Liquid-Crystal Medium for Low-Voltage IPS and FFS Displays
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Solution Overview
Problem
Existing liquid-crystal displays (LCDs) face challenges such as high operating voltage, long response times, low contrast, and inadequate stability under extreme conditions, particularly in mobile applications, due to the use of dielectrically negative liquid crystals.
Innovation Solution
Development of liquid-crystalline media comprising compounds with high dielectric constants parallel and perpendicular to the molecular director, combined with dielectrically positive and neutral compounds, to achieve low threshold voltage, short response times, and high stability, suitable for IPS and FFS displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid-crystalline media with high elastic constants are used to reduce scattering and improve black state representation, then contrast is improved, but rotational viscosity increases leading to longer response times
Solution Approach 1:
The patent modifies the chemical structure of liquid crystal compounds by introducing specific substituents (fluorine atoms, cyano groups, alkoxy chains) to adjust dielectric anisotropy and elastic constants, achieving optimized response times while maintaining good black state representation
Solution Approach 2:
The patent uses multi-component liquid crystal mixtures combining compounds with different properties (some with high elastic constants for good black state, others with low rotational viscosity for fast response), achieving a balanced performance that resolves the contradiction between contrast and response time
2Illumination intensity
If dielectrically negative liquid crystals are used to increase transmission in FFS displays, then brightness is improved, but operation voltage increases
Solution Approach 1:
The patent carefully adjusts dielectric anisotropy to a specific positive range (0.5 ≤ Δε ≤ 10) that enables low operating voltage while maintaining high transmission through optimized interaction with the fringe field in FFS displays
Solution Approach 2:
The patent optimizes local dielectric properties by selecting compounds with specific molecular structures that create favorable electric field distributions in the fringe field switching region, achieving high transmission without requiring high voltages
3Illumination intensity
If liquid-crystalline media with high dielectric constant perpendicular to director are used to improve contrast through higher transmittance, then transmission is improved, but dielectric anisotropy increases leading to higher operation voltage
Solution Approach 1:
The patent optimizes the ratio ε⊥/Δε to a specific range (5 ≤ ε⊥/Δε ≤ 20) that simultaneously achieves high transmittance and low operating voltage by balancing the perpendicular dielectric constant with dielectric anisotropy
4Loss of time
If liquid-crystalline media are used to improve response times through low rotational viscosity, then response time is improved, but contrast may deteriorate
Solution Approach 1:
The patent selects compounds with specific molecular structures (long alkyl chains, rigid mesogenic groups) that provide low rotational viscosity for fast response while maintaining appropriate elastic constants and scattering properties for good contrast
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 LCDs with improved transmission, contrast, and stability under extreme conditions, while maintaining high specific resistance and broad operational temperature range, suitable for various display applications including mobile devices.
Implementation Method 1
dielectrically positive liquid crystals, which comprise one or more compounds having at the same time a high dielectric constant parallel to the molecular director and perpendicular to the molecular director, leading to a large average dielectric constant and a high dielectric ratio and, preferably, to a relatively small dielectric anisotropy at the same time
Implementation Method 2
The liquid crystalline media are distinguished by a particularly good representation of the black state, primarily attributable to their very low scattering. This in turn is brought about especially by their high elastic constants
Implementation Method 3
High elastic constants may lead to higher values of the rotational viscosity (γ1), too. And consequently to higher values of the ratio γ1/k22 of the rotational viscosity (γ1) to the elastic constant for the twist deformation (k22), which then leads to higher response times
Data Source
AI summary
A liquid-crystalline medium, preferably having a nematic phase, comprising one or more compounds of formula Cthe use thereof in an energy-efficient electro-optical display, particularly in an active-matrix display based on the IPS or FFS effect, displays of this type which contain a liquid-crystalline medium of this type, and the use of the compounds of formula C for improvement of the contrast and/or response times of a liquid-crystalline medium which comprises one or more additional mesogenic compounds.