Nano‐domains formation on photoalignment thin film by self‐organized dewetting

A novel discontinuous photoalignment surface with nano‐domains for liquid crystal is developed. The formation of the discontinuous structure is created by self‐organized dewetting, which is regarded as one of the most promising bottom‐up approaches to fabricate nano‐structure. Different dewetting conditions, such as surface roughness, thickness and viscosity, have been investigated. Such discontinuous photoalignment layer can be fabricated on top of another continuous alignment layer to form a new kind of heterogeneous nano‐structured alignment surface – stacked alignment layers. This heterogeneous alignment surface can be used to produce arbitrary pretilt angles for the liquid crystal display. Simulation model has been built to understand the dewetting mechanism. Experiments using photo‐aligned and photo‐polymerisable polymer have been done to verify the dewetting theory. The produced stacked alignment layers are proved to be robust. Moreover, the dewetting processing is a fully controllable process and is compatible with existing manufacturing techniques.     

Large area mold fabrication for the nanoimprint lithography using electron beam lithography

The mold fabrication is a critical issue for the development of nanoimprint lithography as an effective low-cost and mass production process.This paper describes the fabrication process developed to fabricate the large area nanoimprint molds on the silicon wafers.The optimization of e-beam exposure dose and pattern design is presented.The overlayer process is developed to improve the field stitching accuracy of e-beam exposure,and around 10 nm field stitching accuracy is obtained.By means of the optimizatio...     

Arbitrary pretilt and azimuth angles generation by stacked photoalignment layers

We report a method of fabricating a nano‐sized stack alignment layer. The stacked alignment layer consists of nano‐domains of vertical and planar alignment materials. Experiments reveal that photoalignment thin film can undergo dewetting and form discrete nano‐sized domains. Such self‐organized structure creates a discontinuous layer stacked on top of a continuous layer and hence produces an inhomogeneous alignment surface. With two or more different principle alignment directions, this new alignment layer is capable of producing multiple pretilt and azimuth angle domains on a single substrate.     

Single step micro‐patterned liquid crystal photoalignment by patterned quarter‐wave plate

In this article, a method for fabricating the patterned liquid crystal photoalignment structures, in a single step, is proposed. A patterned quarter‐wave plate formed by a photoaligned liquid crystalline polymer film is used as a photomask to generate photoaligned micro‐patterns. Whereas other existing alternatives include complicated fabrication scheme, the proposed method provides an edge with simple one‐step alignment. Moreover, the proposed method offers highly accurate, high resolution, multi micro‐pattern alignment with great repeatability and therefore could find application in wide range of photonic and display devices demanding the micro‐patterned, single of multi domain, alignment. In addition, the structure could be used for optical polarization information storage and patterned alignment structure storage, which could easily be reproduced.     

Single‐cell‐gap transflective liquid‐crystal display and the use of photoalignment technology

Abstract— In this paper, transflective liquid‐crystal‐display (LCD) technology will be reviewed, and several new single‐cell‐gap transflective LCD configurations are proposed. Photoalignment technology is studied especially for transflective‐LCD applications. In order to realize the optimal performance of the display as well as a matched transmittance/reflectance voltage curve (TVC/RVC) for the transflective configurations, two different single‐cell‐gap transflective‐LCD approaches will be discussed. The first one is the dual‐mode single‐cell‐gap approach, in which different liquid‐crystal modes are applied to the transmissive and reflective subpixels of the transflective LCD. The other approach is the single‐mode s ingle‐cell‐gap approach, in which an in‐cell retardation film is applied to adjust the performance and TVC/RVC matching of a transflective LCD. Photoalignment technology is used to fabricate the dual‐mode liquid‐crystal cell in the first approach and also the in‐cell retardation film in the second approach. Prototypes of the proposed configurations have been fabricated, which show good performance and a matched TVC/RVC.     

Bistable FLCOS devices for doubled‐brightness micro‐projectors

Abstract— Optical output is of paramount importance to emerging ultra‐miniature projector products. Experimental bistable ferroelectric liquid‐crystal‐on‐silicon (FLCOS) projection microdisplay devices using newly developed FLC materials aligned on obliquely deposited SiO₂ have been developed. These devices enable the doubling of the illumination duty cycle, and hence doubling of the achievable projector light output, while maintaining a DC‐balanced electrical drive.     

Bistable cholesteric reflective displays: Two‐level dynamic drive schemes

Abstract— Among the many known dynamic drive schemes for bistable cholesteric liquid‐crystal displays, the simplest driving voltage waveforms are realized only in two‐level dynamic drive schemes. Voltage waveforms that are applied to rows and columns of a display in two‐level drive schemes consist of only two voltage levels: U and 0. The addressing speed for these drive schemes is defined by the fast transition time of a cholesteric liquid crystal from the homeotropic state to the transient planar state per row. Two‐level dynamic drive schemes were analyzed. The possibility of increasing the addressing speed will be discussed.     

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.     

Oil thermal annealed nano‐structured indium tin oxide thin films for display applications

Indium tin oxide‐coated thin films (200 nm) are deposited on glass substrates by using R.f. sputtering technique. Here, we investigate the influence of new technique of treatment, which is called as “oil thermal annealing” on the nano‐structured indium tin oxide thin films at fixed temperature (150 °C) which improves adhesion strength, electrical conductivity and optical properties (transmittance) of the films. Oil thermal annealing is used to reduce inherent defects that may be introduced during the prepared thin film and cooling processes. Proposed technique is highly suitable for liquid crystal displays, solar cells and organic light emitting diodes, and many other display‐related applications.     

Domain walls in photoaligned double‐domain twisted‐nematic LCDs

Abstract— Advanced two‐ and three‐dimensional modelling was used to explain microscopic measurements on two different double‐domain twisted‐nematic liquid‐crystal‐display (TN‐LCD) configurations that were made using photoalignment. The shape of domain walls and their effect on the transmitted intensity were described correctly. For some double‐domain configurations, the brightness and contrast of the display will be affected by the domain walls.     

A multistable smectic‐A liquid‐crystal device with low threshold field

Abstract— A multistable liquid‐crystal device has been realized in this study; its smectic‐A LC is oriented by in‐plane and out‐of‐plane electric fields with various amplitudes. This paper introduces improvements made to electrode structure and hybrid surface treatments that have enhanced SmA LC device performance. The driving voltage of the hybrid‐aligned cell has been reduced to 20% of the vertical‐aligned one, and light leakage has been suppressed by out‐of‐plane electric‐field‐strength modulation. The many advantages of this multi‐stabilized LC device could be applied to memory devices and to flexible displays.     

Photoalignment of nematic liquid crystal on polyamic‐acid‐based soluble polyimide with no side fragments

Abstract— The photoalignment of nematic LC on a layer of newly synthesized UV‐sensitive polyimide without side fragments is reported. The photoaligning polymer advantageously differs from other photoaligning materials because of its extremely low sticking effect and residual DC voltage. These parameters, as well as the UV and thermal stability of the alignment, are not worse than those of rubbed polyimides. At the same time, the new material possesses all the advantages of photoaligning polymers.     

New properties and applications of rewritable azo‐dye photoalignment

Abstract— The rewritable azo‐dye photoalignment (ORW) of liquid crystals (LCs) for application in optical rewritable electronic paper has been investigated. It was observed that a periodic change in the azimuthal aligning direction with polarized UV light (365 nm) brings about homeotropic alignment, while utilization of visible light (450 nm) does not affect the LC tilt angle. The wavelength dependence of the ORW photoalignment result and the behavior of the photoinduced anisotropy was explored. The dark amplification of film anisotropy after exposure was observed, which is believed to be the relaxation process related to hydrogen bonding in azo‐dye film. New material, CD1, for azo‐dye rotation photoalignement that possesses a high azimuthal anchoring energy (about 2 × 10^?4 J/m²) was found.     

Bistable SmA liquid‐crystal display driven by a two‐direction electric field

Abstract— A new operation mode of a bistable smectic A (SmA) display using two sets of electrodes, one without specific features to induce homeotropic orientation of the director and the other with an in‐plane pattern to induce planar orientation of the director, has been demonstrated. Both statements of the director orientation are the stable states of SmA liquid crystals. Compared with the electrical addressing mode of a conventional SmA display, the SmA display mode presented in this study exhibits a high contrast ratio, excellent bistability, and reasonably fast switching under the employment of two crossed polarizers. Moreover, gray level can be achieved by regulating the frequency, owing to the formation of the focal‐conic defect. This operation mode of a bistable SmA device demonstrated great potential for the further application in flexible displays.     

Aggregate‐induced emission in light‐emitting liquid crystal display technology

Nowadays, liquid crystal displays (LCDs) with light‐emission are considered as energy‐efficient devices and are promising alternatives to conventional LCDs. To realize such possibility, strong fluorescent materials with a dichroic properties are required. Aggregate‐induced emission (AIE) is an unusual photophysical phenomenon shown by some luminogenic materials that will be highly emissive in their aggregate state. In this work, we studied the AIE effect of a luminescent liquid crystalline molecule TPE‐PPE in our LC system as a luminophore dopant. The result showed the excellent AIE effect that higher concentration of luminogen in the nematic LC host induced stronger luminescent intensity. Through exposure of a photoisomeriable alignment material sulfonic‐dye‐1, the photopatterning of a light‐emitting LC device was achieved with the use of the TPE‐PPE/nematic LC mixture.     

A reflective‐display QR‐LPD®

Abstract— A novel reflective display [Quick‐Response Liquid Powder Display (QR‐LPD®)], has been developed. This paper‐like display has the advantages of outstanding image stability, easy viewing, low‐power consumption, and a high‐response time. QR‐LPD® will be promoted, initially, for use as electronic price‐tag displays for merchandise. In addition, QR‐LPD® is suitable for flexible display applications because it does not require TFT arrays or a high‐temperature process while maintaining an excellent paper‐like image as well as glass‐type display compatibility.     

Luminescent dichroic‐dye‐doped cholesteric liquid‐crystal displays

Abstract— LCDs based on a luminescent dichroic‐dye‐doped non‐absorbing cholesteric LC with positive dielectric anisotropy is proposed. In the initial state, the orientation of the dye molecules provides effective light absorption and irradiation. By applying an electric field to the cell, the absorption and thus the luminescence is absent. A two‐color luminescence could be achieved by sandwiching two cells: the upper cell consists of a cholesteric LC with two dyes (sensitizer and emitter) and is used with an applied voltage (active cell); the lower cell consists of a cholesteric LC doped with one dye and works without applying a voltage (passive cell). The performance characteristics of luminescent dye‐doped cholesteric‐LCDs were investigated.     

Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate

Abstract— A novel illumination system for a liquid‐crystal‐display (LCD) module used in a dual‐display cellular phone has been developed. A double‐surface light‐emitting backlight uses a single light‐guide plate to illuminate both LCDs. A single lightguide, two prism sheets, and four light‐emitting diodes (LED) were used in the new structure, compared with ten components and two sets of light sources with six LEDs in the current backlight. The thickness and power consumption of the new backlight were reduced by a factor of 0.59 and 0.67, respectively.     

Photostable liquid‐crystal guest‐host nano‐materials for display applications

Abstract— We theoretically modeled the optical plasmon absorption of anisotropic metallic nanoparticles in a liquid‐crystal host medium. Metallic nanorods and spheroids act as pleochroic dopants with virtually unlimited photostability. Calculations predict that full‐color displays based on nanorod orientation driven by the transition from homogeneous to homeotropic LC alignment are feasible. These displays are expected to have large viewing angles without the need for polarizers or LC anchoring surfaces.     

A quick‐response liquid‐powder display (QR‐LPD®) with plastic substrate

Abstract— Paper‐like displays as thin as 290 μm have been developed using QR‐LPD technology. We fabricated two types of displays. One is a dot‐matrix type with a 160 × 160 array of pixels and a 3.1‐in.‐diagonal viewable image size. The other is a segmented type for clock use. Each display has a paper‐like appearance and exhibits high contrast. Plastic substrates with a thickness of 120 μm were used, resulting in flexible displays that can be bent up to a radius of curvature of 20 mm.