A NEW MICROSENSOR FOR ENVIRONMENTAL MEASUREMENTS

This paper describes a thin-film sensor, a measuring method that gives it better performance and some applications in the field of combustible gas detection. The sensor consists of a thin layer of metal, several microns thick, several tens of microns wide and about 2 mm long, attached by some thin-layer legs to a glass holder. The whole fabrication is carried out with microelectronic technology. This thin layer is able to support very high temperatures, 800 to 1000-degrees-C for example, and can be maintained at this temperature with only 100 mW of electrical power. The second part of the paper describes a new electrical method allowing the sensor to be used in a pseudo-continuous mode. In 10 ms 900-degrees-C can be obtained and the thin-layer resistance measured. All phenomena that change the temperature, such as velocity, temperature, flow and thermal conductivity, can be measured with this type of sensor. The metal used in this example is platinum, a good catalyst. The sensor can also be used as a combustible gas detector: the temperature change caused by the heat of reaction is measured by the variation of the thin-layer resistance. We give some results obtained with methane. In this application a lifetime of 8 to 12 months is obtained with one 10 ms measurement each 3 s. Each measurement consumes only one millijoule of energy.