Application of fluorine doped SiO2 films for temperature compensated SAW devices

In our paper, we investigates acoustic properties including temperature coefficient of elasticity (TCE) of fluorine doped silicon oxide (SiOF) films and proposes their application to the temperature compensation of radio frequency (RF) surface acoustic wave (SAW) devices. From the Fourier transform infrared spectroscopy (FT-IR), SiOF films were expected to possess good TCE properties. Then we fabricated a series of SAW devices using the SiOF-overlay/Cu-grating/LiNbO₃-substrate structure, and their device performances were evaluated. The experiments showed that the temperature coefficient of frequency (TCF) increases with the fluorine content r, as we expected from the FT-IR measurement. This means that the Si-O-Si atomic structure measurable by the FT-IR governs the TCE behavior of SiO₂-based films even when the dopant is added. In comparison with the pure SiO₂ with the film thickness h of 0.3 wavelengths (λ), TCF was improved by 7.7 ppm/°C without deterioration of the effective electromechanical coupling factor K² when r=3.8 atomic % and h=0.28λ. The F inclusion did not influence the resonator Q factors obviously when r8.8 atomic%.