February 2005

Synopsis: Nanotechnology

Better insulation helps plastic circuits flex toward the market.

By Monya Baker (edit)

Low-Power Organics
Better insulation helps plastic circuits flex toward the market

Context: Computer chips contain millions of transistors made of silicon. But silicon is too brittle to be used in applications such as flexible displays and smart fabrics that monitor vital signs. Such products will require new materials, ideally plastics. But all "organic transistors" so far have required voltages too high and consumed power too quickly to be viable. Researchers from Siemens spin-off Infineon, the University of Stuttgart, and MIT have created organic transistors that seem to surmount these barriers.

Methods and Results: A transistor is an electronic switch that flips when voltage is applied to a wire on top of a semiconductor. However, if the wire comes in contact with the semiconductor, the circuit will leak, or waste, electrical current. So transistors are insulated from the wires that flip them by a layer of material called a "gate dielectric." Fabricating these layers is perhaps the most challenging aspect of building transistors: thinner layers allow operation at lower voltages but are prone to pinhole-like defects through which current can leak. Up to now, organic transistors used dielectrics more than 100 nanometers thick and required more than 20 volts to operate. Infineon's Marcus Halik and his team grew a pinhole-free film only 2.5 nanometers thick from molecules that "self-assemble." Transistors placed atop this film switched using less than two volts and drew even less current than transistors in conventional silicon chips.

Why it Matters: Organic transistors could be used to build displays that bend like paper, cloth that computes, and cheap electronic bar codes. By demonstrating low-voltage organic transistors, researchers may have eliminated a barrier to the commercialization of such devices.

Source: Halik, M. et al. 2004. Low-voltage organic transistors with an amorphous molecular gate dielectric. Nature 431:963-966.