Correlation between fluorine-doped SiO2 films properties and the propagation loss for temperature compensated SAW devices

This paper investigates origin of the excess acoustic propagation loss caused in fluorine doped silicon oxide (SiOF) films with large fluorine content r. The authors proposed to use SiOF films for temperature compensation of radio frequency (RF) surface acoustic wave (SAW) devices because of their large temperature coefficient of elasticity and small acoustic attenuation. It was also reported that when r is too large, the SAW attenuation became very large. The FT-IR measurement showed that the peak frequency ω₄ of the Si-O stretching vibration decreases significantly while its peak width Δω₄ increases dramatically in the situation. The Raman spectroscopy showed that the Raman scattering between 110 and 400 cm^-1 also becomes very strong. No obvious change was observed for the other optical frequencies. These results suggest that the excess propagation loss is mainly caused by the scattering at the damaged SiO₂ network and fluorine termination.