High Frequency Hetero Acoustic Layer SAW Resonator Using Quartz Thin Plate on Sapphire

High-Q quartz (Qz) resonators operating in the GHz range are required for high-frequency timing clock signals to reduce phase noise. The hetero acoustic layer (HAL) structure, which excites higher-order modes, is a good way to obtain high frequencies. In this study, HAL surface acoustic wave (SAW) Qz resonator using a Qz thin plate on SiO2/ sapphire were investigated by theoretically and experimentally. The resonators were fabricated using ST-X Qz, SiO2 and R-cut 73ºX sapphire. The 1st higher-order mode with an impedance (Z) ratio of 17 dB, Q factor of 2,830, and phase velocity of 5,770 m/s was excited. The 2nd higher-order mode with a Z ratio of 9.4 dB, Q factor 4,260 and phase velocity of 5,630 m/s was also excited. The temperature coefficient of frequency (TCF) of the 1st and 2nd higher-order modes were -31.8 ppm/°C and 6.7 ppm/°C, respectively. The performance could be improved by optimizing the Qz thickness, Qz cut angle, electrode design, and fabrication process.