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 × 10⁸% for 0.8% H₂ in air and a superior sensitivity of 4.58 × 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 ∼10 fW (dry air) to ∼20 nW (0.8% H₂ in dry air) and therefore paves the way for a very large-scale integration commercial sensing platform.