Variable property crystal resonators by direct bonding techniques

Novel single-crystal bulk acoustic wave (BAW) resonators have been developed. These resonators realize desired electrical properties by directly bonding piezoelectric single crystals such as LiNbO₃ and LiTaO₃. The direct bonding technique fabricates composite piezoelectric substrates with new electrical properties depend on the combination of bonded wafers. For the first trial, polarization-inverted substrates have been fabricated by directly bonding two wafers of Z-cut LiNbO₃ single crystals having opposite polarization-direction. Second overtone resonators using these substrates provide excellent performance. Typically, the resonator has a high Q-value over 5,000, a figure of merit of 138, a capacitance ratio of 40, a resonant resistance of 30 Ω and a frequency deviation of -50 ppm/°C