GaPO/sub 4/ SAW devices: measured and predicted propagation properties

• Published in: IEEE Symposium on Ultrasonics, 2003 Vol. 1; pp. 110 - 113 Vol.1
• Main Authors: Pereira da Cunha, M., Pollard, T.B., Whitehouse, H., Worsch, P.M.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 2003
• Subjects: Acoustic sensors; Acoustic signal processing; Crystals; Electromechanical sensors; Frequency measurement; Phase measurement; Sensor phenomena and characterization; Strontium; Temperature sensors; Velocity measurement
• ISBN: 0780379225; 9780780379220
• DOI: 10.1109/ULTSYM.2003.1293366

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 (GaPO/sub 4/) is among these crystals, which include lithium tetraborate, langasite, langanite, langatate, potassium niobate, SNGS (Sr/sub 3/NbGa/sub 3/Si/sub 2/O/sub 14/) and STGS (Sr/sub 3/TaGa/sub 3/Si/sub 2/O/sub 14/). In this work theoretical and measured SAW propagation characteristics for phase velocity (v/sub p/), electromechanical coupling (K/sup 2/), diffraction (/spl gamma/), temperature coefficient of frequency (TCP) and fractional frequency variations (/spl Delta/f/fo) along selected GaPO/sub 4/ orientations are reported. Measured propagation properties are compared to calculated values along the propagation directions Euler angles (0/spl deg/, 76/spl deg/, 0/spl deg/), (0/spl deg/, 90/spl deg/, 0/spl deg/), (0/spl deg/, 110/spl deg/, 0/spl deg/), and (0/spl deg/, 130/spl deg/, 0/spl deg/). 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/spl deg/C and 200/spl deg/C for the selected cuts. Fractional frequency variations of about 15 ppm over a 50/spl deg/C span around the turnover temperatures are predicted and measured, comparable to equivalent Y rotated quartz orientations. Values of K/sup 2/ 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 K/sup 2/ of GaPO/sub 4/ with respect to Y rotated quartz orientations.