Browse Prior Art Database

Method of Alignment of Liquid Crystals

IP.com Disclosure Number: IPCOM000112418D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 157K

Publishing Venue

IBM

Related People

Haller, I: AUTHOR

Abstract

Existing methods for in-plane alignment of liquid crystals as applied to large area flat panel displays suffer from problems such as particulate-inducing mechanical motions, poor detectability of defects, incompatibility with other manufacturing steps, or high cost.

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This is the abbreviated version, containing approximately 34% of the total text.

Method of Alignment of Liquid Crystals

      Existing methods for in-plane alignment of liquid crystals as
applied to large area flat panel displays suffer from problems such
as particulate-inducing mechanical motions, poor detectability of
defects, incompatibility with other manufacturing steps, or high
cost.

      Claimed is a method of conferring directionality to surfaces,
mainly for the purpose of aligning liquid crystals in predetermined
directions in the plane of enclosing surfaces, consisting of

o   adhering to said surfaces a viscoelastic polymer layer, bounded
    on its other side by a flexible backing,

o   detaching the bulk of said polymer layer by unidirectional
    pulling in the predetermined direction, leaving only an
    approximately monolayer thickness coating of polymer molecules
    oriented in the direction determined by the direction of pulling,

o   enclosing a thin layer of liquid crystal, by standard techniques,
    between two surfaces pretreated in the above-described manner.

      Liquid crystal display devices require that optic axis of the
liquid crystal be fixed in a predetermined direction at the two
enclosing surfaces.  Numerous methods have been used (as reviewed in
[1,2]).  to pretreat the enclosing surfaces to cause such an
alignment.  The mechanism of alignment is thought [1,2,3]  to be
either a response to topographical variations (grooves) on the
micrometer scale or to electrostatic or van der Waals forces on the
molecular scale (say between an oriented, firmly adsorbed interfacial
molecule and the molecules of the liquid crystal).  When applied to
large area display devices, such as active matrix TFT-LCD's, each of
the currently used alignment methods have substantial drawbacks.  For
example, the most common method consists of mechanical "rubbing" or
"buffing", either by reciprocating motion with respect to, or by a
rotary motion with a velvet cloth, of an (optionally polymer coated)
enclosing surface.  Such mechanical motion is prone to cause
scratching of or deposition of particulates onto a series of
consecutively treated surfaces (which for TFT-LCD's include the
already fabricated active matrix plate containing about a million
thin film transistors), resulting in defects undetected until after
the final assembly of the display.  Another method, evaporation
coating at an oblique angle is not easily compatible with the large
plates used for the TFT-LCD's and requires expensive equipment.
Unidirectional withdrawal of plates from a Langmuir-Blodgett trough
deposits a well-oriented layer only if done exceedingly slowly and is
therefore considered not practical.

      I propose a novel method of forming an oriented monolayer of
adsorbed polymer for the purpose of aligning a subsequently enclosed
liquid crystal layer.  In the first step a thin layer of a randomly
oriented viscoelastic polymer is formed between the surface to be
treated and a flexible backi...