FFS Liquid Crystal Display Negative Dielectric Anisotropy
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Solution Overview
Problem
Current liquid crystal display devices using n-type compositions for FFS mode struggle with achieving optimal dielectric anisotropy, viscosity, and nematic phase-isotropic liquid phase transition temperature, which affects display properties such as transmittance and response speed.
Innovation Solution
A liquid crystal composition with specific compounds having negative dielectric anisotropy, a nematic phase-isotropic liquid phase transition temperature of 60° C. or higher, and a refractive index anisotropy of 0.08 to 0.13, combined with alignment films inducing homogeneous alignment, is used in a structure with a fringing field to maintain parallel liquid crystal molecule alignment, enhancing transmittance and response speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a p-type liquid crystal composition with positive dielectric anisotropy is used in FFS mode, then the voltage can be easily decreased, but the major axis of liquid crystal molecules near the pixel electrode inclines along the fringing field, degrading transmittance
Solution Approach 1:
The patent inverts the conventional approach by using an n-type liquid crystal composition with negative dielectric anisotropy instead of the traditional p-type material. This inversion causes the liquid crystal molecules to align perpendicular to the fringing field rather than parallel, preventing the inclination that degrades transmittance while still enabling voltage reduction for lower power consumption.
Solution Approach 2:
The patent changes the dielectric anisotropy parameter from positive to negative by selecting n-type liquid crystal materials. This parameter change fundamentally alters the molecular response to the fringing field, allowing the major axis to remain perpendicular to the substrate and parallel to the alignment direction, thereby maintaining high transmittance while achieving low voltage operation.
2Illumination intensity
If an n-type liquid crystal composition is used to maintain parallel molecular alignment and high transmittance, then the polarization direction is along the minor axis, but it is difficult to predict performance regarding image sticking and drop marks due to differences from VA mode
Solution Approach 1:
The patent applies local quality by optimizing specific parameters of the n-type liquid crystal composition for FFS mode requirements. The composition is formulated with specific dielectric anisotropy (Δε = -2.0 to -4.0), refractive index anisotropy (Δn = 0.08 to 0.13), and viscosity characteristics that are locally tailored to FFS mode operation, ensuring both high transmittance and reliability by preventing display defects through appropriate material properties.
Solution Approach 2:
The patent incorporates feedback by carefully selecting liquid crystal compounds with specific physical properties that provide stable performance. The composition includes compounds with controlled molecular structures and properties that feedback to maintain consistent alignment and prevent defects like image sticking and drop marks, ensuring reliable operation in FFS mode displays.
3Reliability
If a liquid crystal composition optimized for VA mode is used, then the alignment and electric field characteristics match VA requirements, but it does not provide optimal performance for FFS mode due to differences in alignment direction, electric field direction, and optical properties
Solution Approach 1:
The patent changes multiple parameters simultaneously to optimize for FFS mode: dielectric anisotropy (negative value), refractive index anisotropy (specific range), and viscosity. These parameter changes transform the liquid crystal composition from VA mode optimization to FFS mode optimization, enabling both alignment stability and superior display performance including high transmittance and fast response in the FFS configuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in high-speed response, reduced display defects, and improved display properties for FFS mode liquid crystal display devices, suitable for applications like liquid crystal TVs and monitors.
Implementation Method 1
a liquid crystal composition having a negative dielectric anisotropy... the polarization direction of the n-type liquid crystal composition is a minor-axis direction of the molecules. As a result, the parallel arrangement of the molecule major axes is maintained
Implementation Method 2
an interelectrode distance R between the pixel electrode and the common electrode is smaller than a distance G between the first substrate and the second substrate so that a fringing field is formed between the pixel electrode and the common electrode
Implementation Method 3
alignment films that induce homogeneous alignment and are disposed between the liquid crystal layer and the first substrate and between the liquid crystal layer and the second substrate
Data Source
AI summary
The present invention provides an FFS mode liquid crystal display device that uses a liquid crystal composition which has a negative dielectric anisotropy and can achieve good display properties by being used for FFS mode liquid crystal display devices without degrading the image sticking property of display devices and various properties of liquid crystal display devices, such as dielectric anisotropy, viscosity, nematic phase upper limit temperature, low-temperature nematic phase stability, and γ1. The liquid crystal composition contains at least one compound selected from the group of compounds represented by general formula (I) below and at least one compound selected from the group of compounds represented by general formula (II) below.