Preparation of heterogenous copper-titanium oxides for chemiresistor applications

Abstract

Metal oxide based gas sensors (MOS) found a wide application as modular parts in microelectronic devices due to their technological compatibility, low cost and outstanding sensing capabilities to different chemical species. The functionality of such chemiresistors consists of a change of the electric resistance/impedance of a semiconducting sensitive layer when gases with either oxidizing or reducing properties appear in the surrounding atmosphere. Earlier, the majority of the investigated chemiresistors were based on single phase, homogenous semiconductors. The combination of two different phases and hence the implementation of heterojunctions (HJs) on chemiresistors offers a way to increase the sensor performance, especially the sensitivity of the sensor. In this work, chemiresistors based on CuO-TiO2 acting as p-n heterojunction were developed. Thin sensitive layers were deposited by a two-step process. Cu-Ti thin layers were prepared by ion beam sputtering using an Ar ion beam and, subsequently, oxidized by thermal annealing in air at 400 °C for 7 h. The stoichiometry of the metallic films was analyzed by the Rutherford Back-scattering (RBS) using 2 MeV α-particles. The gas sensing properties of the oxidic thin films (deposited on prefabricated substrates containing interdigital electrodes) were analyzed in an atmosphere containing 100 ppm of either methanol, hydrogen and acetaldehyde or 10.6 ppm of nitrogen dioxide.