In this article, the development history and the technical hurdles of phase-change memory (PCM) are reviewed and recent progress and future directions are discussed. Prospects of PCM for ...storage-class memory (SCM) are discussed in terms of the technical challenges to satisfy the market requirements, mainly for the performance and cost effectiveness. For a more in-depth discussion, PCM is segmented into the memory part, the access device part, and the sensing scheme part. In the memory part, Set (crystallization)-Reset (amorphization) write characteristics and thermal disturbance (TDB) will be reinterpreted in terms of power consumption and performance of SCM. In the access device part, the application history of various devices, such as the transistor, the diode, and the two-terminal selector, will be reviewed and explained based on the process integration issues and area efficiency. In the next part, various sensing schemes used to make a lower read latency, multilevel cell (MLC), and cross point (X-point) are summarized. Thereafter, future directions and possible evolution pathways of 3-D structures, including X-point and vertical X-point (VXP), will be discussed for the first time. Finally, the feasibility of PCM for neuromorphic application will be followed.
Here we propose a concept of conductive dry adhesives (CDA) combining a gecko-inspired hierarchical structure and an elastomeric carbon nanocomposite. To complement the poor electrical percolation of ...1D carbon nanotube (CNT) networks in an elastomeric matrix at a low filler content (∼1 wt %), a higher dimensional carbon material (i.e., carbon black, nanographite, and graphene nanopowder) is added into the mixture as an aid filler. The co-doped graphene and CNT in the composite show the lowest volume resistance (∼100 ohm·cm) at an optimized filler ratio (1:9, total filler content: 1 wt %) through a synergetic effect in electrical percolation. With an optimized conductive elastomer, gecko-inspired high-aspect-ratio (>3) microstructures over a large area (∼4 in.2) are successfully replicated from intaglio-patterned molds without collapse. The resultant CDA pad shows a high normal adhesion force (∼1.3 N/cm2) even on rough human skin and an excellent cycling property for repeatable use over 30 times without degradation of adhesion force, which cannot be achieved by commercial wet adhesives. The body-attachable CDA can be used as a metal-free, all-in-one component for measuring biosignals under daily activity conditions (i.e., underwater, movements) because of its superior conformality and water-repellent characteristic.
Despite its strong potentials in emerging energy applications, near-field thermal radiation between large planar structures has not been fully explored in experiments. Particularly, it is extremely ...challenging to control a subwavelength gap distance with good parallelism under large thermal gradients. This article reports the precision measurement of near-field radiative energy transfer between two macroscale single-crystalline quartz plates that support surface phonon polaritons. Our measurement scheme allows the precise control of a gap distance down to 200 nm in a highly reproducible manner for a surface area of 5×5 mm^{2}. We have measured near-field thermal radiation as a function of the gap distance for a broad range of thermal gradients up to ∼156 K, observing more than 40 times enhancement of thermal radiation compared to the blackbody limit. By comparing with theoretical prediction based on fluctuational electrodynamics, we demonstrate that such remarkable enhancement is owing to phonon-polaritonic energy transfer across a nanoscale vacuum gap.
Molecular dynamics simulations of membrane proteins have provided deeper insights into their functions and interactions with surrounding environments at the atomic level. However, compared to ...solvation of globular proteins, building a realistic protein/membrane complex is still challenging and requires considerable experience with simulation software. Membrane Builder in the CHARMM-GUI website (http://www.charmm-gui.org) helps users to build such a complex system using a web browser with a graphical user interface. Through a generalized and automated building process including system size determination as well as generation of lipid bilayer, pore water, bulk water, and ions, a realistic membrane system with virtually any kinds and shapes of membrane proteins can be generated in 5 minutes to 2 hours depending on the system size. Default values that were elaborated and tested extensively are given in each step to provide reasonable options and starting points for both non-expert and expert users. The efficacy of Membrane Builder is illustrated by its applications to 12 transmembrane and 3 interfacial membrane proteins, whose fully equilibrated systems with three different types of lipid molecules (DMPC, DPPC, and POPC) and two types of system shapes (rectangular and hexagonal) are freely available on the CHARMM-GUI website. One of the most significant advantages of using the web environment is that, if a problem is found, users can go back and re-generate the whole system again before quitting the browser. Therefore, Membrane Builder provides the intuitive and easy way to build and simulate the biologically important membrane system.
Besides high efficiency, the stability and reproducibility of perovskite solar cells (PSCs) are also key for their commercialization. Herein, we report a simple perovskite formation method to ...fabricate perovskite films with thickness over 1 μm in ambient condition on the basis of the fast gas-solid reaction of chlorine-incorporated hydrogen lead triiodide and methylamine gas. The resultant thick and smooth chlorine-incorporated perovskite films exhibit full coverage, improved crystallinity, low surface roughness and low thickness variation. The resultant PSCs achieve an average power conversion efficiency of 19.1 ± 0.4% with good reproducibility. Meanwhile, this method enables an active area efficiency of 15.3% for 5 cm × 5 cm solar modules. The un-encapsulated PSCs exhibit an excellent T
lifetime exceeding 1600 h under continuous operation conditions in dry nitrogen environment.
The demand for wearable strain gauges that can detect dynamic human motions is growing in the area of healthcare technology. However, the realization of efficient sensing materials for effective ...detection of human motions in daily life is technically challenging due to the absence of the optimally designed electrode. Here, we propose a novel concept for overcoming the intrinsic limits of conventional strain sensors based on planar electrodes by developing highly periodic and three-dimensional (3D) bicontinuous nanoporous electrodes. We create a 3D bicontinuous nanoporous electrode by constructing conductive percolation networks along the surface of porous 3D nanostructured poly(dimethylsiloxane) with single-walled carbon nanotubes. The 3D structural platform allows fabrication of a strain sensor with robust properties such as a gauge factor of up to 134 at a tensile strain of 40%, a widened detection range of up to 160%, and a cyclic property of over 1000 cycles. Collectively, this study provides new design opportunities for a highly efficient sensing system that finely captures human motions, including phonations and joint movements.
One of the key challenges in driving multiple light-emitting-diode (LED) strings for a liquid-crystal-display (LCD) backlight system is to ensure uniform current control. Unequal current sharing ...between the strings is due to manufacturing spread and temperature variations. In this paper, a novel current-balancing circuit for LED backlights is proposed. A smart combination of an inherent symmetry of circuit and capacitive balancing mechanism enables an efficient and cost-effective current balancing. The operating principle of the proposed method is analyzed, and an appealing generalization is made. The feasibility of the proposed scheme is verified by developing a hardware prototype with a dimming feature to drive a 100-W edge-type backlight system, having six LED strings for a large-scale LCD panel.
The preparation of effective dispersions of carbon nanotubes (CNTs) presents a major impediment to the extension and utilization of CNTs. CNTs intrinsically tend to bundle and/or aggregate. The ...prevention of such behavior has been explored by testing various surface modification techniques to improve the dispersibility of CNTs in a variety of solvents and polymer matrices. General guidelines for the design of end-use tailor-fit surface modifications to achieve a particular CNT dispersibility have not thus far been articulated. This review aims to identify such guidelines by providing a perspective of the state of the art in surface modifications and the resultant dispersibility of CNTs. Surface modifications and dispersion properties must first be defined by agreeing upon a few new terms, such as the degree of surface modification, degree of substitution, and degree of dispersion, to determine the possible relationship(s) that may exist between surface characteristics and the dispersibility of CNTs. Furthermore, several critical issues that require concerted in-depth studies are discussed with particular emphasis on the quantitative characterization of CNT surface modifications and dispersions. This discussion describes the Flory–Huggins interaction parameter based on the solubility parameter for CNTs, which is correlated with the dispersibility in the surrounding media.
CHARMM is an academic research program used widely for macromolecular mechanics and dynamics with versatile analysis and manipulation tools of atomic coordinates and dynamics trajectories. ...CHARMM-GUI, http://www.charmm-gui.org, has been developed to provide a web-based graphical user interface to generate various input files and molecular systems to facilitate and standardize the usage of common and advanced simulation techniques in CHARMM. The web environment provides an ideal platform to build and validate a molecular model system in an interactive fashion such that, if a problem is found through visual inspection, one can go back to the previous setup and regenerate the whole system again. In this article, we describe the currently available functional modules of CHARMM-GUI Input Generator that form a basis for the advanced simulation techniques. Future directions of the CHARMM-GUI development project are also discussed briefly together with other features in the CHARMM-GUI website, such as Archive and Movie Gallery.
I examine an asymmetric-information model of layoffs (Gibbons andKatz, 1991) by comparing changes in earnings of laid-off workers andd isplacedworkers by plant closings using Korean data. The ...estimation result shows that laid-off male workers experience 11.5% greater earnings losses than those displaced by plant closings. Laid-off workers also have longer unemployment spells. Contrary to previous studies, the signaling effect of layoffs is observednot only in white-collar but also blue-collar occupations in South Korea. The seniority-basedwage payment system andlow unionization rate in South Korea are suggested as possible reasons for this unique finding.
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