Walter R. Curtice

A temperature model for the GaAs MESFET

This paper describes a new two-dimensional method for study of GaAs Schottky-barrier MESFETs. A modified form of the conduction current is used in which transport properties are described in terms of electron temperature rather than electric field. Nonequilibrium velocity effects such as velocity overshoot are included. Results for the one-dimensional GaAs diode and the two-dimensional GaAs MESFET are presented and compared to other studies that utilize the Monte Carlo procedure. Larger values of current cut-off frequency are predicted for submicrometer gate length MESFETs than in previous two-dimensional simulations which utilize the steady-state transport properties.

Pulsed laser-induced single event upset and charge collection measurements as a function of optical penetration depth

We use picosecond laser pulses to investigate single event upsets and related fundamental charge collection mechanisms in semiconductor microelectronic devices and circuits. By varying the laser wavelength the incident laser pulses deposit charge tracks of variable length, which form an approximation to the charge tracks resulting from high energy space particle strikes. We show how variation of the charge track length deposited by laser pulses allows the mechanisms of charge collection in semiconductor devices to be probed in a sensitive manner. With the aid of computer simulations, new insight into charge collection mechanisms for metal–semiconductor field effect transistor (MESFET) devices and heterojunction bipolar transistor devices is found. In the case of the MESFET we point out the correlation between charge collection in the device and the ensuing single event upset in the composite circuit. In favorable cases, we show how probing circuits with tunable laser pulses can estimate a charge collectio...

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 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. >

SIGNIFICANT REDUCTION IN THE SOFT ERROR SUSCEPTIBILITY OF GAAS FIELD-EFFECT TRANSISTORS WITH A LOW-TEMPERATURE GROWN GAAS BUFFER LAYER

The use of a low temperature grown GaAs buffer layer beneath the channel of a metal‐semicon‐ ductor field‐effect transistor is shown via computer simulation to reduce ion‐induced charge collection by two or more orders of magnitude. This reduction in collected charge is expected to reduce the heavy ion soft error rate by four to seven orders of magnitude in GaAs integrated circuits, and could have significant implications for the applicability of GaAs technology in space‐based systems.

Charge-enhancement mechanisms of GaAs field-effect transistors: Experiment and simulation

The charge-collection processes of GaAs field-effect transistors are investigated as a function of the incident laser pulse energy via time-resolved charge-collection measurements and by two-dimensional computer simulation. The measurements and simulations reveal a feature that persists on a time scale of 100 ps, the amplitude of which varies strongly with the injected carrier density (pulse energy). The appearance of this feature is associated with a barrier lowering effect at the source/substrate junction, coupled with the drift-assisted transport of electrons through the substrate to the drain contact. This behavior is similar, but not identical to bipolar-gain models that have been suggested previously. We introduce the concept of ion-track segments and illustrate their utility in interrogating the complex mechanisms of charge collection and enhancement in GaAs FETs.

The performance of submicrometer gate length GaAs MESFET's

The influence of gate length, active layer thickness, and buffer layer current upon the steady-state and RF parameters of short gate length GaAs MESFETs is investigated using a two-dimensional model that accounts for electron energy relaxation effects. For devices of similar pinchoff voltage, the saturation currents are approximately the same, but the presence of substrate conduction in a device greatly reduces its transconductance and gain-bandwidth product. The effect upon frequency response due to gate length, donor profile, gate resistance, and source inductance is numerically evaluated. The model is shown to be in reasonable agreement with measured submicrometer device characteristics.

Charge-collection characteristics of GaAs MESFETs fabricated with a low-temperature grown GaAs buffer layer: computer simulation

Two-dimensional device simulations of GaAs MESFETs fabricated with a low-temperature grown GaAs (LT GaAs) buffer layer reveal a sensitive dependence of the charge-collection characteristics on various structural and operational parameters. Simulations performed for above-band-gap pulsed laser excitation indicate that, even when the bulk of the charge is deposited above the LT region, the improved SEU and charge-collection performance of LT GaAs devices largely is a consequence of the reduced efficiency of the carrier-induced charge-enhancement (gain) mechanisms.

Design, fabrication, and evaluation of 2- and 3-bit GaAs MESFET analog-to-digital converter IC's

the analog-to-digital converter (A/D) is a critical component of a signal processing system. GHz-rate A/Ds will be required in many future systems. While Si bipolar based A/Ds can easily meet 4-6-bit resolution requirements, excessive power dissipation (1 W per bit) limits their operation to 100-400-MHz sampling rates. Recently, GaAs MESFETs have demonstrated high frequency operation with relatively low power dissipation. This paper describes the design of 2- and 3-bit A/Ds using GaAs MESFETs. Monolithic integrated A/D circuits were fabricated and successfully operated at gigahertz sampling rates. This sampling rate is the highest reported for any A/D technology at room temperature. The power dissipation is 150-200 mW per bit. With further improvements in comparator sensitivity, the design can be extended to 4-bit A/D for GHz rate operation.

Analysis of the properties of three-terminal transferred-electron logic devices

A two-dimensional analysis of Schottky-barrier gate GaAs logic devices utilizing the transferred-electron effect is described. The analysis is used to study the basic properties of two devices with anode to cathode spacing of 13 µm and 33 µm. The reduction in current drop due to the presence of the gate is discussed. The switching properties of the 13-µm device are studied for operation with either anode or cathode resistance. A gate delay of 30 ps and a total gate power of 180 mW is estimated.

Charge-collection mechanisms of AlGaAs/GaAs HBTs

AlGaAs/GaAs heterojunction bipolar transistors are investigated via time-resolved and time-integrated laser induced charge-collection measurements and by two-dimensional computer simulation. Both experiment and simulation results suggest that charge collection occurs by a simple model in which carriers created by the ionizing event are collected at the device terminals, with no evidence for charge enhancement processes. The charge-collection efficiency in all cases is less than unity, with the collected charge exhibiting a linear dependence on the deposited charge for all laser wavelengths used (below the saturation limit). The simulation results reveal that the fast and slow contributions to the charge collection transient arise from electron and hole collection, respectively, with the lower mobility of the holes giving rise to their slower collection dynamics.