JPS5910609B2 - surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device having a transducer of a new configuration.

Conventionally, surface acoustic wave devices using piezoelectric thin films include:
A structure as shown in FIG. 1 is used.

That is, in the figure, 1 is a substrate, 2 is a pair of comb-shaped electrodes formed on the surface thereof, 3 is a piezoelectric thin film formed on the surface of the substrate 1 including the surface of electrode 2, and 4 is a counter electrode. in,
This serves to increase the effective electromechanical coupling coefficient of the transducer.

In such a device, the wavelength of the surface acoustic wave at its center frequency is λ.

Then, the dimensions of the comb-shaped electrode λ2 are: the width of the electrode fingers is -j1, and the gap between the electrode fingers is? It is.

Such a configuration is extremely simple and efficient for exciting or receiving surface acoustic waves.

However, the reflection of surface acoustic waves in the transducer is large, which has been a major problem in the design of this type of device.

In order to reduce this reflection, the comb-shaped electrode is made into a so-called split type as shown in FIG.

This is because the width of the electrode fingers, λ0, and the gap between the electrode fingers are W, which are extremely narrow.

If the width of the electrode fingers is narrow, it is natural that the wires are likely to break during manufacturing, which poses a major problem in mass production.

The present invention aims to provide a surface acoustic wave device that can solve such problems.

The following is a cross-sectional view of FIG. 3A and FIG. 3B for one embodiment.
This will be explained using a plan view.

Note that FIG. 3A is a sectional view taken along line cc' in FIG. 3B.

In the figure, 11 is a substrate, on one surface of which a pair of comb-shaped electrodes 12, a piezoelectric film 13, and a counter electrode 14 are sequentially formed.

3 The width of the electrode fingers of the comb-shaped electrode 12 is λ.

, and the electric λ0 The gap between the pole fingers is 1".

The counter electrodes 14 are arranged parallel to each other in the longitudinal direction of the electrode fingers on the gaps between the electrode fingers of the comb-shaped electrode 12 and have a width of 3 λ.

1, the line width and the gap are Wλo and s, respectively
There is L.

The counter electrode 14 and the comb-shaped electrode 12 are arranged so that the center of one electrode is located in the gap between the other electrode.

With this configuration, the conductive film λ of the counter electrode 14.

The end of the comb-shaped electrode 12 and the end of the conductive film of the comb-shaped electrode 12 are shifted by i, and the surface acoustic wave λ at the end.

The reflected waves of the electrode 1 are shifted, and the reflected waves of each cancel each other out, reducing the amplitude.
The same thing can be said even if the positions of 2.14 are swapped with each other.

As long as the relative positional relationship of the electrodes is maintained, the length of the electrode fingers of the so-called weighted transducer, i.e. the comb-shaped electrode, or the conductive film of the counter electrode,
It is also possible to obtain the effect of suppressing reflected waves by changing the weighting characteristics depending on the position.

Furthermore, during manufacturing, errors often occur in the alignment between the comb-shaped electrode and the counter electrode, and the potential of the conductive film of the counter electrode may not be constant.

This can be prevented by electrically connecting the conductive films forming the counter electrode.

The electrical connection may be formed integrally when forming the counter electrode, or may be formed and then connected using a lead wire.

As explained above, the surface acoustic wave device according to the present invention has a comb-shaped electrode arranged on both sides of one side of a piezoelectric thin film, and a conductive film constituting a counter electrode on the other side.
The center thereof is located at the center of the gap between the electrode fingers of the comb-shaped electrode, and the width of the electrode fingers of the comb-shaped electrode and the width of the conductive film of the counter electrode are respectively set to λ0, and the width of the electrode fingers of the comb-shaped electrode is set to λ0. Between 8 λ.

The gap and the gap between the conductive films are respectively j 71-octopus;
It is characterized by.

According to the device having this configuration, triple reflected signals (triple transient echoes) caused by reflection of surface acoustic waves at the electrodes can be suppressed to -40 dB or less with respect to the main signal.

In addition, the width of the electrode fingers and conductive film can be made three times the width of the electrode fingers in a split-type comb type electrode, and the so-called line breakage during photoetching is extremely reduced, greatly increasing the yield of the device. can be lowered to

[Brief explanation of drawings]

7. FIG. 1 is a sectional view of a main part showing a typical structure of a conventional surface acoustic wave device, and FIG. 2 is a view showing the structure of a transducer that similarly reduces reflection of surface acoustic waves. FIG. 3 shows the structure of an embodiment of a surface acoustic wave device according to the present invention, and FIG. 3A is a cross-sectional view of a main part thereof, and FIG. 3B is a plan view showing the positional relationship of its transducers. , 11... substrate, 12... comb-shaped electrode,
13...Piezoelectric thin film, 14...Counter electrode. -37-

Claims (1)

[Scope of Claims] 1. A comb-shaped electrode is arranged on one side of a piezoelectric thin film, and a conductive film constituting a counter electrode is arranged on the other side of the piezoelectric thin film. The width of the electrode fingers of the comb-shaped electrode and the width of the conductive film of the counter electrode are respectively "λ". and F, and the gap between the electrode fingers of the comb-shaped electrode is ``λ
. A surface acoustic wave device (where λ is the wavelength of the surface acoustic wave that falls at the center frequency of this device). 2. The surface acoustic wave device according to claim 1, wherein the conductive films of the opposing electrodes are electrically connected to each other. 3. In the description of claim 1 or 2, the length of at least one of the electrode fingers of the comb-shaped electrode and the conductive film of the counter electrode is changed depending on the position and weighted. A surface acoustic wave device characterized by: