Vertically aligned liquid crystal displays and methods for...

Details Vertically aligned liquid crystal displays and methods for... Vertically aligned liquid crystal displays and methods for...

1998-11-03

2003-02-11

Sikes, William L. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S123000

Reexamination Certificate

active

06519018

ABSTRACT:

TECHNICAL FIELD
The field of this invention is liquid crystal displays.
BACKGROUND OF THE INVENTION
Liquid crystal displays find use in a variety of different applications, such as data displays in watches, calculators and the like, as well as in flat panel displays found in laptop or notebook computers. Liquid crystal displays offer many advantages over alternative technologies, e.g. cathode ray tube based displays, where such advantages include: low power consumption, small size, light weight, and the like. As such, it is believed by many that liquid crystal displays will find wide-spread use in an even larger number of different applications than those in which they currently find use, where it is envisioned that liquid crystal displays will eventually become standard features in desktop computer monitors, televisions, etc.
In typical flat panel displays currently found in many laptop computers, the picture on the screen of the display is composed of many pixels. In each pixel the desired color is created by “mixing” blue, green and red primary colors of different intensities by means of a patterned color filter. The intensity of each color is adjusted by using liquid crystals to change the transmitted light intensity. The liquid crystal (LC) is composed of rod-like molecules which prefer to point in the long direction of the rods. In the most common, so called “twisted nematic” displays, a nematic LC is filled into the gap, a few microns wide, between two polyimide films coated onto indium-tin-oxide (ITO) electrodes which, in turn, are deposited onto two glass-plate polarizers. In order for the display to work, the LC molecules have to be anchored down nearly parallel to the surfaces of the polyimide films such that on opposite sides they point into the perpendicular directions of the two crossed polarizers. The LC molecules thus form a twisted helix from one side to the other in the display. When light traverses such a structure it is polarized by the first polarizer along the long axis of the LC molecules anchored to it. As the light progresses through the LC the polarization of the light changes from linear to elliptical so that part of the light is transmitted by the second, perpendicular polarizer. Since the light transmission depends on the orientation of the LC rods it can be changed by rotation perpendicular to the long axis of the rods. This is accomplished by application of a small voltage, pixel by pixel, by means of microscopic (ITO) electrodes independently driven by a transistor array. As the voltage is increased the LC long axis becomes increasingly parallel to the electric field direction, which is parallel to the light direction. The light polarization becomes less affected by the LC and the light transmission is reduced because of the crossed polarizers.
Conventional twisted nematic displays have two important shortcomings with respect to manufacturing and performance. First, the rubbing processes used in manufacturing are problematic for a number of reasons, including the numerous processing steps required, the potential for contamination and low production yield, and the requirement of wet processing steps. As such, alternative technologies for producing alignment layers have been developed. One such technology that has promise as a substitute for conventional rubbing protocols is ion beam bombardment. Secondly, the displays suffer from a narrow viewing angle. One means of improving the viewing angle of displays is to use methods such that the liquid crystal molecules are aligned perpendicular or nearly perpendicular to the substrate surfaces in the absence of an electric field (black state). Under application of a voltage between the two substrate surfaces the molecules of a negative LC (preferred alignment perpendicular to the electric field) will become more parallel to the substrate surfaces. If the LC rods, upon rotation in the electric field, are at least partially aligned at a 45 degree angle with respect to the two crossed polarizers the cell will transmit light (white state). Such displays are known in the art as homeotropically or vertically aligned (VA) displays. A display is said to be “single domain” if the LC molecules have a single pre-tilt angle along one azimuthal direction of the surface plane (i.e. the long axis of the LC molecules is orientated along in-plane direction and tilted up from that direction by a well defined angle which, in the case of current 12.1 inch SVGA displays, is a few degrees) and hence long axes of all LC molecules appear more or less parallel to each other over the whole display. A multi-domain display contains at least two differently oriented single domain regions such that the two or more single domain regions form a color sub-pixel of the display. In particular, multi-domain vertically aligned (MVA) displays offer ultra wide viewing angles (Kenji Okamato, Nikkei Flat Panel Display, pp. 104-107 (1998)).
Because of the advantages of producing alignment layers through ion beam bombardment protocols and the known advantages of VA liquid crystal displays, there is interest in the field in developing ion beam bombardment methods for producing such displays, in particular of the MVA type.
Relevant Literature
U.S. Patents describing homeotropic liquid crystal displays include U.S. Pat. Nos. 5,757,454; 5,745,205; 5,359,439; 5,315,419; 5,313,562; 5,303,076; 5,268,781; 5,039,185; 4,701,028; 4,564,266; 4,492,432; 4,472,028; 4,411,494; 4,256,377; 4,112,157; 4,022,934; 3,989,354; 3,972,589; the disclosures of which are herein incorporated by reference.
SUMMARY OF THE INVENTION
Vertically aligned (VA) and multi-domain vertically aligned (MVA) liquid crystal displays, and methods for their production and use, are provided. The subject displays comprise alignment structures on a planar substrate which locally align the LC vertical to the planar substrate. The alignment structure is generally made up of at least one wall or pillar, and usually a plurality of walls or pillars, rising from the surface of a planar substrate layer. At least one surface of the wall(s) or pillar(s) has bond anisotropy sufficient such that liquid crystal molecules adjacent to the surface are aligned along the vertical surface of the wall or pillar, i.e. vertically to the planar substrate. As a consequence, homogeneous (parallel) LC alignment relative to the wall surface results providing for a homeotropic (perpendicular) LC alignment relative to the planar substrate and polarizing material. By use of a suitable array of alignment structures, MVA displays may be manufactured. The subject VA and MVA liquid crystal displays find use in a variety of applications, including flat panel displays for computers, both laptop and desktop, in television monitors, and the like.


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