GaAs MESFET Model Research Articles

Physical modeling of GaAs MESFETs in an integrated CAD environment: from device technology to microwave circuit performance

The linkage between a physical device simulator for small- and large-signal characterization and CAD (computer-aided design) tools for both linear and nonlinear circuit analysis and design is considered. Efficient techniques for the physical DC and small-signal analysis of MESFETs are presented. The problem of physical simulation in a circuit environment is discussed, and it is shown how such a simulation makes possible small-signal models accounting for propagation and external parasitics. Efficient solutions for physical large-signal simulation, based on deriving large-signal equivalent circuits from small-signal analyses under different bias conditions, are proposed. The small- and large-signal characterizations allow physical simulation to be performed efficiently in a circuit environment. Examples and results are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GaAs MESFET model for circuit simulation

Abstract This paper describes a generalized circuit model for GaAs MESFETs. The novel features of the model include continuous descriptions for the intrinsic FET, Schottky diode and inter-electrode capacitance, valid both above and below device threshold. The model also displays good agreement with HEMT characteristics.

A new model for the dual-gate GaAs MESFET

The development of a novel GaAs dual-gate MESFET model suitable for the design and analysis of microwave circuits is described. This quasi-two-dimensional physical model is numerically efficient due to a unique formulation of the carrier transport equations. The model includes a comprehensive description of the geometric and material parameters accounting for recess structures, nonuniform doping profiles, current injection into the buffer layer, forward-biased gate conduction, and surface depletion. The accuracy of the model under DC, small-signal, and large-signal operating conditions is assessed by comparing simulated and measured performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Efficient large-signal FET parameter extraction using harmonics

An accurate and truly nonlinear large-signal parameter extraction approach is presented, using not only DC bias and fundamental frequency but also higher harmonic responses. The harmonic balance method for nonlinear circuit simulation, adjoint analysis for nonlinear circuit sensitivity calculation, and state-of-the-art optimization methods are applied. Improvements to the convergence of the optimization process are discussed. An automatic weight assignment algorithm enhancing parameter extraction is given. Numerical results demonstrate that the method is both theoretically and computationally feasible, i.e. it can uniquely and efficiently determined the parameters of the nonlinear elements of the GaAs MESFET model under actual large-signal operating conditions. Numerical results also show that under multibias, multipower inputs, and multifrequency excitations, spectrum measurements can effectively reflect the nonlinearities of the model and improve model reliability when they are used in nonlinear large-signal-model parameter extraction. >

Nonlinear GaAs MESFET modeling using pulsed gate measurements

The effects of traps in GaAs MESFETs are studied using a pulsed gate measurement system. The devices are pulsed into the active region for a short period (typically 1 mu s) and are held in the cutoff region for the rest of a 1-ms period. While the devices are on, the drain current is sampled and a series of pulsed gate I-V curves are obtained. The drain current obtained under the pulsed gate conditions for a given V/sub GS/ and V/sub DS/ gives a better representation of the instantaneous current for a corresponding V/sub gs/ and V/sub ds/ in the microwave cycle because of the effects of traps. The static and pulsed gate curves were used in a nonlinear time-domain model to predict harmonic current. The results showed that analysis using pulsed gate curves yielded better predictions of harmonic distortion than analysis based on conventional state I-V curves under large-signal conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A low-frequency GaAs MESFET circuit model

GaAs MESFETs exhibit low-frequency anomalies which effect the performance of broadband systems. A four-terminal large-signal GaAs MESFET circuit model which predicts may of the low-frequency anomalies discovered in GaAS MESFETs is proposed. The four-terminal model accurately models 'drain lag', frequency dependence of the output resistance, and hysteresis. This model when implemented in a circuit analysis program will enable circuit designs to predict which circuit topologies will be more or less sensitive to the GaAs low-frequency anomalies. >

GaAs MESFET modeling and nonlinear CAD

Equivalent circuit modeling techniques are described for both small-signal and large-signal models of GaAs MESFETs. The use of large-signal model in an interactive program for amplifier analysis is shown. The computed load-pull results and IMD (intermodulation distortion) predictions are shown to be in good agreement with measured data at 10 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A MESFET model for the design of GaAs digital integrated circuits

AbstractAs in the case of Si IC's, it is important to carry out circuit simulation in the development of GaAs digital IC's. This paper discusses a GaAs MESFET model for digital IC design. Since in the Shichman‐Hodges model the parameters are obtained only for the saturation region of the drain current, the model is not accurate in the nonsaturation region. Therefore, we utilized additional parameters in the model for the nonsaturation region to increase accuracy. Approximating the potential distribution in an MESFET channel by that in the MOSFET model, the internal capacitance was obtained analytically as a function of the gate and drain voltages. Using the model obtained as described in the foregoing, the transfer characteristic and operational speed of the DCFL circuit were calculated and the results were in excellent agreement with the experimental results.

Quasi-two-dimensional modeling of GaAs MESFET's

A numerical simulation of GaAs MESFET structures is presented. The approach taken in this paper combines an analytical solution with a full simulation. Poisson's equation, the current continuity equation, and an electron-temperature equation are formulated in terms of a geometry factor that defines the shape of the conducting channel in the MESFET. The transport equations are then solved in one dimension and the channel geometry factor is found analytically. This method was found to be considerably faster than full two-dimensional simulations. The model has been compared to full two-dimensional drift-diffusion and energy-momentum results to determine its validity.

Modeling and characterization of ion-implanted GaAs MESFET's

Accurate modeling of GaAs IC's requires a good fit to the device characteristics over the entire range of gate and drain voltages. However, the existing circuit simulator models suitable for circuit simulation fail in the linear region of the current-voltage characteristics. In this paper, we demonstrate that the nonuniformity of the mobility and doping profiles strongly affects the linear region and propose an analytical model taking this nonuniformity into account. We also present the characterization techniques that relate the model parameters to the device physics and the fabrication methods. Excellent agreement with experimental data is obtained and the model is implemented into our GaAs IC circuit simulator.

A subthreshold current model for GaAs MESFET's

A GaAs MESFET model capable of accurately describing currents in the subthreshold region is described. The model is based on the concept of drain-induced barrier lowering (DIBL) together with the reverse-bias Schottky diode conduction. Agreement between measured and calculated data based on this model was excellent.

Modelling the DC characteristics of GaAs MESFETs for CAD

An empirical formula is presented for the current-voltage characteristics of the GaAs MESFET. The three parameters of the formula can be easily obtained from separate regions in the device DC characteristics. By using this formula the implementation of a new GaAs MESFET model into the source code of SPICE is feasible.

Analytical modeling of the stationary domain in GaAs MESFET's

A theory for stationary domains in GaAs MESFET's is presented. To the lowest order of approximation the theoretical predictions of maximum domain field and domain voltage agree with those for stable, propagating domains in highly doped Gunn diodes. On the basis of model expressions for the field and impurity dependence of the drift velocity and of the diffusion coefficient, analytical expressions are derived for maximum field, voltage, capacitance, and shape of large and small domains. Specific calculations are performed for channel dopings of interest in GaAs MESFET's. The results are of direct interest in the modeling of GaAs MESFET's and integrated Circuits.

Modeling of ion-implanted GaAs MESFET's by the finite-element method

We discuss the results of a new two-dimensional (2-D) finite-element model for GaAs MESFET's made by ion implantation. Several different devices are characterized by varying gate recess and doping profile. The simulation, in qualitative agreement with experimental findings, shows that a FET with a shallow gate recess exhibits a similar behavior to a FET with a deep implantation, i.e., an improvement in linearity, a higher pinch-off voltage, and a decrease in transconductance.

A large-signal GaAs MESFET model implemented on SPICE

A device model that predicts large-signal GaAs MESFET performance has been implemented on the large-scale circuit simulation program SPICE. The model takes into consideration drift velocity saturation, channel length modulation, and subthreshold current effects. In addition, the model depends primarily on physical (i.e. material and geometric) rather than empirical parameters. Combined with the SPICE program, a general CAD tool is formed which can be used to aid in the design of GaAs circuits such a power amplifiers, oscillators, mixers, and fast-switching digital integrated circuits. Model predictions are compared to measured device performance, and limitations of this large-signal circuit design approach are discussed.

A capacitance model for GaAs MESFET's

We present a new analytical model for small signal capacitances of GaAs MESFET's. This model may be used for epitaxially grown as well as ion-implanted FET's because the effects related to the nonuniform doping profile are included. We also take into account backgating, capping, velocity saturation in the conducting channel, and possible Gunn domain formation in the channel at the drain side of the gate. The model explains complicated voltage dependences of the gate-source and gate-drain capacitances of GaAs microwave FET's and is in fair agreement with the experimental results. This analytical model is quite suitable for the computer-aided design of GaAs microwave FET's and integrated circuits.

GaAs MESFET with lateral non-uniform doping

Abstract An analytical model of the GaAs MESFET with arbitrary non-uniform doping is presented. Numerical results for a linear lateral doping profile are given as a special case. Theoretical considerations predict that better device linearity and improved FT can be obtained by using linear lateral doping when doping density increases from source to drain

New modeling of GaAs MESFET's

A first theoretical analysis is given based on a new model of GaAs MESFET's which considers the inherent effects of a free-surface depletion layer between source and gate as well as between gate and drain. Change of surface potential according to the input gate voltage causes variable series resistance and variable gate capacitance to be added to the intrinsic FET. The parasitic effects are now quantitatively estimated and an improved guideline for the design and the fabrication process is given. Detailed calculation of the effects of device parameters for recessed gate structure and some comments on the optimization of n+-layers in self-aligned structure are included. The effects of the interfacial depletion layer between active layer and substrate is also estimated in terms of drain voltage and the ratio of total deep levels density in the substrate to donor density in the active layer.

Accurate modeling for submicrometer-gate Si and GaAs MESFET's using two-dimensional particle simulation

Device characteristics, including nonstationary carrier-transport effects such as velocity overshoot phenomena in submicrometergate Si and GaAs MESFET's, are presented in detail by two-dimensional full Monte Carlo particle simulation. Accurate current-voltage characteristics and transient current response are successfully obtained without relaxation time approximation. Moreover, the carrier dynamics influence on device operation is clarified in a realistic device model, compared with the conventional simulation. It can be pointed out that such nonstationary carrier transport is acutely important for accurate modeling of submicrometer-gate GaAs MESFET's, but is not as important for that of Si MESFET's.

Nonlinear lumped circuit model of GaAs MESFET

A nonlinear lumped Circuit model for GaAs MESFET which includes the effect of Gunn-domain formation under the gate, mobility modulation, and diffusion process in the channel boundary is presented. The important design parameters such as C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</inf> , <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g_{m}, I_{dsat}</tex> , and F <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> , etc. can be derived from the model. The model not only predicts realistically the nonlinear <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</tex> characteristics, but it also provides a closed form design criterion for avoiding instability due to Gunn oscillation. Moreover, a small-signal Circuit model having the same basic circuit structure as the existing empirical small-signal model in [2], [10], [14] can be derived from this nonlinear model. In addition, a two-segment piecewise-linear dc model is derived. This piecewise-linear model contains only four model parameters which can be determined very easily by measurement. Because of its simplicity, this model can be implemented into any CAD system to simulate complex circuits with significantly less CPU time. The simulation results are in excellent agreement with experimental data, and with results obtained by a much more time-consuming two-dimensional calculation.