A novel hydrogen sensor based on Pt/WO3/Si MIS Schottky diode

In this work, we investigate the static and dynamic gas response of Schottky diode based hydrogen sensor employing a Pt/WO₃/n-type Si configuration. The role and importance of tungsten trioxide as an insulating layer within the device is discussed with respect to the measured electronic properties. The WO₃ thin films were deposited using RF reactive magnetron sputtering. The surface morphology was studied by an atomic force microscopy (AFM) and the scan results indicated a smooth film with a roughness of 0.18 Å. From the X-ray photoelectron spectroscopy (XPS) characterization, it can be confirmed that the films were stoichiometric WO₃ with a thickness of about 4 nm (as measured by an ellipsometer). The I-V characteristics and dynamic response with respect to H₂ gas were measured at elevated temperatures from 50°C to 150°C and the results indicate that the H₂ sensitivity of this device can exceed approximately 1000 % with an average response time of less than 10 seconds. We discuss and explain these observations in terms of current transportation mechanisms using the thermionic emission model and the change in the Schottky barrier height.