Tuning of the sensitivity of porous silicon JFET gas sensors

In this work, electrical tuning of the sensitivity of an integrated solid-state gas sensor is demonstrated. The sensor, namely PSJFET - Porous Silicon Junction Field Effect Transistor, consists of a p-channel JFET with an additional PS sensing gate on its top. The sensor current value is proportional to the NO(2) concentration in the environment, that is I(DS)=S center dot[NO(2)], at least in the range investigated (between 100 ppb and 500 ppb). Interestingly, and differently from most of gas sensors reported in the literature, the normalized sensor sensitivity S=dI(DS)/(I(DS0)center dot d[NO(2)]) can be effectively tuned by changing the voltage value of the electrical gate terminal of the JFET device. This feature allows the fabrication of gas sensors with superior performances: for example, it can be exploited to compensate for aging-induced degradation of the sensitivity during the sensor life-time. It is worthy of mentioning that, such an effect can be obtained without any increase of the sensor power dissipation, due to the high impedance of the gate terminal of the PSJFET.