Design and modeling of the electrostatically controlled nanowire FET for ppt-level hydrogen sensing

We present the design of a H2 gas sensor based on palladium (Pd) decorated silicon-on-insulator (SOI) nanowire field effect transistor (FET) with a standard SOI complementary metal-oxide-semiconductor fabrication process, where a top Pd layer plays a dual role of a catalyst and a surrounding metal gate. A numerical study was conducted based on a simplified steady-state model to describe the sensing mechanism of H2 in dry air at 300 K. The simulation is based on the model of dissociative H2 adsorption on the Pd surface and the formation of a dipole layer at the Pd/SiO2 interface. The H atoms induced dipoles lead to a potential drop which exponentially increases the FET drain current and consequently, the sensor response. The FET drain current is controlled by its back-gate bias and by varying the H2 concentrations; it is shown that the drain current response reaches 1.8 x 108% for 0.8% H2 in air and a superior sensitivity of 4.58 x 104%/ppm in the sub-threshold operation regime. The sensor exhibits an outstanding theoretical detection limit of 50 ppt (response of 1%) and an upper dynamic range limit of 7000 ppm which allow for timely and accurate detection of H2 gas presence. The power consumption ranges between similar to 10 fW (dry air) to similar to 20 nW (0.8% H2 in dry air) and therefore paves the way for a very large-scale integration commercial sensing platform.