Shear Mode ZnO Thin Film Applied in FBAR Sensor

In this study, platinum (Pt) and zinc oxide (ZnO) had been adopted as electrode and piezoelectric layer of an FBAR sensor. Based on the off-axis deposition of the ZnO film, longitude and shear modes resonance phenomenon can be approached to sensitive in air and liquid respectively. The preferred orientation and crystal properties of the ZnO film were evaluated by X-ray diffraction (XRD) using a SHIMADZU XRD-6000 with Cu K α radiation. The crosssections of the grain structures of ZnO films were observed by scanning electron microscopy (SEM) (Philips XL40 FESEM). The electrical resistance of the bottom electrode was measured using the van der Pauw four-point probe method. The HP8720 network analyzer and CASCADE probe station (RHM-06/V + GSG 150) were used to measure the frequency responses of FBAR devices. The result of FBAR frequency response in liquid, the quality factor of longitude mode is decayed apparent and shear mode is kept high value. The Pt electrode of FBAR sensor has to withstand attack of acid/alkali solution.