JPH04150108A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To realize a low loss surface acoustic wave element by always making the propagation speed of surface acoustic wave of the electrode digit of a couple of interdigital electrodes arranged opposite to each other equal to the propagation speed of a surface acoustic wave of the inner side signal extraction electrode inserted between the electrode digits, a metallic conductor electrode and the propagation speed of the surface acoustic wave in a free space inserted among the electrodes. CONSTITUTION:The propagation speed of a surface acoustic wave of electrode digits 6, 8 is always made equal to the propagation speed of a surface acoustic wave of inner side signal extraction electrodes 5, 7 inserted between the electrode digits, a metallic conductor electrode 4 and the propagation speed of a surface acoustic wave in a free space inserted among the electrodes. Then the surface acoustic wave radiating from the point A of the interdigital electrode is refracted at the inner side signal extraction electrodes 5, 7 and the metallic film electrode 4 and propagated perpendicularly to the electrode digit 8 in the electrode digit of the tilted interdigital electrode 3 opposite thereto, and reached to a point B. Thus, the increase in the loss of the propagate surface acoustic wave is not entirely caused.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a surface acoustic wave device, and in particular to a surface acoustic wave device used in a receiving section of a radar radio wave measuring device, which The present invention relates to a surface acoustic wave element formed by tilting the truss electrodes.

[Conventional technology]

There are various methods for measuring frequencies in real time in radar radio wave measuring devices and the like. The microscan method is widely used as a system that combines surface acoustic wave dispersion type delay lines with different signs of delay slopes and can display frequency information in real time on the time axis.

The surface acoustic wave dispersion type delay line used in this microscan method is required to have a wide band and relatively low delay dispersion in terms of frequency resolution. for example,
Assuming a frequency band of 500 MHz and a delay dispersion of 1 μs, the frequency resolution will be approximately I MHz, and a microscan equivalent to a 500 channel filter bank will be obtained.

It is difficult to realize surface acoustic waves with such low delay and dispersion using a normal counter-electrode type. In other words, in order to achieve a wide frequency band, it is necessary to raise the center frequency and lower the fractional band, or in this case, if it is achieved using an element with low delay dispersion, the number of electrode finger pairs will be reduced, which will cause an increase in frequency ripple.

On the other hand, if an electrode structure with large delay dispersion is used to reduce ripples in a low range, the length of the interdigital electrode in the surface acoustic wave propagation direction becomes long, and a low delay dispersion of about 1 μs cannot be realized due to the structure. Therefore, a tilted electrode shown in FIG. 2 has been proposed.

In this inclined electrode, the line connecting the centers of the electrode fingers is inclined with respect to the propagation direction of the surface acoustic wave, and the inclined interdigital electrodes 11 and 13 having different degrees of inclination face each other. It is possible to obtain a large delay dispersion with respect to the virtual axis 01 01' provided in a direction perpendicular to the propagation direction of the elastic surface difference of .13, and to make the delay dispersion of the inclined interdigital electrodes 11 and 13 small. Note that 12.14 is an electrode finger, 15.16 is an inner signal extraction electrode, and 17 is a surface acoustic wave.

FIG. 3 is a delay dispersion frequency characteristic diagram of a conventional surface acoustic wave element, where the horizontal axis is the frequency and the vertical axis is the delay time. 21 is the inclined interdigital electrode 11 in FIG. 2 and the virtual axis 0□-〇1 22 is the delay dispersion characteristic between the inclined interdigital interdigital electrode 13 and the virtual axis 0101' in FIG. 2, and 23 is the delay dispersion characteristic of the difference between the delay dispersion characteristics 21 and 22. Therefore, in such a structure, even if the slope is made steeper to increase the value of the delay dispersion characteristic 21.22, if the difference in slope is made smaller,
It is possible to realize an element with less frequency ripple and low dispersion delay as described above.

[Problem to be solved by the invention]

The above-mentioned conventionally proposed inclined interdigital electrode has a second
As shown in the figure, the surface acoustic wave velocity differs between the inclined interdigital interdigital electrode made of the grid electrode, the inner signal extraction electrode made of the −-like electrode, and the free surface where there is no electrode. The surface acoustic wave 17 generated at point A of the slanted interdigital electrode is refracted at B of the inner signal extraction electrode, and further refracted at C of the inner signal extraction electrode of the other corresponding slanted interdigital electrode 13. ] Reach 4. At this time, since the surface acoustic waves are not orthogonal to the electrode fingers 14, there is a drawback that the loss varies depending on the generation point of the surface acoustic waves and therefore the frequency.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a surface acoustic wave element in which an increase in loss due to refraction of surface acoustic waves in inclined interdigital electrodes is significantly suppressed.

[Means to solve the problem]

The surface acoustic wave element of the present invention has a interdigital interdigital electrode consisting of a plurality of electrode fingers and a signal extraction electrode. In a surface acoustic wave element in which a pair of opposing slanted interdigital electrodes are provided on a piezoelectric substrate, the lines of which are formed to be inclined with respect to the propagation direction of surface acoustic waves. A band-shaped metal film electrode is formed on the piezoelectric substrate along the direction in which the pair of inclined interdigital electrodes are formed, and a pair of inner extraction electrodes formed inside the pair of inclined interdigital electrodes are formed on the piezoelectric substrate. The ratio of the length along the surface acoustic wave propagation direction between the pair of boundary lines between the adjacent electrode fingers and the length of the pair of inner signal extraction electrodes and the metal film electrode along the surface acoustic wave propagation direction is It has a configuration in which it remains constant.

Further, the surface acoustic wave element of the present invention has a chirve-shaped configuration in which the electrode finger spacing of the pair of inclined interdigital electrodes is linearly expanded along the propagation direction of the surface acoustic wave.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of a surface acoustic wave element according to the present invention. Inclined interdigital interdigital electrodes 2 and 3 are formed on a piezoelectric substrate 1, and the electrode finger spacing gradually changes along the propagation direction of surface acoustic waves. In FIG. 1, the spacing between the electrode fingers 6.8 of these inclined interdigital electrodes is in the form of a chirve that gradually increases linearly from left to right. Further, a band-shaped metal film electrode 4 is formed between the inner signal extraction electrodes 5 and 7 of each inclined interdigital electrode. As shown in FIG. 1, the width of the metal film electrode 4 is determined by a straight line PQ in the surface acoustic wave propagation direction, that is, in a direction perpendicular to each electrode finger (P, Q are on the boundary between each inner signal extraction electrode and the electrode finger). The structure is such that the point where the curve (2) crosses the inner lead-out electrodes 5, 7 satisfies the relational expressions S and (2).

Here, Vf is the surface acoustic wave propagation velocity on the free surface of the piezoelectric substrate 1, Vm is the surface acoustic wave velocity on the metal film electrode 4 coated with a metal film on the same piezoelectric substrate 1, and Vi is the surface acoustic wave propagation velocity on the free surface of the piezoelectric substrate 1. In the normal case where the electrode-directed elastic surface propagation velocity on the flexible substrate 1 and the electrode finger width and the interval width are equal, approximately the following (
2) It is determined by the formula.

In the surface acoustic wave element having such a configuration, the electrode fingers have the following characteristics: the propagation velocity of the surface acoustic waves of the electrode fingers 6.8, the compression side signal extraction electrode 57 sandwiched between these electrode fingers, the metal film electrode 4, and each of these electrodes. The average propagation velocity of the surface acoustic waves propagating in the free space sandwiched between them is always equal, and the surface acoustic waves radiated from the point A of the inclined interdigital electrode are Although the wave is bent at point 4, it propagates perpendicularly to the electrode finger 8 within the electrode finger of the opposing inclined interdigital electrode 3 and reaches point B, so that there is no increase in the loss of the propagating surface acoustic wave. I can do it.

〔Effect of the invention〕

As explained above, according to the present invention, the propagation speed of the surface acoustic wave of the electrode fingers of a pair of inclined interdigital electrodes arranged opposite to each other, the inner signal extraction electrode sandwiched between these electrode fingers, and the inner signal Since the metal film electrodes formed between the extraction electrodes and these electrodes can always be made equal, the surface acoustic wave emitted from one inclined interdigital electrode is not transmitted within the electrode fingers of the opposing inclined interdigital electrode. This has the effect of completely suppressing the increase in loss of surface acoustic waves caused by propagating perpendicularly to the electrode fingers and being refracted by the electrodes, thereby providing an extremely low-loss surface acoustic wave element.

[Brief explanation of drawings]

FIG. 1 is a plan view of an embodiment of the surface acoustic wave element of the present invention;
FIG. 2 is a plan view of a conventional surface acoustic wave device, and FIG. 3 is a delay dispersion frequency characteristic diagram of the conventional surface acoustic wave device. DESCRIPTION OF SYMBOLS 1... Piezoelectric substrate, 2.3... Inclined interdigital electrode, 4-... Metal film electrode, 5, 7... Inner signal extraction electrode, 6, 8... Electrode finger, 11. 13 sloped blind electrode, 12.14... electrode finger, 15.16... inner signal extraction electrode, 17.18... elastic evaluation plane wave, 21...
Delay dispersion characteristics between the inclined interdigital electrode 11 and the virtual axis 0+0+', 22...The inclined interdigital electrode 13 and the virtual axis 0. -o, delay dispersion characteristics with ', 23...delay dispersion of the difference between delay dispersion characteristics 21 and 22.

Claims (2)

[Claims] 1. The interdigital interdigital electrode consisting of a plurality of electrode fingers and a signal extraction electrode is arranged such that the interdigital interdigital spacing is gradually changed along the propagation direction of the surface acoustic wave, and the center line connecting the centers of each electrode finger is aligned in the propagation direction of the surface acoustic wave. In a surface acoustic wave device in which a pair of opposing inclined interdigital transducer electrodes are provided on a piezoelectric substrate, the pair of inclined interdigital electrodes are disposed on the piezoelectric substrate between the pair of inclined interdigital electrodes. A band-shaped metal film electrode is formed along the direction in which the inclined interdigital electrodes are formed, and a pair of boundaries between a pair of inner extraction electrodes formed inside the pair of inclined interdigital electrodes and the adjacent electrode fingers are formed. The ratio between the length of the line along the surface acoustic wave propagation direction and the length of the pair of inner signal extraction electrodes and the metal film electrode along the surface acoustic wave propagation direction is made constant. surface acoustic wave device. 2. 2. The surface acoustic wave device according to claim 1, wherein the electrode finger spacing of the pair of inclined interdigital electrodes is chirped so as to expand linearly along the propagation direction of the surface acoustic wave.