JPH02250415A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To improve the reflecting efficiency of the open type reflector stably and effectively by specifying the ratio of the width of the conductive strip of the reflector to a conductive strip pitch. CONSTITUTION:In considering that there is a limit of improving the reflecting coefficient by making the film thickness of the conductive strip in the reflector thick, then the duty ratio, that is, the ratio d=a/(a+b) is selected as 1.0>d>=0.54, where (a) is the width of a metallic strip 16a of a reflector 16, and (a+b) is a strip pitch. Thus, the reflection efficiency of the reflector is improved, then the surface acoustic wave device is made small in size.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of a surface acoustic wave device in which a reflector is arranged on the side of an interdigital transducer, and in particular, the present invention relates to an improvement in a surface acoustic wave device in which a reflector is arranged on the side of an interdigital transducer. related to things.

[Conventional technology]

FIG. 2 is a plan view showing an example of a conventional surface acoustic wave device.
, an interdigital transducer 5 having interdigitated interdigitated electrodes 3.4 on a piezoelectric substrate 2 consisting of .
and reflectors 6.7 arranged on both sides of the interdigital transducer 5.

The electrode fingers 3a and 4a of the comb-teeth electrodes 3 and 4 are arranged so as to be inserted into each other as described above. Further, the reflector 6.7 is a so-called open reflector consisting of a plurality of independent conductive strips 6a, 7a arranged parallel to each other.

Surface acoustic wave devices, like other electronic components, are also required to be more compact. Therefore, in the conventional surface acoustic wave device 1, by increasing the reflection efficiency in the reflector 6.7, the size of the reflector 6.7 in the surface wave propagation direction can be reduced, thereby reducing the overall size. is being attempted.

That is, by increasing the film thickness of the conductive strips 6a and 7a, the reflectance per conductive strip is increased, thereby reducing the number of conductive strips.

[Technical problem to be solved by the invention] However,
When the film thickness of the conductive strips 6a, 7a is increased, it is difficult to control the film thickness to be constant, and therefore variations in reflection efficiency tend to occur. Therefore, there was naturally a limit to increasing the film thickness.

On the other hand, regarding the reflection of Rayleigh waves on a piezoelectric substrate made of 128°Y-X, LiNbO5, in an open reflector, the duty ratio of the conductive strip, that is, the ratio of the width of the conductive strip to the conductive strip pitch. It has been reported that the reflection coefficient can be increased when d is set to d≧0.5.

An object of the present invention is to provide a surface acoustic wave device using a piezoelectric substrate made of a 36@rotating Y plate and LiTa01, which can stably and effectively increase the reflection efficiency of an open reflector. .

C Technical! i! ! [Means for solving the problem] The surface acoustic wave device of the present invention rotates by 36°.

A piezoelectric substrate made of LiTaO5 is used, and surface shear waves excited in the piezoelectric substrate are utilized. An interdigital transducer having interdigitated electrodes is formed on the piezoelectric substrate. An open reflector is formed on the side of the interdigital transducer and is formed by a plurality of independent conductive strips arranged in parallel to each other and extending in a direction perpendicular to the direction of surface wave propagation.

The duty ratio of the conductive strip in the reflector, i.e. the ratio d of the width of the conductive strip to the pitch, is:
1.0>d≧0.54.

[Effect]

Considering that there is a limit to increasing the reflection coefficient by increasing the film thickness of the conductive strip in the reflector, in the present invention, the duty ratio of the reflector is set to 1.0>d as described above. By setting ≧0.54, the reflection efficiency is increased as shown in the examples below. That is,
The present invention is characterized in that by setting the duty ratio as described above, the reflection efficiency of the reflector is increased, thereby reducing the size of the surface acoustic wave device.

[Explanation of Examples]

FIG. 1 is a plan view of a surface acoustic wave device according to an embodiment of the present invention. This surface acoustic wave device 11 includes a piezoelectric substrate 12 having a rectangular planar shape and made of 36" Y-X, L 1 Taos.
It is configured using An interdigital transducer 15 is formed in the center of the piezoelectric substrate 12. The interdigital transducer 15 consists of toothed electrodes 13 and 14 that are inserted into each other. It has electrode fingers 13a and 14a.

A pair of reflectors 16.17 are formed outside the interdigital transducer 15 in the surface wave propagation direction.The reflectors 16.17 each extend in a direction perpendicular to the surface wave propagation direction and are mutually It has a plurality of independent conductive strips 16a, 17a arranged in parallel.

The conductive strip is made of metal, such as AIt, or other suitable conductive material.

The feature of this embodiment is that this reflector 16. This depends on the duty ratio of the plurality of conductive strips 16a and 17a that constitute the IT.

That is, as shown in FIG. 3, which is an enlarged cross-sectional view of the main part of the reflector 16, the duty ratio, that is, the strip pitch of the cap a of the conductive strip 16a of the reflector 16 (
The ratio d=a/(a+b) to a+b) is 1.0>
The reason is that d≧0.54. In addition, reflector 1
The 7 side is also configured to have a similar duty ratio.

36 @Y-X, In the conventional structure (Fig. 2) using LiTaOs piezoelectric substrate, the duty ratio of the reflector was about 0.5, but in the present invention, the duty ratio d
The reason why is set to the above-mentioned range is that within this range, the reflection efficiency per conductive strip of the reflector can be effectively increased, thereby making it possible to reduce the size of the reflectors 16 and 17. This will be explained with reference to FIGS. 4 and 5.

FIG. 4 is a diagram showing the reflectance per conductive strip when the deity ratio d is changed in the structure of the embodiment shown in FIG. In addition, in FIG. 4, the reflector 16
．． Three types of characteristics were shown when the film thickness/wavelength (all units are μm) of the conductive strips 16a and 17a in No. 17 were set to 1%, 2%, and 3%.

As is clear from Figure 4, the film thickness/wavelength is 1°2 and 3°.
%, the conductive strip 16a,
The reflectance per 17a is when the duty ratio d is 0.3
It can be seen that it increases monotonically from around 0.8.

Furthermore, Fig. 5 shows the maximum reflection coefficient when the film thickness/wavelength of the conductive strip 168.17a is varied within a range of 3% or less and the duty ratio is varied within a range of up to 1.0. combination (shown by solid line A), an area where the reflection coefficient is within 10% from the maximum (area B with diagonal lines), and a 20% increase in the reflection coefficient when the duty ratio is 0.5. Region C showing a reflection coefficient of is shown.

From FIGS. 4 and 5, in the range where (film thickness/wavelength) is 3% or less, the duty ratio is 0.54 compared to the conventional structure, that is, the duty ratio of the conductive strip is 0.5.
It can be seen that in the above case, the reflection coefficient can be increased by 20%. Therefore, in the present invention, the duty ratio is 0.54
This is said to be the above.

More preferably, when seeking a higher reflection coefficient, the duty ratio d should be selected within the range of region B in FIG. If it is set in the range of 0.65 to 0°9, the reflectance per conductive strip can be increased more effectively.

Although a one-point type surface acoustic wave device using one interdigital transducer is shown as an example, a two-point type surface acoustic wave resonator using two interdigital transducers, The present invention can be applied to surface acoustic wave devices using reflectors, such as filters that use reflectors to reduce loss.

Note that in a resonator with only an interdigital transducer and no reflector, the duty ratio of the interdigital transducer may be increased to increase the reflectance of surface acoustic waves inside the interdigital transducer. However, in a structure like the device of the present invention using a reflector, the surface wave confinement efficiency can also be increased by increasing the duty ratio of the interdigital transducer.

〔Effect of the invention〕

As described above, in the present invention, the duty ratio d is 1. Since it is set in the range of O>d≧0.54, the reflection efficiency in the reflector is effectively increased. Therefore, the number of conductive strips in the reflector can be reduced, and a smaller surface acoustic wave device can be realized. Furthermore, variations in reflection efficiency are less likely to occur, which would occur if the reflection coefficient was increased by increasing the film thickness of the conductive strip.

[Brief explanation of drawings]

FIG. 1 is a plan view of a surface acoustic wave device according to an embodiment of the present invention;
Figure 2 is a plan view of a conventional surface acoustic wave device, and Figure 3 is a plan view of a conventional surface acoustic wave device.
A cross-sectional view showing an enlarged section along the line ■-■ in the figure, Figure 4 is a diagram showing the relationship between the duty ratio d and the reflectance per conductive strip of the reflector, and Figure 5 is the reflection coefficient. FIG. In the figure, 11 is a surface acoustic wave device, 12 is a piezoelectric substrate,
13 and 14 are comb electrodes, 15 is an interdigital transducer, 16 and 17 are reflectors, and 16a and 17a are conductive strips. Fig. 3 1A z Fig. 4 Deng ety.

Claims (1)

[Scope of Claims] A piezoelectric substrate made of a 36° rotated Y plate and LiTaO_3, and a comb-shaped electrode formed on the piezoelectric substrate so as to propagate a surface wave parallel to the X-axis and interposed with each other. The reflector includes an interdigital transducer and a reflector formed by arranging a plurality of independent conductive strips in parallel to each other extending in a direction perpendicular to the surface wave propagation direction on the side of the interdigital transducer to generate surface shear waves. In the surface acoustic wave device used, the ratio d of the width of the conductive strip to the pitch of the conductive strip in the reflector is 1.0>d≧0.5.
4. A surface acoustic wave device characterized by: