Split-Gate Induced High-Field for Impact Ionization Triggered Bipolar Action and Sub-kT/q Switching in Junctionless FET

Abstract

In this article, an energy-efficient, ultra-steep subthreshold slope device based on the split-gate junctionless field-effect transistor (JLFET) has been proposed and investigated. Through split-gate, two regions, namely, channel-1 and channel-2, separated by a gap (<inline-formula><tex-math notation="LaTeX">$L_{gap}$</tex-math></inline-formula>) are created. A high electric field is thus induced at the interface of these two regions, which initiates impact ionization (II) at sub-bandgap drain voltage. The II-generated holes/electrons accumulate in channel-2 of N-JLFET/P-JLFET and set up a floating body that reduces the potential barrier between channel-1 and source of the device resulting in ultra-steep switching. Using a well-calibrated TCAD tool, we analyzed the operation of both N- and P-JLFET. A subthreshold swing (SS) of <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 50&#x00A0;<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>V/decade over nearly three decades of drain current is possible while maintaining a low OFF current of <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> <inline-formula><tex-math notation="LaTeX">$4.9\times 10^{-12}$</tex-math></inline-formula> A/<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m at a drain voltage of 0.4&#x00A0;V for silicon N-JLFET, which is better than any of the results reported so far for the junctionless devices. We have also investigated the impact of various device design parameters such as lengths of channel-1, channel-2, channel doping concentration, <inline-formula><tex-math notation="LaTeX">$L_{gap}$</tex-math></inline-formula>, gate oxide thickness and its permittivity, channel thickness, and dual-metal work function on the device performance.