Angewandte Chemie International Edition

Cover image for Vol. 57 Issue 9

Editor: Neville Compton, Deputy Editor: Frank Maass. Editor Emeritus: Peter Gölitz

Online ISSN: 1521-3773

Associated Title(s): Angewandte Chemie, Chemistry - A European Journal, Chemistry – An Asian Journal, ChemistryOpen, ChemPhotoChem, ChemPlusChem, Zeitschrift für Chemie

Press Release

For full article and contact information, see Angew. Chem. Int. Ed. 2003, 42 (16), 1812 - 1815

No. 16/2003

Unpolished

A simple, robust coating process
for the production of liquid crystal displays

The future is in flat-panel displays. However the production of wide-format displays continues to be very expensive. Researchers working with Roeland Nolte in the Netherlands have now developed a new method that could simplify one problematic step in the production of liquid crystal displays (LCDs).

An LCD is in fact an ensemble of tiny cells, each consisting of two coated glass plates, filled with a liquid crystal material. Generally, liquid crystals are organic molecules that organize themselves into a crystalline structure when in the liquid state. A polarizer, which polarizes the oscillation plane of incoming light in one direction, is applied to the glass plate at the front of the cell. When no voltage is applied, the direction in which the light is polarized as it passes through the liquid crystal layer is rotated by 90°. The polarizer on the rear plate is aligned such that it lets this light pass, and the cell appears transparent. If a voltage is applied, the alignment of the liquid crystals is changed so that the oscillation plane is no longer rotated and the light is thus no longer allowed to pass through the second polarizer. The cell then appears black.

In order to transmit the voltage into the cell, the glass plates are coated with a layer of indium tin oxide (ITO). In addition, a polymer layer must be deposited over the ITO. The polymer layer must then be intensively rubbed in one direction with a velvet-like material. This results in tiny, parallel grooves on the surface. These cause the liquid crystals to adopt the desired orientation. Unfortunately, the polishing process causes a build up of electrostatic charge on the plates. Dust particles are attracted to this and lead to defective pixels. The entire production must therefore be carried out under dust-free clean-room conditions.

This expensive measure could be avoided with the new, extremely simple and robust process. Nolte and his colleagues coat the ITO surface with a special organic compound, which organizes itself into a grooved structure. The researchers discovered that the ITO surface itself contains parallel nanogrooves. Aggregates of the organic compound arrange themselves along these nanogrooves. This again results in a grooved surface, but one whose dimensions are increased by a factor of a thousand. These grooves are equivalent to a conventional velvet-polished polymer layer and are equally effective in forcing the liquid crystals into the desired orientation.

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