A more colourful display

Researchers at Motorola Labs have demonstrated a new display mechanism, called Electrically Tunable Colour (ETC) for colour reflective liquid crystal displays (RLCD).

Researchers at Motorola Labs have invented and demonstrated a new display mechanism, called Electrically Tunable Colour (ETC) for colour reflective liquid crystal displays (RLCD).

According to researchers, the ETC has the potential to significantly improve the appearance of RLCDs. These are the most widely used displays for portable electronic products, such as cell phones and PDAs. Although these displays are popular with electronics manufacturers because of their low power consumption, they are not currently able to deliver the rich colour, contrast and brightness that consumers prefer.

The ETC developed at Motorola Labs, uses an in-plane electrical field to change the colour of light reflected from a cholesteric liquid crystal material between two glass plates. A cholesteric liquid crystal has molecules coiled like springs between the glass plates. The distance between the successive rings of the spring determines the colour of light reflected by the liquid crystal material. An electric field, applied parallel to the glass plates (in-plane), effectively untwists it causing the separation between the rings to increase. This change produces an observable colour shift.

All three primary colours have been demonstrated using a single layer of cholesteric liquid crystal by changing the in-plane voltage. Through this technique, Motorola Labs researchers have demonstrated a larger colour scale than current commercial colour RLCDs.

An additional advantage is the simple structure of the ETC, which has the potential to significantly reduce the final display costs. Current commercial colour RLCDs require a polariser and colour filter combination to generate colour. The underlying display structure is quite complicated and requires a number of optical and electrical layers that absorb light, which is expensive to manufacture and results in a fairly dim and less colorful display.

Another commercial option requires stacking three displays together, one for each primary colour (red, green, blue). Although this method provides brighter and more saturated colors, it can also generate undesirable visual artifacts. Most importantly, there is no established manufacturing process to produce stacked displays and the stacked display is expected to be much more costly and less reliable. Also, the in-plane-switching (IPS) technology needed is already a mature technology.

The most challenging issue remaining is to drive the voltage requirements down. This currently requires more than 100 volts.

Motorola expects to work with established LCD manufacturers to move the technology from laboratory to manufacturing over the next three years through licensing.

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