Application of lithium niobate etch stop technology to SAW pressure sensors

This paper presents a process technology to form thin diaphragms with sealed cavities in a lithium niobate (LiNbO₃) wafer, which will be used for small and sensitive SAW-based pressure sensors. The process technology uses thermal inversion, wet etching with an electroplated Au mask, etch stop at the thermal inversion layer and Au-Au bonding. By the combination of an etch stop and pinhole-free masking, LiNbO₃ thin diaphragms with thicknesses of several tens of mum to 10 mum were fabricated in 128deg Y cut LiNbO₃ wafers. The Au-Au bonding of the LiNbO₃ wafer gave hermetic sealing. In addition the etch profiles of the LiNbO₃ wafer predicted by Wulff-Jaccodine plots and observed in experiments were compared, and good agreement was confirmed.