Polymer-Stabilized TN LCD Fast Response via Voltage Control
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Solution Overview
Problem
Current LCD technologies face challenges in achieving fast response times while maintaining a 90° TN LC director configuration, high transmittance, and low driving voltage, as existing modes like TN, MVA, and IPS struggle with high driving voltage and low contrast ratios when trying to reduce response time.
Innovation Solution
A polymer-stabilized twisted nematic (PS-TN) LCD method involving a chiral dopant to induce a short helical pitch, followed by voltage application to reduce the twist angle to 90° and subsequent polymerization of mesogenic compounds to stabilize the configuration, using a small amount of polymerizable mesogenic compounds in the LC medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a short helical pitch is achieved by doping with chiral nematic LC material, then the decay response time is reduced, but the 270° super-twisted nematic configuration becomes energetically more stable than the 90° TN configuration
Solution Approach 1:
The patent applies parameter changes by carefully controlling the d/p ratio (cell gap to helical pitch ratio) to be within the range 0.4-0.6, and by adjusting the twist angle to 90° through voltage application. This parameter optimization allows the system to maintain the desired 90° TN configuration while achieving fast response times, preventing the spontaneous transformation to the 270° STN configuration.
Solution Approach 2:
The patent employs preliminary action by applying an electric voltage before polymerization to reduce the twist angle from the natural 270° STN configuration to the desired 90° TN configuration. This preliminary voltage application stabilizes the metastable 90° TN state before the polymer network forms, ensuring the correct configuration is locked in during subsequent polymerization.
2Loss of time
If polymer stabilization is applied to maintain 90° TN configuration, then fast response time is achieved, but transmittance and contrast ratio decrease and driving voltage increases
Solution Approach 1:
The patent optimizes the polymer concentration parameter to a specific range of 0.01-0.1 wt% and controls the polymerization degree to achieve optimal performance. This parameter optimization allows the polymer network to provide sufficient stabilization for fast response times while minimizing negative impacts on transmittance and contrast ratio, and maintaining acceptable driving voltage levels.
Solution Approach 2:
The patent applies partial action by using a small amount of polymer (0.01-0.1 wt%) rather than full polymerization. This partial polymerization provides sufficient stabilization to maintain the 90° TN configuration and achieve fast response times, while avoiding the excessive polymer content that would cause severe degradation in transmittance and contrast ratio.
3Speed
If d/p ratio is increased to maintain TN configuration, then fast switching time is enabled, but the 270° STN configuration becomes energetically more stable
Solution Approach 1:
The patent optimizes the d/p ratio parameter to a specific range of 0.4-0.6, which is lower than the conventional 0.5 threshold. This optimized parameter range allows the system to maintain the 90° TN configuration stability while enabling fast switching times, preventing the spontaneous transformation to the 270° STN configuration through careful parameter control.
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 approach enables fast response times, high transmittance, and low driving voltage while maintaining a 90° TN LC director configuration, overcoming the limitations of previous TN and PS-TN LCDs by stabilizing the twisted nematic configuration with polymerization, resulting in improved performance metrics.
Implementation Method 1
The LC medium is doped with a chiral nematic LC material such that a shorter helical pitch (p) of the twisted nematic LC molecules is achieved
Implementation Method 2
the 270° STN configuration can be changed to the 90° TN configuration by applying an electric voltage
Implementation Method 3
the 90° TN configuration can then be stabilized by photopolymerization, e.g. by formation of a polymer network in the LC medium
Data Source
AI summary
The present invention relates to a method of manufacturing a liquid crystal display (LCD) of the polymer stabilized ultra fast (PS-UF) twisted nematic (TN) mode, to an LCD obtained by this method and to an LC medium used therein.