Bimetallic Au–Ag-Modified ZnO-Based MEMS Sensors for ppb-Level Ethanol Detection

Low power consumption and effective ppb-level ethanol sensor are widely used in environmental protection, life sciences, transportation field, and so on. In this work, an impregnation–calcination–photoreduction method was developed to fabricate bimetallic Au–Ag-modified ZnO-based microelectromechanical systems (MEMS). The photoreduction process could simultaneously create abundant reactive oxygen species in ZnO while reducing the noble metal nanoparticles. Gas-sensing performance tests revealed that ZnO loaded with Ag and Au nanoparticles (Irr-0.5Au–0.5Ag/ZnO) exhibited superior gas-sensing capabilities, with a response value of 31.5–20-ppm ethanol at 235 °C. This performance was 15.5 times that of ZnO and 2.7 times that of the monometallic Au-modified material Irr-0.5Au/ZnO. Especially, the lower detection limit for ethanol gas was as low as 9 ppb, indicating its potential for high-sensitivity detection of trace ethanol gas. The lower operating temperature, combined with MEMS technology, significantly reduces the sensor’s power consumption. Irr-0.5Au–0.5Ag/ZnO also demonstrated good linearity for different concentrations of ethanol gas and maintained long-term stability for up to 15 days. The improved sensing performance is mainly attributed to the chemosensitization and electrosensitization effects of the bimetallic Au–Ag and the increased generation of reactive oxygen species.