Steep-Switching Germanium Junctionless MOSFET with Reduced OFF-State Tunneling

Abstract

In this paper, we report on the reduction of the off-state band-to-band tunneling (BTBT) while maintaining sub-60 mV/decade switching in Germanium (Ge) Junctionless (JL) transistor through well-calibrated simulations. Recognizing the product of current density (J) and electric field (E) to be the key generic parameter governing device optimization, it is shown that a device with thicker film operated at lower drain bias (Vds) can sustain impact ionization and limit BTBT, thereby balancing the conflicting requirements of JE for tunneling and impact ionization. An optimal workfunction and gate-to-drain underlap of 5 nm in Ge JL MOSFET can further suppress BTBT while achieving a subthreshold swing of 5 mV/decade with nearly four decades of steep current transition at the threshold voltage along with a low off-current (10-10A) at Vds = 0.9 V. Results highlight new viewpoints for the design optimization of steep-switching Ge JL MOSFETs. © 1963-2012 IEEE.