ABSTRACT This paper demonstrates the evaluation and selection of commercially available LiNbO3 and LiTaO3 single crystals and wafers for surface acoustic wave (SAW) devices using the line-focus-beam ultrasonic material characterization (LFB-UMC) system. This system enables measuring leaky-SAW (LSAW) propagation characteristics precisely and efficiently for a number of specimens. The wafers are prepared from the top, middle, and bottom parts of four 128° YX LiNbO3 and seven X-112° Y LiTaO3 single crystals. For both series of crystals, the measured LSAW velocities increase from top to bottom in the crystals and with the increasing crystal growth number. The velocity changes for all wafers are 0.036% for 128° YX LiNbO3 and 0.035% for X-112° Y LiTaO3, corresponding to changes of 0.038 mol% and 0.075 mol% in Li2O concentration, respectively. Moreover, the inhomogeneity in the first X-112° Y LiTaO3 single crystal caused by some undesirable wafer fabrication processes can be detected precisely, although it is difficult for the conventional methods to obtain such information.
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