The effect of Cu diffusion on the TDDB behavior in a low-k interlevel dielectrics

The effect of Copper on TDDB failure in a structure incorporating a low-k interlevel dielectric was studied theoretically and experimentally. Interdigitated comb capacitor structures were prepared with and without Cu metallization and stressed at 4.0 to 6.6 MV/cm at 150C. The samples without Cu did not fail to over 1800 hours at 4 MV/cm whereas the samples with Cu exhibited a median time to failure (t₅₀) of 45 minutes. At 6.6 MV/cm, the t₅₀ was 1.8 hours for the Cu free samples. This experiment demonstrated the importance of Cu in the TDDB behaviour of low-k dielectrics, but also demonstrated that the presence of Cu was not a necessary condition for failure. The effect of Cu diffusion on TDDB behaviour was studied in the context of the “Impact Damage” model. Both field assisted ionic diffusion and diffusion of neutral Cu was considered. It is seen that the behaviour at low fields near use conditions may have little relationship to the predictions obtained from the results of typical TDDB testing.     

Modelling of electrostatic gate operations in the Kane solid state quantum computer

The nuclear spin quantum computer proposed by Kane [Nature 393 (1998) 133] exploits as a qubit array ³¹P dopants embedded within a silicon matrix. Single-qubit operations are controlled by the application of electrostatic potentials via a set of metallic ‘A’ gates, situated above the donors, on the silicon surface, that tune the resonance frequency of individual nuclear spins, and a globally applied RF magnetic field that flips spins at resonance. Coupling between qubits is controlled by the application of potentials via a set of ‘J’ gates, between the donors, that induce an electron-mediated coupling between nuclear spins. We report the results of the study of the electric field and potential profiles arising within the Kane device from typical gate operations. The extent to which a single nuclear spin can be tuned independently of its neighbours, by operation of an associated A-gate, is examined and key design parameters in the Kane architecture are addressed. Implications for current fabrication strategies involving the implantation of ³¹P atoms are discussed. Solution of the Poisson equation has been carried out by simulation using a TCAD modelling package (Integrated Systems Engineering AG).     

Estimating the number of faults: efficiency of removal, recapture,and seeding

Various experimental designs for estimating the number of faults in a system are studied including: (1) removal of each fault as it is detected; (2) marking of each fault as it is detected; and (3) introduction of a known number of faults into the system followed by (1) or (2). A unified framework is developed for comparing these designs; it also produces simplified estimators having high efficiency relative to maximum likelihood estimators. The designs are compared in terms of: (1) statistical accuracy; and (2) the number of failures that need to occur to achieve a given accuracy. On the basis of these comparisons, some general recommendations are made on the level of seeding as well as the choice of removal or recapture designs. When the testing effort is sufficient so that roughly two thirds of the faults are detected, the removal-design is preferred over the recapture-design, and there are no gains from seeding. However, this conclusion depends on assigning unit cost to all fault detections, which might not always be reasonable     

Effect of the incorporation of interfacial elements on the thermophysical properties of Cu/VGCNFs composites

Vapour grown carbon nanofibres exhibit high mechanical properties and thermal conductivities. Therefore they are potential reinforcements in composites materials for high strength and high thermal conductivity applications. A problem not yet solved is the promotion of an improved copper/carbon interface. Several strategies have been envisaged for the incorporation of alloying elements (Ni, Co, B and Ti) at the interface. These techniques are based on duplex electroless plating coatings (combination of Cu and Ni or Cu and Co), electroless plating of alloys (Cu-B) and addition of metal nanoparticles (Ti) to Cu matrix deposited by electroless plating. The effect of the incorporation of these metallic elements on the microstructure and thermophysical properties is discussed. B and Ti lead to higher interaction at the Cu/C interface over Ni and Co. This allows the reduction of the coefficient of thermal expansion but regarding the thermal conductivity it was not possible to obtain a value higher than that of copper.     

Fractionation of Starch Amylopectin and Amylose by High Performance Gel Filtration Chromatography

A gel filtration chromatographic method has been developed which is capable of fractionating amylose and amylopectin in starch. Three GFC columns (2 × 4000 A and 1 × 300A PL Separation Sciences, Polymer Laboratories Ltd,) are used in series using sodium chloride solution as eluent. Minimal sample preparation is involved which includes a preliminary wetting of powder starch with ethanol followed by dissolution with sodium hydroxide. Since the solvent system is aqueous, cooked starch samples are analysed by direct dissolution with sodium hydroxide. The method shows promise as a rapid technique in elucidating starch structure.     

Mechanical property enhancement in short-fiber composites through the control of fiber orientation during fabrication

The mechanical properties of plastics and elastomers reinforced by short fibers are generally dictated by the selection of matrix and reinforcement. However, the high tensile properties attainable in these systems through laboratory processing techniques are frequently not obtained in conventional fabrication operations. To gain a wider latitude in meeting economic and performance constraints, the control of composite structure in the fabrication step should not be overlooked. Tool geometry and processing conditions can be manipulated specifically to control the fiber orientation distribution in the product. A study of fiber orientation in composite compounds during flow through runners, gates, and dies leads to recommendations for optimizing the directional strength and stiffness according to a kinematic model. Performance data on parts fabricated from various short-fiber composite materials bear out these projections.     

The extrusion and performance of plasticized poly(vinyl chloride) hose reinforced with short cellulose fibers

Short fibers of natural cellulose treated to provide dispersability and strong interfacial bonding are ideal reinforcements for plasticized vinyl compounds. The development of substantial strength and stiffness in unidirectional composites indicates the reinforcing potential of these high aspect-ratio fibers in soft compositions. Special extrusion dies developed to control fiber directionality in rubber extrudates are equally applicable to vinyl hose. The unusual expanding geometry of these tools aligns the fibers toward the circumferential direction to provide optimum reinforcement against contained pressure loading. Thus, reinforced poly(vinyl chloride) air and water hoses can be produced in a single extrusion step, since all of the necessary reinforcement is contained in the compound.     

Towards an end-to-end airborne remote-sensing system for post-hazard assessment of damage to hyper-critical infrastructure: research progress and needs

The objective of this article is to synthesize research findings and requirements pertaining to development of time-sensitive remote-sensing systems (TSRSS) that support decision-making pertaining to post-hazard assessment of damage to what we define as hyper-critical infrastructure (HCI), based on an aerial imaging approach known as repeat station imaging (RSI). The following TSRSS components are addressed and related findings are reported: (1) understanding information requirements of emergency managers pertaining to damage of HCI; (2) flight planning and data capture requirements for supporting bi-temporal RSI pairs; (3) automatic image registration and shadow classification and normalization routines applied to RSI pairs; (4) damage detection and delineation approach that exploits simple temporal differences in image brightness to automatically, reliably, and robustly delineates new cracks associated with damage; and (5) rapid data and information transfer to emergency managers. The highest priority follow-on research topics are: (1) integrating small unmanned aerial systems (sUAS) with the RSI approach, while enabling multiple view perspectives other than vertical (i.e. nadir pointing) and (2) developing and testing of machine learning routines for automatic identification of damage features from RSI pairs, particularly those captured from integrated sUAS–RSI.     

THE UPGRADING OF SOLVENT REFINED COALS AND LIGNITES: DETERMINATION OF AN EFFECTIVE HETEROGENOUS CATALYST CARRIER

The hydrodenitrogenation, hydrodesulfurization and hydrocracking of solvent refined coals and lignites was accomplished with catalysts comprising high surface area, large pore diameter bases impregnated with MoO₃,CoOand WO₃. The most effective catalysts were those which performed well in hydrodenitrogenating nitrocellulose. This indicates that most of the pore diameter is consistently large enough to accommodate molecules of the size of liquified coal and lignite.     

A new family of synthetic diterpenes that regulates cytokine synthesis by inhibiting IkappaBalpha phosphorylation

The synthesis and the biological evaluation of a new family diterpenes are presented. The synthetic studies were inspired by the structural framework of acanthoic acid (1) and yielded a family of compounds that were evaluated as anti-inflammatory agents. Among them, compounds 2, 10, 12, and 16 exhibited a very low nonspecific cytotoxicity and inhibited the synthesis of TNF-alpha with greater than 65 % efficacy at low micromolar concentrations. Cytokine-specificity studies revealed that these compounds also inhibited the synthesis of the proinflammatory cytokines IL-1beta and IL-6, while inhibition of IL-1ra and IL-8 synthesis was marginal and only occurred at high concentrations. Further studies, through EMSA and Western blot analyses, indicated that these compounds decreased the extent of phosphorylation of IkappaBalpha; this suggests that they exert their anti-inflammatory profile by inhibiting NF-kappaB-mediated cytokine synthesis. These findings imply that these diterpenes represent promising leads for the development of novel anti-inflammatory agents.