Simulation study of electrode effect on thin film bulk acoustic resonator for viscosity sensor application

In this paper, we presented the study of electrode effects on the performance of thin film bulk acoustic resonator (FBAR) for viscosity sensor application, where the viscosity sensor is with a structure of the top electrode layer/piezo layer/bottom electrode layer, and the sensor's sensitivity (S) and quality factor (Q) was addressed. Simulation results show that, compared with the case of without electrode, adopting electrode with high characteristic acoustic impedance electrode (Z
_e
) cannot improve S, and S decreases with the thickness of electrode (t
_e
); for the case of electrode with low Z
_e
, S can be improved by choosing an appropriate te, and there exists an optimal te for the maximization S. Moreover, it was found that both the electrode layer and the viscosity of liquid have a great effect on Q. For low viscosity liquid, Q and S can be simultaneously improved by adopting high mechanical quality factor electrode with low Z
_e
and optimization t
_e
. For medium viscosity liquid detection, results show that if Z
_e
is specifically chosen in a small certain range, Q and S can also be simultaneously improved with appropriate te, otherwise a balance should be made for the optimization of S and Q through t
_e
. For the high viscosity liquid, Q has a great deterioration due to heavy liquid loading and the improvement by electrode is weak. These results can be used for the design and application of FBAR viscosity sensors.