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Over the past 15 years, alternative materials similar graphene and carbon nanotubes (CNTs) have been touted as potential solutions to the silicon scaling issues that have left existing microprocessors largely stuck between 3.5 – 5GHz. In both cases, research into the new materials has struggled to create products that could be commercialized. Neither has advanced to the point where they could be integrated into large scale manufacturing. Researchers at the University of Wisconsin accept recently announced a breakthrough, withal — one that could atomic number 82, in the long term, to profitable solutions that incorporate carbon nanotubes in shipping products.

1 of the critical problems facing carbon nanotubes is the difficulty of putting them precisely where they're needed. In the past, manufacturers have achieved 88-94% precision. In 2013, nosotros wrote almost a new sorting method that could achieve 95-98% precision — still well beneath the estimated 99.96% precision the ITRS roadmaps at the time had estimated would be required for commercial manufacturing. At present, the University of Wisconsin has claimed it can achieve purity rates of up to 99.98%.

The paper, published in Science Advances notes:

[Constraints] in CNT sorting, processing, alignment, and contacts requite rise to nonidealities when CNTs are implemented in densely packed parallel arrays such equally those needed for technology… In each scenario, the result has been that, whereas CNTs are ultimately expected to yield FETs that are more conductive than conventional semiconductors for logic applications, CNTs, instead, have underperformed channel materials, such as Si, past sixfold or more than. Likewise, in RF applications, depressed on-state conductance and imperfect saturation characteristics arising from metal CNTs and inter-CNT interactions have express the maximum frequency of oscillation and linearity.

The paper goes on to note how fifty-fifty a single metallic CNT tin can short-circuit a FET (Field Effect Transistor) and result in essentially reduced performance. Building arrays of CNTs at exceptionally high purity isn't optional — it's been a central stumbling block that companies like IBM have sought to solve for years. In order to achieve this milestone, the Wisconsin team uses a technique information technology first discussed in 2014 — floating evaporative self-associates, as shown below.

FESA

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Here's how the team describes its findings.

CNT assortment FETs are demonstrated hither with an on-country conductance of 1.7 mS μm−i and a conductance per CNT equally high equally 0.46 G0, which is vii times higher than previous state-of-the-art CNT array FETs made by other methods. These FETs are nearing the performance of land-of-the-fine art unmarried CNT FETs but in the format of an array in which quasi-ballistic transport is simultaneously driven through many, tightly packed CNTs in parallel, essentially improving the absolute electric current bulldoze of the FETs and, therefore, their utility in technologies.

The exceptional performance of the arrays achieved here is attributed to the combined outstanding alignment and spacing of the CNTs, the postdeposition handling of the arrays to remove solvent residues and the insulating side chains of the polymers that wrap the CNTs, and the exceptional electronic-type purity of the semiconducting CNTs afforded past the utilize of polyfluorenes as CNT-differentiating agents. The performance of previous CNT assortment FETs has non been as high, likely because these FETs accept not simultaneously met all of these attributes.

The team believes information technology has a path forward to keep improving CNT FETs and scaling them upwards to come across modern semiconductor manufacturing. The difficulty of this step, yet, tin can't be overstated. Correct now, the University of Wisconsin is working with one-inch square wafers. Traditional wafers are between 200-300mm — vastly larger than the tiny squares of test fabric that the UW team worked with. The team also benchmarked its results confronting 90nm MOSFETs — and while that'southward not a bad choice for a lab test, electric current semiconductor manufacturing left 90nm backside more than than ten years agone.

If carbon nanotubes could be commercialized, information technology could kickstart semiconductor scaling again, at least for certain applications. Only the road betwixt fifty-fifty this breakthrough and mass commercialization is still a long one — don't expect to see CNTs shipping in logic for another 5-10 years, if it ever does. Other niche applications may notice more immediate benefits. Merely CPUs and SoCs tend to sit at the very forefront of our engineering curve. That makes it comparatively difficult for new technology to offer large enough improvements to overtake the industry.