end part. SOLUTION: The electrodes 3 and 4 are formed on both sides of a piezoelectric resonator 1a using a thin plate-like piezoelectric magnetic plate 2 consisting of lead zirconate titanate PZT, and the inactive parts Y having no electrodes are prepared on both sides and at both ends of the plate 2 with main surfaces having the electrodes 3 and 4 used as the active parts X, respectively. Both parts X and Y are polarized over the front face and in the thickness direction of the resonator 1a. A piezoelectric ceramic sintered body is obtained by pressing and burning a raw material of a prescribed composition and then polished to obtain the plate 2 of the prescribed thickness. Then the electrodes 3 and 4 are formed on both sides of the plate 2 by the screen printing and by means of the silver paste. Thus, the parts X includes the electrodes 3 and 4 and the parts Y include no electrodes 3 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strip-shaped piezoelectric resonator used for a radio device or the like and used for a ladder-type piezoelectric frequency filter or the like in which a plurality of piezoelectric resonators are combined in series and parallel.

[0002]

2. Description of the Related Art A frequency filter of this type is constituted by connecting a plurality of basic unit circuits each having an L-shaped connection of a thick-walled, small-capacitance series resonator and a thin-walled, large-capacity parallel resonator. It is configured to be stored inside. Each of the conventional resonators
Electrodes are formed on both sides of the piezoelectric ceramic plate, and are polarized in the thickness direction to form a strip. The parallel resonator (P) and the series resonator (S) formed of the strip-shaped piezoelectric resonators constitute a frequency filtering circuit as shown in FIG.

[0003]

In the above-described strip-shaped resonator, the piezoelectric transverse effect in which the electric field direction and the polarization direction are different from the vibration direction is used. The electromechanical coupling coefficient (K ₃₁ ) is lower than that of a piezoelectric resonator using the piezoelectric longitudinal effect that matches the above. For this reason, Δf which is the difference between the resonance frequency fr and the anti-resonance frequency fa is relatively small, and there has been a problem that the bandwidth becomes narrow when used in a frequency filter. In particular, in recent years, with the spread of digital communication, a broadband filter has been demanded, and this is a major problem to be solved. An object of the present invention is to solve such a problem of the strip resonator with a simple configuration.

[0004]

SUMMARY OF THE INVENTION According to the present invention, an electrode is polarized in the thickness direction over the entire surface, and electrodes are provided on the front and back main surfaces. This is a strip-shaped piezoelectric resonator used for a frequency filter characterized by forming an active portion.

[0005] In this piezoelectric resonator, when the length of the active portion is set to 51.8 to 86.9% with respect to the total length of the resonator used as a series resonator, the resonance frequency is determined by experiments. And the difference Δf from the anti-resonance frequency became large and good. In particular, an excellent value was obtained at about 58% or more, and it was confirmed that this was suitable as a resonator for a wide-band frequency filter.

Further, in the parallel resonator, the length of the active portion is 59.3 to 7 with respect to the total length.
In the case of 9.9%, Δf was large and good, and particularly, when it was about 71% or more, it showed an excellent value, and it was confirmed that it was suitable as a resonator for a broadband frequency filter.

Here, there is proposed a configuration in which both ends are provided with inactive portions formed by shaving a mountain shape including input and output electrodes on both sides. In such a configuration, a piezoelectric element is formed on the front and back surfaces of the piezoelectric ceramic plate in advance to form a polarized strip-shaped element, and the front and back surfaces are slanted at both ends to remove the electrodes. 1 is formed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A strip-shaped piezoelectric resonator 1a according to the present invention will be described with reference to FIGS. This piezoelectric resonator 1a
Are provided at both ends of a thin piezoelectric ceramic plate 2 made of lead zirconate titanate (PZT) having electrodes 3 and 4 formed on the front and back,
Non-active portions Y, Y having no electrodes are provided on the front and back sides, and the main surface on which the electrodes 3, 4 are provided is an active portion X. Both the active portion and the non-active portion are polarized in the thickness direction over the entire surface (arrow Ps). ) And used as a series resonator S or a parallel resonator P applied to the frequency filter of FIG.

Here, means for forming the strip-shaped piezoelectric resonator 1a will be described in detail with reference to FIGS.

Pb ₃ O ₄ , ZrO ₂ , TiO ₂ , S
b ₂ O ₃ , Nb ₂ O ₅ , Cr ₂ O ₃ are converted to Pb
｛(Sb _1/2 Nb _1/2 ) _0.01 (Cr _{1/2
Nb 1/2) 0.04 Zr 0.49} Ti 0.46} so that the composition formula of _{O 3,} formulated by weighing predetermined amounts, which was added to water in a wet ball mill for 48 hours primary pulverization After drying and calcining at 800 ° C. for 2 hours, water and a PVA-based binder are further added by a wet method, followed by secondary grinding for 72 hours to obtain an average particle size of about 0.5 μm. The slurry obtained here is spray-dried into granules. Next, it is press-formed into a large plate having a thickness of 2.0 mm × 40 mm square using a uniaxial pressing machine. The molding density at this time was 4.6 g / cm ³
It is. Next, baking is performed in an air atmosphere at 940 ° C. for 16 hours to obtain a piezoelectric ceramic sintered body. The sintered body is polished in the thickness direction on the front and back surfaces to obtain a piezoelectric ceramic plate 2 having a thickness of 0.495 mm for a series resonator S and a thickness of 0.175 mm for a parallel resonator P.

Next, on the front and back surfaces of the piezoelectric ceramic plate 2, electrodes 3,
4 was screen printed with a silver paste. At this time, as shown in FIG. 14A, the electrodes 3 and 4 formed on the upper surface in the figure are screen-printed in a predetermined stripe pattern 10 (a pattern in which a silver paste is not applied to inactive portions). Here, the width of the active portion X having the electrodes 3 and 4 is adjusted in advance by a printing pattern.

After the printing, baking is performed at 720 ° C., and after baking, top coating dry silver 11 is applied so as to cover the entire front and back surfaces including the partial electrodes 3 and 4 including the inactive portions Y and Y ( A DC voltage is applied at 80 ° C. and 35 kV / cm for 15 minutes to polarize (arrow Ps). After this polarization, the front and back overcoated silver 10 is removed by washing with an organic solvent.
Thereafter, the obtained large plate element (see FIG.
The piezoelectric resonator 1a is obtained by cutting into a strip shape as shown in FIG. An example of the cut dimensions at this time is that the length used in the series resonator S is 3.28 × width 0.66 × thickness 0.495 (mm), and that the parallel resonator P is used. There is a length 3.49 x width 1.00 x thickness 0.
175 (mm).

As shown in FIGS. 1 and 2, electrodes 3 and 4 are formed on the front and back main surfaces, and these are used as active portions X. At both ends, electrodes 3 and 4 are formed on the front and back surfaces. The resonators S, P polarized in the thickness direction are formed over the entire surface as inactive portions Y, Y. The resonators S and P are applied to the frequency filter shown in FIG.

A large number of samples manufactured by the above-described means and having different length ratios of the active portion X, which are cut out at the above-mentioned outer diameter, are subjected to a difference Δf (kH) between the resonance frequency and the anti-resonance frequency.
z), capacitance Cf (pF) at 100 kHz, resonance frequency fr
, Frequency constant fr × L (Hzm), antiresonant frequency fa, frequency constant fa × L (Hzm), electromechanical coupling coefficient K _{31 of} the piezoelectric transverse effect, and Qm. The results are as shown in Tables 1 and 2.

It is desirable that the widths of the inactive portions Y, Y in the left and right portions are equal in dimension from both ends, and it is separately confirmed that Δf is slightly reduced when the width is nonuniform.

Here, Table 1 below shows the relationship between the length ratio of the active portion X of the series resonator S having the above-described configuration and various characteristics.

[0017]

[Table 1]

FIGS. 3 to 7 are graphs showing the above results, and show the relationship between the length ratio of the active portion X and various characteristics in the series resonator S according to the present invention. is there.

FIG. 3 is a graph showing the relationship between the difference Δf between the resonance frequency fr and the anti-resonance frequency fa and the length ratio of the active portion X. From this graph and Table 1, in the piezoelectric resonator 1a used as a series resonator, the ratio of the length l of the active portion X to the total length L (hereinafter referred to as length ratio) is 5
In the case of 1.8 to 86.99%, the difference Δf between the resonance frequency and the anti-resonance frequency is about 28 kHz or more, which is good. In particular, when about 58% or more, Δf is about 29 kHz.
z or more, showing an excellent value, and it was confirmed that it was suitable as a frequency filter. Incidentally, the length ratio of the active portion of 100% (the front surface and the back surface are all electrodes) is Δf
Was about 26 kHz.

FIG. 4 shows the capacitance Cf (measured frequency f = 10
6 is a graph showing the relationship between the active portion X and the length ratio of the active portion X. This graph shows that the capacitance Cf decreases as the length ratio of the active portion X decreases. Incidentally, the smaller the capacitance of the series resonator S, the better. Therefore, even if the length ratio of the active portion X is reduced, there is no problem.

FIG. 5 is a graph showing the relationship between Qm and the length ratio of the active portion X. From this graph, it can be seen that, even when the length ratio of the active portion X changes, the value does not vary greatly, although the value slightly varies.

FIG. 6 shows the frequency constant (fr × L) and the active portion X.
6 is a graph showing the relationship with the length ratio. From this graph, it can be seen that the frequency constant (fr × L) gradually decreases as the length ratio of the active portion X decreases. Here, L = constant, so this graph corresponds to the characteristic change of the frequency fr.

[0023] Figure 7 is an electromechanical coupling coefficient _{K 31} and the active portion X
6 is a graph showing the relationship with the length ratio. The ratio of the length of the active portion X from the graph of about 73%, the electromechanical coupling coefficient K _{3 1} it can be seen that the maximum.

Table 2 below shows the relationship between the length ratio of the active portion X of the parallel resonator P having the above configuration and various characteristics.

[0025]

[Table 2]

FIGS. 8 to 12 are graphs showing the above-mentioned results for the parallel resonator P. FIG.
Here, FIG. 8 is a graph showing the relationship between Δf and the length ratio of the active portion X. From this graph and Table 2, the one used as the parallel resonator and having the length ratio of the active portion X of 59.3 to 79.9% is the difference Δf between the resonance frequency and the anti-resonance frequency. Is as good as about 23 kHz or more, and particularly at about 71% or more, Δf is about 25 kHz or more, showing an excellent value, and it was confirmed that the Δf is suitable as a broadband frequency filter. Incidentally, the length ratio of the active portion of 100% (the front surface and the back surface are all electrodes) is Δ
f was about 22 kHz.

FIG. 9 shows the capacitance Cf (measured frequency f = 10
0 KHz) and the length ratio of the active portion X. From this graph, it is understood that Cf decreases as the length ratio of the active portion X decreases.

FIG. 10 shows the relationship between Qm and the length ratio of the active portion X. From this graph, it can be seen that Qm does not change significantly even when the length ratio of the active portion X changes.

FIG. 11 shows the relationship between the frequency constant fa × L and the length ratio of the active portion X. From this graph,
It can be seen that the frequency constant fa × L does not change even if the length ratio of the active portion X decreases.

FIG. 12 shows a relationship between the length ratio of the electromechanical coupling coefficient K ₃₁ and the active portion X. The ratio of the length of the active portion X from the graph in 69.3 to 76.5%, it can be seen that the that the electromechanical coupling coefficient _{K 31} were particularly excellent.

As can be understood from Tables 1 and 2 and FIGS. 3 to 12, the series resonators S and the parallel resonators P having different thicknesses each have the same length ratio as the active portion X. It can be seen that the same characteristic is exhibited, the non-active portions Y, Y increase, and the length of the active portion X decreases. Further, Qm did not change much as compared with the case where the length of the active portion X was 100% (the entire surface electrode on the front and back surfaces).

Further, in order to confirm the temperature dependence, a temperature change of -35 ° C. to 85 ° C. was applied to each sample having a different length ratio of the active portion X for the resonance frequency fr and the anti-resonance frequency fa. When the difference between the maximum value and the minimum value is compared with the resonance frequency fr at normal temperature and the anti-resonance frequency fa, it is about 0.2 to 0.4%, and the active portion X is 100%
It was almost the same as at the time. From this, it was confirmed that the length ratio of the active portion X did not change the temperature characteristics. Further, a change with time after reflow (230 to 250 ° C.) was examined as an index of heat resistance. However, it was not found that deterioration depending on the length of the active portion X was caused.

Thus, the strip-shaped resonators utilize a piezoelectric transverse effect in which the direction of the electric field and the direction of polarization are different from the direction of vibration, and therefore, the direction of the electric field and the direction of polarization match the direction of vibration. Electromechanical coupling coefficient is lower than a piezoelectric resonator using the piezoelectric longitudinal effect, and the resonance frequency fr
The difference Δf, which is the difference from the anti-resonance frequency fa, is relatively small, and when used in a frequency filter, there has been a problem that the bandwidth is narrowed. By forming the non-active portions Y, Y on both sides of the resonator 1, Δf increases, so that the above-mentioned disadvantage can be compensated.

15 and 16 show a strip-shaped piezoelectric resonator 1b in which a piezoelectric ceramic plate is formed with tapered inactive portions Y, Y at both ends.

The manufacturing method of the strip-shaped piezoelectric resonator 1b will be described with reference to the flowchart of FIG. Here, the difference from the above embodiment is that the piezoelectric ceramic composition has PbＰ (Sb _1/2
Nb _1/2 ) _0.01 (Cr _1/2 Nb _1/2 )
_0.04 Zr _0.49 Ti _{0 .} Instead of the _{46} O 3,}
Pb ｛(C _{0 1/3} Nb _2/3 ) _0.1 Zr _0.
441 Ti _0.459 ｝ O ₃ +1.0 Gravity% Sb ₂ O
Used as a composition formula represented by ₃ and instead of the press molding for molding, lies in using the extrusion molding of the kneaded material. In the process after the formation of the piezoelectric ceramic plate 2, the electrodes 3 and 4 are formed on the front and back surfaces of the piezoelectric ceramic plate 2 over the entire surface. Then, between the electrodes 3 and 4, 1 at 80 ° C. and 35 KV / cm.
Polarization (arrow Ps) is performed by applying a DC voltage for 5 minutes.

After this polarization, a large plate element (see FIG. 14C)
Is cut into strips as shown by a chain line L. An example of the cut size at this time is, as in FIG. 13, the length used for the series resonator S is 3.28 × width 0.66.
× thickness 0.595 (mm), and for a parallel resonator P, the length is 3.49 × width 1.00 × thickness 0.175 (mm).

Then, both ends of the strip-shaped element thus obtained are cut into a tapered shape including the electrodes 3 and 4 from the front and back, and tapered inactive portions Y and Y are formed on both sides. Thus, the strip-shaped piezoelectric resonator 1b shown in FIGS.

In this configuration, as is apparent from the manufacturing method, the electrodes 3 and 4 are formed on the entire front and back surfaces of the piezoelectric ceramic plate 2, polarized, cut out, and then cut at both ends of the strip-shaped element. Since the inactive portions Y and Y are formed by shaving the front and back sides of the portion in an inclined manner and removing the electrodes 3 and 4,
In the manufacturing process, the electrodes 3 and 4 in which the electrodes for polarization are formed on the entire front and back surfaces can be used as they are, and there is an advantage that it is not necessary to apply and remove dry silver on top coat.

The series resonator S manufactured by the means described above
And the ridge angle θ of the tapered inactive portions Y, Y = 60
° and the difference Δf between the resonance frequency and the anti-resonance frequency.
(KHz), capacitance Cf (pF) at 100 KHz, resonance frequency fr, frequency constant fr × L (Hzm), antiresonance frequency fa
, The frequency constant fa × L (Hzm), the electromechanical coupling coefficient K _{31 of} the transverse piezoelectric effect, and the Qm.

Table 3 shows the characteristic values. Here, "conventional example" in the table shows the characteristics of the element before the inactive portions Y, Y are formed at both ends of the strip-shaped element described above.

[0041]

[Table 3]

When the output waveform of the above-mentioned sample was separately examined, it was confirmed that the sample exhibited a well-balanced resonance waveform without occurrence of a subresonance (spurious).

As described above, even in the configuration having the tapered non-active portions Y, Y shown in FIGS. 15 and 16, the resonance frequency fr and the anti-resonance improved difference Δf between the frequency fa is further electromechanical coupling coefficient K ₃₁ was also improved. Therefore, it was confirmed that the filter was suitable as a broadband frequency filter.

[0044]

According to the present invention, the strip-shaped piezoelectric ceramic plate is polarized in the thickness direction over the entire surface, and non-active portions Y, Y having no electrodes are formed on both sides of the piezoelectric resonator. As a result, the difference Δf between the resonance frequency and the anti-resonance frequency was improved.

For this reason, when this strip-shaped piezoelectric resonator is applied to a series resonator and a parallel resonator, they use a piezoelectric transverse effect in which the direction of electric field and the direction of polarization are different from the direction of vibration. , the electromechanical coupling coefficient _{K 31} is low,
Δf which is the difference between the resonance frequency fr and the anti-resonance frequency fa
Was relatively small, but by forming inactive portions on both sides, it was possible to improve the disadvantages of the strip-shaped piezoelectric resonator used in a wide-band frequency filter, and to reduce the bandwidth of the frequency filter. Can be widened. Moreover, the inactive portion can be easily formed only by omitting the end portions of the electrodes on the front and back surfaces, and therefore, the manufacture is easy, and therefore, the frequency filter characteristics can be easily improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a strip-shaped piezoelectric resonator 1a according to the present invention.

FIG. 2 is a longitudinal sectional side view of a strip-shaped piezoelectric resonator 1a.

FIG. 3 is a graph showing Δf and a length ratio of an active portion in the piezoelectric resonator 1a used for the series resonator S.

FIG. 4 is a graph showing the capacitance Cf at 100 KHz and the length ratio of the active portion in the piezoelectric resonator 1a used for the series resonator S.

FIG. 5 is a graph showing Qm and a length ratio of an active portion in the piezoelectric resonator 1a used for the series resonator S.

FIG. 6 is a graph showing a frequency constant (fr × L) and a length ratio of an active portion in the piezoelectric resonator 1a used for the series resonator S;

[7] In the piezoelectric resonator 1a used in the series resonator S, the graph showing the length ratio of the electromechanical coupling coefficient K ₃₁ and the active portion

FIG. 8 is a graph showing Δf and a length ratio of an active portion in the piezoelectric resonator 1a used for the parallel resonator P.

FIG. 9 is a graph showing the capacitance ratio between the capacitance Cf and the length of the active portion in the piezoelectric resonator 1a used for the parallel resonator P.

FIG. 10 is a graph showing Qm and a length ratio of an active portion in the piezoelectric resonator 1a used for the parallel resonator P.

FIG. 11 is a graph showing a frequency constant (fa × L) and a length ratio of an active portion in the piezoelectric resonator 1a used for the parallel resonator P.

[12] In the piezoelectric resonator 1a for use in the parallel resonator P, a graph showing the length ratio of the electromechanical coupling coefficient K ₃₁ and the active portion

FIG. 13 is a flowchart showing a manufacturing method.

FIG. 14 is an explanatory view showing a polarization means.

FIG. 15 shows a strip-shaped piezoelectric resonator 1 according to another configuration of the present invention.
It is a perspective view of b.

FIG. 16 is a longitudinal sectional side view of a strip-shaped piezoelectric resonator 1b.

FIG. 17 is a flowchart showing a method of manufacturing the strip-shaped piezoelectric resonator 1b.

FIG. 18 is a circuit diagram of a frequency filtering circuit using parallel resonators P and series resonators S made of strip-shaped piezoelectric resonators.

[Description of Signs] 1a, 1b Strip-shaped piezoelectric resonator 2 Piezoelectric ceramic plate 3 Electrode 4 Electrode X Active part Y, Y Non-active part S Series resonator P Parallel resonator

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 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideaki Hiramitsu 14-18 Takatsuji-cho, Mizuho-ku Nagoya-shi Inside Japan Special Ceramics Co., Ltd. (72) Inventor Hirofumi Ozeki 14-18 Takatsuji-cho Mizuho-ku Nagoya-shi Co., Ltd. F-term (reference) 5J108 AA07 BB04 CC04 CC05 CC13 KK07

Claims (4)

[Claims] An inactive portion is formed at both ends by being polarized in the thickness direction over the entire surface and having electrodes on the front and back main surfaces, and removing the electrodes on the front and back of both ends. A strip-shaped piezoelectric resonator used for a frequency filter characterized by the following. 2. A device used as a series resonator, wherein the length of the active portion is 51.8 to 86.
The strip-shaped piezoelectric resonator used in the frequency filter according to claim 1, wherein the frequency is 9%. 3. A resonator used as a parallel resonator, wherein the length of the active portion is 59.3 to 79.
The strip-shaped piezoelectric resonator used in the frequency filter according to claim 1, wherein the frequency is 9%. 4. The frequency filter according to claim 1, further comprising an inactive portion formed by tapering both ends of the piezoelectric ceramic plate including the input / output electrodes on both sides thereof. Strip-shaped piezoelectric resonator.