A simple noise model of a microwave MESFET (MODFET, HEMT, etc.) is described and verified at room and cryogenic temperatures. Closed-form expressions for the minimum noise temperature, the optimum generator impedance, the noise conductance, and the generator-impedance-minimizing noise measure are given in terms of the frequency, the elements of a FET equivalent circuit, and the equivalent temperatures of intrinsic gate resistance and drain conductance to be determined from noise measurements. These equivalent temperatures are demonstrated in the case of a Fujitsu FHR01FH MODFET to be independent of frequency in the frequency range in which 1/f noise is negligible. Thus, the model allows prediction of noise parameters for a broad frequency range from a single frequency noise parameter measurement. The relationships between this approach and other relevant studies are established. >

Modeling of noise parameters of MESFETs and MODFETs and their frequency and temperature dependence

The high electron mobility transistor's (HEMT's) noise behavior is presented from theoretical and experimental points of view. The general method used in the high-frequency noise analysis is described and the different approximations commonly used in the derivation of the noise parameter expressions are discussed. A comparison between the noise performance of both MESFETs and HEMTs is carried out. The measurement techniques providing the noise figure and the other noise parameters are then described and compared. >

Noise modeling and measurement techniques (HEMTs)

This is a review of developments and milestones in the FET and HFET field, including experimental results compared to model predictions. The noise performance of cryogenic FETs and HFETs has made tremendous progress over the last several decades. The most rapid advances seem to have occurred between 1980 and 1995. Three different generations of HFETs were proposed and reduced to practice during that period. Since 1995, no significant new ground has been broken in device technology. However, InP HFET technology has matured and allowed construction of extremely low-noise amplifiers. These amplifiers were used in the construction of several instruments for the investigation of the physics of the early universe.

Extremely low-noise amplification with cryogenic FETs and HFETs: 1970-2004

A simple three-terminal technique for measuring the off-state breakdown voltage of FETs is presented. With the source grounded, current is injected into the drain of the on-state device. The gate is then ramped down to shut the device off. In this process, the drain-source voltage rises to a peak and then drops. This peak represents an unambiguous definition of three-terminal breakdown voltage. In the same scan, a measurement of the two-terminal gate-drain breakdown voltage is also obtained. The method offers potential for use in a manufacturing environment, as it is fully automatable. It also enables easy measurement of breakdown voltage in unstable and fragile devices. >

A new drain-current injection technique for the measurement of off-state breakdown voltage in FETs

A detailed full-wave time-domain simulation model for the analysis of electromagnetic effects on the behavior of the submicrometer-gate field-effect transistor (FET's) is presented. The full wave simulation model couples a three-dimensional (3-D) time-domain solution of Maxwell's equations to the active device model. The active device model is based on the moments of the Boltzmann's transport equation obtained by integration over the momentum space. The coupling between the two models is established by using fields obtained from the solution of Maxwell's equations in the active device model to calculate the current densities inside the device. These current densities are used to update the electric and magnetic fields. Numerical results are generated using the coupled model to investigate the effects of electron-wave interaction on the behavior of microwave FET's. The results show that the voltage gain increases along the device width. While the amplitude of the input-voltage wave decays along the device width, due to the electromagnetic energy loss to the conducting electrons, the amplitude of the output-voltage wave increases as more and more energy is transferred from the electrons to the propagating wave along the device width. The simulation confirms that there is an optimum device width for highest voltage gain for a given device structure. Fourier analysis is performed on the device output characteristics to obtain the gain-frequency and phase-frequency dependencies. The analysis shows a nonlinear energy build-up and wave dispersion at higher frequencies.

Electromagnetic wave effects on microwave transistors using a full-wave time-domain model

Noise modeling in TEGFET's which provides good results in agreement with the experimental findings is presented. The influence of the main technological parameters on the noise figure and associated gain is given for operating frequencies up to 60 GHz. A comparison between TEGFET's and MESFET's is carried out. A new method for calculating the noise and gain performances of FET's is then proposed.

Noise modeling in submicrometer-gate two-dimensional electron-gas field-effect transistors

Using a two-dimensional hydrodynamic energy model incorporating nonstationary electron dynamics and nonisothermal electron transport (which characterizes submicron-gate MODFETs), the main physical phenomena that govern the device performance at 300 K are highlighted. This covers velocity overshoot effects, stationary-domain formation, and real space transfer. The model is then used systematically to predict the precise values of the small-signal parameters for different bias conditions. The potential performance improvement achieved by reducing the gate length below 0.2 mu m is investigated. It is shown that improvement in transconductance is achieved through gate-length reduction if a severe restriction on the aspect ratio is respected. >

MODFET 2-D hydrodynamic energy modeling: optimization of subquarter-micron-gate structures

A novel 2-D numerical model incorporating nonstationary electron dynamics is used to investigate the complex transport phenomena governing the operation of sub-micron gate GaAs MESFET's. A detailed theoretical analysis of different phenomena observed in subhalf micron devices is given. These include velocity overshoot, stationary and travelling domain formation, soft pinch off, excess drain current etc. The small signal parameters g m , g d and C gs and their dependence on bias condition are evaluated. The effects of physical quantities such as mobility and interface barrier on carrier injection and transport and consequently on device performance are presented.

Performance analysis of sub-micron gate GaAs MESFETs

Heterojunction IMPATT diodes make it possible to produce new high conversion efficiency devices, combining a low bandgap semiconductor for the avalanche zone with a large bandgap material for the drift region. In this study, the heterojunction GaInAs/InP which seems particularly attractive is used in various structures. The theoretical predictions of performances are determined by a computer simulation which takes into account the main limitation effects of IMPATT diodes and the influence of particular physical phenomena due to the use of heterojunctions and semiconductors, mainly the influence of injection currents. Potential performances of the proposed structure appear very attractive especially in the millimeter-wave range using a MITATT mode (Mixed-Tunneling-Avalanche-Transit-Time) by combining tunneling current and avalanche multiplication injections.

High efficiency GaInAs/InP heterojunction IMPATT diodes

Analytical formulas for the intrinsic noise sources of both MESFET's and TEGFET's are derived from a numerical noise modeling. Using these expressions the calculated noise figure is in good agreement with experimental findings. The influence of gd and Cgd on the noise figure is then pointed out and a comparison between the kf factor of MESFET's and TEGFET's is presented.

G. Salmer

Papers

Noise modeling in submicrometer-gate two-dimensional electron-gas field-effect transistors

MODFET 2-D hydrodynamic energy modeling: optimization of subquarter-micron-gate structures

Performance analysis of sub-micron gate GaAs MESFETs

High efficiency GaInAs/InP heterojunction IMPATT diodes

A new method for calculating the noise parameters of MESFET's and TEGFET's