Characterization of homogeneity of langasite wafers using bulk-wave measurement

A characterization technique for homogeneity of piezoelectric wafers utilizing bulk-wave measurement was established, and measurements were carried out 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 central frequencies of SAW devices, by measuring the distribution of the frequency constant of thickness-shear mode resonance. The frequency constant, measured by a combination of resonance frequency measurement and thickness measurement in a single wafer, yields a relative accuracy of about ±55 ppm. The distribution of the frequency constant is consistent with that of the phase velocity of SAW obtained by fabricating and measuring SAW devices. The method is both rapid and nondestructive, thus is suitable for routine characterization in the production of piezoelectric wafers. Characterization of langasite wafers using this technique correlated inhomogeneity to the growth conditions of the crystal.