This paper reported the investigation of an infrared (IR) sensitive, ZnO based Film Bulk Acoustic Resonator (FBAR). The resonant frequency of the FBAR decreased under IR illumination, and results demonstrated a linear dependence on IR intensity. The sensing mechanism is attributed to the temperature-dependent Young's modulus of the resonator material (ZnO), which subsequently shifts the resonant frequency. Thickness Field Excitation FBAR and Lateral Field Excitation (LFE) FBAR were fabricated and characterized with detection limits of 0.7 mu W/mm(2) and 2 mu W/mm(2), respectively, but the LFE FBAR exhibited higher IR sensitivity. (C) 2011 Elsevier BM. All rights reserved.