Large-scale flexible electronics are similar in some respects to the active-matrix LCDs found nowadays on virtually every laptop computer, PDA, and cellphone. Like those displays, many types of flexible electronics are much larger than conventional ICs, and they are not built on silicon. The main difference is that the conventional displays are built on brittle, rigid glass plates, while flexible circuits are built on thin, pliable sheets of plastic. Transistors that can bend along with the plastic would have to be very thin—just a fraction of a micrometer. On silicon chips, it isn't the transistors themselves that are inflexible, it's the relatively thick silicon wafer in which the transistors are fabricated.

Two basic alternative materials have the potential to make thin transistors on flexible substrates: amorphous silicon (the technology used in the Samsung display mentioned above) and organic polymers. To understand how the flexible circuits are made, first consider the standard lithography-based process that creates ICs, of both the silicon and plastic varieties.

In logic ICs, transistors act like switches. A voltage on a terminal called the gate turns the transistor on, allowing charge to flow in a "channel" between the other two terminals, which are called the source and the drain. Removing the voltage stops the flow.

As with silicon ICs, large-scale flexible electronics are built up layer by layer. First, the plastic substrate is uniformly coated with a film of the material—either amorphous silicon or an organic polymer—that will form the sources, drains, and channels of the transistors. That layer is covered with a layer of insulation, which is covered in turn by a layer of metal or semiconductor to form the gate. The material on top of this three-layer sandwich is covered with a photosensitive material, or photoresist, which is exposed to a pattern of light that represents the gates in the flexible circuit. Areas of photoresist exposed to the light become soluble. The unexposed regions remain insoluble.

If more than one circuit is to be built on a single substrate, a movable stage that holds the substrate shifts it to a new site, which is exposed to the light pattern next. For conventional silicon ICs, hundreds of chips, each about a square centimeter, are typically made on a single silicon wafer. But because large-scale flexible circuits can be tens of centimeters on a side, a single flexible substrate will usually hold fewer than 10 of them—and, for very large circuits, perhaps just one.

After all of the circuit sites have been exposed, the soluble photoresist is rinsed off, leaving a pattern where the gates are to be located. An etching process takes away all of the gate material not covered by photoresist, leaving the gate pattern. The remaining unexposed photoresist is removed next, exposing the uniform layers of insulator and semiconductor into which the sources and drains will go, along with the gates.

The same basic expose-and-etch process is repeated several times with different patterns of light: first to remove the insulation where the source and drain contacts will go, then to pattern the semiconductor into individual transistors, and finally to create the wires that connect the transistors into circuits.

There are several important differences between this process for making flexible circuits and the one used to make silicon ICs. In the first case, the sources, drains, and channels sit on top of the flexible substrate. But in silicon chips, they are built right into the silicon wafer. For flexible electronics, the gate insulation is deposited onto the flexible substrate, then etched to shape. For silicon wafers, silicon dioxide is used to insulate the gate; it is grown by exposing the silicon wafer to oxygen.

A third important difference is that silicon wafers undergo several heating steps that reduce the resistance of the transistors so they will switch faster. During these steps, temperatures can exceed 1000 ºC. Such heat could melt plastic.

In theory, at least, plastic circuits can be made more cheaply than conventional silicon ICs because the circuits and manufacturing processes are simpler. For example, to get a good yield of working chips, conventional semiconductor plants must essentially rid the air of particles down to sizes of only a few nanometers—about the dimensions of a virus. But because the transistors in flexible electronic circuits are much larger—up to 25 m as opposed to 0.1 m—the allowable particle size is also much larger, which makes the air-filtration task a lot easier and cheaper. Also, an IC can have more than 30 layers of patterned material; flexible circuits—for example, in a flexible display—would typically have only about 10. These differences, however, bring the costs down by perhaps 80 percent, but not to the factor-of-10 reduction that analysts say is needed to make plastic circuits ubiquitous. The tradeoff, of course, is slower circuitry.