Wide-viewing angle multi-domain halftone active matrix liquid crystal display having compensating retardation

• US 5,717,474 A
• Filed: 09/30/1994
• Issued: 02/10/1998
• Est. Priority Date: 09/30/1994
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Sarma, Kalluri R.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Dudek, James A.
• Application Number:
  US08/315,363
• Time in Patent Office: 1,229 Days
• Field of Search: 359/78, 359/84, 359/55, 359/75, 349/117, 349/85, 349/123, 349/144, 349/147, 349/38, 349/39
• US Class Current: 349/85
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• CPC Class Codes: G02F 1/133753 with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle
• CPC Class Codes: G02F 1/133757 with different alignment orientations
• CPC Class Codes: G02F 1/134345 Subdivided pixels, e.g. for grey scale or redundancy
• CPC Class Codes: G02F 2203/30 Gray scale
• CPC Class Codes: G02F 2413/02 Number of plates being 2

Abstract

A multi-domain halftone gray scale active matrix liquid crystal display utilizing a mono-gap configuration for achieving a very wide viewing angle at a low-cost. The substrate of the display has areas having a rub or an alignment of different directions from the direction of the rub or alignment in other adjacent areas. Each pixel of the gray scale matrix has a plurality of subpixels such that each subpixel turns on at a different voltage than that of the other subpixels. The areas involving different rubs or alignments on the substrates may be areas of pixels or subpixels. At least one compensating retardation layer is formed on the display. The technique of enabling the combining of multiple domains and compensation with halftone grayscale pixels results in a display having significantly wider viewing angles than either a multi-domain display or a halftone grayscale display, whether compensated for or not.

Claims

1. A wide viewing angle liquid crystal display comprising:

a first substrate;

a second substrate overlapping, approximately parallel to and at a first distance from said first substrate;

a plurality of pixels situated on and between said first and second substrates;

a first polyimide alignment layer formed on said first substrate, having a first plurality of areas;

a second polyimide alignment layer formed on said second substrate, having a second plurality of areas;

wherein;

each pixel of said plurality of pixels, each area of said first plurality of areas of said first polyimide alignment layer, and each area of said second plurality of areas of said second polyimide alignment layer, are approximately the same size in area, and overlap one another, and are aligned with one another, in a one-to-one fashion;

each area of said first plurality of areas of said first polyimide alignment layer has an alignment direction that is at an approximately 180 degree angle to an alignment direction of adjacent areas of said first plurality of areas of said first polyimide alignment layer;

each area of said second plurality of areas of said second polyimide alignment layer has an alignment direction approximately 90 degrees different from an alignment direction of the area of said first plurality of areas of said first polyimide alignment layer that overlaps the area of said second plurality of areas; and

each pixel of said plurality of pixels, comprises a plurality of subpixels wherein each subpixel has a different turn-on voltage from turn-on voltages of other subpixels of said plurality of subpixels such that an intensity of each pixel changes for different voltages applied to the pixel to provide grayscale capability of the pixel.

2. The display of claim 1 wherein:

each pixel of said plurality of pixels further comprises a dielectric layer formed on said first substrate;

each subpixel comprises;

a first electrode layer formed on said first substrate;

a dielectric layer formed on the first electrode layer; and

a second electrode formed on said dielectric layer.

3. The display of claim 2 further comprising:

a gap, having a liquid crystal material, situated between said first and second polyimide alignment layers;

a polarizer overlapping and approximately parallel to said second substrate; and

a retarding compensating layer overlapping and approximately parallel to said first substrate, for reducing dark state light leakage for off-normal viewing angles caused by birefringence of the liquid crystal material.

4. The display of claim 3 wherein said gap provides color capability to said display.

5. The display of claim 3 wherein said gap is a multi-gap having spacings of at least two distances between the surfaces of said first and second substrates, the distances measured along a line perpendicular to the respective surfaces.

6. A wide viewing angle liquid crystal display comprising:

a first substrate;

a plurality of pixels situated on said first substrate;

wherein;

each pixel of said plurality of pixels has a first ITO layer, divided up into a plurality of subpixels having subpixel electrodes formed on a first surface of a dielectric layer; and

a second ITO layer formed on said first substrate, said ITO layer divided up in to a plurality of various sized control electrodes, each control ITO electrode situated on a second surface of said dielectric layer, and each control ITO electrode proximate to a subpixel electrode of the plurality of subpixel electrodes, one subpixel electrode and one control electrode forming a subpixel control capacitor, for each subpixel;

a first polyimide layer formed on said plurality of pixels, having a first plurality of areas, each area of said plurality of areas being approximately a same size of and congruent to an area of a pixel of said plurality of pixels, each area of the first plurality of areas of said first polyimide layer having an alignment direction different from an alignment direction of each adjacent area of the first plurality of areas of said first polyimide layer;

a second glass substrate;

a common ITO electrode layer formed on said second glass substrate;

a second polyimide layer formed on said common ITO electrode layer, parallel to said first polyimide layer, having a second plurality of areas, each area of said second plurality of areas being approximately a same size of and congruent to an area of said first plurality of areas, each area of said second plurality of areas of said second polyimide layer having an alignment direction different from an alignment direction of an area of said first plurality of areas of said first polyimide layer, that is approximately congruent to the respective area of said second plurality of areas; and

a layer of liquid crystal material situated between said first and second polyimide layers.

7. The display of claim 6 further comprising:

a first polarizer formed on said first glass substrate; and

a second polarizer formed on said second glass substrate.

8. The display of claim 7 further comprising:

a first compensating layer situated approximately parallel and proximate to said first polarizer; and

a second compensating layer situated approximately parallel and proximate to said second polarizer; and

wherein said first and said compensating layers are for reducing dark state light leakage for off-normal viewing angles, caused by birefringence of the liquid crystal material.

9. The display of claim 8 further comprising at least one color filter situated between said second glass substrate and said common ITO electrode layer.

10. The display of claim 9 further comprising an antireflective film formed on said second polarizer.

11. The display of claim 10 further comprising a backlight proximate to said first polarizer.

12. The display of claim 9 further comprising an antireflective film formed on said first polarizer.

13. The display of claim 12 further comprising a backlight proximate to said second polarizer.

14. A wide viewing angle liquid crystal display having a plurality of pixels, wherein each pixel comprises:

a plurality of subpixels wherein each subpixel has a voltage range of operation controlled by a control element at the subpixel in such a way that a majority of the plurality of subpixels operate in a "fully-on" (V_LC >

V_s) or "fully-off" (V_LC <

V_t) mode as selected by a magnitude of applied voltage, resulting in luminance of the pixel as being significantly invariable relative to viewing angle;

a liquid crystal layer, proximate to said plurality of subpixels, having a thickness;

a compensative retardation film, proximate to said liquid crystal layer, for reducing dark state light leakage for off-normal viewing angles due to a birefringence of the liquid crystal layer;

a first polarizer proximate to said plurality of subpixels; and

a second polarizer proximate to said compensative retardation film.

15. The display of claim 14, wherein said first and second polarizers are arranged in a crossed configuration for a normally white mode of operation.

16. The display of claim 15, wherein said compensative retardation film has a negative birefringence.

17. The display of claim 14, wherein said first and second polarizers are arranged in a parallel configuration for a normally black operation.

18. The display of claim 17, wherein said compensation film has a positive birefringence.

19. The display of claim 14, wherein the thickness of said liquid crystal layer is varied to achieve optimum contrast for each of red, green and blue colors.

20. The display of claim 14, wherein each subpixel is divided into a plurality of complementary domains having complementary electro-optical performance to achieve a symmetric electro-optic response for various viewing angles.

21. The display of claim 14, wherein adjacent pixels of a pixel of the plurality of pixels have complementary liquid crystal domains relative to the pixel, resulting in complementary electro-optic performance to achieve a symmetric electro-optic response for various viewing angles.