Liquid Crystal Display Alignment Film Thickness Optimization
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Solution Overview
Problem
Lateral electric field liquid crystal display devices face issues with non-uniform alignment film formation due to step differences on substrates, leading to reduced alignment regulating force and increased display burn-in, particularly in fringe-field switching systems where the rubbing process is non-uniform and productivity is low.
Innovation Solution
A liquid crystal display device design where the alignment film thickness is greater than the electrodes contacting it, ensuring uniformity and flatness, thereby reducing step differences and enhancing the alignment regulating force, which minimizes display burn-in by maintaining sufficient alignment even with charge storage along electric field paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a rubbing process is used to form an alignment film on electrodes with fine step differences, then the alignment film can be formed, but the rubbing process becomes non-uniform causing light leakage and decreased alignment regulating force
Solution Approach 1:
The patent replaces the mechanical rubbing process with an optical alignment process using polarized ultraviolet rays. This substitution eliminates the non-uniform rubbing caused by step differences on the electrode surface, as the optical process is not affected by surface topology. The alignment film is formed uniformly across the entire surface including step difference portions through photoalignment, resolving the contradiction between achieving alignment film formation and maintaining uniformity with sufficient regulating force.
2Manufacturing precision
If an optical alignment process is used to form an alignment film, then uniform alignment can be achieved, but the alignment regulating force becomes small and productivity decreases
Solution Approach 1:
The patent optimizes the thickness parameter of the alignment film to be larger than that of the electrodes, which enhances the alignment regulating force while maintaining the uniformity achieved through optical alignment. Additionally, the refractive index of the alignment film is designed to be higher than that of the liquid crystal, which strengthens the alignment effect. These parameter changes resolve the contradiction by making the optical alignment process produce an alignment film with sufficient regulating force.
3Ease of manufacture
If the alignment film thickness is smaller than the electrode thickness, then the electrode structure is maintained, but step differences cause non-uniform alignment and display burn-in
Solution Approach 1:
The patent addresses the step difference problem by extending the alignment film thickness into the vertical dimension, making it thicker than the electrode thickness. This dimensional change allows the alignment film to bridge over the step differences created by the electrode structure, providing a uniform alignment surface across the entire electrode area. The alignment film effectively levels the surface topology, preventing display burn-in while maintaining ease of electrode fabrication.
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 effectively reduces display burn-in and improves image quality by ensuring a uniform alignment film with sufficient regulating force, even when charges are stored near the electric field paths, maintaining image clarity and reducing alignment failures.
Implementation Method 1
an alignment film is formed by coating an organic material such as polyimide on one electrode and performing a rubbing process of rubbing the organic material with a rubbing cloth
Implementation Method 2
In this alignment process, polarized ultraviolet rays are irradiated onto the surface of the optical reactive polyimide such that an alignment direction according to polarization is formed
Implementation Method 3
a system for generating an electric field in a liquid crystal layer toward a substrate direction and controlling alignment of liquid crystal molecules (hereinafter, referred to as a lateral electric field system)
Data Source
AI summary
Disclosed herein is a liquid crystal display device in which a plurality of electrodes is provided on one of a plurality of substrates with a liquid crystal layer interposed therebetween and liquid crystal molecules configuring the liquid crystal layer are driven by an electric field generated between the pair of electrodes, wherein the one substrate has an alignment film which contacts the liquid crystal layer to regulate an alignment direction of the liquid crystal molecules and is provided so as to cover at least one of the pair of electrodes, and wherein the thickness of the alignment film is larger than that of at least one of the electrodes contacting the alignment film.