Fabrication and calibration of a gas sensor based on chemically vapor deposited WO3 films on silicon substrates: Application to H2 sensing

The electrical resistance of low pressure chemically vapor deposited (LPCVD) WO3 films exhibits reversible changes when gases, such as hydrogen, are present in their environment. Within the frame of this work, WO3 films activated with some gold monolayers were integrated, together with a polysilicon heater and two temperature-sensing resistors, on the same silicon substrate. For the fabrication, processes typically used in the manufacturing of silicon-based integrated circuits were used. After fabrication, dies with dimensions of 5 mm×5 mm have been packed and wire-bonded in classic dual in-line (DIL) packages. The temperature-sensing resistors were calibrated by external heating and monitoring their electrical resistance. Devices were tested in H2 and were found to be sensitive to concentrations down to 100 ppm. Sensitivity was dependent on temperature and H2 concentration. The maximum sensitivity (approximately 50%) was observed at temperatures around 120°C.