As electronic devices become ever more complex, and the densities of components in those devices increases exponentially, we are rapidly approaching the day when the limitations of Moore's Law will be realized. In an effort to avert this eventuality, research has concentrated on moving away from traditional silicon technologies and into the realms of molecule-sized components and alternative materials. In this vein, researchers at the University of Georgia (UGA) and Ben-Gurion University (BGU) in Israel have, for the first time, created a nanoscale electronic diode from a single DNA molecule.
Diodes allow current to flow in one direction in an electric circuit, while blocking current in the opposite direction. Commonly known as "rectifiers" from their common usage in converting alternating current to direct current, diodes are an essential component in a vast range of electronic devices, and are printed in their millions on almost every variety of silicon chip. A simple component, even the smallest diodes are beginning to approach the limits as to how many can be packed onto a single integrated circuit.
"For 50 years, we have been able to place more and more computing power onto smaller and smaller chips, but we are now pushing the physical limits of silicon," says Dr. Bingqian Xu, principal investigator and associate professor in the UGA College of Engineering. "If silicon-based chips become much smaller, their performance will become unstable and unpredictable."
Many smaller components have been created, including an atom-sized optical switch and a molecule-sized diode, but the new diode from UGA and BGU is markedly different in that it is not made from inorganic material but, rather, using DNA - the building blocks of organic life itself.
Ordinarily, diodes are made from silicon with a p-n (positive-negative) junction at the point of contact between a positively "doped" semiconductor (that is, one that has had its electrical properties altered with additives) and a negatively doped one. Fitted with connecting electrodes (an anode on one side and a cathode on the other) at either end, the diode permits electric current to flow in one direction only, whilst blocking it from flowing in the reverse direction.
Using DNA to perform this task, on the other hand, was not simply a matter of fitting an electrode to either end of the molecule and plugging into a circuit whilst hoping for the best. Instead, the researchers found that DNA exhibited the properties of a diode when a smaller molecule known as "coralyne" was inserted into it.
Using a specifically designed single duplex DNA of 11 base pairs (that is, a "short" molecule) the team connected the coralyne-enhanced molecule to an electronic circuit a few nanometers long, and discovered that the current flowing through the DNA was 15 times greater for negative voltages than for positive voltages, thereby showing that the molecule was acting as a diode.
"This finding is quite counterintuitive because the molecular structure is still seemingly symmetrical after coralyne intercalation," said Associate Professor Xu.
According to the researchers, these findings may lead to advanced, smaller and more powerful electronic devices.
"Our discovery can lead to progress in the design and construction of nanoscale electronic elements that are at least 1,000 times smaller than current components," says Associate Professor Xu.
The results of this research were recently published in the journal Nature Chemistry.