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The ability to vary the conductance of a valence-change memristor in a continuous manner makes it a prime choice as an artificial synapse in neuromorphic systems. Because synapses are the most numerous components in the brain, exceeding the neurons by several orders of magnitude, the scalability of artificial synapses is crucial to the development of large scale neuromorphic systems but is an issue which is seldom investigated. Leveraging on the conductive atomic force microscopy method, we found that the conductance switching of nanoscale memristors (∼25 nm2) is abrupt in a majority of the cases examined. This behavior is contrary to the analoglike conductance modulation or plasticity typically observed in larger area memristors. The result therefore implies that plasticity may be lost when the device dimension is scaled down. The contributing factor behind the plasticity behavior of a large-area memristor was investigated by current mapping, and may be ascribed to the disruption of the plurality of conductive filaments happening at different voltages, thus yielding an apparent continuous change in conductance with voltage. The loss of plasticity in scaled memristors may pose a serious constraint to the development of large scale neuromorphic systems. [ABSTRACT FROM AUTHOR]

We show that resistive switching in the SiO2/Cu stack can be modified by a brief exposure of the oxide to an Ar plasma. The set voltage of the SiO2/Cu stack is reduced by 33%, while the breakdown voltage of the SiO2/Si stack (control) is almost unchanged. Besides, the Ar plasma treatment suppresses the negative photoconductivity or optical resistance reset effect, where the electrically formed filamentary conductive path consisting of Cu-ion and oxygen-vacancy clusters is disrupted by the recombination of the oxygen vacancies with nearby light-excited oxygen ions. From the enhanced O-H peak in the Fourier-transform infrared spectrum of the plasma-treated oxide, it is proposed that the Ar plasma has created more oxygen vacancies in the surface region of the oxide. These vacancies in turn adsorb water molecules, which act as counter anions (OH-) promoting the migration of Cu cations into the oxide and forming a more complete Cu filament that is less responsive to light. The finding points to the prospect of a control over the optical resistance reset effect by a simple surface treatment step. [ABSTRACT FROM AUTHOR]

We show that the negative photoconductivity property of the nanoscale filamentary breakdown path in the SiO2 electrolyte of the SiO2/Cu conductive bridge resistive random access memory (CBRAM) stack is affected by the number of positive-voltage sweeps applied to the Cu electrode (with respect to a non-metal counter electrode). The path's photo-response to white light, of a given intensity, is suppressed with an increasing number of applied positive-voltage sweeps. When this occurs, the path may only be disrupted by the light of a higher intensity. It is further shown that the loss of the path's photosensitivity to the light of a given intensity can be recovered using a negative-voltage sweep (which eliminates the path), followed by the reformation of the path by a positive-voltage sweep. The above behavior is, however, not seen in the SiO2/Si stack (which involves a non-metal Si electrode), suggesting that the photo-response modulation effect is related to the Cu electrode. The demonstrated reversible electrical modulation of the path's photo-response may afford greater flexibility in the electro-optical control of the CBRAM device. [ABSTRACT FROM AUTHOR]

Study on complementary resistive switching of TiN/HfOx/TiN memory device has shown that the device is highly susceptible to self-reset, i.e., the device is automatically programmed into the high-resistance state during forming. This is observed in the following opposite-polarity voltage sweep, in which the device exhibits a set behavior (instead of a reset as typically observed in bipolar switching mode). Interestingly, the self-reset behavior is: 1) suppressed in devices with a thin Al2O3 layer inserted in-between the TiN and HfOx and 2) completely eliminated in devices with the TiN cathode replaced by Pt. These results are consistent with a hypothesis that ascribes the self-reset to the migration of oxygen ions from the cathode interfacial oxide into the conducting filament in the HfOx during the forming transient, thus resulting in the disruption of the filament. With the reduction in voltage loading across the cathode interfacial oxide during forming transient in devices with the Al2O3 interlayer and the elimination of interfacial oxide in devices with the Pt cathode, the occurrence of self-reset is reduced or eradicated. [ABSTRACT FROM PUBLISHER]

This study shows that a majority (70%) of TiN/HfOx/TiN devices exhibit failed complementary resistance switching (CRS) after forming. In conjunction with the consistent observation of a large non-polar reset loop in the first post-forming voltage-sweep measurement, it is proposed that breakdown of the TiN/HfOx interfacial oxide layers (crucial in enabling CRS) and the accompanied formation of Ti filaments (due to Ti migration from the TiN cathode into the breakdown path) resulted in CRS failure and the observed non-polar reset behavior. This hypothesis is supported by the significant reduction or complete elimination of the large non-polar reset and CRS failure in devices with a thin Al2O3 layer incorporated at the TiN-cathode/HfOx or both TiN/HfOx interfaces. The higher breakdown field of the thin Al2O3 enables it to sustain the forming voltage until the forming process is interrupted, thus enabling CRS via oxygen exchange with the adjacent vacancytype filament formed in the HfOx. [ABSTRACT FROM AUTHOR]

Nanoscale conducting filament, which forms the basis of the HfO2 resistive memory, is shown to exhibit a "negative photoconductivity" behavior, in that, electrical conduction through it can be disrupted upon white-light illumination. This behavior should be contrasted against the positive photoconductivity behavior commonly exhibited by oxides or perovskites having narrower bandgaps. The negative photoconductivity effect may be explained in terms of a photon-induced excitation of surrounding oxygen ions, which leads to migration and subsequent recombination with vacancies in the conducting filament. The finding suggests possible electrical-cum-optical applications for HfO2-based devices, whose functionality is limited to-date by electrical stimulation. [ABSTRACT FROM AUTHOR]

The role of the bottom interfacial layer (IL) in enabling stable complementary resistive switching (CRS) in the TiN/HfOx/IL/TiN resistive memory device is revealed. Stable CRS is obtained for the TiN/HfOx/IL/TiN device, where a bottom IL comprising Hf and Ti sub-oxides resulted from the oxidation of TiN during the initial stages of atomic-layer deposition of HfOx layer. In the TiN/HfOx/Pt device, where formation of the bottom IL is suppressed by the inert Pt metal, no CRS is observed. Oxygen-ion exchange between IL and the conductive path in HfOx layer is proposed to have caused the complementary bipolar switching behavior observed in the TiN/HfOx/IL/TiN device. [ABSTRACT FROM AUTHOR]

In recent years, dielectric relaxation methods in time and frequency domains have been evolved as a tool for the assessment of transformer insulation. However, it has been observed that the results of these tests are highly influenced by several factors viz. the temperature of the insulation, the magnitude of the test voltage, the geometry of transformer insulation structure. In the present work, a detailed analysis of the influence of the above-mentioned factors on the dielectric response data is presented by performing measurements on a prorated transformer model. A novel experimental procedure is suggested to acquire a database to study the effect of insulation duct geometry on the relaxation measurements. Possible corrective actions are suggested to improve transformer insulation diagnosis. [ABSTRACT FROM PUBLISHER]

Electrical and reliability characteristics of the HfSiOx high-permittivity (high-k) gate dielectric formed via a single-step and a multi-step deposition-cum-annealing method are examined via ultrahigh-vacuum scanning tunneling microscopy (STM). Unlike the single-step high-k, which exhibits coarse granular features indicating that transformation to a polycrystalline phase has occurred, the multi-step high-k of equivalent physical thickness is observed to retain the nanocrystalline STM characteristics following a high temperature (∼1000°C) anneal. After the localized electrical stress using the STM probe, the multi-step high-k film shows better leakage current uniformity and higher breakdown voltage comparing to those of the single-step film, consistent with the results of the metal-oxide-semiconductor capacitor measurements. The improvements may be ascribed to a partially suppressed formation of the grain boundaries in thin films constituting the multi-step dielectric, which reduces the grain-boundary related low-resistance paths through the dielectric. The results indicate that the multi-step deposition process can improve electrical characteristics of the high-k gate dielectrics. [ABSTRACT FROM AUTHOR]

In this brief, high-\kappa HfZrO (via atomic layer deposition) fabricated by a novel multideposition multiroom-temperature annealing (MDMA) technique in ultraviolet-ozone (UVO) ambient is systematically investigated by both electrical and physical characterization and is integrated with a TiN metal gate in a gate-last process. Compared with the conventional rapid-thermal-annealed sample, it is found that the device annealed via MDMA in UVO demonstrates the following: 1) more than one order of leakage current reduction at 25 ^\circ\C and 125 ^\circ\C without an equivalent oxide thickness penalty; 2) less susceptibility to stress-induced degradation; and 3) improved time-dependent dielectric-breakdown lifetime. Grain boundary suppression and healing of oxygen vacancies are believed to be responsible for the improvement, as evidenced by scanning tunneling microscopy and X-ray photoelectron spectroscopy analysis. [ABSTRACT FROM AUTHOR]

Self-assembled GaInNAs quantum dots (QDs) were grown on GaAs (001) substrate using solid-source molecular-beam epitaxy (SSMBE) equipped with a radio-frequency nitrogen plasma source. The GaInNAs QD growth characteristics were extensively investigated using atomic-force microscopy (AFM), photoluminescence (PL), and transmission electron microscopy (TEM) measurements. Self-assembled GaInNAs/GaAsN single layer QD lasers grown using SSMBE have been fabricated and characterized. The laser worked under continuous wave (CW) operation at room temperature (RT) with emission wavelength of 1175.86 nm. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼1.05 kA/cm2 from a GaInNAs QD laser (50 × 1,700 µm2) at 10 °C. High-temperature operation up to 65 °C was demonstrated from an unbonded GaInNAs QD laser (50 × 1,060 µm2), with high characteristic temperature of 79.4 K in the temperature range of 10–60 °C. [ABSTRACT FROM AUTHOR]

From conductive-atomic-force-microscope probe measurement, we show that electrical conduction through a nanoscale percolation path in the MOSFET gate oxide can be disrupted, either completely or partially, by white-light illumination. This phenomenon is consistently observed in the SiO2 and HfO2 gate-oxide materials, and thus is believed to have originated from a common mechanism—light-stimulated oxygen migration and recombination with vacancy sites that constitute the percolation path. The finding points to the prospect of reliability rejuvenation by the light-assisted restoration of postelectrical-breakdown gate oxides, as well as light-enabled memory operation based on logic MOSFET devices. [ABSTRACT FROM AUTHOR]

We show that multistep deposition cum two-step annealing, comprising an ultraviolet ozone (UVO) anneal followed by a low-temperature rapid thermal anneal (RTA), can significantly improve the performance and reliability of a 7.5-\\rm\AA-equivalent-oxide-thickness (EOT) \HfO2/\TiN gate stack, comprising a 25- \\rm\AA \ \HfO2 on \sim\!\!\3\ \\rm\AA\ \SiOx, i.e., prepared from direct \HfO2 deposition onto an HF-last Si surface. The method yields approximately two orders of magnitude reduction in gate current density and approximately an order of magnitude longer time to breakdown, as compared with the as-deposited gate stack. The observed improvements may be attributed to the “repair” of oxygen-vacancy defects at the \HfO2/\Si interface and in the \HfO2 bulk by the absorbed ozone, through thermal activation provided by the RTA step. The findings provide a promising means for realizing low-leakage and reliable sub-1-nm EOT \HfO2/\TiN stacks for high- k last integration. [ABSTRACT FROM AUTHOR]

We provide new insights, via nanoscale TDDB testing, into the bimodal Weibull failure distribution obtained from area scaling of high-\kappa (HK) gate stack. Time-to-breakdown (BD) statistics for grain boundary (GB) and grain in a polycrystalline HK gate stack are obtained individually from localized constant voltage stressing via a scanning tunneling microscope. In spite of an initial difference in the preexisting defect density, no apparent difference in the Weibull slope is observed for the two sets of BD statistics. The bimodal Weibull distribution is shown to be a combined effect: 1) The steep Weibull slope of the lower percentile, arising from large-area devices, is related to BD at GBs, and 2) the upper percentile, arising from small-area devices, is mostly related to grain BDs. In this case, the Weibull slope is reduced by a small fraction of these devices exhibiting early failures due to GB BDs. We show directly that structural defects in an HK dielectric, particularly GBs, play an important role on its BD distribution. [ABSTRACT FROM PUBLISHER]

Self-assembled GaInNAs/GaAsN single layer quantum-dot (QD) lasers grown using solid-source molecular-beam epitaxy have been fabricated and characterized. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼1.05 kA/cm2 from a GaInNAs QD laser (50×1700 μm2) at 10 °C. High-temperature operation up to 65 °C was also demonstrated from an unbonded GaInNAs QD laser (50×1060 μm2), with high characteristic temperature of 79.4 K in the temperature range of 10–60 °C. [ABSTRACT FROM AUTHOR]

We present the results of GaInNAs/GaAs quantum dot structures with GaAsN barrier layers grown by solid source molecular beam epitaxy. Extension of the emission wavelength of GaInNAs quantum dots by ∼170 nm was observed in samples with GaAsN barriers in place of GaAs. However, optimization of the GaAsN barrier layer thickness is necessary to avoid degradation in luminescence intensity and structural property of the GaInNAs dots. Lasers with GaInNAs quantum dots as active layer were fabricated and room-temperature continuous-wave lasing was observed. Lasing occurs via the ground state at ∼1.2 μm, with threshold current density of 2.1 kA/cm2 and maximum output power of 16 mW. [ABSTRACT FROM AUTHOR]

Injuries, accidents or even fatalities while working in pilot plant are reported worldwide. The OSHA Laboratory Standard and Hazard Communication Standard have been used as a guideline to manage safety of laboratories and pilot plant. In spite of the implementation of these standards, incidents which result in injuries and property loss are continuously occurring. The implementation of OSHA Process Safety Management (PSM) Standard in pilot plant is expected to further reduce the risks of accidents. This paper presents a new system for managing process chemicals, technology and equipment information in pilot plant and the concept is developed based on Process Safety Information (PSI) element of PSM 29 CFR 1910.119(d). It provides organized strategies to manage documentations, communicate information, and written program for maintaining, revising and updating related information. Process and Instrumentation Diagram (P&ID) is used as a foundation for data management. Implementation of this system at the CO2 Hydrocarbon Absorption System pilot plant as a case study is examined and discussed. [ABSTRACT FROM AUTHOR]

Abstract: A common heterozygous leucine-rich repeat kinase 2 (LRRK2) mutation 6055G>A transition (G2019S) accounts for about 3–7% of familial Parkinson''s disease (PD) and 1–1.6% sporadic PD in a number of European populations. To determine the prevalence of the G1019S mutation in our Asian population, we conducted genetic analysis of this mutation in 1000 PD and healthy controls. The G2019S mutation was not detected in any of our study subjects. The prevalence of G2019S mutation is rare (<0.1%) in our population, suggesting that occurrence of this mutation may vary amongst different ethnic races. This has important clinical implication when implementing guidelines for genetic testing. [Copyright &y& Elsevier]