Leakage mitigation in NW FET using negative Schottky junction drain and its process variation analysis

Abstract

In this work, a Schottky junction on the drain side employing low workfunction (WF) metal is proposed as a method to suppress the OFF-state leakage in nanowire (NW) field-effect transistor (FET). Instead of a highly n+ doped drain, low WF metal with negative electron Schottky barrier height (SBH) as a drain minimizes the lateral band-to-band tunneling (L-BTBT) considerably. L-BTBT is the movement of carriers (holes) from the drain conduction band into the channel valence band during the OFF-state. Impact of varying WF at channel–drain junction on the device characteristics is studied. It is observed that SBH \(\leqslant 0\) eV is required to mitigate L-BTBT compared to the conventionally doped and junctionless (JL) NW counterpart. Furthermore, unlike L-BTBT, leakage in NW Schottky drain (SD) comprises of holes tunneling through the SB from the metal drain into the channel and is termed as the lateral SB tunneling (L-SBT). In contrast with JL NW FET, the process variation immunity (varying channel doping, \({N}_{\mathrm{Ch}}\) and NW diameter, \({d}_{\mathrm{NW}}\)) and the ON-state current of the proposed device are not compromised at the expense of lower OFF-state L-SBT. Instead, the device is less susceptible to process variations and retains the ON-state performance of the NW MOSFET. For a ± 20% change in \({N}_{\mathrm{Ch}}\), \(\Delta {I}_{\mathrm{OFF}}\)/\({I}_{\mathrm{OFF}}\) of 7% compared to 97% in NW JL FET is observed.