Understanding Smart Sensors - Nomads.usp

The Nature of Semiconductor Sensor Output 61Conductance 10 −7 Ω−1110100908070605040302010H 2CO005001,0001,5002,000Concentration (ppm)Figure 3.6 Conductance change of chemical sensor based on specific gas andconcentration.2,000 ppm of each gas in separate measurements and operating at a minimumtemperature of 250°C.The Jet Propulsion Laboratory (JPL) is investigating a hydrocarbon sensorin which a porous layer of SiC on top of 6H silicon carbide forms the channelof a field-effect transistor (FET) [14]. Ions produced during catalysis of agiven hydrocarbon collect in the porous layer under the gate, affecting thecurrent-voltage relationship of the FET. Circuitry scans the FET at a range ofvoltages and identifies a particular hydrocarbon compound. The intent is tointegrate the sensing functions with additional electronics for an integratedprobe for detecting hydrocarbons. The SiC sensor should be able to operate attemperatures as high as 500°C.3.3.5 Improving Sensor CharacteristicsThe low-level output of the sensors described in this section and the designparameters discussed in Section 3.2.3 are among the characteristics that mustbe considered in the use of a semiconductor sensor in a particular application.Table 3.1 summarizes sensor characteristics and the design areas that arecommonly used to improve those characteristics [15]. Improved sensor