JPH09205339A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave element in which the degradation of the characteristics due to the reflected surface wave from an input comb-line electrode and an output comb-line electrode is prevented. SOLUTION: In the surface acoustic wave element 10 in which an input comb-line electrode 21 and an output comb-line electrode 22 are formed on the surface of a piezoelectric substrate 1, the width of each electrode finger 21a, 21c, 22a and 22c of the input comb-line electrode 21 and the output comb- line electrode 22 is dispersed within ±2% to ±20% of an average electrode finger width W in a state where the location space L of electrode fingers is kept constant.

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 used in, for example, a filter circuit or a resonance circuit for a communication device.

[0002]

2. Description of the Related Art A surface acoustic wave element is known as an element utilizing a surface acoustic wave generated by applying a voltage to a piezoelectric body.

FIG. 4 is an external view of a surface acoustic wave element, and FIG. 5 is a schematic surface view showing a conventional electrode pattern of the surface acoustic wave element. As shown in FIGS. 4 and 5, an input comb electrode 21 and an output comb electrode 22 are formed on the surface of the piezoelectric substrate 1. The input comb electrode 21 is composed of electrode fingers 21a and 21c, a pad electrode 21b electrically connecting the electrode finger 21a, and a pad electrode 21d electrically connecting the electrode finger 21c, and the output comb electrode 22 is an electrode finger. 22a and 22c, a pad electrode 22b electrically connecting the electrode finger 22a, and a pad electrode 22d electrically connecting the electrode finger 22c.

Electrode fingers 21a, 21c, 22a and 22
c is the same rectangular shape formed of straight lines, and is formed from hundreds of linear patterns regularly arranged at predetermined intervals, and the electrode fingers 21a and 21c are alternately opposed to each other. The electrode fingers 22a and the electrode fingers 22c are arranged so as to alternately face each other. The pad electrode 21b is an electrode for electrically connecting the electrode finger 21a and an external circuit, and the pad electrode 21d is an electrode for electrically connecting the electrode finger 21c and an external circuit. The pad electrode 22b is an electrode for electrically connecting the electrode finger 22a and for connecting to an external circuit.
Reference numeral 2d is an electrode for electrically connecting the electrode finger 22c and an external circuit.

Electrode fingers 21a, 21c, 22a and 22
c is usually formed of an aluminum metal thin film, the film thickness is 50 nm to 300 nm, the average electrode finger width W and the electrode finger interval (also referred to as the period) L are in the pass band when the surface acoustic wave element is used as a filter. Corresponding to the wavelength λ of the surface wave corresponding to the center frequency (F0), L = λ and W = λ / 4 are formed as basic dimensions. The interval L and the average electrode finger width W are determined corresponding to the center frequency (F0) of the pass band, and are usually within the range of 0.5 μm to 10 μm.

This electrode pattern is formed by faithfully reproducing the pattern of the photomask by using the photolithography method. At this time, the variation in the width of the electrode fingers on the same chip is 2% or less of the average electrode finger width W.

In FIG. 5, when a high frequency signal is input between a pair of the input comb electrodes 21, that is, between the pad electrodes 21b and 21d, the surface of the piezoelectric substrate 1 is mechanically attached to the surface of the piezoelectric substrate 1 at a cycle corresponding to the distance L between the electrode fingers. Distortion occurs.

This mechanical strain propagates as a surface wave 31 on the surface of the piezoelectric substrate 1 and reaches the output comb-shaped electrode 22. At the output comb-shaped electrode 22, an electromotive force is generated by the mechanical distortion of the propagated surface wave, and is detected as an electric signal. At this time, signal components that do not correspond to the electrode finger spacing L of the input comb electrode 21 and the electrode finger spacing L of the output comb electrode 22 are canceled by a large number of electrode fingers and are not detected as signals.

[0009]

As shown in FIG. 5, when an AC signal is applied to the input comb electrode 21, a surface wave (primary surface wave) 31 travels toward the output comb electrode 22. A part of the secondary surface wave 31 is reflected by the output comb-shaped electrode 22 to become a secondary surface wave 32. The secondary surface wave 32 travels toward the input comb electrode 21 and reaches the input comb electrode 21. The secondary surface wave 32 reaching the input comb-shaped electrode 21 is
The third surface wave 33 is reflected by the input comb-shaped electrode 21.
The tertiary surface wave 33 is output together with the primary surface wave 31 to the output comb-shaped electrode 2
2 is detected.

However, since the electrode fingers have a linear shape and are formed so as not to vary uniformly, the generated reflected surface wave has a wavefront parallel to the electrode finger pattern. For this reason, the phase of the primary surface wave 31 and the phase of the tertiary surface wave 33 may enter the output comb-shaped electrode 22 in opposite phases. In this case, when the surface acoustic wave element is used as a filter, there is a problem that the insertion loss increases as shown by the broken line in the vicinity of the center frequency F0 of the pass band as shown in FIG.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a surface acoustic wave element in which characteristic deterioration due to reflected surface waves from the input comb electrodes and the output comb electrodes is prevented.

[0012]

A surface acoustic wave element according to the present invention is a surface acoustic wave element in which an input comb-shaped electrode and an output comb-shaped electrode are formed on the surface of a piezoelectric substrate, and the positions of the electrode fingers forming each electrode. It is characterized in that the width of each electrode finger is varied by ± 2% to ± 20% of the average width of the electrode fingers while keeping the interval constant.

In the surface acoustic wave element according to the present invention, the width of each electrode finger is varied by ± 2% to ± 20% of the average electrode finger width while maintaining the positional distance between the electrode fingers of each electrode. Therefore, it is possible to prevent the reflected surface waves from being scattered, suppressing the interference between the reflected surface waves, and deteriorating the characteristics.

According to the surface acoustic wave element of the present invention, in the surface acoustic wave element in which the input comb-shaped electrodes and the output comb-shaped electrodes are formed on the surface of the piezoelectric substrate, the electrode fingers constituting the respective electrodes are kept at a constant distance. In this state, an uneven portion having a variation of ± 2% to ± 20% with respect to the average electrode finger width is formed on each electrode finger.

In the surface acoustic wave element according to the present invention, since the concave and convex portions are formed on each electrode finger while the electrode finger positions are maintained, the reflected surface waves are scattered and the reflected surface waves interfere with each other. Is suppressed and the characteristic is prevented from being deteriorated.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a surface acoustic wave device according to the present invention will be described.

FIG. 1 is a schematic surface view showing an electrode pattern of a surface acoustic wave device according to an embodiment of the present invention.

In a surface acoustic wave device 10 according to an embodiment of the present invention, an input comb electrode 21 and an output comb electrode 22 are formed on the surface of a piezoelectric substrate 1. Input comb electrode 2
1 is composed of electrode fingers 21a and 21c, a pad electrode 21b electrically connecting the electrode fingers 21a, and a pad electrode 21d electrically connecting the electrode fingers 21c. The output comb-shaped electrode 22 is composed of electrode fingers 22a and 22c. And a pad electrode 22b electrically connecting the electrode finger 22a and a pad electrode 22d electrically connecting the electrode finger 22c.

Electrode fingers 21a, 21c, 22a and 22
c is a rectangular shape formed of substantially straight lines, and is formed of several hundred linear patterns regularly arranged at a predetermined interval, and the electrode fingers 21a and 21c are alternately arranged to face each other. The electrode fingers 22a and the electrode fingers 22c are arranged so as to alternately face each other. The pad electrode 21b is an electrode for electrically connecting the electrode finger 21a and an external circuit, and the pad electrode 21d is an electrode for electrically connecting the electrode finger 21c and an external circuit. The pad electrode 22b is an electrode for electrically connecting the electrode finger 22a and for connecting to an external circuit.
Reference numeral d is an electrode for electrically connecting the electrode finger 22c and an external circuit.

Electrode fingers 21a, 21c, 22a and 22
c is usually formed of an aluminum metal thin film, and its thickness is 50 nm to 300 nm.

In the present embodiment, the electrode finger widths are W1, W2, and W2, respectively, with respect to the average electrode finger width W (λ / 4).
As W3 and W4. Here, the electrode finger widths W1 and W
2, W3, W4 are + 1%, -2% from the average electrode finger width W,
The width is set to be changed by -3% and + 4%. In this case, the variation of the electrode finger width with respect to the average electrode finger width W is designed to be 7% at maximum. Where the electrode finger spacing L
Is constant and does not change as in the case of the conventional example.

With this structure, the primary surface wave 31 and the tertiary surface wave 33 are scattered, and the primary surface wave 3
Interference between the reflected surface waves of the first and third surface waves 33 is suppressed, and when the surface acoustic wave element 10 is used as a filter,
As shown in FIG. 6, in the vicinity of the center frequency (F0) of the pass band, the insertion loss no longer increases as shown by the solid line.

It should be noted that this variation of the electrode finger width is sufficiently effective in the range of ± 2% to ± 20% with respect to the average electrode finger width W. In order to obtain a variation exceeding ± 20%, it may be necessary to change the manufacturing process.

Next, another embodiment of the present invention will be described.

2 and 3 are a schematic surface view and another enlarged view showing another embodiment of the present invention, in which a part of the input comb-shaped electrode 21 is shown.

In another embodiment of the present invention, FIG.
, The electrode finger width W5 (= 0.80 W) and the electrode finger width W6 (=
The irregular concave and convex portion 30 having a width of 1.2 W) is formed, and the concave and convex shapes of the respective electrode fingers are different.

In another embodiment of the present invention, the electrode finger width is the same as the average electrode finger width W and is the same, but since the different uneven portions 30 are formed on each electrode finger, the reflected surface wave is scattered. Thus, the interference between the reflected surface waves is suppressed.

Although the input comb-shaped electrode 21 has been described above, it goes without saying that the output comb-shaped electrode 22 has the same structure.

The uneven portion 30 having the electrode finger width is ± 2%.
When the change was made within the range of ± 20%, the increase in insertion loss was suppressed and the effect was sufficiently observed. In order to obtain the uneven portion 30 exceeding ± 20%, it may be necessary to change the manufacturing process.

In the above-described one embodiment and other embodiments, it is possible to easily form the surface acoustic wave element of each form on the photomask pattern by the conventional technique, and by using this photomask pattern. It is also easy to form the electrode pattern of each of the above forms on the piezoelectric substrate 1.

In each of the above embodiments, the average electrode finger width W is set to W = λ / 4, but even when the average electrode finger width W is changed according to the required characteristics of the surface acoustic wave filter, The same effect can be obtained. Further, the input comb-shaped electrode 21
Also, the present invention can be applied to a so-called multi-electrode configuration in which a plurality of pairs of output comb-shaped electrodes 22 are provided, and similar effects can be obtained.

[0032]

As described above, according to the present invention, interference between reflected surface waves between the input comb-shaped electrode and the output comb-shaped electrode is reduced, and desired characteristics can be obtained. Further, only the design of the photomask pattern needs to be changed for implementation, and it is not necessary to change the conventional manufacturing equipment.

[Brief description of drawings]

FIG. 1 is a schematic surface view showing an electrode pattern of a surface acoustic wave element according to an embodiment of the present invention.

FIG. 2 is a schematic surface view showing an electrode pattern of a surface acoustic wave element according to another embodiment of the present invention.

FIG. 3 is a schematic enlarged surface view of the shape of an electrode finger showing an electrode pattern of a surface acoustic wave element according to another embodiment of the present invention.

FIG. 4 is an external view of a surface acoustic wave device.

FIG. 5 is a schematic surface view showing an electrode pattern of a conventional surface acoustic wave element.

FIG. 6 is a characteristic diagram for explaining the operation when each of the embodiments of the present invention is used for a filter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 10 ... Surface acoustic wave element 21 ... Input comb-shaped electrode 22 ... Output comb-shaped electrode 21a, 21c, 22a, 22c ... Electrode finger 21b, 21d, 22b, 22d ... Pad electrode 30 ... Uneven portion 31 ... Primary surface Wave 32 ... Secondary surface wave 33 ... Tertiary surface wave L ... Electrode finger spacing W ... Average electrode finger width

Claims (2)

[Claims] 1. A surface acoustic wave device having an input comb-shaped electrode and an output comb-shaped electrode formed on the surface of a piezoelectric substrate, in a state in which the positional intervals of electrode fingers constituting each electrode are kept constant,
A surface acoustic wave device characterized in that the width of each electrode finger is varied by ± 2% to ± 20% of the average width of the electrode finger. 2. A surface acoustic wave device having an input comb-shaped electrode and an output comb-shaped electrode formed on the surface of a piezoelectric substrate, wherein the electrode fingers constituting the respective electrodes are kept at a constant distance.
A surface acoustic wave element, characterized in that each electrode finger is formed with a concavo-convex portion that is changed by ± 2% to ± 20% with respect to the average electrode finger width.