Correlation between rf-sputtering parameters and WO3 sensor response towards ozone

Electrical properties of semiconductor oxide depend on the surrounding composition gas atmosphere. The surface conductivity of the sensor is modified by adsorption of gas species, which affects the space charge region. Tungsten oxide is an n-type metal oxide semiconductor with oxygen vacancies, which act as donors. In the present work we report on the electrical response Of WO3-based sensors for ozone detection. WO3 thin films are deposited by rf reactive magnetron sputtering on a SiO2/Si substrate with interdigitated Pt-micro-electrodes. The influence on the sensor response of processing parameters, such as oxygen partial pressure, self-bias voltage and sputtering time, has been studied. A correlation between sensor response and morphology of the sensor film has been established using AFM and X-ray diffraction (XRD). We have demonstrated that the best response towards ozone has been obtained with the following sputtering parameters: a self-bias voltage of - 200 V, a sputtering time of 10 min, and an(O-2/Ar) ratio of 1. These deposition parameters give films 40 nm thick, with small grains and high roughness. (c) 2007 Elsevier B.V. All rights reserved.