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Flexi-LCD design could revolutionse printed media

This is a combined flexible blue optically rewritable LCD. Credit: Zhang et al

Optoelectronic engineers in China say they have manufactured a special type of liquid crystal display (LCD) that is paper-thin, flexible, light and tough.

The engineers explain that with this technology a daily newspaper could be uploaded onto a flexible paper-like display and updated as fast as the news cycles. Scientists estimate it will be cheap to produce, perhaps only costing $5 for a 5-inch screen.

The team focused on the development of optically rewritable LCDs. Like conventional LCD displays, the display is structured like a sandwich, with a liquid crystal filling between two plates. But, unlike conventional liquid crystals where electrical connections on the plates create the fields required to switch individual pixels from light to dark, optically rewritable LCDs coat the plates with special molecules that realign in the presence of polarized light and switch the pixels.

This, the team explains alleviates the requirement for traditional electrodes, reduces the structure's bulk and allows more choices in the type and thickness of plates. This means the rewritable LCDs are thinner, at less than half a millimeter thick, can be made from flexible plastic, and weigh only a few grams.

Jiatong Sun of Donghua University in China describes that optically rewritable LCDs are durable and cheap to manufacture because of their simple structure and like and energy is only required to switch display images or text. This Sun says results in low running costs because the LCDs don’t require power to sustain an image once it’s written on screen.

The team also studied how spacers – which are used in all LCDs to determine the thickness of the liquid crystal – create the separation of the plastic or glass plates. “We put spacers between glass layers to keep the liquid crystal layer uniform," Sun says.

A constant thickness is necessary for good contrast ratio, response time and viewing angle, Sun adds. However, when plates bend, it forces the liquid crystal away from the impact site and leaves sections of the screen blank. This, Sun explains, means alterations in spacer design are critical to prevent liquid crystal in flexible LCDs from moving excessively. But developing a flexible design that overcomes this barrier has proven challenging.

The researchers tried three different spacer designs and explain they found that a mesh-like spacer prevented liquid crystal from flowing when their LCD was bent or hit. According to Sun, this enabled them to create the first flexible optically rewritable LCD.

The team also looked at colour rendering, saying that previously optically rewritable LCDs had only been able to display two colors at a time. This research has apparently led to the ability for a rewritable LCD to simultaneously display three primary colour, which the team say was achieved by placing a special type of liquid crystal behind the LCD.

To make this into a commercial product, Sun would like to improve the resolution of the flexible optically rewritable LCD. "Now we have three colours, but for full colour we need to make the pixels too small for human eyes to see," Sun ventures.

Author
Bethan Grylls

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