Evaluation of Piezoelectric Ta2O5Thin Films Using Line-Focus-Beam Ultrasonic Material Characterization System

A line-focus-beam ultrasonic material character-rization (LFB-UMC)system provides the velocities and normalized attenuation factor of leaky surface acoustic waves (LSAWs)excited on a water-loaded material surface. The normalized attenuation factor includes leakage loss into water because LSAWs propagate at the boundary between the water and the material. Therefore, to evaluate acoustical loss using the LFB-UMC system, it is necessary to subtract the calculated leakage loss from the measured attenuation. In this study, the evaluation of the acoustical loss of a thin film was examined using an X-axis-oriented tantalum pentoxide (Ta
₂
O
₅
)thin film, but the normalized attenuation factor calculated using the determined material constants was larger than the measured normalized attenuation factor because some material constants could not be accurately determined. However, since the characteristics of high-order LSAWs vary considerably, different elastic properties were observed from those in previous study. Comparing the elastic constants determined from the measured results with the reported values, $C$
₁₂
and $C$
₅₅
were 35% and 14% smaller than the previous values, respectively. By measuring multiple SAW modes, it was observed that some elastic constants greatly differed from those in the previous study.