SAW propagation loss mechanism in piezoelectric ceramics

Abstract

The surface acoustic wave (SAW) propagation loss mechanism of piezoelectric ceramics is examined using lead titanate (PbTiO3) ceramics modified with additives of Nd2O3, MnO2, and In2O3, which have zero temperature coefficients of SAW delay time. The propagation loss L in the frequency range 30 to 300 MHz consists of two parts. One is the Rayleigh scattering loss LS caused by grain, and the other is the true dissipative loss LF caused by internal friction. Thus, total loss results in L(dB/cm) = LS+LF = 3.2×103D3f4+6.8×10−4f2 (where D and f denote average grain size in cm and frequency in MHz, respectively). It is also revealed experimentally that the internal friction causing the latter loss has a close correlation with the dielectric loss through piezoelectric combination. Therefore, materials with fine grain (<0.5 μm) and low dielectric loss (<10−3) must be developed to reduce SAW propagation losses which prevent the piezoelectric ceramics from being used in higher frequency (≳100 MHz) SAW applications. Based on these requirements, fine grained (∼0.5 μm) specimens are fabricated. The propagation losses obtained from these specimens, 9 dB/cm at 100 MHz, are the lowest values ever reported for piezoelectric ceramics. This result suggests that the present ceramics have high potential as materials for high-frequency SAW devices.