In-plane Switching Mode Research Articles

Dynamic geometric phase holography based on in-plane switching liquid crystal

ABSTRACT Liquid crystal geometric phase modulation technology is expected to achieve thin, small and achromatic spatial light modulation, which in turn has the potential to achieve holographic displays with large field angles and high clarity. This article presents a continuous dynamic geometric phase liquid crystal spatial light modulation method based on in-plane switching (IPS) mode. The relationship between geometric phase modulation and driving voltage is calibrated by using interferometry. Two hundred fifty-six phase orders within the phase modulation range of 0~π/2 is achieved. Subsequently, a phase hologram with a modulation range of 0~π/2 was designed by combining the GS (Gerchberg-Saxton) algorithm and single Fourier transform, demonstrating the holographic display capability. This article provides a low-cost approach for dynamic geometric phase holographic display.

The effects of side-chain flexibility on the photosensitivity of polyimide alignment film

ABSTRACT To examine the impact of side-chain flexibility on the photosensitivity of polyimide liquid crystal (LC) alignment films, two polyimides (OD-HAB-CA and OD-HAB6-CA) were synthesised. OD-HAB6-CA contains flexible hexamethylene side chains. This study demonstrates that the OD-HAB-CA alignment film can induce LC molecular alignment after 80 min of non-polarised ultraviolet light (NPUVL) irradiation. In contrast, the OD-HAB6-CA alignment film can achieve the same result after only 35 min of irradiation. This suggests that the flexibility of the side-chain can significantly improve the photosensitivity of the alignment film and shorten the required irradiation time. In addition, OD-HAB-CA and OD-HAB6-CA exhibit good thermal stability and light transmittance properties. The resulting LC cell have pretilt angles of 0.2° and 0.5°, respectively, which are suitable for in-plane switching mode LCDs.

Ideal micro-lenticular lens based on phase modulation of optically isotropic liquid crystal-polymer composite with three terminals

Optical phase modulation in a transparent polymer film composed of nano-sized liquid crystal (LC) droplets embedded within a polymer matrix exhibits a micro-lenticular lensing effect under controlled in-plane field switching (IPS) with interdigitated electrodes. Despite of the lensing effect, the lens profile does not match ideal one and its effective phase modulation is relatively small owing to the weak field strength over the electrodes, which causes an invariant refractive index in these regions. To achieve ideal lens profile and high phase modulation, a vertical electric field is applied between top plane and bottom interdigitated electrodes, while maintaining the in-plane fields between the bottom interdigitated electrodes. The combined effect, referred to as the vertical and in-plane switching (VIS) mode, can achieve larger phase modulation (Δδ) than the IPS mode. Consequently, the proposed micro-lenticular lens has a shorter focal length and a significantly better lens profile, similar to the ideal one. Furthermore, the diffraction efficiency (Df) is effectively improved by ∼ 6.7%, 4%, and 2% for the zeroth (0th), ±1st, and ± 2nd orders, respectively, compared to those in the IPS mode. The improved phase profile with the proposed micro-lenticular device can be used in a switchable lens from 2-dimensions (2D) to 3-dimension (3D) and tunable diffractors.

Journal of the Society for Information Display

Jiun-Haw Lee Editor in Chief The Journal of the Society for Information Display's (JSID's) September and October 2020 issues each feature six papers that report on new research in key areas. Topics include OLED, LCD, thin-film transistors (TFTs), electrophoretic displays, human factors, display measurements, and optics. Furthermore, as a friendly reminder, the 26 “Distinguished Papers, Best of Display Week 2020” published in JSID's April, May, and June 2020 issues will remain open access until the end of the year. A single-cell-gap transflective blue-phase liquid crystal display based on fringe in-plane switching electrodes|Xiang-Yu Zhou et al.|doi:10.1002/jsid.872 In this work, the authors propose a new LCD mode for a transflective blue-phase (TRBP) device, which they refer to as fringe in-plane switching (FIS). This mode combines the advantages of in-plane switching (IPS) and fringe-field switching (FFS). Compared to FFS, FIS has a similar driving voltage but with much higher transmittance. However, FIS has a much lower driving voltage than the IPS mode. By providing fringe and in-plane electric fields simultaneously, the authors obtained a deep-penetrating electric field that greatly improved LCD's transmittance while also lowering the driving voltage. Note that two TFTs were required in a single pixel of FISTRBP-LCD for providing the driving voltage with opposite polarities. Investigation on Ag-containing compound generated in manufacturin go flow-temperature polycrystalline Si active matrix organic light-emitting diode |Yu Jin et al.| doi:10.1002/jsid.895 In this highly practical paper, the authors analyze low-temperature polycrystalline silicon (LTPS) active matrix (AM) OLED's failure caused by silver (Ag) contamination, and explore possible solutions. In observing Ag-contamination in LTPS's real products, they noticed that it resulted in short circuits in certain places. The Ag-compounds originate from the electrochemical formation and are related to migration assisted by an electric field. The authors proposed several methods to alleviate this effect, including a planarization dam that can be used to increase the migration path and weaken the electric field. The paper may stimulate interesting ideas for improving production yield without increasing the complexity during display manufacture. Information About the Journal JSID is published monthly by Wiley. Subscription fees apply, but SID members and student members have free online access via sid.org/Publications.aspx. Many universities also have an institutional subscription. JSID is indexed in the Web of Science. Submit your original manuscript online via mc.manuscriptcentral.com/sid. Author guidelines can be found on the Journal's homepage: tinyurl.com/jsidhome. Editorial board: tinyurl.com/jsideb. Please direct any questions about JSID to its editor in chief at editor@sid.org. EarlyView: accepted papers about to be published can be accessed online via tinyurl.com/jsidev. Invitation to Submit Review Papers The Journal is soliciting review papers on any display-related topic. If you have a great idea for a review paper, please contact the editor at editor@sid.org. Page charges for invited review papers will be waived.

Preparation and performance analysis of novel liquid crystal alignment films based on macromolecular photosensitiser and photosensitive polyimide

ABSTRACT A photosensitive polyimide (BF-CA) and a macromolecular photosensitiser (BB-CA) are successfully synthesised. The BF&BB-CA blend films based on BF-CA and BB-CA can induce uniform alignment of liquid crystal (LC) after the non-polarised ultraviolet light (NPUVL) exposure for 15 min. After exposure for the same time, LC alignment ability of the BF&BB-CA blend films is higher than that of BF-CA films and BB-CA films. The alignment performance of LC and pretilt angles induced by the BF&BB-CA films after treatment at 120°C for 4 h are nearly unchanged, indicating that the prepared films have excellent thermal stability. Furthermore, the pretilt angle of the LC cells is 0.5°, which can be used in In-Plane Switching mode LCD.

Electro-Optical and Dielectric Responses of ZnO Nanoparticles Doped Nematic Liquid Crystal in In-Plane Switching (IPS) Mode

In present work, electro-optical and dielectric characteristics of ZnO nanoparticles (NPs) doped nematic liquid crystal mixture are studied in In-Plane Switching (IPS) mode. Effect of doping of ZnO nanoparticles on phase transition behaviour, threshold and operating voltage were studied. Polarising Optical Microscope (POM) study confirms a reduction in nematic to isotropic (N-I) phase transition temperature after doping of ZnO NPs. A decrease in threshold and operating voltages with better contrast ratio was observed. Further, a significant change in dielectric behaviour of NLC was also perceived in doped sample.

Fast response time of micropixels with in-plane switching of positive liquid crystals using crossed patterned electrodes

Demonstrated herein is a fast in-plane switching (IPS) cell with positive dielectric anisotropy liquid crystals using crossed patterned electrodes in three different conditions. The ineffectiveness of one of these three structures due to the ‘Faraday cage’ effect was shown. With another structure, a fast response time was also shown to be impossible to achieve due to several contrast issues. In the third structure, a fast response time was achieved due to a combination of high-driving and crossed patterned electrodes allowing fast turn-off. Two of the three structures was manufactured. With the first one, an experiment confirmed the ‘Faraday cage’ effect. In the second structure, a response time four to eight times faster than the conventional IPS mode was experimentally demonstrated using two different kinds of liquid crystal.

Traveling Waves in One-Dimensional Electroconvection of Nematic Liquid Crystals

We report ac-driven electroconvection (EC) of nematic liquid crystals (NLCs) in one-dimensional cells employing an in-plane switching mode. The dynamical features of traveling waves (TWs), such as ...

Unsteady characteristics of S-duct intake flow distortion

The unsteady distorted flow fields generated within convoluted intakes can have a detrimental effect on the stability of an aero-engine. The frequency signature in the distorted flow field is of key importance to the engine's response. In this work, time-resolved particle image velocimetry is used to obtain the three-component velocity field at the outlet plane of two S-duct intake configurations for a range of inlet Mach numbers. Proper orthogonal decomposition of the time-resolved velocity data allows the identification of the main frequencies and coherent structures in the flow. The most energetic unsteady structures comprise an in-plane vortex switching mode, associated with a lateral oscillation of the main loss region, and a vertical oscillation of the main loss region. The switching structure occurs at a frequency of St=0.42 and 0.32 for the high and low offset ducts, respectively. The vertical perturbation is associated with a more broadband spectrum between approximately St=0.6–1.0 and St=0.26–1.0 for the high and low offset configurations, respectively. The determined frequencies for these main unsteady flow structures are within the range, which is expected to be detrimental to the operating stability of an aero-engine. The results provide a novel, time-resolved dataset of synchronous velocity measurements of high spatial resolution that enables analysis of the unsteady flows at the exit of complex aero-engine intakes.

Unified Overdrive Technology Applicable to Liquid-Crystal Displays and Organic Light- Emitting Diode Displays Utilizing Linearity of Transitions in Voltage Domain

This paper proposes a new method to determine the overdrive (OD) to improve the response characteristics of displays based on the linearity in voltage domain. The proposed method estimates OD values by using a simple function between the slope of linearity and transition. The values of the function can be determined using only two measurements. The proposed work can be applied to both active-matrix liquid-crystal displays and active-matrix organic light-emitting diode (AMOLED) displays. OD artifacts were observable when OD deviation was over three gray levels. However, the average OD deviations were 1.47, 0.87, and 0.69 when the proposed method was applied to twisted nematic, in-plane switching, and fringe-field switching modes, respectively. The deviation in AMOLED displays was 0.45 gray levels.

81‐2: Novel In‐Plane Switching (IPS) Mode with High Transmittance using Negative Dielectric Liquid Crystal

We propose a novel In‐Plane Switching (IPS) mode with higher transmittance than conventional IPS mode using electrode modification and negative dielectric liquid crystals (nLC). In this configuration, nLC minimize the tilt angle which can prevent the transmittance decrease and therefore transmittance is increased about 20% compare to the conventional IPS mode. Moreover, reflectance of panel is dramatically decreased by substitution of metal electrode.

Electroconvection in one-dimensional liquid crystal cells

We investigate the alternating current (ac) -driven electroconvection (EC) in one-dimensional cells (1DCs) under the in-plane switching mode. In 1DCs, defect-free EC can be realized. In the presence and absence of external multiplicative noise, the features of traveling waves (TWs), such as their Hopf frequency f_{H} and velocity, are examined in comparison with those of conventional two-dimensional cells (2DCs) accompanying defects of EC rolls. In particular, we show that the defects significantly contribute to the features of the TWs. Additionally, owing to the defect-free EC in the 1DCs, the effects of the ac and noise fields on the TW are clarified. The ac field linearly increases f_{H}, independent of the ac frequency f. The noise increases f_{H} monotonically, but f_{H} does not vary below a characteristic noise intensity V_{N}^{*}. In addition, soliton-like waves and unfamiliar oscillation of EC vortices in 1DCs are observed, in contrast to the localized EC (called worms) and the oscillation of EC rolls in 2DCs.

Polyimide-free homogeneous photoalignment induced by polymerisable liquid crystal containing cinnamate moiety

ABSTRACTWe designed and synthesised a reactive mesogen (CRM) containing cinnamate moiety in the core and two acrylate groups at both ends. The structure was characterised by 1H NMR and FT-IR, and its liquid crystalline property was investigated by DSC and POM. The compound showed a nematic phase between 175.2 – 97.5 oC, followed by a smectic C phase between 97.5 and 57.9 oC during the cooling cycle. We proposed a fabrication method to achieve uniaxial homogeneous alignment of liquid crystals by irradiating the CRM-doped LC mixture in a sandwich cell of in-plane switching mode (CRM-IPS) with linearly polarised ultraviolet light. The results indicated that the CRM-IPS cell showed excellent initial dark state with a good alignment state, electro-optical performance and durability. This confirmed that the photo-induced alignment of LCs by CRM possesses outstanding alignment capability compared to the conventional rubbed polyimide alignment layer. We expect that this fabrication method is a promising candidate for cost-effective, green-manufacturing, and high-quality alignment method for the manufacturing of high-resolution liquid crystal displays (LCDs).

Reflective blue phase liquid crystal displays with double-side concave-curved electrodes

ABSTRACTReflective blue phase liquid crystal display (BPLCD) is a promising candidate for field sequential colour displays with reflective liquid-crystal-on-silicon (LCoS). However, the issue of high operation voltage still hinders its widespread applications. We propose a reflective BPLCD with double-side concave-curved electrode and research its operation voltage and electro-optic characteristics in simulation, which is compared to the transmissive mode. The effect of double-side electrodes on horizontal electric field and operation voltage is analysed. The improvement of concave-curved electrodes on reflectance is discussed. A reflective BPLCD has two times the optical path difference compared to the transmissive mode. By using double-side concave-curved electrodes, the reflectance increased by 23% and the operation voltage reduced by 32% compared to the traditional in-plane switching mode. This work enables BPLC to be integrated with reflective LCoS.

Flexoelectric in-plane switching (IPS) mode with ultra-high-transmittance, low-voltage, low-frequency, and a flicker-free image.

The demands for a power-saving mode for displaying static images are ubiquitous not only in portable devices but also in price tags and advertising panels. At a low-frequency driving in liquid crystal displays (LCDs) for low-power consumption, the flexoelectric effect arises even in calamitic liquid crystals and the optical appearance of this physical phenomenon is found to be unusually large, being noticed as an image-flickering. Although the inherent integrated optical transmittance of in-plane switching (IPS) mode is relatively lower than that of fringe-field switching (FFS) mode, the IPS mode shows no static image-flickering but an optical spike (the so-called optical bounce), at the transient moment between signal positive and negative frames. Here, we demonstrate an IPS mode using negative dielectric anisotropy of liquid crystals (Δε < 0) and fine-patterned electrodes (the width w of and the space l between electrodes ≤ 3 μm) with reduced operation voltage (up to 40.7% to a conventional FFS mode with Δε < 0), reduced optical bounce (up to 4.4%. to a conventional FFS mode with Δε < 0) and enhanced transmittance (up to 32.1% to a conventional IPS mode with Δε > 0). We believe the result will contribute not only to the scientific understanding of the optical appearance of flexoelectric effect but also pave the way for engineering of a superior low-power consumption LCD.

Flexoelectric effect in an in-plane switching (IPS) liquid crystal cell for low-power consumption display devices.

Technology of displaying static images in portable displays, advertising panels and price tags pursues significant reduction in power consumption and in product cost. Driving at a low-frequency electric field in fringe-field switching (FFS) mode can be one of the efficient ways to save powers of the recent portable devices, but a serious drop of image-quality, so-called image-flickering, has been found in terms of the coupling of elastic deformation to not only quadratic dielectric effect but linear flexoelectric effect. Despite of the urgent requirement of solving the issue, understanding of such a phenomenon is yet vague. Here, we thoroughly analyze and firstly report the flexoelectric effect in in-plane switching (IPS) liquid crystal cell. The effect takes place on the area above electrodes due to splay and bend deformations of nematic liquid crystal along oblique electric fields, so that the obvious spatial shift of the optical transmittance is experimentally observed and is clearly demonstrated based on the relation between direction of flexoelectric polarization and electric field polarity. In addition, we report that the IPS mode has inherent characteristics to solve the image-flickering issue in the low-power consumption display in terms of the physical property of liquid crystal material and the electrode structure.

New three-gamma-curves-integrated VA LCD design for excellent image quality and enhanced transmittance

ABSTRACTCompared with the in-plane switching (IPS) mode of the liquid crystal display (LCD), the vertical-alignment (VA) LCD mode provides an excellent contrast ratio and a fast response time, but it still has a relative weakness: image quality deterioration as a function of the viewing direction. In the VA mode, the pixel division method, in which two different gamma curves from the divided pixels are integrated, is generally used to improve the off-axis image quality. Reported herein is the new VA mode for enhancing the off-axis image without decreasing the transmittance. The pixels divided into 12 domains instead of 8 using double electrode layers produce three different gamma curves from the high, middle, and low pixels, which are combined and enhance the image quality. In this pixel structure, the middle pixels are formed by two electrode layers and produce the third gamma curve. The new design of the VA mode shows the best off-axis image quality in the VA mode, which is the most comparable with that in the IPS mode, even with the organic light-emitting diode, and will provide a solution for the heavy competition in the ultrahigh-definition (UHD) and large-LCD-TV-panel market in the very near future.

Blue-phase liquid crystal display with high dielectric material

ABSTRACTA blue-phase liquid crystal display (BPLCD) with low operating voltage and high transmittance is demonstrated by using a high dielectric material, which is used as an insulation layer or protrusion fixed on the pixel and common electrodes in in-plane switching (IPS) mode. The operating voltage is reduced to about 14 V and the transmittance is improved for the BPLCD with high dielectric constant protrusion. Compared with the conventional protrusion electrode structure, the proposed protrusion can make manufacturing process simple and easy because the electrode has no complex shape. The results will be significant in designing optimal BPLCDs.

Suppression of Moiré Phenomenon Induced by Metal Grids for Touch Screen Panels

With attempt to suppress the Moire phenomenon, we conduct ray tracing simulations with various metal grids having different degree of randomness (e.g., rectangular, width-altered rectangular, line-shifted rectangular, wavy square, and random metal grids) in the presence of twisted nematic (TN) or in-plane switching (IPS) mode black matrix (BM). We analyze their angular dependence in terms of the standard deviation (SD) calculated from the simulated ray distribution. It is observed that metal grids with a lower degree of randomness exhibit a stronger angular dependence, yet lower SD value over the broader range of crossing angles. Though metal grids with a higher degree of randomness show a weaker angular dependence, yet they bring in higher fluctuation in the SD value due most likely to point defects. The wavy square metal grid results in periodic point defects, whereas the random metal grid gives rise to aperiodic point defects. Through a comparison between simulation and experiment results, we have found that moire patterns are hardly seen to the naked eye when the SD value is less than 10, which provides useful design guidelines of metal grids.

Faster in-plane switching and reduced rotational viscosity characteristics in a graphene-nematic suspension

The in-plane switching (IPS) for a nematic liquid crystal (LC) was found to be considerably faster when the LC was doped with dilute concentrations of monolayer graphene flakes. Additional studies revealed that the presence of graphene reduced the rotational viscosity of the LC, permitting the nematic director to respond quicker in IPS mode on turning the electric field on. The studies were carried out with several graphene concentrations in the LC, and the experimental results coherently suggest that there exists an optimal concentration of graphene, allowing a reduction in the IPS response time and rotational viscosity in the LC. Above this optimal graphene concentration, the rotational viscosity was found to increase, and consequently, the LC no longer switched faster in IPS mode. The presence of graphene suspension was also found to decrease the LC's pretilt angle significantly due to the π-π electron stacking between the LC molecules and graphene flakes. To understand the π-π stacking interaction, the anchoring mechanism of the LC on a CVD grown monolayer graphene film on copper substrate was studied by reflected crossed polarized microscopy. Optical microphotographs revealed that the LC alignment direction depended on monolayer graphene's hexagonal crystal structure and its orientation.