A device oriented model is developed to describe the operation of the junction-gate field-effect transistor (FET) beyond pinch-off. The model is derived on the basis of a generalized structure with an arbitrary channel doping profile. It provides a qualitative and quantitative description of the current conduction mechanism, and is applicable over the entire dynamic range of device operation. Current conduction mechanisms in the vicinity of the source and the drain are examined separately. It is shown that the saturation of carrier drift velocities at high electric fields results in formation of a drain space-charge region of finite length. An approximate solution of the two-dimensional Poisson's equation is developed to describe the potential distribution within this region. A significant result of the device model is the prediction of a finite drain resistance in pinched operation, which shows a strong dependence on the device operation point.

General theory for pinched operation of the junction-gate FET

This paper presents an in-depth theoretical examination of graphene-based field effect transistors, looking at thermal statistics, electrostatics, and electrodynamics. Using a first principles approach, the unique behavior observed in graphene-based field effect transistors, such as the V-shaped transfer characteristic, limited channel pinch-off, and lack of off-state (under gate modulation), are described. Unlike previous attempts, a description of both drift and diffusion currents in the device is presented. The effect of external resistance on steady-state and high-frequency performance is examined. Comparisons of the theoretical results to experimental results are made and show good agreement. Finally, the theoretical work in this paper is used as a basis to discuss the possible source of some observed behavior in practical graphene-based field effect transistors.

A first principles theoretical examination of graphene-based field effect transistors

A model is developed for an ion-implanted MESFET device in terms of the range and straggle parameters of the Gaussian profile. Reasonable approximations are introduced to obtain a closed-form solution for the linear and triode regions of operation. Simplified square-law approximations are obtained under certain conditions and the validity of these forms is discussed. The simplified expressions are compared with those of the MOSFET and parallels are drawn. Data are presented to confirm the dc results of the theory over a wide range of implant parameters and demonstrate the value of the model for computer-aided design applications.

A device model for an ion-implanted MESFET

The small signal properties of field effect devices are treated analytically. The analysis is based upon an active, distributed transmission line analogy to the conductive channel of field effect devices. Within the limitations of the gradual channel approximation, a general analysis is presented which is applicable to both junction and MOS field effect devices. Equivalent circuits are obtained which describe field effect device characteristics in the region below saturation as well as in the current saturation region. Effects of parasitic elements on the terminal y parameters in practical devices are considered. Specific device models are considered for junction devices and MOS devices and the more important equivalent circuit parameters are evaluated in terms of the dc terminal voltages.

Small signal properties of field effect devices

An improved equivalent circuit model of a gallium-arsenide (GaAs) MESFET that is optimized for the design and analysis of precision analog integrated circuits is described. These circuits entail different modeling requirements from digital or microwave circuits, for which existing equivalent circuit models are optimized. Improved techniques are presented to model the drain-to-source conductance, device capacitance, and the functional dependence of drain-to-source current.

An improved GaAs MESFET equivalent circuit model for analog integrated circuit applications

Solutions of field effect equations in which carrier density and space-charge distributions are considered in general form show that the LF terminal characteristics are not strongly dependent on the shape of the distribution curves. General expressions for mutual transconductance, output conductance, junction capacitance and current amplification are derived as functions of the depletion layer thickness at the device boundaries. These expressions are not explicitly dependent on charge distribution. Relationships between the small-signal and dc terminal characteristics depend on the shape of the charge distribution curves but cannot be varied by more than a factor of two. The shape of the device is shown to have secondary importance.

R.R. Bockemuehl

Papers

Analysis of field effect transistors with arbitrary charge distribution