Color gamut change by optical crosstalk in high-resolution organic light-emitting diode microdisplays.

Herein, the color gamut change by optical crosstalk between sub-pixels in high-resolution full-color organic light-emitting diode (OLED) microdisplays was numerically investigated. The color gamut of the OLED microdisplay decreased dramatically as the pixel density of the panel increased from 100 pixels per inch (PPI) to 3000 PPI. In addition, the increase in thickness of the passivation layer between the bottom electrode and the top color filter results in a decrease in the color gamut. We also calculated the color gamut change depending on the pixel structures in the practical OLED microdisplay panel, which had an aspect ratio of 32:9 and a pixel density of 2,490 PPI. The fence angle and height, refractive index of the passivation layer, black matrix width, and white OLED device structure affect the color gamut of the OLED microdisplay panel because of the optical crosstalk effect.

Organic/Inorganic Hybrid Thin-Film Encapsulation Using Inkjet Printing and PEALD for Industrial Large-Area Process Suitability and Flexible OLED Application.

We present herein the first report of organic/inorganic hybrid thin-film encapsulation (TFE) developed as an encapsulation process for mass production in the display industry. The proposed method was applied to fabricate a top-emitting organic light-emitting device (TEOLED). The organic/inorganic hybrid TFE has a 1.5 dyad structure and was fabricated using plasma-enhanced atomic layer deposition (PEALD) and inkjet printing (IJP) processes that can be applied to mass production operations in the industry. Currently, industries use inorganic thin films such as SiNx and SiOxNy fabricated through plasma-enhanced chemical vapor deposition (PECVD), which results in film thickness >1 µm; however, in the present work, an Al2O3 inorganic thin film with a thickness of 30 nm was successfully fabricated using ALD. Furthermore, to decouple the crack propagation between the adjacent Al2O3 thin films, an acrylate-based polymer layer was printed between these layers using IJP to finally obtain the 1.5 dyad hybrid TFE. The proposed method can be applied to optoelectronic devices with various form factors such as rollables and stretchable displays. The hybrid TFE developed in this study has a transmittance of 95% or more in the entire visible light region and a very low surface roughness of less than 1 nm. In addition, the measurement of water vapor transmission rate (WVTR) using commercial MOCON equipment yielded a value of 5 × 10-5 gm-2 day-1 (37.8 °C and 100% RH) or less, approaching the limit of the measuring equipment. The TFE was applied to TEOLEDs and the improvement in optical properties of the device was demonstrated. The OLED panel was manufactured and operated stably, showing excellent consistency even in the actual display manufacturing process. The panel operated normally even after 363 days in air. The proposed organic/inorganic hybrid encapsulant manufacturing process is applicable to the display industry and this study provides basic guidelines that can serve as a foothold for the development of various technologies in academia and industry alike.

Comparative studies on vertical-channel charge-trap memory thin-film transistors using In-Ga-Zn-O active channels deposited by sputtering and atomic layer depositions.

Vertical-channel charge-trap memory thin film-transistors (V-CTM TFTs) using oxide semiconductors were fabricated and characterized, in which In-Ga-Zn-O (IGZO) channels were prepared by sputtering and atomic-layer deposition (ALD) methods to elucidate the effects of deposition process. The vertical-channel gate stack of the fabricated device was verified to be well implemented on the vertical sidewall of the spacer patterns due to excellent step-coverage and self-limiting mechanisms of ALD process. The V-CTM TFTs using ALD-IGZO channel exhibited a wide memory window (MW) of 15.0 V at a VGS sweep of ±20 V and a large memory margin of 1.6 × 102 at a program pulse duration as short as 5 ms. The programmed memory margin higher than 105 did not experience any degradation with time evolution for 104 s. The mechanical durability was also evaluated after the delamination process of polyimide (PI) film. There were no marked variations in charge-trap-assisted MW even at a curvature radius of 1 mm and programmed memory margin even after repeated program operations of 104 cycles. The introduction of ALD process for the formation of IGZO active channel was suggested as a main process parameter to ensure the excellent memory device characteristics of the V-CTM TFTs.

Luminescent silicon nanoparticles for distinctive tracking of cellular targeting and trafficking.

Developing therapeutic nanoparticles that actively target disease cells or tissues by exploiting the binding specificity of receptors presented on the cell surface has extensively opened up biomedical applications for drug delivery and imaging. An ideal nanoparticle for biomedical applications is required to report confirmation of relevant targeting and the ultimate fate in a physiological environment for further verification, e.g. to adapt dosage or predict response. Herein, we demonstrate tracking of silicon nanoparticles through intrinsic photoluminescence (PL) during the course of cellular targeting and uptake. Time-resolved analysis of PL characteristics in cellular microenvironments provides dynamic information on the physiological conditions where the silicon nanoparticles are exposed. In particular, the PL lifetime of the silicon nanoparticles is in the order of microseconds, which is significantly longer than the nanosecond lifetimes exhibited by fluorescent molecules naturally presented in cells, thus allowing discrimination of the nanoparticles from the cellular background autofluorescence in time-gated imaging. The PL lifetime is a physically intensive property that reports the inherent characteristics of the nanoparticles regardless of surrounding noise. Furthermore, we investigate a unique means to inform the lifespan of the biodegradable silicon nanoparticles responsive to local microenvironment in the course of endocytosis. A multivalent strategy of nanoparticles for enhanced cell targeting is also demonstrated with complementary analysis of time-resolved PL emission imaging and fluorescence correlation spectroscopy. The result presents the promising potential of the photoluminescent silicon nanoparticles toward advanced cell targeting systems that simultaneously enable tracking of cellular trafficking and tissue microenvironment monitoring.

Crafting a 1.5 µm pixel pitch spatial light modulator using Ge2Sb2Te5 phase change material [Invited].

For this research, we have developed key technologies for a 1.5 µm pixel pitch spatial light modulator (SLM) using Ge2Sb2Te5 (GST) phase change material. To uniformly modulate each pixel, we designed a lateral pixel structure in which a heating current flows through a bottom indium tin oxide layer. To check hologram reconstruction both after multilevel fabrication processes and before implementing full source and driver circuits, we fabricated an 8K×2K hologram on the topology by changing the GST film's phase using laser irradiation. To overcome the limitation of SLM size, we tested a physical tiling structure and found that flatness of tiled SLMs was the most important factor in the realization of holographic displays.

Correction: Rewritable full-color computer-generated holograms based on color-selective diffractive optical components including phase-change materials.

Correction for 'Rewritable full-color computer-generated holograms based on color-selective diffractive optical components including phase-change materials' by Chi-Young Hwang et al., Nanoscale, 2018, DOI: 10.1039/c8nr04471f.

Rewritable full-color computer-generated holograms based on color-selective diffractive optical components including phase-change materials.

We propose rewritable full-color computer-generated holograms (CGHs) based on color-selective diffraction using the diffractive optical component with the resonant characteristic. The structure includes an ultrathin layer of phase-change material Ge2Sb2Te5 (GST) on which a spatial binary pattern of amorphous and crystalline states can be recorded. The CGH patterns can be easily erased and rewritten by the pulsed ultraviolet laser writing technique owing to the thermally reconfigurable characteristic of GST. We experimentally demonstrate that the fabricated CGH, having a fine pixel pitch of 2 µm and a size of 32.8 × 32.8 mm2, reconstructs the three-dimensional holographic images. In addition, the feasibility of the rewritable property is verified by erasing and rewriting part of the CGH.

Holographic image generation with a thin-film resonance caused by chalcogenide phase-change material.

The development of digital holography is anticipated for the viewing of 3D images by reconstructing both the amplitude and phase information of the object. Compared to analog holograms written by a laser interference, digital hologram technology has the potential to realize a moving 3D image using a spatial light modulator. However, to ensure a high-resolution 3D image with a large viewing angle, the hologram panel requires a near-wavelength scale pixel pitch with a sufficient large numbers of pixels. In this manuscript, we demonstrate a digital hologram panel based on a chalcogenide phase-change material (PCM) which has a pixel pitch of 1 µm and a panel size of 1.6 × 1.6 cm2. A thin film of PCM encapsulated by dielectric layers can be used for the hologram panel by means of excimer laser lithography. By tuning the thicknesses of upper and lower dielectric layers, a color-selective diffraction panel is demonstrated since a thin film resonance caused by dielectric can affect to the absorption and diffraction spectrum of the proposed hologram panel. We also show reflection color of a small active region (1 µm × 4 µm) made by ultra-thin PCM layer can be electrically changed.

Nonvolatile memory thin-film transistors using biodegradable chicken albumen gate insulator and oxide semiconductor channel on eco-friendly paper substrate.

Nonvolatile memory thin-film transistors (TFTs) fabricated on paper substrates were proposed as one of the eco-friendly electronic devices. The gate stack was composed of chicken albumen gate insulator and In-Ga-Zn-O semiconducting channel layers. All the fabrication processes were performed below 120 °C. To improve the process compatibility of the synthethic paper substrate, an Al2O3 thin film was introduced as adhesion and barrier layers by atomic layer deposition. The dielectric properties of biomaterial albumen gate insulator were also enhanced by the preparation of Al2O3 capping layer. The nonvolatile bistabilities were realized by the switching phenomena of residual polarization within the albumen thin film. The fabricated device exhibited a counterclockwise hysteresis with a memory window of 11.8 V, high on/off ratio of approximately 1.1 × 10(6), and high saturation mobility (µsat) of 11.5 cm(2)/(V s). Furthermore, these device characteristics were not markedly degraded even after the delamination and under the bending situration. When the curvature radius was set as 5.3 cm, the ION/IOFF ratio and µsat were obtained to be 5.9 × 10(6) and 7.9 cm(2)/(V s), respectively.