GAS SENSITIVE FIELD-EFFECT DEVICES FOR HIGH-TEMPERATURES

Field effect sensors based on metal-oxide-silicon carbide (MOSiC) devi ces are used as high temperature gas sensors. They are sensitive to, f or example, saturated hydrocarbons and hydrogen and can be operated up to at least 800 degrees C, which make them suitable for several types of combustion control. A metal gate with two layer platinum and a buf fer layer of tantalum silicide in between gave a large increase in the long term stability of the sensors. At temperatures below 600 degrees C, the response to ethane in oxygen was shown to have a threshold at a ratio of about 0.38 for the ethane-to-oxygen concentrations. Below t his ratio, the surface can be considered as mainly oxygen covered and the response is small. Above this ratio the metal surface is probably mainly hydrogen covered and the response is considerably larger.