Friday, April 27, 2007

Thick-Film Gas Sensors Technology

Usually a thick-film gas sensor means a metal-oxide semiconductor sensor obtained by thick-film screen-printing technology. The chemically sensitive layer consists of a paste prepared from metal-oxide powder, inorganic additives and organic binders.
The paste is printed over an alumina substrate containing metal film electrodes and a back heating resistor; the paste is then sintered in a thermal or IR belt furnace.
Thick-film gas sensors are known for their high sensitivity especially for the large specific surface available for the chemisorption’s reactions. Moreover, with the proper choice of the semiconductor oxide and of the catalyst used, the sensing film can enhance the selectivity of the device towards a particular set of gases.
At room temperature the kinetics of the chemisorption’s reaction is too slow and not fully reversible, thus these sensing films are usually operated at temperatures ranging from 200 to 400°C. For this reason the overall power consumption of these devices is in general of the order 500 mW, mainly because of convection heat losses.
In next post I will describe all parts a thick-film-based gas sensor in detail.

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