What is a quantum interference effect transistor and how would it work?

The quantum interference effect transistor (QuIET) is a single-molecule device to control electric current between two terminals. It works by using the wave-like, rather than particle-like, properties of electrons.

When the transistor is off, the special symmetry of certain aromatic molecules causes destructive interference of the electron waves, which prevents current from flowing through the device. By changing the voltage of a third terminal, one can break the molecular symmetry, so that the electron waves no longer cancel out, and current can flow through the device.

What gives your design the edge over today's technologies?

The QuIET has two major advantages over current semiconductor devices, apart from its extremely small size. The first advantage is that its operation could be much cooler than that of a standard transistor. In a conventional transistor, a lot of heat is generated by raising and lowering an energy barrier to turn the current off and on. In the QuIET, no energy barrier is necessary to block the current flow; this is achieved by wave interference.

The second major advantage of the QuIET is its electrical robustness. If one tried to scale conventional semiconductor devices down to a size of one nanometer, their operation would be extremely sensitive to tiny device-to-device variations; even a single atom out of place could push such a device out of its operating range. The active element of the QuIET is a molecule that can be fabricated with atomic precision by synthetic chemistry, and its operation is not sensitive to small variations in the structure of the metal/molecular terminals contacting the molecule.

How far away do you think the scientific community is from realizing such a device?

We believe it is possible to make a QuIET in the laboratory using a combination of current techniques, such as mechanically-controllable break junctions and scanning probe microscopy, although this will be a very challenging task! It's hard to say how long it will be until the QuIET is ready for mass production.

Looking at the challenges, what do you feel is the biggest hurdle?

The biggest experimental hurdle in building a QuIET is bringing three leads close enough together with precision, which has never been done before. Nonetheless, over the last few years we have seen a plethora of new techniques which indicate that the field is moving in this direction.

What steps are you taking to get the idea off the ground?

Our group is working to improve the accuracy of the theory by going beyond the mean-field treatment of electron-electron interactions. We are also studying the effect of using terminals other than bulk metal electrodes to contact the molecule.

On the practical side, the University of Arizona's Office of Technology Transfer (see links) is actively seeking industrial partners for this venture - we are very keen for someone to build a real device in the lab.

The researchers presented their work in issue 42 of Nanotechnology - a special issue devoted to a better understanding of the function and design of molecular-scale devices that are relevant to future electronics and sensor technology.

•  About Nanotechnology issue 42

This special issue of the journal, edited by Predrag Krstic (Oak Ridge National Laboratory), Anatoli Korkin (Nano & Giga Solutions, Inc.), Nongjian Tao (Arizona State Uni) and Erica Forzani (Arizona State Uni), is free to read online for an extended period until the end of December 2007. Please visit http://www.iop.org/journals/nano/specialissue.

To find out more about Nanotechnology, including benefits for authors and guidelines on writing for the journal, please visit http://nanotechweb.org/cws/journals/featured.