Very small-sized resonator IF filter using shear horizontal wave on quartz substrate

Abstract

A shear horizontal (SH) wave is excited by composing interdigital transducers (IDTs) and reflectors consisting of films made of heavy metal on ST cut 90/spl deg/-X propagation quartz substrate (propagation direction is perpendicular to X-axis). This wave has a large electromechanical coupling factor, a large reflection coefficient and an excellent temperature characteristic. The square of the electromechanical coupling factor is 2.0-2.6 times, the reflection coefficient at reflector's grating electrodes is 30 times as large as that of Rayleigh wave on an ST cut X propagation quartz substrate, and the temperature coefficient of frequency is equal to that. The authors applied this SH wave to filters for the first intermediate frequency (first IF) stage of a global system for mobile communications (GSM). As a result, we succeeded in developing the low loss and very small-sized filter (3/spl times/3/spl times/1.03 mm: typical dimensions) having a high rejection out of band for the first time.