Explicit continuous models for both double-gate (DG) and surrounding-gate (SG) MOSFETs are presented. These models evolve from previous DG and SG MOSFETs models, which need to solve implicit equations for intermediate parameters by numerical iteration or the table lookup method. By developing approximate explicit solutions for the intermediate parameters, we can express the drain current, terminal charge, transconductance, and transcapacitance as explicit functions of applied voltages as well as the structural parameters. High accuracy and efficiency, combined with inherited favorable features from the previous models, make these new models suitable for circuit simulation programs.

Explicit Continuous Models for Double-Gate and Surrounding-Gate MOSFETs

In this paper, the implications of inversion charge linearization in compact MOS transistor modeling are discussed. The charge-sheet model provides the basic relation among inversion charge and applied potentials, via the implicit surface potential. A rigorous derivation of simpler relations among inversion charge and applied external potentials is provided, using the technique of inversion charge linearization versus surface potential. The new concept of the pinch-off surface potential and a new definition of the inversion charge linearization factor are introduced. In particular, we show that the EKV charge-based model can be considered as an approximation to the more general approach presented here. An improvement to the EKV charge-based model is proposed in the form of a more accurate charge–voltage relationship. This model is analyzed in detail and shows an excellent agreement with the charge sheet model. The normalization of voltages, current and charges, as motivated by the inversion charge linearization, results in a major simplification in compact modeling in static as well as non-quasi-static derivations.

Inversion charge linearization in MOSFET modeling and rigorous derivation of the EKV compact model

This work describes an advanced physics-based compact MOSFET model (SP). Both the quasistatic and nonquasi-static versions of SP are surface-potential-based. The model is symmetric, includes the accumulation region, small-geometry effects, and has a consistent current and charge formulation. The surface potential is computed analytically and there are no iterative loops anywhere in the model. Availability of the surface potential in the source-drain overlap regions enables a physics-based formulation of the extrinsic model (e.g., gate tunneling current) and allows for a noise model free of discontinuities or unphysical interpolation schemes. Simulation results are used to illustrate the interplay between the model structure and circuit design.

SP: an advanced surface-potential-based compact MOSFET model

A surface potential (SP)-based analytical model for intrinsic charges in AlGaN/GaN high electron mobility transistor devices is presented. We have developed a precise analytical method to calculate the Fermi-level position Ef from a consistent solution of Schrodinger's and Poisson's equations in the quantum well, considering the two important energy levels. The accuracy of our Ef calculation is on the order of femto-volts for the full range of bias voltage. The SP calculated from Ef is used to derive an analytical model for intrinsic charges in these devices. The model is in excellent agreement with experimental data.

Analytical Modeling of Surface-Potential and Intrinsic Charges in AlGaN/GaN HEMT Devices

This is the first book dedicated to the next generation of MOSFET models. Addressed to circuit designers with an in-depth treatment that appeals to device specialists, the book presents a fresh view of compact modeling, having completely abandoned the regional modeling approach.

Mosfet Modeling for Circuit Analysis and Design

Surface-potential-based models are among the most accurate and physically based compact MOSFET models available today. However, the need for iterative computations of the surface potential limits their computational efficiency, which is critical in CAD applications. The existing closed-form approximations for the surface potential are based on empirical smoothing functions and have the accuracy of about 2–3 mV which is not always adequate for an accurate modeling of MOSFET characteristics, especially transconductances and transcapacitances. In this work, we present and verify an extremely accurate and computationally efficient closed-form approximation, which can serve as a basis for advanced surface-potential-based MOSFET models.

Analytical approximation for the MOSFET surface potential

Analytical approximation for the MOSFET surface potential is important for the development of the computationally efficient surface-potential-based compact MOSFET models. In the previous work such an approximation was developed in the gradual channel approximation. Here we present an extended version which takes into account the lateral field gradient essential in small-geometry transistors.

T.L. Chen

Papers

Analytical approximation for the MOSFET surface potential

An extended analytical approximation for the MOSFET surface potential