Local Joule Heating Research Articles

Effect of temperature distribution and current crowding on the performance of lateral GaN‐based light‐emitting diodes

AbstractCurrent crowding effect is detrimental for the performance of light‐emitting diodes (LEDs), causing non‐uniform light emission and local heat generation. In particular, heat generated by non‐uniform current distribution can badly influence the performance of LED devices. In this paper, we examine the temperature distributions of lateral InGaN/GaN multiple‐quantum‐well LEDs in relation to current crowding, using both simulation and experimental results. Simulation results are obtained from a 3‐dimensional electrical circuit model consisting of resistances and intrinsic diodes. Temperature and luminance distributions are investigated by images taken by an infrared camera and a charge‐coupled‐device camera, respectively. Finally, the internal quantum efficiency is taken for each device and compared. We show that the thermal property in the lateral LED is affected by the current crowding due to the local Joule heating nearby electrodes. Therefore, uniform current spreading is very important not only for uniform luminance distribution but also for good thermal property in the LED device. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermoelectrical manipulation of nanomagnets

We investigate the interplay between the thermodynamic properties and spin-dependent transport in a mesoscopic device based on a magnetic multilayer (F/f/F), in which two strongly ferromagnetic layers (F) are exchange-coupled through a weakly ferromagnetic spacer (f) with the Curie temperature in the vicinity of room temperature. We show theoretically that the Joule heating produced by the spin-dependent current allows a spin-thermoelectronic control of the ferromagnetic-to-paramagnetic (f/N) transition in the spacer and, thereby, of the relative orientation of the outer F-layers in the device (spin-thermoelectric manipulation of nanomagnets). Supporting experimental evidence of such thermally-controlled switching from parallel to antiparallel magnetization orientations in F/f(N)/F sandwiches is presented. Furthermore, we show theoretically that local Joule heating due to a high concentration of current in a magnetic point contact or a nanopillar can be used to reversibly drive the weakly ferromagnetic spacer through its Curie point and thereby exchange couple and decouple the two strongly ferromagnetic F-layers. For the devices designed to have an antiparallel ground state above the Curie point of the spacer, the associated spin-thermionic parallel to antiparallel switching causes magnetoresistance oscillations whose frequency can be controlled by proper biasing from essentially dc to GHz. We discuss in detail an experimental realization of a device that can operate as a thermomagnetoresistive switch or oscillator.

Field assisted sintering of nickel nanoparticles during in situ transmission electron microscopy

This study reports the in situ transmission electron microscopy (TEM) observation of pressure-less field-assisted sintering of agglomerated nanometric nickel particles. Scanning tunneling microscopy inside the TEM was used to apply an electrical current directly to the powder particles. Electrical testing during the experiment reveals that consolidation occurs in the absence of an external heat source. Neck formation between adjacent particles and attendant increase in local Joule heating causes rapid densification. The results represent a first stepping stone towards achieving a fundamental mechanistic understanding of the atomic-scale processes that enable field-enhanced sintering of conductive nanogranular materials.

Defect-driven room-temperature coalescence of double-walled carbon nanotubes

Room-temperature (RT) coalescence of double-walled carbon nanotubes has been observedfor the first time. A combined pre-treatment of localized electron irradiation, Joule heating,and electromigration leads to the formation of large vacancy clusters, which cansurvive for tens of seconds during surface reconstruction. The dangling bonds ofthe edge atoms are highly reactive and thus promote the coalescence even atRT.

Evolution of resistive switching over bias duration of single Ag2S nanowires

We report resistive switching in single Ag2S nanowires contacted with two silver electrodes. The resistance evolution over time was studied by persistently applying a fixed 0.1 V bias at 10 K, and it is found that the device alternated at the ON and OFF states. The resistive switching behaviors are ascribed to the formation and rupture of metallic Ag filament inside the Ag2S nanowire. The wait time for such switching was significantly longer than those previously reported (a few seconds for the initial switching on, by Liang et al., [Small 1, 971 (2005)]), which was discussed by considering the local Joule heat and charge accumulation during the wait time. The devices may have potential applications on nonvolatile memory.

Nonpolar resistive switching in the Pt/MgO/Pt nonvolatile memory device

Nonpolar resistive switching (RS), which is the coexistence of unipolar and bipolar RS characteristics, in the Pt/MgO/Pt memory device with the nonforming nature is demonstrated. The nonforming nature is ascribed to the relatively high defect density of the MgO film deposited by using the ion beam sputtering in Ar atmosphere. The results of Auger electron spectroscopy and x-ray photoelectron spectroscopy analyses combing with the temperature dependence of resistance suggest that metallic Mg filaments are formed in the low resistance state. The voltage-polarity-independent RESET process implies that filaments may be ruptured by local Joule heating, leading to nonpolar characteristics.

Localized Joule heating produced by ion current focusing through micron-size holes

We provide an experimental demonstration that the focusing of ionic currents in a micron size hole connecting two chambers can produce local temperature increases of up to 100 °C with gradients as large as 1°K μm−1. We find a good agreement between the measured temperature profiles and a finite elements-based numerical calculation. We show how the thermal gradients can be used to measure the full melting profile of DNA duplexes within a region of 40 μm. The possibility to produce even larger gradients using submicron pores is discussed.

Investigation of Joule Heating Effect in Various Stages of Electromigration in Flip-chip Solder Joints by Infrared Microscopy

AbstractThe Joule heating effect at various stages under electromigration of flip-chip Sn3.5Ag solder joints was investigated under a current of 0.5 A at 100°C. During various stages of electromigration, voids may form and propagate and Joule heating effect may vary at different void sizes. To verify the void nucleation and propagation on Joule heating effect during electromigration process, the solder bump was stressed for different lengths of time and then examined by Kelvin bump probes and infrared microscopy. We found that voids started to form at approximately 1.2 times of the initial bump resistance. Then the voids propagated when the bump resistance increased. In addition, the temperature of the solder joints increased with the bump resistance and the increase of current stressing time. It increased very slowly in initial stages. In the last stage, the temperature of the solder bump increased rapidly due to the increase of the bump resistance and the local Joule heating effect.

Sensitive detection of H2S using gold nanoparticle decorated single-walled carbon nanotubes.

Herein, we demonstrate that highly sensitive conductometric gas nanosensors for H(2)S can be synthesized by electrodepositing gold nanoparticles on single-walled carbon nanotube (SWNT) networks. Adjusting the electrodeposition conditions allowed for tuning of the size and number of gold nanoparticles deposited. The best H(2)S sensing performance was obtained with discrete gold nanodeposits rather than continuous nanowires. The gas nanosensors could sense H(2)S in air at room temperature with a 3 ppb limit of detection. The sensors were reversible, and increasing the bias voltage reduced the sensor recovery time, probably by local Joule heating. The sensing mechanism is believed to be based on the modulation of the conduction path across the nanotubes emanating from the modulation of electron exchange between the gold and carbon nanotube defect sites when exposed to H(2)S.

Current-Density Dependence on Ag eFUSEs With TiN Underlayers

Silver-based metallization has been studied for a potential application as an electrically programmable fuse (eFUSE) device by local Joule heating induced at high current densities. Three different line widths (3.8, 6.3, and 10 mum) are investigated by subjecting them to extremely high current-density conditions. Based on short median lifetime and the topography of the failure sites, the dominant failure mechanism in Ag eFUSEs with TiN barrier layer under these current densities is examined. Evaporation times have also been calculated to correlate the Ag properties with the median failure time. The barrier layer has an important role to play in determining the failure time in these types of eFUSEs.

Azimuthally correlated ablation between z-pinch wire cores

Azimuthally correlated wire core ablation was compared for closely spaced versus widely spaced wires in a 1 MA Z-pinch. X-ray point-projection diagnostics revealed that 240 μm spaced wires exhibited a correlation coefficient approaching unity in both real space and in k-space. This correlated ablation between wires at a fixed axial location is believed to occur due to an enhanced, localized Joule heating. Wires separated by 2.47 mm or greater were uncorrelated in real space, but correlated in k-space, indicating the ablation structure between wires was shifted in phase.

Low Temperature Growth of High-Quality Carbon Nanotubes by Local Surface Joule Heating without Heating Damage to Substrate

In this study, a low temperature growth of high-quality carbon nanotubes on glass substrate using a local surface heating without heating damage to substrate was tried and characterized. The local joule heating was induced to only Ni/Ti metal film on glass substrate by applying voltage to the film. It was estimated that local surface joule heating method could heat the metal surface locally up to around <TEX>$1200^{\circ}C$</TEX> by voltage control. We could successfully obtain high-quality carbon nanotubes grown at <TEX>$300^{\circ}C$</TEX> by applying 125 V for joule heating as same as carbon nanotubes grown at <TEX>$900^{\circ}C$</TEX>.

Electrically driven PEDOT/PSS actuators

The film made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) was prepared by casting and electrical conductivity, tensile properties, electromechanical response, and moisture sorption isotherm of the PEDOT/PSS film were investigated. A linear expansion of the PEDOT/PSS film occurred with increasing ambient humidity, where the strain of the film in a RH range from 20 to 90%RH was 3.3%. Upon application of an electric field, the film underwent significant contraction in ambient air. The degree of contraction increased as the applied voltage became higher and the value attained 2% at 35 V, which was nearly twice as that of polypyrrole films. The principle lay in the desorption of water vapor due to local Joule heating, where the electric field controlled an equilibrium of water vapor sorption. The moisture sorption isotherm of the PEDOT/PSS film indicated that the interaction between water and PEDOT/PSS was superior to that between water molecules, in which isosteric heat of sorption decreased with an increase in the sorption degree and the value reached to the heat of water condensation.

A comparative study of the dendritic avalanche in MgB2 thin films synthesized by pulsed laser deposition and hybrid physical chemical vapor deposition methods

It is known that MgB2 thin films synthesized by using hybrid physical chemical vapor deposition (HPCVD) do not show dendritic avalanche, which is in contrast to those prepared by using pulsed laser deposition (PLD). To find the cause that makes the difference between the two cases, we studied the microscopic film structure by the scanning electron microscopy and the magnetic hysteresis by using the superconducting quantum interference device magnetometry. The critical current density (Jc), estimated from the magnetic hysteresis based on the Bean’s critical-state model, shows a much higher Jc in the PLD film than in a HPCVD film. This indicates higher vortex pinning in the PLD film. We surmise that high local joule heating beyond the high Jc in the PLD film, as a vortex penetrates into the superconducting thin film, gives a path for the next vortex and induces a positive feedback effect that is absent in the HPCVD film.

Temperature measurement at flip chip solder joint during electromigration test

Measuring the real temperature of a flip chip solder joint during an electromigration test has been a problem because of its small size and the local Joule heating due to a large applied current. A unique method that employs the electrical resistance change in the junction line between two solder joints was introduced to determine the temperature of the solder joint. The change in resistance was converted into temperature using a thermal coefficient of resistance of the junction line. The method accurately measured temperatures of the solder joint within 2 K until the solder joint resistance change ratio reached 100% due to growth of an electromigration void.

Localized ionization patches in the nighttime ionosphere of Mars and their electrodynamic consequences

Using an electron transport model, we calculate the electron density of the electron impact-produced nighttime ionosphere of Mars and its spatial structure. As input we use Mars Global Surveyor electron measurements, including an interval when accelerated electrons were observed. Our calculations show that regions of enhanced ionization are localized and occur near magnetic cusps. Horizontal gradients in the calculated ionospheric electron density on the night side of Mars can exceed 10 4 cm −3 over a distance of a few tens of km; the largest gradients produced by the model are over 600 cm −3 km −1. Such large gradients in the plasma density have several important consequences. These large pressure gradients will lead to localized plasma transport perpendicular to the ambient magnetic field which will generate horizontal currents and electric fields. We calculate the magnitude of these currents to be up to 10 nA/m 2. Additionally, transport of ionospheric plasma by neutral winds, which vary in strength and direction as a function of local time and season, can generate large (up to 1000 nA/m 2) and spatially structured horizontal currents where the ions are collisionally coupled to the neutral atmosphere while electrons are not. These currents may contribute to localized Joule heating. In addition, closure of the horizontal currents and electric fields may require the presence of vertical, field-aligned currents and fields which may play a role in high altitude acceleration processes.

Self-Accelerated Thermal Dissolution Model for Reset Programming in Unipolar Resistive-Switching Memory (RRAM) Devices

This paper addresses the numerical modeling of reset programming in NiO-based resistive-switching memory. In our model, we simulate electrical conduction and heating in the conductive filament (CF), which controls the resistance of the low resistive (or set) state, accounting for CF thermal-activated dissolution. Employing CF electrical and thermal parameters, which were previously characterized on our NiO-based samples, our calculations are shown to match experimental reset and retention characteristics. Simulations show that reset transition is self-accelerated as a consequence of a positive feedback between the thermal dissolution of the CF and local Joule heating in the CF bottleneck, which can account for the abrupt resistance transition in experimental data. Finally, the model is used to investigate the reduction of the reset current, which is needed for device application.

Growth study of silicon nanowires by electron microscopies

We present a method that allows the synthesis of silicon nanowires (Si NWs) using Au or Ga as catalyst solvent in a scanning electron microscopy. The method is based on localized joule heating of tungsten wires to activate vapor–liquid–solid Si nanowire synthesis. Directly from scanning electron microscopy images we observe two different growth mechanisms for each catalyst solvent (Au and Ga). Since the conductive tungsten wires can be elaborated by focused ion beam induced deposition on 50-nm-thick Si 3N 4 membranes, we will show that transmission electron microscopy characterizations can be deduced from as-deposited .silicon nanowires.

Electric-Current-Induced Liquid Al Deposition, Reaction, and Flow on Cu Rails at Rail&amp;#x2013;Armature Contacts in Railguns

When a railgun is fired, the aluminum armature typically undergoes melting at the rail-armature contacts and deposits liquid metal on the rails. Rail life is affected by these deposits. Localized aluminum armature melting has been attributed to current crowding and localized Joule heating. This paper reports on 1) the characterization of debris on fired rails and their role in rail damage and 2) experiments to elucidate the role of electric current in the transport of liquefied armature material along the rail surfaces. A miniature static railgun model was constructed by wrapping an Al foil around a quartz core and placing the Al foil in contact with two thin-film Cu stripes deposited on Si substrates. In this arrangement, the Cu thin films simulated the surface skins on the two rails, whereas the Al foil represented the skin of the armature. The circuit was subjected to a constant current under high vacuum and various ambient temperatures. The part of the Al foil in contact with Cu melts quickly due to Joule heating, and the liquefied Al starts flowing down the negative rail. In all instances, the direction of liquid flow was from the positive to the negative terminal. The kinetics of Al migration was measured, and it was found that the activation energy for Al migration is close to that for self-diffusion in liquid Al. The observed liquid transport is attributable to liquid electromigration under the influence of the applied current.

DCフラッシュ熱間溶接プロセスの加熱機構について

It hasn't been well known which heat of joule and arc discharge is dominant factor in flash welding process. The objective of this study is to clarify heating mechanism of flashing. The flashing is a cycle consisting of local contact, joule heating, melting, spattering and arc discharge. Numerical model of flashing cycles was developed by assuming initial contact conditions. It has been evaluated heat input and welding parameters of DC flash welding. As the results, arc discharge heat is higher than joule heat for a wide range of flash current. Optimum flashing of DC is large contact and low frequency compared with general continuous flashing of AC. Heat input and platen velocities are 50% higher than those of AC at the same conditions and welding quality. The calculated velocities and crater depth of DC flashing are in good agreement with hot-billets welding data. It was found that DC flash welding compares very favorably with AC for short-time welding.