Bistable Twisted Nematic Liquid Crystal Display with Dual Frequency Operation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bistable twisted nematic liquid crystal displays (LCDs) with 180-degree twist states are difficult to switch and require strong asymmetric anchoring and thin cell gaps, making them less efficient compared to 360-degree twist state displays.
Innovation Solution
A bistable liquid crystal device with asymmetric alignment layers and dual frequency liquid crystals, where the pretilt angles and anchoring energies on both substrates are carefully controlled to achieve equal stability in twist states, allowing for easier switching and a simpler driving scheme, even with larger cell gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If strong asymmetric anchoring and thin cell gaps are used to achieve bistability in 180-degree twisted nematic LCD, then bistability is achieved, but switching becomes difficult and device complexity increases
Solution Approach 1:
The patent changes the cell gap parameter from thin (required for Dozov π-BTN) to thick (greater than 2 μm), and adjusts the pretilt angles and anchoring energies to compensate, enabling bistability without strong asymmetric anchoring and thin cell gaps, thus improving switching ease
Solution Approach 2:
The patent uses asymmetric alignment layers with different pretilt angles (θ1 and θ2) on the two substrates to create the necessary asymmetry in the liquid crystal cell, allowing bistability to be achieved with relaxed cell gap requirements and improved switching characteristics
2Stability of the object's composition
If thin cell gaps are used to achieve bistability in twisted nematic LCD, then bistability is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the cell gap from thin (requiring high precision) to thick (greater than 2 μm, easier to manufacture), and adjusts other parameters (pretilt angles, anchoring energies) to maintain bistability, thereby reducing manufacturing precision requirements
3Ease of operation
If dual frequency liquid crystals are used with asymmetric alignment layers, then switching ease is improved and cell gap can be larger, but device complexity increases
Solution Approach 1:
The patent uses dual frequency liquid crystals that change their dielectric anisotropy sign based on the driving frequency, allowing the same physical structure to be controlled by dynamic frequency adjustment, which simplifies the driving scheme compared to requiring complex asymmetric anchoring structures
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 enables easy switching between low and high twist states with a simpler driving scheme and allows for larger cell gaps, improving the bistability and optical properties of the LCD, while maintaining equal stability in both states under no voltage bias.
Implementation Method 1
Both classes of bistable liquid crystal displays are based on the twisted nematic effect in a liquid crystal display. They are based on the interplay between the elasticity of the liquid crystal and the surface anchoring conditions.
Implementation Method 2
They are based on the interplay between the elasticity of the liquid crystal and the surface anchoring conditions.
Implementation Method 3
The first alignment layer induces a pretilt angle θ1 between the liquid crystal layer in contact with the first alignment layer. The second alignment layer induces a second pretilt angle θ2 between the liquid crystal layer in contact with the second alignment layer.
Implementation Method 4
The liquid crystal layer is of the dual frequency type. It has a positive dielectric anisotropy when the driving voltage is a low frequency AC signal of sinusoidal or pulsed type. It has a negative dielectric anisotropy when the driving voltage is a high frequency AC signal of sinusoidal or pulsed type.
Data Source
AI summary
The invention provides a bistable twisted nematic liquid crystal display, comprising a first substrate having thereon a first conductive layer and a first alignment layer; a second substrate having thereon a second conductive layer and a second alignment layer; a liquid crystal layer in the first and second alignment layers; an alignment layer on each of the substrates, the alignment layer imparting a preferred direction for liquid crystal molecules near the alignment layer, and possessing different azimuthal and polar anchoring energies when used to align a liquid crystal layer: the alignment layers being rubbed in such a way to give a stable twist angle of the liquid crystal of φ where φ can be any value in between −45° to +45°; and wherein the d/p ratio of the liquid crystal layer is between the values of 0.15+0.5φ/π and 0.35+0.5φ/π.