In-plane Switching Research Articles

Pixel Design Optimization of Fringe-Field Switching Mode for Applying Negative Liquid Crystals in High-Resolution Mobile Displays

We demonstrate an optimized fringe-field switching pixel structure to apply negative liquid crystals (nLCs) for high-resolution mobile displays. Pixel transmittance can be improved by applying nLCs, but the driving voltage increases because $\Delta \varepsilon$ of the nLC is lower than that of the positive LC (pLC). In spite of applying an nLC, a similar driving voltage can be achieved by changing the pixel structure. It is easy to obtain a low driving voltage in a strong electric field by applying a thinner passivation layer using photo acryl (PAC). In addition, while the edge electrodes of the conventional ${\rm V}_{\rm com}$ -on-top (VOT) structure are operated with in-plane switching, all electrodes of the pixel-on-top (POT) structure are operated with fringe-field switching. Therefore, the driving voltage can be reduced by applying a POT structure with PAC. Furthermore, crosstalk can be improved because the capacitance $(C_{\rm dp})$ between data lines and pixel electrodes is reduced by applying a POT structure. As a result, applying the proposed structure with nLC has two advantages. First, transmittance increases by more than 20% based on 4.5-in-high definition pixels. Second, crosstalk in the POT structure is more stable than that in the VOT structure, despite variations in low gate voltage $({\rm V}_{\rm GL})$ . Consequently, because of higher transmittance and stable crosstalk, the proposed POT structure with nLC can be used for mobile displays.

Nematic liquid crystal anchoring strengths of high density polymer brush surfaces

The azimuthal anchoring coefficient A2 of a nematic liquid crystal (NLC) on high-density polymer brushes was investigated using the threshold voltage for the in-plane switching of LC cells consisting of polymer-grafted substrates. A2 was affected by the bulk glass transition temperature (Tg) of the grafted polymers and decreased with increasing temperature. The NLCs on poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA) and poly(styrene) (PS) brushes had an A2 of 10−5 J m−2 at 25°C. In contrast, the NLC on a poly(hexyl methacrylate) (PHMA) brush exhibited a small A2 (1.1 × 10−6 J m−2) at 25°C and was oriented along the electrodes owing to the brush surface unevenness. With increasing temperature to 90°C, A2 of the NLCs on the PEMA and PS brushes decreased to the values of 10−7 J m−2, and the NLCs were oriented similar to the PHMA brush cell. Although the Tgs of PMMA and PS are similar, at 90°C the A2 of the NLC on the PMMA brush was 4.5 × 10−6 J m−2 and required a magnetic field for LC orientation. Such a difference in A2 is explained by the fact that PS has better compatibility with the NLC than PMMA.

Low voltage blue-phase liquid crystal display with triple-penetrating fringe fields

A low voltage polymer-stabilised blue-phase liquid crystal display (PSBP-LCD) with triple-penetrating fringe fields (TPFF) is proposed. The PSBP-LCD employs in-plane switching (IPS) electrodes and two etched substrates to generate the TPFF. These fields including strong horizontal electric fields are symmetrically distributed across the entire LC layer, so large phase retardation along the beam path is accumulated. As a result, the proposed structure successfully reduces the operating voltage below 10 V. Moreover, the proposed structure can obtain a wider viewing angle and a higher transmittance than the traditional IPS structure because of the generated multi-domain structures in the etched areas.

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.

A Power-Efficient Driving Method for In-Plane Switching-Mode TFT-LCD Using a Negative Liquid Crystal

This paper presents an effective driving method to reduce the power consumption of an in-plane switching (IPS) mode thin-film transistor liquid crystal display (TFT-LCD) with a negative liquid crystal (LC). Despite the higher transmittance efficiency of the negative LC, it is not effective to reduce the power consumption of the IPS mode TFT-LCD because of the driving voltage, which is 30% higher than that of the positive LC. To complement the higher driving voltage, the driving method, which can modulate the amplitude of the common voltage (VCOM) inversion without side effects, is proposed for low power consumption. In addition, a novel pixel structure is developed to reduce the data load. The measured power consumption is 22.5 W at the full white gray level in a 17-in full high-definition (FHD) IPS mode TFT-LCD. The measured result shows that the proposed method can reduce the power consumption by 19% and 10% as compared to that of the conventional method using the negative LC and positive LC, respectively.

Effects of chiral dopant on electro-optical properties of nematic liquid crystal cells under in-plane switching and non-uniform vertical electric fields

The electro-optical properties of the chiral nematic liquid crystal cell, driven by in-plane switching and non-uniform vertical electric fields, are investigated. The Bragg reflection, threshold voltage, and helical configuration are significantly related with the chiral dopant concentration. Through the driving-mode switching, two bistable helical structures without holding voltages are developed. The behavior of voltage- and temperature-dependent light reflection associated with the helical structure transition is also revealed. A fast bistable switching response (~5 ms) is successfully achieved by the three-terminal-electrode architecture. Further, the proposed cell shows a display time of over 6 hr in the unplugged power state.

Coplanar switching of polarization in thin films of vinylidene fluoride oligomers

Switching of vinylidene fluoride oligomer thin with molecular chains aligned normal to the substrate and exhibiting a preferential in-plane have been investigated using coplanar geometry of inter-digital via high-resolution It has been shown that in-plane switching proceeds via non-180° rotation of dipoles mediated by non-stochastic expansion, and coalescence of domains. As-grown multidomain configuration is found to be strongly pinned aided by charged and the electrically induced (in-plane) mono-domain states relax to the as-grown state. The observed (approximately 0.6 MV/m) is two to three orders of magnitude smaller than that for the oligomer with out-of-plane It is suggested that the low steric hindrance to the rotation of molecular dipoles gives rise to the observed low

Performance enhancement using a non-uniform vertical electric field and polymer networks for in-plane switching of multi-pretilt, vertically aligned liquid crystal devices.

A simple and reproducible alignment method for fabricating vertically aligned (VA) liquid crystal (LC) cells with a multi-pretilt structure is developed. A non-uniform vertical electric field is employed in the LC/monomer mixed cells during the photocuring process, and two pretilt domains with a functional small pretilt angle (∼1.6°) in the stabilized VA LC/polymer cells are achieved. The enhanced electro-optical performance of the cell driven by an in-plane switching field is demonstrated. Compared to the pure cell, the 2 wt.% pretilt angle cell shows 36%, 64%, and 76% improvement in the optical switch, the gray-level rise time, and the gray-level fall time responses, respectively, which are obtained at a low driving voltage (≤12 V). When applied to LC devices, the proposed method not only effectively benefits the LC molecular alignment, but it also significantly boosts the electro-optical performance.

High transmittance in-plane switching liquid crystal mode using double-exposed UV alignment method

In general, the super in-plane switching (S-IPS) liquid crystal (LC) mode is widely used for LCD applications because of its wide-viewing properties. However, it can also diminish the aperture ratio in active areas due to the zigzag pattern. In this paper, we proposed an IPS LC mode that has wide-viewing properties even if the stripe-patterned electrodes, which can provide a high transmittance property, are applied using the double-exposed UV alignment method to the upper/lower domain of the active area. The initial alignment direction of the upper/lower domain was optimized with simple experiments and we achieved both the superior dark level in the initial mode and wide-viewing properties in the applied voltage mode. As a result, we obtained an increased aperture ratio of about 10% and a higher optical transmittance of 15% compared to the conventional S-IPS LC cell because of the high aperture ratio without any optical loss of the initial dark state and viewing angle property.

High performance liquid crystal displays with a low dielectric constant material

We report high performance liquid crystal displays (LCDs), including fringe field switching (p-FFS) and in-plane switching (p-IPS), with a small average dielectric constant (e) but positive dielectric anisotropy material. Our low e based p-FFS and p-IPS LCDs offer several attractive properties, such as high transmittance, low operation voltage, fast response time (even at −20°C), which is particularly desirable for outdoor applications of mobile or wearable display devices, and suppressed flexoelectric effect. Combining these advantages with the inherent outstanding features, such as wide viewing angle, no grayscale inversion, negligible color shift, and pressure resistance, the low e LC based p-FFS and p-IPS are strong contenders for next-generation mobile displays, and high resolution and high frame rate TVs.

Polarized UV cured reactive mesogens for fast switching and low voltage driving liquid crystal device.

Uniaxial alignment of liquid crystals (LCs) is prerequisite for a vast number of LC applications. To accomplish stable and uniform LC orientation, an alignment process to orient the LCs is required. Herein, we demonstrate a simple strategy for fabricating novel LC alignment layers that ensures well aligned LC, superior switching without any capacitance hysteresis, low transmittance loss, and high thermal stability with sufficient anchoring action. Thin films of reactive mesogens (RMs) were transferred onto conventional homeotropic polyimides from a UV-cured RM stamp via contact printing. LC displays using defect free RM/PI polymeric stacks exhibited superior electro-optic (EO) properties to those containing rubbed PI layers. This approach allows for the fabrication of various-mode LC displays such as twisted nematic (TN), in-plane switching (IPS), and optically compensated bend (OCB) mode LCDs by changing the combinations of RMs, base PIs and LCs.

Zig-zag wall lattice in a nematic liquid crystal with an in-plane switching configuration.

Liquid crystals displays with tailoring electrodes exhibit complex spatiotemporal dynamics when a large voltage is applied. We report experimental observations of the appearance of a programmable zig-zag lattice using an in-plane-switching cell filled with a nematic liquid crystal. Applying a small voltage to a wide range of frequencies, the system exhibits an Ising wall lattice. Increasing the voltage, this lattice presents a spatial instability generating an undulating wall lattice, and to higher voltages it becomes zig-zag type. Experimentally, we characterize the bifurcations and phase diagram of the wall lattice. Theoretically, we develop, from first principles, a descriptive model. This model has a good qualitative agreement with experimental observations.

Polymer-encapsulated blue phase liquid crystal droplets

We have demonstrated polymer-encapsulated blue phase (PEBP) liquid crystal droplets in electro-optical films with in-plane electric field switching. The PEBP films are prepared via solvent evaporation-induced phase separation of a mixture of blue phase liquid crystal (BPLC) and polymer latex. The PEBP films, laminated between two indium–tin-oxide coated conductive substrates, enable switching between light-scattering and transparent states in response to electric fields applied across the film. The PEBP films also allow in-plane switching to induce birefringence between crossed polarizers at low switching voltage and with fast response time.

Enhanced electro-optical properties of vertically aligned in-plane-switching liquid crystal displays employing polymer networks

The electro-optical properties of vertically aligned in-plane switching (VA-IPS) liquid crystal (LC) cells are transformed by polymer networks. Three kinds of monomer materials are separately mixed with nematic E7 LC. The threshold voltage behavior reveals the strongest anchoring effect from the cross-linking TA-9164 polymer cell, which sustains good light transmittance at higher voltages and significantly improves the display responses. Without overdrive, the rising-time response of the TA-9164 polymer cell is comparable to that of the pure cell under overdrive. This paper demonstrates that a suitable monomer material applied to VA-IPS LC cells can boost their electro-optical performance.

Fast in-plane switching of negative liquid crystals using crossed patterned electrodes

We demonstrated fast in-plane switching (IPS) of negative liquid crystals by using crossed patterned electrodes. Switching to the bright state can be achieved by applying an in-plane field using the bottom patterned electrodes, whereas switching to the dark state can be obtained by applying an in-plane field using the top patterned electrodes. We obtained, experimentally, turn-off switching that was four times faster than that of the conventional IPS mode.

Switching Properties in Magnetic Tunnel Junctions With Interfacial Perpendicular Anisotropy: Micromagnetic Study

The role of universal memory can be successfully satisfied by magnetic tunnel junctions (MTJs) where the writing mechanism is based on spin-transfer torque (STT). An improvement in the switching properties (lower switching current density maintaining the thermal stability) has been achieved in MTJs with interfacial perpendicular anisotropy (IPA) at the interface between CoFeB and MgO. In this paper, micromagnetic simulations point out the influence of IPA and saturation magnetization (MS) on the properties of fast magnetization reversal achieved in 5, 10, and 20 ns. Both cases of in-plane and out-of-plane free layer are considered. In addition, the thermal effect is included for the in-plane switching at 20 ns and a complete analysis of energy dissipation during the switching is illustrated. This paper can provide useful information for the design of STT-based memories.

P‐114: A Liquid Crystal Mode with Combined Fringe and In‐Plane Switching Fields by Using a Bottom Floating Electrode

AbstractWe demonstrate a liquid crystal (LC) mode switched by combined fringe and in‐plane switching (IPS) fields, which are self‐adjusted by adopting a bottom floating electrode for enhanced electro‐optical properties. In our LC mode structure, conventional IPS electrodes are formed as pixel electrodes and common electrodes on an insulating layer, and floating electrodes that are patterned per the sub‐pixels are formed under the insulating layer. When the areas of the pixel and common electrodes are same, the voltage of the bottom floating electrode is spontaneously determined to be half the value of the pixel voltage, which ideally generates symmetric fringe fields with both pixel and common electrodes. Due to the in‐plane fields additionally generated between the pixel and common electrodes, the proposed LC structure shows higher transmittance than fringe‐field switching (FFS) and IPS LC modes. Transmittance of the conventional FFS and IPS LC modes is highly sensitive to the in‐plane electrode's width and spacing condition, but the proposed LC mode shows good transmittance without degradation under large variation condition of the in‐plane electrode's spacing‐to‐width ratio.

P‐57: Development of 5‐inch FHD IPS‐LCD Adopting New Pixel Structure Using Wall Electrodes

AbstractWe have developed a 5‐inch Full‐HD (FHD) in‐plane switching (IPS) liquid crystal display (LCD) adopting wall electrodes perpendicular to the substrate. The structure shields unnecessary electric fields from signal lines and adjacent pixel electrodes by a common electrode. The structure realizes a transmittance higher than conventional IPS‐LCDs by using a small wall electrode.

P‐132: Novel Pixel Design for Super‐Multi‐Domain Polymer Sustained Alignment LCD Technology

AbstractNew super‐multi‐domain polymer sustained alignment (PSA) liquid crystal displays are developed. Compared to the conventional approach, it has the merits of simpler structure, lower cost, and better transmittance. Moreover, premium picture quality with very little oblique gamma distortion and color shift like in‐plane switching (IPS) mode is obtained.

A hysteresis-free polymer-stabilised blue-phase liquid crystal

We report a polymer-stabilised blue-phase liquid crystal (BPLC) in an in-plane-switching (IPS) cell with negligible hysteresis and good stability. Long ultraviolet (UV) wavelength and top-side (no IPS electrode) exposure create uniform polymer network, which in turn helps to suppress hysteresis. The effect of photoinitiator is also investigated. Although a BPLC precursor without photoinitiator requires a higher UV dosage to stabilise the polymer network, it is favourable for keeping high resistivity and reducing image sticking.