Organic Electronics: A Cleaner Substitute for Silicon. (Environews Innovations)
Frazer, Lance, Environmental Health Perspectives
Until recently, plastics--ubiquitous in most areas of modern life--had yet to make inroads into the electronics industry; their molecular configuration made them nonconducive to electrical flow, limiting their uses to shells for computers and insulation for wires. But the last few years have brought discoveries that plastic polymers can be manipulated so they may be fashioned into transistors, conductors, and other electrical components. Such uses for these carbon/hydrogen/oxygen-based polymers are the subject of the field of organic electronics.
"This is a rapidly developing industry," says Michael Schen, group leader of the Electronics and Photonics Group of the National Institute of Standards and Technology Advanced Technology Program. "We are hearing about a wide variety of potential applications, [including] transistors, electronic circuits, high-density energy storage devices, advanced emissive displays, and advanced photovoltaics." And the benefits of plastics are substantial--in many cases, researchers are finding they offer a safer, cheaper, lighter alternative to silicon.
Safer, Cheaper, Lighter
Schen says organic electronics involves a much smaller set of hazardous compounds and materials than more traditional technologies. Gone are the arsenic (used in semiconductor manufacture), phosphine (used in transistor manufacture), lead (used in the phosphorescent coating in a traditional cathode ray tube, or CRT), and mercury (used in backlights).
Silicon and silicon-based components require millions of gallons of water and temperatures of 300-500[degrees]C to manufacture. A wide range of solvents are used in silicon and in semiconductor manufacture, including highly toxic xylene and toluene. The semiconductor industry uses hundreds of thousands of gallons of such solvents annually.
In contrast, says Stewart Hough, vice president of business development for Cambridge Display Technology, his company can create components at atmospheric pressure, and at temperatures of no more than 150[degrees]C. And, although the company does use solvents with its organic technology, "we can make ten thousand displays with one liter of standard organic solvent," he says. Furthermore, says Bernard Kippelen, an associate professor of optical sciences at the University of Arizona Optical Sciences Center, it may be possible to design organics that are soluble in less harmful solvents.
Polymers also are lighter and can cost much less to manufacture, although cost comparisons vary. Kippelen says his center's deposition machine is capable, after adaptation, of applying multilayer metal and organic layers as thin as 10 nanometers to a flexible plastic substrate at a cost approaching 1 cent per square centimeter (compared to a dollar or so to produce a square centimeter of silicon substrate). "Organic fabrication is compatible with plastic substrates, which means you can use a very low-cost ... substrate," he says. "Additionally, organics are good for large-area needs. For example, if you need a piece of silicon for a fingerprint recognition device, that one-square-centimeter piece of highly purified silicon"--which is quite large in terms of ultrapure silicon usage--"will be very expensive."
According to Kippelen, an organic photovoltaic cell could weigh 100 times less than a silicon-based cell. And, he says, "the promise with organics is related to the lower cost of the raw materials, in particular the substrate on which the device is built--a silicon wafer is more expensive than a sheet of plastic."
Experts generally concede that polymers won't be replacing silicon in certain applications, such as computer semiconductors, because silicon will always be significantly faster. However, plastics can serve as a substitute in applications where silicon is either impractical or too expensive to use. And improvements are on the way. "The technology is admittedly not at the same stage of maturity as something like LCD [liquid crystal display] technology, but this is a technology with great promise," Hough says. …