Experimental and predicted SAW temperature behavior of langatate

Recent investigations on langatate (LGT) have shown that it has several attractive acoustical properties, in particular: (i) a measured bulk acoustic wave (BAW) resonators quality factor frequency product (Qf) of 16 million, comparable to that of AT cut quartz; (ii) high piezoelectric coupling orientations, up to 0.5% for surface acoustic waves (SAWs), about five times larger than that of ST-X quartz; (iii) low power flow angle orientations in the vicinity of high coupling orientations; (iv) phase velocities about 20% smaller than those of ST-X quartz, facilitating the production of smaller lower frequency devices; (v) the existence of pseudo SAW modes for higher frequency applications. To date the temperature behavior of this material has not been studied for SAW orientations. We report both predictions and experimental results on the SAW temperature fractional frequency variation (Δf/fo) and the temperature coefficient of delay (TCD) for several LGT orientations on the plane with Euler angles: [0° 132° ψ]. The temperature behavior has been measured directly on SAW wafers from 10° to 200°C, and the results are compared with numerical predictions using our recently measured temperature coefficient constants for LGT. Calculated contour plots of the TCD are given for orientations in the neighborhood of the plane where the experiments were done. This research work has also uncovered temperature compensated orientations, which we have experimentally verified, with parabolic behavior, turn over temperatures in the 130 to 160°C range, and Δf/fo within 1000 ppm variation from 10 to 260°C, appropriate for higher temperature device applications