Analysis of the potential upon the floating gate of an FGMOSFET used as a gas sensor

Gas sensor structures using metal oxides as sensing layers are widely used, but commonly the resistance variation of these layers is used to correlate this parameter with gas concentration. Here, we show that the sensitivity of a Floating-gate MOSFET (FGMOSFET) can be used also in gas detection by taking advantage of those ions derived from the chemical reaction between either reducing or oxidizing gases and a sensing layer, like metal oxides. This principle has been used in pH meter of solutions but by using a non-standard technology. This work suggests a structure that can be designed and fabricated by using standard CMOS technology. It should be stressed that this technology is compatible with MEMS. In this design, semiconducting metal oxides heated to temperatures up to 400 C can be used. In order to assess such a possibility, the results from an equivalent circuit using a conventional MOSFET and an iron oxide-pyrrole film as the sensing element are shown.