IN-SITU MODIFICATION OF THE NOX SENSITIVITY OF THIN DISCONTINUOUS PLATINUM FILMS AS GATES OF CHEMICAL SENSORS

It is shown how chemically sensitive metal-oxide semiconductor field-e ffect transistors with a thin discontinuous platinum gate can be modif ied for the detection of NOx. After a pulse of ammonia the sensors sho w an increased sensitivity to NOx. The threshold voltage shift induced by NOx is opposite to the direction before the ammonia pulse. The thr eshold voltage now increases due to NOx exposure, while hydrogen, ammo nia and hydrocarbons cause a decrease of the threshold voltage. The te mperature dependence of the NOx sensitivity suggests that after the am monia pulse there are two competing polarisation phenomena caused by t he interaction between NOx and the sensing surface. The results are of general interest since they indicate how thin sensing layers can be m odified after fabrication to promote sensitivity towards specific mole cules. Furthermore they shed some new light on the detection mechanism s of thin discontinuous metal gates.