JPS61220515A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To eliminate the need for a duplicated exposure process and to obtain a desired reflecting characteristic by changing periodically a pitch width between a line and a space of a grating reflector. CONSTITUTION:A space 13 having a different pitch is inserted between a string 11 and a string 12 having the same pitch of the line 14 and the space 15 of the grating reflector. In taking the combination of the lines and spaces as one section, the grating reflector consists of lots of the sections. In the section, the strings 11 and 12 are composed in terms of vectors by the space 13 at the center so as to move the center frequency of the reflecting characteristic. Thus, as the lines and spaces of the grating reflectors 22 and 23, the same width of the lines and spaces of an interdigital electrode 24 and the duplicated exposure process is not required.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a surface acoustic wave device having interdigital electrodes and a grating reflector on a piezoelectric substrate, and the present invention relates to a surface acoustic wave device having interdigitated electrodes and a grating reflector on a piezoelectric substrate. The present invention relates to a surface acoustic wave device in which a desired reflection characteristic can be obtained by changing the characteristics of the surface acoustic wave.

[Conventional technology]

A surface acoustic wave resonator has been put into practical use as a surface acoustic wave device using a conventional grating reflector. As a technique for improving the performance of this surface acoustic wave resonator, a configuration in which the entire electrode periodic pitch of the grating reflector is slightly larger than the electrode periodic pitch of the interdigital electrodes is used, for example, in TUno.
The paper “Optimization of quar
tz SAW resorator 5truatur
e with groove gratings”,
IBEB+i'rausvol, 5U-29,46,
p29 (J (1982)).

[Problem that the invention seeks to solve]

In the production of photomasks for surface acoustic wave resonators with conventional configurations, it is necessary to create subtle dimensional differences between the grating reflector and the interdigital electrodes, which requires extremely high precision and requires manufacturing time. It has the disadvantage of being difficult. Specifically, when producing high-precision photomass flakes, electron beam exposure is usually used, but this process requires a pattern tater, so the pattern dimensions are quantized, resulting in rounding errors. In order to avoid this, the patterns that normally require slight dimensional differences are double-exposed with different reduction ratios for each pattern, thereby achieving very large dimensional differences. However, in this process, due to double exposure, errors occur in the position of each pattern. Additionally, since double exposure is required, the time required increases, which inevitably increases the price of the photomask.

[Problem '(+: Means for solving the problem)] The object of the present invention is to provide a surface acoustic wave device in which all of the above-mentioned drawbacks are eliminated.

In the surface acoustic wave device of the present invention, in an elastic surface acoustic wave device having interdigital electrodes and a grating reflector on a piezoelectric substrate, each line or space separated by a predetermined number of fc has a width equal to that of an adjacent line or space. Lines with different widths are placed between spaces.

〔Example〕

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

FIG. 1 shows an embodiment of the present invention T29, showing a part of a grating reflector. In the non-embodiment, spaces 13 having a different pitch are interposed between the periodic rows 11 and 12 of the same pitch of lines 14 and spaces 15. Assuming that the grating shown in FIG. 1 is one section, the grating reflector is constructed by arranging a large number of this one section. In this one section, the periodic sequences 11 and 12 are vector-synthesized by the central space 13, and it is possible to reduce the center frequency of the reflection characteristics.

FIG. 2 shows an elastic optical 7i7I wave device of the present invention. The lines and spaces of the grating reflectors 22 and 23 on the piezoelectric substrate 21 are made different from that of the apparent periodic pitch full interdigital electrode 24 by also using a width of the same dimensions as the lines and spaces of the interdigital electrode 24. ing.

Now, the substrate material is ST-cut crystal, the grating reflector is made of an all-aluminum film, and the thickness of this aluminum film is λ-
1,6 (%), and the center frequency of the stop band fof
FIGS. 3 and 4 show the reflection characteristics at the period LVC of each electrode of the grating reflector when there are two types near 100 (MIloo) (and 1 (OT″lz)).

FIG. 3 is a characteristic diagram illustrating the case where conventional breeching electrodes with equal intervals are used and the case where the grating electrode of the present invention is used. Conventional period La k 20
．． 1 (μm), period Lb i20 in the case of the present invention
．． 0 (μm) and 20.5 (μm), and 100 pads were used for the grating electrode.As is clear from FIG. 1, the characteristics of the two completely matched.

FIG. 4 shows the characteristics when the conditions of FIG. 3 and the number of grating electrodes are the same except for the number of grating electrodes. Here, the number of electrodes was 500. In this case as well, the characteristics of the conventional case and the case of the present invention completely matched.

〔Effect of the invention〕

As described above, in the present invention, the center frequency of the reflection characteristic can be shifted, and in particular, the center frequency of the reflection characteristic can be shifted all the way using the same pitch as the periodic pitch of the interdigital electrodes. It does not require a heavy exposure process, can be manufactured with high precision, in a short time, and at low cost, and has the advantage of providing high Q characteristics.

[Brief explanation of drawings]

FIG. 1 is a plan view showing one section of the grating reflector of the present invention, FIG. 2 is a plan view showing an embodiment of the present invention, and FIG.
FIG. 4 and FIG. 4 are diagrams showing the reflection characteristics of the device of the present invention. 11.12... Grating, 13... Space, 21... Piezoelectric substrate, 22.23... Grating reflector, 24 - Cross-finger electrode.

Claims (1)

[Claims] In a surface acoustic wave device having interdigitated electrodes and a grating reflector on a piezoelectric substrate, a line or space having a width different from the width of an adjacent line or space is arranged for each line or space separated by a predetermined number. A surface acoustic wave device comprising the grating reflector.