JPS61192112A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To obtain the title device with a wide specific band, flat band, small size and low insertion loss by selecting the distance between an exciting crossdigital electrode and a reception crossdigital electrode and between a grating reflector and both the said electrodes respectively to a specific value. CONSTITUTION:The exciting crossdigital electrode 43 and the reception crossdigital electrode 42 are arranged with a distance l1[=(2n+1)L/4<l1<(n+1)L/2; n+0,1,2...] and the distance between the grating reflectors 44, 45 and both the said electrodes is arranged with an internal l2 and l3[=(4m+1)L/8<l2,l3<(4m+7)L/8; m=0,1,2...], where L is the period of electrodes 42, 43. Thus, plural resonance modes exist and the broad pass band is attained. Since the energy is confined between the reflectors 44 and 45, low loss is attained. Further, miniaturization is attained in terms of structure.

Description

[Detailed description of the invention] The present invention relates to a surface acoustic wave device.

Some conventional surface acoustic wave devices include grating reflectors and surface acoustic wave transducers for excitation and reception, and are mainly used as resonator oscillators. 1st
The figure shows an example of the configuration of a conventional surface acoustic wave device. In this example, the interdigital electrodes 12 and 1 are arranged so that a maximum standing wave is generated between the two grating reflectors 14 and 15, and the standing waves are most efficiently received and excited.
3 gold is placed. In this case, a transmission characteristic 1 cfl exhibits a sharp resonance characteristic, and is usually used as a two-terminal pair resonator. The arrangement conditions of the interdigital electrodes and the grating reflector are as follows: where the electrode period of the interdigital electrodes is tL, the distance ta between the interdigital receiving electrode 12 and the excitation interdigital electrode 13, and the distance ta between the receiving interdigital electrode 12 and the excitation interdigital electrode 13; Cross-finger electrode 12 and gray n', m, m' = 0.1.2-)
The selected tale (WI (Haydl, etal, 197
6 Ultrason, 8ymp, Proc, *0.1
．． 2...) (Oyamada, Yoshikawa; Journal of the Acoustical Society of Japan, 33.NO, IO, P2S5 (1
977)).

The transmission characteristics of the conventional surface acoustic wave device shown in Fig. 1 are resonance characteristics with sharper peaks than those shown in Figs.
There is a drawback that the fractional band of B is 0.5% or less. Furthermore, since only a single-peak passband can be realized, the range of application as a filter is extremely limited.

Furthermore, there is an example in which a filter is constructed by connecting a plurality of resonators with transmission characteristics as shown in Fig. 2 (L, A, Co1
dren etal; Proc, IEEE, vo
1, 67°, p. 147, 1979), the filter has a complicated shape, making it difficult to downsize and reduce the cost.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a compact elastic surface arytenoid rIL with a wider specific band and a flat band, and a low insertion loss, compared to the conventional one.

In the surface acoustic wave device of the present invention, a plurality of grating reflectors and at least one excitation interdigital electrode and reception interdigital electrode disposed between the grating reflectors are formed on a piezoelectric substrate. In the surface acoustic wave device in which the electrode period of the interdigital electrode is L, the excitation interdigital electrode is arranged in front of the grating reflector, the excitation interdigital electrode and the reception interdigital electrode. distance!
24m+1 and t @ (=-L (l z, j B <4!
! -! -! -L; my0, 1.2...).

Next, the present invention will be explained in detail with reference to the drawings. FIG. 4 is a plan view showing one embodiment of the present invention. In this embodiment, interdigital electrodes 42 and 43 for reception and excitation are used.
With an electrode period IL of , the interdigital electrodes 42 and 43
The distance between L1'to, 42L.

The distance t2 between the grating reflector 44 and the interdigital electrode 42 and the distance 1st between the grating reflector 45 and the interdigital electrode 43 are set to be 0.7 OL, respectively.

When the distance condition is set in this way, a plurality of resonance modes exist, and it becomes possible to widen the passband.

Figure 5 shows the transmission characteristics of this embodiment. Compared to the conventional characteristics, the in-band characteristics change from a single peak to a flat characteristic.
The 3dB bandwidth was more than doubled. Furthermore, energy is confined between the grating reflectors 44 and 45, resulting in low loss. Furthermore, structurally, there is no significant difference in size or shape compared to conventional surface acoustic wave devices, and miniaturization is possible. As described above, the present invention has the advantage of achieving relatively narrow and flat characteristics in the band, as well as miniaturization and low loss.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an example of a conventional surface acoustic wave device, FIGS. 2 and 3 are diagrams showing the transmission characteristics of a conventional surface acoustic wave device, and FIG. 4 is a plan view showing an example of a conventional surface acoustic wave device. Floor plan shown and! ! FIG. 5 is a diagram showing the transmission characteristics of the surface acoustic wave device according to the present invention. In the figure, 11...piezoelectric substrate, 12.13...
. . . Cross-finger electrode, 14. 15 . . . Grating reflector, 41 . . . Piezoelectric substrate, 42.
43...Cross-finger electrode, 44.45...
・Grating reflector. V-1 Besshi 2'TiJ cold 4 pieces

Claims (1)

[Claims] A plurality of grating reflectors and at least one excitation interdigital electrode and reception interdigital electrode disposed between the grating reflectors are formed on a piezoelectric substrate, and the electrode period of the interdigital electrode is In the surface acoustic wave device where L is L, the distance between the excitation interdigital electrode and the reception interdigital electrode is l_1(=(2n+1)/4L<l
_1<(n+1)/2L: n=0, 1, 2...
), and the grating reflector, the excitation interdigital electrode, and the reception interdigital electrode are arranged at distances l_2 and l_3 (=(4m+1)), respectively.
/8L<l_2, l_3<(4m+7)/8L:m=0
, 1, 2...).