14 DAY TRIAL // One of the main engines of our civilization as we know it is the miniaturization of the transistor, the main gateway inside microprocessors. Over the past couple of decades, the race has been on to produce the smallest, most efficient transistors, and also to fit as many of them as possible in a small space. But, at this point, the materials that set the basis for this technology are beginning to reach their limits, and researchers are looking for new ones to take their place. One possibility, scientists and industry representatives say, would be silicon-germanium nanowires.
Developed by a group of experts at the University of California in Los Angeles (UCLA) Henry Samueli School of Engineering and Applied Science, the Purdue University and IBM, the new nanostructures are now efficient enough to be used in the next generation of transistors, the experts say. The semiconducting wires have been successfully grown to needed proportions, the experts announce, underlying the fact that the innovation could be used to produce faster, smaller and more powerful electronics to power tomorrow's world.
The nanowires the team produced can be grown to several millimeters in length, but have a diameter of only a few tens to a few hundreds of nanometers (billionths of a meter), Suneel Kodambaka explains. The UCLA professor of materials science and engineering is also the coauthor of a new study detailing the findings, which appears in the November 27 issue of the top journal Science.
“We are excited for two reasons. One is that we have extended our knowledge of the fundamental physics of the process by which nanowires grow. The other is the improved prospect of using nanowires in high-performance electronic devices,” IBM Nanoscale Materials Analysis Department Manager Frances Ross, who is also the corresponding author of the Science paper, adds. “The nanowires are so small you can place them in virtually anything. Because of their small size, they are capable of having distinctly different properties, compared to their bulk counterparts,” Kodambaka says.
Another great feat of the nanowires achieved by the group is the fact that it managed to create them out of alternating layers of silicon and germanium. It also made them defect-free, and with an atom-scale resolution, meaning that they are atomically sharp at their junctions. Such close interfaces allow the material to carry electrons (electrical current) very well, thus boosting the abilities of the transistors, and of the processors themselves. “We think this study is significant because it provides a solution to the problem of growing sharp interfaces in nanowires, thereby addressing an important limitation in the growth of nanowires,” Ross says.
“The challenge was to create a really sharp interface between the silicon and germanium in each wire. So we cooled the liquid droplets until they solidified. This allowed us to get rid of excess silicon in the alloy. Then, germanium wire segments could be grown on the silicon with the introduction of germanium vapor, and sharp interfaces formed,” Kodambaka adds of the production process and the difficulties facing the team's efforts.