Trap-Assisted Gas Sensing Mechanism in ${\rm Pd/TiO}_{2}/{\rm SiO}_{2}/{\rm SiC}$ Capacitors at High Temperatures

We demonstrate that the gas concentration in a high-temperature environment can be measured using the leakage current through a dielectric stack on silicon carbide, comprising silicon dioxide and titanium dioxide. The variation in the leakage current may be explained by the trap-assisted conduction model, where the barrier height is observed to be dependent on the concentration of gas. The behavior of the sensors under exposure to hydrogen and oxygen is shown and we propose that the observed change may be explained by the change in band bending under the oxide layer. The sensitivity of this detection technique is not influenced by the electric field across the dielectric and is better than 50 ppm. The use of a low electric field in comparison to conventional capacitance-based measurements offers the possibility of lomg-term operation at elevated temperatures.