Investigations of STGS, SNGS, CTGS, & CNGS materials for use in saw applications

Langasite structure compounds have been the focus of much consideration recently, given their higher electromechanical coupling and similar temperature behavior to that of quartz. Recent investigations have begun on four new materials, STGS, SNGS, CTGS, and CNGS. These langasite structure crystals show great promise for use in SAW applications. In some respects, STGS, SNGS, CTGS, and CNGS exhibit better SAW material properties than the LGX materials (langasite, langanite, and langatate) previously studied. For example, SNGS and STGS have higher electromechanical coupling than LGX, in excess of 0.6% and 0.5%, respectively. In addition, all four materials have lower densities resulting in higher phase velocities. Along with previously studied trigonal 32 class materials, there is a good possibility that temperature compensated cuts exist. Recent results are reported for SAW material parameters and device performance at various propagation directions on Y-cut STGS, SNGS, CTGS, and CNGS wafers. These results include coupling coefficient, phase velocity, transducer capacitance, and temperature coefficient of delay (TCD). Experimental measurements of metal strip reflectivity are shown for various metal thicknesses. Measured SAW resonator Q data are also presented. The measurement procedures and the parameter extraction methods for these experiments are discussed. A comparison of the data with previously reported parameters on LGX is presented and a discussion of the results is provided.