Standardized evaluation of chemical compositions of LiTaO/sub 3/ single crystals for SAW devices using the LFB ultrasonic material characterization system

Abstract

The line-focus-beam ultrasonic material characterization (LFB-UMC) system is applied to compare and evaluate tolerances provided independently for the Curie temperature T(C) and lattice constant a to evaluate commercial LiTaO3 single crystals by measuring the Rayleigh-type leaky surface acoustic wave (LSAW) velocities V(LSAW). The relationships between V(LSAW), and T(C) and a measured by individual manufacturers were obtained experimentally using 42 degrees Y X-LiTaO3 wafers as specimens from three crystal manufacturers. In addition, the relationship between V(LSAW) and SH-type SAW velocities V(SAW) 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 T(C) tolerance of +/-3 degrees C and the a tolerance of +/-0.00002 nm through the common scale of V(LSAW) or V(SAW) demonstrated that the a tolerance is 1.6 times larger than the T(C) tolerance. Furthermore, we performed a standardized comparison of statistical data of T(C) and a for LiTaO3 crystals grown by two manufacturers during 1999 and 2000, using V(LSAW). 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.