Near-Zero TCF of HAL SAW Resonator with LiTaO 3 -on-Quartz Structure

This paper reports the recent progress of a new type of hetero acoustic layer (HAL) surface acoustic wave (SAW) resonators using a $0.44 \text{to} 1.12 \mu \mathrm{m}$ thick rotated-Y LiTa03 (LT) plate and a near ST-cut quartz substrate. This material combination was selected, because quartz has a higher velocity of leaky SAW than LT and a positive temperature coefficient of frequency (TCF). An impedance ratio of 82 dB and a Bode Q of 3, 000 were obtained, and TCFs at series and parallel resonance were measured to be +2 and −10 ppm/PC, respectively. Compared with the characteristics of a standard 42°YX LT SAW resonator fabricated in the same facility, the impedance ratio is higher by 31 dB, the bode Q is 6.3 times higher, and the TCFs at series and parallel resonance are as small as 1/25 and 1/6, respectively.