Showing papers by "David P. Norton published in 2009"

Potential late-onset Alzheimer's disease-associated mutations in the ADAM10 gene attenuate α-secretase activity

Abstract: ADAM10, a member of a disintegrin and metalloprotease family, is an α-secretase capable of anti-amyloidogenic proteolysis of the amyloid precursor protein. Here, we present evidence for genetic association of ADAM10 with Alzheimer's disease (AD) as well as two rare potentially disease-associated non-synonymous mutations, Q170H and R181G, in the ADAM10 prodomain. These mutations were found in 11 of 16 affected individuals (average onset age 69.5 years) from seven late-onset AD families. Each mutation was also found in one unaffected subject implying incomplete penetrance. Functionally, both mutations significantly attenuated α-secretase activity of ADAM10 (>70% decrease), and elevated Aβ levels (1.5–3.5-fold) in cell-based studies. In summary, we provide the first evidence of ADAM10 as a candidate AD susceptibility gene, and report two potentially pathogenic mutations with incomplete penetrance for late-onset familial AD.

High mobility InGaZnO4 thin-film transistors on paper

Abstract: We report on the fabrication and the electrical properties of amorphous (α-)InGaZnO4 thin-film transistors deposited on cellulose paper by sputtering at room temperature. The 150-μm-thick paper was used as both a gate dielectric and a substrate for device structural support. The transistors on paper were patterned by lithography and operated in enhancement mode with a threshold voltage of 3.75 V, and exhibited saturation mobility, subthreshold gate-voltage swing, and drain current on-to-off ratio of ∼35 cm2 V−1 s−1, 2.4 V decade−1, and ∼104, respectively. These results verify that simple cellulose paper is a good gate dielectric as well as a low-cost substrate for flexible electronic devices such as paper-based displays.

REVIEW OF RECENT ADVANCES IN TRANSITION AND LANTHANIDE METAL–DOPED GaN AND ZnO

Abstract: Wide band gap semiconductors such as GaN and ZnO have continued to be at the forefront of spintronics research due to the demonstration of room-temperature ferromagnetism in these materials. A goal of this research is the fabrication of a spintronic device that may provide easy incorporation into existing GaN and ZnO technologies, higher integration density, and less power consumption that its electronic counterparts while achieving similar speeds. The progression of the ferromagnetic metals incorporated into GaN has moved from transition metals to rare earth metals such as the lanthanides. The properties of transition metal–doped ZnO thin films for the two most studied transition metal dopants, namely Mn and Co, are also discussed in this review.

Nucleation of epitaxial yttria-stabilized zirconia on biaxially textured Ñ001Ö Ni for deposited conductors

Abstract: The nucleation of (001)-oriented yttria-stabilized zirconia (YSZ) directly on the (001) Ni surface is realized via nucleation on an oxygen-terminated nickel surface using pulsed-laser deposition. Under conditions where the nickel surface is either oxygen free or substantially covered with NiO, a mixed orientation of YSZ occurs. The epitaxial YSZ layer grown on a biaxially textured Ni(001) surface was used as a single buffer layer for a high temperature superconducting coated conductor architecture, yielding superconducting YBa2Cu3O7 films with high critical current densities, Jc. This architecture eliminates the necessity for a multilayer buffer architecture, since high Jc superconducting films are achieved with no intermediate buffer layer between the (001) YSZ and the biaxially textured metal.

Transparent dual-gate InGaZnO thin film transistors: OR gate operation

Abstract: Transparent dual-gate (DG) InGaZnO4 thin film transistors for OR logic operation were fabricated on a glass substrate. A 100-nm-thick SiO2 layer used as both top and bottom gate dielectrics was deposited by plasma enhance chemical vapor deposition at 200°C. Compared to bottom gate, top gate thin film transistors (TFTs) exhibited better device performance with higher saturation mobility, drain current on-to-off ratio, lower threshold voltage, and subthreshold gate-voltage swing. This improved performance was mainly attributed to low process-induced damage or low parasitic capacitance between gate and source/drain and low parasitic resistance between channel and source/drain in top-contact TFT configuration (coplanar type). DG-mode TFTs showed saturation mobility of ∼16.9cm2V−1s−1, drain current on-to-off ratio of ∼1×106, subthreshold gate-voltage swing of ∼0.33Vdecade−1, and threshold voltage of ∼1.25V. The results demonstrate that DG InGaZnO4 TFTs are effective in improving the device performance because ...

Properties of reactively sputtered W–B–N thin film as a diffusion barrier for Cu metallization on Si

Abstract: Thin films of W–B–N (10 nm) have been evaluated as diffusion barriers for Cu interconnects. The amorphous W–B–N thin films were prepared at room temperature via reactive magnetron sputtering using a W2B target at various N2/(Ar + N2) flow ratios. Cu diffusion tests were performed after in-situ deposition of 200 nm Cu. Thermal annealing of the barrier stacks was carried out in vacuum at elevated temperatures for one hour. X-ray diffraction patterns, sheet resistance measurement, cross-section transmission electron microscopy images, and energy-dispersive spectrometer scans on the samples annealed at 500°C revealed no Cu diffusion through the barrier. The results indicate that amorphous W–B–N is a promising low resistivity diffusion barrier material for copper interconnects.

Chemical vapor deposition of WNxCy using the tungsten piperidylhydrazido complex Cl4(CH3CN)W(N-pip): Deposition, characterization, and diffusion barrier evaluation

Abstract: The tungsten piperidylhydrazido complex Cl4(CH3CN)W(N-pip) (1) was used for film growth of tungsten carbonitride (WNxCy) by metal-organic chemical vapor deposition (CVD) in the absence and presence of ammonia (NH3) in H2 carrier. The microstructure of films deposited with NH3 was x-ray amorphous between 300 and 450°C. The chemical composition of films deposited with NH3 exhibited increased N levels and decreased C levels over the entire deposition temperature range (300–700°C) as compared to films deposited without NH3. As determined by x-ray photoelectron spectroscopy, W is primarily bonded to N and C for films deposited at 400°C, but at lower deposition temperature the binding energy of the W–O bond becomes more evident. The growth rates of films deposited with NH3 varied from 0.6A∕min at 300°C to 4.2A∕min at 600°C. Over 600°C, the growth rate decreased when using NH3 presumably due to parasitic gas phase reactions that deplete the precursor. Diffusion barrier properties were investigated using Cu∕WNxCy...

Interface dependent electrical properties of amorphous InGaZnO4 thin film transistors

Abstract: The performance of amorphous InGaZnO4 thin film transistors with three different gate dielectrics (SiO2, SiON, and SiNx) is reported. The gate dielectric films were prepared by plasma enhanced chemical vapor deposition with SiH4, N2O, and NH3 gases at 250°C. Current-voltage (C-V) and refractive index characterization showed that different film compositions were achieved when changing the flow rate of N2O in the precursor gas mixture. The use of SiNx films reduced the interfacial roughness of the channel/gate dielectric by a factor of 2.3 compared to SiO2. This results in an improvement of saturation mobility of the thin film transistors (TFTs) by a similar factor. An enhancement of subthreshold gate-voltage swing and drain current on-to-off ratio for TFTs with SiNx was also attributed to the reduction of the trap density at the channel/gate-dielectric interface.

Rectifying ZnO : Ag ∕ ZnO : Ga Thin-Film Junctions

Abstract: The synthesis and properties of Ag-doped ZnO thin films and junctions grown by pulsed-laser deposition are examined. Hall measurements indicate that silver-doped ZnO films can be p-type when deposited at relatively low temperature with hole concentrations on the order of 10 19 cm -3 . Photoluminescence reveals a near-bandedge emission at room temperature with little or no visible emission due to midgap states. The properties of Ag-doped ZnO/Ga-doped ZnO thin-film junctions deposited on c-plane sapphire were also examined. Current-voltage measurements across the junction showed rectifying behavior with a turn-on voltage of 3.0 V. Light emission was detected for junctions under bias.

Persistent photoconductivity in MgZnO alloys

Abstract: The electrical characteristics and persistent-conductivity effects in MgZnO:P alloys grown by the method of pulsed laser deposition on undoped n-ZnO substrates are systematically investigated. It is shown that the pronounced persistent conductivity and the persistent photocapacitance related to the presence of high-barrier electron traps for electron capture are observed in initial unannealed layers. These traps are located in the lower half of the band gap and have the optical ionization threshold of 2.8 eV and the electron-capture barrier height of ∼0.4 eV. Alongside such centers, the hole traps with the ionization energy of 0.14 eV are also observed. The annealing at 850°C transforms the material into that of p-type conductivity with the depth of dominant phosphorus-related acceptors close to 0.2 eV. The conductivity compensation and the formation of hole traps with the activation energy of 0.14 and 0.84 eV in the n-ZnO substrate are also observed, and these traps are associated with the acceptor-defect diffusion into the substrate at annealing.

Ferromagnetism in Transition‐Metal Doped ZnO

Abstract: ZnO is an attractive candidate for spintronics studies because of its potential for exhibiting high Curie temperatures and the relative lack of ferromagnetic second phases in the material. In this paper, we review experimental results on transition-metal (TM) doping of ZnO and the current state of theories for ferromagnetism. It is important to re-examine some of the earlier concepts for spintronics devices, such as the spin field-effect transistor, to account for the presence of the strong magnetic field that has deleterious effects. In some of these cases, the spin device appears to have no advantage relative to the conventional charge-control electronic analog. We have been unable to detect optical spin polarization in ZnO.