Investigation of GeO2 thin film properties for improvement of temperature coefficient of frequency of SAW devices

We have investigated the temperature dependent elastic constants of SiO₂ and GeO₂. For this purpose, the phase velocity of the layered system has to be calculated using surface acoustic wave (SAW) differential delay lines on LiNbO₃ substrates. Both SiO₂ and GeO₂ have a positive temperature coefficient of velocity. The GeO₂ layer shows a significant reduction of the phase velocity compared to SiO₂ which yields to an improved energy trapping of the surface acoustic wave in the overlay. However, severe stability issues arise using the GeO₂ layer.