Applicability of LiNbO/sub 3/, langasite and GaPO/sub 4/ in high temperature SAW sensors operating at radio frequencies

The applicability of LiNbO/sub 3/, langasite and GaPO/sub 4/ for use as crystal substrates in high temperature surface acoustic wave (SAW) sensors operating at radio frequencies was investigated. Material properties were determined by the use of SAW test devices processed with conventional lithography. On GaPO/sub 4/, predominantly surface defects limit the accessible frequencies to values of 1 GHz. Langasite SAW devices could be operated up to 3 GHz; however, high acoustic losses of 20 dB//spl mu/S were observed. On LiNbO/sub 3/, the acoustic losses measured up to 3.5 GHz are one order of magnitude less. Hence, SAW sensors capable of wireless interrogation were designed and processed on YZ-cut LiNbO/sub 3/. The devices could be successfully operated in the industrial-scientific-medical (ISM) band from 2.40 to 2.4835 GHz up to 400/spl deg/C.