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27 Sep 2007
A reflective flat-panel display that exhibits color tuning across the entire visible spectrum could be a valuable power saver.
A flat-panel display that can be electrically tuned to reflect colors across the entire visible spectrum has been developed by researchers in Canada and the UK. What's more, since the device, which is based on photonic crystals, is reflective, which means that no power is wasted for backlighting. (Nature Photonics 1 468)
"The full-color tuning of such devices is unprecedented. There is no similar technology on the market," André Arsenault, researcher at the University of Toronto, told optics.org. "Our technology enables bright and rich colors at reduced costs.
The devices can be tuned from 425 nm to 900 nm, which corresponds to a voltage change of less than 2 V. "Our devices operate at low voltages and currents, and consumes zero power between switching," commented Arsenault. "Since ambient light is used to light up our displays, they are viewed just as well in bright sunlight as in indoor light."
According to Arsenault, the most important result is that they now have one material that can produce the whole spectrum of colors. "We don't need to pattern different types of materials to get different primary colors, and we don't need the expensive color filters that are used in every single color display on the market," he explained. "The potential to simplify manufacturing is tremendous, and the display brightness can be boosted to its full potential since no additional layers are getting between our material and the consumer."
Test samples on the order of 1 cm2 have been made, although the team is able to produce films as large as a few hundred square centimeters. "We are still on the lab scale, but there does not seem to be a fundamental limit to an increase in display size," commented Arsenault.
The active material in the display is a nanocomposite, similar in structure to natural gemstone opal. "We incorporate electroactive polymers into these composites, making them responsive to applied voltages," explained Arsenault. "As we apply a voltage, we cause a structural change in the material that changes the reflected color. By gradually increasing the voltage, we can span the whole visible spectrum, and even the UV and IR ranges."
Arsenault explains that applying a voltage to the electroactive polymer charges the material, causing it to expand. This expansion pushes the spheres in the material apart, and the greater the separation, the greater the increase in reflected wavelength. When the voltage is reversed, the polymer discharges and so shrinks back to its original size. The spheres then come closer together and the reflected wavelength decreases.
The team is now working to produce devices at a low enough cost to capture market interest. "We are currently developing this technology for a variety of targeted applications, in conjunction with some industrial partners aiding both in development and production," concluded Arsenault.
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