Leakage Optimization of the Buried Oxide Substrate of Nanosheet Field-Effect Transistors

Abstract

In this work, a new buried oxide nanosheet field-effect transistor (BO-NSFET) structure is proposed for the first time as a strategy for improving the leakage of 3-nm stacked nanosheet field-effect transistors (NSFETs) by locally inserting an oxide material only under the gate region. NSFETs with punchthrough stoppers (PTSs) doping of the substrate region have been widely adopted to reduce substrate leakage; however, band-to-band tunneling (BTBT) under negative bias remains a serious problem in such devices. By only inserting the oxide material under the gate region, the electric field from the gate to the drain–substrate junction is dispersed. Furthermore, since there is no oxide material under the source and drain (S/D) region, there is no stress reduction along the channel direction coming from the silicon-on-insulator (SOI) structure. We performed technology computer-aided design (TCAD) simulations, and the results show that the proposed structure effectively reduces both the tunneling current in the NSFET with PTS structure and the OFF-current in the NSFET without PTS structure, compared with those of conventional NSFETs.