In this work, fabrication and characterization of a film bulk acoustic wave resonator (FBAR) using ZnO as a piezo-electric layer is reported. The electrical characteristics of the FBAR devices with structures Pt/ZnO/Pt are studied having two different kinds of geometry, i.e. square and pentagon shape of the piezo-electric material (ZnO). The effect of geometry of the piezo-electric materials on the resonator performance is investigated in terms of input impedance (Zin), scattering parameter (S11) and phase by varying the frequency. Area of the Pt/ZnO/Pt based resonator is 280 μm × 280 μm. Thickness of the piezo-layer (ZnO) in the resonators is 2.8 μm. Thickness of the top and bottom electrodes is 0.2 µm. The resonance frequency, anti-resonance frequency, coupling coefficient and quality factor of pentagon shaped resonator are found to be 0.927 GHz, 0.929 GHz, 0.54% and 885, respectively. The performance of pentagon shaped FBAR is observed to be superior than that of its square-shaped counterparts.