Oxide Buildup Research Articles

Two-dimensional methodology for modeling radiation-induced off-state leakage in CMOS technologies

A modeling approach using two-dimensional device simulations is presented, which enables the extraction of parameters for the radiation-induced parasitic MOSFET created at the edge of the shallow trench isolation (STI) oxide. With the model, one can estimate drain-to-source off-state leakage current (I/sub OFF/) resulting from build-up of oxide trapped charge (N/sub OT/). The impact of nonuniform N/sub OT/ build-up in the STI resulting from total ionizing dose (TID) exposure and external bias conditions is analyzed through volumetric simulations and compared to experimental data. Saturation for the off-state leakage current as a function of trapped charge is also investigated.

Negative bias temperature instability mechanisms in p-channel power VDMOSFETs

The negative bias temperature stress induced instabilities of threshold voltage in commercial p-channel power VDMOSFETs have been investigated. The threshold voltage shifts, which are more pronounced at higher voltages and/or temperatures, are caused by the NBT stress induced buildup of both oxide trapped charge and interface traps. However, the observed power low time dependencies of threshold voltage shifts are found to be affected mostly by the oxide trapped charge. The results are analysed in terms of the mechanisms responsible for buildup of oxide charge and interface traps, and the model that explains experimental data is discussed in details.

Improved glutathione status in young adult patients with cystic fibrosis supplemented with whey protein

Background: The lung disease of cystic fibrosis is associated with a chronic inflammatory reaction and an over abundance of oxidants relative to antioxidants. Glutathione functions as a major frontline defense against the build-up of oxidants in the lung. This increased demand for glutathione (GSH) in cystic fibrosis may be limiting if nutritional status is compromised. We sought to increase glutathione levels in stable patients with cystic fibrosis by supplementation with a whey-based protein. Methods: Twenty-one patients who were in stable condition were randomly assigned to take a whey protein isolate (Immunocal, 10 g twice a day) or casein placebo for 3 months. Peripheral lymphocyte GSH was used as a marker of lung GSH. Values were compared with nutritional status and lung parameters. Results: At baseline there were no significant differences in age, height, weight, percent ideal body weight or percent body fat. Lymphocyte GSH was similar in the two groups. After supplementation, we observed a 46.6% increase from baseline ( P<0.05) in the lymphocyte GSH levels in the supplemented group. No other changes were observed. Conclusion: The results show that dietary supplementation with a whey-based product can increase glutathione levels in cystic fibrosis. This nutritional approach may be useful in maintaining optimal levels of GSH and counteract the deleterious effects of oxidative stress in the lung in cystic fibrosis.

Application of electromagnetic forces to reduce tundish nozzle clogging

This paper considers the problem of oxide build-up within a tundish nozzle when casting aluminum killed steel. Water model studies have shown that the clogging problem may be very dependent on the flow pattern in the nozzle entry region. In particular, the studies show that the flow can separate within the entrance region of the nozzle, leading to the development of a stagnation zone that can trap oxide particles. This paper proposes that the stagnation zone can be substantially reduced, if not eliminated, through the use of electromagnetic forces. To generate the required electromagnetic force, two systems are considered. The first is based on injecting a DC current; the second by using electromagnetic induction. Both methods are described in this paper. Order of magnitude calculations are provided to illustrate that both methods are essentially feasible. The performance of each method in terms of modifying the turbulent flow characteristics in the nozzle entry region is then examined using a numerical model. It is shown that both methods can greatly reduce the recirculation zone. A cylindrical nozzle was chosen for the model studies since it represents a worst case situation. On the basis of the model studies, it can be concluded that whereas both of the proposed methods have the potential to reduce the troublesome recirculation zone, the induction method appears to be simpler in terms of practical implementation.

Co-adsorption of Fluoride and Hydroxide Ions on Ag(111) in Alkaline Electrolytes: Electrochemical and SHG Studies

Abstract Hydroxide (OH−) adsorption at Ag(111)/alkaline electrolyte interfaces is the initial step leading to the formation of surface oxide. We investigate how OH− anion adsorption is influenced by co-adsorption of supporting electrolyte anions (F−). Pure NaF and NaOH as well as mixed electrolytes ranging from pH=5.8 to 14 are investigated. The rotational anisotropy of the second harmonic generation (SHG) signal is measured to distinguish adsorptive processes from structural changes on the Ag surface. Our results clearly show a cross-over from F−-dominated to OH−-dominated adsorption, while both species remain charged upon adsorption. At more positive potentials, but below the reversible potential of bulk oxide growth, OH is discharged leading to sub-monolayer oxide build-up, whereas in acidic electrolyte, Ag is dissolved. At intermediate pH, the formation of a structured OH−/F− co-adsorbed layer is proposed.

Calibrated pneumoperitoneal venting to prevent N2O accumulation in the CO2 pneumoperitoneum during laparoscopy with inhaled anesthesia: an experimental study in pigs.

Nitrous oxide (N2O) accumulates in the CO2 pneumoperitoneum during laparoscopy when N2O is used as an adjuvant for inhaled anesthesia. This may worsen the consequences of gas embolism and introduce a fire risk. In this study, we quantified the pneumoperitoneal gas venting necessary to prevent significant contamination by inhaled N2O. Four domestic pigs (26-30 kg) were anesthetized and ventilated with 66% N2O in oxygen. A CO2 pneumoperitoneum was insufflated and maintained at a pressure of 12 mm Hg. Each animal underwent three experimental conditions, in random sequence, for 70 min each: 1) no pneumoperitoneal leak, 2) leak of 2 L every 10 min (12 L/h), and 3) leak of 4 L every 10 min (24 L/h). Every 10 min, pneumoperitoneal gas samples were analyzed for fractions (FPn) of N2O and CO2. Without leaks, FPnN2O increased continually and reached 29.58% +/- 3.15% at 70 min. With leaks of 2 and 4 L every 10 min (12 and 24 L/h), FPnN2O reached a plateau of <10% after 30 min. We conclude that calibrated pneumoperitoneal venting of 12 or 24 L/h is enough to prevent the constitution of potentially dangerous pneumoperitoneal gas mixtures if venting is constant. External venting calibrated at four or eight initial pneumoperitoneal volumes per hour with compensation by fresh CO2 is sufficient to prevent nitrous oxide buildup of more than 10% in the pneumoperitoneum during laparoscopy with inhaled general anesthesia if venting is constant.

Proton radiation response mechanisms in bipolar analog circuits

The experimental data presented in this paper indicate that the doping and geometry of critical transistors are the primary factors that affect the proton responses of the LM124 and LM148 operational amplifiers. The data also reveal that the electrical responses of these circuits and their input transistors to the combined effects of displacement damage and defects introduced by ionizing radiation are nonlinear. Analysis, supported by device simulation, shows that shifts in device parameters (surface potentials, carrier concentrations, etc.) caused by the buildup of oxide and interfacial defects affect the recombination rate due to traps resulting from displacement damage in the bulk silicon. This nonlinearity complicates the analysis of proton radiation effects and can have a significant impact on the qualification of analog parts for use in space environments.

Dynamic stability of field emission from molybdenum microtips exposed to oxygen

The emission current in a molybdenum field emission array can decrease by 50% in 1000 s at an oxygen pressure of 10−6 Torr. To overcome this disadvantage of molybdenum microtips, the effectiveness of dynamic surface cleaning has been investigated in a single-aperture gated-diode configuration. For dynamic surface cleaning, tip surface oxide buildup is balanced by tip oxide removal due to sputtering by ions created in ionizing collisions with field-emitted electrons. The present results demonstrate stable dynamic cleaning with clean and partially oxidized molybdenum tips for currents ranging from 10−11 to 10−9 A with oxygen exposures of up to 1000 L. For currents above 10−9 A, ion bombardment causes the tip shape to become unstable leading to failure with increasing oxygen exposure.

Origins of total-dose response variability in linear bipolar microcircuits

LM111 voltage comparators exhibit a wide range of total-dose-induced degradation. Simulations show this variability may be a natural consequence of the low base doping of the substrate PNP (SPNP) input transistors. Low base doping increases the SPNPs collector to base breakdown voltage, current gain, and sensitivity to small fluctuations in the radiation-induced oxide defect densities. The build-up of oxide trapped charge (N/sub OT/) and interface traps (N/sub IT/) is shown to be a function of pre-irradiation bakes. Experimental data indicate that, despite its structural similarities to the LM111, irradiated input transistors of the LM124 operational amplifier do not exhibit the same sensitivity to variations in pre-irradiation thermal cycles. Further disparities in LM111 and LM124 responses may result from a difference in the oxide defect build-up in the two part types. Variations in processing, packaging, and circuit effects are suggested as potential explanations.

Experimental and analytical evaluation of damage processes in thermal barrier coatings

Progressive damage evolution was evaluated using microscopy on samples subjected to a series of different thermal cycle profiles. Fick’s law was used to describe the thermally grown oxide (TGO) buildup during early cycles. A correlation of damage thickness and oxide thickness for different thermal cycle profiles was established. The importance of this correlation is that, for a given thermal cycle profile and number of cycles, the oxide thickness can be calculated analytically using Fick’s law, and from this thickness one can determine the interlayer separation (damage thickness). Both oxidation kinetics and interlayer separation (delamination) appear to have significant roles with respect to spallation. As early microcracks coalesce to form major delamination cracks or interlayer separation, the susceptibility for coating buckling is increased. The delamination cracks finally consume the TGO layer. Progressive microcrack linking is a possible mechanism to develop such critical delamination crack lengths. Physical evidence of buckling was found in specimens prior to complete spallation.

Modeling of the Transition From Active to Passive Oxidation of Si(100)

ABSTRACTFor a Si(100)2×1 surface exposed to oxygen, there is a transition from etching (“active” oxidation via removal of SiO) to “passive” oxidation (buildup of an oxide film) with decreasing surface temperature. The transition depends sensitively on a competition between SiO desorption, and oxide island formation. We analyze these processes utilizing both ab-initio quantum chemistry studies of key energetics and lattice-gas models for the cooperative behavior.

Alternatives to Hydrogen Fluoride for Photoelectrochemical Etching of Silicon

Photoelectrochemical etching of silicon in nonaqueous solutions without the use of free‐fluoride or HF has been demonstrated. Silicon was electrochemically oxidized and dissolved using stable, fluoride containing salts in acetonitrile solutions. The current‐voltage behavior of silicon in acetonitrile solutions containing tetrabutylammonium tetrafluoroborate or tetrabutylammonium hexafluorophosphate were similar. The voltammetry of silicon in solutions containing tetrabutylammonium trifluoromethylsulfonyl, potassium hexafluoroarsenate, or sodium hexafluoroantimonate showed large hysteresis indicating the presence of silicon oxide on the surface. Although the dissolution rate of silicon dioxide was negligible in the absence of free‐fluoride or HF, the oxidation and dissolution of silicon could be maintained, even when thin oxides were formed. Photocurrent oscillations associated with the buildup and removal of oxides were observed when traces of water were present. © 1999 The Electrochemical Society. All rights reserved.

Combined Zero- and First-Order Kinetic Model of the Degradation of TCE and cis-DCE with Commercial Iron

The design of a permeable iron wall depends to a great extent on the transformation kinetics of the chlorinated compounds. Therefore these degradation kinetics of TCE and cis-DCE with commercial iron and their dependence on the properties of the compounds and on the experimental conditions were studied in mixed-batch and column experiments. Since our data cannot sufficiently be described by a pseudo-first-order kinetics, we successfully applied an enhanced model accounting for both zero- and first-order kinetics. The fitted kinetic parameters, however, were found to depend on the experimental conditions and compound properties, which is interpreted in terms of different rate-limiting processes. The zero-order rate constant turned out to be twice as high for cis-DCE as for TCE in both experimental systems. Despite its slower transformation without transport control, the first-order rate constant was about 4 times higher for TCE than for cis-DCE in the mixed-batch vials. We attribute this to the lower water solubility and thus higher sorptivity of TCE at the polished iron surface. In the column experiments, transformation without transport control was twice as fast as in the batch experiments for both compounds. cis-DCE was degraded faster than TCE in the zero- and first-order region. At higher influent concentrations, the zero- and first-order rate constant of TCE decreased, which we assume to be due to the buildup of iron oxides, and transport to the reactive sites was found to depend a little on flow velocity. Due to the slow first-order kinetics of both compounds, we assume diffusion within micropores to be rate-limiting in flow-through systems. These variations in the kinetic parameters of the combined zero- and first-order model suggest that transport and sorption to reactive sites contribute to kinetic control of the degradation of chlorinated ethenes in addition to charge-transfer processes.

Combustion of Aluminum particles in flows of reactive gase

A model is proposed for the burning of individual aluminum particles in gas mixtures containing several oxidizing reagents, which included the buildup of oxide on an aluminum particle, the evaporation kinetics of Al, and surface chemical reactions. An analysis is made of calculations using this model with different gas flow parameters for particles with dimensions of 10–140 μm burning in air or in the gasification products of the solid fuel. A number of aspects of the combustion of aluminum particles are revealed which affect the burning time and the fraction of Al2O3 formed on a particle. the main feature associated with kinetic limitations and oxide buildup is a strong disequilibrium of the combustion process. The model provides a good description of the experimental dependence of the burning time of Al particles on their size and on the major flow parameters. The calculated fraction of Al2O3 which accumulates on a burning particle is in satisfactory agreement with experimental data.

The influence of stacking fault energy on the wear resistance of nickel base alloys

An effort has been made in the present investigation to correlate the deformation and sliding wear resistance of a series of nickel-cobalt and nickel-copper single phase, fcc, solid-solution alloys with their stacking fault energy (SFE) by conducting reciprocating sliding wear tests against a diamond ball in ambient air. The surface damage has been characterized through scanning electron microscopy and X-ray photoelectron spectroscopy. For the nickel-cobalt alloys the measured wear rates were found to be mostly controlled by work-hardening and fatigue fracture of the near surface region and a good correlation was obtained between the wear rates and the SFE of these alloys. The same trend has also been observed in nickel-copper alloys having less than 50 wt.% copper. In higher alloy compositions, however, it was found that the influence of SFE on the wear rate is overshadowed by the beneficial lubricating effect of build-up of copper oxides on the wearing alloy surface.

Investigation of the ozone formation process in a nanosecond microwave discharge in air and oxygen

Results are presented from an investigation of the dynamics of ozone formation in a freely localized discharge generated by a periodic train of 3-cm nanostructured microwave pulses in oxygen and air at a pressure p=3–30 Torr. Conditions for the efficient generation of ozone in air with the minimum production of nitrogen oxides are demonstrated experimentally. It is shown that when the microwave pulse repetition frequency is high, heating of the gas and the buildup of nitrogen oxides in the discharge in air reduce the ozone formation efficiency while under prolonged exposure the ozone formed initially is destroyed. The energy cost of forming ozone in oxygen and air is determined as a function of the microwave pulse length and repetition frequency and the gas pressure. The lowest energy cost of forming a single ozone molecule in these experiments is 16 eV per molecule for a discharge in air and 4 eV per molecule in oxygen. It was observed that circulating the gas through the discharge zone enhances th ozone formation efficiency. It is shown that there are optimal conditions for ozone formation as a function of the reduced electric field in the plasma.

An Experimental Investigation Into the Relationship Between Temperature-Time History and Surface Roughness in the Spray Quenching of Aluminum Parts

Repeated heat-quench cycles of Al-1100 samples resulted in increased surface roughness and corresponding shifts in the temperature-time cooling curve towards shorter overall quench periods. Three different types of initial surface roughness were applied to the test samples: polished, particle blasted, and milled finishes. For each of the three test surfaces, cooling curve shifts during repeated heat-quench cycles were accompanied by surface roughening, the shift was smallest with the milled sample. The surface roughness was examined with the aid of scanning electron microscopy, surface contact profilometry, and X-ray photoelectron spectroscopy. Surface profiles obtained via the profilometer revealed, on a relative basis, significant changes in surface roughness on the polished and particle blasted surfaces but not on the milled (roughest) surface. The roughening was the result of (a) hydrogen diffusion associated with oxidation, (b) oxidation buildup, and, to a lesser extent, (c) expulsion of impurities along dendrite boundaries. The hydrogen diffusion caused localized pressure buildup within the surface and along grain boundaries resulting in the formation of both microscopic (1 to 10 μm) features on the polished and particle blasted surfaces and relatively large (20 to 1000 μm) bumps and blisters on the particle blasted surface. It is shown how these wide spectrum surface roughness features affect cooling rate by (a) raising the Leidenfrost temperature separating the film and transition boiling regimes, (b) increasing the number of boiling sites on the quenched surface, and (c) altering the impact dynamics of the spray drops.

Activation Studies with a Precipitated Iron Catalyst for Fischer-Tropsch Synthesis: II. Reaction Studies

Effects of pretreatment conditions on catalyst performance (activity, selectivity, and stability with time) during Fischer-Tropsch (FT) synthesis were studied in a fixed-bed reactor using a commercial precipitated iron catalyst (100 Fe/5 Cu/4.2 K/25 SiO2 on a mass basis). The catalyst activity increased slightly with time-on-stream after hydrogen reductions, which was accompanied with conversion of metallic iron and part of iron oxides to ϵ′-carbide (ϵ′-Fe2.2C). Initial activity of the H2-reduced catalyst at 280°C for 8 or 24 h was markedly lower than that obtained in other tests. This is attributed to slow carburization of large oxide particles and partial poisoning of catalyst sites by migration of sulfur from the bulk to the surface of the catalyst during the reduction. Pretreatments with carbon monoxide and syngas resulted in partial conversion of Fe2O3 to χ-carbide (χ-Fe5C2). During FT synthesis the CO- and the syngas-pretreated catalyst deactivated slowly with time-on-stream, due to partial conversion of χ-carbide to less active iron oxide phases and buildup of carbonaceous deposits which block the active sites. The hydrogen-reduced catalyst at 280°C, for 1-24 h, produced more methane and gaseous hydrocarbons than the CO- or the syngas-pretreated catalyst and favored secondary reactions (1-olefin hydrogenation, isomerization, and readsorption).

On the mechanism of hydrogen transport through the passive oxide film on iron

Hydrogen permeation experiments have been performed to investigate the hydrogen transport through the passive oxide film formed on the exit surface of iron membranes. Charging procedure, membrane thickness and thermal treatment were selected to allow fast stepwise changes between well-defined values of hydrogen input fugacity at the metal/oxide interface. The oxide was formed by anodic polarization of the iron exit surface in 0.1 N NaOH solution. Hydrogen permeation was studied at different stages of the film growth process, at times ranging from 150 to 3 × 10 5 s from the beginning of anodic polarization. The temperature range was 298 K ⩽ T ⩽ 348 K. The metallic phase can be regarded as an iron-hydrogen alloy where sudden changes in hydrogen contents can be achieved. Both steady state hydrogen flow and iron flow through the oxide film (oxide build-up current) can be described in terms of ion jumps between potential wells under the influence of a high electric field (hopping model). An ionic charge ratio of migrating species Z H/ Z fe of ca 0.3 was experimentally found.

Three-point method of prediction of MOS device response in space environments

A method for low-dose-rate MOS device response prediction based on the linear dependence between positive oxide charge anneal and interface states build-up is presented and experimentally verified. A linear relationship is seen to exist between the build-up of slow interface states and oxide trapped hole annealing. The physical explanation of the correlation between the number of trapped holes annealed and the number of interface states generated can be given in both hydrogen and trapped hole conversion models on a phenomenological basis. It is suggested that there is a one-to-K/sub Oi/ relationship (where K/sub Oi/ is some phenomenological constant) between the number of trapped holes annealed and the number of interface states generated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>