Jinhyung Lee

Corrugated Sapphire Substrates for Organic Light-Emitting Diode Light Extraction

In an organic light-emitting diode (OLED), only about 20-30% of the generated light can be extracted because of the light lost to the thin film guided modes and surface plasmon. Using corrugated high-index-refractive substrates, the thin film guided modes can be effectively out-coupled from the device because of the high index substrate and the loss to the surface plamon is suppressed due to the corrugated structure. With an additional macro lens attached to the substrate to extract the substrate mode, we finally demonstrated a green phosphorescent OLED with an extremely high external quantum efficiency of 63%.

Evaluation of fluorinated polyimide etching processes for optical waveguide fabrication

Fluorinated polyimides have attracted much attention as potential materials for optical waveguide fabrication due to their high thermal stability, humidity resistance, as well as low optical loss in the wavelength region of optical communications. For the fabrication of optical waveguide structures, reactive ion etching (RIE) has been widely used. According to our study, the highest etch rate obtained with vertical profile for RIE of fluorinated polyimides with O 2 plasma was 300 nm/min. Inductively coupled plasma (ICP) etching of Ultradel® 9020D fluorinated polyimide has been conducted to obtain waveguide channels with higher etch rate and more vertical profile than is possible with RIE. The etch rate and the etch profile have been investigated as a function of ICP power, r.f. chuck power, O 2 flow rate, and chamber pressure. Etch rates of 1700 nm/min to 2200 nm/min with vertical profile and smooth sidewall were obtained by ICP etching at an ICP power of 500 W, r.f. chuck power of 150 W to 350 W, chamber pressure of 5 mTorr and O 2 flow rate of 40 sccm. Under these conditions there was no appreciable change in the etch rate with chamber pressure in the range 5-20 mTorr.

Simple and Reliable Lift-Off Patterning Approach for Graphene and Graphene–Ag Nanowire Hybrid Films

We present a simple, ultrasonic vibration-assisted lift-off-based patterning approach for graphene and graphene-Ag nanowire (NW) hybrid films. A 20 μm width pattern with uniform and smooth pattern edges was neatly defined on various rigid and flexible substrates. The patterned graphene-Ag NW electrodes showed a low sheet resistance of 19 Ω/sq with a high transmittance of 93% at 550 nm, a robust stability against oxidation, and a high reliability under a bending test. The electrodes also exhibited markedly higher performance than that of commercial fluorine-doped tin oxide electrodes for dye-sensitized solar cells. Given its low-cost, high throughput, and nondamaging effect, this simple and reliable patterning approach stimulates the practical applications of graphene-based flexible transparent electrodes in soft electronic and optoelectronic devices.

Single-Step Synthesis of Cubic Y2O3:Eu3+ Nanophosphor by Flame Spray Pyrolysis

In this report, we investigated a single-step process for formation of high crystallinity Y2O3:Eu3+ red nanophosphor by flame spray pyrolysis (FSP) without post-heat treatments. Crystallinity of as-formed nanophosphor particle was improved by addition of urea to the nitrate-based liquid precursor. Urea increased the temperature in the flame zone thus ensuring Y2O3:Eu3+ formation at higher flame temperature. Higher temperature reached during combustion of urea promoted the formation of better crystallinity, nano-sized and spherical-shaped particles. The effect of urea in the precursor to obtain high-efficiency Y2O3:Eu3+ nanophosphor was studied.

State of the art of IT-based high precision patch/implant system technology development for building/large structure safety management in Korea

Damage to infrastructure is a real concern at present, caused primarily by worldwide climate anomalies, global warming, and natural disasters. Korea has begun research to develop a high precision patch/implant system using new IT as a basis, as critical element in building/large structure safety management, to adjust to this situation. Technologies which must be developed for this research are those which measure and evaluate the soundness and safety of structures based on the measurements of an attached sensor. During the research period, optical fiber sensor patches and wireless sensor capsule implants along with various sensor technologies, stress sensing and structure condition evaluation technologies, high durability sensors and low-power compact smart structure sensors will be developed effectively for network hardware technologies. Similarly high precision image processing for automatic crack extraction will be developed along with radiation sensor application technologies, combined management/control technologies for development systems, and practical technologies for building/large structure development systems. Through the results, we hope to acquire higher sensor system performance with a measurement scope (for precision, etc.) goal at least 200% better than conventional sensor systems. The goal is to attain safety management planning and commercialization for automatic and high technology buildings/large structures. If such research is successfully developed, groundbreaking developments for maintenance related facilities is expected.

Monitoring system for bolt joints on steel structures

The bolt joints on steel structures are exposed to the possibility of damage, and thus, require intensive care. Usually, periodic inspections are conducted at the cost of time and money. However, it is very difficult to check so many bolts carefully. The purpose of this study is to propose a system that can more efficiently monitor the tightness/looseness of these bolts. The proposed bolt fastening monitoring system is comprised of sensors that are attached to nuts and a data receiving terminal, which gathers information. The reed switch consists of two thin, metallic contacts enveloped in a glass tube and is an electrical switching sensor that is triggered ON or OFF by changes in the surrounding magnetic field. The verification tests showed that bolt loosening can be effectively detected, proving the applicability of this system to the maintenance of the bolt joints of steel structures. The newly developed sensor system is expected to solve conventional sensor problems by enabling measurement of structural members which was not previously possible, thus providing a basis for a new technology in the construction industry by applying IT to construction technology.

Micro-architecture embedding ultra-thin interlayer to bond diamond and silicon via direct fusion

The continuous demand on miniaturized electronic circuits bearing high power density illuminates the need to modify the silicon-on-insulator-based chip architecture. This is because of the low thermal conductivity of the few hundred nanometer-thick insulator present between the silicon substrate and active layers. The thick insulator is notorious for releasing the heat generated from the active layers during the operation of devices, leading to degradation in their performance and thus reducing their lifetime. To avoid the heat accumulation, we propose a method to fabricate the silicon-on-diamond (SOD) microstructure featured by an exceptionally thin silicon oxycarbide interlayer (∼3u2009nm). While exploiting the diamond as an insulator, we employ spark plasma sintering to render the silicon directly fused to the diamond. Notably, this process can manufacture the SOD microarchitecture via a simple/rapid way and incorporates the ultra-thin interlayer for minute thermal resistance. The method invented herein expects to minimize the thermal interfacial resistance of the devices and is thus deemed as a breakthrough appealing to the current chip industry.

Novel rapid polishing process for fabrication of sapphire windows

Sapphire is uniquely suitable for sensor windows of electro-optical systems due to its high transparency, high mechanical strength, and chemical inactivity. Unfortunately, these same characteristics also cause polishing of sapphire windows to be extremely difficult and slow. Hence the challenge is to develop a process for affordable production of large area sapphire windows with low-roughness, low-stress and without surface and subsurface damage. Here we report a novel rapid chemical mechanical polishing process that increases the material removal rate during polishing of sapphire by greater than twofold over conventional processes. Such a process can also produce angstrom level surface finish.

Test bed bridge integration for safety network management system

As a first step for the safety network integration, test bed bridge was integrated by using the FBG sensor system. For the operating efficiency of the bridge monitoring system, software which can control the conventional sensor system and fiber optic sensor system concurrently was developed. Measuring item was limited to the strain, and the other measuring items such as acceleration or displacement will be applied to the bridge next research period. Beside these items, image processing device was installed to the test bed bridge, and the applicability of these data was considered. As a result of strain measurement, the data from fiber optic sensor system were high stable and reliability, and the problems or advanced parts will be suggested during the test bed bridge operation in the future.