JPH0124369B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric filter used in a short wave band of several MHz or more, and in particular, an object of the present invention is to provide an energy trap type piezoelectric filter that uses a high-order width vibration mode of a piezoelectric strip. do.

Conventionally, various vibration modes have been used in piezoelectric filters, so-called ceramic filters, depending on the application, such as the frequency and fractional bandwidth used. When the frequency is several MHz or less, a vibration mode in which the entire plate vibrates, such as contour vibration of a circular or square plate or length vibration of a rectangular wave, is used.
On the other hand, when the frequency is from several MHz to several tens of MHz, a so-called energy confinement vibration mode is used in which vibration energy is locally concentrated at the center of the piezoelectric ceramic plate.

In the former type of filter that uses contour vibration or length vibration, supporting the element and taking out the electric terminal are done by pressing a metal terminal plate with small protrusions on the vibration node, or by using a thin lead wire at the vibration node. The pressure welding method has reliability problems such as peeling of the electrode at the pressure welding part and poor contact due to mechanical vibration, and the soldering method makes the soldering work difficult. Moreover, there was a drawback that characteristics varied widely depending on the support.

On the other hand, in filters that utilize the latter type of energy trapping, the connection to the lead terminals is made by soldering at the edge of the board, which has little effect on vibration, so it is reliable with less variation in characteristics. A filter with high performance can be obtained. but,
Conventional energy confinement resonators utilize a thickness vertical mode or a thickness shear mode, so their resonant frequency is determined by the thickness of the ceramic substrate. Therefore, if an attempt is made to lower the resonance frequency, the thickness of the substrate will increase, and the external dimensions will increase in proportion to this. For this reason, the applicable frequency for energy confinement is HF over several MHz.
It has been considered difficult to realize an energy trapping filter for medium wave bands of several MHz or less.

In order to solve such problems, the present inventors have disclosed Japanese Patent Application Laid-open No. 134817/1983 and Japanese Patent Application Laid-open No. 56-134817.
In No. 134818, we proposed a filter that utilizes the width vibration of a thin piezoelectric strip, and showed that it was possible to create a compact piezoelectric filter for medium-wave bands.

However, these filters utilize the lowest-order fundamental width vibration among width vibrations, and therefore the upper limit of the applicable frequency is about 2 to 3 MHz.

The present invention utilizes even higher-order width vibrations, and utilizes several M
The purpose of this design is to provide a compact piezoelectric filter suitable for shortwave bands of Hz or higher.

That is, the present invention provides a piezoelectric filter that utilizes width vibration, in which a plurality of strip-shaped electrodes that utilize width vibration are formed in the center of a rectangular piezoelectric thin plate in the longitudinal direction. The plurality of vibration modes are arranged so that the driving electric field is applied to a position where the stress is maximum for a predetermined mode of vibration and a position where stress is zero for other higher-order vibration modes and fundamental vibration modes. This single mode piezoelectric filter is characterized in that it is provided with strip-shaped electrodes, and these strip-shaped electrodes are used as input/output and common grounding electrodes, and these extraction electrodes are provided on the periphery of both sides of the thin plate.

The present invention also provides a multi-mode piezoelectric filter in which a plurality of strip-shaped electrodes are formed in the longitudinal center of a rectangular piezoelectric thin plate and two width vibration energy confinement resonators are provided adjacently to each other. Each resonator has a position where the stress is maximum for a predetermined mode of vibration among the higher-order vibration modes of the width vibration, and the stress is 0 for other higher-order vibration modes and fundamental vibration modes. The plurality of strip-shaped electrodes are provided at such positions that a driving electric field is applied thereto, and furthermore, the strip-shaped electrodes, which are the driving electrodes of the resonators on both sides of the thin plate in the longitudinal direction, This is a multi-mode piezoelectric filter that utilizes high-order width vibration, and is characterized in that extraction electrodes are provided on the periphery of both sides of the thin plate.

There are an infinite number of high-order width vibrations in the piezoelectric strip. In these higher-order modes, the thickness vibration and the resonant frequency approach or overlap, so the ones that are practically useful are the lower-order 2 modes.
Next-order, third-order, and fourth-order modes are considered. Below, a single mode filter and a multimode filter will be described as energy trapping filters of the present invention that utilize modes of these orders.

First, the configuration of a single mode filter according to the present invention is shown in FIGS. 1 and 2.

FIG. 1 shows the case where high-order width longitudinal vibration and high-order width shear vibration using the piezoelectric longitudinal effect are used, and FIG. 2 shows the case where the high-order width longitudinal vibration using the piezoelectric transverse effect is used.

In each figure, a, b, c are quadratic, cubic, respectively.
The configuration when using the 4th mode is shown. In FIG. 1, a piezoelectric ceramic strip 10 polarized in the width direction in the case of transverse longitudinal vibration and in the longitudinal direction in the case of transverse shear vibration is used, and an electrode as shown in the figure is provided on one side of the piezoelectric ceramic strip 10. Symbols 11 and 13, 15 and 17, 19 and 21 in the figure are input/output side electrodes,
Furthermore, 12 and 14, 16 and 18, and 20 and 22 are drawn out and connected to the peripheral portion by a common electrode. A dowel is attached to each peripheral extraction electrode corresponding to the electrodes 11 to 22. 1 and 2 are input/output lead terminals, and 3 is a grounding lead terminal.

In this filter, other width vibrations having a different order N from the mode of use become spurious, so in practical use it is necessary to use electrodes that suppress this. A specific example of such an electrode configuration will be described below.

First, in the case of using the secondary mode in Figure 1a, 3
In order to suppress the second-order and fourth-order modes, the center of the gap _g1 between the electrodes 11 and 12 is made to coincide with the position where the third-order mode stress is zero. Also, if the gap between electrodes 12 and 13 is g ₂ and the gap between electrodes 13 and 14 is g ₃ , then the centers of gaps g ₂ and g ₃ are set at the position where the fourth-order mode stress is 0. .

In the case of using the 3rd mode shown in figure b, the 2nd, 4th
In order to suppress the second-order and fifth-order modes, as shown in the figure, the center of the gap g ₁ is made to coincide with the center of the plate width where the stress of the second-order and fourth-order modes becomes 0, and the gaps g ₂ and g ₃ are Adjust the center to the position where the stress of the 5th mode is 0. Furthermore, in FIGS. 1a and 1b, the magnitudes of g ₂ and g ₃ are adjusted so that the driving forces for the primary (fundamental) mode cancel each other out, thereby suppressing the primary mode.

In addition, in the case of using the 4th mode in Figure 1c, 3
In order to suppress the second, fifth, and sixth modes, the center of gap g ₁ is aligned with the position where the stress of the third and sixth modes is 0, and the centers of gap g ₂ and g ₃ are aligned with the position where the stress of the fifth mode is 0. Form the electrode so that it is aligned with the 0 position. Furthermore, the magnitudes of g ₂ and g ₃ are adjusted so that the driving forces for the secondary mode cancel each other out, thereby suppressing that mode.

By employing the electrode configuration as described above, it is possible to achieve good characteristics with less spurious.

In the case of width-longitudinal vibration using the piezoelectric transverse effect shown in Figure 2, the excitation electric field is applied in the thickness direction, so strip electrodes are provided at the parts corresponding to the gaps g ₁ , g ₂ , and g ₃ in Figure 1. The widths are b ₁ , b ₂ , and b ₃ . In this configuration, the spurious of this width vibration is also suppressed and good filter characteristics are realized.

Next, as a specific example of a multi-mode filter using high-order width vertical vibration utilizing piezoelectric transverse effect, the configuration of a dual mode is shown in FIG. a in the figure,
b and c indicate cases of use in secondary, tertiary, and quartic modes, respectively. In this multi-mode filter, as shown in the figure, two energy trapping filters are placed symmetrically adjacent to a region of length 2l + 2l' in the central length direction of a piezoelectric ceramic strip having a width of 2H and polarized in the thickness direction. A resonator is provided, and these are placed in the center.
It is constructed by elastically connecting in a length region of 2l'. That is, in FIG. 2a, one resonator is composed of an electrode 111 and a common electrode 113, and the other resonator is composed of an electrode 112 and a common electrode. 130 and 131 are back electrodes. In this case, the center of each strip electrode in the width direction is aligned with the position where the stress in the usage mode is maximum. Thus, only the utilization mode is most strongly excited. Figure 2b,
In c, the electrodes constituting each resonator are divided so that the center of the electrode strip is located at the point of maximum stress in the third and fourth modes, respectively. In FIG. 2b, 115 and 118 are common electrodes, which connect electrode 116 and one resonator to electrode 117.
and constitute the other resonator. In FIG. 2c, electrodes 122 and 125 are common electrodes, and electrodes 120 and 1
23 constitutes one resonator, and the electrodes 121, 12
4 constitutes the other resonator. If the width of each strip electrode is made equal, spurious vibrations of the 5th order or lower in Figures 3a and 3c, and 4th or lower width vibrations in Figure 3b will be suppressed, resulting in a good structure with less spurious over a wide frequency range. Filter characteristics are realized.

As an example of the present invention, the prototype filters shown in FIGS. 1b and 3b using third-order width longitudinal vibration will be described in detail.

Example 1 Three PbTiO ₃ piezoelectric ceramic strips polarized in the width direction had an electrode configuration as shown in Fig. 1b.
We prototyped a 4.5 MHz single mode filter that utilizes widthwise longitudinal vibration, and connected two of them in cascade as shown in Figure 4a, and the characteristics in that case are shown in Figure 4b. however,
The dimensions of this filter element are: length l ₀ = 10 mm, width
2H=1.4mm, thickness 2t=0.1mm, electrode length 2l
=2mm. Looking at the characteristics in Figure 3b, we see that the first order,
Although spurious amplitude vibrations of the second, fourth, and fifth orders occur, it is clear that they are suppressed to about -20 dB by the electrode configuration described above.

Example 2 A 10.7 MHz double mode was generated using third-order width longitudinal vibration of a Pb(Zr, Ti) O ₃ piezoelectric ceramic strip polarized in the thickness direction with the electrode configuration shown in Figure 3b. I made a prototype filter. This is shown in Figure 5a. The filter characteristics are shown in FIG. 5b. This filter has a 3dB specific bandwidth of 1.5% and a passband loss of 2dB
It was hot. Fourth and fifth order width longitudinal vibrations (WE ₄ and WE ₅ ) and thickness shear vibration (TS) on the high frequency side
However, attenuation of 20 dB or more is secured over a wide frequency range. The element dimensions of this filter are l ₀ = 4 mm, 2H = 0.5 mm,
2t=45μm, l=0.3mm, 2l'=0.2mm.

The conventional 10.7MHz energy confinement filter using longitudinal vibration has a side of approximately 5mm and a thickness of
Although it is composed of a 0.2 mm piezoelectric ceramic square plate, this filter is extremely small compared to this, and the element size has been significantly reduced.

The present invention has been described above, and by utilizing high-order vibration, it has become possible to provide a piezoelectric filter that is extremely small and has good characteristics. The filter of the present invention is extremely useful as a piezoelectric filter in the short wave band of several MHz to +several MHz, and can be said to have an extremely large industrial effect.

[Brief explanation of drawings]

FIG. 1 shows the structure of a single mode filter using high-order width vertical vibration and high-order width shear vibration using the piezoelectric longitudinal effect according to the present invention. Figure A shows the case of using the secondary mode, Figure B shows the case of using the tertiary mode, and Figure C shows the case of using the quartic mode. FIG. 2 is a diagram showing the configuration of a transverse effect type single mode filter, showing a top view, a bottom view, and the relationship between the stress distribution of each order mode. FIG. 3 shows the structure of another embodiment of the present invention, showing the electrode structure on the front and back surfaces and the structure of the electrodes on the front and back surfaces, showing the structure of a dual mode filter using high-order width vertical vibration of the piezoelectric transverse effect, and This shows the relationship between mode stress distribution and a
The figure shows the case of using the secondary mode, the figure b shows the case of using the tertiary mode, and the figure c shows the case of using the fourth mode. Figure 4 shows piezoelectric longitudinal effect utilization 3 according to the present invention.
This is a diagram showing the characteristics of a 4.5MHz single mode filter using vertical vibration, and Figure a is its circuit configuration diagram.
Figure b shows the filter characteristics. Figure 5 shows an example using the third-order width vertical vibration using the piezoelectric transverse effect according to the present invention.
This figure shows the characteristics of a dual mode filter in the 10.7 MHz band, where figure a is its circuit configuration diagram and figure b shows its filter characteristics. In the figure, 1... Input lead terminal, 2... Output lead terminal, 3... Common ground lead terminal, 10... Rectangular piezoelectric thin plate, 11, 13, 15, 17, 1
9, 21, 111, 112...input/output electrode, 1
1', 13', 15', 17', 19', 21'... Same as above extraction electrode, 12, 14, 16, 18, 2
0, 22... Common ground electrode, 12', 14', 1
6', 18', 20', 22', 115, 118, 1
22,125... Same as above extraction electrode.

Claims (1)

[Scope of Claims] 1. In a piezoelectric filter that utilizes width vibration, in which a plurality of strip-shaped electrodes that utilize width vibration are formed in the center of a rectangular piezoelectric thin plate in the longitudinal direction, the higher order of the width vibration is provided. The drive electric field is applied to the position where the stress is maximum for a predetermined mode of vibration among the vibration modes of , and the position where the stress is zero for other higher-order vibration modes and fundamental vibration modes. 1. A single mode piezoelectric filter comprising a plurality of strip-shaped electrodes, these strip-shaped electrodes serving as input/output and common grounding electrodes, and lead-out electrodes provided on the periphery of both sides of the thin plate. 2. In a multi-mode piezoelectric filter in which a plurality of strip-shaped electrodes are formed in the longitudinal center of a rectangular piezoelectric thin plate and two width vibration energy confinement resonators are provided adjacently, each of the resonators is A driving electric field is applied at a position where stress is maximum for a predetermined mode of vibration among the higher-order vibration modes of the width vibration, and at a position where stress is zero for other higher-order vibration modes and fundamental vibration modes. It is constructed by providing the plurality of strip-shaped electrodes at such positions that the strip-shaped electrodes are connected to each other, and the lead-out electrodes from the respective strip-shaped electrodes, which are drive electrodes of the resonators on both sides of the thin plate in the longitudinal direction, are connected to each other. A multi-mode piezoelectric filter that uses high-order width vibration and is characterized by being provided on the periphery of both sides of a thin plate.