GaAs MESFET Model Research Articles

Enhanced GaAs MESFET CAD model for a wide range of temperatures

We describe a new and enhanced GaAs MESFET model suitable for implementation in computer aided design (CAD) software packages such as, for example, SPICE. The model accurately reproduces both above-threshold and subthreshold characteristics of GaAs MESFET's in a wide temperature range, from 77 K to 350/spl deg/C. The current-voltage characteristics are described by a single continuous, analytical expression for all regimes of operation. The physics-based model includes effects such as velocity saturation in the channel, drain induced barrier lowering, finite output conductance in saturation, bias dependent series source and drain resistances, effects of bulk charge, bias dependent average low-field mobility, frequency dependent output conductance, backgating and sidegating, and temperature dependent model parameters. The output resistance and the transconductance are also accurately reproduced, making the model suitable for analog CAD.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling MESFET's for inter-modulation analysis in RF switches

This paper describes a new model for a resistive GaAs MESFET and its application to calculations of intermodulation distortion in switches. The model uses an expression for the I/V characteristics of the device whose parameters are fit to the static I/V and its derivatives. This new model provides a reliable means of describing the nonlinear distortion generated by a MESFET switch.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Nonlinear integral modeling of dual-gate GaAs MESFET's

A nonlinear integral approach is adopted for the modeling of Dual-Gate GaAs MESFET's (DGFET's) in the framework of Harmonic-Balance circuit analysis. In particular, the model enables the computation of the large-signal performance of DGFET's directly on the basis of DC characteristics and small-signal bias-dependent admittance parameters without requiring complex procedures for parameter extraction. The validity of the approach is confirmed by accurate physics-based numerical simulations of a DGFET mixer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Considerations for improving the accuracy of large-signal GaAs MESFET models to predict power amplifier circuit performance

Several approaches to large-signal GaAs MESFET modeling are considered as they apply to the design of high-efficiency portable communications equipment. The validity of each modeling approach is examined by comparing simulations to the fundamental and harmonic output power of a MESFET using load pull to represent typical amplifier load lines. Two effects which are believed to influence model accuracy are considered: 1) low-frequency dispersion in output conductance, and 2) modulation of the threshold voltage as a function of drain-source voltage. The results suggest that improved modeling of the modulation in threshold voltage with respect to drain-source voltage provides significantly more accurate predictions. In contrast, for these applications, when conventional approaches for adding low-frequency dispersion effects to the model were implemented, inaccurate predictions resulted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Single event induced charge transport modeling of GaAs MESFETs

Two-dimensional computer simulations of charge collection phenomena in GaAs MESFETs have been performed for alpha and laser ionization. In both cases, more charge is collected than is created by the ionizing event. The simulations indicate that a bipolar transport mechanism (t<60 ps) and a channel modulation mechanism (t>40 ps) are responsible for this enhanced charge collection. The first mechanism is a bipolar type effect that injects charge into the bulk of the device and is collected at the drain due to the electric field. The second is a back channel turn-on mechanism that is associated with a positive hole density located beneath the channel and exists on a much longer time scale. These results show that electrons supplied by the source implant are responsible for charge collected at the drain in excess of any collected deposited charge.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

SIMULATION OF THE ELECTRICAL BEHAVIOUR OF GaAs MESFETS WITH DOPING AND LOW‐FIELD MOBILITY PROFILES IN THE ACTIVE LAYER

A quasi‐two‐dimensional analytical model for GaAs MESFETs is proposed. It enables the calculation of the dc, the small‐signal, and the noise behaviour of GaAs MESFETs and takes into account both doping and low‐field mobility profiles in the active layer of the transistor. It is shown that the profile of the low‐field mobility near the bottom of the active layer has a considerable influence on the minimum noise figure.

Non-quasi-static transient and small-signal two-dimensional modeling of GaAs MESFET's with emphasis on distributed effects

The operation of micron and submicron GaAs MESFETs under high-speed transient and high-frequency small-signal conditions is analyzed using a two-dimensional model. The effects of displacement currents, dipole due to negative differential mobility or current continuity, and two-dimensional transport are emphasized. The origin of delay effects, such as the phase delay incorporated in small-signal models, is explored in order to relate it to the behavior under switching conditions. Broadband expressions for the extraction of a complete small-signal model are presented. Using the expressions derived, the variation of model elements with frequency and the effect of this on the unilateral gain of the device are studied.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Yield optimization using a GaAs process simulator coupled to a physical device model

A physics-based large-signal GaAs MESFET model and circuit simulator has been developed to predict and optimize the yield of GaAs MESFET designs before fabrication. Device acceptance criteria include both small- and large-signal RF operating characteristics such as small-signal gain, maximum power added efficiency, and output power at 1-dB gain compression. Channel doping details are described on the basis of processing specifications for parameters such as material deposition, ion implantation, and implant annealing. Monte Carlo techniques are used to estimate yield when disturbances in the physical parameters are modeled as multivariate Gaussian distributions. The yield estimator is integrated with an optimizer so that a design can be centered for maximum yield in the presence of process disturbances.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A large-signal GaAs MESFET model for nonlinear circuit simulation

A GaAs MESFET large-signal model suitable for use in time-domain circuit simulation CAD tools such as PSPICE has been developed. The improved model includes accurate analytic representation of the transconductance and conductance dependence upon the operating voltages. The new model gives better fit to GaAs MESFET I-V characteristics over a wider bias voltage range compared with the Curtice quadratic model. It also provides a simpler and more efficient parameter acquisition procedure in comparison to the TriQuint model. The procedure for extracting the model parameters using the bias dependence of the small-signal elements is also described. >

Comments on "A self-backgating GaAs MESFET model for low-frequency anomalies

For the original article see ibid., vol.37, no.10, p.2148-57 (1990). The commenter maintains that some basic equations of the model in the above-titled paper by M. Lee and L. Forbes are questionable. Particularly, the development of the equations for calculating the small-signal output conductance is questioned.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Simulation and Modeling-implementing GaAs device models with SPICE

A method for evaluating the accuracy of a device model and its tendency toward convergence problems before implementing it as a SPICE primitive is presented. Two different GaAs MESFET models suitable for analyzing nonlinear analog and microwave circuits are implemented using generic SPICE primitives. It is shown that no modification to the SPICE program is required. Controlled sources are extensively used in implementing the models using this method.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Five-parameter DC GaAs MESFET model for nonlinear circuit design

An improved gallium arsenide (GaAs) MESFET model for nonlinear large-signal circuit design is described, together with the parameter estimation and optimisation techniques. The new model is based on the work of Curtice and offers significant advantages in the simulation of the device in the low-current region. This is achieved by modelling the bias dependency of the pinch-off voltage. Data showing the bias dependency of the device model parameters is provided and a comparison between the new model, the Curtice model and the Schichman-Hodges FET model is made, with the use of a wide variety of different size devices. The software modules for the automated characterisation and modelling of GaAs devices are also described.

Power law GaAs MESFET model

A power law model for the GaAs MESFET is presented. It is shown that the model is applicable to MESFETs with high or low pinch-off voltages by simply varying the exponent of the power law term. The model parameters are quickly and easily obtained by a straightforward characterization process. The model was implemented in a GaAs integrated circuit simulator and used to simulate device current-voltage characteristics. >

Novel and accurate compact DC model of GaAs MESFET for large-signal computer calculations

In this Letter, a novel MESFET model in a form suitable for implementation in nonlinear circuit simulators is presented. The proposed model not only covers the entire areas of the DC curves of the device, but its modelling parameters can also be extracted easily with no need for optimisation codes. Results show that the proposed model solves the severe problem of fitting the device in the depth of the pinch-off region (the general problem of all the published models with no exception, even for the most popular used by Curtice). Typical CPU times for evaluating the modelling parameters for the commercial chip NEC71000 device using our model and Curtice&apos;s are in the range of 1 : 25.

A diffusion model of subthreshold current for GaAs MESFETs

A subthreshold current model for GaAs MESFETs with arbitrary channel doping profile is derived based on carrier diffusion in the depleted channel. Within the subthreshold regime, the gate voltage creates a potential barrier inside the depleted channel for electrons. Electrons are injected across the barrier from source electrode into the channel, and subsequently diffuse to the drain electrode. Excellent agreement has been obtained between the model and measured data on ion-implanted GaAs MESFETs for different gate lengths, various drain and gate bias conditions, and operating temperatures from 100 to 350 K. Our physical model also agrees well with the published empirical model and has identified the relationship between the model fitting parameters and the device physical parameters.

MESFET models for microwave CAD applications

AbstractA review of active device models for microwave CAD simulators is presented. Large‐signal, nonlinear models are of particular interest. The basic techniques employed in deriving equivalent circuit and physically based models are reviewed. Various methods for solving the semiconductor device equations to establish physically based models are indicated. Finally, it is proposed that physically based, analytic GaAs MESFET models offer an attractive compromise between simulation efficiency and quantitative accuracy. The use of such a model is demonstrated by several examples, including comparison with experimental data. These models are suitable for use in comprehensive CAD workstation environments and allow process‐type device models to be interfaced directly with RF circuit simulators.

An improved GaAs MESFET model for SPICE

A SPICE model for modeling GaAs MESFET devices more accurately is discussed. In particular, small-signal parameters are accurately modeled over a wide range of bias conditions. These results were achieved by modifying the model equations of H. Statz et al. (see IEEE Trans. Electron. Devices, vol.3, no.2, p.160-9, 1987) to better represent the variation of I/sub ds/ as a function of the applied voltage. The model applies over a large range of pinch-off voltages, allows size scaling of devices, and is suited for modeling R/sub ds/ changes with frequency. The Statz equations are used to represent diode characteristics and capacitive components of the model. >

A self-backgating GaAs MESFET model for low-frequency anomalies

A self-backgating GaAs MESFET model which can simulate low-frequency anomalies has been developed by including deep-level trap effects. These cause transconductance reduction due to electron emission from EL2 in the depletion width change at the edge of the Schottky gate junction and the output conductance to increase due to the time-dependent net negative charge concentration in the semi-insulating substrate as a result of self-backgating with the applied signal frequency. This model has been incorporated in PSPICE and includes a time-dependent I-V curve model, a capacitance model, an RC network describing the effective substrate-induced capacitance and resistance, and a switching resistance providing device symmetry. An analytical capacitance model describes the dependence of capacitance on V/sub gs/ and V/sub ds/ and includes the channel-substrate junction modulation by the self-backgating effect. A transit-time delay is also included in the transconductances, g/sub m/ and g/sub mbs/, for model accuracy and to describe the phase shift of S-parameters. Measured data correspond to simulations by this model of the low-frequency anomalous characteristics, voltage-dependent capacitances, and S-parameters of conventional GaAs MESFETs for linear and microwave circuit design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Quasi-two-dimensional MESFET simulations for CAD

A comprehensive quasi-two-dimensional simulation that has been applied to the design and modeling of submicrometer recessed-gate GaAs MESFETs is described. A detailed energy transport model using a fast and accurate algorithm is solved. The model accounts for avalanche breakdown and gate conduction. DC and microwave characteristics are obtained from the model. An accurate approach for simulating frequency-, amplitude-, and bias-dependent two-port RF parameters is described, and the results obtained are compared to measured data. The agreement between measured and predicted data is found to be excellent. >

Intrinsic GaAs MESFET equivalent circuit models generated from two-dimensional simulations

An accurate, physically based two-dimensional GaAs MESFET model is used to generate small-signal and large-signal equivalent circuit models useful for the evaluation of GaAs device structures and GaAs integrated circuits. The models and the simulation techniques described provide a useful means of evaluating RF performance on the basis of the physical properties of the FET. As an example, the small- and large-signal device characteristics are evaluated as a function of drain-source bias voltage and lattice temperature for a 0.8- mu m gate length FET. The small-signal results show severe degradation of frequency response with increase of drain-source bias voltage because of a high electric field in the conduction channel. The large-signal results show that the decrease in RF power capability with temperature increase is primarily due to declining current capability with temperature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>