Investigation of Threshold Voltage Definition for Nanosheet MOSFETs by Using Quantum Drift Diffusion Model

Abstract

In this paper, we investigate the analytical definition of the threshold voltage of nanosheet MOSFETs using the quantum drift diffusion (QDD) model. The QDD model is a device simulator that can simulate the quantum confinement effects in the inversion layer of advanced MOSFETs. We have analyzed three-dimensional characteristics of a nanosheet MOSFET with a sheet width of 10 nm, a sheet thickness of 4 nm, and an equivalent oxide thickness of 0.35 nm in the QDD model. We have investigated the analytical definition of threshold voltage in the nanosheet MOSFET using the Q_TH definition proposed by Takeuchi et al. and the 2ψ_B definition that has been widely used in the past. For the nanosheet MOSFET, the threshold voltage in the Q_TH definition is 0.40 V, and the threshold voltage in the 2ψ_B definition is obtained to be 0.19 V. The threshold voltage by electrical definition is 0.36 V. The difference is 0.04 V by the Q_TH definition, and 0.17 V by the 2ψ_B definition. In nanosheet MOSFETs, the threshold voltage obtained by the Q_TH definition is closer to the threshold voltage obtained by the electrical definition than the threshold voltage obtained by the 2ψ_B definition.