Plasma‐beam alignment of passive liquid crystals (Invited Paper)

Abstract— A plasma‐beam process, developed for the alignment of liquid crystals (LC) in electro‐optic applications, has been successfully applied to align “non‐standard” LC, such as crystalline materials with LC phases at elevated temperatures and reactive mesogenes. In addition to the high alignment quality of the materials, there is no need for an intermediate layer between the substrate and the LC layer. Furthermore, the construction of our source simplifies the alignment procedure of large‐area rigid substrates and the roll‐to‐roll processing of flexible films. This method opens new horizons for optical retarders and polarizers, as well as anisotropic semiconducting films for organic electronics.     

Ferroelectric liquid crystal aligned on SiO2 thin films using ion‐beam deposition

Abstract— Results for a ferroelectric‐liquid‐crystal (FLC) display cell, aligned on inorganic SiO₂ thin‐film surfaces by using oblique ion‐beam sputtering deposition on the substrates, is presented. A large deposition angle from 60° to 80° can be employed for the thin alignment layer, with thicknesses varying from 5 to 40 nm. Two types of uniform alignment, chevron (before electrical treatment) and quazi‐bookshelf (after electrical treatment), were studied. High‐quality alignment on large‐sized substrates was also easily be achieved because of the linear design of the ion‐beam sputtering source, which was previously a significant challenge for FLC on SiO_x layers.     

Medical displays by using plasma‐beam‐alignment technology

Abstract— Novel anode layer plasma within minimum chamber space was developed for non‐contact alignment process. The plasma‐treated polyimide (PI) surface showed no particle contamination and no micro‐scratches. Surface morphology was investigated by using scanning electron microscope (SEM), an atomic force microscope (AFM), and X‐ray photoemission spectroscopy. The different oxygen‐to‐carbon ratio ([O]/[C] ratio) for XPS spectra indicated a composition change after plasma treatment. Surface pretilt angles were varied from 0 to 2.1° under different plasma exposure times. Finally, a prototype 20.8‐in. QXGA IPS‐mode gray‐scale medical liquid‐crystal display was successfully demonstrated with high contrast ratio, excellent uniformity, and wide viewing angle using this new plasma‐beam‐alignment technique.     

Surface modified solution‐derived nickel oxide film via ion‐beam irradiation as a liquid crystal alignment layer

In this article, we demonstrate the liquid crystal (LC) alignment characteristics of solution‐derived nickel oxide (NiO) film modified with ion‐beam (IB) irradiation. Cross‐polarized optical microscopy and pretilt angle measurements verified that uniform LC alignment was achieved using the NiO film as an alignment layer regardless of IB incidence angle. Contact angle measurements revealed that all of the NiO films had a deionized water contact angle below 90°, which indicates that they had hydrophilic surfaces that had an effect on the homogeneous LC alignment. Atomic force microscopy was conducted to determine the physical surface modification due to the IB irradiation, which showed that it reduced the size of the surface grains with agglomerations depending on the surface tilt from the IB incidence angle. Furthermore, microgroove structures strongly related to uniform LC alignment were observed after IB irradiation. Chemical surface modification was investigated via an X‐ray photoelectron spectroscopy analysis which revealed that IB irradiation modified the chemical bonds in the NiO film, and this affected the LC alignment state. Thus, these results indicate that using NiO film exposed to IB irradiation as an alignment layer is a suitable method for LC applications.     

Defect‐free half‐V‐mode ferroelectric liquid‐crystal device

Abstract— The horizontal chevron defect found in a half‐V‐mode ferroelectric‐liquid‐crystal (HV‐FLC) device can be suppressed by lowering the FLC's total free energy. The energy levels between spontaneous polarization (PS) up and down domains were degenerated by asymmetrical‐alignment treatments. The difference in the polar surface coefficient (γ²) was the key to suppressing the alignment defect. Alignment layers with opposite surface polarities and different anchoring energies were applied to control the sign and value of γ². The asymmetric cells of PIrub ‐ PIplasma (rubbed polyimide and plasma‐treated polyimide surfaces), PVArub ‐ PIplasma (rubbed polyvinyl alcohol and plasma‐treated polyimide surfaces), and PVArub ‐ PIplasma (both rubbed PI and PVA) alignment conditions presented defect‐free alignment textures under a slow‐cooling process. Among these different alignment treatments, the PVArub ‐ PIrub treated cell demonstrated the best alignment result, benefited by the largest difference in polar surface coefficient.     

Tuning the alignment of liquid crystals by means of nano‐structured surfaces (Invited Paper)

Abstract— The solid‐surface/liquid‐crystal interactions, defining the field‐free alignment of the liquid crystal in conventional liquid‐crystal displays, are playing a vital role in their optical appearance and performance. Nano‐scale changes in the solid‐surface structure induced by light have been recently shown to affect the anchoring strength and the easy‐axis direction. Fine tuning of the anchoring strength is also demonstrated by nano‐structuring of the Langmuir‐Blodgett monolayer employed as liquid‐crystal alignment layers promoting homeotropic orientation. On the basis of nano‐engineering of the surface alignment properties, two novel alignment concepts have been introduced: electrically commanded surfaces (ECS) and high‐performance alignment layers (HiPAL). Nano‐structured polymers related to these concepts have been designed, synthesized, and used as materials for alignment layers in LCDs. ECS materials belong to the category of active alignment materials designed to mediate switching of the liquid crystal, whereas the HiPAL materials make possible the control of the molecular tilt angle in a broad range, from 0° to 90°, and they seem to enable the control of the anchoring strength as well. The nano‐structured alignment materials are strong candidates for implementation in a new generation of advanced liquid‐crystal displays and devices.     

Novel alignment technique for liquid crystal using hydrophilic/hydrophobic pattern layer

Abstract— We have developed a novel method of aligning liquid‐crystal (LC) molecules that employs a layer patterned with hydrophilic and hydrophobic regions fabricated by the photocatalysis of TiO₂. This method provides a resolution on the order of 10μm for the alignment of LC molecules without the need for protrusions or patterned electrodes. Using this method, we achieved the continuous multidomain vertical alignment of LC molecules.     

Photo‐aligned photonic ferroelectric liquid crystal fibers

Preliminary studies of photonic crystal fibers (PCFs) partially infiltrated with photo‐aligned ferroelectric liquid crystals (FLCs) under the influence of external electric field are reported. The proper alignment of the FLC molecules is achieved by generating a photo‐aligning layer on the inner side of the PCF microcavities. The sulfonic azo dye, which is used as an alignment layer, offers a variable anchoring energy depending on the irradiation energy, and thus, a good control on the FLC alignment inside microchannels is possible. Moreover, a state of polarization of the light being guided inside the PCF infiltrated selectively with FLC changes under the influence of external electric field.     

Multistable electro‐optical modes in ferroelectric liquid crystals

Abstract— Multistable electro‐optical modes exist under certain conditions in ferroelectric liquid‐crystal (FLC) cells, which means that any light‐transmission level can be memorized after the driving voltage is switched off. The multistability is responsible for three new electro‐optical modes with different shapes of the gray‐scale curve that can be either S‐shaped (double or single dependent upon the applied‐voltage pulse sequence and boundary conditions) or V‐shaped dependent upon boundary conditions and FLC cell parameters. The origin of these modes will be described.     

Field‐induced photo‐reactive alignment technology for the vertical‐alignment liquid‐crystal mode

Abstract— An advanced vertical‐alignment liquid‐crystal (VA‐LC) technology based on field‐induced photo‐reactive alignment (FPA) as an advanced alignment mode for VA is proposed. FPA realizes uniform alignment and a faster rising response time, especially at high voltage. This technology can generate a pre‐tilt angle only by using photo‐reactive alignment material so that the tact time is shorter and the long‐term reliability is higher than that of conventional photo‐reactive processes, which require additional photo‐reactive monomers. The advanced hybrid FPA was developed by adopting both the tilted alignment with a pre‐tilt angle and conventional vertical alignment. By using an advanced hybrid structure, the response time and contrast ratio can be further improved.     

Second wind of the oblique deposition method of liquid‐crystal alignment: Ion‐beam sputtering technique

Abstract— Liquid‐crystal (LC) alignment on SiO_x films produced by ion‐beam sputtering deposition was comprehensively studied. The conditions for planar, tilted planar, homeotropic, and tilted homeotropic LC alignment of high uniformity were determined. The alignment photostability and aging issue are discussed. An original sputtering system based on the anode‐layer source excelling in high reliability and quality of sputtered coatings were used. Because this system can be easily scaled up, the alignment treatment of the large‐area alignment substrates, including those used in modern LCD manufacturing, can be realized. The advantages of the sputtering LC alignment technique, in comparison with its vapor‐deposition predecessor, are described.     

Advanced monochrome gray‐scale TFT‐LCD using diamond‐like‐carbon/ion‐beam alignment technology

Abstract— A novel liquid‐crystal alignment method, diamond‐like carbon and ion beam alignment (DLC/IB) technology, was announced at the 2001 SID Symposium. And since December 2001, a new‐generation ion‐beam machine has been placed into the manufacturing line of IDTech. DLC/IB technology is mainly used for medical displays, which require a monochrome high‐density and super‐uniform display. We report on the latest developments of these advanced monochrome displays.     

Plasma beam alignment for the large‐area substrates: Equipment and process

Abstract— We have developed an effective method for liquid‐crystal alignment of the large‐area substrates. This method is based on the oblique treatment of the alignment substrates with a “sheet” of accelerated plasma generated by the anode layer source of the “race track” geometry. During this treatment, the substrate or source is cyclically translated in the direction perpendicular to the plasma “sheet.” This method provides planar, tilted, and vertical liquid‐crystal alignment with excellent uniformity and reproducibility and easy axis control in the azimuthal and polar planes.     

Homeotropic alignment of liquid crystals on ITO surface using LBL assembly

In this work, the very thin layer‐by‐layer (LBL) film that was constructed by dip coating method on indium tin oxide surface can be used in liquid crystal (LC) displays devices. The obtained results indicate that the ultrathin LBL film shows the homeotropic alignment layer, and a uniform vertical alignment of LC molecules was gained very easily. The progress of vertical‐aligned LC cells with a LBL layer was evaluated. The obtained threshold voltage and response time of the LC cell were 2.472 V and 12.5 ms, respectively. So, the competitive performance of the LC cell could allow new sign at a low‐cost budget with rubbing process in LC display technology.     

Photostability of liquid crystals and alignment layers

Abstract— Photostability of liquid‐crystal (LC) materials and surface alignment layers was evaluated using a UV lamp and a blue laser beam. Both organic polyimide (PI) and inorganic silicon‐dioxide (SiO₂) alignment layers were studied under nitrogen environment. Two commercial TFT‐grade LC mixtures (low‐birefringence MLC‐9200‐000 and high‐birefringence TL‐216) were used for comparisons. Results indicate that SiO₂ alignment layers are much more robust than PI layers, and low birefringence LCs are more stable than the high‐birefringence ones. At the He‐Cd laser wavelength (λ = 442 nm), both LC mixtures and SiO₂ alignment layers are hardly damaged. To lengthen the lifetime of an LCD projector, inorganic SiO₂ alignment layers, high‐optical‐density UV filter, long cutoff‐wavelength blue filter, and short‐conjugation (low birefringence) LC materials should be considered.     

Optimization of photo‐aligned ferroelectric liquid‐crystal display under passively addressed driving

Abstract— A ferroelectric liquid‐crystal (FLC) passively addressed 64 × 64 display based on the photo‐alignment technique has been developed. The display matrix has dimensions of 33 × 33 mm², and the FLC layer thickness is about 5 μm. Asymmetric boundary conditions, when only one of ITO surfaces of the display matrix is covered with the photo‐aligning layer while another one is not, have been used for providing both high contrast ratio and steady multiplex operation. The electro‐optical performance of the 5‐μm FLC display is presented, including bistable switching in static operation, optimization in multiplexing operation, and gray‐scale generation.     

Electrically suppressed helix ferroelectric liquid crystals for modern displays

In this article, we disclose electrically suppressed helix ferroelectric liquid crystal (ESHFLC) that is characterized by high optical quality and fast response time at the cost of extremely small driving voltage. These unique features of the ESHFLCs are highly sensitive to the anchoring energy that should be smaller and comparable to the elastic energy of the ferroelectric liquid crystal helix. The photo alignment, which offers good control on the anchoring energy by means of the irradiation energy, is critically important to lock the optimum parameters of the ESHFLC display cell. An example of field sequential color display with the frame frequency of 240 Hz at the driving voltage of 2 V has been demonstrated.     

Transflective ferroelectric liquid‐crystal display with a single‐cell gap

Abstract— A ferroelectric liquid‐crystal (FLC) display was optimized as a transflective liquid‐crystal display (LCD). In this configuration, the single‐cell‐gap approach was considered. The optimized configuration exhibits a high contrast ratio, wide viewing angles, and achromatic (black/white) switching in both the transmissive and reflective modes. Because no double‐cell‐gap structure, no subpixel separation, and no patterning polarizers and retarders are included in the configuration, the configuration is easy to fabricate and also possess a perfect dark state. This configuration is also suitable for bistable applications.     

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

Abstract— 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.