Liquid-Crystal Medium for FFS and IPS Displays
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Solution Overview
Problem
Current liquid-crystal compositions for FFS and IPS displays suffer from long addressing times, inadequate resistivity, high operating voltages, and poor low-temperature stability, while also requiring high energy consumption and having limited shelf life, which hinders their performance in achieving high contrast ratios and fast response times.
Innovation Solution
A liquid-crystal medium with positive dielectric anisotropy, comprising specific compounds that balance dielectric constants and rotational viscosities, along with stabilizers, to enhance stability and response times, thereby improving the performance of FFS, HB-FFS, and IPS displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional liquid-crystal compositions are used in FFS and IPS displays, then the displays can operate, but they suffer from long addressing times and slow response times
Solution Approach 1:
The patent modifies the physical and chemical parameters of the liquid-crystal composition by selecting compounds with specific molecular structures (cyclic compounds with particular ratios of polar to non-polar groups) and controlling composition ratios to achieve optimal dielectric anisotropy and rotational viscosity values, thereby resolving the contradiction between addressing time and response time performance
Solution Approach 2:
The patent creates a composite liquid-crystal medium by combining multiple cyclic compounds (first, second, and third cyclic compounds) with specific structural characteristics in defined ratio ranges, where each component contributes different properties that collectively achieve both fast addressing and reliable response times
2Power
If conventional liquid-crystal compositions are used, then the displays can function, but they require excessively high operating voltages
Solution Approach 1:
The patent changes the dielectric parameters of the liquid-crystal composition by selecting compounds with high dielectric anisotropy and optimizing composition ratios, which reduces the threshold voltage and operating voltage requirements while maintaining display functionality, thereby resolving the contradiction between power requirements and ease of operation
Solution Approach 2:
The patent adopts molecular structures from high-performance liquid crystals (such as cyclic compounds with oxygen-containing groups) and replicates their beneficial electrical properties in the new composition, achieving low operating voltage characteristics without sacrificing other performance aspects
3Reliability
If conventional liquid-crystal compositions are used, then the displays can operate, but they have inadequate resistivity and poor low-temperature stability
Solution Approach 1:
The patent creates a composite formulation combining cyclic compounds with specific functional groups (carboxyl, hydroxyl, amino groups) in controlled ratios, where the synergistic interaction between components provides both high resistivity and maintained operational stability across a wide temperature range from -30°C to +80°C
Solution Approach 2:
The patent introduces compounds with specific local molecular characteristics (polar groups at particular positions in cyclic structures) that locally enhance resistivity and temperature stability properties, allowing the overall composition to maintain reliability while adapting to different temperature conditions
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 medium achieves high brightness, transmittance, and contrast ratios with fast addressing times and improved stability at both low and high temperatures, reducing rotational viscosity and enhancing reliability, particularly when used in active-matrix displays.
Implementation Method 1
Liquid-crystalline materials for IPS displays of this type are described, for example, in DE 195 28 104. Furthermore, so-called 'fringe-field switching' (FFS) displays have been reported... which contain two electrodes on the same substrate... A strong, so-called 'fringe field' is thereby generated, i.e. a strong electric field close to the edge of the electrodes, and, throughout the cell, an electric field which has both a strong vertical component and also a strong horizontal component.
Implementation Method 2
Liquid-crystal compositions which are suitable for LCDs and especially for FFS and IPS displays are known from, for example, JP 07-181 439 (A), EP 0 667 555, EP 0 673 986, DE 195 09 410, DE 195 28 106, DE 195 28 107, WO 96/23 851 and WO 96/28 521. However, these compositions have certain disadvantages. Amongst other deficiencies, most of them result in disadvantageously long addressing times...
Data Source
AI summary
The present invention relates to liquid-crystalline (LC) media having positive dielectric anisotropy and to liquid-crystal displays (LCDs) containing these media, especially to displays addressed by an active matrix and in particular to LC displays of the TN, PS-TN, STN, TN-TFT, OCB, IPS, PS-IPS, FFS, HB-FFS PS-FFS, SA-HB-FFS, polymer stabilised SA-HB-FFS, positive VA or positive PS-VA type.