Single-crystalline LiNbO₃ Film based Piezoelectric Sensors for Ultra-precision Pressure-sensing Applications

This work presents the fabrication and characterization of a sub-GHz plate-wave-based pressure sensor relying on an ultra-thin (360 nm) single-crystalline LiNbO ₃ film. The proposed devices exhibit multiple resonant modes which are characterized and analyzed by a precise 3D plate wave resonator model based on finite element analysis (FEA). Generally, the main resonant modes correspond to the Shear-horizontal ( SH ) and anti-symmetric ( A ) Lamb waves. To overcome the high-temperature coefficient of LiNbO ₃ thin film, a thick layer (~4 μm) of SiO ₂ was used to compensate for the temperature drift of the devices; the calculated temperature coefficients of frequency ( TCFs ) for the multi-resonant modes are lower than -27 ppm/K. The frequency and return loss (S ₁₁ ) shift of the plate wave devices, the pressure sensitivity, and the pressure coefficient of frequency ( PCF ) were experimentally evaluated and analyzed. All the resonant modes show high PCF even with relatively lower operating frequencies (< 1 GHz). Especially it has been observed that the first-order anti-symmetric (A1) Lamb wave is ultra-susceptible to pressure changes, which presented a record high value of ~600 ppm/Bar and excellent linearity over the tested 0.6 to 1.8 Bar pressure range. The results show that the developed sensor has sufficiently high sensitivity and can be used for precise absolute pressure sensing.