JPS59221022A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To reduce the level of an undesired spurious and to obtain the desired frequency characteristics by shifting the thinning cycles of electrode fingers between the input and output comb-shaped electrodes and then shifting the cycles of the electrode fingers which are distributed with the cyclic intervals of said electrodes. CONSTITUTION:When an electrode is formed on a crystal substrate with aluminum, the central frequency is set at 600MHz together with the number of pairs of input and output comb-shaped electrodes set at 300 respectively. Then two pairs are thinned and a pair is left as it is with the input comb-shaped electrode. While five pairs are thinned and a pair is left with the output comb-shaped electrode. As a result, the same average sound speed is obtained among electrode parts. In order to obtain the coincident central frequency, the intervals of electrode fingers are set at lin and lout for input and output comb-shaped electrodes 2 and 3 respectively. In this case, lin=1.306mum and lout=1.308mum are satisfied to obtain 600X10<6>=3135X10<5>/4lin=3140X10<6>/4lout. Thus the same frequency is obtained between electrodes 2 and 3, and therefore the desired frequency characteristics can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to surface acoustic wave devices such as surface acoustic wave filters and surface acoustic wave oscillators.

Conventional structure and its problems Conventionally, in a piezoelectric transducer with a comb-shaped electrode structure formed on an elastic substrate, electrode fingers of input comb-shaped electrodes and output comb-shaped electrodes are A method of periodically thinning out was used. As a result, if thinning is performed, for example, leaving one pair for every n pairs of electrode fingers, as shown in FIG.
・1/n・λ, (n+1)n・λI (n+2)/
Surface waves are excited even at wavelengths of n·λ, . Therefore, the input comb-shaped electrode.

The frequency of unnecessary spurious signals excited by the input comb-shaped electrode and the output comb-shaped electrode was shifted by shifting the thinning period of the electrode fingers of the output comb-shaped electrode, thereby lowering the spurious level. However, if the rate of thinning of the electrode fingers of the input comb-shaped electrode and the output comb-shaped electrode differs, the 1-tal length of the electrode width per unit length of the elastic substrate differs. Therefore, the input comb-shaped electrode,
The average sound speed of each electrode part of the output comb-shaped electrode is different,
The frequency expressed by f=V/λ (f: frequency, v:, speed of sound, λ: wavelength) differs for each electrode as shown in Figure 2, and the desired characteristics could not be obtained due to frequency characteristic insertion loss, etc. . In addition, the broken line A in FIG.

B shows input electrode characteristics and output electrode characteristics, respectively, and solid line C shows overall characteristics.

Purpose of the Invention The present invention aims to eliminate such conventional drawbacks, and aims to obtain desired characteristics by changing the electrode finger spacing of the input comb-shaped electrode and the output comb-shaped electrode to match the center frequencies. be.

Structure of the Invention In order to achieve this object, the present invention shifts the thinning period of the input comb-shaped electrode and the output comb-shaped electrode, and further shifts the period of the electrode fingers arranged at periodic intervals of the input comb-shaped electrode and the output comb-shaped electrode, respectively. In this configuration, the electrodes are shifted so that the center frequencies of the electrodes coincide with each other.

With this configuration, it is possible to reduce the level of unnecessary spurious and obtain desired characteristics such as frequency characteristics and insertion loss.

DESCRIPTION OF EMBODIMENTS An embodiment of a surface acoustic wave device in which electrodes are formed of aluminum on a quartz substrate will be described.

We experimentally determined the relationship between electrode film thickness and sound speed when changing the thinning ratio. The results are shown in FIG.

The center frequency is 600 MHz, the number of pairs of input and output comb-shaped electrodes is 300, and the input comb-shaped electrodes are thinned out by 2 pairs, leaving 1 pair, and the output comb-shaped electrodes are thinned out by 5 pairs, leaving 1 pair. The average sound speed was kept the same. If the aluminum electrode thickness is 1600 mm, the center frequency deviation of each electrode will be about 1 MHz, and the -3 dB bandwidth will be about 10% narrower.
Insertion loss increases by approximately 2 dB.

Therefore, as shown in FIG. 4, when the distance between the electrode fingers of the input comb-shaped electrode 2 and the output comb-shaped electrode 3 provided on the elastic substrate 1 is 'in' out, 600×10 −3
136X10/46in: 3140X106/4'
'1n=1.306μm, 1Ou so that o u t
If t=1.3o8 μm, the frequencies of the input comb-shaped electrode and the output comb-shaped electrode match, and desired characteristics can be obtained.

Effects of the Invention As described above, according to the present invention, it is possible to lower the level of unnecessary spurious components and obtain desired frequency characteristics without increasing insertion loss. In particular, when narrowband frequency characteristics are required, such as when configuring an oscillator by combining a surface acoustic wave delay element with a feedback amplifier circuit, it is necessary to increase the gain of the amplifier circuit when insertion loss increases. Furthermore, when it is necessary to reduce the unnecessary spurious level in order to obtain stable oscillation, the present invention can provide a significant effect.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams illustrating the characteristics of conventional surface acoustic wave devices, and Figure 3 is the relationship between electrode film thickness and average sound speed when changing the thinning ratio of electrode fingers of the surface acoustic wave device. FIG. 4 is a schematic diagram showing a surface acoustic wave device according to an embodiment of the present invention. 1...Elastic substrate, 2...Input comb-shaped electrode,
3...Output comb-shaped electrode. Range 1 Figure 1 Rangichi Figure 2 - Zhou Langku Figure 3 θ, / 0.2 0.3 Chamber diameter ■Ki (K
H) Figure 4

Claims (2)

[Claims] (1) The period of thinning out the electrode fingers of the input comb-shaped electrode and the output comb-shaped electrode is shifted, and the period of the electrode fingers arranged at periodic intervals between the input comb-shaped electrode and the output comb-shaped electrode is also shifted. Surface acoustic wave device/ (2) When the thinning of electrode fingers is set to b for every d pair of electrode fingers for the input comb-shaped electrode and d for every C pair of electrode fingers for the output comb-shaped electrode, the average sound velocity at the electrode part is vin I.
vout + the distance between each electrode finger 'in+'ou
When t, Z'in/'in-υ. ut/1ou
2. The surface acoustic wave device according to claim 1, wherein the comb-shaped electrodes are arranged so as to be t.