T. A. Grotjohn

Temperature dependence and post-stress recovery of hot electron degradation effects in bipolar transistors

The authors present the results of a study of the BJT (bipolar junction transistor) degradation process due to hot electrons with the goal of better understanding the degradation rate of current gain and noise characteristics under various temperature and bias conditions. Degradation was produced by reverse biasing (-4 V) the base emitter junction of bipolar transistors at various temperatures (-75 to 240 C), with stress periods ranging from 1/60th of a second to over 1000 h. Post-stress recovery of the degradation was studied using both high-temperature annealing and base-emitter forward biases. Two mechanisms which decrease the rate of degradation at higher temperatures are the reduction in the number of hot electrons at higher temperatures and the simultaneous annealing of the states produced by hot electrons at higher temperatures. Experimental data are used to develop a model description of the hot-electron-induced gain degradation process which includes both the temperature dependence of the number of hot electrons and the temperature dependence of a simultaneous repassivation process which is observed at high ambient temperatures.<<ETX>>

The design and application of electron cyclotron resonance discharges

During the past ten years electron cyclotron resonance (ECR) plasma-processing technology has matured into a diverse assortment of ECR plasma reactor and plasma source design concepts and has been extensively applied to numerous low-pressure plasma processing applications. This paper reviews the substantial progress made in the design and application of ECR plasma technology in recent years. Five representative ECR reactor/source designs from large-area 450-cm/sup 2/ discharges to compact plasma sources inserted into molecular-beam epitaxy (MBE) machines are described in detail. The performance of these ECR devices is evaluated by computing performance figures of merit from the available experimental data. These calculations are then compared with the behavior as predicted from a global model of the discharge. This comparison suggests that global plasma models can be employed as an approximate method for ECR reactor design. More extensive diagnostics and numerical models that investigate the spatial variation of ion density and ion energy distributions are also presented. Several illustrative ECR plasma-processing applications are discussed. These include submicron etching of silicon, etching of III-V and II-VI electronic and photonic devices, and the epitaxial growth of GaN. The variety and the sophistication of these applications demonstrate that low-pressure high-density ECR plasma processing technology has evolved into a very useful, versatile group of plasma-processing machines.

Modelling the electromagnetic field and plasma discharge in a microwave plasma diamond deposition reactor

Abstract A numerical model which includes an electromagnetic field model and a fluid plasma model has been developed for a microwave cavity plasma reactor used for diamond thin film deposition. The microwave plasma reactor modelled is a cylindrical, single mode excited cavity with an input power probe for coupling the microwave energy into the cavity. The time-varying electromagnetic fields inside the resonant cavity are obtained by applying the finite difference time domain (FDTD) method to solve Maxwells equations. The microwave electric field interactions with the plasma discharge are described using a finite difference solution of the electron momentum transport equation. The characteristics of the discharge are simulated using a fluid plasma model which solves the electron and ion continuity equations, electron energy balance equation, and the Poisson equation. The spatial electric field patterns, power absorption patterns, and quality factor of the cavity loaded with a hydrogen discharge are investigated in the moderate pressure range (40–60 Torr). The physical behaviour of the diamond deposition discharge, such as plasma density, electron temperature, and plasma potential, are also simulated and analysed for various input conditions. The simulated results are compared with experimental data.

MODELING THE ELECTROMAGNETIC EXCITATION OF A MICROWAVE CAVITY PLASMA REACTOR

The electromagnetic excitation of a discharge‐loaded microwave cavity plasma reactor used for diamond thin film deposition has been numerically modeled in the time domain. This reactor model simulates a three‐dimensional, cylindrical, single‐mode excited cavity including the input power coupling probe. The time‐varying electromagnetic fields inside the resonant cavity, both inside and outside the discharge region, are obtained by applying a finite‐difference time‐domain method to solve Maxwell’s equations. The boundary conditions and electromagnetic field excitation methods of this model are discussed. The microwave electric field interactions with the plasma discharge are described using a finite‐difference solution of the electron momentum transport equation. The spatial electric field patterns, power deposition patterns, stored energy, and quality factor of a cavity loaded with hydrogen discharges at various pressures (20–70 Torr) are simulated and compared with experimental data.

A parametric short-channel MOS transistor model for subthreshold and strong inversion current

The authors present a parametric model which covers the subthreshold and strong inversion regions with a continuous transition between these regions. The effects included in the model are mobility reduction, carrier velocity saturation, body effect, source-drain resistance, drain-induced barrier lowering, and channel-length modulation. The model simulates accurately the current characteristics as well as the transconductance and output conductance characteristics which are important for analog circuit simulation.

Compact microwave re-entrant cavity applicator for plasma-assisted combustion

Advantages of combining an electrical discharge with combustion include a faster process, higher intensities, leaner combustion, pollutant reduction by altering by-products of combustion, improved fuel efficiency by achieving more complete combustion, more reliable ignition of combustion, and combustion across a wider range of pressures, temperatures and mixture stoichiometries. The benefits may also include the operation of combustion processes at extreme limits, such as aerospace applications at high speeds and altitudes.

Microwave plasma-assisted premixed flame combustion

A compact microwave plasma/combustion torch has been operated at atmospheric pressure in both plasma-only and plasma-assisted premixed combustion modes. The torch burns CH4∕O2 mixtures with plasma enhancement that modifies combustion, flame structure, flame size, and flame power density. The microwave energy also extends the fuel-lean burn limits.

Microwave-Plasma-Coupled Re-Ignition of Methane-and-Oxygen Mixture Under Auto-Ignition Temperature

The re-ignition phenomenon is observed when fuel/oxidizer is re-introduced into an atmospheric-pressure plasma discharge generated by cutting off the gas flow in a re-entrant microwave-plasma applicator system used for plasma-assisted ignition and combustion research works. Results indicate that, for re-ignition to occur, the electric field must be strong enough to fully establish a weakly ionized and self-sustained plasma discharge, and with elevated radical concentrations. The re-ignition was possible at gas flow speeds higher than typical flame propagation rates, and temperature measurements (thermocouple and N2 emission) reveal that re-ignition occurs under auto-ignition temperatures. The high-speed imaging of the flame propagation shows that it is a two step process of initiating a fast pyrolysis flame, which, in turn, stabilizes and starts the direct coupling process of the plasma energy into the flame for full re-ignition to occur.

Hot-electron-induced degradation and post-stress recovery of bipolar transistor gain and noise characteristics

Hot-carrier-induced degradation and post-stress recovery of bipolar transistor gain and low-frequency noise are investigated. Forward-bias recovery allows a partial reversal of degradation, and is believed to be due primarily to a reduction of the number of electrons trapped in the oxide. Thermal annealing, which is capable of removing interface states as well, produces a larger recovery of both gain and noise performance measures. >

Fabrication and properties of ultranano, nano, and microcrystalline diamond membranes and sheets

Thin diamond membranes and free-standing sheets are of interest for a variety of potential applications. This article describes the film nucleation, microwave plasma-assisted chemical-vapor-deposition synthesis, and subsequent processing steps required to make free-standing strong and flexible diamond foils of several cm2. Films are initially deposited on silicon wafers as ultrananocyrstalline, nanocrystalline, or microcrystalline diamond by varying selected deposition parameters including gas composition, nucleation, power, substrate temperature, and pressure. Subsequently the diamond is separated from the original substrate and applied either to new substrates or to frames. Diamond membranes and sheets with thickness between 1 and 3μm have been fabricated from each of these film types. The sheets are drapable and can be applied to curved surfaces and wrapped around cylinders. Properties of the films including optical transmission, Young’s modulus and fracture strength are described. Several examples of ...