A Schottky diode composed of Pd directly on SiC has been studied extensively. The diode has been shown to be very sensitive to hydrogen concentration either by measuring the forward current or the capacitance of the diode. The detection of propylene has been demonstrated either in inert or oxygen-bearing environments. The magnitude of the propylene signal has been shown to be temperature dependent. A sensor package which includes a temperature detector and heater is being developed.
Present work is centered on stabilizing the sensor for long-term, high temperature operation.
The High Speed Research program is very interested in decreasing NOx emissions. The objective of our work is to monitor the NOx in the engine emission stream and use this signal to control the engine parameters in such a way as to reduce NOx. Two approaches to NOx detection are being investigated. One is a SiC-based Schottky diode sensor as discussed with the hydrogen detection but with a gate that is NOx sensitive. The second approach uses a tin-oxide based sensor processed in such a way so as to insure stable operation.