[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

Damascene copper electroplating for on-chip interconnections, a process that we conceived and developed in the early 1990s, makes it possible to fill submicron trenches and vias with copper without creating a void or a seam and has thus proven superior to other technologies of copper deposition. We discuss here the relationship of additives in the plating bath to superfilling, the phenomenon that results in superconformal coverage, and we present a numerical model which accounts for the experimentally observed profile evolution of the plated metal.

Damascene copper electroplating for chip interconnections

Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state-of-the-art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active-sites with improved electrochemical efficiencies in future.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201700464

Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes: Mechanisms, Challenges, and Prospective Solutions

Hybrid supercapacitors with their improved performance in energy density without altering their power density have been in trend since recent years. The hybrid supercapacitor delivers higher specific capacitance in comparison to the existing electric double layer capacitor (EDLC) and pseudocapacitors. Generally, the asymmetric behavior of hybrid supercapacitors which is the combination of EDLC and pseudocapacitor acts as an enhancer in its respective capacitance values. This asymmetric approach marks a new beginning towards the much-needed pollution free, long lasting and proficient energy-storing performance. Corresponding to their utilization in hybrid electric vehicles and similar sort of power necessity based devices; the research in developing new advanced storage devices finds an enormous and vast future ahead. The most significant factor for the energy efficient applications demands a considerably higher ratio of surface to the volume by incorporation of new materials. This review article gives an overview of recent advances in the development of hybrid supercapacitors, storage mechanism, criteria of formation, components, different electrode and electrolyte materials, electrochemical profile assessment, design fabrication and their applications.

A review on recent advances in hybrid supercapacitors: Design, fabrication and applications

Polymer films fabricated on a silicon substrate has been widely used as an insulation film due to its low-cost processing and excellent dielectric performance. Polymethyl methacrylate (PMMA) is a widely used thin film material. The dielectric properties of PMMA film can be further improved by the porosity process. However, the porous PMMA film is prone to non-uniform pore sizes and through-hole defects, which affect insulation performance in practical applications. In this paper, we reported an approach to optimize the pore structure of PMMA film on the previously prepared porous silicon layer (PSL). We first prepared the PSL on the substrate by the electrochemical etching process. Then, the substrate was directly dipped into an acidic aqueous media to graft the PMMA film by a one-step method. The PSL thickness could be controlled by adjusting etching time. The effects of PSL on the pore structure of the PMMA film were studied. Besides, the thickness of porous PMMA film could be controlled by the proportion of grafting solution and the grafting time. The results show that the growth rate of porous PMMA film is the fastest when the electrochemical etching time is about 90 s. Compared with a flat surface, PSL provides more Si–H active sites. With the same grafting conditions, the presence of the PSL helps to accelerate the grafting reaction in the early stage. PMMA film was finally obtained with the porous network structure. More importantly, the obtained porous PMMA film has a lower dielectric constant (e1= 1.9~1.5) than general PMMA (e1= 2.9~2.5). The obtained porous PMMA film is potential to be used in semiconductor industry.

Grafting of a porous polymethyl methacrylate (PMMA) film on the silicon surface with low dielectric constant

The mechanical strength of low dielectric constant interlayer dielectric film (low-k layer) materials is lower. In the future, the low-k layer will continue to advance the dielectric constant and reduce the material elasticity, with the development of the wafer foundry technology, more and more low-k material have been used in the wafer manufacture which caused the topside layer of the wafer become more and more crisp, it is more easier caused the peeling and topside chipping issue during the dicing process, so the blade saw is not applicable for this product, laser grooving technology is as a matter of course to develop. This study is to show the laser grooving application at the wafer saw process, setup DOE study on the key parameters, laser power, frequency and feed speed, to verify and get the best result.

Laser Grooving Technology Study at Dicing Process in Wafer Level Package

3D NAND flash memory based on MONOS structure offers a new path to break through the limitation of memory capacity of 2D NAND flash. Thickness of top oxide layer and bottom oxide layer of MONOS directly influence performance of device. Technology Computer Aided Design(TCAD), as the most effective and powerful tool to study the electrical properties of various semiconductor devices, can be used to reveal the influence. In this paper, P/E cycle of MONOS device with varied thickness of high-k aluminum oxide and tunneling layer are investigated with Fowler-Nordheim tunneling model being put into consideration. Furthermore, threshold voltage and data retention of MONOS device with optimized thickness of oxide layers are characterized as well, which leave a novel route for related device design and optimization.

Effect of oxide layers on MONOS device performance based on TCAD simulation

The oxidation behavior of Sn-9Zn-3Bi-xCr(x=0, 0.1, 0.3, 0.5) solders under 250°C has been investigated as a function of exposure time. The evolution of surface and cross-sectional microstructure has been examined through back-scattered electron detector (BSE). Energy-dispersive x-ray spectroscopy (EDX) and x-ray diffractometer analysis (XRD) were also carried out to check the overall composition of the different samples. An oxidation model for Sn-9Zn-3Bi-xCr solders was proposed. The poor oxidation resistance of the solders is attributed to the oxidation of Zn-rich phase and other Zn atoms which diffused to the β-Sn matrix grain boundaries, forming ZnO. Two kinds of Sn-Zn-Cr phases, along the grain boundaries of β-Sn matrix and across the Zn-rich phase, were detected in Cr-bearing solder alloys, which kept the oxygen from diffusing into the bulk of the solder. Adding a small amount of Cr can improve the oxidation resistance of the solders, and the Sn-9Zn-3Bi-0.3Cr alloy had the best oxidation resistance. After 25h of aging under 250°C, the both the two kinds of Sn-Zn-Cr phases re-crystallize.

Oxidation behavior of Sn-9Zn-3Bi-xCr solders under high-temperature exposure

In this paper, the Sn-3.5Ag solder bumps were prepared successfully by two-step electroplating method. The effect of reflow time on shear property of solder bumps and Cu was investigated. After shear tests, the shear strength of Sn-3.5Ag solder bumps peaked at the reflow time of 60s, and then decreased with further increasing reflow time. It was considered that the variation of shear strength was closely related to the interfacial microstructure between the solder and Cu. Scallop-like Cu6Sn5 intermetallic compound (IMC) formed toward solder were observed after reflowing for 30s. As the reflow time increasing, the morphology of Cu6Sn5 IMCs changed from scallop-like type to the thin, long, hexagonal and rod-like type, and the grain size of Cu6Sn5 increased. The large hexagonal rod-like weakened the interfacial connection and made part of the IMCs exposed to the fracture surface. In addition, the bumps displayed good ductility after reflowing for a short period of time, while tended to be more brittle as the reflow time increasing.

Ming Li

Papers

Grafting of a porous polymethyl methacrylate (PMMA) film on the silicon surface with low dielectric constant

Laser Grooving Technology Study at Dicing Process in Wafer Level Package

Effect of oxide layers on MONOS device performance based on TCAD simulation

Oxidation behavior of Sn-9Zn-3Bi-xCr solders under high-temperature exposure

Effect of reflow time on shear property of two-step electroplated Sn-3.5Ag solder bumps