NO₂ gas sensing properties of Pd/WO₃ films prepared by glancing angle deposition

The fabrication procedure of gas sensing films deposited by physical vapor deposition is more compatible with the micro-electro-mechanical system (MEMS) process. However, low sensitivity and high working temperature of gas sensing films limit their application. In this work, tungsten trioxide (WO₃) films were deposited on silicon oxide by glancing angle deposition (GLAD), and palladium (Pd) was deposited onto the WO₃ layer. Then, the morphology, structure, and nitrogen dioxide (NO₂) gas sensing properties of the Pd/WO₃ films were studied. The results show that the Pd/WO₃ films may comprise discrete Pd islands and columnar WO₃ nanorods. The nanostructure can detect 0.5 ppm NO₂ at 150 °C with a sensitivity of 1.85 and possesses good selectivity, which can be mainly attributed to large specific surface area of nanorods, catalysis of Pd, and Schottky barrier between Pd and WO₃. Therefore, the Pd/WO₃ nanostructure prepared by GLAD has great potential in the field of NO₂ MEMS sensors.