Electrode effects on mass sensitivity of GaN thin film bulk acoustic wave resonator sensors

In this paper, the electrode effects on mass sensitivity of GaN thin film bulk acoustic wave resonator (FBAR) sensors have been studied. The equation of electric impedance of FBARs with structure of mass sensitive layer/electrode/GaN/electrode has been derived by one dimensional transmission line model for frequency calculation. In the simulation, to produce shear mode acoustic 2μm GaN with 42.8° c-axis tilted angle was particularly chosen for liquid application; to investigate the effects of electrode on mass sensitivity, the acoustic characteristic impedance of electrode changes from 2.37×10⁶Ω to 5.916×10⁷Ω, and its thickness changes from 0 to 2000 nm. It was found that the thickness and acoustic characteristic impedance of electrode has great effects on the mass sensitivity; compared to non-electrode case, electrode with high acoustic characteristic impedance (higher than GaN) decreases mass sensitivity, while electrode with low acoustic characteristic impedance (lower than GaN) increases mass sensitivity, and maximum sensitivity can be achieved by the optimization of electrode material and thickness. The simulation results can be used for the design and application of GaN FBAR sensors.