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Open Access Publications from the University of California

Compact modeling of Double-Gate MOSFETs

Abstract

Double-Gate (DG) MOSFET is a newly emerging device that can potentially further scale down CMOS technology owing to its excellent control of short channel effects. Currently, much research effort is devoted to the development of DG MOSFETs. This dissertation focuses on the compact modeling of DG MOSFETs, aiming to extract the physics of DG MOSFETs and provide a tool for simulating DG MOSFET circuits. We start from the basic Poisson's equation and current continuity equation to rigorously derive the long-channel drain current model without the charge sheet approximation. The model is based on an analytical solution to the potential distribution at any point in the DG MOSFET. It employs one single equation to cover all the operation regions: linear, saturation, and subthreshold, continuously with no fitting parameter. Volume inversion, a non-charge-sheet phenomenon in symmetric DG MOSFETs, is accurately captured by the model. For AC and transient simulations, analytical charge and capacitance models are developed. Both symmetric and asymmetric DG MOSFET models are verified by extensive two dimensional numerical simulations. For small-geometry devices, compact models of the physical phenomena such as short channel effects are developed. In the development of the compact models, special attention is paid to ensure the model is symmetric and continuous in all the operation regions. Quantum effect is also incorporated in the long channel core model. As body doping may be needed to adjust the threshold voltage, we also studied the body doping effect on DG MOSFET and concluded that lightly doped DG MOSFETs can be modeled by adding a threshold voltage shift to the undoped DG MOSFET model. The model has been implemented into SPICE3 and Verilog-A platforms so that it can be used by circuit designers. In the implementation, Newton method is used for solving an implicit equation in the calculation of drain current. We also calibrated the model with respect to the published hardware data to affirm its consistency with the experimental I-V curves. Finally, the model has been released in public domain http ://taur.ucsd.edu/̃hlu for circuit simulation

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