Mirror Cell Reflective Wavelength Band Expansion

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Solution Overview

Problem

Current display devices with mirror cells struggle to expand the reflection wavelength band effectively, leading to limited color gamut and increased complexity in achieving both reflective and transmissive modes.

Innovation Solution

Incorporating a reactive liquid crystal layer between the alignment films in a mirror cell, which includes cholesteric liquid crystals and reactive liquid crystals, allows for the expansion of the reflection wavelength band by varying the pitch of the cholesteric liquid crystals through UV curing, enabling the reflection of all visible wavelengths in a single layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If multiple cholesteric liquid crystal layers with different pitches are stacked to expand the reflection wavelength band, then the reflection wavelength band is expanded, but the device complexity and number of layers increase

Engineering Contradiction:

Improvereflection wavelength bandVSAvoidnumber of liquid crystal layers

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The liquid crystal layer is segmented into multiple regions with different pitch values (first region with pitch P1, second region with pitch P2, third region with pitch P3). This spatial segmentation allows different wavelength bands to be reflected simultaneously within a single layer, avoiding the need to stack multiple layers while still achieving broadband reflection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the liquid crystal layer are assigned different local pitch characteristics. The first region has pitch P1 for reflecting a specific wavelength band, the second region has pitch P2 for another wavelength band, and the third region has pitch P3 for a third wavelength band. This local quality variation enables a single layer to perform the function previously requiring multiple stacked layers.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If a gradient pitch structure is used to broaden the reflection band, then the reflection wavelength range is expanded, but the manufacturing precision requirements increase

Engineering Contradiction:

Improvereflection wavelength rangeVSAvoidpitch control precision

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

Instead of implementing a continuous gradient pitch structure that would require precise control of pitch variation across the entire layer, the invention segments the pitch into discrete values (P1, P2, P3) in different regions. This segmentation simplifies the manufacturing process by reducing the precision requirements for pitch control while still achieving broadband reflection through the combination of multiple discrete pitch regions.

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If conventional liquid crystal cells are used for both reflective and transmissive modes, then the display device can switch modes, but the structure becomes complex and driving voltage increases

Engineering Contradiction:

Improvereflective and transmissive mode switchingVSAvoidmirror cell structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The liquid crystal layer with multiple pitch regions is designed to perform multiple functions simultaneously. By controlling the orientation of liquid crystal molecules in different regions, the same layer can reflect light in mirror mode or transmit light in display mode, eliminating the need for separate structures for each mode and reducing overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 solution simplifies the mirror cell structure, reduces driving voltage and production costs, and achieves a thin form factor by diversifying the pitch of cholesteric liquid crystals, thereby enhancing the light reflection wavelength band and maintaining neutral reflection colors.

Implementation Method 1

the cholesteric liquid crystal has been used in reflective display devices... the wavelength of the light to be reflected is expressed as a product of the average refractive index of liquid crystals and the pitch of cholesteric liquid crystals

Methodology Applied

Scientific EffectCholesteric liquid crystal reflection: Cholesteric Liquid Crystal

Implementation Method 2

Methodology Applied

Scientific EffectPhoto polymerization: Photopolymerisation

Data Source

PatentUS10824033B2Mirror cell and display device comprising the same

Publication Date: 2020.11.03 LG DISPLAY CO LTD

AI summary

A mirror cell and a display device are disclosed. The mirror cell includes a lower substrate, which includes a lower alignment film and a lower electrode, an upper substrate, which opposes the lower substrate and includes an upper alignment film and an upper electrode, a liquid crystal layer, which is disposed between the lower alignment film and the upper alignment film and includes a cholesteric liquid crystal and a reactive liquid crystal, and a reactive layer, which is disposed between the upper alignment film and the liquid crystal layer and includes a same kind of reactive liquid crystals as the reactive liquid crystal in the liquid crystal layer.