Metal strip reflectivity and NSPUDT orientations in langanite, langasite, and gallium phosphate

New materials of the trigonal 32 class have received much attention recently, due to their quartz-like temperature behavior and the promise of higher electromechanical coupling coefficients. The magnitude and phase of the reflection coefficient of the metal strips that form the SAW transducers and reflector structures is critical information that allows proper device designs and optimal material surface orientation. This paper describes an investigation of the magnitude and phase of the SAW metal strip reflectivity in some new materials and along new orientations. The materials are langanite, langasite, and gallium phosphate (GaPO₄). The results are presented as contour plots of the magnitude and phase of the reflection coefficient. In addition, the phase velocity, temperature coefficient of delay, electromechanical coupling coefficient (K²), and power flow angle are given, thus allowing proper orientation selection for SAW device designs. The results presented highlight the reflection coefficient calculations in the selection of natural single-phase unidirectional transducer orientations (NSPUDT) for these new materials. As a result of the present work, reflection coefficient magnitudes 5 times larger than that of the well-known quartz NSPUDT orientation [Euler angles: 0° 132.75° 25°] can be obtained with the new materials, for orientations where the optimum NSPUDT reflection coefficient phase criterion is met. The new materials discussed here provide an opportunity to design shorter and higher-bandwidth devices due to the increased K², the higher reflection coefficient, and the lower phase velocities. All this while maintaining the excellent temperature insensitivity characteristic of quartz. The orientation regions suggested in this paper for the new materials are thus very promising for low loss, high performance consumer and communications SAW designs, such as NSPUDT filters, resonator based filters, and- other devices that can benefit from a high metal strip reflectivity.