Poor old carbon nanotubes. CNTs have long been heralded as the new wonder material, especially in electronics applications where their charge-carrier mobility was able to outperform silicon—according to some estimates by a factor of 10—but researchers have struggled to find a satisfactory proposal for getting them into some kind of ordered array.
While researchers have continued for the last 20 years to push CNTs beyond a single transistor or attempted to use their propensity for forming a rat’s nest as a strength rather than a weakness, they have faced the unexpected problem over the last decade of their toxicological issues.First, the research hasn’t progressed quite as hoped. Then, environmental, health, and safety concerns presented an entirely new challenge. But—as though those two weren’t enough—along comes a new wonder material: graphene.
As I said, poor old CNTs. So it should come as no surprise in the tale of woe that has followed CNTs that NIST should report CNTs have a major reliability issue in electronics.
The research was presented in a paper at the recent IEEE Nano 2011 in Portland, Oregon. From the NIST Web site:
One of the authors of the paper, Mark Strus, a NIST postdoctoral researcher, suggested that while this research may spell the end for CNTs as “the replacement for copper in logic or memory devices,” there still remained the possibility of using the material for “interconnects for flexible electronic displays or photovoltaics.” That is, of course, when just looking at CNTs’ use as an interconnect. The field of research for CNTs has become so broad over the past 20 years that they are being tested for use in fields as divergent as electrodes in lithium-ion batteries to improving medical imaging.
“…NIST researchers fabricated and tested numerous nanotube interconnects between metal electrodes. NIST test results, described at a conference this week, show that nanotubes can sustain extremely high current densities (tens to hundreds of times larger than that in a typical semiconductor circuit) for several hours but slowly degrade under constant current. Of greater concern, the metal electrodes fail—the edges recede and clump—when currents rise above a certain threshold. The circuits failed in about 40 hours.”
We haven’t yet reached the point of singing CNTs swan song.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.