Optimization of SAW sensors with a structure ZnO–SiO2–Si to detect volatile organic compounds

Surface acoustic waves (SAW) devices are fabricated on ZnO piezoelectric films by reactive sputtering on SiO2–Si substrates with different O2 concentrations (7.5%, 10%, 15%) in Ar plasma. Crystalline structures and roughness characteristics of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements, respectively. Preparation conditions were optimized to obtain films of good quality suitable for the fabrication of SAW devices. Different designs of these ZnO structures have been characterized through RF measurements in order to choose the best design with the purpose of realizing a SAW sensor with good characteristics to detect volatile organic compounds (VOCs). The best design of structure (W = 80λ, L = 100λ, N = 72) has been covered with polyepichlorohydrine (PECH) obtaining the best responses for toluene and above all with the ZnO film prepared with a 10% O2 concentration.