Optoelectronic engineers in China and Hong Kong have manufactured a special type of liquid crystal display (LCD) that is paper-thin, flexible, light, and tough. With this, a daily newspaper could be uploaded onto a flexible paper-like display that could be updated as fast as the news cycles. It sounds like something from the future, but scientists estimate it will be cheap to produce, perhaps only costing $5 for a 5-inch screen.

Combined flexible blue optically rewritable LCD. (Image courtesy of Zhang et al.)

The team focused on two key innovations for achieving the highly flexible designs. The first is the recent development of optically rewritable LCDs. Like conventional LCD displays, the display is structured like a sandwich, with a liquid crystal filling between two plates. 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 to switch the pixels. This removes the need for traditional electrodes, reduces the structure's bulk, and allows more choices in the type and thickness of the plates. Consequently, optically rewritable LCDs are thinner than traditional LCDs. At less than half a millimeter thick, they can be made from flexible plastic, and weigh only a few grams.

Optically rewritable LCDs are durable and cheap to manufacture because of their simple structure. Moreover, like an electronic paper screen in an e-book, energy is only required to switch display images or text. Therefore, running costs are low because these new LCDs don't need power to sustain an image once it is written on the screen. The second innovation involves the spacers that create the separation of the plastic or glass plates. Spacers are used in all LCDs to determine the thickness of the liquid crystal. A constant thickness is necessary for good contrast ratio, response time, and viewing angle. When the plates bend, it forces the liquid crystal away from the impact site and leaves sections of the screen blank. So, changes in spacer design are critical to prevent the liquid crystal from moving excessively. The researchers tried three different spacer designs and found that a mesh-like spacer prevented liquid crystal from flowing when their LCD was bent or hit.

An additional innovation involved improved color rendering. The scientists report that until this study, optically rewritable LCDs had only been able to display two colors at a time. Their LCD, however, simultaneously displays the three primary colors. They achieved this by placing a special type of liquid crystal behind the LCD, which reflects red, blue and green. To make this into a commercial product, the researchers now want to improve the resolution of the display.

For more information, contact Julia Majors at This email address is being protected from spambots. You need JavaScript enabled to view it., 301-209-3090.

Photonics & Imaging Technology Magazine

This article first appeared in the September, 2018 issue of Photonics & Imaging Technology Magazine.

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