Abstract
Evidence for the sensitivity to ethanol vapour of a modified n-channel FET structure, based on Si, was found. The detection is based on the increase in the drain current (at constant drain voltage) in the presence of ethanol vapour. Good ethanol sensitivity can be obtained using thin and ultrathin Si0 2 as well as a plasma nitrided thin thermal SiO 2 layer as an active dielectric. The response time is within seconds and the response range covers more than five decades for 100% ethanol vapour concentration in the working cell. The structure may operate as an alcohol sensor for about 150 measurement cycles without loss of detection speed or accuracy. The experimental results provide evidence that the rapid increase of the drain current is closely related to positive charge build-up in the structure during ethanol vapour exposure. Some concepts are proposed for the interpretation of the results obtained, including arguments used to isolate the contribution of the surface oxide charge on one hand, and the charge in the oxide and in the interface states on the other, to the total positive charge generated.
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