In nanoscale metal-oxide-semiconductor field-effect transistors (MOSFETs), excess noise has been experimentally observed as the channel length is scaled down. Theoretical analyses indicate that as the channel length decreases, the dominant component of excess noise gradually changes from modified thermal noise to suppressed shot noise. However, no clear quantitative analysis has been provided regarding the specific conditions for this transition. In this paper, based on a device current model, we analyze the transition conditions under which shot noise replaces thermal noise as the dominant component of excess noise. In the modeling process, we comprehensively consider short-channel effects, including the electric field distribution, mobility reduction caused by electron temperature gradients, and the hot-carrier effect. Meanwhile, we use 3D Monte Carlo simulations to analyze the channel current noise components in MOSFETs with different channel lengths, and we simulate the effects of drain–source voltage, gate voltage, temperature, and substrate doping density on the transition of excess noise components. The simulation results show that the transition trend of excess noise components is consistent with predictions from the physical model: the critical channel length for the transition from thermal noise to shot noise in nanoscale MOSFETs is approximately 20 nm. The model and simulation results presented in this paper agree with reported experimental measurements and provide a theoretical foundation for the quantitative analysis of excess noise components in nanoscale MOSFETs.
Zhang et al. (2026) studied this question.