Gas sensing with field effect devices
The gas detection principle of field effect (FE) sensors with catalytic metal gates is based on the change of the electric field at the semiconductor surface region introduced by gases. This changes the number of mobile carriers in the semiconductor and therefore the electrical characteristics of the device.
FE devices typically have a metal insulator semiconductor (MIS) part of the device where the metal layer is a catalytic metal or a combination of several catalytic metals. For non-porous catalytic metal films hydrogen containing molecules may dissociate and the so formed hydrogen atoms diffuse rapidly through the metal film and become trapped at the metal-insulator interface, see Fig. 1. The interface hydrogen induces an effective change of the metal workfunction which can be modelled as a dipole layer.
Fig. 1. An MIS device with a catalytic metal layer can act as a filter which only allows hydrogen containing molecules to be detected.
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Last updated: 04/29/09