Some laws are made to be broken, and others are made to be followed. A team
of IBM Researchers
in collaboration with two Swiss partners are looking to keep one law in particular
alive and well for another 15 years: Moore's Law. The law states that the number
of transistors that can be placed inexpensively on an integrated circuit will
double every 18 months. More than 50 years old, this law is still in effect,
but to extend it as long as 2020 will require a change from mere transistor
scaling to novel packaging architectures such as so-called 3D integration, the
vertical integration of chips.
The end result is a diamond-like carbon material that virtually doesn’t
wear, mass-produced at the nanoscale. The new nano-sized tip, researchers say,
wears away at the rate of only one atom per micrometer of sliding on a substrate
of silicon dioxide, much lower than that for a silicon oxide tip which represents
the current state-of-the-art. Consisting of carbon, hydrogen, silicon and oxygen
molded into the shape of a nano-sized tip and integrated on the end of a silicon
microcantilever for use in atomic force microscopy, the material has technological
implications for atomic imaging, probe-based data storage and emerging applications
such as nanolithography, nanometrology and nanomanufacturing.
The importance of the discovery lies not just in its size and resistance to
wear but also in the hard substrate against which it was shown to perform well
when in sliding contact: silicon dioxide. Because silicon—used in almost
all integrated circuit devices—oxidizes in atmosphere, forming a thin
layer of its oxide, this system is the most relevant for nanolithography, nanometrology
and nanomanufacturing applications.
Probe-based technologies are expected to play a dominant role in many such
technologies; however, poor wear performance of many materials when slid against
silicon oxide, including silicon oxide itself, has severely limited their usefulness
in the laboratory.
Researchers built the material from the ground up, rather than coating a nanoscale
tip with wear-resistant materials. The collaboration team used a molding technique
to fabricate monolithic tips on standard silicon microcantilevers. A bulk processing
technique is available that has the potential to scale up for commercial manufacturing.
Robert Carpick, professor in the Department of Mechanical Engineering and Applied
Mechanics at Penn, and his research group had previously shown that carbon-based
thin films, including diamond-like carbon, had low friction and wear at the
nanoscale; however, it has been difficult to fabricate nanoscale structures
made out of diamond-like carbon until now.
Understanding friction and wear at the nanoscale is important for many applications
that involve nanoscale components sliding on a surface.
“It is not clear whether materials that are wear-resistant at the macroscale
will exhibit the same property at the nanoscale,” lead author Harish Bhaskaran,
who was a postdoctoral research at IBM during the study, said.
Defects, cracks and other phenomena that influence material strength and wear
at macroscopic scales are less important at the nanoscale, which is why nanowires
can, for example, show higher strengths than bulk samples.
The study, published in the current edition of the journal Nature Nanotechnology,
was conducted collaboratively by Carpick and postdoctoral researcher Papot Jaroenapibal
of the Department of Mechanical Engineering and Applied Mechanics in Penn’s
School of Engineering and Applied Science; Bhaskaran, Bernd Gotsmann, Abu Sebastian,
Ute Drechsler, Mark A. Lantz and Michel Despont of IBM Research-Zurich; and
Yun Chen and Kumar Sridharan of the University of Wisconsin. Jaroenapibal currently
works at Khon Kaen University in Thailand, and Bhaskaran currently works at
Research was funded by a European Commission grant and the Nano/Bio Interface
Center of the University of Pennsylvania through the National Science Foundation.