A symmetric unified transport and charge model for metal–oxide–semiconductor field-effect transistor from diffusive to ballistic regimes

Abstract

This paper presents a symmetric unified transport compact model for metal–oxide–semiconductor field-effect transistors (MOSFETs) that bridges drift-diffusion (DD) and ballistic transport (BT) regimes. The proposed model self-consistently accounts for both current and charge across the DD–BT transition. Quantum capacitance and carrier transport are incorporated into the charge density formulation. Drain-side velocity saturation and the source-side thermal velocity limit are unified within a single framework using a physically motivated high-field scattering length, enabling accurate modeling from DD square-law behavior to the ballistic limit. In addition, a physical channel charge and capacitance model is developed to capture capacitance reduction in the quasi-ballistic regime, which is not considered in standard compact models. The model is verified using theoretical analysis and experimental data from MOSFETs with multiple channel lengths, achieving accurate fitting using only physically motivated model parameters. The formulation is continuous and symmetric, and it passes both DC and AC symmetry tests.