Negative Capacitance Gate-All-Around Nanowire FETs for Highly Sensitive Catalytic Metal Gate Gas Sensors

This work presents a class of gate-all-around (GAA) nanowire (NW) field-effect transistor (FET)-based hydrogen (H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>) gas sensor with a ferroelectric (FE) layer in its gate stack. Palladium (Pd) is used as the catalytic gate metal, where the adsorption of H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas onto Pd surface alters the work function of Pd, causing a shift in surface potential, drain current, and threshold voltage characteristics, thereby enabling the detection of H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas. The FE layer introduces negative capacitance (NC) effect, which lowers the subthreshold swing (SS) below the Boltzmann limit of 60 mV/decade and offers steep switching characteristics, leading to enhanced sensitivity. The performance of the proposed sensor is evaluated by combining the solutions of one-dimensional (1D) Landau-Khalatnikov (L-K) equation with three-dimensional (3D) technology computer-aided design (TCAD) simulations. The sensitivity of the NC-GAA-NW FET sensor, at different gas pressures, is extracted from the transfer characteristics, in terms of the shift in drain current (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</sub>) and threshold voltage (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub>) with change in gas pressure. Furthermore, the shift in output characteristics and SS at various gas pressures have been explored, in addition to the temperature dependence of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</sub>. Leveraging the steep switching behavior, the NC-GAA-NW FET gas sensor exhibits more than 22× higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</sub> in the subthreshold region of operation and ~30% enhancement in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> than the baseline GAA-NW FET sensor when the H<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas pressure is 10-15 Torr.