Electrical properties of Ta/sub 2/O/sub 5/ gate dielectric on strained-Si

High dielectric constant (high-k) thin Ta/sub 2/O/sub 5/ films have been deposited on tensilely strained silicon (strained-Si) layers using a microwave plasma enhanced chemical vapour deposition technique at a low temperature. The deposited Ta/sub 2/O/sub 5/ films show good electrical properties as gate dielectrics and are suitable for microelectronic applications. The feasibility of integration of strained-Si and high-k dielectrics has been demonstrated.     

Analytical Modeling of the Propagation of a Thermal Reaction Front in Condensed Systems

An improved analytical model for combustion synthesis has been developed. The features of the model include consideration of the thermophysical and chemical properties of both the reactants and products, as well as considerations of porosity for both reactants and products. An analysis of the variation of the dimensionless velocity with the variation of dimensionless thermal conductivity, density, and heat capacity is carried out. The equations for the combustion temperature and combustion velocity with the inclusion of nonreacting diluents and different thermophysical and chemical properties of the reactants and products is also developed. An equation for the velocity as a function of the nonmelting reactant radius and the different thermophysical and chemical properties of the reactants and products is derived using a diffusion kinetic equation. Master plots for general solid–solid reaction systems, which relate dimensionless velocity, thermal conductivity, density, and heat capacity, are presented. Application of this model to the combustion synthesis of TiC has been carried out to study the variation of combustion front motion with the radius of carbon particles. A comparison of velocities for NiAl predicted by the model as a function of the reactant porosity is presented and compared with the experimentally determined value. The comparison is noted to be close except when the thin zone approximation is no longer valid.     

Influence of state of stress on mixed mode stable crack growth through D16AT aluminium alloy

The stable crack growth through three-point bend (TPB) and stiffened and unstiffened compact tension (CT) specimens of D16AT aluminium alloy has been studied both theoretically and experimentally. The specimen thickness is 8 mm. The variation of load with crack opening displacement, the extent of stable crack growth, the cumulative plastically deformed zone and crack edge profiles have been obtained experimentally. These are also predicted theoretically under the assumption of either a state of plane stress or plane strain using a finite element scheme and the COA criterion. Generally, the experimental results agree well with the predictions based on the plane stress condition. There appears to be no significant variation in size of the experimental cumulative plastic zone across the specimen thickness, thereby indicating that the constraint on the plastic zone does not develop near the mid-thickness region.     

A novel technique for RTP annealing of compound semiconductors

We introduce for the first time a novel rapid thermal processing (RTP) unit called Zapper™, which has recently been developed by MHI Inc. and the University of Florida, for high temperature thermal processing of semiconductors. This Zapper™ unit is capable of reaching much highertemperatures (>1500°C) than conventional tungsten–halogen lamp RTP equipment and achievinghigh ramp-up and ramp-down rates. We have conducted implant activation annealing studies ofSi⁺-implanted GaN thin films (with and without an AlN encapsulation layer) using the Zapper™ unit at temperatures up to 1500°C. The electrical property measurements of such annealed samples have led to the conclusion that high annealing temperatures and AlN encapsulation are needed for the optimum activation efficiency of Si⁺ implants in GaN. It has clearly been demonstrated that the Zapper™ unit has tremendous potential for RTP annealing of semiconductor materials, especially for wide band-gap (WBG) compound semiconductors that require very high processing temperatures.     

Hole mobility enhancement in strained-Si p-MOSFETs under high vertical field

The growth of a high quality, step-graded lattice-relaxed SiGe buffer layer on a Si(100) substrate is investigated. p-MOSFETs were fabricated on strained-Si grown on top of the above layer. Carrier confinement at the type-II strained-Si/SiGe buffer interface is observed clearly from the device transconductance and C-V measurements. At high vertical field, compared to bulk silicon, the channel mobility of the strained-Si device with x=0.18 is found to be about 40% and 200% higher at 300 K and 77 K respectively. Measurements on transconductance enhancement are also reported. Data at 77 K provide evidence of two channels and a large enhancement of mobility at high transverse field.     

Numerical analysis for micropyretic synthesis of NiAl intermetallic compound

A numerical investigation of the micropyretic synthesis response parameters of the Ni-Al stoichiometric compound was undertaken. The influence of the enthalpy of the combustion reaction,Q, activation ienergy,E, amount of diluent, pre-exponential factor,K ₀, and initial temperatureT ₀, on the combustion velocity, temperature, and mode was studied. The porosity of the unreacted compact, which is related to the initial compaction pressure, was considered in the calculation. It was found that the change in porosity significantly affects the thermal conductivity and the length of the pre-heat zone as also do the temperature patterns and propagation velocities. The combustion front was noted to be extinguished if the temperature in the reaction zone became lower than the melting point of the aluminium phase. This result was obtained simply by considering the changes in the thermal conductivity after the melting of aluminium without having to invoke any changes in the rate of reaction after the melting. A comparison of the numerical data with the experimental and analytical results was also made.     

Underpinning-based simultaneous extraction of contiguous sections of a thick coal seam under weak and laminated parting

Around 12.5 m-thick Zero seam of Chirimiri colliery underneath Bartunga hill of M/s South Eastern Coalfield Limited (SECL) was found in two sections; 3.5 m top and 6.0 m bottom section, with a highly laminated 3.0-m-thick parting between the two sections. The laminated parting, comprised of alternate layers of shale, carbonaceous shale, coal and mudstone, was found to be incompetent for safe and clean underground working of both sections. Both top and bottom sections were developed on superimposed pillars along the floor using roof bolts. Based on laboratory testing and investigations on simulated models, an idea of underpinning was conceived for simultaneous depillaring of both the contiguous sections. Taking advantage of presence of openings in the top section, the laminated parting and roof coal band of bottom section was reinforced simultaneously by a full-column grouted cable bolt of suitable length from the floor of the top section. Underpinning consolidated parting stability through reinforcement and provided additional thickness to the critical parting thickness as the roof coal band of the thick bottom section is stitched together with the parting. Maintaining superimposition of workings in the two sections, pillars of both the sections were extracted by splitting and slicing. Splits and slices of the bottom section did not experience roof instability problems due to the presence of the reinforced overlying roof coal band and parting by underpinning. The roof coal of the bottom section was blasted down on retreat. Consolidation of the multi-layered parting by underpinning did not allow separation and collapse of its mudstone/shale layers resulting in clean coal blasted from the roof. Underpinning-based simultaneous depillaring of the contiguous sections proved its technological feasibility and success through field trials.     

The catalytic steam gasification of chars from various sources by K2CO3

Gasification of a char prepared from hydrocracked residuum was compared with the gasification of chars prepared from bituminous and sub-bituminous Canadian coals, wood and graphite. Each material was mixed with 10 mass per cent K₂CO₃ and pyrolyzed up to 900°C. The yield of char was inversely proportional to the amount of volatile matter in the original material. The char prepared from hydrocracked residuum was different from the others. The other chars all followed zero-order gasification kinetics. Gasification of char prepared from the residuum was first-order in the solid. The development of a liquid phase during the pyrolysis of the residuum to char may explain this difference. The gasification rate of the char. from residuum was slower than the rates with the two coal chars and the wood char, but faster than the gasification rate of graphite. A combination of transient experiments and X-ray photoelectron spectroscopic (XPS) measurements indicated that hydrogen was formed almost instantaneously when steam reacted with the char. XPS spectra at liquid nitrogen temperature indicated that during gasification the formation of carbon oxygen bonds proceeded in the following sequence: COH, CO and CO.     

Behavior of vertically irregular structures near mines: Comparison of responses under seismic and mine blast-induced ground motion

Due to architectural and functional considerations, buildings with irregular configurations are frequently constructed with rapid urbanization. During a seismic or blast activity, the performance of a building depends on various factors like adequate lateral strength, stiffness, ductility, regularity, and the extent of simplicity in the configuration. The irregular distributions of the stiffness, mass, and strength in the plan and height of the building create irregularity within the structures. The purpose of this study is to understand the nature of response under seismic ground motion and that obtained from ground vibration generated due to mine blasts if such buildings are situated near mines. This study also emphasizes on identifying the critical location of stress concentration of the structures under both seismic and mine blast-induced ground motion. Base shear, fundamental natural periods, mode shapes, and member forces for a few buildings with typical irregular configurations and similar buildings with regular counterparts are obtained. Nonlinear dynamic analysis has been carried out on irregular buildings for confirming the trends in behavior observed from linear dynamic analysis. Since the mine blasts take place sequentially, the study also aims to prescribe a suitable delay interval between such series blasts to minimize the vulnerability of vertically irregular seismic structures to the possible extent.