Spray on display

Making a complete display by simply painting a number of layers on any carrier material must seem barely credible to anyone familiar with the many-step and time-consuming production process currently used in the production of displays.

Yet it has become much closer to reality with a new manufacturing technology for Liquid-Crystal Displays (LCDs) described by Philips scientists in this week's issue of Nature.

Traditionally, LCDs are produced by so-called cell-technology, where two glass plates, containing electrodes, switches, and colour filters are carefully connected using spacers, so that a cell of controlled thickness is formed.

The cells are then filled with liquid crystal in a time consuming and expensive process called vacuum suction. In the new technology, the liquid-crystal cells can be made without resorting to the vacuum suction process.

This is achieved by a process called photo-enforced stratification (PES) which uses UV radiation to form closed cells of liquid crystals in a two step procedure.

First, a complex blend, containing liquid crystal and a polymer-forming material, is applied onto the substrate in one of the coating steps. Subsequently, the layer is exposed to ultraviolet radiation, which causes the blend to split up into two separate parts: a liquid crystal part and a polymer part.

During the first step, only a part of the layer is exposed, which causes the formation of rigid walls of polymer material making up the sides of the individual cells. During the second step, the complete layer is exposed, causing the formation of a liquid-crystal layer on the bottom and a polymer cover layer on top of the cells.

A top substrate is then no longer necessary; this not only reduces cost but also yields very thin displays.

The process is claimed to be suitable for manufacturing displays in a reel-to-reel process, the ultimate low-cost, large-area manufacturing solution, whereby devices are made on large sheets which run continuously through the process.