Reel to Real: Prospects for Flexible Displays
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Reel to Real: Prospects for Flexible Displays Kimberly Allen Director of Technology and Strategic Research iSuppli/Stanford Resources
Although it is tempting to begin with a standard opening statement like “Flexible displays have been generating much recent interest,” the fact is that flexible displays have fascinated people for about 50 years and have been discussed seriously for at least 20 years. The difference now is that display and backplane technology have evolved to the point where reasonably attractive-looking demonstrations of flexible screens are possible. This has had two effects. It has spurred an intense drive to finally realize the long-time dream of flexible displays. And it also has allowed industry participants to experience directly the real-world challenges of building these displays, rather than granting them the luxury of imagining that products were just around the corner. Flexible displays may be defined in a number of ways. Here, the following types are included: • • •
Curved or conformed, but not flexed during use Mildly flexible, but not designed for severe treatment such as rolling Fully flexible, like paper or cloth
Not included are displays built on plastic but used in a flat, rigid form—such as those employed solely for ruggedness or light weight. (These flat plastic displays have been commercialized in small quantities for cell phones.) An exception is made for dynamic signage due to the use of roll-to-roll manufacturing. Also not included are glass-based panels that use novel display technology, such as electronic books made with electrophoretic ink on glass (e.g., Sony’s Librie). Technology Flexible displays may be made on metal foil, very thin glass, or a variety of plastics. In a sense, the substrate material plays the pivotal role in the viability of the flexible display as a competitive product offering. Substrate materials are key to meeting cost, performance, reliability, and manufacturing goals for flexible electronics and displays. Rather than starting with form and function, the venture into making flexible displays must begin with the choice of a proper substrate material. Intrinsic tradeoffs abound. Thin glass (50-200 microns) has excellent barrier and optical qualities and a low price, but is very difficult to handle in manufacturing. Stainless steel foil requires a nontransmissive display technology and cannot handle multiple bends, but is also a good barrier.
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Plastic is the key material choice, allowing reasonable tradeoffs in mechanical, optical, and chemical performance. Multilayer “engineered” substrates will be required for most practical applications. Heat-stabilized PET and PEN seem promising for standard flexible displays, and PAR or even PC-based materials could serve in some cases. Major improvements are still needed in thin-film barrier layers (water penetration, durability to flexing). The electronics may be inorganic or organic. Silicon-based TFTs and metallic leads are easier to fabricate, although changes are needed to do the processe
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