Han-Jin Ahn

Liquid Crystal Lens for Compensation of Spherical Aberration in Multilayer Optical Data Storage

In multilayer recording, it is strongly required to compensate the spherical aberration caused by a difference in substrate thickness. A novel liquid crystal (LC) lens is designed and fabricated to compensate the spherical aberration in this study. The new structure of the LC lens includes both concave and convex surfaces, which can compensate the spherical aberration with a relatively long range. Since a previously developed LC panel showed a very low tolerance to the shift of an objective lens, a new component has been proposed with a special LC lens structure to improve both the tolerance and compensation range. By optimized curvature control with a spherical LC lens, the aberration of a Blu-ray optical pickup can be maintained at 0.018λrms even for a thickness variation of ±25 µm. Finally, the LC lens has been fabricated using a standard one drop filling (ODF) process and evaluated by measuring the variation in focal length as a function of applied voltage.

Liquid Crystal Alignment Effects and Electro Optical Performances of Twisted Nematic-Liquid Crystal Display Using Ion-Beam Alignment Method on Nitrogen-doped Diamond Like Carbon Thin Film Layer

Nitrogen-doped diamond-like carbon (NDLC) thin films exhibit a high electrical resistivity that is similar to the properties shown by diamond-like carbon (DLC) thin films. The diamond-like transport property in NDLC thin films comes from a material consisting of sp2-bonded carbon versus the sp3-bonded carbon of DLC. In addition, NDLC thin films have a better thermal stability than the DLC thin films, because C:N bonding in the NDLC thin films is stronger against thermal stress than C:H bonding in the DLC thin films. The liquid crystal (LC) alignment effects of ion beam irradiation on the NDLC thin films and the electro optical (EO) performances of the ion-beam-aligned twisted nematic (TN)-liquid crystal display (LCD) with oblique ion beam exposure on an NDLC thin film surface were studied. A good uniform nematic liquid crystal (NLC) alignment with ion beam exposure on the NDLC thin films was observed. In addition, good EO properties, a residual DC property and particularly the good thermal stability of the ion-beam-aligned TN-LCD on NDLC thin films was achieved.

Liquid Crystal Alignment Effects using a Sio Thin Film

ABSTRACT We studied the nematic liquid crystal (NLC) aligning capabilities using the new alignment material of a SiO thin film. The homogenous alignment was obtained by using ion beam (IB) exposure on the SiO thin film, when positive type NLC (Δϵ > 0) was injected into the LC cell. However, the homeotropic alignment was obtained using ion beam exposure on the SiO thin film, when negative type NLC (Δϵ > 0) was injected into the LC cell. The LC aligning capability on the SiO thin film depends on the dielectric anisotropy type of LC.

The Alignment Effect of Nematic Liquid Crystal on NDLC Thin Films Surface

ABSTRACT We studied the nematic liquid crystal (NLC) aligning capabilities using the new alignment material of Nitrogen doped diamond-like carbon (NDLC) thin film. The NDLC thin film exhibits high electrical resistivity and thermal conductivity that are similar to the properties shown by diamond-like carbon (DLC) thin films. The diamond-like properties and nondiamond-like bonding make NDLC an attractive candidate for applications. A high pretilt angle of about 9.9° by ion beam (IB) exposure on the NDLC thin film surface was measured. A good LC alignment is achieved by the IB alignment method on the NDLC thin film surface at annealing temperature of 200°C. The alignment defect of the NLC was observed above annealing temperature of 250°C. Consequently, the high pretilt angle and the good LC alignment by the IB alignment method on the NDLC thin film surface can be achieved.

Investigation of the Alignment Phenomena on the a-C:H Thin Films by PECVD System using Ion-beam Alignment Method

We studied the nematic liquid crystal (NLC) aligning capabilities using the new alignment material of a-C:H thin film by plasma enhanced chemical vapor deposition (PECVD) system for 30 sec under 30W rf power at a gas pressure of 1.4＊10-1/ torr. A high pretilt angle of about 5 by ion beam exposure on the a-C:H thin film surface was measured. A good LC alignment by the ion beam alignment method on the a-C:H thin film surface was observed at annealing temperature of 250, and the alignment defect of NLC was observed above annealing temperature of 300. Consequently, the high LC pretilt angle and the good thermal stability of LC alignment by the ion beam alignment method on the a-C:H thin film by PECVD method as working gas at 30W rf bias condition can be achieved.

A Study on Electro-Optical Characteristics of the Ion Beam Aligned Fringe-Field Switching (FFS) Cell on the Inorganic Thin Film

ABSTRACT In this study, we investigated the electro-optical (EO) characteristic of fringe-field switching (FFS) mode cell by the ion beam alignment method on the a-C:H thin film. The suitable inorganic thin films for FFS cell and the aligning capabilities of nematic liquid crystal (NLC) using the new alignment material of a-C:H thin film were studied. An excellent voltage-transmittance (V-T) and response time curve of the ion beam aligned FFS cell was observed with oblique ion beam exposure on the a-C:H thin films. Also, the V-T hysteresis characteristics of the ion beam-aligned FFS cell with IB exposure on the a-C:H thin films is almost the same as that of the rubbing-aligned FFS cell on a polyimide (PI) surface.

Electro-optical characteristics of ion-beam-aligned FFS-LCDs on diamond-like-carbon thin film

— A fringe-field-switching (FFS) mode cell having LC alignment has been developed by using a non-rubbing method, a ion-beam-alignment method on a-C:H thin film, to analyze the electro-optical characteristics of this cell. The suitable inorganic thin film for FFS-LCDs and the alignment capabilities of nematic liquid crystal (NLC) have been studied. An excellent voltage-transmittance (V-T) and response-time curve for the ion-beam-aligned FFS-LCDs were observed using oblique ion-beam exposure on DLC thin films.

Liquid Crystal Alignment on the SiC Thin Film by the Ion Beam Exposure Method

We studied the nematic liquid crystal (NLC) aligning capabilities using the new alignment material of the SiC (Silicon Carbide) thin film. The SiC thin film exhibits good chemical and thermal stability. The good thermal and chemical stability makes SiC an attractive candidate for electronic applications. A vertical alignment of nematic liquid crystal by ion beam exposure on the SiC thin film surface was achieved. The about of stable pretilt angle was achieved at the range from to of incident angle. The good LC alignment is maintained by the ion beam alignment method on the SiC thin film surface at high annealing temperatures up to .

A Study on Electro-optical Characteristics of the Ion Beam Aligned FFS Cell on a Inorganic Thin Film

In this paper, we intend to make fringe-field switching (FFS) mode cell by the ion beam (IB) alignment method on the a-C：H thin film, to analyze electro-optical characteristics in this cell. We studied on the suitable inorganic thin film for fringe-field switching (FFS) cell and the aligning capabilities of nematic liquid crystal (NLC) using the alignment material of a-C：H thin film as working gas at 30 W rf bias condition. A high pretilt angle of about 5 by ion beam (IB) exposure on the a-C：H thin film surface was measured. Consequently, the high pretilt angle and the good thermal stability of LC alignment by the IB alignment method on the a-C：H thin film surface as working gas at 30 W rf bias condition can be achieved. An excellent voltage-transmittance (V -T) and response time curve of the IE-aligned FFS-LCD was observed with oblique IB exposure on the a-C：H thin films. Also, AC V-T hysteresis characteristics of the IB-aligned FFS-LCD with IE exposure on the a-C：H thin films is almost the same as that of the rubbing-aligned FFS cell on a polyimide (PI) surface.