Short-channel MESFETs Research Articles

A new model of noise characteristics of SiC Schottky barrier MESFET with deep impurity levels and traps

Noise characteristics of silicon carbide Schottky barrier field effect transistors (MESFET) are examined for the case of the operation in small-signal regime and the presence of deep impurity levels and electron traps in the band gap of the channel. A new model of calculations of noise is suggested. It is shown that the noise measure of the short channel MESFET can be decreased within certain high frequency range.

Noise as a diagnostic tool for quality and reliability of electronic devices

Experimental facts about noise are presented which help us to understand the correlation between noise in a device and its reliability. The main advantages of noise measurements are that the tests are less destructive, faster and more sensitive than DC measurements after accelerated life tests. The following topics are addressed: 1) the kind of noise spectra in view of reliability diagnostics such as thermal noise, shot noise, the typical poor-device indicators like burst noise and generation-recombination noise and the 1/f/sup 2/ and 1/f noise; 2) why conduction noise is a quality indicator; 3) the quality of electrical contacts and vias; 4) electromigration damage; 5) the reliability in diode type devices like solar cells, laser diodes, and bipolar transistors; and 6) the series resistance in modern short channel MESFET, MODFET, and MOST devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An analytical threshold voltage and subthreshold current model for short-channel MESFETs

Short-channel effects on the subthreshold behavior are modeled in self-aligned gate MESFETs with undoped substrates through an analytical solution of the two-dimensional Poisson equation in the subthreshold region. Based on the resultant potential solution, simple and accurate analytical expressions for short-channel threshold voltage, subthreshold swing, and subthreshold drain current are derived. These are then used to develop an expression for minimum acceptable channel length. A comparative study of the short-channel effects in MESFETs with doped and undoped substrates indicates that channel lengths will be limited to 0.15-0.2 mu m by subthreshold conduction. Besides offering insight into the device physics of the short-channel effects in MESFETs, the model provides a useful basis for accurate analysis and simulation of small-geometry GaAs MESFET digital circuits. >

Optically controlled current-voltage characteristics of ion-implanted MESFETs

Optically controlled MESFETs are useful as optical devices for optical communications, and as photodetectors. In this paper, a theoretical model for the I– V characteristics of these MESFETs is presented. The model considers the nonuniform Gaussian doping for ion-implanted channels. It takes both the photogenerated carriers as well as the doping generated residual carriers into account. It is noted that the density of photogenerated carriers in the channel due to diffusion is much less than that due to drift. Treatment both under gradual channel approximation and saturation velocity approximation has been presented. The gradual channel and the velocity saturation approximations are applied to study the I– V characteristics of long-channel and short-channel MESFETs, respectively. Results for both long-channel and short-channel MESFETs indicate that drain saturation current and transconductance can be improved by properly fixing the optical flux, and the absorption coefficient of the material.

Source and drain resistance studies of short-channel MESFETs using two-dimensional device simulators

A method for calculating the parasitic source and drain resistances in MESFETs using two-dimensional device simulators is discussed. The source and drain resistances are calculated using the power dissipation and the electron heating in the parasitic resistance regions of the device structure. The parasitic resistances are calculated as a function of both the gate and the drain bias voltages. The resistance calculation method for MESFETs has been applied to three semiconductor device simulators: a drift-diffusion method simulator, an energy transport method simulator, and a Monte Carlo particle method simulator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-performance short-channel MESFETs with WSiN gate suppressing As-outdiffusion (SAINT-GEN.II)

The formation of a highly conductive channel, which is one of the most effective methods to achieve high-performance GaAs MESFETs, requires that As-outdiffusion during high-temperature annealing be suppressed, because As vacancy creates more implanted Si acceptors, decreasing channel conductance. A refractory metal, WSiN, that effectively suppressing As-outdiffusion has been applied in an n/sup +/-self-aligned ion-implantation MESFET technology (SAINT-GEN.II), and the performance of the fabricated FETs experimentally evaluated. The device structure studied had a 10-keV implanted shallow channel with a buried p-layer and an Au-coated WSiN gate. A 630 mS/mm maximum transconductance at gate voltage of 0.6 V and 510 mS/V-mm K-value at threshold voltage of -0.14 V were obtained. A 920 mS/mm intrinsic transconductance was estimated from source resistance of 0.51 Omega -mm. The gate resistance was as small as 3 mu Omega -cm. A cutoff frequency as high as 96 GHz was obtained by extrapolating the current gain of 0.5 to 25.5 GHz at the correct 6 dB/octave. The effective saturation velocity is estimated at 1.8*10/sup 7/ cm/s. This represents an 80% improvement of velocity overshoot compared to long-gate MESFETs. The characteristics of a 23-stage ring oscillator using direct-coupled FET logic (DCFL) circuits with a propagation delay time of 6.7 ps/gate have also been investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Monte Carlo particle simulation of a GaAs short-channel MESFET

A Monte Carlo particle simulation of a 0.25 μm-long gate (and 0.25 μm-long channel) GaAs MESFET having a practical doping density and sitting on a substrate is carried out. Extremely high values of gm and Idss of 643 mS/mm and 5.35 mA/20 μm were obtained. The near-ballistic nature of the electron transport in the FET was confirmed.

Physical basis of short-channel MESFET operation II: Transient behavior

The large-signal switching behavior of planar short-channel metal-semiconductor field-effect transistors (MESFET's) is simulated numerically. First, the intrinsic response of the MESFET is simulated in two space dimensions and time, using measured electric-field-dependent drift velocities and diffusivities in the conventional semiconductor equations; results of the intrinsic device simulations are then used to study the circuit behavior of Si and GaAs MESFET's in two-input NOR circuits. Although the simulated 1-µm-gate Si and GaAs MESFET's have intrinsic response times of 11 and 9 ps to a gate pulse of - 2 V, for fan-in and fan-out = 2, the Si and GaAs NOR gates have average gates delays of 318 and 118 ps, respectively, for 1-µm gate lengths. The power-delay products for these 1-µm-gate Si and GaAs circuits are 1.8 and 1.5 pJ, respectively. These results are compared with measured data and their physical basis is discussed.

Physical basis of short-channel MESFET operation

MESFETs made of Si, GaAs and InP have been numerically analyzed in two dimensions using the Cornell University Program for Integrated Devices, in order to give physical insight into MESFET operation. Equilibrated electron drift velocity-versus-electric field characteristics and field-dependent anisotropic diffusivities are used in the analysis. Predicted figures of merit, such as cutoff frequency and gate-source capacitance, are compared with experimental results obtained by other authors. Electron transit time, and hence f/SUB T/, in 0.5- and 1.0-/spl mu/m-gate Si, GaAs, and InP FETs is shown to be largely unrelated to the value of low-field mobility in these materials at drain voltages in excess of 1 V. The results relate to the choice of materials for devices in both VLSI digital circuits and microwave linear circuits.

Physical basis of short-channel MESFET operation

Metal-semiconductor field-effect transistors (MESFET's) made of Si, GaAs, and InP have been numerically analyzed in two dimensions using the Cornell University Program for Integrated Devices (CUPID), in order to give physical insight into MESFET operation. Equilibrated electron drift velocity-versus-electric field characteristics and field-dependent anisotropic diffusivities are used in the analysis. Predicted figures of merit, such as cutoff frequency and gate-source capacitance, are compared with experimental results obtained by other authors. Electron transit time, and hence f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> , in 0.5- and 1.0-µm-gate Si, GaAs, and InP FET's is shown to be largely unrelated to the value of low-field mobility in these materials at drain voltages in excess of 1 V. The results relate to the choice of materials for devices in both VLSI digital circuits and microwave linear circuits.