Symmetric physics-based compact core model for double-gate junctionless transistors with ungated extensions

This work presents a physics-based compact model for double-gate junctionless field-effect transistors, with emphasis on accurately capturing the impact of ungated source/drain extensions on the drain current characteristics. The model is validated against two-dimensional device simulations performed using Silvaco ATLAS for two channel doping concentrations and a wide range of ungated extension lengths. To isolate the contribution of the access regions and clarify the effective channel length, all mobility degradation models were disabled in the simulations, allowing the observed current degradation to be attributed solely to the series resistance of the ungated extensions. The proposed formulation includes an analytical factor ξ that accounts for the reduced electrostatic influence of the source and drain terminals on the channel potential, as well as a closed-form expression for the fringe capacitance associated with the ungated regions. The resulting drain current model demonstrates very good agreement with numerical simulations across different geometries and doping levels. Model symmetry is further verified through a Gummel symmetry test, confirming the physical consistency of the formulation. Owing to its analytical nature and physical transparency, the proposed model is well suited to serve as a core building block for higher-level compact models of JL devices.