JPS5848516A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To decrease the deterioration in characteristics due to overetching and with low spurious response and at high yiled, by impriving the arrangement and shape of an interdigital electrode formed on a piezoelectric substance substrate. CONSTITUTION:A comb tooth part A of an interdigital electrode 2 is constituted by arranging electrodes of a prescribed width W1 at an interval (d). Non comb- tooth parts B, C are constituted by alternately arrnging two types of electrodes, W2, W3 of width where W3>W1>W2 at the interval (d). The widths W1-W3 are set to satisfy expressions, where the wavelength of surface acoustic waves propagated on a piezoelectric substance substrate 1 is denoted as lambda0. Thus, since the number of elecrodes for the parts A and B, C is made equal, the disturbance of wave surface of the surface acoustic waves due to overetching at the formation of electrodes can be obtained, allowing to obtain excellent characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device in which interdigital electrodes are formed on a piezoelectric substrate.

When constructing a Lyrutor or the like in a surface acoustic wave device, interdigital electrodes are formed on a piezoelectric substrate. Conventionally, interdigital Iw electrodes are electrodes with a width of λo/40, where the wavelength of the surface acoustic wave is λ0. A so-called solid electrode structure is known, which is constructed using an electrode having a width of λo/8, and a so-called solid electrode structure, which is constructed using an electrode having a width of λo/8.

Solid Kame electrodes have the advantage of having a large electrode width, which reduces the number of disconnection accidents during manufacturing and improves yield. is large, and has the disadvantage of generating a spurious signal at -. In this respect, the split electrode has the advantage that it has the effect of canceling out the zero reflection of the surface wave caused by the difference in the above-mentioned blue-tatami impedance, and can produce low spurious.

The one shown in FIG. 1 is known as an example of an interdigital electrode that effectively takes advantage of the advantages of both solid electrodes and sugerite electrodes. This is disclosed in U.S. Pat. No. 4,023,124, and the interdigital electrode has a meshing part A made up of a solid electrode 11, and a non-meshing part B and C made up of split electrodes 12m and 12b.
It is composed of In addition, split electrode IJl*
, 11b, 12b is a Dan electrode that does not contribute to the excitation of surface acoustic waves. Further, in order to change the excitation intensity in the propagation direction of the surface acoustic wave, the electrode length of one meshing portion A is changed to perform weighting.

According to this configuration, by using a split electrode in combination, it is possible to reduce the serge resistance, and even if one sedge electrode is partially disconnected, electrical continuity between the meshing part A and the non-meshing parts B and C can be maintained. As a result, the yield is good.

□ However, as is clear from the figure, the number of electrodes is different between the meshing part and the non-meshing part. Meshing part ^ and non-meshing part 8. The electrode occupancy rate (total electrode width along the surface acoustic wave propagation direction) differs between C and C. This is because the absolute reduction in the electrode width due to over-etching is almost constant, regardless of the original width of the electrode. Therefore, the 7C% electrode occupancy is due to the large number of non-meshing parts compared to the meshing parts. The part tlf,d decreases more.

This means that the wavefront of the surface acoustic wave emitted from the interdigital electrodes is disturbed, which causes deterioration of frequency characteristics when a filter array is configured.

The present invention has been made in view of the above points, and its purpose is to provide a surface acoustic wave device having interdigital electrodes with high yield, low spurious, and whose characteristics are not susceptible to overetching. It's about doing.

The present invention achieves the above object by improving the arrangement shape of interdigital electrodes formed on a piezoelectric substrate. The non-meshing part is W.
)W.

〉Wl width Vl'l #w, with a spacing d
When λ is the wavelength of the surface acoustic wave propagating on the piezoelectric substrate, W l %
It is characterized in that W @ is set to satisfy the following formula % (1) (2) (3).

According to the present invention, since the number of interdigital electrodes between the meshing part and the non-meshing part is small, the wavefront of the elastic surface wave is not disturbed due to over-etching during electrode formation, and good characteristics can be obtained. It will be done. Furthermore, the same effects as those of the conventional method can be obtained in terms of yield and suppression of stress.

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which 1 beam, 1
NbO, , LiTa0. Piezoelectric substrates such as 2 are fabricated by vapor-depositing a metal thin film of the thickness of an aluminum thin film on the substrate 1.

This is an interdigital electrode formed by etching.

The interdigital electrode 2 is a pair of comb-shaped electrodes that are meshed without contact, with a meshing part A and non-meshing parts B and C.
It consists of , interdigital electrode, in the interlocking part A of 2, W which is an element of each comb-shaped electrode
Electrodes having a constant width of l are arranged at intervals of d.

Here - as an example, W @ , -, iλ· in λObd. On the other hand 1. W snow in non-meshing parts B and C.

When two types of electrodes 22 and 23 with a width of Wl are connected with a distance of d and 1 d - sλ, then
・Set to . These values of W i −W @ X8 4 satisfy the above formulas (1) to (3).

In addition, in this example, in order to provide desired frequency characteristics when realizing a surface acoustic wave router, etc., the length of the electrode 1 of the meshing part A is changed depending on the arrangement, and the excitation intensity of the elastic surface is changed. It is changed in the propagation direction. This is so-called weighting, and this weighting is set, for example, so that it is large at the middle part and small at both ends.

When the interdigital electrode 2 is configured in this way, as is clear from the figure, the number of electrodes 21 forming the meshing part A and the number of electrodes 22 and 23 forming each of the non-meshing parts B and C are λ Therefore, even if over-etching occurs during the formation of the interdigital electrode 2, the electrode occupancy ratio can be kept equal between the meshing part A and the non-meshing parts B and C. That is, the total electrode width experienced by surface acoustic waves propagating on the substrate 1 is 1 dA, B, C.
It is the same in all regions, and there is no problem where the wave surface is disturbed.

In addition, in the non-meshing portions B and C, both reflected waves are canceled out because @W is held. Also, from the electrode 22 to the electrode 2
The reflected wave at the inter-electrode gap in the part reaching 3 and the reflected wave in the inter-electrode gap in the part from electrode 23 to electrode 23 are (
Since there is a phase difference of W1+d)X2 and λ0, both of these reflected waves are also canceled out. Therefore, the occurrence of reflected waves due to the difference in blue-tatami impedance is reduced, and spurious waves can be reduced.

Furthermore, according to this configuration, since the electrode 221d corresponding to the striped electrode is used only in a part of the interdigital electrode 2, the yield can be improved compared to the case where the interdigital electrode is configured only with spurious electrodes. is possible.

In particular, in this embodiment, the electrode 22 of width W1 is used as a dummy electrode that does not directly contribute to the excitation of surface acoustic waves, and is connected to the electrode 21 of the meshing part A related to the excitation of surface acoustic waves. Non-meshing part B, coelectric *z 5ttcl
Since electrodes having a width W, . This is electrodes 21-23
Of these, the electrode 22 is the most likely to cause disconnection, but if the electrode 22
This is because even if a wire breakage occurs in a portion of the wire, the performance of the surface acoustic wave element tl is hardly affected.

In this way, according to the present invention, the yield is good and the f+ is low.
Accordingly, it is possible to provide a surface acoustic wave device that has a low surface acoustic wave pattern and exhibits less deterioration in characteristics due to overetching during manufacturing.

It should be noted that the values of W- to Wj and d given in the above embodiments are just examples, and it goes without saying that the same effect can be obtained as long as the values satisfy equations (1) to (3).

[Brief explanation of the drawing]

FIG. 1 is a plan view of a conventional surface acoustic wave device, and FIG. 2 is a plan view of a 12-plane acoustic wave device according to an embodiment of the present invention. 1 - piezoelectric substrate, 2 - interdigital electrode, A.
・Matching part, B, C-・Non-meshing part, 21~23°Jj"
ll [pole.

Claims (1)

[Scope of Claims] (1) In a surface acoustic wave device in which interdigital electrodes are formed on a piezoelectric substrate, the meshing portion of the interdigital electrodes is constructed by arranging electrodes having a constant width w10' at intervals d. and the non-meshing part is W's >vvt >W
It is constructed by alternately arranging two types of electrodes with widths W, , W, l, and hl, and further, W1 to W, are the wavelengths of the surface acoustic waves propagating on the piezoelectric substrate, λ. 1. A surface acoustic wave device characterized in that the surface acoustic wave device is set to satisfy the following formula % (1) (2) (3) when 0. (2) A claim characterized in that an electrode having a width of W1 is used as the electrode of the non-meshing part connected to the electrode of the meshing part. (3) The length of 11 poles of the meshing part of the interdigital electrode is changed in the arrangement direction. The surface acoustic wave device fit according to claim 1, characterized in that ζ.