Low-resistivity Region Research Articles

Analysis of copper ion filaments and retention of dual-layered devices for resistance random access memory applications

For improvement of switching uniformity, we propose a dual-layer structure with different resistance values in each layer. During the forming process, a current path is created in a high-resistance region which localizes filament formation in ultra-thin low resistance regions. The localized filament, whose existence is confirmed by conductive atomic force microscopy (CAFM), dramatically improves switching uniformity. In addition, pulse switching is demonstrated by application of alternating voltages of ±2 V for 1 μs. Analysis of Cu ion retention provides considerable insight into the resistance memory. A dual-layer oxide with excellent device performance and yield shows good promise for future non-volatile memory applications.

Distribution of crustal fluids in Northeast Japan as inferred from resistivity surveys

We carried out magnetotelluric (MT) surveys in central northeastern Japan. Two-dimensional resistivity profiles along three survey lines show similar features each other. By comparing the resistivity distribution to the distribution of seismic velocities, we inferred the distribution and flow of crustal fluids. Three fluid flow paths were detected based on the distribution of regions of low resistivity. The first path ascends from the top of the upper mantle, passes through the lower crust, and reaches the surface, forming a fluid chamber within the lower or middle crust. This path is related to the volcanic activity in the backbone range. The second path rises from the first fluid chamber and has produced small fluid reservoirs on both sides of the backbone range. These small reservoirs are considered to be related to the seismicity of the region. The third path is located to the east of the volcanic front and represents another fluid flow path from the uppermost mantle to the lower crust that may have formed a small fluid reservoir to the east of the volcanic front.

Evaluation of surface characteristics under fretting of electrical contacts: Removal behaviour of hot dipped tin coating

The fretting corrosion behaviour of hot dipped tin coating is investigated at low fretting cycles at ±25 μm displacement amplitude, 0.5N normal load, 3 Hz frequency, 45–50% relative humidity, and 25 ± 1 °C temperature. The typical characteristics of the change in contact resistance with fretting cycles are explained. The fretted surface is examined using laser scanning microscope, scanning electron microscope and energy dispersive X-ray analysis to assess the surface profile, extent of fretting damage, extent of oxidation and elemental distribution across the contact zone. The interdependence of extent of wear and oxidation increases the complexity of the fretting corrosion behaviour of tin coating. The variation of contact resistance clearly revealed the fretting of tin coating from 50 to 1200 cycles and the fretting of the substrate above 1200 cycles. The observed low and stable contact resistance region and the fluctuating resistance region at various fretting cycles are explained and substantiated with Scanning electron microscopy (SEM), laser scanning microscope (LSM) and energy dispersive analysis of X-rays (EDAX) analysis results of the fretted surface.

Current Conduction Mechanism for Low-molecular Organic Nonvolatile Memory

AbstractOrganic devices fabricated with a top metal layer/conductive organic layer/middle metal layer/conductive organic layer/bottom metal layer structure have been reported to demonstrate nonvolatile memory behavior such as an after writing (Ion)/after erasing (Ioff) performance of > 1 × 101 and a response time of ∼10 ns, when the organic conductive layers were AIDCN (2-amino-4, 5-imidazoledicarbonitrile), Alq3 (Aluminum tris(8-hydroxyquinoline)), or α-NPD. We fabricated an organic nonvolatile memory device with a structure of α-NPD/Al nanocrystals surrounded by Al2O3/α-NPD/Al, where α-NPD was N,N'-bis(1-naphthyl)-1,1'biphenyl4-4''diamine. A layer of Al nanocrystals, confirmed by a 1.25-MV high voltage transmission-electron-microscope, was uniformly produced between the α-NPD layers by Al layer evaporation at 1.0 Å/sec on the α-NPD followed by O2 plasma oxidation. We confirmed a conduction bistability of ∼102 and a threshold voltage for a set state of 3 V. Al nanocrystals surrounded by amorphous Al2O3 were formed in the α-NPD. They presented seven different reversible current paths for an electron charge or discharge on the nanocrystals. The current slightly increased with an applied bias from 0 V to Vth (a high resistance state (Ioff)), abruptly increased with an applied bias from Vth to Vp, decreased with an increasing applied bias from Vp to Ve (a negative differential resistance (NDR) region), and slightly increased with an applied bias above Ve. After sweeping the first applied voltage from 0 to 10 V (erase), a second applied bias was swept from 0 to Vp (program), where the current followed a high resistance state (Ioff). Next, a third applied bias was swept from 0 to Vp again, where the current followed a low resistance state (Ion). Surprisingly, the ratio of Ion to Ioff was ∼1×102, which is enough current difference to be nonvolatile memory behavior. These I-V characteristics under a positive applied bias were symmetrically repeated under a negative applied bias. All the current sweeping paths were reproducible and symmetrical for an applied bias polarity. In particular, our device demonstrated multi-level nonvolatile memory behavior. It also revealed the current conduction mechanism for each of its operation regions. We observed that the high resistance and low resistance regions followed space-charge-limited current conduction, the Vth to Vp and VNDR to Ve regions followed precisely thermionic-field-emission current conduction, and the above Ve regions followed space-charge-limited current conduction.

Li diffusion in spinel LiNi0.5Mn1.5O4 thin films prepared by pulsed laser deposition

Spinel LiNi0.5Mn1.5O4 thin film electrodes of 0.5 μm thickness were prepared on polished stainless steel (SS) substrates by pulsed laser deposition. Kinetics and mass-transport of Li intercalation/deintercalation were investigated by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT). The CV measurements indicate that there exists a small amount of Mn3 + in the film and Li transportation is controlled by diffusion at high scan rates. EIS measurements show a potential independent low charge-transfer resistance region between 4.1 and 4.7 V and a stable surface layer resistance through the full potential range. The chemical diffusion coefficients of Li in the LiNi0.5Mn1.5O4 thin film obtained by EIS and PITT have been found to be in the range of 10−12–10−10 cm2 s−1 depending on the electrode potential. Two minima were found for from PITT at potentials close to the peak potentials of the corresponding CV.

Formation of low-resistivity region in p-Si substrate of SiGe/Si episystem by remote-hydrogen plasma treatment

We have studied effects of hydrogen treatment on the resistivity profile of the SiGe/Si episystem by spreading resistance (SR) method. In this paper, we present experimental findings that hydrogen treatment reduces the resistivity at a specific part in the Si substrate region. This position was confirmed to be under the interface between SiGe and Si that emerged on the bevel surface during hydrogen treatment. We investigated the depth of resistivity-reduced regions which was formed by various hydrogenating conditions and found that the region was extended to the same depth as the penetration depth of hydrogen. We concluded that the low-resistivity region was formed under the influence of hydrogen introduced from bevel surface. We attributed this resistivity reduction to formation of some defects which originally existed at the interface and diffused into Si substrate with hydrogen.

Lateral conductivity of p-type doped Si/Ge island structures

Numerical calculations of the conductance in structures with doping modulated along the current-flow direction are carried out taking into account band offsets at the interfaces between high-and low-resistivity regions. It is found that such structures exhibit S-shaped current-voltage characteristics; in the limiting case, there should be a negative-conductance region, with the abruptness of the heterojunction between the narrow-and wide-gap sections of the structure and the doping level being the critically important parameters in the theory. p-type Si/Si{sub 1-x}Ge{sub x} island structures with different sizes of islands and different band offsets were grown by molecular-beam epitaxy. Theoretical results are compared with the data on lateral conductance of the grown structures.

Drug policy for visceral leishmaniasis: a cost‐effectiveness analysis

To facilitate the choice of the best visceral leishmaniasis (VL) treatment strategy for first-line health services in (VL)-endemic areas, we compared in a formal decision analysis the cost and the cost-effectiveness of the different available options. We selected four drug regimens for VL on the basis of frequency of use, feasibility and reported efficacy studies. The point estimates and the range of plausible values of effectiveness and cost were retrieved from a literature review. A decision tree was constructed and the strategy minimizing the cost per death averted was selected. Treatment with amphotericin B deoxycholate was the most effective approach in the baseline analysis and averted 87.2% of all deaths attributable to VL. The least expensive and the most cost-effective treatment was the miltefosine regimen, and the most expensive and the least cost-effective was AmBisome treatment. The cost of drug and medical care are the main determinants of the cost-effectiveness ranking of the alternative schemes. Sensitivity analysis showed that antimonial was competitive with miltefosine in the low-resistance regions. In areas with >94% response rates to antimonials, generic sodium stibogluconate remains the most cost-effective option for VL treatment, mainly due to low drug cost. In other regions, miltefosine is the most cost-effective option of treatment, but its use as a first-line drug is limited by its teratogenicity and rapid resistance development. AmBisome in mono- or combination therapy is too expensive to compete in cost-effectiveness with the other regimens.

Deposition of Particles on Ocular Tissues and Formation of Krukenberg Spindle, Hyphema, and Hypopyon

Eye diseases, such as Krukenberg's spindle, hyphema, and hypopyon, are related to the deposition of specific particles such as pigmentary cells, leukocytes, and erythrocytes. These particles are circulated by the aqueous humor (AH) and tend to deposit in regions of low velocities or high resistance. In the present paper, numerical simulations are reported of the AH flow and particle transport, and the particle concentration predictions are qualitatively compared to clinical images. The particle concentration distributions provide an understanding of the likely sources of deposition and the origin of the deposited particles. Pigmentary cells are seen to concentrate in a vertical band on the corneal surface consistent with clinical observations of Krukenberg's spindle. Leukocytes and erythrocytes are seen to collect at the bottom of the anterior chamber similar to the observations made for hypopyon and hyphema. These results confirm the potential of using numerical calculations in order to obtain a better understanding of the particle transport and deposition patterns in the anterior chamber of the eye.

Local resistance measurement across grain boundaries in low-temperature polycrystalline silicon layer of thin film transistor using scanning spreading resistance microscopy

Local resistance distribution in a low-temperature polycrystalline Si layer of a thin film transistor with a lightly doped drain (LDD) structure was investigated using scanning spreading resistance microscopy. The local resistance around the grain boundaries was found to be lower than that at grain insides in the drain, LDD, and channel regions. At the center of the grain boundaries, however, slightly higher resistance part was sandwiched between low resistance regions. Identifying the drain, the LDD, and the channel regions is succeeded by an analysis in which only the lower local resistances were used.

Effect of temperature on the fretting corrosion of tin plated copper alloy contacts

The effect of temperature on the fretting corrosion behaviour of tin plated copper alloy contacts in the temperature range of 25–185 °C, is addressed in this paper. The change in contact resistance with fretting cycles at various temperatures was determined. The contact zone after fretting corrosion test was analyzed using laser scanning microscope, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray spectrometry (EDX), to assess the surface profile, phase content, morphology and compositional changes across the interface. The study reveals that temperature has a greater influence on the extent of fretting corrosion of tin plated copper alloy contacts. The softening of tin is responsible for the extended region of low contact resistance observed at 85 °C. The increase in thickness and the resistance of Cu–Sn intermetallic compounds (IMCs) is responsible for the decrease in surface roughness and the drastic increase in the contact resistance at higher temperatures. The study suggests that the tin plated copper alloy contact system should be considered as copper alloy/IMC/Sn/SnO 2 instead tin plated copper alloy. During fretting corrosion test at elevated temperatures, once the top surface layers are worn out, the contact interface is transformed from tin versus tin-to-tin-intermetallic versus tin-intermetallic. The study concludes that tin plated copper alloy contacts are not suitable for high temperature applications.

Magnetotelluric evidence for a deep-crustal mineralizing system beneath the Olympic Dam iron oxide copper-gold deposit, southern Australia

The iron oxide copper-gold Olympic Dam deposit, situated along the margin of the Proterozoic Gawler craton, South Australia, is the world's largest uranium deposit and sixth-largest copper deposit; it also contains significant reserves of gold, silver, and rare earth elements. Gaining a better understanding of the mechanisms for genesis of the economic liberalization is fundamental for defining exploration models in similar crustal settings. To delineate crustal structures that may constrain mineral system fluid pathways, coincident deep crustal seismic and magnetotelluric (MT) transects were obtained along a 220 km section that crosses Olympic Dam and the major crustal boundaries. In this paper we present results from 58 long-period (10–104 s) MT sites, with site spacing of 5– 10 km. A two-dimensional inversion of MT data from 33 sites to a depth of 100 km shows four notable features: (1) sedimentary cover sequences with low resistivity ( 1000 Ω·m) Archean crustal core from a more conductive crust and mantle to the north (typically <500 Ω·m); (3) to the north of Olympic Dam, the upper-middle crust to ∼20 km is quite resistive (∼1000 Ω·m), but the lower crust is much more conductive (<100 Ω·m); and (4) beneath Olympic Dam, we image a low-resistivity region (<100 Ω·m) throughout the crust, coincident with a seismically transparent region. We argue that the cause of the low-resistivity and low-reflectivity region beneath Olympic Dam may be due to the upward movement of CO2-bearing volatiles near the time of deposit formation that precipitated conductive graphite liberalization along grain boundaries, simultaneously annihilating acoustic impedance boundaries. The source of the volatiles may be from the mantle degassing or retrograde metamorphism of the lower crust associated with Proterozoic crustal deformation.

The perceived roughness of resistive virtual textures

In previous work, we demonstrated that people reliably perceive variations in surface roughness when textured surfaces are explored with a rigid link between the surface and the skin [e.g., Klatzky and Lederman 1999; Klatzky et al. 2003]. Parallel experiments here investigated the potential of a force-feedback mouse to render surfaces varying in roughness. The stimuli were surfaces with alternating regions of high and low resistance to movement in the x (frontal) dimension (called ridges and grooves, respectively). Experiment 1 showed that magnitude ratings of roughness varied systematically with the spatial period of the resistance variation. Experiments 2 and 3 used a factorial design to disentangle the contributions of ridge and groove width. The stimuli constituted eight values of groove width at each of five levels of ridge width (Experiment 2) or the reverse (Experiment 3). Roughness magnitude increased with ridge width while remaining essentially invariant over groove width. Kinematic variations in exploration were observed across the surfaces. The data point to the promise of using inexpensive devices to create virtual textural variations under conditions of unconstrained exploration.

Variation in boron doping by planar diffusion – a comparative study of computational hydrodynamics and experimental observations

Resistivity maps for Si wafers processed using BN solid sources and hydrogen injection were compared to convective flow patterns predicted computationally. The convective flow patterns were found to mirror the resistivity maps, with low velocity flow domains being associated with high resistivity regions on the wafer and high velocity flow with low resistivity regions. Subtle changes in both the flow patterns and resistivity maps as a function of location within the furnace were consistently reflected in both computed flow domains and measured resistitivies. Finally, axially eccentric placement of the wafer–source stack was found to promote convection between wafer–source pairs by as much as a factor of five.

Temperature dependent resistivity in the low-resistance region for diffusive transport in two dimensions

The interpretation of the metal-insulator transition phenomena in disordered two-dimensional electron systems in terms of density-dependent scaling variables suggests the existence of a quantum critical point at some critical electron density. However a first principles scaling theory based on renormalization group (RG) methods predicts a strong temperature dependence of the dimensionless resistivity $\mathcal{R}(T)$, even at small $\mathcal{R}(T)$, that is not observed. The observed properties are in fact consistent with a weakly disordered Fermi liquid, and there are no indications of strong temperature dependence induced by scaling. While the RG expansion in a power series in $\mathcal{R}(T)$ has only been evaluated to lowest order, this should be sufficient to describe experiments in the region of very small $\mathcal{R}$. A further apparent anomaly is a return from metal-like to insulating-like behavior for increasing density. We explain these fundamental discrepancies between the first principles theory and experiment. We find that the $\mathcal{R}⪡1$ data in the currently attainable temperature range are in a weak scaling regime described by the logarithmic approximation. We independently determine the density dependent prefactor of the logarithm using data for the spin susceptibility and effective mass. We find good agreement between theory and experiment for $\mathcal{R}(T)$ in the diffusive regime. We point out that there are corrections to the leading logarithm approximation that should be observable at still lower temperatures.

The hydraulic and electrical fractal dimension of regolith

Electrical and electromagnetic (EM) geophysical data from a line or grid are usually converted into two- or three-dimensional resistivity models of the Earth. In regions of relatively uniform geology, variability of measurements are assumed to be random and Gaussian, such that the Earth models are found from a maximum likelihood approach. In this paper, we show that such variability is not Gaussian, and has a scale-length dependence, expressed as a fractal dimension. We argue that the fractal dimension of electrical and EM data is causally determined from Earth heterogeneity, which provides a link with hydraulic conductivity in porous and fractured media that also has a fractal dimension. This paper presents initial analyses of data from two sites within South Australia. NanoTEM time domain electromagnetic (TEM) data were collected at Tunkillia in the Gawler Craton with a target of identifying palaeochannels for gold exploration. Analysis of survey data revealed a good correlation between regions of low resistivity and high fractal dimension. On the other hand, a river-borne NanoTEM survey of the River Murray sediments showed much lower correlation. We conclude that analysis of the variability of EM data may provide useful additional constraints on subsurface properties.

Ground uplift detected by precise leveling in the Ontake earthquake swarm area, central Japan in 2002–2004

Repeated precise leveling in the earthquake swarm area of Ontake, central Japan has revealed uplift of 3–6 mm in proximity to the epicentral region of the most active earthquake cluster in 2002–2004. Although the uplift is small, the vertical displacement is significant even considering leveling error. This uplift is associated with increases in 3He/4He ratios and CO2 δ13C values at a mineral spring in the region, indicating an upper mantle contribution. A region of low resistivity at a depth of 2 km beneath the uplift area has also been inferred, suggesting that the observed uplift is related to changes in a shallow seismogenic layer due to increased hydrothermal input from the earthquake swarm area.

Activity of Elbrus Volcano (North Caucasus)

This paper summarizes the results of the work done by Russian geoscientists in the area of Elbrus volcanic center from the end of the XX to the beginning of the XXI century. It is shown that the results of the geological and geophysical studies of the Elbrus Volcano, including the dating of its historic eruptions, the anomalous velocities of longitudinal waves, the regions of low resistivity, poor tectonic dislocations, the gravity and temperature anomalies, and the resonance specifics of the igneous rocks suggest that Elbrus is an active volcano underlain by molten igneous rocks. The geological characteristics obtained in this study for the geological structures in the Elbrus area can be used for the mathematical modeling of the wave processes induced in the layered rocks of this volcanic cone.

High-resolution mapping of nonuniform carrier transport at contacts to polycrystalline CdTe/CdS solar cells

We demonstrate a spectroscopic technique based on scanning tunneling microscopy that provides high-resolution maps of local carrier transport across contacts to polycrystalline thin-film solar cells. Using this technique, preferential transport channels across a p+-ZnTe/p-CdTe back contact of a p-CdTe/n-CdS solar cell are imaged with 20 nm spatial resolution. Transport across this contact is highly nonuniform. Large areas of high resistance coexist with nanoscale low-resistance regions that are strongly correlated with grain boundaries in the CdTe absorber. These results suggest an important role of grain boundaries as near-contact conducting channels.

The electrical structure of the Slave craton

The Slave craton in northwestern Canada, a relatively small Archean craton (600×400 km), is ideal as a natural laboratory for investigating the formation and evolution of Mesoarchean and Neoarchean sub-continental lithospheric mantle (SCLM). Excellent outcrop and the discovery of economic diamondiferous kimberlite pipes in the centre of the craton during the early 1990s have led to an unparalleled amount of geoscientific information becoming available. Over the last 5 years deep-probing electromagnetic surveys were conducted on the Slave, using the natural-source magnetotelluric (MT) technique, as part of a variety of programs to study the craton and determine its regional-scale electrical structure. Two of the four types of surveys involved novel MT data acquisition; one through frozen lakes along ice roads during winter, and the second using ocean-bottom MT instrumentation deployed from float planes. The primary initial objective of the MT surveys was to determine the geometry of the topography of the lithosphere–asthenosphere boundary (LAB) across the Slave craton. However, the MT responses revealed, completely serendipitously, a remarkable anomaly in electrical conductivity in the SCLM of the central Slave craton. This Central Slave Mantle Conductor (CSMC) anomaly is modelled as a localized region of low resistivity (10–15 Ω m) beginning at depths of ∼80–120 km and striking NE–SW. Where precisely located, it is spatially coincident with the Eocene-aged kimberlite field in the central part of the craton (the so-called “Corridor of Hope”), and also with a geochemically defined ultra-depleted harzburgitic layer interpreted as oceanic or arc-related lithosphere emplaced during early tectonism. The CSMC lies wholly within the NE–SW striking central zone defined by Grütter et al. [Grütter, H.S., Apter, D.B., Kong, J., 1999. Crust–mantle coupling; evidence from mantle-derived xenocrystic garnets. Contributed paper at: The 7th International Kimberlite Conference Proceeding, J.B. Dawson Volume, 1, 307–313] on the basis of garnet geochemistry (G10 vs. G9) populations. Deep-probing MT data from the lake bottom instruments infer that the conductor has a total depth-integrated conductivity (conductance) of the order of 2000 Siemens, which, given an internal resistivity of 10–15 Ω m, implies a thickness of 20–30 km. Below the CSMC the electrical resistivity of the lithosphere increases by a factor of 3–5 to values of around 50 Ω m. This change occurs at depths consistent with the graphite–diamond transition, which is taken as consistent with a carbon interpretation for the CSMC. Preliminary three-dimensional MT modelling supports the NE–SW striking geometry for the conductor, and also suggests a NW dip. This geometry is taken as implying that the tectonic processes that emplaced this geophysical–geochemical body are likely related to the subduction of a craton of unknown provenance from the SE (present-day coordinates) during 2630–2620 Ma. It suggests that the lithospheric stacking model of Helmstaedt and Schulze [Helmstaedt, H.H., Schulze, D.J., 1989. Southern African kimberlites and their mantle sample: implications for Archean tectonics and lithosphere evolution. In Ross, J. (Ed.), Kimberlites and Related Rocks, Vol. 1: Their Composition, Occurrence, Origin, and Emplacement. Geological Society of Australia Special Publication, vol. 14, 358–368] is likely correct for the formation of the Slave's current SCLM.