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Pixel Structure for High Aperture Ratio Active Matrix Liquid Crystal Displays

IP.com Disclosure Number: IPCOM000119037D
Original Publication Date: 1997-Nov-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 84K

Publishing Venue

IBM

Related People

Lien, S-CA: AUTHOR [+2]

Abstract

In Active Matrix Liquid Crystal Displays (AMLCDs), certain edges of the pixel flag (typically the top and left sides) exhibit disclination lines and reverse tilt in the liquid crystal. This is due to the interaction of liquid crystal alignment (in the diagonal rubbing direction) and the lateral electric field between the pixel and adjacent signal lines. These regions are optically inactive and allow unwanted light leakage, which decreases the contrast ratio. These regions are typically about three microns wide and must be masked by a black matrix layer, usually formed on the top plate (Fig. 1). The area taken by the black matrix over these edge regions and allowances for alignment tolerance both decrease the aperture ratio of the display.

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Pixel Structure for High Aperture Ratio Active Matrix Liquid Crystal
Displays

      In Active Matrix Liquid Crystal Displays (AMLCDs), certain
edges of the pixel flag (typically the top and left sides) exhibit
disclination lines and reverse tilt in the liquid crystal.  This is
due to the interaction of liquid crystal alignment (in the diagonal
rubbing direction) and the lateral electric field between the pixel
and adjacent signal lines.  These regions are optically inactive and
allow unwanted light leakage, which decreases the contrast ratio.
These regions are typically about three microns wide and must be
masked by a  black matrix layer, usually formed on the top plate
(Fig. 1).  The area  taken by the black matrix over these edge
regions and allowances for alignment tolerance both decrease the
aperture ratio of the display.

      A new pixel structure is shown in Fig. 2, in which the Indium
Tin Oxide (ITO) pixel flag region is extended above the adjacent data
and gate lines.  The ITO and signal line levels are separated from
each other by the passivation insulator layer, typically composed of
inorganic SiO2 or SiNx materials.  Alternatively, the passivation
insulator could consist of an organic dielectric, such as an acrylic
copolymer, polyimide, or perflourocyclobutene material.  Since the
ITO region extends over the signal lines, all lateral field lines and
optically inactive regions are eliminated, and there are no gap
regions at the cell periphery.  The area available for light
transmission is increased from about 33% in the conventional
structure (Fig. 1) to about  66% (Fig. 2) with the overlapping flag.

      Ideally, with the overlapping pixel structure, the black matrix
layer in the top plate cou...