Advanced Electrical Devices Research Articles

A direct FE2 method for concurrent multilevel modeling of a coupled thermoelectric problem – Joule heating effect – in multiscale materials and structures

Coupled thermoelectric problem significantly affects the performance of electric devices, while there seems to be no method for concurrent multiscale modeling of such problems, which significantly limits the development of advanced electric devices consisting of multiscale structures. To this end, a Direct FE2 (D-FE2) method is proposed for concurrent multiscale modeling of a typical type of coupled thermoelectric problems, i.e., Joule heating effect, in heterogeneous materials and structures. To enforce energy equilibrium and realize information transfer between the macro- and meso‑scales, the Hill-Mandel homogenization condition was generalized to account for both thermal and electric energy, while periodic boundary conditions derived from kinematic constraints were prescribed to both electric potential and temperature to link meso‑scale RVEs to macro-elements in the D-FE2 model. The proposed D-FE2 method can be easily implemented using the available feature “Multiple Points Constraint (MPC)” in many commercial FE software. A series of numerical examples including steady-state analysis and transient analysis of fiber composites, porous materials and lattice structures validate the favorable accuracy and efficiency of the proposed D-FE2 method in modeling the Joule heating phenomenon in multiscale materials and structures. This also implies the promising potential of the proposed D-FE2 method in modeling and design of large-scale electric devices with multiscale structures.

A new strategy to improve the dielectric properties of cellulose nanocrystals (CNCs): Surface modification of small molecules

Nanocellulose finds various applications in advanced electrical devices due to its impressive mechanical properties, thermal stability, and degradability. Cellulose nanocrystals (CNCs) with excellent dielectric properties may act as a fresh dielectric plastic. In this study, a new strategy of small molecule modification was used to improve the dielectric constant, breakdown strength, and band gap of the CNCs. The dipole moments, dipole density, and the anisotropic impact of surface groups on the dielectric constant were studied. The number of sulfates in the CNCs showed a gradient due to alkali treatment and sulfonation, which allowed for a controlled range of the dielectric constant of nanocellulose between 4.9 and 11.9. TEMPO oxidation (2,2,6,6-tetramethylpiperidine-1-oxyl) and cyanoethylation of the CNCs further increased the dielectric constant to 11.1 and 13.2, respectively, and the dielectric loss 10−1. By understanding and innovating organic polymer dielectrics, we can provide significant benefits to the electronics and device industries.

Enhanced energy storage properties of all-polymer dielectrics by cross-linking

Polymer dielectrics with good energy storage properties are need for advanced electric devices. Herein, a new class of all organic dielectric cross-linkable polymers, poly(methyl methacrylate-glycidyl methacrylate) (P(MMA-GMA)) prepared by radical polymerization, is reported. A comprehensive investigation was conducted to examine the impact of the cross-linked monomer GMA content on the energy storage properties. The crosslinking significantly enhances the breakdown strength and suppresses the leakage currents. Consequently, the copolymer P(MMA-GMA) containing 7 mol% GMA exhibits a high discharge energy density of 16.5 J/cm3 at 750 MV/m, coupled with a high discharge efficiency of 82%. Even at an elevated temperature of 100 °C, it still possesses a good energy performance of a discharge energy density of 12.1 J/cm3 and a relatively high efficiency of 80.1% at 650 MV/m. This study offers a simple and effective approach to fabricating all-organic polymer dielectrics with good energy storage properties.

Heat transfer analysis in a longitudinal porous trapezoidal fin by non-Fourier heat conduction model: An application of artificial neural network with Levenberg–Marquardt approach

Thermal critical issues commonly occur in advanced electrical devices as a response to excessive heat generation or a loss in efficient surface area for heat exclusion. This issue can be addressed by utilizing the extended surface to improve the heat transfer performance of the devices. Thus, the present analysis is devoted to scrutinizing the non-Fourier unsteady heat transference of a trapezoidal porous fin. Levenberg–Marquardt technique of backpropagation artificial neural network (LMT-BANN) is employed here to analyze the thermal variation in the fin. The developed governing equation is the hyperbolic heat conduction equation (HHCE), which is transformed into a dimensionless partial differential equation (PDE) using dimensionless variables. LMT-BANN is employed on thermal numerical data and is developed to trace numerical approximation of fin problem using a methodology that includes testing, training, and validation. A graphical visualization of the consequences of thermal variables on the temperature field is presented. The notable evidence of this study reveals that as the magnitude of the convection factor increases, thermal dissipation through the fin gradually decreases. Further, the LMT-BANN technique has been determined to be an effective, reliable, and rapidly convergent stochastic computational solver that can be used effectively for examining the thermal model.

Emerging Synthesis Strategies of 2D MOFs for Electrical Devices and Integrated Circuits.

The development of advanced electronic devices is boosting many aspects of modern technology and industry. The ever-increasing demand for advanced electrical devices and integrated circuits calls for the design of novel materials, with superior properties for the improvement of working performance. In this review, a detailed overview of the synthesis strategies of 2D metal organic frameworks (MOFs) acquiring growing attention is presented, as a basis for expansion of novel key materials in electrical devices and integrated circuits. A framework of controllable synthesis routes to be implanted in the synthesis strategies of 2D materials and MOFs is described. In short, the synthesis methods of 2D MOFs are summarized and discussed in depth followed by the illustrations of promising applications relating to various electrical devices and integrated circuits. It is concluded by outlining how 2D MOFs can be synthesized in a simpler, highly efficient, low-cost, and more environmentally friendly way which can open up their applicable opportunities as key materials in advanced electrical devices and integrated circuits, enabling their use in broad aspects of the society.

Direct Wiring of Liquid Metal on an Ultrasoft Substrate Using a Polyvinyl Alcohol Lift-off Method.

In recent years, wiring and system construction on ultrasoft materials such as biological tissues and hydrogels have been proposed for advanced wearable devices, implantable devices, and soft robotics. Among the soft conductive materials, Ga-based liquid metals (LMs) are both biocompatible and ultrasoft, making them a good match for electrodes on the ultrasoft substrates. However, gels and tissues are softer and less wettable to the LMs than conventional soft substrates such as Ecoflex and polydimethylsiloxane. In this study, we demonstrated the transfer of LM paste composed of Ga-based LM and Ni nanoparticles onto ultrasoft substrates such as biological tissue and gels using sacrificial polyvinyl alcohol (PVA) films. The LM paste pattern fabricated on the PVA film adhered to the ultrasoft substrate along surface irregularities and was transferred without being destroyed by the PVA film before the PVA's dissolution in water. The minimum line width that could be wired was approximately 165 μm. Three-dimensional wiring, such as the helical structure on the gel fiber surface, is also possible. Application of this transfer method to tissues using LM paste wiring allowed the successful stimulation of the vagus nerve in rats. In addition, we succeeded in transferring a temperature measurement system fabricated on a PVA film onto the gel. The connection between the solid-state electrical element and the LM paste was stable and maintained the functionality of the temperature-sensing system. This fundamental study of wiring fabrication and system integration can contribute to the development of advanced electric devices based on ultrasoft substrates.

An overlooked issue for high-voltage Li-ion batteries: Suppressing the intercalation of anions into conductive carbon

Summary High-voltage Li-ion batteries have been extensively studied to increase energy density of batteries. However, their cycling stability has remained poor, despite various strategies being proposed to overcome the issues of high-potential cathodes, such as electrolyte oxidation and transition metal dissolution. Herein, we report anion intercalation into the cathode conductive carbon as an overlooked yet critical issue. We propose a concentrated sulfolane (SL)-based electrolyte that prevents anion intercalation via two mechanisms: (1) by offering a high activation barrier to intercalation via its strong anion-Li+ interaction and (2) by forming a sulfur-containing, anion-blocking SL-derived interphase. This electrolyte, used with graphitized acetylene black, which is oxidatively stable but usually susceptible to anion intercalation, enables the stable operation of a Li2CoPO4F/graphite full cell (cut-off voltage = 5.2 V), with 93% capacity retention after 1,000 cycles and an average Coulombic efficiency of ≥99.9%. This is a pivotal strategy to enhance the reversibility of >5 V Li-ion batteries on a commercial level.

Flame-retardant poly(vinyl alcohol)/MXene multilayered films with outstanding electromagnetic interference shielding and thermal conductive performances

With the miniaturized and high-frequency development in electronic products, polymeric films synchronously with high electromagnetic interference (EMI) shielding effectiveness (SE) and thermal conductivity (TC) are urgently needed. In this work, poly (vinyl alcohol)/transition metal carbide (PVA/MXene) films featured with alternating multilayered structure were fabricated through multilayered casting. The continuous MXene layer provided a compact network for conducting heat and electron, endowing the multilayered film with excellent EMI SE and TC synchronously. In particular, the 27-μm-thick PVA/MXene multilayered film (containing 19.5 wt% MXene in total) exhibited an electrical conductivity of 716 S/m, a maximum EMI SE of 44.4 dB and a specific EMI SE (SSEt) of 9343 dB cm2 g−1. Meanwhile, the multilayered film showed a high in-plane TC of 4.57 W/mK, enhanced by almost 23-fold compared with that of neat PVA. Moreover, the multilayered architecture endowed the film with remarkable anti-dripping performance. This work provides a novel and feasible strategy for fabricating flame-retardant polymeric thermal conductive and EMI shielding films, which will have enormous prospect in advanced electrical devices.

UPDATE ON THE ANALYSES OF THE LARGEST BIPOLAR CASE-CONTROL EXOME SEQUENCING DATASET TO DATE

In electrical applications for alumina, it is predominantly used as an insulator. Indeed the first commercial application for alumina was electrical: spark plug insulators, an application that alumina continues to dominate to the present day. Alumina is an outstanding electrical insulator because it uniquely combines eight key attributes: (1) It's electrical resistivity is one of the highest of all known materials; (2) the dielectric loss tangent of alumina is among the lowest of all known materials; (3) high mechanical strength; (4) thermal stability up to 1700oC; (5) outstanding corrosion resistance; (6) the moderately high thermal conductivity of alumina makes it an effective insulating heatsink; (7) thermal expansion matching with silicon which is important when used as a semiconductor substrate (SOI—silicon on insulator); (8) low cost—compared to the alternative materials of comparable outstanding electrical resistivity such as aluminium nitride, silicon nitride, and beryllium oxide. There are three main industrial electrical roles in which alumina is used: (1) Macro-insulators (spark plug insulators, power transmission systems); (2) Micro-insulators (insulating substrates in microelectronic devices); (3) Insulating electrical feedthrough seal in sealed advanced electrical devices. There are also numerous minor applications for alumina as an electrical insulator. This chapter will overview the electrical properties of alumina, and explore in detail applications (1) Macro-insulators and (2) Micro-insulators. Insulating electrical feedthrough seals and the associated area of alumina-metal bonding will be explored in Chapter 14.

Optical Properties and Luminescence Behaviour of PP/Clay Nanocomposites

Silicate nanocomposites might be a great source of innovation for the development of advanced electrical devices since filler introduction improves mechanical properties, thermal stability and some electrical properties. In a first part of this paper we summarize results obtained by photoluminescence and UV-visible absorption spectroscopy. The optical balance (absorption vs. diffusion) is discussed and a detailed photoluminescence emission spectra analysis is provided. Grafting maleic anhydride (MA) on PP chains induces the formation of a broad absorption band (250-450nm) and changes in the photoluminescence emission spectrum whereas clay introduction increases light diffusion. In a second part we discuss results obtained using different luminescence techniques (recombination-induced luminescence - RIL-, thermoluminescence and electroluminescence) in order to characterise charge recombination mechanisms and the nature of trapping centres in such materials.

Isotropic etching of SiGe alloys with high selectivity to similar materials

An isotropic etching process was developed in order to remove the sacrificial SiGe layer in Si/SiGe/Si stacks and thus obtain a cavity between the Si layers. This process is shown to be selective versus silicon as long as some SiGe remains, but the Si etch rate increases suddenly when the SiGe disappears. A mechanism based on the preferential action of fluorine species is proposed. It is corroborated by the results obtained on advanced electrical devices.

UHV-TEM/REM Study of Palladium Silicide Islands Grown on Silicon (111) 7×7 Surface

Abstract The growth of self-organized nanoislands and nanowires on a substrate has been extensively studied with a view to fabricating the new functional materials and advanced electric devices. in the present work, Pd silicide islands and wires grown on Si (111) 7x77×7surface were observed in situ by ultrahigh vacuum transmission and reflection electron microscopy (UHV-TEM/REM). Pd was deposited on Si (111) 7×7 surface at about 700 K using an electron beam evaporator attached to the column of a UHV microscope. Two kinds of specimens were prepared: a <111> oriented rectangular specimen with a thin area, whose (111) top surface was observed by plan viewed TEM, and a <110> oriented bulk rectangular specimen, whose (111) side surface was observed by REM Figure la shows a REM image of Si (111) 7×7 surface. An incident electron beam is directed from the top to the bottom of the figure, which is foreshortened in the beam direction.