UV sensing using film bulk acoustic resonators based on Au-ZnO/piezoelectric-ZnO/Al structure

摘要

A new type of ultraviolet (UV) light sensor based on film bulk acoustic wave resonator (FBAR) is proposed. The new sensor uses gold and a thin n-type ZnO layer deposited on the top of piezoelectric layer of FBAR to form a Schottky barrier. The Schottky barrier's capacitance can be changed with UV light, resulting in an enhanced shift in the entire FBAR's resonant frequency. The fabricated UV sensor has a 50?nm thick n-ZnO semiconductor layer with a carrier concentration of ~ 1017?cm?3. A large frequency downshift is observed when UV light irradiates the FBAR. With 365?nm UV light of intensity 1.7?mW/cm2, the FBAR with n-ZnO/Au Schottky diode has 250?kHz frequency downshift, much larger than the 60?kHz frequency downshift in a conventional FBAR without the n-ZnO layer. The shift in the new FBAR's resonant frequency is due to the junction formed between Au and n-ZnO semiconductor and its properties changes with UV light. The experimental results are in agreement with the theoretical analysis using an equivalent circuit model of the new FBAR structure.