Showing papers on "Barrier layer published in 2012"

Electron Tunneling through Ultrathin Boron Nitride Crystalline Barriers

Abstract: We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.

Solid-oxide fuel cell

Abstract: A solid oxide fuel cell (10) comprises a solid electrolyte layer (30), a barrier layer (40), and a cathode (50) The cathode (50) includes a cathode current collecting layer (51) and a cathode active layer (52) The cathode active layer (52) includes a plurality of micro-cracks (SL) in an interface region (52a) within a predetermined distance (Da) from the interface (P2) between the cathode current collecting layer (51) and the cathode active layer (52)

Silicon carbide semiconductor device

Abstract: This silicon-carbide semiconductor device (101) has a silicon-carbide substrate (10), a main electrode (52), a first barrier layer (70a), and a wiring layer (60). The main electrode (52) is provided directly on top of the silicon-carbide substrate (10). The first barrier layer (70a) is provided on top of the main electrode (52) and is made from a conductive material that does not contain aluminum. The wiring layer (60) is provided on top of the first barrier layer (70a), is isolated from the main electrode (52) by the first barrier layer (70a), and is made from a material that does contain aluminum.

Magnetic sensor having a high spin polarization reference layer

Abstract: A magnetic sensor configured to reside in proximity to a recording medium during use having a high spin polarization reference layer stack above AFM layers. The reference layer stack comprises a first boron-free ferromagnetic layer above the AFM coupling layer; a magnetic coupling layer on and in contact with the first boron-free ferromagnetic layer; a second ferromagnetic layer comprising boron deposited on and contact with the magnetic coupling layer; and a boron-free third ferromagnetic layer on and in contact the second ferromagnetic layer. A barrier layer is deposited on and in contact with the boron-free third ferromagnetic layer. In one aspect of the invention, the magnetic coupling layer may comprise at least one of Ta, Ti, or Hf. A process for providing the magnetic sensor is also provided.

Two-photon excitation in an intermediate band solar cell structure

Abstract: We present evidence for the production of photocurrent due to two-photon excitation in an intermediate band solar cell structure. The structure consists of an n-GaNAs intermediate band layer sandwiched between a p-AlGaAs emitter and an n-AlGaAs barrier layer with suitable doping level to block electron escaping from the intermediate band to the bottom n-GaAs substrate. Multi-band transitions observed in two-photon excitation experiments are explained using photo-modulated reflectance spectrum, and further support for intermediate band solar cell operation of this structure is given by current-voltage measurements.

Double-layer graphene and topological insulator thin-film plasmons

Abstract: We present numerical and analytical results for the optical and acoustic plasmon collective modes of coupled massless-Dirac two-dimensional electron systems. Our results apply to topological insulator (TI) thin films and to two graphene sheets separated by a thin dielectric barrier layer. We find that, because of strong bulk dielectric screening, TI acoustic modes are locked to the top of the particle-hole continuum and, therefore, probably unobservable.

Spin torque transfer magnetic tunnel junction fabricated with a composite tunneling barrier layer

Abstract: A STT-RAM MTJ is disclosed with a composite tunnel barrier comprised of a CoMgO layer that contacts a pinned layer and a MgO layer which contacts a free layer. A CoMg layer with a Co content between 20 and 40 atomic % is deposited on the pinned layer and is then oxidized to produce Co nanoconstrictions within a MgO insulator matrix. The nanoconstrictions control electromigration of Co into an adjoining MgO layer. The free layer may comprise a nanocurrent channel (NCC) layer such as FeSiO or a moment dilution layer such as Ta between two ferromagnetic layers. Furthermore, a second CoMgO layer or a CoMgO/MgO composite may serve as a perpendicular Hk enhancing layer formed between the free layer and a cap layer. One or both of the pinned layer and free layer may exhibit in-plane anisotropy or perpendicular magnetic anisotropy.

Underlayers for heat assisted magnetic recording (HAMR) media

Abstract: Various embodiments provide for a heat assisted magnetic recording (HAMR) media comprising: a magnetic recording layer; a barrier layer disposed under the magnetic recording layer; a first underlayer disposed under the barrier layer; and an amorphous seedlayer disposed under the first underlayer. For some embodiments, the recording medium may comprise: a magnetic recording layer including FePt alloy, a CoPt alloy, or a FePd alloy; a barrier layer including MgO, TiC, TiN, CrN, TiCN, β-WC, TaC, HfC, ZrC, VC, NbC, or NiO; a first underlayer including RuAl-oxide, NiAl, FeAl, AlMn, CuBe, or AlRe; or an amorphous seedlayer including a Cr—X alloy, where X comprises Al, B, C, Cu, Hf, Ho, Mn, Mo, Ni, Ta, Ti, V, W, or Ru.

Electronic properties of Cu(In,Ga)Se2 solar cells on stainless steel foils without diffusion barrier

Abstract: Compared with rigid glass, manufacturing of Cu(In,Ga)Se2 (CIGS) solar cells on flexible stainless steel (SS) substrates has potential to reduce production cost because of the application of roll-to-roll processing. Up to now, high-efficiency cells on SS could only be achieved when the substrate is coated with a barrier layer (e.g. SiOx or Si3N4) for hindering the diffusion of impurities, especially Fe, into the CIGS layer. In this paper, the effect of these impurities on the electronic transport properties of the device is investigated. Using admittance spectroscopy, the presence of a deep defect level at around 320 meV is observed, which deteriorates the efficiency of the solar cells. Furthermore, it is shown that reducing substrate temperature during CIGS deposition is an effective alternative to a barrier layer for reducing diffusion of detrimental Fe impurities into the absorber layer. By applying a CIGS growth process for deposition at low substrate temperatures, an efficiency of 17.7%, certified by Fraunhofer Institute ISE, Freiburg, was achieved on Mo/Ti-coated SS substrate without an additional metal-oxide or metal-nitride impurity diffusion barrier layer. Copyright © 2012 John Wiley & Sons, Ltd.

Coated article including low-emissivity coating, insulating glass unit including coated article, and/or methods of making the same

Abstract: Certain example embodiments relate to a coated article including at least one infrared (IR) reflecting layer of a material such as silver or the like in a low-E coating, and methods of making the same. In certain cases, at least one layer of the coating is of or includes nickel and/or titanium (e.g., NixTiyOz). The provision of a layer including nickel titanium and/or an oxide thereof may permit a layer to be used that has good adhesion to the IR reflecting layer, and reduced absorption of visible light (resulting in a coated article with a higher visible transmission). When a layer including nickel titanium oxide is provided directly over and/or under the IR reflecting layer (e.g., as a barrier layer), this may result in improved chemical and mechanical durability. Thus, visible transmission may be improved if desired, without compromising durability; or, durability may simply be increased.

Low-crystallization temperature MTJ for Spin-Transfer Torque Magnetic Random Access Memory (STTMRAM)

Abstract: A spin-torque transfer memory random access memory (STTMRAM) element is disclosed and has a fixed layer, a barrier layer formed upon the fixed layer, and a free layer comprised of a low-crystallization temperature alloy of CoFeB—Z where Z is below 25 atomic percent of one or more of titanium, (Ti), yittrium (Y), zirconium (Zr), and vanadium (V), wherein during a write operation, a bidirectional electric current is applied across the STTMRAM element to switch the magnetization of the free layer between parallel and anti-parallel states relative to the magnetization of the fixed layer.

Effect of Anodizing Potential on the Formation and EIS Characteristics of TiO2 Nanotube Arrays

Abstract: In the present work, well ordered arrays of Ti0 2 nanotubes were obtained by anodization at different voltages of Ti foil in a solution containing anhydrous ethylene glycol + 0.27 M NH 4 F and 0.2 wt% water. A detailed study has been performed to evaluate the morphology and electrochemical characteristics of the anodized Ti foil synthesized in different anodization potentials. Correlation between the physical properties and the dimensional aspect of TiO 2 nanotubes was examined. In this paper, we report the electrochemical characteristics of the Ti/TiO 2 nanotube surfaces from Tafel plots. The electronic properties ofTi02 nanotubular layers were also determined by electrochemical impedance spectroscopy analysis (EIS). EIS is considered to be a valuable tool that allows determining barrier oxide parameters. A linear dependence of barrier thickness on the anodizing voltage was verified from 20 to 50 V, the proportionality constant of the barrier layer thickness in relation to the applied anodizing voltage was estimated from the proposed equivalent circuit.

Perpendicular MTJ stacks with magnetic anisotropy enhancing layer and crystallization barrier layer

Abstract: Magnetic tunnel junctions (MTJ) suitable for spin transfer torque memory (STTM) devices, include perpendicular magnetic layers and one or more anisotropy enhancing layer(s) separated from a free magnetic layer by a crystallization barrier layer. In embodiments, an anisotropy enhancing layer improves perpendicular orientation of the free magnetic layer while the crystallization barrier improves tunnel magnetoresistance (TMR) ratio with better alignment of crystalline texture of the free magnetic layer with that of a tunneling layer.

Magnetoresistance effect in L10-MnGa/MgO/CoFeB perpendicular magnetic tunnel junctions with Co interlayer

Abstract: The fully perpendicular magnetic tunnel junctions (p-MTJs) based on L10-MnGa and thin CoFeB electrodes with MgO barrier were reported in this letter. A thin Co layer was introduced between the MnGa layer and the MgO barrier layer to investigate interfacial effect on the device’s magnetic and transport properties. The magnetoresistance ratio improved significantly due to the Co insertion, and reached 40% at room temperature (80% at 5 K) when the Co thickness was 1.5 nm. Moreover, the junctions with Co interlayer exhibited four low-resistance states in one full cycle rather than two in normal MTJs. The physical origin was discussed by considering the coupling between MnGa and Co layers.

Some personal adventures in passivity—A review of the point defect model for film growth

Abstract: A review is presented of the history of the development of the Point Defect Model (PDM) for the growth and breakdown of passive films that form on the surfaces of reactive metals in contact with corrosive, condensed phase environments. The PDM has passed through three generations, with each successive generation addressing issues that have arisen from experiment. Thus, the first Generation model (PDM-I), which was developed in the late 1970s/early 1980s, assumed that the passive film was a single defective oxide layer that contained cation vacancies and oxygen vacancies that were generated and annihilated at the metal/film and film/solution interfaces. This model was inspired by the work by Wagner on high temperature oxidation. As with gas-phase systems, the film was assumed not to dissolve. However, it soon became evident that this model could not account for the properties of the passive state on metals in contact with aqueous environments and, accordingly a Generation II model (PDM-II) was developed to address these issues. PDM-II incorporated the bi-layer structure of the film comprising a defective oxide (or hydride) barrier layer that grows into the metal and an outer layer that forms by precipitation of material from the reaction of cations transmitted through the barrier layer with species in the environment (including water, CO32−, HS−, etc.), introduced metal interstitials to the suite of defects, recognized barrier layer dissolution, and recognized the need to classify reactions as to whether they are lattice conservative or non-conservative. PDM-II has enjoyed considerable success and the author knows of no instance where it has been demonstrated to be at odds with experiment when confluence between experiment and theory has been demonstrated. A Generation III model (PDM-III) has been recently developed to extend the theory to those cases (e.g., the valve metals) where the outer layer is so resistive that it controls the impedance of the interface and hence the corrosion rate. A fourth generation model that will describe passivity on alloys is now under development. The experimental evidence upon which each generation is based is reviewed.

Effect of quantum well cap layer thickness on the microstructure and performance of InGaN/GaN solar cells

Abstract: A two-step GaN barrier growth methodology was developed for InxGa1−xN/GaN multiple quantum well solar cells in which a lower temperature GaN cap layer was grown on top of the quantum wells (QWs) and then followed by a higher temperature GaN barrier layer. The performance of the solar cells improved markedly by increasing the low temperature GaN cap layer thickness from 1.5 to 3.0 nm. High-angle annular dark field scanning transmission electron microscopy and atom probe tomography measurements showed that increasing the GaN cap layer thickness improved the uniformity and increased the average indium content of the QWs.

Method of forming a semiconductor device

Abstract: A method of forming a semiconductor device includes forming an under-bump metallurgy (UBM) layer including a barrier layer and a seed layer over the barrier layer; and forming a mask over the UBM layer. The mask covers a first portion of the UBM layer, and a second portion of the UBM layer is exposed through an opening in the mask. The first portion of the UBM layer includes a barrier layer portion and a seed layer portion. A metal bump is formed in the opening and on the second portion of the UBM layer. The mask is then removed. A wet etch is performed to remove the seed layer portion. A dry etch is performed to remove the barrier layer portion. By using the embodiments, the undercuts to barrier layer, if any, is significantly reduced to 1 [mu]m or even less. With a well-controlled process, the undercuts were essentially eliminated in experiments. Accordingly, the reliability of the metal bump formation process and the redistribution line formation process is significantly improved due to the reduced delamination caused by the undercuts.

On the formation of barrier layers and associated vertical temperature inversions: A focus on the northwestern tropical Atlantic

Abstract: [1] A unique barrier layer (BL) system in terms of persistence, extension, and associated subsurface temperature maximum is present seasonally in the northwestern tropical Atlantic. Based on climatological output of a general circulation ocean model, we show here that its development consists of two phases. In summer, the BL is relatively shallow and thin but subsurface temperature maxima are intense. The latter develop as a result of the specific seasonality of the freshwater discharge in this area, which limits the mixed layer to a very thin depth while the intense radiative heat flux penetrates significantly below, thereby heating the subsurface waters protected from air-sea interactions and inducing a barrier layer between the mixed layer and the ocean interior. In winter, the BL development is due to a surface decrease in salinity associated with the surface freshwater capping, which decouples the pycnocline, and hence the winter mixed layer, from the thermocline. The mechanism is ubiquitous in the sense that it is very similar to that of other areas at the same latitude, as well as at high latitudes in regions of seasonal surface freshening. Results are discussed in the light of a simple linear equation linking the BL development to time evolution of Sea Surface Temperature and Sea Surface Salinity stratification.

Fabrication of magnetic tunnel junctions with a bottom synthetic antiferro-coupled free layers for high sensitive magnetic field sensor devices

Abstract: Magnetic tunnel junctions with a Ni80Fe20/Ru/Co40Fe40B20 synthetic antiferro-coupled bottom free layer and an MgO barrier layer have been fabricated. Double annealing process was carried out in order to obtain linearity against magnetic field with hysteresis-free resistance response. The effect of the annealing temperature and NiFe thickness in the free layer on the magnetic field sensor performance was investigated. We have observed a very high sensitivity of 25.3%/Oe while keeping linearity.

Normally-off semiconductor devices

Abstract: Normally-off semiconductor devices are provided. A Group III-nitride buffer layer is provided. A Group III-nitride barrier layer is provided on the Group III-nitride buffer layer. A non-conducting spacer layer is provided on the Group III-nitride barrier layer. The Group III-nitride barrier layer and the spacer layer are etched to form a trench. The trench extends through the barrier layer and exposes a portion of the buffer layer. A dielectric layer is formed on the spacer layer and in the trench and a gate electrode is formed on the dielectric layer. Related methods of forming semiconductor devices are also provided herein.

Barrier Layer Effect on the Electron Transport of the Dye-Sensitized Solar Cells Based on TiO2 Nanotube Arrays

Abstract: We have studied the effect of the barrier layer on the electron transport of dye-sensitized solar cells (DSSCs) based on TiO2 nanotube arrays. The barrier layer of TiO2 nanotubes, corresponding to ...

Sub-50-nm $\hbox{In}_{0.7}\hbox{Ga}_{0.3}\hbox{As}$ MOSFETs With Various Barrier Layer Materials

Abstract: Sub-50-nm In0.7Ga0.3As MOSFETs with high-k dielectric Al2O3 have been demonstrated and investigated. The device performance of buried-channel In0.7Ga0.3As MOSFETs with various barrier layer materials (i.e., InP and InAlAs) has been analyzed and compared to that of devices without a barrier layer. The 40-nm-gate-length In0.7Ga0.3 As MOSFETs with InP/InAlAs barrier exhibit a subthreshold swing of 130 mV/dec, a drain-induced barrier lowering of 174 mV/V, and an extrinsic transconductance of 570 mS/mm at Vds = 1 V. Scaling behaviors of buried-channel In0.7Ga0.3As MOSFETs with and without a barrier layer material have also been analyzed.

Transistor device and materials for making

Abstract: This application relates to graphene based heterostructures and transistor devices comprising graphene. The heterostructures comprise i) a first graphene layer; ii) a spacer layer and iii) a third graphene. The transistors comprise (i) an electrode, the electrode comprising a graphene layer, and (ii) an insulating barrier layer.