Twisted-Nematic LCD Optical Compensation Films
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Solution Overview
Problem
Normally-white twisted-nematic-mode LCD devices face challenges in achieving a high contrast ratio and wide viewing angle due to residual retardation in the LC layer, especially when displaying black color, as the LC molecules near the interfaces cannot be tilted effectively by the applied voltage, leading to insufficient compensation by retardation films.
Innovation Solution
The configuration includes first and second optical compensation films with their optical axes parallel to the equivalent refractive index ellipsoids of the residual retardation at the interfaces, allowing effective compensation of residual retardation and improving the contrast ratio and viewing angle, particularly by aligning the optical axes of the compensation films with the longer axes of the refractive index ellipsoids projected onto the substrate surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If retardation films are used to compensate for refractive index anisotropy, then viewing angle characteristic is improved, but residual retardation at interfaces remains uncompensated
Solution Approach 1:
The patent divides the optical compensation function into two parts: retardation films for the bulk LC layer and optical compensation films with negative uniaxial optical characteristics for the interface regions. This segmentation allows each component to address specific zones, with the optical compensation films specifically targeting the residual retardation at interfaces that retardation films cannot compensate.
Solution Approach 2:
The optical compensation films act as intermediary elements between the polarization films and the LC layer, specifically addressing the residual retardation at the interfaces. These films have negative uniaxial optical characteristics that counterbalance the positive residual retardation caused by the orientation films, thereby improving contrast ratio without affecting the viewing angle compensation provided by the retardation films.
2Illumination intensity
If voltage is applied to tilt LC molecules for black color display, then contrast is improved, but LC molecules near interfaces cannot be tilted effectively
Solution Approach 1:
The patent converts the harmful effect of residual retardation at interfaces (caused by inability to tilt LC molecules near interfaces) into a beneficial configuration by introducing optical compensation films with negative uniaxial optical characteristics. These films are specifically oriented to counterbalance the residual retardation, transforming the interface defect into a controlled optical compensation mechanism that improves overall contrast ratio.
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
This configuration enhances the viewing angle characteristic to 80 degrees or more in the horizontal direction while maintaining a contrast ratio of 10:1 or above, effectively reducing light leakage in slanted viewing directions and improving the overall display performance.
Implementation Method 1
first and second optical compensation films, with their optical axes parallel to the equivalent refractive index ellipsoids of the residual retardation at the interfaces, allowing effective compensation of residual retardation
Implementation Method 2
aligning the optical axes of the compensation films with the longer axes of the refractive index ellipsoids projected onto the substrate surfaces
Implementation Method 3
LC molecules having a twisted angle of around 90 degrees, and the LC molecules are twisted by 90 degrees in the longer axis thereof from the first substrate to the second substrate
Implementation Method 4
the polarization axes thereof are disposed perpendicular to each other and thus the LCD device exhibits white color upon application of no electric field
Data Source
AI summary
A normally-white twisted-nematic mode LCD device includes a first optical compensation film between a light-incident-side polarization film and an LC cell, and a second optical compensation film between a light-emitting-side polarization film and the LC cell. The optical axis of the first (second) optical compensation film projected onto the substrate surface is substantially parallel to the longer axis of an equivalent refractive index ellipsoid of a residual retardation of the LC layer in the vicinity of a light-incident-side (light-emitting-side) substrate upon display of black color.