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Reflective display technology operates in all light levels

Start-up company Liquavista is proposing a new display technology as the ideal solution for mobile and portable displays. The effect which the company intends to exploit is not new, but no one has previously developed the approach to construct a display technology for volume production. The phenomenon is electrowetting, and it uses a cell (for displays, a pixel) containing two immiscible liquids (oil and water). Applying a voltage to the cell changes the state of the surface, over its active area, from hydrophilic to hydrophobic. In one condition the oil lies in an even layer across the cell: in the other, electrical charges and surfacetension effects repel it to accumulate in one corner of the pixel cell. Load the oil with a coloured dye or an opaque material, and you have the basis of an optical switching element. Liquavista, a spin-off from Philips that has just received € 12 million in venture funding, says that it can build displays using this effect, whose fabrication will re-use much of the technology that LCD-panel construction presently employs—the active matrix, the glass substrate and much of the production process are easily adaptable. What such a display offers, the company says, is the only technology that can work in all modes of illumination—transmissive, transfl ective or fully refl ective. It is the latter that the company is promoting for use in hand-held devices; with no backlight a refl ective electrowetting display will use ambient light to give a bright, but lowpower, display in daylight and under artifi cial lighting. Contrast stays constant under changing incident lighting. For colour use, Liquavista says it can build either an LCD-like RGB array, or a stacked CMY fi lter structure, mimicking the colour-printing process electronically. However, fi rst products are likely to be monochrome, TN-type small panels for applications such as cellphone secondary displays. By loading the oil-dye carrier with any given colour, Liquavista can match the colour scheme of a product or corporate logo in the display.The technology is capable of switching at video speeds and of supporting gray-scale shading, and Liquavista says it has demonstrated pixel densities of up to 160 pixels per inch. —Liquavista, www.liquavista.com.