SH1Mode Plate Wave Resonator on LiTaO3 Thin Plate with Phase Velocity over 13,000 m/s

In this study, a first shear horizontal mode (SH
1
mode resonator) for high-frequency filters were investigated. From FEM simulation, it was confirmed that the SH
1
mode plate wave had a high phase velocity of 20 km/s and a high electro-mechanical coupling factor (k
²
) of 14% on (0°, 60°-70°, 0°) LiTaO
3
(LT) with a thickness of 0.1λ (λ: wavelength). The high k
²
was achieved by forming an electrically shorted plane on the bottom LT surface (opposite side of an interdigital transducer electrode, IDT). The SH
1
mode plate wave resonator was fabricated on a 0.5 µm thick LT film supported with a Si substrate. The IDT had a λ of 4.5 µm and a thickness of 100 nm (0.02λ). The fabricated SH
1
mode plate wave resonator showed a resonance frequency (f
r
) of 2.78 GHz, anti-resonance frequency (f
a
) 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 (Q
m
) of Cu IDT used in the fabrication and the not optimized fabrication process.