Love-Wave-Type/Rayleigh-Wave-Type SAW Resonators with Thick Al-Grating Structure

摘要

A Love-wave SAW propagating on a thick Al grating on a LiNbO_3 piezoelectric substrate exhibits a resonant characteristic with an extremely small capacitance ratio γ (= 3.0) while it elastically couples with Rayleigh waves in a complex manner. In the application to a resonator, the Rayleigh wave becomes spurious and must be suppressed sufficiently. With a view to development of a broadband SAW resonator for a VCO, the propagation/reflection characteristics of this Love-wave/Rayleigh-wave configuration are analyzed. The following results are found by simulation and experiments. (1) Both the Love wave and Rayleigh wave have extremely wide reflection bandwidths. (2) Two types of spurious Rayleigh wave appear in the resonant characteristics. (3) The stopband of the Rayleigh wave is superior in reflection characteristic to the Love wave. It is also demonstrated experimentally that a broadband SAW-VCO can be realized if the VCO oscillation frequency is chosen within the Rayleigh wave stopband after the Al film thickness is optimized.