Poly-gate sidewall oxidation induced submicrometer MOSFETdegradation

The effect of poly-gate sidewall oxidation on short-channel MOSFET behavior is examined. The gain, threshold voltage, and apparent electrical channel length are shown to be very sensitive to the location of the n^- junction edge with respect to the poly-gate edge for a lightly-doped-drain NMOS transistor. New guidelines for the design of submicrometer MOSFETs based on an analysis of the sidewall oxidation of the polysilicon after gate definition are proposed     

The effects of boron penetration on p+ polysilicon gatedPMOS devices

The penetration of boron into and through the gate oxides of PMOS devices which employ p⁺ doped polysilicon gates is studied. Boron penetration results in large positive shifts in V_FB , increased PMOS subthreshold slope and electron trapping rate, and decreased low-field mobility and interface trap density. Fluorine-related effects caused by BF₂ implantations into the polysilicon gate are shown to result in PMOS threshold voltage instabilities. Inclusion of a phosphorus co-implant or TiSi₂ salicide prior to gate implantation is shown to minimize this effect. The boron penetration phenomenon is modeled by a very shallow, fully-depleted p-type layer in the silicon substrate close to the SiO ₂/Si interface     

Cytoplasmic redox potential affects energetics and contractile reactivity of vascular smooth muscle

Variations in the cytoplasmic redox potential (Eh) and NADH/NAD ratio as determined by the ratio of reduced to oxidized intracellular metabolite redox couples may affect mitochondrial energetics and alter the excitability and contractile reactivity of vascular smooth muscle. To test these hypotheses, the cytoplasmic redox state was experimentally manipulated by incubating porcine carotid artery strips in various substrates. The redox potentials of the metabolite couples [lactate]/[pyruvate]i and [glycerol 3-phosphate]/[dihydroxyacetone phosphate]i varied linearly (r=0.945), indicating equilibrium between the two cytoplasmic redox systems and with cytoplasmic NADH/NAD. Incubation in physiological salt solution (PSS) containing 10 mm pyruvate ([lact]/[pyr]=0.6) increased O2 consumption approximately 45% and produced anaplerosis of the tricarboxylic acid (TCA cycle), whereas incubation with 10 mm lactate-PSS ([lact]/[pyr]i=47) was without effect. A hyperpolarizing dose of external KCl (10 mM) produced a decrease in resting tone of muscles incubated in either glucose-PSS (-0.8+/-0.8 g) or pyruvate-PSS (-2.1+/-0.8 g), but increased contraction in lactate-PSS (1.5+/-0.7 g) (n=12-18, P<0.05). The rate and magnitude of contraction with 80 mm KCl (depolarizing) was decreased in lactate-PSS (P=0.001). Slopes of KCl concentration-response curves indicated pyruvate>glucose>lactate (P<0.0001); EC50 in lactate (29. 1+/-1.0 mM) was less than that in either glucose (32.1+/-0.9 mm) or pyruvate (32.2+/-1.0 mM), P<0.03. The results are consistent with an effect of the cytoplasmic redox potential to influence the excitability of the smooth muscle and to affect mitochondrial energetics.     

Disposable polysilicon LDD spacer technology

An advanced 0.5-μm CMOS disposable lightly doped drain (LDD) spacer technology has been developed. This 0.5-μm CMOS technology features surface-channel LDD NMOS and PMOS devices, n⁺/p⁺ poly gates, 125-A-thick gate oxide, and Ti-salicided source/drain/gate regions. Using only two masking steps, the NMOS and PMOS LDD spacers are defined separately to provide deep arsenic n⁺ regions for lower salicided junction leakage, while simultaneously providing shallow phosphorus n^- and boron p^- regions for improved device short-channel effects. Additionally, the process allows independent adjustment of the LDD and salicide spacers to optimize the LDD design while avoiding salicide bridging of source/drain to gate regions. The results indicate extrapolated DC hot-carrier lifetimes in excess of 10 years for a 0.3-μm electrical channel-length NMOS device operated at a power-supply voltage of 3.3 V     

Characterization of stoichiometric adsorption complexes in H-ZSM-5 using microcalorimetry

We have used microcalorimetry to examine the stoichiometric adsorption complexes formed by ammonia, pyridine, and isopropylamine at the A1 sites in H-ZSM-5. The results show that the heats of adsorption for each adsorbate are constant up to a coverage of one molecule /Al, implying that all of the acid sites in H-ZSM-5 are equivalent in strength. The adsorption energies of the complexes formed by ammonia, pyridine, and isopropylamine were found to be 150, 200, and 240 kJ/mol, respectively. Comparison of these values with a simple potential-energy model which assumes that the heat of adsorption scales linearly with gas phase proton affinities suggests that proton transfer dominates the interaction between the adsorbate and the acid site, but that other factors must also be included.     

Impaired microvascular vasoconstrictive responses to vasopressin in septic rats

We have previously demonstrated that chronic alcohol consumption (8 to 10 weeks with ethanol as 36% of the caloric intake) does not exacerbate the effects of ischemia reperfusion injury on the heart. In those same studies, however, Gram-negative sepsis caused myocardial depression in both control and alcoholic rats, but also protected hearts from further damage due to ischemia-reperfusion. In the present study, we determined if preconditioning, a very short ischemia-reperfusion episode that protects the heart from more prolonged ischemia, would have similar effects on hearts from alcoholic and control rats with or without sepsis. Thus, rats were fed a liquid diet supplemented with ethanol or dextrin for 8 to 10 weeks. Some alcoholic and control rats were made septic with Escherichia coli injected into the subcutaneous space, whereas others received an injection of sterile saline. Isolated, isovolumically beating hearts were studied the following day. Hearts were made ischemic for 5 min, reperfused for 5 min, and then made ischemic for 35 min and reperfused for 25 min. Data from similar groups of hearts receiving only 35 min ischemia, and studied at the same time as the present groups, have been previously reported. The 5-min preconditioning episode was more effective in protecting hearts in the alcohol group than in the control group. Postischemic left ventricular developed pressure and +dP/dtmax were not significantly decreased from the preischemic values in the alcohol group, but were significantly decreased in the control group. The time to recovery of spontaneous contractions was decreased by preconditioning in the alcohol group but not in the control group, and the recovery of coronary flow was enhanced in the alcohol group, but not in the control group by pre-conditioning. Thus a single 5-min ischemic procedure was effective in protecting the heart from prolonged ischemia in the alcohol group, whereas it was not sufficient to elicit protection in the control group. Sepsis depressed preischemic function in both groups, but recovery from ischemia was complete.     

A physical model for boron penetration through thin gate oxidesfrom p+ polysilicon gates

Based on numerical device and process simulation, it is shown that enhancement of the boron diffusivity by as much as 300 times in the thin gate oxide results in a very shallow exponential p-type profile in the underlying silicon substrate. The effect of fluorine and phosphorus coimplantation into the p-type polysilicon gate is modeled by changes in the boron diffusivity in the gate oxide and segregation at the polysilicon-oxide interface. An inverse PMOS short-channel behavior in which the threshold voltage becomes more negative with decreasing channel length is modeled by two-dimensional boron segregation effects caused by the poly gate oxidation     

Steam reforming of tar in hot syngas cleaning by different catalysts: Removal efficiency and coke layer characterization

Syngas produced by biomass and waste gasification processes must be adequately clean of tar compounds before being utilized in value-added applications. Syngas cleaning by tar cracking at high temperatures is a promising technique that can utilize different kinds of catalysts. However, their use is limited by the deposition of coke layers, which induces a masking phenomenon on the active surface, and, consequently, the rapid deactivation of the catalyst. This study addresses how the temperature (750 and 800°C) and the steam concentration (0% and 7.5%) can affect the extent of water–gas and reforming reactions between steam and coke deposits. Two catalysts were used: a market-available activated carbon and an iron-based alumina catalyst. The tests showed better performance of the Fe/γ-Al₂O₃ catalyst. A mass increase of the bed was measured in tests with both the catalysts, which confirms the deposition of the coke layer produced by tar dehydrogenation and carbonization. Scanning electronic microscopy-energy-dispersive X-ray analysis (SEM-EDX) and Raman spectroscopy were utilized to investigate the nature of coke layers over the catalyst surface, with the aim of acquiring information about their reactivity towards the water gas reaction. SEM-EDX observations indicate that the thickness of these carbon layers is less than 2 μm. Raman spectra suggest a negligible effect of the reaction temperature in the tested range and, in particular, that the amorphous nature of coke layers deposited in the presence of steam is relatively more graphitic than that obtained without steam.     

The effect of biased spacers on LDD MOSFET behavior

The concept of using LDD spacers that are independently biased with respect to the gate electrode is presented. It is shown that the lateral electric field is strongly influenced by the drain polysilicon spacer potential. Depending on the N^- dose, the peak substrate currents can be either enhanced or reduced by shorting the drain polysilicon spacer to the drain potential. Short-channel LDD MOSFETs have been fabricated with polysilicon LDD spacers shorted to the source and drain electrodes by titanium silicide     

Improved risk stratification in unstable angina: identification of patients at low risk for in-hospital cardiac events by admission echocardiography

BACKGROUND: Current protocols for risk stratification of patients with acute chest pain syndromes rely on clinical parameters and are oriented toward identification of patients at high risk for adverse cardiac events; however, this paradigm for risk stratification does not adequately address the observation that adverse cardiac events are relatively uncommon in this population. In an era of cost containment, consideration also should be given to identification of patients at low risk for adverse cardiac events, who may be safely discharged without expensive inpatient hospitalization. HYPOTHESIS: The purpose of this study was to develop echocardiographic predictors that identify unstable angina patients at low risk for adverse cardiac events and that discriminate between low- and high-risk patients. METHODS: The predictive accuracy of retrospectively determined echocardiographic predictors were compared in a population-based sample of 66 consecutive unstable angina patients undergoing echocardiography within 24 h of admission. RESULTS: Echocardiographic predictors of adverse events included wall motion score index > or = 0.2, ejection fraction < or = 40%, and mitral regurgitation severity > 2. One or more echocardiographic predictors of adverse events were present in 32 patients (48%). A composite echocardiographic predictor of adverse events was specific, had a high positive predictive value for the identification of high-risk patients, and discriminated between unstable angina patients at high and low risk for adverse cardiac events. CONCLUSION: Echocardiographic predictors of adverse events are specific and discriminate between unstable angina patients at high and low risk for adverse cardiac events.