Catalytic bead sensor

Abstract: An integrated catalytic combustion H 2 sensor has been fabricated by using MEMS technology. Both the sensing elements and the reference elements could be integrated into the suspended micro heaters connected in a suitable circuit such as a Wheatstone configuration with low power consumption. Two sensitive elements and two reference sensors were integrated together onto a single chip. The size of chip was 5.76 mm 2 and the catalytic combustion sensor showed high response to H 2 at operating voltage of 1 V. The response and recovery times to 1000 ppm H 2 were 0.36 s and 1.29 s, respectively.

Abstract: A new integrated catalytic gas sensor for detecting flammable gases or flammable vapours has been fabricated on silicon with thin film deposition and silicon micromachining techniques. This device is realized on the principle of the conventional catalytic gas sensor known under the name of ‘Pellistor’. The detection principle of this gas sensor is based on the measurement of heat emitted by the combustion of the gas with atmospheric oxygen on a small catalytic surface. The sensitive element and the reference element are integrated together on the same chip of size 2.84×2.46 mm2. This double structure requires a very low electrical power of typically 100 mW at an operating temperature of 400 °C. The excellent thermal insulation is realized by a 0.6 μm thin silicon nitride membrane. The sensitivity of the sensor is about 13 mV/% methane in air.

Abstract: The detection of combustible gases with the aid of the heat exchange in chemical reactions on a solid surface has been known for many years. A large number of this type of sensor is used for gas detection. One of them is the Si-Planar-Pellistor, a small gas sensor, produced by Si micromachining technology. The advantage of this sensor is the low power consumption and the very low thermal time constant. A problem of all sensors using this method of heat exchange is the cross-sensitivity to most combustible gases. In this paper it will be shown how the cross-sensitivity can be reduced by using an integrated Si-Planar-Pellistor array or a single pellistor sensor operating at different working points as a quasi array in connection with signal evaluation by pattern recognition (PARC).