Acoustic velocity homogeneity evaluation of POI materials using three-parameter analysis of Brillouin oscillation

Abstract Piezoelectric films on insulator (POI) are preferred materials for high performance 5G RF filters, and the inhomogeneity of the in-plane acoustic velocity in piezoelectric single-crystal thin films hinders mass production. This study fully considers the significant differences in optical transparency among three layer POI structures. High-precision, non-destructive testing of the longitudinal acoustic velocity consistency of piezoelectric films was conducted using time-domain Brillouin scattering technology. To address the impact of refractive index spatial heterogeneity on the test results, this study proposes a three-parameter analysis of Brillouin oscillation, enabling direct inversion measurements of thickness and acoustic velocity and effectively reducing the errors in acoustic velocity measurement caused by refractive index heterogeneity. Using this approach, in-plane thickness and acoustic velocity homogeneity analyses were performed on Z -cut LiNbO 3 films. After eliminating the influence of the refractive index, the acoustic velocity of Z -cut LiNbO 3 showed a peak abnormal decrease of –3.45%, which may be dominated by the spatial gradient of the intrinsic parameters of the material.