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

By composing interdigital transducers (IDTs) and reflectors consisting of f ilms made of a heavy metal such as Au. Ta or W on an ST cut 90 degreesX pro pagation (direction perpendicular to X-axis) quartz substrate, the authors realized a new type of shear horizontal (SH) wave. This wave has an excelle nt temperature characteristic. a large electromechanical coupling factor (k ), and a large reflection coefficient at reflector electrodes. The square o f this electromechanical coupling factor (k(2) = 0.28 similar to 0.34%) and the reflection coefficient at reflector electrodes are 2.2 similar to 2.6 times and 30 similar to 35 times, respectively, as large as those of a Rayl eigh wave on an ST cut X propagation quartz substrate. The authors applied this technology to filters for the first intermediate frequency (first IF) stage of a global system for mobile communications (GSM) in the nominal cen ter frequency from 200 to 400 MHz. As a result, we succeeded in developing the first IF filter having a low insertion loss, an excellent temperature c haracteristic (frequency shift: 1 ppm/degreesC) and a small package size (3 x 3 mm(2)), which is as small as a radio frequency (RF) surface acoustic w ave (SAW) filter. for the first time.