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Displays Journal
Posted on March 1, 2005 by  & 

Advanced electrochromic displays find markets

IDTechEx believes that there is a substantial market for low cost display technologies and the massive bias towards research on OLEDs does not reflect this. However, things are changing. A technique used to cut headlight glare in cars' rear-view mirrors had been modified to create a new loc sot display for MP3 players and mobile phones. Called a NanoChromic Display (NCD) it was demonstrated recently by Dublin based Ntera on a converted iPod.
Unlike LCDs, these displays can be viewed from almost any angle in a wide range of lighting conditions, like printed text on paper. They require very little power, if any, to maintain an unchanging image. At the heart of this NCD is an electrochromic material, which is normally transparent but turns blue when a negative charge is applied. It requires no moving parts, making NCDs unique among other electronic paper technologies, such as electrophoretic displays.
Electrochromic material has been used in the past to darken rear view mirrors in cars. Aveso have used printed electrochromic displays on gift cards, smart labels and smart cards. In Ntera's display, an array of transparent electrodes made of metal oxide semiconductor, mounted on a transparent film, allows it to produce images with a resolution of about 0.25 millimeters or 100 dots per inch. Adding an opaque white layer of titanium dioxide behind the electrochromic layer creates a white background to the monochromatic images that makes them more readable. The company is also planning eventually to develop a colour display. Aveso, a spin out of Dow Chemical and formerly known as Commotion solutions, have a range of colored electrochromic inks.

Different displays for different applications

Adrian Geisow, head of display research at Hewlett Packard Labs in Bristol, UK, agrees with us. He says there should be room for a variety different types of display. "Historically there has never been a universal display. They all have trade-offs," he says.
Displays that require no power to maintain the image might be best suited for poster-like advertising banners. Others may be more suited to mobile devices that show prices in supermarkets, where power consumption is less important than the ability to change prices quickly throughout the store. So far, none of the companies making electronic paper has been able to achieve good high-resolution colour images.
Although Ntera's NCDS have no moving parts, unlike electrophoretics, the displays are unable to switch pixels on and off fast enough to be used in TVs or in streaming video and computer monitor. This is because electrochromic displays take some time to build up charge.
Ntera hopes that its display will give it the edge in applications that require high definition. It has designed the electrodes to have an uneven surface, maximising the number of electrochromic molecules that make contact with it. This creates a denser, better-defined image: it also allows the pixels to be switched on and off faster.
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