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 (LiNbOa) wafer, which will be used for small and sensitive SAW-based pressure sensors. The process technology uses thermal inversion, wet stretching 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, LiNbOa thin diaphragms with thicknesses of several tens of jim to 10 fim were fabricated in 128° Y cut LiNbC 3 wafers. The Au-Au bonding of the LiNbOa wafer gave hermetic sealing. In addition the etch profiles of the LiNbC 3 wafer predicted by Wulff-Jaccodine plots and observed in experiments were compared, and good agreement was confirmed.