Finally, E-Paper Screens Made of Real Paper!

In December, electrical engineers at the University of Cincinnati reinvented the wheel. By applying electric fields to nonglass materials, they discovered they could make an e-paper display screen using the unlikeliest of materials—paper.

By Tarah Knaresboro


The American Chemical Society (ACS)

January 26, 2011 3:30 PM Text Size: A . A . A
This discovery has big implications for the future of the screen: Making a display out of regular old paper could maximize affordability, decrease environmental impact and also save space, since a paper screen has the potential to roll up and pull out. So is it time to throw out our retro flatscreens and make room for paper television? Not just yet. The future is exciting, but looking at the essential components of a display screen reveals some big roadblocks on the way to shoving a 78-inch screen into your cup holder.

The Cost

Scott Birnbaum, VP of the LCD Business at Samsung, says the most expensive thing about making a screen isn't about any individual part, but building factories to produce new technology. "The newest factories are three to five billion dollars," he says. Rather than the scientific progress, developing the infrastructure to produce and advance rollable screens is the most restrictive obstacle on the way to revolutionizing display screens.

Sigurd Wagner, professor of electrical engineering at Princeton University, agrees. There are "no fundamental obstacles" in producing a rollable pullout display. But the support for it is limited, which slows technology development.

The Parts: What Stays, What Goes?

The high-end screens these days are usually plasma or LCD panels. But there are elements inherent in the production of those screens that are incompatible with rollability. For example, according to Birnbaum, all LCD screens boil down to the same few elements: the back piece is a slab of glass, and overlaid on that are the transistors; the transistor pattern determines the resolution quality of the screen. After that, there's a layer of liquid crystal, which modulates the light coming through. Next, there's the array of tiny color filters, which enables the screen to capture color information. Finally, the polarizer directs the light out through the last piece of glass.

Liquid crystal mandates the use of glass, and while glass can be made thin and to some extend bendable, it wouldn't roll up. Likewise, plasma screens need glass panels to hold in the gases that allow it to function. Making a pullout screen requires finding an alternative to traditional screen-production methods, one that doesn't require glass.

Durability Concerns

But viable substitutes for glass are proving hard to come by, especially considering it also provides an excellent seal against humidity, says Wagner. Also, a "famous phenomenon" arises when the flexible display is applied to a glass-substitute host such as a plastic or metal: the shearing force between the two materials makes the display peel off. The host holds up against the bending and rolling but can't stay affixed to the screen well enough to be a passable substitute.

The discovery that a screen can be applied to paper tackles the back pane of glass, which is half the problem, but the big open question is whether anything can adequately protect the video paper, or whether the screen can become cheap enough to function as a less durable, disposable display.  

Lighting It Up

Thinking about the screen's light source is also important since it has a big impact on the display's brightness, power capacity and even thinness. CCFL, or cold cathode fluorescent lighting, is "traditional backlight technology," according to Birnbaum. It's essentially a miniature fluorescent lamp behind all the other components of a screen. "That's the technology used in a lot of standard displays." Making a screen this way adds a lot of bulk, restricting reliability.

Newer screens replace the old backlights with LEDs, which can be placed along the edges of a screen instead of behind everything. Birnbaum says the dawn of LED technology brought display screens from three to four inches thick to about one-third of an inch, an impressive leap. All that's needed is a thin light guide plate, which diffuses and brightens the light leaving the display.

Eliminating the standard backlight allowed for much more slender screens, which Wagner says has been instrumental in getting screens down a workable size. "You can make anything foldable and rollable if you make it thin enough," he says. It is unclear how all the elements will play together to light up future models of the pullout screen, but as displays get thinner, flexibility gets easier.  

Powering The Screen

Wagner says that "it's been predicted that pullout displays will have lower power needs than liquid crystal displays, but it hasn't happened yet. Liquid crystal production is a little bit further; they have tricks to curb power consumption." One such trick is PenTile technology, which Samsung acquired in 2008. It capitalizes on the amount of time people spend looking at the color white (quite a lot, it turns out, due to all the text people tend to read). Normally, screens use a color filter for red, green and blue, and different combinations achieve different colors. Making white involves cranking up each of the colors to the highest level, which combine to form a bright white. "So the more white on display, the more light it consumes," says Birnbaum. The PenTile technology involves a different subpixel structure—in addition to the red, green and blue subpixels, a white one is added. Now, anytime white must be displayed, just one subpixel must be activated instead of the previous three. This can increase the display's brightness or lower the power needed to run it.

Rollable screens are too new on the market to have established shortcuts like this, and it could be a while before they catch up. "There's no fundamental difference in the power needs, but it needs development," Wagner says.  

An Interactive Display

Another potential obstacle for the rollable screen concerns touch and multitouch capability. If a screen is to be touch-sensitive, additional layers must be added to the screen. Multitouch, which is what smartphones use, requires a glass insulator coated with a conductive layer, and when a human finger (also a conductor) touches the surface, it distorts the screen's electrostatic field, enabling the device to figure out the location of the touch and perform further processing. Again, the rollable screen suffers from its lack of glass.

Also, because touch technology is added on top of the display, it's prone to scratches, which decrease performance. Protecting the screen becomes an issue once more, and it remains to be seen whether a rollable screen has the capacity to be multitouch as well as durable.   

The Time Frame

With so many hurdles to jump over, when can we expect to see the first mass-produced roll-out screen? Wagner, who has worked on designing flexible screens for 15 years, guesses in three to five years. Andrew Steckl, the researcher who made a screen on paper, concurs.


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