Conventional Barrier Research Articles

Dramatic reduction of read disturb through pulse width control in spin torque random access memory

Magnetizations dynamic effect in low current read disturb region is studied both experimentally and theoretically. Dramatic read error rate reduction through read pulse width control is theoretically predicted and experimentally observed. The strong dependence of read error rate upon pulse width contrasts conventional energy barrier approach and can only be obtained considering detailed magnetization dynamics at long time thermal magnetization reversal region. Our study provides a design possibility for ultra-fast low current spin torque random access memory.

Comparison of hot corrosion behaviors of plasma-sprayed nanostructured and conventional YSZ thermal barrier coatings exposure to molten vanadium pentoxide and sodium sulfate

Abstract The purpose of the current study was evaluation and comparison of hot corrosion behaviors of plasma-sprayed conventional and nanostructured yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs). Hot corrosion studies were performed on the surface of coatings in the presence of a molten mixture of V 2 O 5 +Na 2 SO 4 at 1000 °C for 30 h. Results indicated that the hot corrosion mechanisms of conventional and nanostructured YSZ coatings were similar. The reaction between corrosive salt and Y 2 O 3 produced YVO 4 , leaching Y 2 O 3 from YSZ and causing the detrimental phase transformation of zirconia from tetragonal to monoclinic. The nanostructured coating, as compared to its conventional counterpart, in spite of a further reaction with the corrosive salt, showed a higher degradation resistance during the hot corrosion test due to increased compliance capabilities resulting from the presence of an extra source of porosity associated with the nano-zones.

A mechanism study of sound wave-trapping barriers

The performance of a sound barrier is usually degraded if a large reflecting surface is placed on the source side. A wave-trapping barrier (WTB), with its inner surface covered by wedge-shaped structures, has been proposed to confine waves within the area between the barrier and the reflecting surface, and thus improve the performance. In this paper, the deterioration in performance of a conventional sound barrier due to the reflecting surface is first explained in terms of the resonance effect of the trapped modes. At each resonance frequency, a strong and mode-controlled sound field is generated by the noise source both within and in the vicinity outside the region bounded by the sound barrier and the reflecting surface. It is found that the peak sound pressures in the barrier's shadow zone, which correspond to the minimum values in the barrier's insertion loss, are largely determined by the resonance frequencies and by the shapes and losses of the trapped modes. These peak pressures usually result in high sound intensity component impinging normal to the barrier surface near the top. The WTB can alter the sound wave diffraction at the top of the barrier if the wavelengths of the sound wave are comparable or smaller than the dimensions of the wedge. In this case, the modified barrier profile is capable of re-organizing the pressure distribution within the bounded domain and altering the acoustic properties near the top of the sound barrier.

(Invited) Development of Multifunctional Liner/Barrier Systems for Sub-14nm Metallization

Mixed phase materials composed of refractory metal-based pairs such as Ru/TaN and Ru/WCN, grown by plasma enhanced atomic layer deposition (PEALD), can perform as directly platable Cu diffusion barriers which can be scaled to thicknesses of ~2-3nm. While such direct plate liners employ conventional barrier materials such as TaN and WCN, direct plate liner extendibility may be enhanced by employing a barrier metal with a lower intrinsic resistivity without the presence of carbide or nitride phases that are effective at preventing the diffusion of Cu. In considering suitable materials for this application, both the ability to support copper electrodeposition as well as good intrinsic copper and oxygen diffusion barrier performance are critical characteristics. Accordingly, dopant metals such as Co are selected as materials to investigate for replacement of conventional barrier materials in direct plate barriers by combining with Ru to form RuCo mixtures.

Electron transport across a metal-organic interface: Simulations using nonequilibrium Green's function and density functional theory

We simulate the electron transport across the Au(111)-pentacene interface using nonequilibrium Green's functions and density-functional theory (NEGF-DFT), and calculate the bias-dependent electron transmission. We find that the electrical contact resistance is dominated by the formation of a Schottky barrier at the interface, and show that the conventional semiconductor transport models across Schottky barriers need to be modified in order to describe the simulation data. We present an extension of the conventional Schottky barrier transport model, which can describe our simulation results and rationalize recent experimental data.

A nucleation-growth model of nanowires produced by the vapor-liquid-solid process

Within the framework of the vapor-liquid-solid process of Si nanowire growth, an expression describing the Si nanowire growth rate is derived and fitted to multiple experimental data sets with excellent agreement. The derivation is based on the two-dimensional island nucleation-growth process which appeared to have been first mentioned by Givargizov and Chernov [Sov. Phys. Crystallog. 18, 89 (1973)]. This nucleation-growth process is in principle different from the conventional diffusion limited or reaction barrier limited processes.

Structural stability of thermoelectric diffusion barriers: Experimental results and first principles calculations

This study demonstrates the feasibility of producing a tantalum nitride (TaN) thin film as a diffusion barrier and buffer layer for p-type bismuth telluride [(Bi,Sb)2Te3] thermoelectric devices. A network of TaN with nitrogen (N) incorporation is structurally more stable on (Bi,Sb)2Te3 than the conventional Ni diffusion barrier because of less inter-diffusion and a greater likelihood of stoichiometry in the TaN/(Bi,Sb)2Te3 interface. The atomic inter-diffusion between the barrier layers and (Bi,Sb)2Te3 was evaluated in terms of interface adhesion energy using nanoscratching, and proved with first-principles calculations.

Efficient generation of ozone in arrays of microchannel plasmas

Ozone is produced efficiently in arrays of low-temperature, linear microplasmas having a trapezoidal or parabolic cross-sectional profile and generated within nanoporous alumina (Al2O3) microchannels. Fabricated from aluminum foil by wet chemical processing, micropowder ablation, and one photolithographic step, arrays of microchannel plasma devices 3 cm in length and 250 µm in width at the aperture of the channel produce spatially uniform glow discharges in O2 feedstock gas at a pressure of 1 atm and flow rates of 0.25–2.5 standard litres per minute. Several device and array structures, incorporating embedded electrodes and Al/Al2O3 or glass channels, have been fabricated and tested extensively. A design based solely on microchannels fabricated in nanoporous alumina, flanked by Al electrodes buried in the channel wall, is found to be superior in performance to other materials and geometries. Altering the electric field profile inside the microchannels (by means of the electrode geometry) is found to have a significant impact on the reactor efficiency. Ozone output is observed to scale linearly with the number of microchannels in the array and the feedstock gas flow rate. Efficiencies and O3 concentrations surpassing 85 g kWh−1 and 17 g m−3, respectively, have been measured, and arrays as large as 120 microchannels have been realized to date. The results presented here suggest a new approach to plasma-chemical reactors, one in which ‘massively parallel’ processing of one or more gases in non-streamer (glow) discharges efficiently produces products of commercial value in thousands of micropores or microchannels fabricated in recyclable and inexpensive materials. Reductions of an order of magnitude in the weight and volume of microplasma-based O3 reactors, relative to conventional dielectric barrier discharge technology, appear to be feasible.

Crash Wall Design to Protect Mechanically Stabilized Earth Retaining Walls

Mechanically stabilized earth (MSE) retaining walls are used to provide roadway elevation for bridge approaches, underpass frontage roads, and other roadway elevation applications. Vehicular traffic may exist on the high (fill) side of the MSE retaining wall, the low side, or both sides. For traffic on the high side, a conventional traffic barrier might be placed on or near the top of the wall and mounted on a moment slab or a bridge deck. For traffic on the low side, a conventional traffic barrier might be installed adjacent to the wall or the wall itself may serve as the traffic barrier. Typical MSE wall panels are not designed to resist vehicle impacts. Therefore, structural damage to the wall panels and the earth fill would require complicated and expensive repairs. A simple reinforced-concrete crash wall constructed in front of the MSE wall panels could significantly reduce damage to the panels. It might prove practical to implement such a design to reduce costly repairs to the MSE wall structure. In this paper, LS-DYNA finite element analysis code was used to model and analyze a sacrificial crash wall design to determine its effectiveness in protecting an MSE retaining wall. Based on the LS-DYNA simulations, a crash wall that is 8 in. (0.2 m) thick is considered to be an adequate design to reduce damage to the MSE wall.

Improved efficiency droop characteristics in an InGaN/GaN light-emitting diode with a novel designed last barrier structure

In this study, the characteristics of nitride-based light-emitting diodes with different last barrier structures are analysed numerically. The energy band diagrams, electrostatic field near the last quantum barrier, carrier concentration in the quantum well, internal quantum efficiency, and light output power are systematically investigated. The simulation results show that the efficiency droop is markedly improved and the output power is greatly enhanced when the conventional GaN last barrier is replaced by an AlGaN barrier with Al composition graded linearly from 0 to 15% in the growth direction. These improvements are attributed to enhanced efficiencies of electron confinement and hole injection caused by the lower polarization effect at the last-barrier/electron blocking layer interface when the graded Al composition last barrier is used.

RADIO FREQUENCY MAGNETIZATION NONVOLATILITY

Long time magnetization thermal switching under small amplitude high frequency excitation is analyzed. Approaches based upon conventional time-dependent energy barrier are not sufficient to describe magnetization nonvolatility under GHz excitations. Methods based upon large angle nonlinear magnetization dynamics are developed for both coherent and noncoherent magnetization switching. This dynamic approach is not only important for fundamental understanding of magnetization dynamics under combined radio frequency excitations and thermal fluctuations, but also critical for practical design of emerging spintronic devices. When applied to spin torque random access memory read operations, as sensing current duration reaches nanosecond, dynamic approach gives a switching probability estimation orders of magnitude different from that obtained from conventional time-dependent energy barrier approach.

Millimeter-wave hybrid un-cooled narrow-gap hot-carrier and Schottky diodes direct detectors

Un-cooled narrow-gap mercury-cadmium-telluride (MCT) semiconductor thin layers grown on GaAs substrates that are hybridized with antennas on low permittivity dielectric substrates were considered as 128–144 GHz direct detection 6-element bolometers. Noise equivalent power (NEP) of such detectors in observed frequency range ν ≈ 128–144 GHz reaches NEP300K ≈ 2.6 × 10−10 W/Hz1/2 (with calculated gain G ≈ 9 dBi). To compare the results obtained, the measurements of GaAs conventional Schottky barrier diode detectors were fulfilled in the same conditions and similar to MCT bolometers NEP was observed.

Blue InGaN Light-Emitting Diodes With Multiple GaN-InGaN Barriers

Optical performance of blue InGaN light-emitting diodes (LEDs) with multiple GaN-InGaN barriers is investigated. The energy band diagrams, light-current performance curves, and internal quantum efficiency are studied numerically. The simulation results show that the InGaN LED has markedly improved the optical performance when the first conventional GaN barrier is replaced by the GaN-InGaN-GaN barrier, in which the indium composition is less than 5%, with other GaN barriers remain unchanged. The improved performance is due to the enhanced injection efficiency of holes and relatively uniform distribution of electrons and holes.

An autostereoscopic liquid crystal display with a polarized parallax barrier

Abstract An autostereoscopic liquid crystal display (LCD) with a polarized parallax barrier (PPB) is proposed. To separate multi-view images, the PPB and a polarizer array are added into a conventional thin film transistor (TFT) LCD. Every subpixel of the proposed autostereoscopic LCD has two independent and isometric electrodes on the surface of the color filter. The corresponding structure of the display and the calculation equations for the PPB are described in detail. A prototype of the display is developed. The luminance distribution of the prototype along the horizontal direction is measured. The simulation results indicate that the display presents stereoscopic images without crosstalk at the optimal view distance. Compared with the autostereoscopic display with conventional parallax barrier, the proposed autostereoscopic LCD provides higher quality stereoscopic images.

Fabrication and Evaluation of Plasma-Sprayed Nanostructured and Conventional YSZ Thermal Barrier Coatings

Yttria stabilized zirconia (YSZ) nanostructured and conventional coatings have been prepared by atmospheric plasma spraying (APS) on NiCoCrAlY-coated superalloy substrates. Bonding strength test was carried out based on the ASTM-C-633-01. To evaluate thermal insulation value of coatings, the thermal insulation capability test was designed and administered. Field emission scanning electron microscope (FESEM) and X-ray diffractometry (XRD) were employed to characterize the microstructures and the phase compositions of the powders and coatings. Nanostructured YSZ coating exhibited a bimodal microstructure consisting of nanosized particles retained from the powder and microcolumnar grains formed through the resolidification of the molten part of powder, whereas the microstructure of conventional YSZ coating consisted of columnar-grain splats. Both nanostructured and conventional YSZ coatings consisted of the non-transformable tetragonal phase. The results revealed that nanostructured coating, due to unique microstructure container of nanozones, presented improved bonding strength and thermal insulation capability as compared to the conventional coating. Keywords: Thermal barrier coating, nanostructure, microstructure, YSZ, plasma spraying, bonding strength, thermal insulation capability

Relativistic Double Barrier Problem with Three Transmission Resonance Regions

We obtain exact scattering solutions of the Dirac equation in 1 + 1 dimensions for a double square barrier vector potential. The potential bottom between the two barriers is chosen to be higher than 2mc2, whereas the top of the barriers is at least 2mc2above the bottom. The relativistic version of the conventional double barrier transmission resonances is obtained for energies within ±mc2from the height of the barriers. However, due to our judicious choice of potential configuration we also find two more (subbarrier) transmission resonance regions below the conventional one. Both are located within the two Klein energy zones and characterized by resonances that are broader than the conventional ones. The design of our double barrier so as to enable us to establish these two new subbarrier transmission resonance regions is our main finding.

Tantalum Nitride for Copper Diffusion Blocking on Thin Film (BiSb)2Te3

ABSTRACTThis study demonstrates the feasibility of introducing a TaN thin film as a copper diffusion barrier for p-type (BiSb)2Te3 thermoelectric material. Compared to conventional Ni diffusion barrier, remarkably little void generation in Cu bulk or near Cu/TaN interface originated from Cu penetration is observed for TaN barrier after suffering the thermal budget of close to soldering. Diffusion behaviors of the barriers were analyzed by transmission electron microscopy (TEM) and energy dispersive spectrometry (EDS) to make a deep understanding in clarifying interface diffusion effects among the Cu electrode, the barrier layer, and the (BiSb)2Te3thermoelectric layer.

Ultimate limits of conventional barriers and liners-implications for the extendibility of copper metallization

As allowable layer thicknesses shrink to the nanometer scale, metallization is facing fundamental limitations in the ability to extend conventional copper metallization schemes. The use of novel materials in the barrier/liner/seed stack can offer some relaxation of these roadblocks. For example, the development of a directly-platable barrier, thus avoiding the need to deposit a liner and seed, could offer potential benefits for scaling of copper past the 22 nm generation. This talk will introduce some of these emerging options and describe their performance compared with conventional copper barrier seed-based interconnects.

Evaporation protons from 8B+58Ni at near barrier energies

Yields of evaporated protons from the 8B+58Ni reaction are measured at backward angles, for several near barrier energies. Statistical model calculations using the code PACE are used to extrapolate the measurements to the whole angular region in order to get angle integrated cross sections. Fusion cross sections are deduced by using the calculated proton multiplicities. The obtained fusion excitation function shows a large enhancement as compared to BPM calculations using conventional barrier parameters.

Trapezoid mesa trench metal-oxide semiconductor barrier Schottky rectifier: an improved Schottky rectifier with better reverse characteristics

An improved structure of Schottky rectifier, called a trapezoid mesa trench metal-oxide semiconductor (MOS) barrier Schottky rectifier (TM-TMBS), is proposed and studied by two-dimensional numerical simulations. Both forward and especially better reverse I—V characteristics, including lower leakage current and higher breakdown voltage, are demonstrated by comparing our proposed TM-TMBS with a regular trench MOS barrier Schottky rectifier (TMBS) as well as a conventional planar Schottky barrier diode rectifier. Optimized device parameters corresponding to the requirement for high breakdown voltage are given. With optimized parameters, TM-TMBS attains a breakdown voltage of 186 V, which is 6.3% larger than that of the optimized TMBS, and a leakage current of 4.3×10−6 A/cm2, which is 26% smaller than that of the optimized TMBS. The relationship between optimized breakdown voltage and some device parameters is studied. Explanations and design rules are given according to this relationship.