SH₁Mode Plate Wave Resonator on LiTaO₃Thin Plate with Phase Velocity over 13, 000 m/s

In this study, a first shear horizontal mode (SH1 mode resonator) for high-frequency filters were investigated. From FEM simulation, it was confirmed that the SH1 mode plate wave had a high phase velocity of 20 km/s and a high electro-mechanical coupling factor (k2) of 14% on (0°, 60°-70°, 0°) LiTaO3 (LT) with a thickness of 0.1 (: wavelength). The high k2 was achieved by forming an electrically shorted plane on the bottom LT surface (opposite side of an interdigital transducer electrode, IDT). The SH1 mode plate wave resonator was fabricated on a 0.5m thick LT film supported with a Si substrate. The IDT had a of 4.5m and a thickness of 100 nm (0.02). The fabricated SH1 mode plate wave resonator showed a resonance frequency (fr) of 2.78 GHz, anti-resonance frequency (fa) of 2.92 GHz, a bandwidth (BW) of 5%, and an impedance (Z) ratio of 38 dB. The anti-resonant phase velocity was calculated as high as 13, 050 m/s, which showed a potential for high frequency filters. The poor impedance ratio was caused by the low mechanical quality factor (Qm) of Cu IDT used in the fabrication and the not optimized fabrication process.