Surface acoustic wave device

Abstract

A SAW device employing a quartz substrate having device size smaller than that of conventional structure and exhibiting a high Q and excellent frequency-temperature characteristics. An IDT (2) consisting of a plurality of interdigital electrode fingers is mounted on a piezoelectric substrate (1) and grating reflectors (3a, 3b) are arranged on the both sides of the IDT (2). The piezoelectric substrate (1) is a flat quartz plate where the cut angle theta of a rotary Y-cut quartz substrate is set in the range of -64.0 1 / 2 < theta < -49.3 1 / 2 in the counter clockwise direction from the crystal Z-axis and the propagating direction of surface acoustic wave is set at 90 DEG +-5 DEG with respect to the crystal X-axis, and the exciting acoustic wave is SH wave. The IDT (2) and the reflectors (3a, 3b) are composed of Al or an alloy principally comprising Al and the electrode film thickness standardized by wavelength H / lambda is set in the range of 0.04 < H / lambda < 0.12, where lambda is the wavelength of surface acoustic wave.

Description

technical field [0001] The present invention relates to a surface acoustic wave device using a quartz substrate in which the device size is reduced, the Q value is increased, and the frequency-temperature characteristics are improved. Background technique [0002] In recent years, surface acoustic wave (hereinafter referred to as SAW) devices have been widely used as components of mobile communication terminals, in-vehicle equipment, and the like, and are highly required to be miniaturized, have high Q values, and have excellent frequency stability. [0003] As a SAW device that realizes these needs, there is a SAW device using an ST-cut quartz substrate. The ST-cut quartz substrate is a cut name of a quartz plate having a face (XZ' plane) obtained by rotating the XZ plane at an angle of 42.75° from the Z crystal axis with the X crystal axis as the rotation axis, and this ST cut quartz The substrate uses a SAW (hereinafter referred to as ST-cut quartz SAW) that is a (P+SV) ...

AI Technical Summary

Problems solved by technology

However, when the resonance frequency is 200MHz, the Q value reaches saturation close to 4% λ, but the Q value obtained at this time becomes only about 20000, compared with ST-cut quartz SAW resonators, which can only be obtained with ST-cut quartz SAW The Q value in the resonator is approximately equal to the Q value

For this reason, it is considered that since SAW cannot be sufficiently concentrated on the surface of the piezoelectric substrate when the film thickness is in the range of 2% λ or more to 4% λ or less, reflection cannot be effectively utilized

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