Pd/AlN/SiC thin-film devices for selective hydrogen sensing

A hydrogen sensing device has been fabricated using a 1500- Angstrom -thick AlN layer interposed between a SiC substrate and a Pd gate. This device behaves as a rectifying diode. Hydrogen in the gas flow causes a shift in the forward conduction and the sensitivity of the device is found to increase with the total flow rate. At a device temperature of 300 degreesC and a flow rate of 1000 sccm, the typical forward current of similar to1 mA increases by 10% for 10 ppm hydrogen, independent of the presence of oxygen or CO in the gas flow. The shift is also independent of the presence of propane. However, for very large concentrations of propane a slight response can be discerned, due to the presence of some hydrogen resulting from the incipient decomposition of the hydrocarbon at elevated temperature. (C) 2001 American Institute of Physics.