Next hot trend for appliances: FLEXIBLE DISPLAYS

That's because new electroluminescent (EL) displays targeting appliances are thin and flexible enough to be cut with ordinary shears. The display panels come from U.K.-based Pelikon and are said to offer better graphics than traditional LCDs and LEDs.

Large segments, backlighting, and displays on the same panel which remain hidden until in use; the ability to cut any shape; and buttons and lit icons in the same position all mean EL is well suited for white-goods applications. Thinness lets the displays be sited in new places that add to differentiation and consumer convenience. Keys that only light when needed, combined with fully logic-controlled interfaces, can significantly simplify design of the electromechanical components, final assembly of the product, and consumer/product interaction when the product is in use.

EL technology is an efficient form of light production that generates no heat. Traditionally taking the form of wires, panels, or strips, an organic phosphor is sandwiched between two conductors. When an ac signal of enough voltage and frequency is applied to the conductors, an electric field is formed across the phosphor. This causes the phosphor to emit visible light.

Pelikon is using EL technology to construct light emitting, low-information content displays where every segment is driven directly. The units are printed using thick-film deposition on to a flexible plastic substrate, with the complete display measuring around 400-m m thick. The Pelikon technique uses inorganic phosphors subject to about 200 Vac at between 70 and 10 kHz, although the typical driving frequency is about 400 Hz. Proprietary Asic drivers power the EL display. Each Asic can drive as many as 64 lit areas of 1.7 cm2. Asics can combine to handle up to 128 channels. Chip-on-Board (COB) is a high-voltage Asic segment driver, which is controlled using a low-cost, lowvoltage, 8-bit microcontroller. This controls display functions such as brightness, reducing the burden on the product's own electronics.

"That fact that you can cut the EL display to any shape has an immediate impact on product design given that LCD and LED panels are both limited to being rectangular," says Pelikon's Chris Barnardo. Because EL displays are surface emitters, it is possible to cover them with several colored filters. Light shines through them even with graphics printed on. Displays can also be designed to merge into the product surface when not lit. "For example, you can have a white overlay for white goods," explains Barnardo. "If you put that over an LCD unit, you wouldn't see anything at all as white is a scattering filter. And for a vacuum fluorescent display that's typically back a centimeter from the front face, the scattering would put it out of focus. Again, you wouldn't see it," he adds. However, an EL unit remains clear and bright.

The company is developing a display that can curve. This will offer more options over where a component can be seated. "Previously, designers wanting a curved and shaped display had to settle for a box surrounded by a really fat bezel to incorporate the curves," says Barnardo. "Moreover, because you can cut our displays, they needn't be situated in one monolithic block. You've got much more freedom in the shape."

The fact that displays are flexible lets them serve as lighted buttons. "Our remote-control designs have metal dome buttons under the surface of the display which gives a good tactile feel," says Barnardo. "There's no hassle as with a normal touch screen where you don't know whether you've pressed it or not. It's straightforward to design where the display elements and icons are in exactly the same place as the actual buttons."