The relationship between gate bias and hot-carrier-inducedinstabilities in buried- and surface-channel PMOSFETs

For accurate predictions of device reliability with respect to hot-carrier effects, it is necessary to establish worst-case stress bias conditions. Detailed measurements of hot-carrier-induced instabilities in short-channel PMOSFETs have revealed that stress gate bias conditions corresponding to peak gate currents result in maximum shifts in device parameters. However, for some parameters, notably those measured at low drain bias, comparable shifts are observed for stress gate bias conditions that correspond to peak substrate currents. These observations are valid for both buried-channel (n-type polysilicon gate) and surface-channel (p-type polysilicon gate) PMOSFETs. An interpretation of these results based on the generation of tapped oxide charge and interface traps is proposed     

Localized interface trap generation in SILO-isolated MOSFETs duringPECVD nitride passivation

The authors report the generation of interface traps during the plasma-enhanced chemical vapor deposition of silicon nitride passivation in MOS structures that utilize a sealed-interface local oxidation scheme (SILO) for device isolation. These traps are highly localized at the boundaries between gate and field oxides, causing enhanced subthreshold conduction. Localized interface traps of this type were not observed in identical MOS structures that use conventional LOCOS (local oxidation of silicon) isolation and were eliminated by thermal anneals at 450°C. Anneals in hydrogen ambients resulted in enhanced rates of hot-carrier-induced degradation. The high densities and localized nature of these anomalous traps make possible a novel mode of device operation in which source-drain conduction is strongly modulated by substrate bias     

Low-coherence interferometric sensor system utilizing an integrated optics configuration

The implementation of a twin Mach-Zehnder reference interferometer in an integrated optics substrate is described. From measurements of the fringe visibilities, an identification of the fringe order is attempted as a way to provide an absolute sensor for any parameter capable of modifying the difference in path length between two interfering optical paths.     

A proposed framework for hydrogeological conceptual modelling

The process whereby hydrogeologists interpret the available information to produce a justifiable set of simplifying assumptions to describe a groundwater system is called conceptual modelling. Although this process is inherent in all hydrogeological assessments and can therefore be regarded as synonymous with hydrogeological practice there are no standard specifications for it. A framework for conceptual modelling has been designed to both assist in the planning and process of the work and to provide an audit trail to facilitate independent scrutiny. The application of this framework is illustrated by two case histories, one of a small-scale investigation for a proposed cemetery and the other of an investigation of the migration of a large-scale sulphate plume in a public supply aquifer. This framework is applicable across the full range of scales of hydrogeological systems, and indeed is readily extendable to other analogous areas of endeavour in the management of natural resources.     

Neuropsychological aspects of multiple sclerosis

Since S. Rao's ["Neuropsychology of Multiple Sclerosis: A Critical Review," A Journal of Clinical and Experimental Neuropsychology, Vol. 85, pp. 503-542] (1986) seminal review, considerable research has been undertaken on the neuropsychological consequences of multiple sclerosis. This review incorporates the research literature of the last decade in presenting an overview of the current state of our knowledge concerning the etiology, course, symptoms, assessment, consequences, and treatment of multiple sclerosis (MS). The concept of subcortical dementia is revisited in light of the most recent literature documenting the neuropsychological deficits in patients with MS. The view that cognitively heterogeneous patient groups may disguise more specific patterns of focal neuropsychological impairment is considered. A critical review of the recent literature is also presented, detailing the degree to which recent research has addressed the areas of research need identified by Rao in 1986. Given recent advances in our knowledge, the need for more attention to be directed toward the evaluation of rehabilitation and psychological intervention is highlighted.     

Elastic constants of a fluorozirconate glass

Measurements have been made of the pressure and temperature dependences of the velocities of longitudinal and transverse ultrasonic waves in a glass having the composition 0.58ZrF₄: 0.34BaF₂: 0.08ThF₄. The experimental results are used to obtain the elastic constants and their pressure and temperature dependences, the Debye temperature (300K) and the acoustic mode Grüneisen gammas (γ₁₁ = 2.6, γ₄₄ = 0.9). In contrast to BeF₂ or silica-based glasses this material is well-behaved elastically.     

Synthesis of Al-substituted 11 Å tobermorite from newsprint recycling residue: a feasibility study

Newsprint recycling is responsible for significant volumes of secondary waste material for which further reprocessing and market development would be beneficial. In response to this problem, a layer lattice, ion exchange material, Al-substituted 11 Å tobermorite, has been synthesised from newsprint recycling residue comprising gehlenite (Ca₂Al₂SiO₇), akermanite (Ca₂MgSi₂O₇), β-dicalcium silicate (Ca₂SiO₄) and anorthite (CaAl₂Si₂O₈) under hydrothermal conditions at 100 °C in the presence of NaOH. The hydrogarnet phase, katoite (Ca₃Al₂SiO₁₂H₈), was also formed. Similar treatment regimes in the presence of LiOH and KOH did not yield significant quantities of Al-substituted 11 Å tobermorite. A batch sorption study confirmed that the Al-substituted 11 Å tobermorite-bearing product was effective in the exclusion of Cd²⁺, Pb²⁺ and Zn²⁺ from acidified aqueous media. The potential to enhance the yield of Al-substituted 11 Å tobermorite relative to that of katoite and thus optimise the ion exchange efficiency of the product is discussed with respect to its application to heavy metal-contaminated wastewater treatment.     

A HORIZONTAL WELLPOINT AS A LOW-IMPACT WATER SOURCE IN A DUNE-SANDS AQUIFER

A horizontal wellpoint groundwater source was constructed to supply irrigation water to a golf course from a coastal dune-sands aquifer in an area which has vulnerable wetland habitats of European importance. The source was designed to abstract the required quantities with less drawdown, compared with that from a conventional vertical wellpoint system, thus reducing any potential threat to the nature-conservation sites. Pump testing of the source showed that the yield was more than adequate to meet the needs of the Golf Club and to allow efficient operation of the computer-controlled course irrigation system. Data from observation wells indicated that there was no drawdown beyond the golf-course boundaries and none of the nature-conservation sites would be affected. The horizontal wellpoint method, which has not been widely applied in the UK, could have wider applications for irrigation water users who need to abstract water from shallow aquifers.     

Use of the polysilicon gate layer for local interconnect in a CMOStechnology incorporating LDD structures

In conventional single-level polysilicon technologies, the polysilicon gate layer can be used as an interconnect layer through buried contacts between polysilicon and one type of junction (usually n ⁺) in the underlying substrate. The formation and characteristics of buried contacts between n⁺ and p⁺ junctions and a single polysilicon gate layer are discussed. In addition, it is shown that the obstacles posed by the inclusion of oxide-sidewall spacers (common in present-day VLSI CMOS technologies) are surmountable with respect to the formation of useful buried contacts and the resultant local interconnect level that they provide