Local Joule Heating Research Articles

Extraordinary effect of the δ phase on the electrically-assisted deformation responses of a Ni-based superalloy

The effect of the δ phase (Ni3Nb) on the electrically-assisted (EA) deformation responses, particularly stress, elongation and dislocation distribution, of the Ni-based superalloy is still unknown up to now, though it is clear as nonnegligible on the quasi-static and hot deformation processes. Therefore, the effect of the δ phase during the electrically-assisted tension were experimentally investigated and analyzed with comparison to that in the hot tension process. Generally, the δ phase existing in the Ni-based superalloy always causes the reduction of flow softening and elongation during cold and the initial stage of hot tension processes. What is distinct, the δ phase promotes the flow softening effect and elongation during the EA tension. In addition, the dislocation-free ring around the δ phase was firstly observed during the EA tension. The mechanism of these macro and micro extraordinary phenomena is concluded as that the δ phase causes serious lattice distortion and dislocation pile-up around itself, which leads to an extremely high temperature due to the local Joule heating effect. The faster elimination of dislocation pile-up in the local area because of the local higher temperature results in the dislocation-free ring phenomenon and the significant improvement of flow softening effect and elongation.

Investigation of the Electrical, Optical, and Mechanical Properties of Ag Nanowire Conducting Electrode

Silver (Ag) nanowire having mean diameter and length of about 170.42 nm and 20.01 µm were prepared by the polyol process in ethylene glycol. Ag nanowires transparent conducting electrodes were then fabricated by depositing the Ag nanowires in ethanol and ink formulation on polymer substrates using a Meyer rod. The Ag nanowire electrodes exhibit an optical transmittance of about 68 % due to the large diameters of the as synthesized Ag nanowires. On the other hand, the sheet resistance was measured to be about 148 ohms/sq. When expose in air for 10 weeks, the sheet resistance increase to about 13 kohms/sq. Localized Joule heating during application of electrical stress of about 2 V for 7 days has resulted in the Ag nanowire degradation.

Enhancement of hydrogen microcombustion via field-emission dielectric barrier discharge

A particle-in-cell (PIC) model is constructed for a ∼100 μm field-emission dielectric barrier discharge (FE-DBD) actuator in atmospheric pressure mixtures of oxygen, hydrogen, and water vapor. The discharge is characterized, including the effects of gas temperature and gas composition. Quantities relevant to plasma-coupled combustion, such as Joule heating, Lorenz body force, and radical generation are estimated for gas temperatures and compositions relevant for combustion energy conversion. Due to its low ionization energy, O2 increases the magnitude of Joule heating and body forces in the discharge. However, water vapor weakens these effects because of its high ionization energy and many excitational degrees of freedom that remove energy from electrons through inelastic collisions. At higher gas temperatures the discharge becomes more diffuse on account of lower gas densities. At room temperature, and operated at an easily achieved 300 V at 10 MHz, the FE-DBD produces both intense local body forces (107 N/m3) and Joule heating (109 W/m3) at the corner of the exposed electrode. A boundary layer model provides an estimate that the FE-DBD can induce flow velocities of around 10–20 m/s and temperature increases of around 5–20 K in room temperature H2/O2/H2O mixtures. Sources based on the PIC model are applied in continuum simulations of non-premixed hydrogen combustion in a microchannel. Without the FE-DBD, the inflow of fuel and oxygen is hindered by viscous losses, thermal conduction to wall boundaries, and thermal expansion of gasses, leading to flame extinction. The FE-DBD actuators pre-heat and dissociate the fuel and produce body forces that counter viscous resistance, sustaining combustion. In another example, FE-DBD plasma coupling reduces the autoignition time of a stoichiometric, 950 K H2-O2 mixture from 117 μs to 49 μs.

Local Joule Heating Mimicking Electroresistance‐Like Behavior in Antiperovskite Mn3GaC

AbstractElectroresistance has become a stimulating research topic because of its potential applications in next‐generation nonvolatile memory technology. Here, an electroresistance‐like behavior of the antiperovskite Mn3GaC compound around the antiferromagnetic–intermediate phase transition is reported. A high sensing current significantly decreases the fraction of the antiferromagnetic phase of higher resistivity relative to the intermediate phase of lower resistivity upon warming, showing a resistivity change up to 50%. Through extensive studies of the resistivity at different sample locations and of the magnetization under applied current, it is unambiguously shown that this electroresistance‐like behavior originates from the local Joule heating of the sample due to high‐resistive lead contacts and not from an intrinsic effect. These findings open an available avenue to explore electroresistance‐like behavior by achieving phase coexistence of a high‐ and low‐resistivity phase under the driving force of local Joule heating.

Enhanced multimaterial 4D printing with active hinges

Despite great progress in four-dimensional (4D) printing, i.e. three-dimensional (3D) printing of active (stimuli-responsive) materials, the relatively low actuation force of the 4D printed structures often impedes their engineering applications. In this study, we use multimaterial inkjet 3D printing technology to fabricate shape memory structures, including a morphing wing flap and a deployable structure, which consist of active and flexible hinges joining rigid (non-active) parts. The active hinges, printed from a shape memory polymer (SMP), lock the structure into a second temporary shape during a thermomechanical programming process, while the flexible hinges, printed from an elastomer, effectively increase the actuation force and the load-bearing capacity of the printed structure as reflected in the recovery ratio. A broad range of mechanical properties such as modulus and failure strain can be achieved for both active and flexible hinges by varying the composition of the two base materials, i.e. the SMP and the elastomer, to accommodate large deformation induced during programming step, and enhance the recovery in the actuating step. To find the important design parameters, including local deformation, shape fixity and recovery ratio, we conduct high fidelity finite element simulations, which are able to accurately predict the nonlinear deformation of the printed structures. In addition, a coupled thermal-electrical finite element analysis was performed to model the heat transfer within the active hinges during the localized Joule heating process. The model predictions showed good agreement with the measured temperature data and were used to find the major parameters affecting temperature distribution including the applied voltage and the convection rate.

Transient Thermal Characterization of AlGaN/GaN HEMTs Under Pulsed Biasing

The development of steady-state thermal characterization techniques for AlGaN/GaN high-electron mobility transistors (HEMTs) has been used to measure the device’s peak temperature under DC conditions. Despite these methods enabling the accurate quantification of the device’s effective thermal resistance and power density dependence, transient thermometry techniques are necessary to understand the nanoscale thermal transport within the active GaN layer where the highly localized joule heating occurs. One technique that has shown the ability to achieve this is transient thermoreflectance imaging (TTI). The accuracy of TTI is based on using the correct thermoreflectance coefficient. In the past, alternative techniques have been used to adjust the thermoreflectance coefficient to match the correct temperature rise in the device. This paper provides a new method to accurately determine the thermoreflectance coefficient of a given surface and is validated via an electrical method: gate resistance thermometry (GRT). Close agreement is shown between the temperature rise of the passivated gate metal measured by TTI and the averaged gate temperature monitored by GRT. Overall, TTI can now be used to thermally map GaN HEMTs under pulsed conditions providing simultaneously a submicrosecond temporal resolution and a submicrometer spatial resolution.

Hole-alleviated trap transport in dielectrics

At present, the nature of ionic conductivity in dielectrics remains unclear. It is believed that the ionic transport is due to local Joule heating. In this paper, another ionic conductivity mechanism is proposed and considered. Taking into account the two-band conductivity, the diffusion and drift of traps in a dielectric are studied after the holes are captured on them. It is assumed that capturing holes onto traps leads to a significant decrease in their activation energy, which, in turn, leads to an increase in ionic conductivity in dielectrics. Considering the drift and diffusion of traps with captured holes, it was possible to describe the high conductivity in thin Si3N4 films.

Sintering and tribomechanical properties of gel-combustion-derived nano-alumina and its composites with carbon nanotubes

Fully pure nano-α-alumina (Al2O3) was prepared following gel-combustion method. Near theoretically dense monolithic Al2O3 and its composites reinforced with multiwalled carbon nanotubes (MWCNTs) were prepared using spark plasma sintering (SPS) at 1500 °C under 40 MPa within 10 min. The shrinkage curves were guided in sequence by the crystallization of the amorphous mass followed by a solid-state sintering. The differential nature of electrical conductivity of both composite phases resulted in enhanced densification through localized joule heating. Formation of ~ 1-μm-sized equiaxed matrix grains with uniform distribution of structurally survived CNTs in it was observed in the sintered composites. Within the investigated loading span, the highest Vickers hardness (HV) values were obtained only at 0.5 wt% MWCNT loading in matrix Al2O3. Improvements in HV values for the composites at 0.2 and 2 kgf indentation loads were found to be ~ 18 and ~ 12%, respectively, in comparison with those obtained for pure matrix phase. Quantitative indentation size effect analyzed through standard mathematical models indicated the role of matrix grain refinement and proper matrix–filler load sharing in changing the true hardness. On the contrary, increased CNT concentration leaded to increased sensitivity toward size effect due to the extreme flexible nature of the filler. Unlubricated linear scratch experiments revealed ~ 30–45% lower specific wear rate (WR) values of the composite specimens compared to SPS-processed monolithic Al2O3. Microstructure and scar profile observations were utilized to describe such enhanced wear resistance of present composites.

Carrier Transport of Silver Nanowire Contact to p-GaN and its Influence on Leakage Current of LEDs

The authors investigated the silver nanowires (AgNWs) contact formed on p-GaN. Transmission line model applied to the AgNWs contact to p-GaN produced near ohmic contact with a specific contact resistance (ρsc) of 10−1∼10−4 Ω·cm2. Noticeably, the contact resistance had a strong bias-voltage (or current-density) dependence associated with a local joule heating effect. Current-voltage-temperature (I-V-T) measurement revealed a strong temperature dependence with respect to ρsc, indicating that the temperature played a key role of an enhanced carrier transport. The local joule heating at AgNW/GaN interface, however, resulted in a generation of leakage current of light-emitting diodes (LEDs) caused by degradation of AgNW contact.

Demonstration of a Curable Nanowire FinFET Using Punchthrough Current to Repair Hot-Carrier Damage

Device degradation caused by gate oxide damage in a FinFET on silicon-on-insulator is recovered using punchthrough current via a silicon fin. As the high level of drain current flows under a punchthrough mode, localized Joule heat driven by drain current, enough to anneal the gate oxide, is induced in the channel. This selectively cured localized damage in the FinFET. The dependence of recovery on the gate length, substrate material underneath the channel, and the proper range of annealing voltage are investigated.

Mechanism for the macro and micro behaviors of the Ni-based superalloy during electrically-assisted tension: Local Joule heating effect

Electrically-assisted manufacturing (EAM) is used for forming difficult-to-form materials such as the Ni-based superalloy in recent years. Compared to the hot deformation, EAM is a more convenient and effective method. However, the mechanism for the macro and micro behaviors of the materials with EAM is still a controversial issue. Thus, in this work, the electrically-assisted (EA) tension tests of the Ni-based superalloy were carried out with different parameters, and the macro and micro behaviors of the material were studied and discussed. Besides the reduction of yield strength (YS) and flow stress, the Portevin-Le Chatelier (PLC) effect appears during the EA tension and is more significant than that during the hot tension at the same temperature. The critical temperature for the PLC effect is the same with different strain rates under a fixed peak current density. Essentially, the directional distribution of dislocations and the earlier precipitation of the second phase can also be the main causes for the PLC effect. According to the existing theories and the electric treatment experiments that the higher percentage of defects or the second phase in metal result in more significant temperature rise, the local high temperature which induced by local Joule heating effect exists in the critical areas. It may be the main mechanism resulting in the macro and micro behaviors of alloy during the EA tension. Furthermore, recrystallization is experimentally observed when the measured temperature is much lower than the critical temperature for recrystallization due to the local Joule heating effect.

Thermoreflectance imaging of electromigration evolution in asymmetric aluminum constrictions

Electromigration (EM) is a phenomenon whereby the flow of current in metal wires moves the underlying atoms, potentially inducing electronic interconnect failures. The continued decrease in commercial lithographically defined feature sizes means that EM presents an increasing risk to the reliability of modern electronics. To mitigate these risks, it is important to look for novel mechanisms to extend lifetime without forfeiting miniaturization. Typically, only the overall increase in the interconnect resistance and failure voltage are characterized. However, if the current flows non-uniformly, spatially resolving the resulting hot spots during electromigration aging experiments may provide better insights into the fundamental mechanisms of this process. In this study, we focus on aluminum interconnects containing asymmetric reservoir and void pairs with contact pads on each end. Such reservoirs are potential candidates for self-healing. Thermoreflectance imaging was used to detect hot spots in electrical interconnects at risk of failure as the voltage was gradually increased. It reveals differential heating with increasing voltage for each polarity. We find that while current flow going from a constriction to a reservoir causes a break at the void, the identical structure with the opposite polarity can sustain higher current (J = 21 × 106 A/cm2) and more localized joule heating and yet is more stable. Ultimately, a break takes place at the contact pad where the current flows from narrow interconnect to larger pads. In summary, thermoreflectance imaging with submicron spatial resolution provides valuable information about localized electromigration evolution and the potential role of reservoirs to create more robust interconnects.

Electrothermal Annealing to Enhance the Electrical Performance of an Exfoliated MoS2 Field-Effect Transistor

An electrothermal annealing (ETA) was applied to improve the ON-state current ( ${I} _{ \mathrm{\scriptscriptstyle ON}}$ ) of an exfoliated MoS2 field-effect transistor (FET). The ETA uses localized Joule heat generated by current flowing through the source and drain of the device. Process-induced contaminants in both the MoS2 channel and MoS2-metal junctions were reduced. Electrical characterization, including the extraction of mobility and parasitic resistance, was performed to analyze the annealing effects. Numerical thermal simulations were also performed to provide insight on parameters to optimize the ETA process since the MoS2 flakes have diverse sizes and asymmetric shapes in the exfoliation-based MoS2 FETs.

Understanding Graphics on a Scalable Latching Assistive Haptic Display Using a Shape Memory Polymer Membrane.

We present a fully latching and scalable 4 × 4 haptic display with 4 mm pitch, 5 s refresh time, 400 mN holding force, and 650 μm displacement per taxel. The display serves to convey dynamic graphical information to blind and visually impaired users. Combining significant holding force with high taxel density and large amplitude motion in a very compact overall form factor was made possible by exploiting the reversible, fast, hundred-fold change in the stiffness of a thin shape memory polymer (SMP) membrane when heated above its glass transition temperature. Local heating is produced using an addressable array of 3 mm in diameter stretchable microheaters patterned on the SMP. Each taxel is selectively and independently actuated by synchronizing the local Joule heating with a single pressure supply. Switching off the heating locks each taxel into its position (up or down), enabling holding any array configuration with zero power consumption. A 3D-printed pin array is mounted over the SMP membrane, providing the user with a smooth and room temperature array of movable pins to explore by touch. Perception tests were carried out with 24 blind users resulting in 70 percent correct pattern recognition over a 12-word tactile dictionary.

LF Noise Analysis for Trap Recovery in Gate Oxides Using Built-In Joule Heater

The importance of the reliability of gate oxide materials is increasing continuously as CMOS technology advancing. Joule heating to induce localized high temperature via a built-in gate heater has recently been introduced as a rapid and efficient method to cure instances of gate oxide damage, including damaged interface traps and bulk traps in the gate oxide. In this paper, spatially distributed deep oxide traps were generated by Fowler–Nordheim (FN) stress, and a recovery process by electrothermal annealing (ETA) using local Joule heat was clearly demonstrated with low-frequency (LF) noise characteristics. The generation and recovery of the oxide traps were quantitatively analyzed with LF noise, and the results showed that the border traps generated by the FN stress were cured by ETA. The recovery process was predominantly affected by the applied gate voltage and the duration. Excessive gate voltage beyond the critical value permanently destroyed the gate oxide. The effect of a forming gas annealing (FGA) process on the gate oxide traps was also analyzed with LF noise and compared with that of ETA. Although electrical Joule heating was applied under a condition of ambient air, not hydrogen-rich atmosphere, the passivation effect was superior to that of a FGA process conducted in diluted H2 ambient.

Investigation of the Impact of High Temperatures on the Switching Kinetics of Redox‐Based Resistive Switching Cells using a High‐Speed Nanoheater

AbstractIonic transport greatly influences the switching kinetics of filamentary resistive switching memories and depends strongly on temperature and electric fields. To separate the impact of both parameters on the switching kinetics and to further deepen the understanding of the influence of local Joule heating, a nanometer‐sized heating structure is employed. It consists of a 100 nm wide Pt electrode which, due to Joule heating, serves as heating source upon an electrical stimulus. These self‐heating properties are underlined by a 3D finite elements simulation model, which confirms a temperature increase of almost 500 K. Experimental electrical pulse measurements indicate that for this temperature a steady state is achieved in less than 100 ns. By employing this heating structure, kinetic measurements of a Pt/Ta2O5/Ta cell are performed at different temperatures and reveal that significantly decreased SET times are obtained with increasing temperature. This effect is accompanied by an increasing slope of the current prior to the SET event. The experimental results are further confirmed by predictions of an analytical model based on ionic conduction.

Temperature Evolution in Nanoscale Carbon-Based Memory Devices Due to Local Joule Heating

Tetrahedral amorphous (ta-C) carbon-based memory devices have recently gained traction due to their good scalability and promising properties like nanosecond switching speeds. However, cycling endurance is still a key challenge. In this paper, we present a model that takes local fluctuations in sp $^{2}$ and sp $^{3}$ content into account when describing the conductivity of ta-C memory devices. We present a detailed study of the conductivity of ta-C memory devices ranging from ohmic behavior at low electric fields to dielectric breakdown. The study consists of pulsed switching experiments and device-scale simulations, which allows us for the first time to provide insights into the local temperature distribution at the onset of memory switching.

Theoretical and experimental investigations of local overheating at particle contacts in spark plasma sintering

This paper analyzes the heating of TiAl powders at particle scale in spark plasma sintering (SPS). During SPS processing, the powder particles are subjected to uniaxial pressing and small contact areas are formed between particles. Numerical simulations are performed on a representative cell of the material and qualitatively compared to experiments. In order to understand the heating mechanisms involved in SPS, two models are analyzed. The first one considers only heat diffusion in the material. The second one associates local Joule heating due to current concentration and heat diffusion. In TiAl alloys, the γ-α phase transition at 1335°C was used as marker of the temperature reached locally. More than 100 particle necks of several samples of 100μm diameter Ti48Al48Cr2Nb2 powders processed by SPS were investigated to detect overheating marks. Simulations clearly show high current concentration in and close to the necks, but both simulations and experiments show that there is no heat concentration close to the necks for this size of particles. Simulations show that this is due to fast heat dissipation in small particles: centimetric or higher size particles would be required to observe significant overheating.

Electro-Thermal Annealing Method for Recovery of Cyclic Bending Stress in Flexible a-IGZO TFTs

Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) fabricated by low-temperature processes on a flexible substrate can easily be degraded by mechanical deformation. Furthermore, lower performance in terms of the initial characteristics and reliability levels compared to those fabricated on glass substrates with relatively high heat treatments is inevitable. To solve these problems, a local electro-thermal annealing (ETA) method was applied to flexible a-IGZO TFTs processed at low temperature to enhance the inferior initial characteristics and reliability under a bending state. The enhancement of the characteristics and reliability by ETA can be attributed to the reduction of defects related to the oxygen through a localized Joule heat treatment with an extremely short duration (~1 ms). In addition, the effectiveness of ETA to recovery from bending stress even under harsh cyclic bending operation (strain condition of 0.833%) is verified.

Multi-scale mechanics and electrical transport in a free-standing 3D architecture of graphene and carbon nanotubes fabricated by pressure assisted welding

A free-standing, 3D nanohybrid structure is fabricated by welding 2D graphene (Gr) and 1D carbon nanotubes (CNT) by localized Joule heating under high pressure. Multi-scale mechanical properties and electrical transport behavior of the hierarchical nanostructure are investigated. Nanoindentation revealed anisotropy in mechanical properties with respect to the orientation of the graphene layers. CNTs were found to act as anchors between graphene layers during in situ indentation, enhancing the resistance to failure. Gr-CNT is characterized by excellent damping capability, with loss tangent values as high as 0.8. Anisotropy in loss tangent was observed, indicating the potential to dissipate energy in a desired orientation while allowing unattenuated energy transfer in the other orientation. A two-fold increase in electrical conductivity is observed (∼108 S/cm) as compared to pure graphene monolith (∼55 S/cm) fabricated by the same technique. In addition, out-of-graphene plane conductivity is also improved by 23% due to nanotube addition. CNTs act as conduction pathways and compensate for resistance at interfaces and linkages in the hybrid. Development of a large-scale 3D architecture with strongly bonded nano-constituents and excellent electrical transport opens up scope for numerous applications, such as nano-microelectromechanical systems, sensors, dampers, precision systems, thermal management, and scaffolds for tissue and neural engineering.