• Transactions on Electrical and Electronic Materials
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• v.12 no.5
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• pp.189-192
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• 2011

A flexible back-light unit (FBLU) is fabricated by embedding plasma discharge clusters in a flexible polymer matrix. The brightness uniformity of an FBLU was measured for various combinations of optical sheets and compared with the simulated results for various bending angles. A gap between light sources causes distinctive integrated brightness curves which have two inflection points depending on bending angle. The brightness distribution of a simulated BLU was in good agreement with that of an actual plasma BLU except for a dark area that appeared at the center of the simulated BLU. The real and simulated BLUs both clearly showed an angle dependency caused by mirror images located between point light sources. On the basis of these results, it is suggested that these mirror-like images could be a major factor in determining the characteristics of FBLUs.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.39.2-39.2
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• 2011

With the steady increase in the demand for flexible devices, mainly in display panels, researchers have focused on finding a novel material that have excellent electrical properties even when it is bended or stretched, along with superior mechanical and thermal properties. Graphene, a single-layered two-dimensional carbon lattice, has recently attracted tremendous research interest in this respect. However, the limitations in the growing method of graphene, mainly chemical vapor deposition on transition metal catalysts, has posed severe problems in terms of device integration, due to the laborious transfer process that may damage and contaminate the graphene layer. In addition, to lower the overall cost, a fabrication technique that supports low temperature and low vacuum is required, which is the main reason why solution-based process for graphene layer deposition has become the hot issue. Nonetheless, a direct deposition method of large area, few-layered, and uniform graphene layers has not been reported yet, along with a convenient method of patterning them. Here, we report an evaporation-induced technique for directly depositing few layers of graphene nanosheets with excellent uniformity and thickness controllability on any substrate. The printed graphene nanosheets can be patterned into desired shapes and structures, which can be directly applicable as flexible and transparent electrode. To illustrate such potential, the transport properties and resistivity of the deposited graphene layers have been investigated according to their thickness. The induced internal flow of the graphene solution during tis evaporation allows uniform deposition with which its thickness, and thus resistivity can be tuned by controlling the composition ratio of the solute and solvent.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.1
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• pp.13-20
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• 2012

In this paper, we present the result of an investigation pertaining to the pipe stiffness of buried flexible pipes. Pipe stiffness (PS) formula for the parallel plate loading condition is derived based on the elasticity theory. Vertical and horizontal displacements are also derived. Vertical deflection is always larger than the horizontal deflection because some of energy due to overburden load is stored in the pipe but the difference is negligibly small. In the study, mechanical properties of the flexible pipes produced in the domestic manufacturer are tested and the results are reported in this paper. In addition, pipe stiffness is determined by the parallel plate loading tests and the finite element analysis. The difference between test and analysis is less than 14% although there are significant variations in the mechanical properties of the pipe material. Therefore, it was found that the finite element analysis can be used to predict the pipe stiffness instead of conducting parallel plate loading test.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.469.2-469.2
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• 2014

All-solid-state solar cell based on Chloride doped organometallic halide perovskite, (CH3NH3)PbIxCl3-x, has achieved a highly power conversion efficiency (PCE) to over 15% [1] and further improvements are expected up to 20% [2]. In this way, solar cells using novel light absorbing perovskite material are actively being studied as a next generation solar cells. However, making solution-process require high temperature up to $500^{\circ}C$ to form compact hole blocking layer and sinter the mesoporous oxide scaffold layer. Because of this high temperature process, fabrication of flexible solar cells on plastic substrate is still troubleshooting. In this study, we fabricated highly efficient flexible perovskite solar cells with PCE in excess of 11%. Atomic layer deposition (ALD) is used to deposit dense $TiO_2$ as hole blocking layer on ITO/PEN substrate. The all fabrication process is done at low temperature below $150^{\circ}C$. This work shows that one of the important blueprint for commercial use of perovskite solar cells.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.155-163
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• 2005

Pressure heating rollers with temperature control were mounted to a flat cable laminating machine (FCLM). Pressure heating rollers should be heated up to the setting temperature $(175^{\circ}C)$ and kept on to producing good quality flexible flat cables (FFC). Existing Pressure heating rollers took more than 70minutes to the setting temperature and did not keep on the setting temperature in production. Temperature controller, electric power controller, material and diameter of rollers and heat capacities were changed to improve the temperature control of the pressure heat rollers for better production of the FFC. Thus, the reaching time to the setting temperature (RT), temperature stability time (TST) and temperature hunting (TH) were measured and compared with the existing pressure rollers case. The RT of A roller was shortened by 50minutes, and B roller was shortened by 15minutes. The TST of A roller was shortened by 13minutes, and B roller was shortened by 15minutes. The THs of both A and B rollers were settled up to ${\pm}5^{\circ}C$. Finally, the productivity of the FCLM and the quality of the FFC were increased.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.575-579
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• 2005

A beautiful, flexible active-matrix electrophoretic display (AM-EPD) device is reported. The flexible AM-EPD device has a $40.0{\times}30.0\;mm^2$ display area, measures about 0.27 mm in thickness, weighs about 0.45 g and possesses only 20 external connections. The flexible AM-EPD device displays clear black-and-white images with 5 gray-scales on $160{\times}120$ pixels. The display is free from residual image problems, because we use an area-gray-scale method on $320{\times}240$ EPD elements, each of which is driven with binary signals. Each pixel consists of 4 EPD elements. In addition, since the response time of the electrophoretic material is as long as approximately 400 ms and since the display possesses a large number of EPD elements, we have developed a special driving method suitable for changing EPD images comfortably. A complete image is formed on the AM-EPD device, consisting of a reset frame and several, typically 6, image frames.

• Journal of the Semiconductor & Display Technology
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• v.11 no.1
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• pp.29-33
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• 2012

In this study, we have investigated the structural and electrical characteristics of IZO thin films deposited under hydrogen atmosphere on flexible substrate for the OLED (organic light emitting diodes) devices. For this purpose, PES was used for flexible substrate and IZO thin films were deposited by RF magnetron sputtering under hydrogen ambient gases (Ar, $Ar+H^2$) at room temperature. In order to investigate the influences of the hydrogen, the flow rate of hydrogen in argon mixing gas has been changed from 0.1sccm to 0.5sccm. All the samples show amorphous structure regardless of flow rate. The electrical resistivity of IZO films increased with increasing flow rate of $H^2$ under $Ar+H^2$. All the films showed the average transmittance over 85% in the visible range. The OLED device was fabricated with different IZO electrodes made by configuration of IZO/$\acute{a}$-NPD/DPVB/$Alq_3$/LiF/Al to elucidate the performance of IZO substrate. OLED devices with the amorphous-IZO (a-IZO) anode film show good current density-voltage-luminance characteristics. This suggests that flat surface roughness and low electrical resistivity of a-IZO anode film lead to more efficient anode material in OLED devices.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.135-135
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• 2016

Recently flexible electrode materials have attracted attention in various electrical devices. In general, copper(Cu) is widely used electrical conductive material. However, Cu film showed drastically reduction of electrical conductivities under an applied tensile strain of 10%. These poor mechanical characteristics of Cu have difficulty applying in flexible electronic applications. In this study, mechanical flexibilities of Cu thin film were improved by hybridization with carbon nanotubes(CNTs) and laser sintering. First, thin carbon nanotube films were fabricated on a flexible polyethylene terephthalate(PET) substrate by using ultrasonic spray coating of CNT dispersed solution. After then, physically connected CNT-Cu NPs films were formed by utilizing ultrasonic spray coating of Cu nanoparticles dispersed solution on prepared CNT thin films. Finally, CNT-Cu thin films were firmly connected by laser sintering. Therefore, electrical stabilities under mechanical stress of CNT-Cu hybrid thin films were compared with Cu thin films fabricated under same conditions to confirm improvement of mechanical flexibilities by hybridization of CNT and Cu NPs.

• Structural Engineering and Mechanics
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• v.44 no.4
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• pp.521-538
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• 2012

In this study, the transverse vibrations of an axially moving flexible beams resting on multiple supports are investigated. The time-dependent velocity is assumed to vary harmonically about a constant mean velocity. Simple-simple, fixed-fixed, simple-simple-simple and fixed-simple-fixed boundary conditions are considered. The equation of motion becomes independent from geometry and material properties and boundary conditions, since equation is expressed in terms of dimensionless quantities. Then the equation is obtained by assuming small flexural rigidity. For this case, the fourth order spatial derivative multiplies a small parameter; the mathematical model converts to a boundary layer type of problem. Perturbation techniques (The Method of Multiple Scales and The Method of Matched Asymptotic Expansions) are applied to the equation of motion to obtain approximate analytical solutions. Outer expansion solution is obtained by using MMS (The Method of Multiple Scales) and it is observed that this solution does not satisfy the boundary conditions for moment and incline. In order to eliminate this problem, inner solutions are obtained by employing a second expansion near the both ends of the flexible beam. Then the outer and the inner expansion solutions are combined to obtain composite solution which approximately satisfying all the boundary conditions. Effects of axial speed and flexural rigidity on first and second natural frequency of system are investigated. And obtained results are compared with older studies.

• Structural Engineering and Mechanics
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• v.29 no.5
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• pp.489-504
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• 2008

In piezoelectric flexible structures, the contribution of vibration modes to the dynamic response of system may change with the location of piezoelectric actuator patches, which means that the ability of actuators to control vibration modes should be taken into account in the development of modal reduction model. The spatial $H_2$ norm of modes, which serves as a measure of the intensity of modes to system dynamical response, is used to pick up the modes included in the reduction model. Based on the reduction model, the paper develops the state-space representation for uncertain flexible tructures with piezoelectric material as non-collocated actuators/sensors in the modal space, taking into account uncertainties due to modal parameters variation and unmodeled residual modes. In order to suppress the vibration of the structure, a dynamic output feedback control law is designed by imultaneously considering the conflicting performance specifications, such as robust stability, transient response requirement, disturbance rejection, actuator saturation constraints. Based on linear matrix inequality, the vibration control design is converted into a linear convex optimization problem. The simulation results show how the influence of vibration modes on the dynamical response of structure varies with the location of piezoelectric actuators, why the uncertainties should be considered in the reductiom model to avoid exciting high-frequency modes in the non-collcated vibration control, and the possiblity that the conflicting performance specifications are dealt with simultaneously.