GaPO4 SAW devices: measured and predicted propagation properties

New piezoelectric crystals capable of providing higher electromechanical coupling than quartz, while maintaining temperature compensated characteristics comparable to quartz, are in demand for communications, sensors, and signal processing applications. In response to this demand, several new crystals have been recently developed and characterized for acoustic wave applications. Gallium Orthophosphate (GaPO₄) is among these crystals, which include lithium tetraborate, langasite, langanite, langatate, potassium niobate, SNGS (Sr₃NbGa₃Si₂O₁₄) and STGS (Sr₃TaGa₃Si₂O₁₄). In this work theoretical and measured SAW propagation characteristics for phase velocity (v_p), electromechanical coupling (K²), diffraction (γ), temperature coefficient of frequency (TCP) and fractional frequency variations (Δf/fo) along selected GaPO₄ orientations are reported. Measured propagation properties are compared to calculated values along the propagation directions Euler angles (0°, 76°, 0°), (0°, 90°, 0°), (0°, 110°, 0°), and (0°, 130°, 0°). The measured phase velocities for these orientations agree with the calculated values to within 0.4% for the propagation directions investigated. The measured TCF values agree with the predicted values showing temperature compensated behavior between 70°C and 200°C for the selected cuts. Fractional frequency variations of about 15 ppm over a 50°C span around the turnover temperatures are predicted and measured, comparable to equivalent Y rotated quartz orientations. Values of K² ranging from 0.3% to 0.5% are calculated and extracted from the experimental data for the selected orientations mentioned, confirming up to four times higher K² of GaPO₄ with respect to Y rotated quartz orientations.