PORTLAND, Ore. Moore's Law predicts that chip densities will continue to rise merely by scaling them to smaller and smaller dimensions. Unfortunately, as the thickness of silicon layers shrink to the nanoscale, their resistance tends to increase, potentially breaking Moore's Law by capping the utility of further density increases.
Now, University of Wisconsin researchers have discovered a surface-treatment that reverses that trend, enabling nanoscale membranes of silicon to conduct better as they get thinner, thereby extending Moore's Law all the way to atomic dimensions.
"If you make silicon half as thick, you would expect it to conduct half as well," said Paul Evans a materials science and engineering professor on the Madison campus. "But it turns out that silicon can conduct even better at the nanoscale if the surface is well prepared."
Evans worked with fellow professors Mark Eriksson, Irena Knezevic and Max Lagally along with research scientists Donald Savage, and doctoral candidates Pengpeng Zhang, Emma Tevaarwerk and Byoung-Nam Park.
The team discovered that as silicon layers dip below 200 nanometers in thicknesswhat they consider "nanomembranes"the normal determinants of conductivity, such as dopants, become irrelevant. Instead, it is the atomic accuracy of the surface that determines conductivity.
In fact, the team found that when atomically accurate silicon nanomembranes were cleaned free from oxide contaminations, they became 10 times more conductive. As nanomembrane thickness shrunk toward 10 nanometers, a careful surface preparation could increase conductivity by as much as 1 million-fold.
"What this tells us is that if you're building nanostructures, the surface is what's really important," said Evans.