Evaluation and selection of LiNbO/sub 3/ and LiTaO/sub 3/ substrates for SAW devices by the LFB ultrasonic material characterization system

This paper demonstrates the evaluation and selection of commercially available LiNbO/sub 3/ and LiTaO/sub 3/ 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/spl deg/YX LiNbO/sub 3/ and seven X-112/spl deg/Y LiTaO/sub 3/ 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/spl deg/YX LiNbO/sub 3/ and 0.035% for X-112/spl deg/Y LiTaO/sub 3/, corresponding to changes of 0.038 mol% and 0.075 mol% in Li/sub 2/O concentration, respectively. Moreover, the inhomogeneity in the first X-112/spl deg/Y LiTaO/sub 3/ 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.