We introduce a simple method for fast switching of vertically-aligned nematic liquid crystals (LC... more We introduce a simple method for fast switching of vertically-aligned nematic liquid crystals (LCs). When an electric field is applied to a patterned vertical alignment (PVA) LC cell, virtual walls are formed in the middle of the gaps between and at the center of the patterned electrodes. These virtual walls formed in a PVA cell results in the turn-off time being dependent on the pitch of the patterned electrodes as well as the cell gap. Therefore, a short response time can be achieved by fine patterning of pixel electrodes without requiring additional fabrication steps or complicated drive schemes. A similar behavior has been observed in switching of vertically-aligned LCs with positive dielectric anisotropy by an in-plane electric field.
A new linear solvation energy relationships of empirical solvent scales with the Kamlet–Abboud–Ta... more A new linear solvation energy relationships of empirical solvent scales with the Kamlet–Abboud–Taft parameters sets for nematic liquid crystal.
We propose a chiral-nematic liquid crystal (CN-LC) device that reflects the infrared light, where... more We propose a chiral-nematic liquid crystal (CN-LC) device that reflects the infrared light, where the planar state is transparent over the entire visible wavelengths and the focal conic state scatters the light achromatically. The proposed CN-LC device can be operated at a low voltage because of the long pitch. A liquid crystal display (LCD) switchable between reflective and transmissive modes can be realized by stacking a CN-LC layer and a nematic LC layer.
A novel method for switching the viewing-angle of a liquid crystal display is proposed by using a... more A novel method for switching the viewing-angle of a liquid crystal display is proposed by using a polymernetworked liquid crystal cell in combination with a collimated backlight system. The bright state for a wide viewing-angle is obtained aligning liquid crystals randomly in polymer-networked structure, which diffuses a collimated backlight. The liquid crystals homogeneous-aligned by in-plane switching are operated as the bright state for a narrow viewing-angle since a collimated backlight passes through the liquid crystal layer intactly. It is demonstrated experimentally that the viewing-angle can be controlled omni-directionally without an additional panel or an additional backlight system.
In this paper we report the optimization of the electrode structure for a single gamma curve in a... more In this paper we report the optimization of the electrode structure for a single gamma curve in a single‐cellgap transflective IPS LCD. We optimized the distances between electrodes and the angles between LC directors and electrodes to achieve a single gamma curve.
We propose a method for fast grey-to-grey (GTG) switching of a homogeneously aligned liquid cryst... more We propose a method for fast grey-to-grey (GTG) switching of a homogeneously aligned liquid crystal (LC) cell. Homogeneously aligned LCs are instantly vertically aligned by applying a vertical electric field for a short time before switching to a target grey level. Once the LCs are vertically aligned, we apply an in-plane voltage higher than the data voltage that corresponds to a target grey level, while maintaining the vertical electric field. Then, at the time the vertical field is removed, we apply a data voltage required for switching to the target grey level. We experimentally demonstrated GTG switching of a homogeneously aligned LC cell, which is 11 times faster than a fringe-field switching cell.
We propose a method for fast switching of nematic liquid crystals with neither alignment material... more We propose a method for fast switching of nematic liquid crystals with neither alignment materials nor alignment process. A three-terminal electrode structure is used to apply in-plane and vertical electric fields to randomly-aligned liquid crystals. A vertical field is applied to align liquid crystals vertically for the dark state, whereas an in-plane field is applied to align liquid crystals homogeneously for the bright state. We obtained the turn-on time of 1.2 ms and turn-off time of 0.5 ms in the three-terminal electrode structure with neither alignment materials nor alignment process. However, three-terminal electrode structure with neither alignment material nor alignment process shows low transmittance. For higher transmittance, we mixed reactive mesogen and nano-particles with anisotropic molecular shape to liquid crystals. As a result, we obtained a transmittance similar to the conventional fringe field switching mode and achieved the total response time of less than 3 ms.
The flexoelectric effect of a rod-like nematic liquid crystal (pentyl-cyanobiphenyl, 5CB) doped w... more The flexoelectric effect of a rod-like nematic liquid crystal (pentyl-cyanobiphenyl, 5CB) doped with bent-core liquid crystals with a high kink angle ∼130° was studied. Although the previous theoretical models predicted that such highly-kinked molecules with a longitudinal dipole moment would have no significant influence on the flexoelectric effect, the 5CB mixture doped with 7.0 wt% bent-core liquid crystal with a longitudinal dipole moment showed greater flexoelectric anisotropy 37.2 pC m−1 compared to the pure 5CB 10.3 pC m−1. From the small angle X-ray scattering experiments, the bent-core liquid crystal was found to form local domains surrounded with 5CB molecules and the varied orientation and shape of the assembled complexes were considered to be related to the greater flexoelectric anisotropy.
The authors demonstrate through dark injection space-charge-limited current (DI-SCLC) and trap-fr... more The authors demonstrate through dark injection space-charge-limited current (DI-SCLC) and trap-free SCLC measurements that an indium tin oxide (ITO)/buckminsterfullerene (C60) electrode can form a quasi-Ohmic contact with N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine (NPB). The DI-SCLC results show a clear peak current along with a shift of the peak position as the field intensity varies, implying an Ohmic (or quasi-Ohmic) contact. A theoretical simulation of the SCLC also shows that ITO/C60 forms an Ohmic contact with NPB when the electric field intensity is higher than 30 kV/cm. The Ohmic contact makes it possible to estimate the NPB hole mobility through the use of both DI-SCLC and trap-free SCLC analysis.
A novel method to measure the cell gap of a single-polarizer reflective twisted nematic liquid cr... more A novel method to measure the cell gap of a single-polarizer reflective twisted nematic liquid crystal (TN LC) cell by using a spectrometer is proposed. By rotating a LC cell, we can measure the cell gap of a LC cell as well as the wavelength dependence of retardation Δn d.
In this paper, we report the effects of an argon (Ar) ion beam surface treatment of a SiO2 dielec... more In this paper, we report the effects of an argon (Ar) ion beam surface treatment of a SiO2 dielectric layer in organic thin-film transistors. We compared the electrical properties of pentacene deposited on a SiO2 layer after O2 plasma or Ar ion beam treatment and characterized the states of the surface of the dielectric by atomic force microscopy and X-ray
We studied the bistable switching behavior of a 90°-twisted liquid crystal cell that has two stab... more We studied the bistable switching behavior of a 90°-twisted liquid crystal cell that has two stable states: clockwise and counterclockwise twists. Switching between the two states can be made by applying a vertical or an in-plane electric field. We found the optimum rubbing angle for low voltage operation of a bistable twisted-nematic cell.
A pixel isolation wall of liquid crystal display is fabricated by utilizing the excellent phase s... more A pixel isolation wall of liquid crystal display is fabricated by utilizing the excellent phase separation between liquid crystal molecules and fluorinated UV-curable polymers. Due to the strong immiscibility of the fluorinated monomers, the segregation of the material occurs effectively to form a polymer wall during the UV exposure. Twisted nematic liquid crystal cells with fluorinated polymer wall are fabricated for the comparison with other devices made of ordinary polymer wall. The fluorinated polymer wall device exhibits enhancement of contrast due to the suppression of the light leakage through the polymer wall as well as reduced saturation voltage by anchoring enhancement.
The optimized configurations to use a bistable chiral-splay nematic liquid crystal cell as transm... more The optimized configurations to use a bistable chiral-splay nematic liquid crystal cell as transmissive and reflective display are calculated using the Mueller matrix method. By numerical calculation, nontwist 0° splay state of bistable states is optimized so that the dark state is completely achieved over the entire visible-wavelength range. Based on the optimized conditions, we have experimentally demonstrated a high-contrast ratio of 200:1 in transmissive display and 40:1 in reflective display without using a wideband retardation film.
We introduce a simple method for fast switching of vertically-aligned nematic liquid crystals (LC... more We introduce a simple method for fast switching of vertically-aligned nematic liquid crystals (LCs). When an electric field is applied to a patterned vertical alignment (PVA) LC cell, virtual walls are formed in the middle of the gaps between and at the center of the patterned electrodes. These virtual walls formed in a PVA cell results in the turn-off time being dependent on the pitch of the patterned electrodes as well as the cell gap. Therefore, a short response time can be achieved by fine patterning of pixel electrodes without requiring additional fabrication steps or complicated drive schemes. A similar behavior has been observed in switching of vertically-aligned LCs with positive dielectric anisotropy by an in-plane electric field.
A new linear solvation energy relationships of empirical solvent scales with the Kamlet–Abboud–Ta... more A new linear solvation energy relationships of empirical solvent scales with the Kamlet–Abboud–Taft parameters sets for nematic liquid crystal.
We propose a chiral-nematic liquid crystal (CN-LC) device that reflects the infrared light, where... more We propose a chiral-nematic liquid crystal (CN-LC) device that reflects the infrared light, where the planar state is transparent over the entire visible wavelengths and the focal conic state scatters the light achromatically. The proposed CN-LC device can be operated at a low voltage because of the long pitch. A liquid crystal display (LCD) switchable between reflective and transmissive modes can be realized by stacking a CN-LC layer and a nematic LC layer.
A novel method for switching the viewing-angle of a liquid crystal display is proposed by using a... more A novel method for switching the viewing-angle of a liquid crystal display is proposed by using a polymernetworked liquid crystal cell in combination with a collimated backlight system. The bright state for a wide viewing-angle is obtained aligning liquid crystals randomly in polymer-networked structure, which diffuses a collimated backlight. The liquid crystals homogeneous-aligned by in-plane switching are operated as the bright state for a narrow viewing-angle since a collimated backlight passes through the liquid crystal layer intactly. It is demonstrated experimentally that the viewing-angle can be controlled omni-directionally without an additional panel or an additional backlight system.
In this paper we report the optimization of the electrode structure for a single gamma curve in a... more In this paper we report the optimization of the electrode structure for a single gamma curve in a single‐cellgap transflective IPS LCD. We optimized the distances between electrodes and the angles between LC directors and electrodes to achieve a single gamma curve.
We propose a method for fast grey-to-grey (GTG) switching of a homogeneously aligned liquid cryst... more We propose a method for fast grey-to-grey (GTG) switching of a homogeneously aligned liquid crystal (LC) cell. Homogeneously aligned LCs are instantly vertically aligned by applying a vertical electric field for a short time before switching to a target grey level. Once the LCs are vertically aligned, we apply an in-plane voltage higher than the data voltage that corresponds to a target grey level, while maintaining the vertical electric field. Then, at the time the vertical field is removed, we apply a data voltage required for switching to the target grey level. We experimentally demonstrated GTG switching of a homogeneously aligned LC cell, which is 11 times faster than a fringe-field switching cell.
We propose a method for fast switching of nematic liquid crystals with neither alignment material... more We propose a method for fast switching of nematic liquid crystals with neither alignment materials nor alignment process. A three-terminal electrode structure is used to apply in-plane and vertical electric fields to randomly-aligned liquid crystals. A vertical field is applied to align liquid crystals vertically for the dark state, whereas an in-plane field is applied to align liquid crystals homogeneously for the bright state. We obtained the turn-on time of 1.2 ms and turn-off time of 0.5 ms in the three-terminal electrode structure with neither alignment materials nor alignment process. However, three-terminal electrode structure with neither alignment material nor alignment process shows low transmittance. For higher transmittance, we mixed reactive mesogen and nano-particles with anisotropic molecular shape to liquid crystals. As a result, we obtained a transmittance similar to the conventional fringe field switching mode and achieved the total response time of less than 3 ms.
The flexoelectric effect of a rod-like nematic liquid crystal (pentyl-cyanobiphenyl, 5CB) doped w... more The flexoelectric effect of a rod-like nematic liquid crystal (pentyl-cyanobiphenyl, 5CB) doped with bent-core liquid crystals with a high kink angle ∼130° was studied. Although the previous theoretical models predicted that such highly-kinked molecules with a longitudinal dipole moment would have no significant influence on the flexoelectric effect, the 5CB mixture doped with 7.0 wt% bent-core liquid crystal with a longitudinal dipole moment showed greater flexoelectric anisotropy 37.2 pC m−1 compared to the pure 5CB 10.3 pC m−1. From the small angle X-ray scattering experiments, the bent-core liquid crystal was found to form local domains surrounded with 5CB molecules and the varied orientation and shape of the assembled complexes were considered to be related to the greater flexoelectric anisotropy.
The authors demonstrate through dark injection space-charge-limited current (DI-SCLC) and trap-fr... more The authors demonstrate through dark injection space-charge-limited current (DI-SCLC) and trap-free SCLC measurements that an indium tin oxide (ITO)/buckminsterfullerene (C60) electrode can form a quasi-Ohmic contact with N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine (NPB). The DI-SCLC results show a clear peak current along with a shift of the peak position as the field intensity varies, implying an Ohmic (or quasi-Ohmic) contact. A theoretical simulation of the SCLC also shows that ITO/C60 forms an Ohmic contact with NPB when the electric field intensity is higher than 30 kV/cm. The Ohmic contact makes it possible to estimate the NPB hole mobility through the use of both DI-SCLC and trap-free SCLC analysis.
A novel method to measure the cell gap of a single-polarizer reflective twisted nematic liquid cr... more A novel method to measure the cell gap of a single-polarizer reflective twisted nematic liquid crystal (TN LC) cell by using a spectrometer is proposed. By rotating a LC cell, we can measure the cell gap of a LC cell as well as the wavelength dependence of retardation Δn d.
In this paper, we report the effects of an argon (Ar) ion beam surface treatment of a SiO2 dielec... more In this paper, we report the effects of an argon (Ar) ion beam surface treatment of a SiO2 dielectric layer in organic thin-film transistors. We compared the electrical properties of pentacene deposited on a SiO2 layer after O2 plasma or Ar ion beam treatment and characterized the states of the surface of the dielectric by atomic force microscopy and X-ray
We studied the bistable switching behavior of a 90°-twisted liquid crystal cell that has two stab... more We studied the bistable switching behavior of a 90°-twisted liquid crystal cell that has two stable states: clockwise and counterclockwise twists. Switching between the two states can be made by applying a vertical or an in-plane electric field. We found the optimum rubbing angle for low voltage operation of a bistable twisted-nematic cell.
A pixel isolation wall of liquid crystal display is fabricated by utilizing the excellent phase s... more A pixel isolation wall of liquid crystal display is fabricated by utilizing the excellent phase separation between liquid crystal molecules and fluorinated UV-curable polymers. Due to the strong immiscibility of the fluorinated monomers, the segregation of the material occurs effectively to form a polymer wall during the UV exposure. Twisted nematic liquid crystal cells with fluorinated polymer wall are fabricated for the comparison with other devices made of ordinary polymer wall. The fluorinated polymer wall device exhibits enhancement of contrast due to the suppression of the light leakage through the polymer wall as well as reduced saturation voltage by anchoring enhancement.
The optimized configurations to use a bistable chiral-splay nematic liquid crystal cell as transm... more The optimized configurations to use a bistable chiral-splay nematic liquid crystal cell as transmissive and reflective display are calculated using the Mueller matrix method. By numerical calculation, nontwist 0° splay state of bistable states is optimized so that the dark state is completely achieved over the entire visible-wavelength range. Based on the optimized conditions, we have experimentally demonstrated a high-contrast ratio of 200:1 in transmissive display and 40:1 in reflective display without using a wideband retardation film.
Uploads
Papers by Tae-Hoon Yoon