Surface acoustic wave hydrogen sensors based on ZnO nanoparticles incorporated with a Pt catalyst

This paper describes the fabrication and characterization of surface acoustic wave (SAW) hydrogen sensors using ZnO nanoparticles incorporated with a Pt catalyst for hydrogen detection at room temperature. The Pt/ZnO nanoparticle sensing layer was deposited onto SAW delay line sensor-based interdigitated electrodes (IDTs)/aluminum nitride (AlN)/silicon (Si) structure. The average ZnO crystallite sizes varied from 30 nm to 40 nm and were synthesized by a sol–gel method and deposited onto SAW sensors by spin coating. The Pt-like catalyst was deposited onto ZnO nanoparticles by RF sputtering for 2 s. The effect of ZnO crystalline quality, crystallite size and humidity on hydrogen sensing performance was evaluated. Moreover, the sensitivity of SAW delay line sensors as they depend on conventional structures and layered structures were also characterized in this work. The SAW delay line sensors using AlN/Si structures have fundamental frequency of 129.28 MHz for uncoated, 128.85 MHz and 126.93 MHz for coated Pt/ZnO sensing layer corresponding to the conventional and layered structures, respectively. The layered SAW structure using Pt/ZnO nanoparticles as sensing layer show frequency shift of 55 kHz in 1% H2 concentration at room temperature with good repeatability and stability.