Switching Liquid Crystal Cell Research Articles

An in-plane switching liquid crystal cell with weakly anchored liquid crystals on the electrode substrate

We present the “one-side zero-anchoring in-plane switching” (OZ-IPS) mode in liquid crystal displays (LCDs) comprising an electrode substrate onto which poly(hexyl methacrylate) chains are grafted and a counter substrate coated with a rubbed polyimide film.

Field-symmetrization to solve luminance deviation between frames in a low-frequency-driven fringe-field switching liquid crystal cell.

The development of low-frequency-driven liquid crystal displays (LCDs) has recently received intense attention to open up low-power consumption display devices, such as portable displays, advertising panels and price tags. In fringe-field switching (FFS) LCD mode, a unidirectional electric field gives rise to head-tail symmetry breaking in liquid crystals, so that the flexoelectric effect, a coupling between the elastic distortion and the electric polarization, becomes enormously significant. The effect is thus linked to an unusual optical effect, which badly damages the quality of images by image-flickering, and this image-flickering is mainly caused by transmittance difference between the applied signal frames. Here, we intensively investigate the mechanism of the transmittance deviation, and propose an essential and promising approach to solve the poor image-quality, that is, symmetrization of electric fields between the frames. The result of our work clearly demonstrates that the field-symmetry is crucial to reduce the image-flickering, and it can be obtained by optimization of the thickness of an insulation layer with respect to the ratio of the space between electrodes to the electrode width.

Time-Sequential Ultraviolet Exposure to Alignment Layers Embedded With Reactive Mesogen for High-Speed In-Plane Switching Liquid Crystal Cell

We propose a time-sequential ultraviolet (UV) exposure process that can improve the surface anchoring energy of photopolyimide (PI) embedded with reactive mesogen (RM) in high-speed liquid crystal (LC) display devices. To increase the anchoring energy of the PI layer, a separated UV exposure process of polymerization for the embedded RM material and PI layer is required [1] – [8] . In this paper, we propose a novel single-frequency UV exposure method that can perform the separated polymerization of the UV alignment layer and the embedded RM material by optimizing the intensity of the exposure UV light. Using the proposed UV exposure method, we polymerize the RM material during the first 4 s, and then accomplish the polymerization of the UV alignment layer sequentially. To demonstrate the electro-optical performance, we measure the surface anchoring energy and the optical response time of in-plane switching LC cell. The measured results show that the surface anchoring energy and the optical response time are improved by more than 2.5 times and 28.2%, respectively, compared with the conventional UV exposure.

Harnessing diffraction grating in an in-plane switching cell submitted to zigzag lattice.

Programmable diffraction gratings are relevant in optical data processing. One of the adequate device candidates is the in-plane switching liquid crystal cell. This technology, developed initially for liquid crystal screens, has also been studied with two inter-digital electrodes as a diffraction grating. Recently, the apparition of programmable zigzag wall lattices in an in-plane switching configuration has been reported. Here, we report a theoretical and experimental study of programmable diffraction grating in an in-plane switching cell.

Fast fringe-field switching of a liquid crystal cell by two-dimensional confinement with virtual walls.

We report a simple method for reducing the response time of a fringe-field switching liquid crystal cell by using two-dimensional confinement of the liquid crystals. Through both numerical calculations and experiments, we show that the switching speed can be increased by several fold in a fringe-field switching cell by simply using a rubbing angle of zero, which causes virtual walls to be built when an electric field is applied between the interdigitated electrodes and the common electrode, without requiring additional fabrication steps or complicated drive schemes. Furthermore, the devices fabricated with this method exhibit a reduced color shift and excellent dynamic stability, even with a high applied voltage and under external pressure.

Determination of the flexoelectric coefficient (e1–e3) in nematic liquid crystal by using fully leaky optical-guided mode

Fully leaky optical-guided mode was employed to determine the difference in the splay and bend flexoelectric coefficient (e1–e3) in negative nematic liquid crystal MS-N01300-000. The experimental curves of reflectivity versus internal angle (angle of incident light to the liquid crystal) were obtained when a laser beam passed through the hybrid-aligned nematic in-plane switching liquid crystal cell; the cell was embedded in pyramid-coupled waveguide with different alternating current (AC) and direct current (DC) voltages. The curves of the applied DC with voltage similar to that of AC shift to the left or the right. Experimental results were then compared with theoretical results derived from elastic continuum theory and multi-layer optical theory of liquid crystals. The approximate value of the flexoelectric coefficient (e1–e3) of MS-N01300-000 is 9.0 × 10−11 C/m.

Effect of surface anchoring energy on electro-optic characteristics of a fringe-field switching liquid crystal cell

Surface anchoring strength of the alignment layer on liquid crystal (LC) determines electro-optic characteristics in the LC devices. This paper investigates how azimuthal and polar anchoring strength affects the electro-optic performance of a fringe-field switching (FFS) mode associated with electrode structure, cell gap and dielectric anisotropy of the LC by numerical simulation. Our important findings in the FFS mode are that both azimuthal and polar anchoring energy can considerably affect the operating voltage and also maximum transmittance when using a LC with positive dielectric anisotropy; however, when using a LC with negative dielectric anisotropy only azimuthal anchoring energy affects electro-optic characteristics. The study proposes an optimal design of an alignment layer for maximizing transmittance in the FFS mode.

High Speed In-Plane Switching Liquid Crystal Cell by Using Photo Alignment Method

We proposed a fast response time in-plane swithcing (IPS) liquid cryatal (LC) mode in the photo-alignment layer. In order to achieve the fast response time, we first enhanced the anchoring energy of the photo-alignment layer by coating the reactive mesogens (RMs) which can modify the surface condition and also applied the low cell property in the LC cell by using the positive A-plate with same effective retardation as the LC layer. In the experiments, we demonstrated that the coated RM layer can make the strong surface anchoring energy because of its strong polymer chain by the UV exposure and also confirmed the improved response time in the low cell gap IPS cell. As measured results, the response time of the proposed IPS LC cell could be improved over 56.86% and 62.18% compared with that of a conventional photo-aligned IPS cell with/without RM coating, respectively because of the low cell gap property.

Electro-optical properties of photochemically stable polymer-stabilized blue-phase material

Polymer-stabilized blue-phase liquid crystal (BPLC) comprising fluorinated compounds with high resistivity and photochemical stability is demonstrated. The Kerr constant, driving voltage, and response time of this BPLC are measured using an in-plane switching liquid crystal cell. At 20 °C, the measured total response time is faster than 0.7 ms and Kerr constant is 2 nm/V2. This fluorinated BPLC material is a promising candidate for next-generation photonic and display devices, because it can be used in active matrix addressed devices.

Flexoelectric Effect in a HAN-IPS Cell

Flexoelectric properties are evident in experiments preformed with hybrid aligned nematic. In this article, the flexoelectric effect in a hybrid aligned nematic in-plane switching liquid-crystal cell is investigated. The equations for the distribution of the liquid-crystal director and the expression of critical voltage in the one-constant approximation are obtained. The results of computer simulation show that the value of angle φ exceeds 90 degrees and closes to 180 degrees between the bottom substrate and the mid-layer.

In‐plane switching liquid crystal cell with a mixed bent electrode structure for fast response time

A bent electrode structure is proposed in the super in‐plane switching (S‐IPS) liquid crystal (LC), as it can re duce the response time without loss of transmittance in the bright state. The electrode angle in each position of the bent electrode was optimized to simultaneously achieve high transmittance and fast response time. The electro‐optical characteristics of the proposed LC cell structure were experimentally compared with those of the conventional cell. It was observed that the response time became over 8% shorter without loss of transmittance when the proposed bent structure was applied.

In-Plane-Switching Liquid Crystal Cell with Zigzag Electrodes for Tansflective Displays

We propose the optical configurations of an in-plane switching liquid crystal cell for transflective displays. Zigzag electrodes are used to switch LC directors in different directions to simultaneously achieve a high transmittance of the transmissive part and a high reflectance of the reflective part. We demonstrated the high optical performances of the proposed configurations. To reduce the parallax problem, retardation layers are formed inside the cell.