ABSTRACT The line-focus-beam ultrasonic material characterization (LFB-UMC) system is applied to compare and evaluate tolerances provided independently for the Curie temperature TC and lattice constant a to evaluate commercial LiTaO3 single crystals by measuring the Rayleigh-type leaky surface acoustic wave (LSAW) velocities VLSAW. The relationships between VLSAW, and TC and a measured by individual manufacturers were obtained experimentally using 42°YX-LiTaO3 wafers as specimens from three crystal manufacturers. In addition, the relationship between VLSAW and SH-type SAW velocities VSAW that are actually used for the SAW device wafers was obtained through calculations, using the chemical composition dependences of the acoustical physical constants for LiTaO3 crystals reported previously. The result of a comparison between the TC tolerance of ± 3°C and the a tolerance of ± 0.00002 nm through the common scale of VLSAW or VSAW demonstrated that the a tolerance is 1.6 times larger than the TC tolerance. Furthermore, we performed a standardized comparison of statistical data of TC and a for LiTaO3 crystals grown by two manufacturers during 1999 and 2000, using VLSAW. The results clarified the differences of the average chemical compositions and of the chemical composition distributions among the crystal ingots between the two manufacturers. A guideline for the standardized evaluation procedure has been established for the SAW-device wafer specifications by the LFB-UMC system.
© 2002, by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.