High frequency lamb wave resonator using LiNbO3 thin film by CVD

It has been considered that it is difficult to realize higher frequency devices than 3 GHz by using conventional surface acoustic wave (SAW) substrate. In order to realize a high frequency device, there are some methods such as using a high velocity substrate or shortening a wavelength (lambda) of an interdigital transducer (IDT). However, almost of all conventional SAW substrates have a low velocity and it is difficult to shorten the lambda of IDT because of too narrow fingers. A Lamb wave has a high velocity and a large coupling factor when a LiNbO₃ plate is thiner than 0.2 lambda. As it is difficult to realize a very thin LiNbO₃ crystal plate, author use a thin epitaxial LiNbO₃ film deposited by a chemical vapor deposition (CVD). As the result, authors realized a high frequency 4.5 GHz of Lamb wave resonator composed of an electrode/thin epitaxial LiNbO₃ film/air gap/base-substrate for the first time. The resonator showed a high velocity of 14,000 m/s, a large impedance ratio of 52 dB, and a wide bandwidth of 7.2% without spurious response due to SH₀ mode.