Investigation of spacer-engineered stacked nanosheet tunnel FET with varying design attributes

Abstract

The stacked nanosheet field-effect transistors (SNS-FETs) are potential contenders for sub-7 nm technology. Device miniaturization leads to a larger off-state current and a higher subthreshold slope in SNS-FETs. Unlike SNS-FETs, the stacked nanosheet tunnelling field effect transistors (SNS-TFETs) function as switches in integrated circuits, featuring high performance and low power consumption. The endeavour aims to investigate how each design parameter optimises the switching characteristics of the SNS-TFET device. This paper examines various design attributes, such as different dielectric spacer materials, nanosheet width (NW), nanosheet thickness (NT), source doping, drain doping, etc. The Cogenda Visual TCAD serves as a tool for conducting device simulations. According to the simulation study, the use of a high-k hafnium dioxide (HfO2) spacer produces a higher switching ratio ( 7.28×1011 ) and a lower subthreshold swing (20.303 mV/decade). Using either low-k or no spacers reduces the overall gate capacitance and unit frequency gain compared to high-k spacers. Upscaling the nanosheet width (10 to 50 nm) enhances the switching ratio by 1.11×101 and transconductance by 61.92%. Downscaling the nanosheet thickness (6 to 4 nm) at the optimized nanosheet width (50 nm) improves the switching ratio by 1.88. Increasing the gate length from 8 to 16 nm reduces the leakage current by 2.34×10−2 A and improves the switching ratio by 2.90×101. An increase in the source doping level from 1×1020 to 5×1020 cm−3 results in a 1.07×102 decrease in the switching ratio and a 2.48-fold increase in the subthreshold swing. Furthermore, the findings indicate that drain doping is crucial in determining ambipolar current. In SNS-TFET, ambipolar current reduces significantly when drain doping is 1×1017 cm−3. Thus, the proposed work addresses the limitations of scaling and optimised design parameter characteristics for low-power nanoscale circuits.