JPH03217109A - Surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To improve the reflection efficiency to reduce the insertion loss without increasing the pattern size by increasing the angle of inclination of a reflection electrode. CONSTITUTION:The surface of a piezoelectric substrate 1 and a reflection electrode side face 3a form an angle theta in the section of a reflection electrode 3. The characteristic of the insertion loss of a surface acoustic wave resonator for the change of this angle theta of inclination is shown in the Figure. This Figure shows that the insertion loss is reduced as the angle theta of inclination is increased. The surface acoustic wave reflection electrode is so formed that the angle thetaof inclination between the side face and the piezoelectric substrate surface in the section in the direction of surface acoustic wave propagation is 60 to 75 deg.. For the purpose of obtaining a desired electrode width W, a photomask where the electrode pattern width is extended by an extent corresponding to the etching time is used to expose a resist to light.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a surface acoustic wave resonator used in RF converters and the like.

(mouth) Conventional technology FIG. 3 is a diagram showing a surface acoustic wave resonator.

(1) is a piezoelectric substrate made of LiTaOs or the like, and (2) is a surface acoustic wave excitation electrode for exciting surface acoustic waves, which is formed in an interdigital manner on the piezoelectric substrate (1). (
3) (4) are surface acoustic wave reflecting electrodes placed on both sides of the surface acoustic wave excitation electrode (2) to face each other. These electrodes (2), (3), and (4) are made of Aj, etc., and are formed into a predetermined shape by photo-etching.

The operation of such a surface wave resonator will be briefly explained.

When an electric signal of a predetermined resonance frequency is applied to the excitation electrode (2), a surface acoustic wave is excited on the surface of the piezoelectric substrate (1.). The excited surface acoustic waves pass through the reflective electrodes (3) (4
) and becomes a standing wave by repeating reflection between the reflective electrodes (3) and (4). Then, the excitation electrode (
2) and oscillates at a predetermined frequency.

In such a surface acoustic wave resonator, the electrode formed by etching has a trapezoidal cross-sectional shape in the propagation direction (A) of the surface acoustic wave with a long lower side. FIG. 4 shows a cross-sectional view of the reflective electrode (3) in the propagation direction of surface acoustic waves.

Conventionally, the reflective electrode (3) has a cross-sectional inclination angle (θ°) (the electrode side surface (3a) in the electrode (3) cross section and the piezoelectric substrate (1)) in order to easily obtain the desired electrode width (W) by etching.
) The angle formed with the surface was approximately 55 degrees. this is,
This is because the inclination angle (θ°) of the cross section of the reflective electrode (3) and the width (W) of the formed electrode are both determined by the etching time. The longer the etching time, the tilt angle of the electrode obtained (
θ゛) becomes larger and the electrode width (W) becomes narrower.

(c) Problems to be Solved by the Invention In order to improve the insertion loss of the surface acoustic wave resonator, it is necessary to increase the reflection efficiency of the reflection electrodes (3) and (4). One way to increase reflection efficiency is to use reflective electrodes (3) (4).
) or increase the aperture length. However, this method has a problem in that the electrode pattern size becomes large.

Also, Japanese Patent Application Laid-open No. 168410/1983 (11031{
9/25) discloses a surface acoustic wave resonator that solves this problem. In this surface acoustic wave resonator, three reflective electrodes are formed by sequentially and alternately stacking low-density layers and high-density layers, thereby increasing the reflection efficiency of the reflective electrode.

However, since such a surface acoustic wave resonator requires alternating stacking of low-density layers and high-density layers, there are problems in that the number of manufacturing steps increases and two types of electrode materials are required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a surface acoustic wave resonator with improved insertion loss without increasing the electrode pattern size or increasing the number of manufacturing steps.

(2) Means for Solving the Problems In view of the above-mentioned problems, the present invention includes a piezoelectric substrate, a surface acoustic wave excitation electrode formed on the piezoelectric substrate, and an elastic A surface acoustic wave resonator comprising a surface acoustic wave reflecting electrode, wherein the reflecting electrode is characterized in that the angle between the side surface and the piezoelectric substrate surface in a cross section in the surface acoustic wave propagation direction is in the range of 60 degrees to 75 degrees. That is.

4 (e) By defining the above-mentioned angle of the cross section of the working reflective electrode within the above range, the mass of the reflective electrode increases compared to when this angle was conventionally set at around 55 degrees, so the reflection efficiency of the reflective electrode increases. improves.

(f) Example An embodiment of the present invention will be described below.

The electrode configuration of the surface acoustic wave resonator of the present invention is, for example, a third
This is similar to the conventional example shown in the figure. FIG. 1 is a sectional view of a reflective electrode portion of the surface acoustic wave resonator in the surface acoustic wave propagation direction. (1) is a piezoelectric substrate made of LiTags or the like, and (3) is a reflective electrode made of Al or the like formed on the piezoelectric substrate (1). (θ) is an inclination angle, and indicates the angle formed between the surface of the piezoelectric substrate (1) and the side surface (3a) of the reflective electrode in the cross section of the reflective electrode (3).

FIG. 2 shows the insertion loss characteristics of the surface acoustic wave resonator when changing the tilt angle (θ). From this figure, it can be seen that the insertion loss decreases as the tilt angle (θ) increases. For example, when the inclination angle (θ) is 60 degrees, it is improved by about 0.05 dB compared to when it is 55 degrees.

Insertion loss can be improved by increasing the tilt angle (θ), but it cannot be increased too much. This is because the tilt angle (θ) of the reflective electrode is determined by the etching time as described above. That is, the tilt angle (θ
), it is necessary to take longer etching time. Increasing the etching time increases the electrode width (
W) becomes that much thinner. Therefore, the desired electrode width (W
), it is necessary to expose the resist using a photomask whose electrode pattern width is increased by an amount corresponding to the etching time. If the electrode pattern width of the photomask is wide, the spacing between the electrode patterns of the photomask becomes narrow, so that the resist may not be sufficiently exposed and etching may not be performed satisfactorily.

Therefore, in the surface acoustic wave resonator of the present invention, in consideration of productivity, the upper limit of the inclination angle (θ) is set to 75 degrees as defined in the claims.

As described above, by increasing the inclination angle (θ) of the reflective electrode, the reflection efficiency is improved, thereby improving the insertion loss.

(g) Effects of the invention The surface acoustic wave resonator of the invention has a reflective electrode with an inclination angle of 60
By setting the angle between degrees and 75 degrees, insertion loss can be improved without increasing the pattern size.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the reflective electrode portion of the surface acoustic wave resonator of the present invention in the surface acoustic wave propagation direction, FIG. FIG. 3 is a plan view showing a surface acoustic wave resonator, and FIG. 4 is a cross-sectional view of a reflective electrode portion of the surface acoustic wave resonator made by Yomei in the surface acoustic wave propagation direction. (1)...Piezoelectric substrate, (2)...Surface acoustic wave excitation electrode, (3)...Surface acoustic wave reflecting electrode.

Claims (1)

[Claims] (1) In a surface acoustic wave resonator comprising a piezoelectric substrate, a surface acoustic wave excitation electrode formed on the piezoelectric substrate, and a surface acoustic wave reflection electrode disposed opposite to the surface acoustic wave excitation electrode, the elastic A surface acoustic wave resonator characterized in that the surface acoustic wave reflecting electrode has an angle between the side surface and the surface of the piezoelectric substrate in a cross section in the surface acoustic wave propagation direction in a range of 60 degrees to 75 degrees.