JPH09148879A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make manufacture deviation in resonance frequency small without altering material machining, a process, etc., by relating the line width and space width of an IDT electrode and the line width and space width of a reflector according to specific expressions. SOLUTION: On a piezoelectric substrate 1, the IDT electrode 2 and reflectors 3 on both its sides are provided. Then the relations of L1/(L1+L2)>=0.65 and R1/(R1+R2)>=0.65 are satisfied, where L1 is the electrode finger width (line width) of the IDT electrode 2, L2 the space width, R1 the line width of the reflectors 3, and R2 the space width. When a crystal ST cut is used as the piezoelectric substrate 1, H/λ/>=0.015 is set, where H is the electrode film thickness and λ is the wavelength of a surface acoustic wave. When the electrode film thickness H is larger than 1.5% of the wavelength of a surface wave λ, standard deviation in resonance frequency, i.e., variance becomes smaller and smaller as the line occupation rate is made larger and larger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device in which resonance frequency deviation is suppressed as much as possible and frequency adjustment is unnecessary.

[0002]

2. Description of the Related Art In recent years, surface acoustic wave devices have been used in many electronic devices, and especially in wireless devices such as mobile phones due to their high frequency and small size. FIG.
Fig. 1 shows a schematic diagram of the electrode configuration of a conventional 1-port resonator. The IDT electrodes 2 are arranged on the main surface of the piezoelectric substrate 1 along the propagation direction of the surface wave, and grating reflectors (hereinafter,
The reflectors 3 and 3 are arranged at a required distance from the IDT electrode 2. The IDT electrode 2 and the reflectors 3 and 3 are simultaneously formed by depositing an alloy containing aluminum as a main component on the piezoelectric substrate by vapor deposition or sputtering and using a photoetching method including the lead electrode and the like.

In the one-port resonator of FIG. 1, the IDT electrode 2
Since the surface wave excited by is propagated to the left and right around the IDT electrode, the reflectors 3 composed of a large number of electrode fingers are arranged on both sides of the IDT electrode to reflect the vibration energy toward the center of the IDT electrode. The structure is designed to minimize leakage to the surrounding area. Also, the resonance frequency of the surface wave resonator is roughly
It depends on the distance L between the IDT electrodes (corresponding to half the wavelength),
More specifically, the film thickness of the IDT electrode and the reflector, the etched line width, and the like affect variations in the same wafer.

When the resonance frequency is less than the required value, it is necessary to individually adjust the frequency. As one of the adjusting methods, there is a method of forming a dielectric film on the main surface of the surface wave resonator by vapor deposition, sputtering or the like, and changing the propagation velocity of the surface wave to adjust the frequency. Another method is to dry-etch the electrodes of the surface acoustic wave resonator or dry-etch the surface of the piezoelectric substrate to change the frequency. Which method to use depends on device usage,
It is determined in consideration of the piezoelectric material and the electrode material.

[0005]

However, a means for adjusting the frequency by depositing a dielectric film on the main surface of the surface acoustic wave resonator is also possible by dry etching the electrode or the piezoelectric substrate on the main surface. Both the means for adjusting the frequency need to adjust the frequency for each of the surface acoustic wave resonators, and the frequency adjustment requires a huge number of steps, resulting in an expensive component. The present invention has been made to solve the above problems, and an object of the present invention is to provide a surface acoustic wave device in which the frequency deviation is suppressed as much as possible.

[0006]

In a surface acoustic wave device having an IDT electrode and reflectors on both sides of the IDT electrode on a piezoelectric substrate, the electrode finger width of the IDT electrode (hereinafter, referred to as line width) is L1 and the space width is Let L2 be the line width of the reflector and R2 be the space width L1 / (L1 + L2) ≧ 0.65 and R1 / (R1 +
The surface acoustic wave device is characterized by satisfying the relationship of R2) ≧ 0.65. In the case where a quartz ST cut is used as the piezoelectric substrate, H / λ ≧ 0.015 is set when the electrode film thickness is H and the wavelength of the surface acoustic wave is λ, and the above line width is And a surface acoustic wave device satisfying the relationship of space width.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. First, in order to help understanding of the present invention, the Institute of Electronics and Communication Engineers Technical Report MW82
-59 (1982), Uno et al., Briefly describes the part related to the present invention. A part of the cross section taken along the line AA in FIG. 1 is shown in FIG. L1 and L2 are IDTs
The line width and space width of the electrode 2, and R1 and R2 are the line width and space width of the reflector 3. According to the same paper, as shown in FIG. 2, the pitch half cycle of the IDT electrode or the reflector, that is, L1 + L2 or R1 + R2
The ratio of the line width to
It is shown that t = 0.55 is most desirable as the line occupancy, and relatively uniform and good resonance characteristics can be obtained in the range of 0.45 <t <0.65. However, this is Q and crystal impedance (C
It does not mention the relation between the frequency variation of the surface acoustic wave resonator and the line occupation rate.

Therefore, the inventor of the present application has found that the line occupancy is 0.
The resonance frequency was measured in detail using three types of surface wave resonators of 3, 0.5 and 0.7. 3 as a piezoelectric substrate
4.5 ° quartz ST cut substrate is used, and IDT logarithm is 2
00 pairs, the number of reflectors on both sides is 424, and the crossover length is W =
It was set to 20λ. Further, as shown in FIG. 1, the IDT cycle is λ =
7.217 μm, pitch of reflectors P = 3.6235 μ
m. In FIG. 3A, line occupancy ratios of 0.3 and 0.5
And 0.7, the average value of the resonance frequency and the actual measurement value of the standard deviation thereof when the normalized film thickness H / λ is changed from about 1% to 2.4% are shown. In addition, the line occupancy rate is used as a parameter so that it is easy to visually understand, and the horizontal axis indicates the film thickness H (%).
FIG. 3B shows a diagram in which the standard deviation of the resonance frequency is taken on the vertical axis. As is apparent from FIGS. 3A and 3B, the electrode film thickness H is 1.5 of the wavelength λ of the surface wave.
It can be seen that the standard deviation of the resonance frequency, that is, the variation becomes smaller as the line occupancy increases when the thickness is larger than%. This tendency is not observed when H / λ is 1%, but this is considered to have little effect on the resonance frequency when the electrode film thickness is small, because variations in the line width due to etching are small. .

In FIG. 4A, the number of samples is 36, the resonance frequency is about 430 MHz, and the normalized film thickness H / λ is about 2.
% And line occupancy t = 0.5, it is a diagram showing a histogram of the resonance frequency, and the standard deviation is about 0.0695M.
Hz. FIG. 4B shows a histogram of resonance frequencies when the number of samples is 36, the resonance frequency is about 430 MHz, the normalized film thickness H / λ is about 2%, and the line occupancy t = 0.7. In the figure, the standard deviation is about 0.0299.
MHz. When the IDT electrodes and reflectors of the surface acoustic wave resonator have the same shape, number of logarithms, number of films, and film thickness, when the line occupancy t = 0.7, the standard deviation is larger than when t = 0.5. It can be seen that is reduced to about 43%.

Another example of the standardized film thickness is shown in FIG. 5A, in which the number of samples is 33, the resonance frequency is approximately 430 MHz, and the standardized film thickness H / λ is approximately 2.4%. , A graph showing a resonance frequency histogram when the line occupancy t = 0.5, and the standard deviation is about 0.128 MHZ. In FIG. 5B, the number of samples is 34, the resonance frequency is about 430 MHz, the normalized film thickness H / λ is about 2.4%,
It is a figure showing the histogram of resonance frequency in case line occupancy t = 0.7, and standard deviation is about 0.0417MHz. When the IDT electrode and the reflector of the surface acoustic wave resonator have the same shape, number of logarithms, number of films, and film thickness, the line occupation rate t
It can be seen that when = 0.7, the standard deviation is reduced to about 33% compared to the case of t = 0.5.

As described above with reference to FIGS. 3 to 7, by making the line occupancy rate larger than the value disclosed by Uno et al. It was found that the surface wave resonator with small deviation can be manufactured by the same process as the conventional one.

Although the 1-port surface wave resonator has been described above as an example, the present invention is not limited to this. A 2-port surface wave resonator, a sliding wave resonator, a leaky surface wave resonator, and a Love wave type resonance are provided. And a multi-pair IDT electrode type surface acoustic wave resonator. Also, piezoelectric substrates other than quartz, such as LiTa
A substrate of O ₃ , LiNbO ₃ , Li ₂ B ₄ O ₇ or the like may be used. It goes without saying that the present invention can also be applied to a resonator filter using the above wave.

[0013]

Since the present invention is configured as described above, it is possible to perform the processing without changing the material processing or the process.
Since the manufacturing deviation of the resonance frequency can be made small, it is not necessary to adjust the frequency in the subsequent process, and there is a remarkable effect in that a large number of good surface wave devices can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic view of a 1-port surface acoustic wave resonator.

FIG. 2 is a diagram showing a cross-sectional view of a surface acoustic wave device, and is a diagram illustrating a line width, a space width, and a line occupation rate t.

FIG. 3A is a diagram showing a relationship between a line occupancy rate, a normalized film thickness and a frequency standard deviation, and FIG. 3B is a graph showing the relationship shown in FIG. 3A.

FIG. 4A shows a normalized film thickness of about 2% and a line occupancy of 0.
5 is a frequency histogram, and (b) is a frequency histogram when the normalized film thickness is about 2% and the line occupancy is 0.7.

FIG. 5A is a frequency histogram when the normalized film thickness is about 2.4% and the line occupancy rate is 0.5, and FIG. 5B is the normalized film thickness about 2.4% and the line occupancy rate is 0.7. It is a frequency histogram in the case of.

[Explanation of symbols]

 1 Piezoelectric substrate 2 IDT electrode 3 Reflector 1

Claims (2)

[Claims] 1. A surface acoustic wave device having an IDT electrode and reflectors on both sides of the piezoelectric substrate, wherein a line width of the IDT electrode is L1, a space width is L2, and a line width of the reflector is R1. When the width is R2, L1 / (L1 + L2) ≧ 0.65 and R1 / (R1 +
A surface acoustic wave device having a relationship of R2) ≧ 0.65. 2. When a quartz ST cut is used as the piezoelectric substrate, H / λ ≧ 0.015 is set, where H is the electrode film thickness and λ is the wavelength of the surface acoustic wave. Item 1. The surface acoustic wave device according to item 1.