JP2002217663A - High frequency triple mode piezoelectric filter and frequency adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for improving a frequency adjustment method for a high frequency triple mode piezoelectric filter. SOLUTION: In the frequency adjustment method for the high frequency triple mode piezoelectric filter, a piezoelectric board having a recessed part on one main face is user. An electrode on one edge of three electrodes on the surface and the whole electrode on the rear face function as a driving electrode, and the other electrodes are short-circuited with the whole electrode. According to the resonance characteristics offered from a one terminal pair resonator, a small mass is applied to the central electrode and a large mass is applied to the edge electrode concurrently to carry our frequency adjustment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency triple mode piezoelectric filter and a method of adjusting the frequency thereof, and more particularly to an improvement of a frequency adjustment method of the high frequency triple mode filter.

[0002]

2. Description of the Related Art In recent years, high-frequency piezoelectric devices, especially multi-mode piezoelectric filters using a quartz substrate (hereinafter, referred to as multi-mode filters) are small, lightweight, robust and have excellent frequency-temperature characteristics. Widely used for mobile phone terminals. FIG. 4A is a plan view showing a configuration of a conventional triple mode filter, and the quartz substrate 31 is shown in FIG.
Pairs of electrodes 32-33, 34-3 opposed on the main surface of
5, 36-37 are arranged close to each other, and a lead electrode is extended from each electrode pair toward the end of the quartz substrate 31 and 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.
1 ', T2', and T3 'are connected to form a common terminal Tc, and the input / output terminals T1-Tc and T3-Tc are terminated appropriately so as to function 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.

A method of adjusting the frequency of a triple mode filter is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 7-189883. 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, 36-37 are the same, the resonance characteristics as shown in the upper part of FIG. 5 are exhibited. . Therefore, if 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. That is, the frequency fluctuation of f2 moves larger than f1 and f3. Frequency f
1 and the frequency shift amount of 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 large, and the frequency difference (f
2′−f1 ′) is significantly smaller than (f2−f1). This is because the antisymmetric zero-order mode A ₀ (resonance frequency f
The vibration displacement of 2) becomes 0 at the center of the electrode 34, and the vibration displacement of the electrode 3
The maximum displacement is exhibited in the approximate center of 2,36. This is because, as is well known, when the mass is added to the vibrating portion of the vibrating body, if the mass is added to the position where the vibration displacement is maximum, the amount of frequency change becomes maximum. Conversely, when the masses of the electrodes at both ends are uniformly removed by 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.

Next, as shown at the right end of FIG.
When mass is added only to the center electrode 34 among the electrodes,
The mode having a large frequency change is the symmetric zero-order mode S ₀ (frequency f1), and the next is the symmetric first-order mode S ₁ (frequency f1).
3) The mode with less frequency variation is the antisymmetric zero-order mode A ₀ (f2). Therefore, when the mass is added to the central electrode 34 of the triple mode filter to reduce the frequency, the frequency difference (f3′−f1 ′) is kept almost constant because the frequency variation of the antisymmetric zero-order mode A ₀ is small. The frequency difference (f3'-f2 ') can be reduced as it is. Conversely, the mass of the electrode 34 is removed and the frequency difference (f3'-f
2 ′) can be increased.

Further, even if a mass is added to any of the electrodes of the triple mode filter, the overall frequency is affected to some extent, so that a method of reducing the overall frequency without breaking the respective frequency arrangements is required. Are the electrodes 33, 35, 3
If the mass is added to the whole of 7 using a method such as vapor deposition,
The three frequencies can be translated.

[0006]

However, the above-described method of adjusting the frequency of a triple mode filter is applicable to a conventional triple mode filter using a flat quartz substrate, but FIG. As shown in the drawing, three electrodes 42, 43, and 44 are arranged close to each other on a high-frequency piezoelectric substrate in which a concave portion 41 is formed by means of etching or the like on a quartz substrate 40, and an entire surface electrode 45 is disposed on the concave side. The high frequency triple mode filter described above has a problem that it cannot be applied for the following reason. That is, the thickness of the thin portion (vibrating portion) of the concave portion 41 needs to be processed to be as thin as ten and several microns in order to obtain a high frequency.
In many cases, the parallelism or flatness is not good. For example, as shown in FIG. 8, electrodes 42, 4 are provided on a substrate whose thickness gradually decreases from the left end to the right end in the figure.
3 and 44 and the whole surface electrode 45 are attached, and the electrodes 43, 44 and 4
5 is short-circuited, and the resonance characteristics of the one-port resonator viewed from T1-Tc are measured, for example, as shown in the lower part of FIG. That is, each electrode pair 42-45, 43-45,
Since the resonance frequencies of the electrodes 44-45 are significantly different, the coupling between the electrodes becomes extremely weak. In the case of the shape of the vibrating part as shown in FIG. Although S ₀ is (resonance frequency f1) is strongly excited, antisymmetric zero-order mode a ₀ (resonance frequency f2), resonance level of symmetry primary mode S ₁ (resonance frequency f3) is extremely small, the other as the case In some cases, detection may not be possible because of the resonance caused by this mode.

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 terminals T1-Tc side are as shown in the lower part of FIG. The symmetric first-order mode (S ₁ ) is strongly excited due to weak coupling between the electrodes, but other symmetric zero-order modes S
₀ (resonance frequency f1) and the resonance level of the antisymmetric zero-order mode A ₀ (resonance frequency f2) are extremely small. Therefore, in the case of the resonance characteristic 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 first-order mode S ₁ (f3), the antisymmetric zero-order mode A ₀ (f2) Greatly shifts in frequency, and the resonance frequency of the symmetric zero-order mode S ₀ (f1) and the resonance frequency of the antisymmetric zero-order mode A ₀ (f2) become closer as shown in the lower part of FIG.
When mass is added to the electrodes 43 and 44 as shown in the upper right of FIG. 11, the antisymmetric zero-order mode A ₀ (f2) approaches the symmetric first-order mode S ₁ (f3) as shown in the lower part. As a result, there is a problem that the frequency adjustment method of the conventional triple mode filter 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 has a technique capable of adjusting the frequency of a high-frequency triple mode filter even when the flatness and parallelism of a high-frequency piezoelectric substrate are poor, and adjusting the filter characteristics to predetermined filter characteristics. The purpose is to provide.

[0008]

To achieve the above object, a triple mode piezoelectric filter according to the present invention and a method for adjusting the frequency thereof are provided by a piezoelectric filter having a concave portion formed on one main surface. In a frequency adjustment method of a high-frequency triple mode piezoelectric filter in which three electrodes are arranged close to a flat surface side of a substrate and a whole surface electrode is provided on a concave surface side, an electrode at one end of the three electrodes and the whole surface electrode Is the drive electrode,
According to the resonance characteristics exhibited by the one-terminal pair resonator in which the other electrodes are short-circuited to the entire surface electrodes, the frequency is adjusted by simultaneously adding a large amount of mass to the center electrode and adding a large amount of mass to the end electrodes. This is a method of adjusting the frequency of the triple mode piezoelectric filter. According to a second aspect of the present invention, there is provided a triple mode piezoelectric filter configured using the frequency adjustment method according to the first aspect.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1A is a plan view showing a configuration of a triple mode filter according to the present invention,
A part of one main surface of the quartz substrate 1 is formed with a concave portion 2 serving as a vibrating portion by means of etching or the like, and the entire surface electrode 3 is formed on the concave surface to be connected to the terminal Tc. On the other hand, three electrodes 4, 5, and 6 are arranged close to each other on the flat side, and lead electrodes extend from the electrodes 4, 5, and 6 toward the end of the quartz substrate 1, and terminals T1 and T2 are respectively provided. , T3 to form a high frequency triple mode filter. Figure 1
(B) shows a case where the respective electrodes are connected so as to function as a triple mode filter, and terminals T1-Tc, T3-T
By providing an appropriate termination to each of c, it functions as a bandpass filter. FIG. 1 (c) shows a frequency adjusting mask 7a having a triangular or rectangular hole according to the present invention.
FIG. 7B is a view showing a state in which the frequency is performed by covering the triple-mode filter element 7b with a mass. The mass is added to almost the entire surface of the end electrode 6 through the mask 7b, but the mask 7a is formed on the central electrode 5. Accordingly, the mass is added to only a part of the electrode 5.

A feature of the present invention is that, instead of adding a mass to each electrode in substantially the same area as the electrode 6 (electrode 4) or the electrodes 5, 6 (electrodes 4, 5) as in the prior art,
By adding mass to almost the entire surface of the electrode 6 (electrode 4), a part of the electrode 5, for example, １ ／ of the electrode, a symmetric zero-order mode (f1), an antisymmetric zero-order mode (f2), and a symmetric first-order mode The resonance frequencies of (f3) do not approach each other, and the resonance level increases. Therefore, it is possible to adjust the frequency while checking the frequency and level of each mode.

FIG. 2 is a diagram showing the frequency characteristics when the frequency of the triple mode filter is adjusted using the triangular frequency adjustment mask according to the present invention. First, the terminal T
When the frequency characteristics of the triple mode filter element are measured from 1-Tc, the case shown in the upper part of FIG. 2 is assumed. When the electrodes 5 and 6 are covered with a mask as shown in FIG. 1 (c) 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 described above, when the level of each mode is increased, the resonance frequency of each mode can be measured with high accuracy, and thereafter, the frequency may be adjusted to a desired frequency by a conventional adjustment method. FIG.
This is an example in which a high frequency triple mode filter in a 30 MHz band is frequency-adjusted using the frequency adjustment mask according to the present invention, and is measured as a one-port resonator.

Although an example of a triple mode filter using quartz for the piezoelectric substrate has been described above, the present invention is not limited to this, and the present invention is not limited to this. Other piezoelectric substrates, such as lithium tetraborate, lithium tantalate, and langasite May be applied to a triple mode filter using. Further, the shape of the frequency adjustment mask does not necessarily have to be a triangular shape, but may be any shape as long as the mass added 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.
Adjustment may be made so that the electrode film is thinly removed. Also in this case, the amount of shaving the central electrode and the electrode at one end may be different at the same time.

[0013]

As described above, the present invention is constructed as described above, and the invention according to claim 1 has a method of adjusting the frequency of the high frequency triple mode filter which is far superior to the conventional adjustment method by trial and error. Effect. According to the second aspect of the present invention, since no extra mass is added to each electrode, there is an effect that a filter with little spurious or the like can be obtained.

[Brief description of the drawings]

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,
(C) is a plan view in the case where the triple mode filter element is covered with a frequency adjustment mask.

FIG. 2 is a diagram illustrating frequency characteristics before and after frequency adjustment.

FIG. 3 is a diagram showing frequency characteristics after the frequency adjustment of each electrode is completed.

FIG. 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 conventional method of adjusting the frequency of a triple mode filter.

FIG. 6 is a diagram illustrating a conventional method of adjusting the frequency of a 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 vibrating portion of the piezoelectric substrate is not uniform (the thickness decreases from left to right in the figure).

FIG. 9 shows frequency characteristics when the vibrating portion of the piezoelectric substrate is not uniform (the 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 the addition of mass to the second and third electrodes and frequency characteristics.

[Explanation of symbols]

 1 ··· Piezoelectric substrate 2 ··· Recess 3 ··· Full-surface electrode 4, 5,6 ··· Electrode T1, T2, T3, Tc ··· Terminal 7 ··· Frequency adjustment mask 8,9 ··· Additional mass

Claims (2)

[Claims] 1. A frequency adjusting method for a high frequency triple mode piezoelectric filter in which three electrodes are arranged close to a flat surface side of a piezoelectric substrate having a concave portion formed on one main surface, and all electrodes are provided on the concave surface side. , The electrode at one end of the three electrodes and the entire surface electrode are used as drive electrodes, and the other electrode is less likely to be provided at the center electrode in accordance with resonance characteristics exhibited by a one-port resonator that is short-circuited with the entire surface electrode. A frequency adjustment method for a triple mode piezoelectric filter, wherein a large amount of mass is simultaneously added to an end electrode to adjust a frequency. 2. A triple mode piezoelectric filter which is constructed by using the frequency adjustment method according to claim 1.