SAW reflection characteristics and NSPUDT orientations on langasite

Langasite (LGS, La/sub 3/Ga/sub 5/SiO/sub 14/) single crystal is an attractive substrate for SAW devices requiring good temperature stability and high electromechanical coupling constant K/sup 2/. However, the SAW reflection characteristics due to a strip electrode on LGS have not been reported so far. It is necessary for designing the SAW devices such as SPUDT based filters and resonators with grating reflector. Recently several research groups have shown theoretically and experimentally that the (0/spl deg/,140/spl deg/,22/spl deg//spl sim/24/spl deg/) cut on LGS is a very promising cut. This cut is characterized by zero TCD, moderately high K/sup 2/, and zero power flow angle. In this paper, we describe the analytical results of SAW reflection characteristics using coupled-mode and perturbation theories. From the analysis of reflection characteristics, we found that (0/spl deg/,140/spl deg/,22/spl deg//spl sim/24/spl deg/) cut is the excellent natural single phase unidirectional transducer (NSPUDT) orientations with large directivity as well as zero TCD, high K/sup 2/, and zero power flow angle.