Kyong Chan Heo

Flexible Reflective Color Displays using Thermochromic Pigments

This research presents a flexible reflective thermochromic display (TCD) comprised of thermochromic pigments and a patterned indium tin oxide (ITO) film coated on a polyethylene naphthalate (PEN) substrate, and the displays thermo-optical characteristics. The display showed maximum red, green, and blue reflectances of 30%, 38%, and 29%, respectively. Furthermore, the display exhibited a continuous grey color when the temperature was changed continuously. As a flexible display, the display showed reliable thermo-optical performance without image damage even when highly bent. We expect the proposed TCD will be used in outdoor information display applications where low cost is a key factor.

Reflective Thermochromic Display on Polyethylene Naphthalate Film

A reflective flexible display was fabricated by placing a thermochromic pigment on a polyethylene naphthalate (PEN) substrate coated with an indium tin oxide (ITO) film, and its thermo-optical characteristics were investigated. The reflective thermochromic display showed good image quality with a reflectance of approximately 65%. As a flexible display, the display showed reliability without damage to the image even after the display was bent strongly. The reflective display cell exhibits continuously the gray level according to the temperature controlled by applied voltage. This low cost display is expected be used in outdoor poster applications where information needs to be presented clearly.

Shape-modification of patterned nanoparticles by an ion beam treatment

This paper evaluated a practical approach to the fabrication of arrays of non-spherical nanoparticles by colloidal etching without a mask involving exposure to a low energy ion beam. A spherical nanoparticle array was transferred using a soft nanolithography technique, which is a simple and effective pattern transfer method for nanostructures on the surface of thin adhesive polymers on a planar substrate, after placing the spherical nanoparticles on a patterned PDMS [poly(dimethysiloxane)] stamp produced from a patterned Si wafer. The resulting non-spherical nanoparticle array was driven from a spherical nanoparticle array shape-modified by ion beam irradiation. A well-arrayed layer of cone-like-shapes were produced using a head-on ion beam for different exposure times. Also, a variety of mushroom-like-shapes depending on the exposure angle were produced on a substrate with a well-arranged spherical nanoparticle array. This technique has potential applications in nanophotonics, field emission displays (FEDs) and microfluid.

Reflective color display using thermochromic pigments

A reflective thermochromic display fabricated by a very simple method using three kinds of thermochromic pigments is produced and its thermo-optical characteristics are investigated. The display exhibits maximum red, green, and blue reflectances of 38%, 30%, and 35%, respectively. The reflective display cell shows continuous gray color with changing temperature, which is crucial for multicolor displays. It also shows an excellent viewing angle above 80° without any of the additional optical components that are required in liquid crystal displays. We expect that this display technology will be used for outdoor billboard information display applications.

Liquid Crystal Lens Array with Thermally Controllable Focal Length and Electrically Convertible Lens Type

This paper reports the fabrication of a lenticular liquid crystal (LC) lens array with thermally tunable focus and with the function of a convertible lens type, using the surface structure of a UV-curable polymer and a twisted-nematic (TN) LC cell. The TN LC cell makes the LC lenticular lens function as a converging or diverging lens by controlling electrically the polarization of input light. Therefore, the focal lengths for both the converging and diverging lenses, which can be switched from the TN cell, can be tuned by changing the effective refractive index of the LC by Joule heating of the transparent electrode. As a result, the focal length of the lens with the E7 LC was changed continuously from 8.7 to 31.2 mm for the converging lens type and from -9.8 to -14.2 mm for the diverging lens when the temperature was increased from 25 to

High contrast reflective liquid crystal display using a thermochromic reflector

56^{\circ}C

Characteristics of Ion Beam Assisted ITO Thin Films Deposited by RF Magnetron Sputtering

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Electro-Optical Characteristic of Two Domain Normally Black Electrically Controlled Birefringence Mode with Patterned Electrode Structure

This paper presents a reflective liquid crystal display (LCD) with a high contrast ratio (CR) combined with mono-type thermochromic materials to solve the low CR of reflective type LCDs. Here, reflective, wide-band, electrically controlled birefringence mode was used as the optical liquid crystal (LC) mode, and a thermochromic material was used as the reflector for the white state and an absorber for the dark state. The combination of LCD and thermochromic material can have a synergistic effect in achieving a better display. By controlling the reflectance of the thermochromic reflector using Joule heating, the proposed reflective LC cell exhibited a high CR of approximately 70:1. The figure was extremely high compared to the approximately 10:1 of a typical reflective LC cell with an optically wide band design. The proposed LC cell configuration is expected to find many outdoor applications which can admit slow response speed.

A Reflective Display Based on Thermochromic Pigment

Indium tin oxide (ITO) thin films have been deposited onto glass substrates at low temperature (100 °C) by the ion beam assisted RF magnetron sputter technique at different ion beam energy. The structural, surface morphology and electrical characteristics of the ITO thin films were investigated as a function of ion beam assisted energy. With increasing ion beam assisted energy from 0 eV to 100 eV, electrical resistivity of the ITO films reduced from 1.13 × 10−3 Ω·cm to 5.5 × 10−4 Ω·cm. Hall mobility and carrier concentration slightly increased, which attribute to slightly the crystal growth and harden ITO film. The preferential crystalline orientation of the sputtered films is observed gradually a change from the (222) to the (400) crystalline orientation with increasing ion beam assisted energy.

Effects of an additional magnetic field in ITO thin film deposition by magnetron sputtering

We present a normally black patterned electrically controlled birefringence [NB-PECB] mode with patterned electrode structure to improve the low contrast ratio of the general electrically controlled birefringence [ECB] mode and the gray inversion of twist nematic mode [TN]. The electrode structure used in the patterned vertical alignment [PVA] electro-optic mode is adopted in our proposed NB-PECB mode to produce two domains that are required for improving viewing angle uniformity. A λ/2 plate is also used to generate normally black state. Simulated results show the proposed mode can improve the gray inversion and the contrast ratio, compared with the two domain TN mode and the two domain ECB mode.