Researchers at the University of Pennsylvania have
developed a reliable, reproducible method for parallel fabrication of
multiple nanogap electrodes, a development crucial to the creation of
mass-produced nanoscale electronics.
Charlie Johnson, associate professor in the Department of
Physics and Astronomy and the Department of Materials Science and
Engineering at Penn, and colleagues created the self-balancing
single-step technique using feedback controlled electromigration, or
FCE. By using a novel arrangement of nanoscale shorts they showed that
a balanced self-correcting process occurs that enables the simultaneous
electromigration of sub-5 nm sized nanogaps. The nanogaps are
controllably formed by carefully applying an electric current which
pushes the atoms of the metallic wire through the process of
electromigration.
In the study, the researchers described the simultaneous
self-balancing of as many as 16 nanogaps using thin sheets of gold and
FCE methodology originally developed at Penn. Using electron-beam
lithography, Penn researchers constructed arrays of thin gold leads
connected by narrow constrictions that were less than 100 nm in width.
Introducing a voltage forced electrons to flow through these narrow
constrictions in the gold, meeting with greater resistance as each
constriction narrowed in response to electromigration. The narrower the
constriction, the more the electrons were forced to the other, wider
constrictions, in order to take a path of least resistance. This
balanced interplay ensured that the electromigration process occurred
simultaneously between the constrictions. After a few minutes, the
applied electrons narrowed the constrictions until they opened to form
gaps of roughly one nanometer in size with atomic-scale uniformity. By
monitoring the electric-current feedback, researchers could adjust the
size of the nanogaps as well.
Nanotechnology shows promise for revolutionizing materials and
electronics by reducing the size and increasing the functionality of
new composite materials; however, creating these materials is time
consuming and costly, and it requires precise control at the atomic
level, a scale that is difficult or impossible to achieve with current
technology.
During the last several years there has been progress towards
developing single nanometer-sized gaps and nanodevices. Yet their
extremely low reproducibility has hindered any real chance of their use
on the industrial scale, which is crucial to the development of the
complex circuits that would be required to build, for example, a
computer out of nanoelectronics.
“Reproducibility is one of the major issues facing
nanotechnology, and it’s required us to depart from the
standard ways of achieving this in micro-electronics
processing.” Said Douglas Strachan of the Department of
Materials Science and Engineering and the Department of Physics and
Astronomy at Penn. “When you first hear of opening up a wire
with a current, you usually think of a fuse. To think that this sort of
technique could actually lead to atomically-precise nanoelectronics is
sort of mind blowing.”
Danvers Johnston of the Department of Physics and Astronomy
said, “Since it is impossible to mold nanoscale-size objects
with any other lab tools, we direct the electrons to get them to do the
work for us.”