Picosecond Acoustic Interferometry for Characterizing Properties of SiO₂ layer in POI Materials

Piezoelectric film materials on insulators (POI) play a pivotal role in improving the operating frequency and comprehensive performance of RF surface acoustic wave filters. In addition to choosing appropriate substrates and high-quality piezoelectric films, the SiO2 layer should also behave well in bonding, temperature compensation and waveguiding. However, assessing the acoustic properties of the SiO2 remains a formidable challenge. This study explores the application of Picosecond Acoustic Interferometry (PAI) as a direct method for assessing the acoustic properties of SiO2 layer in POI materials. By analyzing Brillouin oscillation induced by ultrasound propagating within transparent film, PAI establishes a direct relationship between oscillation frequency and sound velocity. The sound velocity, thickness, attenuation coefficient of SiO2 layers grown with two distinct methods in POI sample are accurately measured with PAI. This study demonstrates that PAI provides an effective solution for assessing the acoustic properties of SiO2 layer in POI Materials.