The polymer-stabilized vertically aligned (PS-VA) liquid crystal display (LCD) driving mode has high potential for manufacturing low power consuming displays due to the higher transmittance and fast response as compared with the existing patterned vertically aligned and multi-domain vertically aligned modes. In this paper we have investigated the reaction mechanisms of monomer?liquid crystal blends to form a surface pre-tilt angle of liquid crystal in vertical alignment LCD associated with a fishbone electrode structure. The observed sizes of polymer bumps formed on the substrates were found to be dependent on the exposed UV wavelength and were almost equal in both top and bottom substrates. When a large UV wavelength was used, the phase separation mechanism of monomer in PS-VA mode was found nearly isotropic rather than anisotropic in contrast to the previous studies.

https://iopscience.iop.org/article/10.1088/0022-3727/44/32/325104/pdf

Phase separation of monomer in liquid crystal mixtures and surface morphology in polymer-stabilized vertical alignment liquid crystal displays

A comparative study of the electrical characteristics and device instabilities in InGaZnO thin-film transistors (IGZO-TFTs) with four different high-k gate dielectrics (Al2O3, HfO2, Ta2O5, and ZrO2) has been conducted. High-k gate dielectrics have a sufficiently low leakage current for the gate insulator of IGZO-TFTs and ZrO2 has the highest dielectric constant, followed by Ta2O5, HfO2, and Al2O3. However, the charge trapping in high-k gate dielectrics induced the bias stress instability and degradation of IGZO-TFTs over time. In particular, the positive bias stress (PBS) and positive bias temperature stress (PBTS) caused a large positive threshold voltage (Vth) variation due to electron trapping, while the negative bias stress (NBS) and negative bias temperature stress (NBTS) brought about a much smaller Vth shift. In particular, the Al2O3 and HfO2 gate insulators have significant threshold voltage shifts for the PBS and PBTS measurements. Among the four different high-k gate dielectrics, ZrO2 is the most promising high-k gate dielectric for the IGZO-TFTs because of its high dielectric constant, low subthreshold swing, high mobility, large drive current, small hysteresis, and high on/off current ratio.

https://iopscience.iop.org/article/10.7567/JJAP.52.06GE05/pdf

Comparative Study of Device Performance and Reliability in Amorphous InGaZnO Thin-Film Transistors with Various High-k Gate Dielectrics

An innovative liquid crystal display (LCD), incorporating in-plane switching mechanism with LC nanoencapsulation, is developed and its electro-optic (EO) performances are characterized. The nanoencapsulated LCDs exhibit electric-field induced transitions from an optically-isotropic state to an anisotropic one based on Kerr effect. Extremely small size of LC droplets embedded in the nanoencapsulated layer, less than a quarter of wavelength of incident light, appear transparent in the voltage-off state and gradually becomes birefringent in response to applied voltage, exhibiting the optical behavior of uniaxial retarder. Due to optically-isotropic nature and a large Kerr effect, they show wide viewing angle characteristics and good EO performances.

/pdf/optically-isotropic-nanoencapsulated-liquid-crystal-displays-42dsic8dfe.pdf

Optically-isotropic nanoencapsulated liquid crystal displays based on Kerr effect.

The majority of electro-optical devices use transparent conductive oxide (TCO) electrodes such as indium tin oxide (ITO) in their structure. In this study, we manufactured aluminum zinc oxide (AZO) and gallium zinc oxide (GZO) TCO films on glass substrates and demonstrate suitability of these materials for application as transparent electrodes of liquid crystal displays (LCD). We have established a deposition process for the fabrication of AZO and GZO coated glass substrates with average transmittance of 93% and 92% in the visible spectrum, and the sheet resistivity without annealing of ∼120 Ω/□. Using photolithographic patterning and wet etching of AZO and GZO films, we have successfully fabricated laboratory prototypes of twisted nematic, vertical alignment, in-plane switching, and fringe-field switching LCDs. The electro-optical performance of AZO and GZO prototypes is comparable to those of the ITO prototypes of identical design. The AZO and GZO have demonstrated great potential to compete with ITO as low-cost TCOs for display applications. Our findings validated by numerical analyses will be useful for the development of TCOs alternative for display and other optical or electro-optical applications.

High-Performance and Low-Cost Aluminum Zinc Oxide and Gallium Zinc Oxide Electrodes for Liquid Crystal Displays

A device for operating viewing angle-switchable liquid crystal displays has been developed based on an optically isotropic liquid crystal (OILC). The device comprises two panels, main and switching. Depending upon the voltage applied, the optical state of the OILC layer in the switching panel can be changed to the anisotropic uniaxial state, taking on the role of a positive C film. In this manner luminance at oblique polar angles can be suppressed, resulting in a dark image at an off-normal axis, at the same time retaining good image quality in the normal direction. Depending on the switching of the OILC layer, wide or narrow angles of viewing can be obtained.

Luminance-controlled viewing angle-switchable liquid crystal display using optically isotropic liquid crystal layer

The light efficiency of the homogeneously aligned liquid crystal (LC) mode driven by fringe electric fields depends on the magnitude of the dielectric anisotropy when using a LC with positive dielectric anisotropy. However, this dependency is not observed when using a LC with negative dielectric anisotropy. This difference is mainly associated with the molecular reorientation especially in the tilt angle of the LC between the edges and the centers of the pixel electrodes in the voltage-on state. This paper explores the dependence of the light efficiency of the device on the magnitude of the dielectric anisotropy of the LC for both types of the LCs as functions of other cell parameters such as the rubbing angle and the cell gap.

Light efficiency of the fringe-field switching mode depending on magnitude of dielectric anisotropy of liquid crystal associated with cell gap and rubbing angle

Colour tracking behaviour is observed in most liquid crystal displays. In in-plane switching and vertical alignment devices, the colour chromaticity in the normal direction changes linearly from bluish- to yellowish-white as the grey level is increased from the dark to white state. Interestingly, abnormal behaviour in colour tracking is observed in fringe-field switching devices using a liquid crystal with positive dielectric anisotropy, such that the colour chromaticity changes from bluish to yellowish up to a certain grey level, then turns around and becomes bluish-white as the grey level is further increased to the fully white state. According to our theoretical and experimental results, this ‘turn around’ effect in the colour tracking of the fringe-field switching mode is associated with the generation of a tilt angle of the liquid crystal molecules with increasing voltage in the electrode position where the light modulation is associated with the polarisation rotation.

Abnormal behaviour in colour tracking characteristics of the fringe-field switching liquid crystal display

This paper focuses on optimization of electrode shape in polymerstabilized blue phase or nanostructured liquid crystal composites to lower operating voltage and improve light efficiency. The electrode with taper angle of reverse elliptic shape decreases operating voltage by 18.9% and improves transmittance by 29.8% compared to that in conventional electrode structure. Additionally, the performance of the device such as contrast ratio and viewing angle characteristic is improved.

13.2: Optimization of Electrode Shapes for High Performance Optically Isotropic Liquid Crystal Display

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Light efficiency of the fringe-field switching mode depending on magnitude of dielectric anisotropy of liquid crystal associated with cell gap and rubbing angle

Abnormal behaviour in colour tracking characteristics of the fringe-field switching liquid crystal display

13.2: Optimization of Electrode Shapes for High Performance Optically Isotropic Liquid Crystal Display