The Temperature Coefficients of Frequency of Surface Acoustic Wave Devices With SiOxNy Passivation Films on LiTaO3 Substrates

This work assessed the possible correlation between the refractive index of a SiO
_x
N
_y
passivation film on a surface acoustic wave (SAW) device and the temperature coefficient of frequency (TCF) of the device itself. The data demonstrate that the refractive index does correlate with the TCF as well as the frequency of the one-port resonator. SiO
_x
N
_y
passivation films having an optimal refractive index can potentially suppress the frequency shifts caused by the deposition of such layers, and can change the TCF from that for a Si
₃
N
₄
film to that for SiO
₂
. The results also show that the coupling coefficient of the one-port resonator increases when using a SiO
_x
N
_y
film with a lower refractive index, which changes the TCF such that this value approaches that for a SiO
₂
film. Finite-element method spectral domain analyses established that the frequency responses of the one-port resonators were affected by the velocity and temperature coefficient of velocity of the dielectric films deposited on the interdigital transducer electrodes. Thus, adjusting the refractive index of the SiO
_x
N
_y
film can be used to control the properties of an SAW device, including the TCF.