Improving the Signal Resolution of Semiconductor Gas Sensors to High-Concentration Gases

Abstract Detecting high-concentration gases is challenging by metal oxide semiconductor (MOX) gas sensors, because the voltage signal would become saturated. In order to solve this problem, the zooming p+n field-effect transistors (FETs) circuit has been designed, combining an n-type enhancement-mode FET (EMFET) and a p-type depletion-mode FET (DMFET). This designed zooming p+n FETs can endow MOX gas sensors with the high signal resolution of ∼3.0 V/decade to the 100–2 000 ppm (part per million) acetone gas, triple that of MOX gas sensors without FETs (∼0.8 V/decade). Meanwhile, this zooming technology is also suitable for detecting other gases at high-concentration, such as 1%–20% LEL (lower explosion limit) methane. The principle of zooming p+n FETs is that with increasing the gas concentration, the suppressing role of the EMFET is firstly induced leading to a reduced signal resolution to the low-concentration target gas; then its suppressing effect becomes saturated and the DMFET starts to switch from ON state to OFF state in the high-concentration target gas, resulting in an amplifying effect herein and thus an enhanced signal resolution. This circuit is promising for the high-concentration gas detection as well as for the multi-functional gas detector design.