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Interface states in high-temperature gas sensors based on silicon carbide

2003; IEEE Sensors Council; Volume: 3; Issue: 5 Linguagem: Inglês

10.1109/jsen.2003.817154

1558-1748

Peter S. Tobias, B. Golding, Ruby N. Ghosh,

Gas Sensing Nanomaterials and Sensors

Silicon carbide (SiC)-based metal-insulator-semiconductor devices are attractive for gas sensing in automotive exhausts and flue gases. The response of the devices to reducing gases has been assumed to be due to a reduced metal work function at the metal-oxide interface that shifts the flat band capacitance to lower voltages. We have discovered that high temperature (700 K) exposure to hydrogen results not only in the flat-band voltage occurring at a more negative bias than in oxygen, but also in the transition from accumulation (high capacitance) to inversion (low capacitance) occurring over a relatively narrow voltage range. In oxygen, this transition is broadened, indicating the creation of a high density of interface states. We present a model of the hydrogen/oxygen response based on two independent phenomena: a chemically induced shift in the metal-semiconductor work function difference and the passivation/creation of charged states at the SiO 2 -SiC interface that is much slower than the work function shift. We discuss the effect of these results on sensor design and the choice of operating point.