Making electronic devices from semiconducting polymers is not a new idea, but it has been so far almost limited to displays, like organic light-emitting diode (OLED) display technology. (Check "An Organic Revolution for Display Technology?" for example.)
In "Plastic Chips: New materials boost organic electronics," Science News writes that researchers at Northwestern University and Lucent Technologies have developed "a new class of organic semiconductor materials that could hasten the arrival of what could be the electronics revolution's next big wave."
Until recently, the fabrication of plastic electronics has been limited by the number of molecular building blocks suitable for making semiconducting polymers. Transistors -- which are the switches in an integrated circuit -- require two types of semiconductor materials: n-type and p-type. In n-type materials, charge flows through the material via electrons. P-type materials transport charge through "holes," places where electrons are missing.
"Yet, most of the organic materials examined so far have all been p-type," says lead investigator Tobin Marks at Northwestern. Existing n-type organics are rare and unstable. "So there's a real need for n-type materials," he says.
For a graphical explanation about the difference between n-type and p-type semiconductor s, please read this page about doped semiconductors.
Now, let's look at the technical aspects of these new materials.
[Marks] team's new class of molecules assembles into semiconductors of both p- and n-type. A rod-shaped organic molecule made of six thiophene units forms the basis for each type of material. Each thiophene, in turn, is a ring of five carbons and one sulfur. When the researchers replaced the rod's two end thiophenes with a perfluoroarene group (a ring of six carbons decorated with fluorines), the organic molecule behaved like an n-type semiconductor. When the researchers instead replaced the next two thiophenes from the ends, the molecule behaved as a p-type semiconductor.
Here is an image of these organic molecules yielding both n-type (left) and p-type (right) semiconductors for plastic electronic devices (Credit: Angewandte Chemie International Edition).
So what's next?
So far, the team has fabricated prototype transistors from the materials, which performed just as well as existing organic semiconductors do, as measured by the mobility of the electrons and holes.
Marks predicts that low-cost, even disposable plastic electronic devices, such as smart cards, electronic tags for tracking inventory, and chemical sensors, will emerge in the next couple of years.
Source: Alexandra Goho, Science News Online, August 28, 2003
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