Pixels by the Yard: HP Prints Flexible Screens Like Newsprint

A flexible computer screen—one that you can roll up and stick in your pocket—is coming closer to reality.

By Stephen Cass|Wednesday, May 13, 2009
Hunter Freeman

For those of us old enough to remember the original Knight Rider, using a computer once meant sitting in front of a specialized particle accelerator. This bulky device smashed electrons into a phosphorescent screen that displayed your text in exciting white-on-black, green-on-black, or the supersnazzy yellow-on-black.

Since then, flat-panel technology has revolutionized desktop and laptop screens (and TV, of course). But these can be expensive, and they are awkward to carry around. Wouldn’t it be nice to have a cheap display that rolls up like a projector screen when not in use? A new approach being developed by Hewlett-Packard and Arizona State University would solve both problems by inexpensively “printing” displays onto a flexible plastic backing.

Engineers have long suspected that the solution to the cost and portability problems of today’s flat screens lies in changing the manufacturing process. Flat-panel displays are essentially big integrated circuits, with millions of transistors that turn pixels on and off across the display. To make these circuits, manufacturers have traditionally used what is called a batch process: A group of displays-in-the-making move together from machine to machine as they go through different construction stages. A faster method would be to use a so-called roll-to-roll process, where a continuous sheet of flexible material is fed into one end of the machinery and a processed product rolls out the other end, similar to how a newspaper press operates.

The stumbling block has been that making integrated circuits requires applying different templates as layers of circuitry are built up. When each new template is applied, it must align precisely with what has gone before. Unfortunately, a sheet of material is prone to stretch or otherwise drift out of alignment as it moves through the machine. The new process created by HP Labs allows a combined template for the entire circuit to be bonded to the sheet at the beginning of the operation. So as the sheet stretches or moves, the template follows along, and misalignments are eliminated.

HP Labs cannot yet estimate the cost of its process, but the company is aiming for a small fraction of the $100-per-square-foot price tag of conventional flat-panel products. The first use for the HP technology will be in a wrist-mounted display being created for soldiers as part of an army research project. It should be ready in about two years. Other potential applications range from e-books to flexible cell phones.

Stephen Cass

How It Works
In traditional display manufacturing, features are etched into the surface of a multilayer semiconductor stack (green, blue, and red layers in the diagram at right) that sits atop a substrate (yellow); here we show just one small part of a large array of components. The etching is carried out by a hot gas, or plasma. A template, or mask, is placed on the semiconductor stack (A), and wherever the shadow of the mask falls, that part of the semiconductor stack resists being etched away by the plasma (B). Creating complex features requires repeated masking and etching (C and D), and each mask must be perfectly positioned. If the substrate moves or is stretched relative to the mask, the circuit will not be etched properly.

In the new process, called Self-Aligned Imprint Lithography, the template is a three-dimensional polymer material (E) that is etched simultaneously with the semiconductor stack to produce the desired circuit features (F). The height of the polymer controls which parts are etched. Because this material will stretch to match any distortions, a flexible substrate, such as a plastic, can be used to make the backing material of the display.

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