Characterization of homogeneity of langasite wafers using bulk-wave measurement

A characterization technique for homogeneity of piezoelectric wafers utiliz ing bulk-wave measurement was established. and measurements were carried ou t on langasite (LGS: La3Ga5SiO14) wafers fabricated in our laboratory. The technique is capable of predicting the homogeneity of the phase velocity of a surface acoustic wave (SAW), which determines the deviation of the centr al frequencies of SAW devices, by measuring the distribution of the frequen cy constant of thickness-shear mode resonance. The frequency constant, meas ured by a combination of resonance frequency measurement and thickness meas urement in a single wafer, yields a relative accuracy of about +/- 55 ppm. The distribution of the frequency constant is consistent with that of the p hase velocity of SAW obtained by fabricating and measuring SAW devices. The method is both rapid and nondestructive. thus is suitable for routine char acterization in the production of piezoelectric wafers. Characterization of langasite wafers using this technique correlated inhomogeneity to the grow th conditions of the crystal.