Effects of heat treatment on Ta2O5 sensing membrane for low drift and high sensitivity pH-ISFET

This paper presents a new approach for reducing the drift and improving the sensitivity of a pH-ISFET by varying the heat treatment condition of the Ta2O5 sensing membrane. A Ta2O5 pH-ISFET which was heat-treated at various temperatures, showed very different sensing characteristics 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, which is maybe related to a densification effect of the film in an amorphous state with a low leakage current. Furthermore, the Ta2O5 pH-ISFET which was heat-treated in O-2, showed good sensitivity, which is maybe associated with an increase of O-sites at the surface. The Ta2O5 pH-ISFET fabricated by the above method showed good linearity, high sensitivity (58-59 mV) over a wide pH range (pH 2-12) and low long-term drift (0.03-0.05 pH/day).