EFFECTS OF HEAT-TREATMENT ON TA2O5 SENSING MEMBRANE FOR LOW DRIFT ANDHIGH-SENSITIVITY PH-ISFET

This paper presents a new approach for reducing the drift and improvin g the sensitivity of a pH-ISFET by varying the heat treatment conditio n of the Ta2O5 sensing membrane. A Ta2O5 pH-ISFET which was heat-treat ed at various temperatures, showed very different sensing characterist ics such as sensitivity, long-term drift, etc. When heat-treated in O- 2 ambient at 400 degrees C for 1 h, Ta2O5 pH-ISFET showed low drift, w hich is maybe related to a densification effect of the film in an amor phous state with a low leakage current. Furthermore, the Ta2O5 pH-ISFE T which was heat-treated in O-2, showed good sensitivity, which is may be associated with an increase of O-sites at the surface. The Ta2O5 pH -ISFET fabricated by the above method showed good linearity, high sens itivity (58-59 mV) over a wide pH range (pH 2-12) and low long-term dr ift (0.03-0.05 pH/day).