Katsu Takeda

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 LiNbO/sub 3/ and LiTaO/sub 3/. 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 LiNbO/sub 3/ 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 /spl Omega/ and a frequency deviation of -50 ppm//spl deg/C.

Even-order thickness-shear mode resonators using X-cut LiTaO/sub 3/ plates realized by a direct bonding technique

Even-order thickness-shear mode resonators with good temperature characteristics have been achieved by applying direct-bonding techniques to X-cut LiTaO/sub 3/ single crystals. The variations in the resonance frequency of their main fast thickness shear mode was less than 500 ppm over the temperature range of -10 to 60/spl deg/C. Moreover, the results of studies on strip type chip resonators using direct-bonded x-cut LiTaO/sub 3/ wafers suggest that fabrication of small sized resonators with no spurious response is feasible. Their typical Q-value was between 3000 and 5000, and the resonant resistance was 10-20 /spl Omega/ at 13 MHz. These values an ideal for a range of applications. We confirmed that the direct bonding technique was particularly suitable for realizing high frequency resonators because the thickness of the resonator could be double that of a conventional fundamental resonator.