LT/Quartz HAL SAW Resonator with Large LT Thickness over Severalfold Wavelength

A Hetero Acoustic Layer (HAL) surface acoustic wave (SAW) device is a new class of SAW device using a thin LT or LN layer rigidly mounted on a substrate. In the past reports, the LT layer was as thin as 0.13-0.221 (<; 0.7 μm for 1 GHz devices) to obtain a high impedance ratio (e.g. >80 dB), but this range of thickness is not easy to control in mass-production. In this study, we investigated the design space at larger LT thickness by FEM simulation. In the design space near the conventional one, in-band ripples and/or out-of-band spurious responses are generated. If a 1.4 times thicker Al or Cu electrode is combined with a LT layer thicker than a specific value (1λ for Al and 4λ for Cu), however, the ripples and spurious responses almost disappear and the deterioration of impedance ratio is limited. On the other hand, by using further thicker electrodes, a higher mode of SAW is excited preferentially at 2-2.6 times higher frequency than the fundamental mode.