JP4701504B2 - Manufacturing method of triple mode piezoelectric filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-frequency triple mode piezoelectric filter and a frequency adjustment method thereof, and more particularly to an improvement of a frequency adjustment method of a high-frequency triple mode filter.
[0002]
[Prior art]
In recent years, high-frequency piezoelectric devices, particularly multimode piezoelectric filters using a quartz substrate (hereinafter referred to as multimode filters) are small, light and robust, and have excellent frequency temperature characteristics. Widely used.
FIG. 4A is a plan view showing the configuration of a conventional triple mode filter, and three pairs of electrodes 32-33, 34-35, and 36-37 facing each other are arranged close to each other on the main surface of the quartz substrate 31. FIG. At the same time, a lead electrode extends from each electrode pair toward the end of the crystal substrate 31 and is connected to the terminals T1-T1 ′, T2-T2 ′, T3-T3 ′ to form a triple mode filter. FIG. 4B is a diagram showing the connection of each electrode in order to function as a filter. The terminals T2-T2 ′ are short-circuited, and T1 ′, T2 ′, T3 ′ are connected to form a common terminal Tc. By providing appropriate terminations to the output terminals T1-Tc and T3-Tc, it functions as a band-pass filter.
It is well known that the electrodes 33, 35, and 37 are connected to function as a triple mode filter even as one common electrode.
[0003]
A method for adjusting the frequency of the triple mode filter is disclosed in, for example, Japanese Patent Laid-Open No. 7-189884. In FIG. 4B, when the terminals T3 and Tc are short-circuited to form a one-terminal pair resonator of T1-Tc, the resonance frequencies are set to f1, f2, and f3 from a low frequency. Here, if the flatness and parallelism of the quartz substrate 31 are ideal and the mass loads of the electrode pairs 32-33, 34-35, and 36-37 are the same, the resonance as shown in the upper part of FIG. It exhibits characteristics. Therefore, when mass is added only to the electrodes at both ends of the three electrodes arranged side by side as shown in the right end of FIG. 5, the resonance characteristic becomes the resonance characteristic shown in the lower stage. That is, the frequency fluctuation of f2 moves largely compared to f1 and f3. The frequency shift amounts of the frequency f1 and the frequency f3 are substantially the same, and the frequency difference (f3′−f1 ′) is substantially the same as (f3−f1), but the change amount of the frequency f2 is increased, and the frequency difference (f2′− f1 ′) is significantly smaller than (f2−f1).
This is because the vibration displacement of the antisymmetric zero-order mode A ₀ (resonance frequency f2) is 0 at the center of the electrode 34 and exhibits the maximum displacement at the approximate center of the electrodes 32 and 36. This is because, as is well known, when mass is added to the vibrating part of the vibrating body, the amount of frequency change is maximized if added to a position where the vibration displacement is maximum.
Conversely, if the masses of the electrodes at both ends are evenly scraped with an electron beam or the like, (f3′−f1 ′) is almost constant and the frequency difference (f2′−f1 ′) is (f2−f1). It will increase in comparison.
[0004]
Next, when mass is added only to the central electrode 34 among the three electrodes arranged side by side as shown at the right end of FIG. 6, the mode with a large frequency change amount is the symmetric zero-order mode S ₀ (frequency f1). The next is the symmetric primary mode S ₁ (frequency f3), and the mode with little frequency variation is the antisymmetric zero-order mode A ₀ (f2). Therefore decreasing the frequency by adding mass to the center of the electrode 34 of the triple mode filter, since the frequency variation of the anti-symmetric zero order mode A ₀ is small, and held frequency difference (f3'-f1 ') substantially constant The frequency difference (f3′−f2 ′) can be reduced as it is. Conversely, the mass of the electrode 34 can be scraped off and the frequency difference (f3′−f2 ′) can be increased.
[0005]
In addition, even if mass is added to any electrode of the triple mode filter, it affects the overall frequency to some extent, so a method for lowering the overall frequency without breaking each frequency array is necessary. If mass is added to the whole 33, 35, 37 using a method such as vapor deposition, the three frequencies can be moved in parallel.
[0006]
[Problems to be solved by the invention]
However, the frequency adjustment method of the triple mode filter as described above was applicable to a triple mode filter using a conventional flat plate crystal substrate, but the crystal substrate 40 as shown in a sectional view in FIG. A high-frequency triple mode filter in which three electrodes 42, 43, and 44 are arranged close to each other on a high-frequency piezoelectric substrate having a recess 41 formed by means of etching or the like and a full-surface electrode 45 is provided on the recess side is There was a problem that it could not be applied for the reason described in. That is, the thickness of the thin part (vibration part) of the recessed part 41 needs to be processed as thin as several tens of microns in order to obtain a high frequency, and the parallelism or flatness is good as shown in the upper part of FIGS. Often not. For example, as shown in FIG. 8, the electrodes 42, 43, 44 and the entire surface electrode 45 are attached to a substrate whose thickness gradually decreases from the left end to the right end in the drawing, and the electrodes 43, 44, 45 are short-circuited. Then, when the resonance characteristic of the one-terminal-pair resonator as viewed from T1-Tc is measured, for example, the characteristic is as shown in the lower part of FIG. That is, since the resonance frequencies of the electrode pairs 42-45, 43-45, and 44-45 are significantly different, the coupling between the electrodes is extremely weak, and in the case of the shape of the vibrating portion as shown in FIG. It is driven by electrodes 42-45 symmetrically zero-order mode S ₀ (resonance frequency f1) but is strongly excited, antisymmetric zero-order mode A ₀ (resonance frequency f2), symmetrical primary mode S ₁ (resonance frequency f3 ) Becomes extremely small, and in some cases, the resonance level may be hidden behind resonances in other modes and cannot be detected.
[0007]
Conversely, when the thickness of the substrate gradually increases from the left end to the right end in the figure as shown in the upper part of FIG. 9, the resonance characteristics driven from the terminal T1-Tc side are between the electrodes as shown in the lower part of the figure. Since the coupling is weak, the symmetric first-order mode (S ₁ ) is strongly excited, but the resonance levels of the other symmetric zero-order mode S ₀ (resonance frequency f1) and anti-symmetric zero-order mode A ₀ (resonance frequency f2) are Extremely small.
Therefore, in the case of the resonance characteristics as shown in the upper left of FIG. 10, if mass is added to the electrode 44 to increase the resonance level of the symmetric primary mode S ₁ (f3), the antisymmetric zero-order mode A ₀ (f2) As shown in the lower part of FIG. 10, the resonance of the symmetric zero-order mode S ₀ (f1) and the resonance frequency of the anti-symmetric zero-order mode A ₀ (f2) approach each other. Further, as shown in the upper right of FIG. 11, when mass is added to the electrodes 43 and 44, the antisymmetric zero-order mode A ₀ (f2) approaches the symmetric primary mode S ₁ (f3) as shown in the lower stage. Thus, there has been a problem that the conventional triple mode filter frequency adjustment method cannot be applied to the frequency adjustment of the high frequency triple mode filter.
The present invention has been made in order to solve the above-described problem, and it is possible to adjust the frequency of the high-frequency triple mode filter even when the flatness and parallelism of the high-frequency piezoelectric substrate are poor, and to adjust the frequency to a predetermined filter characteristic. The purpose is to provide.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a method of manufacturing a triple mode piezoelectric filter according to the present invention includes three electrodes disposed on a flat surface side of a piezoelectric substrate having a recessed portion formed on one main surface, and on the recessed surface side. In the step of adjusting the frequency of the triple mode piezoelectric filter with full-surface electrodes, one terminal pair resonance in which the electrode at one end of the three electrodes and the full-surface electrode are used as drive electrodes and the other electrodes are short-circuited with the full-surface electrodes. According to the resonance characteristics exhibited by the child , the mass when the frequency is adjusted by simultaneously adding mass to the center electrode and the end electrode is larger in the end electrode than in the center electrode. And In the method of manufacturing a triple mode piezoelectric filter, the step of adjusting the frequency further includes a step of placing a mask with a hole on the flat surface side and applying a mass to the center and end electrodes. The hole is wider in a region exposing the end electrode than in a region exposing the central electrode. And a triple mode piezoelectric filter is manufactured by the manufacturing method including the process of adjusting said frequency.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.
FIG. 1A is a plan view showing a configuration of a triple mode filter according to the present invention, in which a concave portion 2 serving as a vibration portion is formed on a part of one main surface of a quartz substrate 1 by means of etching or the like. At the same time, the entire surface electrode 3 is provided on the concave surface and connected to the terminal Tc. On the other hand, three electrodes 4, 5, 6 are arranged close to each other on the flat side, and lead electrodes extend from the electrodes 4, 5, 6 toward the end of the crystal substrate 1, respectively, and are connected to terminals T 1, T 2, respectively. , T3 to form a high frequency triple mode filter.
FIG. 1B shows a case where the respective electrodes are connected so as to function as a triple mode filter. The terminals T1-Tc and T3-Tc function as bandpass filters by providing appropriate terminations. FIG. 1 (c) is a diagram showing a state in which the frequency adjustment is performed by covering the triple mode filter element with frequency adjusting masks 7a and 7b each having a triangular or rectangular hole according to the present invention. Mass is added to almost the entire surface of the electrode 6 through the mask 7b, but mass is added to only a part of the electrode 5 through the mask 7a on the central electrode 5.
[0010]
The feature of the present invention is that the mass of the electrodes 6 (electrodes 4) or the electrodes 5 and 6 (electrodes 4 and 5) is not added to the respective electrodes as in the conventional case. 4) Almost the entire surface, part of the electrode 5, for example, ¼ of the electrode, is added with mass, so that the symmetrical zero-order mode (f1), anti-symmetric zero-order mode (f2), and symmetrical first-order mode (f3) The resonance frequencies do not approach each other and the resonance level increases. Therefore, the frequency can be adjusted while checking the frequency and level of each mode.
[0011]
FIG. 2 is a diagram showing frequency characteristics when the frequency adjustment of the triple mode filter is performed using the triangular frequency adjustment mask according to the present invention. First, when the frequency characteristic of the triple mode filter element is measured from the terminal T1-Tc, the case shown in the upper part of FIG. When the electrodes 5 and 6 are covered with a mask as shown in FIG. 1C and mass addition is started, the level of each mode increases as shown in the lower part of FIG. 2, and the measurement of the resonance frequency becomes easy. As the level of each mode increases in this way, the resonance frequency of each mode can be measured with high accuracy, and thereafter, it may be adjusted to a desired frequency by a conventional adjustment method.
FIG. 3 shows an example in which a 130 MHz band high-frequency triple mode filter is frequency-adjusted using a frequency-adjusting mask according to the present invention and measured as a one-terminal-pair resonator.
[0012]
In the above, an example of a triple mode filter using crystal as a piezoelectric substrate has been described. However, the present invention is not limited to this, and other piezoelectric substrates, such as piezoelectric substrates such as lithium tetraborate, lithium tantalate, and langasite are used. You may apply to a triple mode filter.
Further, the shape of the frequency adjustment mask is not necessarily a triangular shape, and may be a shape in which the mass addition attached to the center electrode and the end electrode is different.
In the above description, the method of adjusting the frequency of the triple mode filter by adding mass has been described. However, the electrode film may be adjusted to be thinly cut. In this case as well, the amount of the central electrode and the electrode at one end may be scraped simultaneously.
[0013]
【The invention's effect】
Since the present invention is configured as described above, according to the first aspect of the present invention, the frequency adjustment method of the high-frequency triple mode filter exhibits an effect far superior to the conventional adjustment method based on trial and error. According to the second aspect of the present invention, since no extra mass is added to each electrode, a filter with less spurious and the like can be obtained.
[Brief description of the drawings]
FIG. 1A is a plan view showing a configuration of a triple mode filter according to the present invention, FIG. 1B is a diagram showing a connection method of each electrode, and FIG. 1C is a frequency adjustment mask on the triple mode filter element. FIG.
FIG. 2 is a diagram illustrating frequency characteristics before and after frequency adjustment.
FIG. 3 is a diagram illustrating frequency characteristics after frequency adjustment of each electrode is completed.
4A is a plan view showing a configuration of a conventional triple mode filter, and FIG. 4B is a diagram showing a connection state of each electrode when functioning as a filter.
FIG. 5 is a diagram illustrating a frequency adjustment method of a conventional triple mode filter.
FIG. 6 is a diagram illustrating a frequency adjustment method of a conventional triple mode filter.
FIG. 7 is a cross-sectional view showing a configuration of a conventional high-frequency triple mode filter.
FIG. 8 shows frequency characteristics when the vibration part of the piezoelectric substrate is not uniform (thickness decreases from left to right in the figure).
FIG. 9 shows frequency characteristics when the vibration part of the piezoelectric substrate is not uniform (thickness increases from left to right in the figure).
FIG. 10 is a diagram showing a relationship between mass addition to a third electrode and frequency characteristics.
FIG. 11 is a diagram showing the relationship between mass addition to the second and third electrodes and frequency characteristics.
[Explanation of symbols]
1 .. Piezoelectric substrate 2 .. Recessed portion 3 .. Full surface electrodes 4, 5, 6 .. Electrodes T 1, T 2, T 3, Tc... Terminal 7.

Claims (2)

In the step of adjusting the frequency of the triple mode piezoelectric filter in which three electrodes are disposed on the flat surface side of the piezoelectric substrate having a concave portion formed on one main surface and the entire surface electrode is provided on the concave surface side, Depending on the resonance characteristics exhibited by the one-terminal-pair resonator in which the electrode at one end of the electrode and the full-surface electrode are used as the drive electrode and the other electrode is short-circuited with the full-surface electrode, the mass is applied to the center electrode and the end electrode. The method of manufacturing a triple mode piezoelectric filter, wherein the mass when the frequency is adjusted by adding simultaneously is larger in the end electrode than in the center electrode .   2. The method of manufacturing a triple mode piezoelectric filter according to claim 1, wherein the step of adjusting the frequency includes a step of placing a mask with a hole on the flat surface side and applying a mass to the center and end electrodes. And the hole is wider in a region where the end electrode is exposed than in a region where the central electrode is exposed.

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