Quantitative characterization of the fabrication processes of domain-inverted layers in LiTaO₃ by the line-focus-beam ultrasonic material characterization system

Application of the line-focus-beam ultrasonic material characterization system was extended to evaluate Z-cut LiTaO₃ substrates with domain-inverted layers fabricated by proton exchange and quick heat treatment (QHT), and their fabrication processes and systems. Three Z-cut LiTaO₃ substrates were proton-exchanged at 260 °C for 20 min; heat-treated for 30 s at 520, 540, and 560 °C, with a temperature increase rate of 80 °C/s; and annealed at 420 °C for 6 h. Slab-type domain-inverted layers with 0.50, 1.94, and 3.26-μm depths on the -Z surfaces and proton-exchanged layers on both the -Z and +Z surfaces were formed. Leaky surface acoustic wave (LSAW) velocities for both surfaces were measured in a frequency range of 100–300 MHz and found to exhibit different dispersion characteristics. Intrinsic LSAW velocity changes caused by the formation of domain-inverted layers were obtained from differences in the LSAW velocities for both surfaces. The velocity changes decreased with increases in the product fH of the ultrasonic frequency f and the domain-inverted layer thickness H. Relationships among the LSAW velocity changes, thicknesses of the domain-inverted layers, and process temperatures in QHT were experimentally obtained. An LSAW velocity variation of 2.6 m/s for the Y-axis propagation at 225 MHz was detected by a homogeneity evaluation on a specimen QHT-processed at 540 °C and annealed. This corresponded to a layer thickness variation of 0.20 μm and a QHT temperature variation of 2.9 °C. © 2002 American Institute of Physics.