4.5 GHz Lamb wave device composed of LiNbO3 thin film

A high frequency device of 3 GHz or more is required, for instance, for future 4-th generation mobile phone system in Japan. Using a substrate with a high velocity is one method to realize a high frequency elastic device. A lamb wave has a high velocity when the substrate thickness normalized by a wavelength (lambda) of an elastic wave is thin. It is difficult to make a very thin crystal plate in order to realize a high frequency device. The authors have attempted to fabricate a lamb wave device using a c-axis orientated thin LiNbO₃ film deposited by a chemical vapor deposition system (CVD). A lamb wave resonator composed of a interdigital transducer (IDT)/thin LiNbO₃ film/air gap/base substrate has shown a high frequency of 4.5 GHz, which corresponds a high velocity of 14,000 m/s, and an excellent characteristics such as an impedance ratio of 52 dB and a wide band of 7.2%.