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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Investigation of electromigration in In{sub 2}Se{sub 3} nanowire for phase change memory devices

The decomposition of In{sub 2}Se{sub 3} nanowire phase change memory devices during current-driving operation was investigated. The devices were subjected to thermal/electrical stress with current density and electric field during the reset operation at 0.24–0.38 MA/cm{sup 2} and 5.3–6.4 kV/cm, respectively. After multiple operation cycles, a change in morphology and composition of the In{sub 2}Se{sub 3} nanowire was observed and led to the device failure. The transmission electron microscopy and energy dispersive analysis indicate that electromigration causes the catastrophic failure by void formation where In atoms migrate toward the cathode and Se atoms migrate toward the anode depending on their electronegativities.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electromigration-induced back stress in critical solder length for three-dimensional integrated circuits

Because of the miniaturization of electronic devices, the reliability of electromigration has become a major concern when shrinking the solder dimensions in flip-chip joints. Fast reaction between solders and electrodes causes intermetallic compounds (IMCs) to form, which grow rapidly and occupy entire joints when solder volumes decrease. In this study, U-grooves were fabricated on Si chips as test vehicles. An electrode-solder-electrode sandwich structure was fabricated by using lithography and electroplating. Gaps exhibiting well-defined dimensions were filled with Sn3.5Ag solders. The gaps between the copper electrodes in the test sample were limited to less than 15 μm to simulate microbumps. The samples were stressed at various current densities at 100 °C, 125 °C, and 150 °C. The morphological changes of the IMCs were observed, and the dimensions of the IMCs were measured to determine the kinetic growth of IMCs. Therefore, this study focused on the influence of back stress caused by microstructural evolution in microbumps.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Electromigration kinetics and critical current of Pb-free interconnects

Electromigration kinetics of Pb-free solder bump interconnects have been studied using a single bump parameter sweep technique. By removing bump to bump variations in structure, texture, and composition, the single bump sweep technique has provided both activation energy and power exponents that reflect atomic migration and interface reactions with fewer samples, shorter stress time, and better statistics than standard failure testing procedures. Contact metallurgies based on Cu and Ni have been studied. Critical current, which corresponds to the Blech limit, was found to exist in the Ni metallurgy, but not in the Cu metallurgy. A temperature dependence of critical current was also observed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Tuning the local temperature during feedback controlled electromigration in gold nanowires

Feedback controlled electromigration (FCE) in metallic nanowires has been widely used for various purposes. However, the control of the local temperature during FCE remains a challenge. Here, we report that the environment temperature can be used as a knob to tune the local temperature during FCE in gold nanowires. FCE was performed in gold nanowires at various environment temperatures ranging from 4.2 K to 300 K. We find that the dissipated power normalized by the cross section area of the nano constriction is linearly proportional to the environment temperature. Interestingly, the estimated local maximum temperature parabolically depends on the environment temperature. A minimum in the local temperature can be reached if an appropriate environment temperature is chosen. Our findings are well supported by the finite element simulation. Moreover, the data indicates the coupling between FCE triggering current density and local temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Microstructure, impurity and metal cap effects on Cu electromigration

Electromigration (EM) lifetimes and void growth of pure Cu, Cu(Mn) alloy, and pure Cu damascene lines with a CoWP cap were measured as a function of grain structure (bamboo, near bamboo, and polycrystalline) and sample temperature. The bamboo grains in a bamboo-polycrystalline grained line play the key role in reducing Cu mass flow. The variation in Cu grain size distribution among the wafers was achieved by varying the metal line height and wafer annealing process step after electroplating Cu and before or after chemical mechanical polishing. The Cu grain size was found to have a large impact on Cu EM lifetime and activation energy, especially for the lines capped with CoWP. The EM activation energy for pure Cu with a CoWP cap from near-bamboo, bamboo-polycrystalline, mostly polycrystalline to polycrystalline only line grain structures was reduced from 2.2 ± 0.2 eV, to 1.7 ± 0.1 eV, to 1.5 ± 0.1 eV, to 0.72 ± 0.05 eV, respectively. The effect of Mn in Cu grain boundary diffusion was found to be dependent on Mn concentration in Cu. The depletion of Cu at the cathode end of the Cu(Mn) line is preceded by an incubation period. Unlike pure Cu lines with void growth at the cathode end and hillocks at the anode end of the line, the hillocks grew at a starting position roughly equal to the Blech critical length from the cathode end of the Cu(Mn) polycrystalline line. The effectiveness of Mn on Cu grain boundary migration can also be qualitatively accounted for by a simple trapping model. The free migration of Cu atoms at grain boundaries is reduced by the presence of Mn due to Cu-solute binding. A large binding energy of 0.5 ± 0.1 eV was observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Density functional theory study of the influence of segregation of S or Fe impurities on electromigration in nano-grained copper interconnects

The reliability of the circuits in the modern microelectronic devices remains, during last decades, one of the key topics in research and gains an attention for improving the promising candidates for conductors. Improvement of materials for such applications can be obtained by both electronic and compositional optimization. Ab initio calculations using full potential linearized augmented plane wave method in density functional theory are applied to explain the reduction in electromigration effect in the vicinity of grain boundaries (GB) in nano-structured Cu due to the segregation of some additives to the GB. Several possible mechanisms are considered. It is demonstrated that S atoms segregated to GB of nano-structured Cu lead to the growth of effective mass of the electrons. This decreases the mobility of electrons in external electric field, and, correspondingly, the momentum that they may transfer to atoms in collisions. Fe atoms segregated to GB of Cu create new empty states at the top of the valance band. These non-occupied states may stimulate the current of holes when external electric field is applied to the system, creating the “hole wind” in the direction opposite to the current of electrons. Such “hole wind” will compensate the forces generated by the electron current and therefore will reduce the total momentum transfer between charge carriers and atoms. The calculated electron density maps show that S and Fe segregating to Cu GB increases the strength of covalent bonds reducing the diffusion of Cu atoms in the vicinity of GB.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural tuning of nanogaps using electromigration induced by field emission current with bipolar biasing

We report a new method for fabrication of Ni nanogaps based on electromigration induced by a field emission current. This method is called “activation” and is demonstrated here using a current source with alternately reversing polarities. The activation procedure with alternating current bias, in which the current source polarity alternates between positive and negative bias conditions, is performed with planar Ni nanogaps defined on SiO{sub 2}/Si substrates at room temperature. During negative biasing, a Fowler-Nordheim field emission current flows from the source (cathode) to the drain (anode) electrode. The Ni atoms at the tip of the drain electrode are thus activated and then migrate across the gap from the drain to the source electrode. In contrast, in the positive bias case, the field emission current moves the activated atoms from the source to the drain electrode. These two procedures are repeated until the tunnel resistance of the nanogaps is successively reduced from 100 TΩ to 48 kΩ. Scanning electron microscopy and atomic force microscopy studies showed that the gap separation narrowed from approximately 95 nm to less than 10 nm because of the Ni atoms that accumulated at the tips of both the source and drain electrodes. These results show that the alternately biased activation process, which is a newly proposed atom transfer technique, can successfully control the tunnel resistance of the Ni nanogaps and is a suitable method for formation of ultrasmall nanogap structures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Simultaneous fabrication of nanogap electrodes using field-emission-induced electromigration

We present a simple technique for simultaneous control of the electrical properties of multiple Ni nanogaps. This technique is based on electromigration induced by a field emission current and is called “activation.” Simultaneous tuning of the tunnel resistance of multiple nanogaps was achieved by passing a Fowler–Nordheim (F-N) field emission current through an initial group of three Ni nanogaps connected in series. The Ni nanogaps, which had asymmetrical shapes with initial gap separations in the 80–110-nm range, were fabricated by electron-beam lithography and a lift-off process. By performing the activation procedure, the current–voltage properties of the series-connected nanogaps were varied simultaneously from “insulating” to “metallic” via “tunneling” properties by increasing the preset current of the activation procedure. We can also simultaneously control the tunnel resistances of the series-connected nanogaps, which range from a resistance of the order of 100 TΩ–100 kΩ, by increasing the preset current from 1 nA to 30 μA. This tendency is quite similar to that of individually activated nanogaps, and the tunnel resistance values of the simultaneously activated nanogaps were almost the same at each preset current. These results clearly imply that the electrical properties of the series-connected nanogaps can be controlled simultaneously via the activation procedure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Pre-determining the location of electromigrated gaps by nonlinear optical imaging

In this paper we describe a nonlinear imaging method employed to spatially map the occurrence of constrictions occurring on an electrically stressed gold nanowire. The approach consists at measuring the influence of a tightly focused ultrafast pulsed laser on the electronic transport in the nanowire. We found that structural defects distributed along the nanowire are efficient nonlinear optical sources of radiation and that the differential conductance is significantly decreased when the laser is incident on such electrically induced morphological changes. This imaging technique is applied to pre-determine the location of the electrical failure before it occurs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Electromigration Effect on Vacancy Islands Nucleation on Si(100) Surface during Sublimation

By means of in situ ultrahigh vacuum reflection electron microscopy, the nucleation of vacancy islands on wide terraces of the Si(100) surface is investigated. The temperature dependence of the displacement of a vacancy island nucleation center is determined in the process of heating a sample with a dc electric current. On the basis of a theoretical model, the effective electric charge of addimers is estimated in the direction across dimer rows of the surface. The effective charge has a positive sign and does not exceed 15 units of the elementary charge in the temperature range of 1020–1120°C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The transport behavior of As, Cu, Pb, and Zn during electrokinetic remediation of a contaminated soil using electrolyte conditioning

Electrokinetic remediation (also known as electrokinetics) is a promising technology for removing metals from fine-grained soils. However, few studies have been conducted regarding the transport behavior of multi-metals during electrokinetics. We investigated the transport of As, Cu, Pb, and Zn from soils during electrokinetics, the metal fractionation before and after electrokinetics, the relationships between metal transport and fractionation, and the effects of electrolyte conditioning. The main transport mechanisms of the metals were electroosmosis and electromigration during the first two weeks and electromigration during the following weeks. The direction of electroosmotic flow was from the anode to the cathode, and the metals in the dissolved and reducible-oxides fractions were transported to the anode or cathode by electromigration according to the chemical speciation of the metal ions in the pore water. Moreover, a portion of the metals that were initially in the residual fraction transitioned to the reducible and soluble fractions during electrokinetic treatment. However, this alteration was slow and resulted in decreasing metal removal rates as the electrokinetic treatment progressed. In addition, the use of NaOH, H3PO4, and Na2SO4 as electrolytes resulted in conditions that favored the precipitation of metal hydroxides, phosphates, and sulfates in the soil. These results demonstrated that metal removal was affected by the initial metal fractionation, metal speciation in the pore solution, and the physical–chemical parameters of the electrolytes, such as pH and electrolyte composition. Therefore, the treatment time, use of chemicals, and energy consumption could be reduced by optimizing pretreatment and by choosing appropriate electrolytes for the target metals.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Photovoltaic switching mechanism in lateral structure hybrid perovskite solar cells

In this study, long range electromigration of methylammonium ions (MA + ) in methyl ammonium lead tri-iodide (MAPbI 3 ) film is observed directly using the photo­thermal induced resonance technique. The electromigration of MA + leads to the formation of a lateral p-i-n structure, which is the origin of the switchable photovoltaic effect in MAPbI 3 perovskite devices.

14 SOLAR ENERGY↗
DOE OSTI2015

In Situ TEM Study of Reversible and Irreversible Electroforming in Pt/Ti:NiO/Pt Heterostructures

Experimental verification of the microscopic origin of resistance switching in metal/oxide/metal heterostructures is needed for applications in non-volatile memory and neuromorphic computing. Numerous reports suggest that resistance switching in NiO is caused by local reduction of the oxide layer into nanoscale conducting filaments, but few reports have shown experimental evidence correlating electroforming with site-specific changes in composition. We have investigated the mechanisms of reversible and irreversible electroforming in 250–500 nm wide pillars patterned from a single Ta/Ti/Pt/Ti-doped NiO/Pt/Ta heterostructure and have shown that these can coexist within a single sample. We performed in situ transmission electron microscopy (TEM) electroform- ing and switching on each pillar to correlate the local electron transport behavior with microstructure and composition in each pillar. DFT calculations fitted to electron energy loss spectroscopy data showed that the Ti-doped NiO layer is partially reduced after reversible electroforming, with the formation of oxygen vacancies ordered into lines in the <110> direction. However, under the same probing conditions, adjacent pillars show irreversible electroforming caused by electromigration of metallic Ta to form a single bridge across the oxide layer. We propose that the different electroforming behaviors are related to microstructural variations across the sample and may lead to switching variability.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Two-Dimensional Porous Electrode Model for Capacitive Deionization

Here, ion transport in porous conductive materials is of great importance in a variety of electrochemical systems including batteries and supercapacitors. We here analyze the coupling of flow and charge transport and charge capacitance in capacitive deionization (CDI). In CDI, a pair of porous carbon electrodes is employed to electrostatically retain and remove ionic species from aqueous solutions. We here develop and solve a novel unsteady two-dimensional model for capturing the ion adsorption/desorption dynamics in a flow-between CDI system. We use this model to study the complex, nonlinear coupling between electromigration, diffusion, and advection of ions. We also fabricated a laboratory-scale CDI cell which we use to measure the near-equilibrium, cumulative adsorbed salt, and electric charge as a function of applied external voltage. We use these integral measures to validate and calibrate this model. We further present a detailed computational study of the spatiotemporal adsorption/desorption dynamics under constant voltage and constant flow conditions. We show results for low (20 mM KCl) and relatively high (200 mM KCl) inlet ion concentrations and identify effects of ion starvation on desalination. We show that in both cases electromigrative transport eventually becomes negligible and diffusive ion transport reduces the desalination rate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗