A refined method to determine the elastic constants of SiO2 thin films

We use differential delay lines to extract the phase velocity of a SAW on a LiNbO₃ substrate covered with thin SiO₂ films which have been deposited by a plasma enhanced chemical vapour deposition (PECVD) and a physical vapour deposition (PVD) process. The variation in film thickness of the PVD process between the differential delay lines has to be corrected to a reference thickness which is done by signal processing. The accuracy of the results allows the determination of the elastic constants (c₁₁ and c₄₄) and the density ρ of the PECVD thin film within an accuracy of ±2.4% and of the PVD SiO₂ process within an accuracy of ±4.1% by fitting corresponding simulations.