Highly sensitive ZnO thin film bulk acoustic resonator for hydrogen detection

We apply a thin film bulk acoustic resonator for hydrogen detection. The resonator working at 2.39 GHz consists of a ZnO piezoelectric stack and an Al/W Bragg reflector. A Pd film is coated on the top of a piezoelectric film as the electrode and sensing coating to capture hydrogen. The resonance frequency of the resonator reduces progressively with the increase of hydrogen concentration due to the mass addition on the Pd layer after hydrogenation. The experimental results show that our proposed sensor can yield the sensitive, linear, reversible, repeatable and stable responses to hydrogen in the concentration range of 0.05%-3% at room temperature. The limit of detection at room temperature is as low as 0.05%. This study proves that the thin film bulk acoustic resonator is a promising and feasible platform for the hydrogen sensor working at room temperature.