High Current Density Applications Research Articles

Effect of binder on the electrochemical performance of activated carbon electrodes obtained from waste hazelnut shells: Comparison of PTFE and PVDF

In this study, the electrochemical performance of the electrode materials based on two commonly used binders –poly(vinylidene difluoride) (PVDF) and poly(tetrafluoroethylene) (PTFE)– was introduced. The electrochemical performance of the activated carbon electrodes was explored by performing cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques. The results showed that the activated carbon electrode prepared at 500 °C with PTFE (AC-500-PTFE) exhibited higher capacitance values at low current rates than the one with PVDF (AC-500-PVDF). The results also revealed that the capacitance values of the AC-500-PVDF electrode for the current rates higher than 1.5 A g−1 were higher than the AC-500-PTFE electrode. The implemented transmission line equivalent circuit model for impedance showed that the capacitance inside the pores was higher for the AC-500-PVDF, and the higher capacitance on the electrode surface was obtained for the AC-500-PTFE. As a result, it is recommended to prefer PTFE binder for low current density, yet a PVDF binder for high current density applications.

Analysis of Electrochemical Performance with Dispersion Degree of CNTs in Electrode According to Ultrasonication Process and Slurry Viscosity for Lithium-Ion Battery.

Lithium-ion batteries (LIBs) continue to dominate the battery market with their efficient energy storage abilities and their ongoing development. However, at high charge/discharge C-rates their electrochemical performance decreases significantly. To improve the power density properties of LIBs, it is important to form a uniform electron transfer network in the cathode electrode via the addition of conductive additives. Carbon nanotubes (CNTs) with high crystallinity, high electrical conductivity, and high aspect ratio properties have gathered significant interest as cathode electrode conductive additives. However, due to the high aggregational properties of CNTs, it is difficult to form a uniform network for electron transfer within the electrode. In this study, to help fabricate electrodes with well-dispersed CNTs, various electrodes were prepared by controlling (i) the mixing order of the conductive material, binder, and active material, and (ii) the sonication process of the CNTs/NMP solution before the electrode slurry preparation. When the binder was mixed with a well sonicated CNTs/NMP solution, the CNTs uniformly adsorbed to the then added cathode material of LiNi0.6Co0.2Mn0.2O2 and were well-dispersed to form a flowing uniform network. This electrode fabrication process achieved > 98.74% capacity retention after 50 cycles at 5C via suppressed polarization at high current densities and a more reversible H1-M phase transition of the active material. Our study presents a novel design benchmark for the fabricating of electrodes applying well-dispersed CNTs, which can facilitate the application of LIBs in high current density applications.

Accelerated Solder Interconnect Testing Under Electromigratory and Mechanical Strain Conditions

Abstract Continuous power density increases and interconnect scaling in electronic packages raises risk of electromigration (EM) induced failures in high current interconnects. Concurrently, thermal cycling fatigue also places interconnects at risk of reliability failure during electronics' operating lifetime. These two differing failure mechanisms are historically treated separately, but in operation, the combination of EM effects and thermal cycling can act synchronously in accelerating failure. Presently, there is no model to predict the complexity of reliability estimation arising from these interacting failure modes but is certainly important for high current density applications. In this work, a novel testing system has been employed to facilitate the estimation of the reliability of solder interconnects under the combined influence of EM and mechanical strain. The system subjects solder interconnects to high current density, elevated ambient temperature, and a constant tensile stress while recording the change in electrical resistance and change in length of the solder over time. The solder samples were created using two copper wires connected by a eutectic Pb/Sn solder ball to imitate flip-chip or BGA packaging interconnects, allowing for controlled testing conditions in order to demonstrate the combined effects of a mechanical load and EM on the lifetime of a solder joint. A significant reduction in lifetime was observed for samples that endured the coupled accelerating factors. Comparing the experimental results of different current densities at different stress levels provided a new outlook on the nature of coupled failure acceleration in solders. This novel test methodology can inform model generation for better anticipating the failure rate of solder interconnects which naturally experience multiple stress inputs during their lifetime.

Ultrahigh On‐Current Density of Organic Field‐Effect Transistors Facilitated by Molecular Monolayer Crystals

AbstractOrganic semiconductor materials are not recognized as a system for high current density applications due to the generally low mobility and high contact resistance. In this work, solution‐processed organic molecular monolayer crystals (1L‐crystals) as the active layers in field‐effect transistors, demonstrating high current density application are utilized. The 1L‐crystal‐based devices exhibit high intrinsic mobility of 10.9 cm2 V–1 s–1 and a contact resistance as low as 28 Ω cm, offering unprecedently high width‐normalized current density up to 19 µA µm–1 and 1.2 MA cm–2 normalized by cross‐section area. Joule heating effects in these high current devices are investigated. At a current density of 7 µA µm–1, 1L‐crystal‐based transistor works stably within 1000 consecutive scans. Above this current density, thermal degradation in the current starts to occur and pulsed mode operation can restrict the degradation. The 1L‐crystals exhibit superiority in high‐current and potential high‐frequency applications, which can expand the current boundary of organic semiconductor materials.

Vertically Aligned n-Type Silicon Nanowire Array as a Free-Standing Anode for Lithium-Ion Batteries.

Due to its high theoretical specific capacity, a silicon anode is one of the candidates for realizing high energy density lithium-ion batteries (LIBs). However, problems related to bulk silicon (e.g., low intrinsic conductivity and massive volume expansion) limit the performance of silicon anodes. In this work, to improve the performance of silicon anodes, a vertically aligned n-type silicon nanowire array (n-SiNW) was fabricated using a well-controlled, top-down nano-machining technique by combining photolithography and inductively coupled plasma reactive ion etching (ICP-RIE) at a cryogenic temperature. The array of nanowires ~1 µm in diameter and with the aspect ratio of ~10 was successfully prepared from commercial n-type silicon wafer. The half-cell LIB with free-standing n-SiNW electrode exhibited an initial Coulombic efficiency of 91.1%, which was higher than the battery with a blank n-silicon wafer electrode (i.e., 67.5%). Upon 100 cycles of stability testing at 0.06 mA cm−2, the battery with the n-SiNW electrode retained 85.9% of its 0.50 mAh cm−2 capacity after the pre-lithiation step, whereas its counterpart, the blank n-silicon wafer electrode, only maintained 61.4% of 0.21 mAh cm−2 capacity. Furthermore, 76.7% capacity retention can be obtained at a current density of 0.2 mA cm−2, showing the potential of n-SiNW anodes for high current density applications. This work presents an alternative method for facile, high precision, and high throughput patterning on a wafer-scale to obtain a high aspect ratio n-SiNW, and its application in LIBs.

Leveling Transient and Spatial Gradients in Planar Solid Oxide Cells Using Spatially Varied Microstructures: A Numerical Study

Sharp spatial and transient gradients of overpotential, current density, gas species and temperature within planar solid oxide cells (SOCs) can lead to increased degradation rates, decreased active area utilization and high thermal stresses. Such issues will lead to decreased cell efficiency and functional lifetime while increasing the risk of sudden cell failure due to cracking or delamination. Spatial gradients occur in part due to the interconnect geometry. Commonly, the electrochemical reaction rate within SOC electrodes is disproportionately higher near the inlet regions of the fuel or steam channels and decreases towards the outlets as the concentrations of fuel or steam decreases for fuel cell and electrolysis modes, respectively. Transient gradients occur on short time scales due to rapid fluctuations in loading during ramp up or ramp down and for reversible operation when the current direction is reversed. It might be possible to greatly reduce both transient and spatial gradients by controlling the reaction rate distribution within SOC electrodes through the strategic manipulation of the electrode active layer microstructures. Advances in additive manufacturing techniques now facilitate the design of engineered electrodes with precisely controlled microstructure properties such as pore size, porosity and volume ratios of active layer materials (i.e. Ni or YSZ). The purpose of the present study is to explore the impact and possible benefits of applying functionally graded or regionally altered microstructural properties in the active layer of planar SOCs using a previously developed transient 3D multiphysics performance model of commercial sized planar SOCs. Percolation theory is used to estimate properties such as triple phase boundary (TPB) density and tortuosities from the applied variations of particle sizes, volume fractions and pore former properties as shown in Figure 1(a). It is shown that indeed both spatial and transient gradients can be significantly decreased by engineering gradients in composition and microstructure. For example, under the extreme conditions of ramping up from 0 to 0.75 A/cm2 current density and 75% H2 utilization in fuel cell mode, the multiphysics performance model predicts a nearly 300K temperature increase in approximately 100s for the baseline case as shown in Figure 1(d). Applying linear gradients of porosity and Ni/YSZ ratios such that TPB density increases from the fuel inlet to outlet significantly decreases this temperature gradient by 25-100K. However, there may be a tradeoff in terms of overall performance with decreasing steady state cell voltage corresponding with decreased temperature gradients. This is partly associated with the decreased temperature itself as the reaction kinetics are assumed to increase with increasing temperature resulting in decreased overpotential at the TPBs. Additional impacts of these and other functionally graded microstructures include decreased current density gradients and more uniform oxygen reduction in the oxygen electrode compared to the baseline case. Results indicate that functionally graded electrode microstructures could be designed based on the desired operating conditions to reduce degradation and thermal stresses within cell and stack assemblies. Such electrode designs have the potential to significantly reduce cell failure rate and increase cell lifetime particularly in transient loading and/or high current density applications. Figure 1

High-Performance Triangular Miniaturized-LEDs for High Current and Power Density Applications

This work proposes an effective electrode length model and reveals for the first time the relationship between this model and the mesa shape effect. On the basis of this model, we demonstrate high-performance triangular miniaturized-LEDs (mini-LEDs) and benchmark to the conventional square, and circular shapes of the same mesa area. Here, we systematically study the impact of shaping in mini-LEDs both theoretically and experimentally, which is fundamentally different than that of the conventional regular-sized LEDs. We find that, at the current level of 200 mA, the triangular mini-LEDs deliver an enhancement of 36.4% in the optical output power and a decrease of 9.6% for the forward voltage compared to the commonly used square ones, and also an enhancement of 24.6% in the optical output power and a decrease of 14.3% for the forward voltage compared to the circular ones. The superior optical performance is proved to result from longer effective n-electrode length in the case of the triangular mini-LEDs, which suppresses the self-heating effect and thus well preserves the internal quantum efficiency, whereas the light extraction efficiency and the heat dissipation for the triangular shape are not significantly increased for such small mesa sizes, unlike conventional broad-area LEDs. Meanwhile, the reduced voltage is revealed to stem from the decreased n-GaN resistance. Different than conventional LEDs, these findings therefore indicate that the effective n-electrode length matters substantially for the miniaturized-LEDs.

A method for realizing robust micro-scale electromagnetic actuators for high current density applications

A method for realizing robust micro-scale electromagnetic actuators for high current density applications

The Optimum Electrolyte Parameters in the Application of High Current Density Silver Electrorefining

Increasing silver production rate has been a challenge for the existing refining facilities. The application of high current density (HCD) as one of the possible solutions to increase the process throughput is also expected to reduce both energy consumption and process inventory. From the recently-developed models of silver electrorefining, this study simulated the optimum electrolyte parameters to optimize the specific energy consumption (SEC) and the silver inventory in the electrolyte for an HCD application. It was found that by using [Cu2+] in electrolyte, both objectives can be achieved. The suggested optimum composition range from this study was [Ag+] 100–150 g/dm3, [HNO3] 5 g/dm3, and [Cu2+] 50–75 g/dm3. HCD application (1000 A/m2) in these electrolyte conditions result in cell voltage of 2.7–3.2 V and SEC of 0.60–1.01 kWh/kg, with silver inventory in electrolyte of 26–39 kg silver for 100 kg per day basis. The corresponding figures for the conventional process were 1.5–2.8 V, 0.44–0.76 kWh/kg, and 15.54–194.25 kg, in respective order. These results show that, while HCD increases SEC by app. 30%, the improvement provides a significant smaller footprint as a result of a more compact of process. Thus, applying HCD in silver electrorefining offers the best solution in increasing production capacity and process efficiency.

Copper decorated ZnO nanowires material: Growth, optical and photoelectrochemical properties

Abstract To reveal the photoelectricchemical (PEC) properties modulation and its mechanism is beneficial to the exploration of novel materials with excellent properties as well as the realization of their practical application. In this paper, uniform copper-decorated ZnO nanowires (Cu@ZnO NWs) were successfully prepared via the two-step chemical vapor deposition and then magnetron sputtering method. The structure, morphology, and composition of Cu@ZnO NWs at different sputtering time (ST) and sputtering power (SP) were characterized. The result of morphology characterization show of Cu on the surface ZnO NWs can be controlled by ST and SP adjustment. The optical and PEC properties of Cu@ZnO NWs were studied. All samples showed a strong linear absorption band due to the inherent absorption band of the ZnO nanowires in the near-ultraviolet range. The addition copper did not make any significant difference in its band gap. However, due to the surface plasmon resonance (SPR) absorption of the Cu nanostructures, the absorption spectrum peak at 558 nm is exhibited. The photoluminescence (PL) results proved two emission peaks for the Cu@ZnO NWs, which the sharp ultraviolet (UV) emission peak corresponding to the near band edge emission, and broad visible range originates from the electron-hole recombination at a deep level, caused by oxygen vacancy or zinc interstitial defects and the UV/visible emission peaks of Cu@ZnO NWs are weaker/stronger than that of pure ZnO nanowires. The PEC characteristics showed an increase/decrease in the current density of Cu@ZnO Nws with different ST/SP compared to that of unmodified ZnO nanowires. The experimental result shows that the PL and PEC properties of ZnO nanowires were regulated by Cu nanostructures with different morphologies. The ease of the synthesis route and the remarkable PL and PEC properties offer metal-semiconductor compound nanostructure materials as a promising electron source for high current density applications.

Enhancement of Photoelectrochemical Performance of Ag@ZnO Nanowires: Experiment and Mechanism

This paper focuses on the enhancement of photoelectrochemical (PEC) performance of uniform silver nanoparticles-decorated ZnO (Ag@ZnO) nanowires, which have been synthesized by two-step chemical vapor deposition to prepare ZnO nanowires then magnetron sputtering method to deposit Ag nanoparticles. Moreover, we analyzed the mechanisms of the PEC behavior of the Ag@ZnO nanowires. The PEC characteristics show that the current density of Ag@ZnO nanowires increased comparing to that of unmodified ZnO nanowires. The optimized content of the Ag-decorated ZnO photoelectrode is up to the maximum photocurrent density of 24.8 μAcm-2at 1 V vs. Ag/AgCl, which was almost four times than that of the unmodified ZnO photoelectrode. Based on the surface plasmon resonance (SPR), effect of Ag nanoparticles was enhanced PEC performance of the Ag@ZnO nanowires. Because SPR effect of Ag nanoparticles extended the light absorption and enhanced the separation efficiency of the photogenerated electron-hole pairs. The remarkable PEC properties offer metals-semiconductor compound nanostructures materials as a promising electron source for high current density applications.

Edge-driven nanomembrane-based vertical organic transistors showing a multi-sensing capability

The effective utilization of vertical organic transistors in high current density applications demands further reduction of channel length (given by the thickness of the organic semiconducting layer and typically reported in the 100 nm range) along with the optimization of the source electrode structure. Here we present a viable solution by applying rolled-up metallic nanomembranes as the drain-electrode (which enables the incorporation of few nanometer-thick semiconductor layers) and by lithographically patterning the source-electrode. Our vertical organic transistors operate at ultra-low voltages and demonstrate high current densities (~0.5 A cm−2) that are found to depend directly on the number of source edges, provided the source perforation gap is wider than 250 nm. We anticipate that further optimization of device structure can yield higher current densities (~10 A cm−2). The use of rolled-up drain-electrode also enables sensing of humidity and light which highlights the potential of these devices to advance next-generation sensing technologies.

Towards high rate Li metal anodes: enhanced performance at high current density in a superconcentrated ionic liquid

Application of high current density demonstrated enhanced cycling efficiency and the formation of a stable and LiF dominated SEI providing a new path to enable fast charge battery technologies.

Synthesis, electrical and ultrafast nonlinear optical properties of Sn–ZnO composite film

Tin (Sn)- zinc oxide (TZO) composite films were successfully synthesized by the magnetron sputtering. Structure and morphology of the TZO composite films with different sputtering conditions (growth time, direct current sputtering powers and substrate temperature) were characterized. X-ray diffraction (XRD) patterns confirmed characteristic peaks of ZnO and SnO2 without any alloys distinct phases. The scanning electron microscope (SEM) micrographs revealed that the average grain size of crystallites was found to increase with increasing growth time and sputtering powers, respectively. The optical, electrical and ultrafast nonlinear optical characterizations of the TZO composite films with different growth time were studied. The effect of Sn content on the optical and electrical properties of the TZO composite films was analyzed. As growth time increasing, the optical gap of TZO composite films increased and then decreased. The Hall test results showed that Sn enhanced the carrier concentration of ZnO film. The carriers of TZO composite films range from 10−15 to 10−19/cm3 in concentration. Meanwhile, from the femtosecond Z-scan experimental results, the samples showed the change from reverse saturable absorption to saturable absorption with increasing growth time. The values of the nonlinear absorption coefficient for the TZO composite films with four growth time were 4.628 × 10−7 m/W, 6.016 × 10−8 m/W, 5.245 × 10−8 m/W and 4.407 × 10−8 m/W, respectively. The ease of the synthesis route and the remarkable electrical and ultrafast nonlinear optical properties offer TZO films as a promising electron source for high current density and nonlinear optical applications.

Simple and Efficient Preparation of a Single-Crystal LaB6 Field Emission Tip

Single-crystal LaB6 field emission tips have strong anti-poisoning ability, good emission stability, high emission current density and mature applications. As such, they have attracted much attention in field emission research. In this paper, an electrochemical corrosion device is designed to enable the simple and efficient preparation of single-crystal-LaB6 tips with different radius of curvature values. Computer simulation technology is used to study the field emission behavior of the single-crystal LaB6 tip and provides the theoretical basis for the calculation of field emission current density. The results show that the preparation process is automated, more efficient and more controllable than previous methods. When the applied voltage was 2250 V, the single-crystal LaB6 tip achieved maximum emission current density of 2.05 × 104 A/cm2 at a radius of curvature of 0.5 μm.

Study of the magnetization loss of CORC® cables using a 3D T-A formulation

A Conductor on Round Core (CORC®) cable wound with a high temperature superconductor is an important cable concept for high current density applications. The design of a CORC cable makes understanding its electromagnetic performance—for example its AC losses—challenging. This paper presents a thorough study of CORC cables by combining experimental and numerical methods. In particular, it focuses on understanding how the cable structure influences the magnetization losses and on how these can be reduced. A novelty of this paper lies in the use of a new T-A formulation, which, for the first time, is employed for three-dimensional modelling of a CORC cable with real geometry. The use of the new T-A formulation in finite element software enables the study of how the winding direction and multiple-layer structure affect the magnetization losses of CORC cables. Moreover, influence of striation in CORC cables is studied as an effective way to reduce their losses. A CORC cable with striated tapes shows a significant magnetization loss reduction at high magnetic fields, in comparison to its counterpart without striated tapes. At low magnetic fields, tape striation leads to an increase in loss when the number of filaments is low, then the loss drops with a further increase in the number of filaments, but this loss reduction is much weaker than that at high fields. This paper provides an efficient tool for investigating the electromagnetic behaviour of CORC cables, which can provide valuable guidance in designing CORC cables with minimized losses for high energy physics and energy conversion applications.

30μm Thick Cu RDL in WLCSP

In situations where a device may have an interconnect pad arrangement in wafer level packaging, an additional layer of lateral connections may be employed to rearrange the connections in a manner suitable for wafer level processing. This additional layer is known as a redistribution layer, or RDL, and fabricated from a thin layer of metal with dielectrics in between. An RDL is used for higher electrical performance and complex routing to meet electrical requirements. As the importance of high power and power management in electronics products continue to rise, so also will the demands for power ICs to handle ever higher voltages without appreciably adding size and heat to the end product. Using thicker Cu metallization in an RDL is an ideal choice that accommodates high current density and lower resistance for high power applications. Assembling multiple chips in multiple layers requires more electrical connections, which in turn requires both thinner lines within the RDL and an increase in the number of RDL layers. The RDL line width of WLCSP started at over 20μm, but has already been reduced to 10~15μm in HVM. Industry players are now working in R&D to develop 2μm wide and even smaller line/space (L/S) capability to meet the requirements of today's high-end applications. In this study, we present the development of 20–30 μm thick plated Cu RDL for high power and high current density applications. Using a plated Cu process and photo-sensitive spin-on-dielectrics materials, thick Cu RDL was achieved with the AR 1:1 design rule and the reliability assessment was carried out with JEDEC reliability test conditions. A 2-layer Cu RDL (total 6-mask process with UBM) was developed and characterized for its component and board level reliability for 5×5/7×7mm, 0.35/0.4mm ball pitch WLCSP test vehicles.

(Invited) Recent Advances in Porous Silicon Based Microelectronic Devices

Historically, electronics was the first discipline that exploited the properties of porous silicon (PSi) in the 1970’s [1]. Two decades later, a huge development of the studies about PSi has been observed since an efficient photoluminescence of this material was discovered. During this fruitful period, microelectronic devices also benefited from the progresses made in the domain of semiconductor electrochemical etching and from the comprehension of the unique properties of PSi. In particular, it was found that radio-frequency (RF) devices can took advantages of the isolating properties of PSi [2]. Indeed, highly resistive substrates are generally required to reduce eddy currents and capacitive couplings and then, to get high performance passive devices. The insulating properties of PSi, combined with the ability to locate these areas in different resistivity wafers, make this material promising in terms of development of monolithic insulator/semiconductor substrates [3]. In this presentation, we will present the recent advances that have been performed in GREMAN in the field of RF devices that integrate PSi. A specific emphasis will be put on thin and free-standing PSi membranes and 3D structures for high current density applications. In addition, we will describe the way PSi could be used as insulating material in power AC Switch. Many architectures involving PSi peripheries can lead to subsequent performance and reliability improvements [4, 5, 6]. In particular, by forming a relatively thick PS layer in a TRIAC periphery, low leakage currents (<10 μA) have been demonstrated up to a few hundred volts for both bias signs. We will demonstrate that, at present, there is no doubt about benefits PSi can bring to microelectronic devices. Many other applications that require a silicon substrate such as integrated sensors [7], solar cells [8], conductive via [9] or energy micro-sources [10, 11] can also be of great interest for the microelectronics industry. For instance, we will show in details that porous silicon could also be useful for acoustic transducers as an integrated backing material in order to enhance the imaging quality. Nevertheless, until now, PSi is not widely introduced in electronic component manufacturing. This point will also be discussed.

High-rate Li4Ti5O12/porous activated graphene nanoplatelets composites using LiOH both as lithium source and activating agent

The Li4Ti5O12/activated graphene nanoplatelets (Li4Ti5O12/a-GNPs) composites are prepared via a low-cost, green, one-pot hydrothermal process by using LiOH both as lithium source and activating agent for the first time. The LiOH solution concentration and hydrothermal time are optimized to obtain the pure Li4Ti5O12/a-GNPs. The synergistic effects of the nanosized Li4Ti5O12 and the three-dimensional porous a-GNPs endow the composites with convenient lithium ion diffusion channels and efficiently conductive structures for electron and ion transport. As anticipated, the Li4Ti5O12/a-GNPs deliver an outstanding rate capability of 125 and 113 mA h g−1 at 80 and 100 C, respectively, and an excellent cycling stability with 90.21% capacity retention after 2000 cycles at 10 C. These results are much better than those of the Li4Ti5O12/GNPs and pure Li4Ti5O12, demonstrating Li4Ti5O12/a-GNPs are promising anode materials for lithium-ion batteries of high current density applications.

Interface Characterization of Al–Cu Microlaminates Fabricated By Electrically Assisted Roll Bonding

Interface characteristics of Al/Cu microlaminates fabricated by an electrically assisted roll bonding (EARB) process were studied to understand the underlying physical/chemical phenomena that lead to bond strength enhancement when applying electrical current during deformation. Peel tests were conducted for the Al/Cu roll-bonded laminates produced under 0 A, 50 A, and 150 A applied current. After peel tests using a microtensile machine, the fractured surfaces of both the Al and Cu–sides were examined using scanning electron microscopy (SEM) for fractography and SEM-based energy dispersive (EDS) analysis. Results revealed the strong dependence of the fracture path and its morphology on the strength of the bond, which is influenced by various phenomena occurring at the interface during EARB, such as microextrusion through surface microcracks, possible formation of intermetallic components and thermal softening during simultaneous application of strain and high current density.