High velocity lamb waves in LiTaO3 thin plate for high frequency filters

Abstract

First anti-symmetric (A₁) mode Lamb wave propagating in a LiTaO₃ thin plate at an Euler angle around (0°, 45°, 0°) has a high velocity. Both phase velocity and electromechanical coupling factor have been evaluated at different propagation angles (0°, 45°, ψ°). A₁ mode Lamb wave at (0°, 45°, 0°) offers the highest velocity and largest electromechanical coupling factor, thus proving suitable for high frequency devices. Leaky Lamb waves' velocities have been measured for A₀ and zero-th symmetric (S₀) modes at different propagation angles by ultrasonic microscopy and are almost similar to the calculated Lamb wave velocities. Whereas Ai mode Lamb wave response has been evaluated at (0°, 42°, 0°), (0°, 42°, 45°) and (0°, 42°, 90°) using a network analyzer. The influence of Al-interdigital transducers' (IDT) thickness on the reflection coefficient has been evaluated for thin (0°, 39°, 0°) LiTaO₃. An IDT's thickness larger than 0.03λ (λ is the wavelength) is needed to fabricate A₁ mode Lamb wave resonators.