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Electronic paper reaches video speeds

26 Sep 2003

Electronic paper that could display color images in real time is unveiled in this week’s Nature.

Physicists at Philips Research in the Netherlands have developed a new way to make "electronic paper" that could display moving images. Robert Hayes and Johan Feenstra say that their electrowetting technique could be used to make a reflective display that is four times brighter than reflective liquid-crystal displays (LCDs). Their approach relies on using low voltages to move a colored film of oil (Nature 425 383).

Electronic paper combines the advantageous viewing characteristics of conventional paper with the ability to electronically manipulate the information displayed on the paper. Researchers have made electronic paper before but it has always been expensive and slow to switch from one color to another.

Hayes and Feenstra started by coating a white polymer foil substrate with a patterned electrode layer and a hydrophobic fluoropolymer insulator. The electrode layer was made of indium tin oxide and was just 15 nm thick. Then they made small 'walls' to define the pixels and added a layer of coloured oil - about 10 microns thick - followed by a layer of water.

In the absence of any applied voltage the colored oil forms a flat film between the water and fluoropolymer, which results in a colored pixel. When the researchers apply a voltage of about -20 volts between the electrode and water, the interfacial tension between the water and the fluoropolymer changes. This means that the system is no longer stable and the water causes the oil to move to one side, thus exposing the white surface beneath.

Switching between white and colored reflections takes less than 10 milliseconds, which is fast enough for video displays. The researchers also found that if they added a second layer of oil, they could further improve the reflectivity - to four times that of an LCD.

"Achieving high reflectivity and video-speed capability are needed for reflective displays to be successful," Hayes told PhysicsWeb. "Our new display technology is an important step in both these directions." The duo says that as well electronic paper, their technique will be useful to make displays for mobile and outdoor applications. "We now hope to industrialize this new technology and make larger, active-matrix displays," said Hayes.

Belle Dumé is Science Writer at PhysicsWeb.

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