SENSITIVITY OF A MODIFIED GATELESS FET STRUCTURE TO ETHANOL VAPOR

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 prese nce of ethanol vapour. Good ethanol sensitivity can be obtained using thin and ultrathin SiO2 as well as a plasma nitrided thin thermal SiO2 layer as an active dielectric. The response time is within seconds an d the response range covers more than five decades for 100% ethanol va pour concentration in the working cell. The structure may operate as a n alcohol sensor for about 150 measurement cycles without loss of dete ction speed or accuracy. The experimental results provide evidence tha t the rapid increase of the drain current is closely related to positi ve charge build-up in the structure during ethanol vapour exposure. So me concepts are proposed for the interpretation of the results obtaine d, including arguments used to isolate the contribution of the surface oxide charge on one hand, and the charge in the oxide and in the inte rface states on the other, to the total positive charge generated.