Liquid crystal display cell with fast response and continuous gray scale

• US 20110285928A1
• Filed: 05/18/2011
• Published: 11/24/2011
• Est. Priority Date: 05/18/2010
• Status: Active Grant

• Current Assignee: Hong Kong University of Science and Technology
• Original Assignee: Hong Kong University of Science and Technology
• Inventors: Murauski, Anatoli Alexandrovich, Pozhidaev, Evgeny Pavlovich, Chigrinov, Vladimir Grigorievich, Kwok, Hoi Sing
• Granted Patent: US 8,755,022 B2
• Time in Patent Office: Days
• US Class Current: 349/33
• CPC Class Codes: G02F 1/1416 Details of the smectic layer structure, e.g. bookshelf, chevron, C1 and C2
• CPC Class Codes: G02F 2203/34 Colour display without the use of colour mosaic filters

Abstract

The invention relates to liquid crystal display cells with fast response and continuous gray scale. The liquid crystal cell is based on a field-sequential color system (“FSC”) and comprises a chiral smectic liquid crystal whose helix pitch is less than thickness of liquid crystal layer placed between two polarizers, as well as a source of voltage applied to electrodes of the cell, wherein the amplitude of the applied voltage is less than the critical voltage amplitude of the helix unwinding. The liquid crystal has one steady state corresponding to twisted helix without applied voltage. In this case, the principal optical axis coincides with the helical axes, but deviates from steady state under the action of a driving voltage, providing thereby an electro-optical response of the display which exhibits gray scale in light transmission or reflection that is continuous, hysteretic-free and non-sensitive to the driving voltage polarity, if the steady orientation of the principle axes is parallel or perpendicular to the light polarization plane and the driving voltage frequency is between 10 Hz and 5 kHz. In embodiments with very short helix pitches, the cells may be free from selective reflection and diffraction in the visible spectral range. Different embodiments of the invention may use ferroelectric liquid crystal, ferroelectric liquid crystal, or antiferroelectric liquid crystal.

Claims

1. A liquid crystal display cell with fast response and continuous gray scale comprising:

a chiral smectic liquid crystal layer positioned between two substrates with a helix pitch that is less than the thickness of the liquid crystal layer;

at least one polarizer positioned outside of the substrates; and

a voltage source for applying a driving voltage to the liquid crystal display cell.

2. The liquid crystal display cell of claim 1, wherein the liquid crystal display cell is part of a field sequential color (FSC) liquid crystal display.

3. The liquid crystal display cell of claim 1, wherein the chiral smectic liquid crystal layer is ferroelectric liquid crystal layer of chiral smectic C* phase with helical structure has a pitch smaller than the thickness of the liquid crystal layer.

4. The liquid crystal display cell of claim 1, where the chiral smectic liquid crystal layer represents a ferrielectric liquid crystal of any chiral smectic phase with helical structure having a pitch smaller than a thickness of the liquid crystal layer.

5. The liquid crystal display cell of claim 1, where the chiral smectic liquid crystal layer represents an antiferroelectric liquid crystal of chiral smectic CA* phase with helical structure having a pitch smaller than a gap between the first and the second substrates.

6. A field sequential color display device of claim 2, where a source of R (red), G (green) and B (blue) colors of illuminating lights applied to pixels sequentially in time are light emitting diodes.

7. The liquid crystal display cell of claim 1, where the driving voltage is formed by a thin films transistors (TFT) matrix.

8. The liquid crystal display cell of claim 1, where the substrates are made of glass or plastic and covered with indium thin oxide (ITO) layers.

9. The liquid crystal display cell of claim 3, wherein the helix axes and the principle optical axes are parallel or perpendicular to the polarizer plane in the absence of an applied voltage.

10. The liquid crystal display cell of claim 4, wherein the helix axes and the principle optical axes are parallel or perpendicular to the polarizer plane in the absence of the applied voltage.

11. The liquid crystal display cell of claim 5, wherein the helix axes and the principle optical axes are parallel or perpendicular to the polarizer plane in the absence of the applied voltage.

12. The liquid crystal display cell of claim 1, wherein the liquid crystal cell further comprises at least one aligning layer, wherein the at least one aligning layer is one of the group comprising:

a photo-alignment layer, a rubbed polyimide layer, and an aligning layer formed by oblique evaporation.

13. The liquid crystal display cell of claim 1, wherein the liquid crystal cell comprises two polarizers, wherein the two polarizers are crossed.

14. The liquid crystal display cell of claim 1, wherein the liquid crystal cell is reflective and only one polarizer is used.

15. The liquid crystal display cell of claim 1, wherein the driving voltage comprises voltage pulses.

16. The liquid crystal display cell of claim 1, wherein the driving voltage comprises symmetric rectangular alternative sign voltage pulses.