PIEZOELECTRIC MATERIALS FOR ACOUSTIC-WAVE APPLICATIONS

Piezoelectric materials for acoustic wave applications have changed markedly over the past 20 years in terms of both the types of materials available and the quality of individual samples. The total family of acoustic wave materials now includes piezoelectric glass-ceramics having crystallographic and polar orientation and crystals having symmetry classes mm2, 32, 3m, 4mm, 6mm, and 43mBAR. The symmetry classes 6mm and 43mBAR also occur frequently in piezoelectric semiconductor materials that are now available in both bulk and thin-film configurations. In this paper, we bring together and extract the various reported values of the material constants mainly of interest for surface acoustic wave (SAW) device applications. We identify for the user community those sets of constants from which SAW design calculations can reliably be made, and discuss the constants and their reliability for langasite, lithium niobate/lithium tantalate, and dilithium tetraborate. The relevant material constants include: mass density rho, elastic stiffness c(ij), piezoelectric stress e(ij), dielectric permittivity epsilon(ii), and the thermal expansion coefficients alpha(ii). Except for the semiconductor materials, only data published after 1978 are included, since the reference literature (Landolt-Bornstein) amply covers those years prior to 1978.