“Making carbon nanotube transistors that are better than silicon transistors is a big milestone”.
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The nanotubes must make good electrical contacts with the metal electrodes of the transistor.
For the first time, scientists have built a transistor out of carbon nanotubes that can run nearly twice as fast as its silicon counterparts. According to IBM researchers, nanotube electronics could be operational sooner than expected, perhaps within the decade.
“This achievement has been a dream of nanotechnology for the last 20 years”, said study co-author Michael Arnold, a UW-Madison professor of materials science and engineering.
The highly efficient carbon nanotube transistors are a massive first step towards the use of carbon nanotubes in many semiconductor electronics technologies, such as high-speed wireless communications.
However, like any dream of such magnitude, there were obstacles, in particular, engineers had difficulty isolating the desired, pure carbon nanotubes from impurities such as metallic nanotubes. The tubes need to be as pristine as possible for their stellar properties to shine, otherwise they massively underperform.
“The end result are nanotubes with less than 0.01 percent metallic impurities, integrated on a transistor that was able to achieve a current that was 1.9 times higher than the most state-of-the-art silicon transistors in use today”, he says. This has proven very hard to control as we’re in the nanorange, or scales hundreds of times smaller than the thickness of a human hair. This is a self-assembly phenomenon triggered by rapidly evaporating a carbon nanotube solution. The team solved this minor setback by baking the insulating layer in a vacuum oven which removed this insulating interface.
The researchers also developed a treatment that removes residues from the nanotubes after they’re processed in solution. Semiconducting nanotubes can be used to build transistors, for example, and could even replace silicon in a host of future nanoelectronics devices because they are tiny, but can still carry huge amounts of current. Researchers say the transistors are especially promising for wireless communication technologies that depend on a lot of current that flow across a small area.
Carbon nanotubes (CNTs) are tantalizing candidates for semiconductor electronics due to their exceptional charge transport properties and one-dimensional electrostatics. There are also applications in energy since carbon nanotubes can up the efficiency of solar panels.
Work is now underway to adapt the new device to the geometry in traditional silicon transistors, and the technology has been patented through the Wisconsin Alumni Research Foundation. They are also busy developing high-performance radio frequency amplifiers.
“There has been a lot of hype about carbon nanotubes that hasn’t been realized, and that has kind of soured many people’s outlook”, he added. But we think hype is deserved. The effect has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors, CNTs, instead, have underperformed channel materials, such as Si, by sixfold or more. The result is that these CNT array FETs have a conductance that is seven times higher than any previous reported CNT array FET. This breakthrough in CNT array performance is a critical advance toward the exploitation of CNTs in logic, high-speed communications, and other semiconductor electronics technologies.
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The researchers, reporting their work in Science Advances DOI: 10.1126/sciadv.1601240, say that they are now working on further increasing the current density of their CNT-array FETs.
