Single molecule transistor

Researchers in Canada have designed and tested a new concept for a single molecule transistor.


Principal investigator Dr. Robert Wolkow, postdoctoral fellow Dr. Paul Piva and a team of researchers from the University of Alberta and the National Institute for Nanotechnology of the Canadian National Research Council have designed and tested a new concept for a single molecule transistor.



They have shown, for the first time, that a single charged atom on a silicon surface can regulate the conductivity of a nearby molecule. Their research is published in the June 2, 2005 edition of the scientific journal Nature.



Miniaturisation of microelectronics has a finite end based on today’s technology. A new concept to circumvent the limits of conventional transistor technology was needed. The authors conducted an experiment to examine the potential for electrical transistors on a molecular scale. Their approach has solved what has been an insurmountable hurdle to making a molecular device: getting connections onto a single molecule.



They demonstrated that a single atom on a silicon surface can be controllably charged, while all surrounding atoms remain neutral. A molecule placed adjacent to that charged site is ‘tuned’, which allows electrical current to flow through the molecule from one electrode to another. The current flowing through the molecule can be switched on and off by changing the charge state of the adjacent atom.



“We have shown the potential for devices of unheard-of smallness and unheard-of efficiency,” says Dr. Wolkow. “A technology based on this concept would require much less energy to power, would produce much less heat, and run much faster.



Wolkow’s team solved the connection problem by using the electrostatic field emanating from a single atom to regulate the conductivity of a molecule, allowing an electric current to flow through the molecule. These effects were easily observed at room temperature, in contrast to previous molecular experiments that had to be done at temperatures close to absolute zero in order to measure a conductivity change.



Another significant aspect of this breakthrough is the fact that only one electron from the atom is needed to turn molecular conductivity on or off. On a conventional transistor, this gating action requires about one million electrons.



“This concept could circumvent the limits of conventional transistor technology and permit miniaturisation on a nanometric scale. In our case, we also have a potentially powerful green technology because of its minimal power and material requirements, and the biodegradable nature of the device.”



Wolkow says that although his results represent a key step toward molecular electronics, more steps are required. He advocates doing research on hybrid molecular/silicon devices. “This way, we can piggyback on all the great capacity that has already been established for silicon, and just supplement it. Our prototype works on silicon–thus allowing the old technology to merge with the new.”


“I am optimistic that molecular electronic devices can be made using our method because I don’t see a reason why the remaining hurdles can’t be overcome. And given the promise of such devices–great speed, small size, and high efficiency–the hurdles are definitely worth tackling.”