Researchers used a rapid-deposition process to attach an aligned array of carbon nanotubes on a 1-inch X 1-inch substrate. (via WISC)
Materials engineers from the University of Wisconsin have finally developed a process that turns carbon nanotubes into resistors that can outperform traditional silicon or even gallium-based transistors. How much faster are they compared to silicon- 1.9-times faster to be exact, making them a viable candidate for batteries with longer life, faster Wi-Fi and faster processors.
Scientists have been trying for years to replace silicon with carbon but some issues were holding them back, most notably getting pure nanotubes with limited defects and putting them in a structured order. Without those, their performance is limited, disrupting their semiconducting properties- essentially underperforming when compared to using traditional materials. To get the near-perfect nanotubes separated from the subpar tubes, the engineers turned to a solution of polymers to sort-out the imperfect (metallic) tubes, leaving only high-quality carbon semiconducting tubes. The engineers then baked the arrays in a vacuum to get rid of the polymers insulating layer between the nanotubes and the resistor’s electrodes.
To get the nanotubes in alignment and parallel on a wafer, the engineers used a process called floating evaporative self-assembly.
Another problem the engineers needed to tackle was getting the nanotubes in perfect alignment with equal spacing deposited on a substrate. To do this, the team turned to a process known as floating evaporative self-assembly (FESA), which is done by dropping the nanotube solution in a water bath and then vertically dunking the substrate in and out of the bath, This process causes the tubes to self-align with equal spacing when the nanotube solution evaporates.
With that issue out of the way, the engineers then proceeded to turn the nanotubes into a functioning transistor by first coating the new wafer with a PMMA resist (polymeric material) and then patterned using electro-beam lithography. After that process, the unwanted or defective material is etched away from the wafer. Acetone is then used to clear away the rest of the PMMA material and then palladium contacts are added to the nanotubes resulting in a FET (field Effect Transistor.
Don’t expect to see these new nanotube transistors in mobile devices or PCs anytime soon however, as there are many refinements they must undergo before they can be mass-produced, including scaling up the manufacturing process and adapting them to current silicon-based geometries. Still, it will not be that far off before these issues are resolved, making the future look that much brighter and faster.
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