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MIT engineers build advanced microprocessor out of carbon nanotubes

Posted By Graphene Council, The Graphene Council, Tuesday, September 3, 2019

After years of tackling numerous design and manufacturing challenges, MIT researchers have built a modern microprocessor from carbon nanotube transistors, which are widely seen as a faster, greener alternative to their traditional silicon counterparts.

The microprocessor, described today in the journal Nature, can be built using traditional silicon-chip fabrication processes, representing a major step toward making carbon nanotube microprocessors more practical.

Silicon transistors — critical microprocessor components that switch between 1 and 0 bits to carry out computations — have carried the computer industry for decades. As predicted by Moore’s Law, industry has been able to shrink down and cram more transistors onto chips every couple of years to help carry out increasingly complex computations. But experts now foresee a time when silicon transistors will stop shrinking, and become increasingly inefficient.

Making carbon nanotube field-effect transistors (CNFET) has become a major goal for building next-generation computers. Research indicates CNFETs have properties that promise around 10 times the energy efficiency and far greater speeds compared to silicon. But when fabricated at scale, the transistors often come with many defects that affect performance, so they remain impractical.

The MIT researchers have invented new techniques to dramatically limit defects and enable full functional control in fabricating CNFETs, using processes in traditional silicon chip foundries. They demonstrated a 16-bit microprocessor with more than 14,000 CNFETs that performs the same tasks as commercial microprocessors. The Nature paper describes the microprocessor design and includes more than 70 pages detailing the manufacturing methodology.

The microprocessor is based on the RISC-V open-source chip architecture that has a set of instructions that a microprocessor can execute. The researchers’ microprocessor was able to execute the full set of instructions accurately. It also executed a modified version of the classic “Hello, World!” program, printing out, “Hello, World! I am RV16XNano, made from CNTs.”

“This is by far the most advanced chip made from any emerging nanotechnology that is promising for high-performance and energy-efficient computing,” says co-author Max M. Shulaker, the Emanuel E Landsman Career Development Assistant Professor of Electrical Engineering and Computer Science (EECS) and a member of the Microsystems Technology Laboratories. “There are limits to silicon. If we want to continue to have gains in computing, carbon nanotubes represent one of the most promising ways to overcome those limits. [The paper] completely re-invents how we build chips with carbon nanotubes.”

Joining Shulaker on the paper are: first author and postdoc Gage Hills, graduate students Christian Lau, Andrew Wright, Mindy D. Bishop, Tathagata Srimani, Pritpal Kanhaiya, Rebecca Ho, and Aya Amer, all of EECS; Arvind, the Johnson Professor of Computer Science and Engineering and a researcher in the Computer Science and Artificial Intelligence Laboratory; Anantha Chandrakasan, the dean of the School of Engineering and the Vannevar Bush Professor of Electrical Engineering and Computer Science; and Samuel Fuller, Yosi Stein, and Denis Murphy, all of Analog Devices.

Fighting the “bane” of CNFETs

The microprocessor builds on a previous iteration designed by Shulaker and other researchers six years ago that had only 178 CNFETs and ran on a single bit of data. Since then, Shulaker and his MIT colleagues have tackled three specific challenges in producing the devices: material defects, manufacturing defects, and functional issues. Hills did the bulk of the microprocessor design, while Lau handled most of the manufacturing.

For years, the defects intrinsic to carbon nanotubes have been a “bane of the field,” Shulaker says. Ideally, CNFETs need semiconducting properties to switch their conductivity on an off, corresponding to the bits 1 and 0. But unavoidably, a small portion of carbon nanotubes will be metallic, and will slow or stop the transistor from switching. To be robust to those failures, advanced circuits will need carbon nanotubes at around 99.999999 percent purity, which is virtually impossible to produce today.  

The researchers came up with a technique called DREAM (an acronym for “designing resiliency against metallic CNTs”), which positions metallic CNFETs in a way that they won’t disrupt computing. In doing so, they relaxed that stringent purity requirement by around four orders of magnitude — or 10,000 times — meaning they only need carbon nanotubes at about 99.99 percent purity, which is currently possible.

Designing circuits basically requires a library of different logic gates attached to transistors that can be combined to, say, create adders and multipliers — like combining letters in the alphabet to create words. The researchers realized that the metallic carbon nanotubes impacted different pairings of these gates differently. A single metallic carbon nanotube in gate A, for instance, may break the connection between A and B. But several metallic carbon nanotubes in gates B may not impact any of its connections.

In chip design, there are many ways to implement code onto a circuit. The researchers ran simulations to find all the different gate combinations that would be robust and wouldn’t be robust to any metallic carbon nanotubes. They then customized a chip-design program to automatically learn the combinations least likely to be affected by metallic carbon nanotubes. When designing a new chip, the program will only utilize the robust combinations and ignore the vulnerable combinations.

“The ‘DREAM’ pun is very much intended, because it’s the dream solution,” Shulaker says. “This allows us to buy carbon nanotubes off the shelf, drop them onto a wafer, and just build our circuit like normal, without doing anything else special.”

Exfoliating and tuning

CNFET fabrication starts with depositing carbon nanotubes in a solution onto a wafer with predesigned transistor architectures. However, some carbon nanotubes inevitably stick randomly together to form big bundles — like strands of spaghetti formed into little balls — that form big particle contamination on the chip.  

To cleanse that contamination, the researchers created RINSE (for “removal of incubated nanotubes through selective exfoliation”). The wafer gets pretreated with an agent that promotes carbon nanotube adhesion. Then, the wafer is coated with a certain polymer and dipped in a special solvent. That washes away the polymer, which only carries away the big bundles, while the single carbon nanotubes remain stuck to the wafer. The technique leads to about a 250-times reduction in particle density on the chip compared to similar methods.

Lastly, the researchers tackled common functional issues with CNFETs. Binary computing requires two types of transistors: “N” types, which turn on with a 1 bit and off with a 0 bit, and “P” types, which do the opposite. Traditionally, making the two types out of carbon nanotubes has been challenging, often yielding transistors that vary in performance. For this solution, the researchers developed a technique called MIXED (for “metal interface engineering crossed with electrostatic doping”), which precisely tunes transistors for function and optimization.

In this technique, they attach certain metals to each transistor — platinum or titanium — which allows them to fix that transistor as P or N. Then, they coat the CNFETs in an oxide compound through atomic-layer deposition, which allows them to tune the transistors’ characteristics for specific applications. Servers, for instance, often require transistors that act very fast but use up energy and power. Wearables and medical implants, on the other hand, may use slower, low-power transistors.  

The main goal is to get the chips out into the real world. To that end, the researchers have now started implementing their manufacturing techniques into a silicon chip foundry through a program by Defense Advanced Research Projects Agency, which supported the research. Although no one can say when chips made entirely from carbon nanotubes will hit the shelves, Shulaker says it could be fewer than five years. “We think it’s no longer a question of if, but when,” he says.

Tags:  Analog Devices  Carbon Nanotubes  Graphene  Max M. Shulaker  MIT  transistor 

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From 2D to 1D: Atomically quasi '1D' wires using a carbon nanotube template

Posted By Graphene Council, The Graphene Council, Wednesday, April 24, 2019
Updated: Tuesday, April 23, 2019
Researchers from Tokyo Metropolitan University have used carbon nanotube templates to produce nanowires of transition metal monochalcogenide (TMM), which are only 3 atoms wide in diameter. These are 50 times longer than previous attempts and can be studied in isolation, preserving the properties of atomically quasi "1D" objects. The team saw that single wires twist when perturbed, suggesting that isolated nanowires have unique mechanical properties which might be applied to switching in nanoelectronics.

Two-dimensional materials have gone from theoretical curiosity to real-life application in the span of less than two decades; the most well-known example of these, graphene, consists of well-ordered sheets of carbon atoms. Though we are far from leveraging the full potential of graphene, its remarkable electrical and thermal conductivity, optical properties and mechanical resilience have already led to a wide range of industrial applications. Examples include energy storage solutions, biosensing, and even substrates for artificial tissue.

Yet, despite the successful transition from 3D to 2D, the barrier separating 2D and 1D has been significantly more challenging to overcome. A class of materials known as transition metal monochalcogenides (TMMs, transition metal + group 16 element) have received particular interest as a potential nanowire in precision nanoelectronics. Theoretical studies have existed for over 30 years, and preliminary experimental studies have also succeeded in making small quantities of nanowire, but these were usually bundled, too short, mixed with bulk material or simply low yield, particularly when precision techniques were involved e.g. lithography. The bundling was particularly problematic; forces known as van der Waals forces would force the wires to aggregate, effectively masking all the unique properties of 1D wires that one might want to access and apply.

Now, a team led by Assistant Professor Yusuke Nakanishi from Tokyo Metropolitan University has succeeded in producing bulk quantities of well-isolated single nanowires of TMM. They used tiny, open-ended rolls of single-layered carbon, or carbon nanotubes (CNTs), to template the assembly and reaction of molybdenum and tellurium into wires from a vapor. They succeeded in producing single isolated wires of TMM, which were only 3-atoms thick and fifty times longer than those made using existing methods. These nanometer-sized CNT "test tubes" were also shown to be not chemically bound to the wires, effectively preserving the properties expected from isolated TMM wires. Importantly, they effectively "protected" the wires from each other, allowing for unprecedented access to how these 1D objects behave in isolation.

While imaging these objects using transmission electron microscopy (TEM), the team found that these wires exhibited a unique twisting effect when exposed to an electron beam. Such behavior has never been seen before and is expected to be unique to isolated wires. The transition from a straight to twisted structure may offer a novel switching mechanism when the material is incorporated into microscopic circuits. The team hope the ability to make well-isolated 1D nanowires might significantly expand our understanding of the properties and mechanisms behind the function of 1D materials.

Tags:  2D materials  Carbon Nanotubes  Graphene  nanoelectronics  Tokyo Metropolitan University  Yusuke Nakanishi 

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Carbon nanotubes can be produced in a new way by twisting ribbon-like graphene

Posted By Graphene Council, The Graphene Council, Monday, February 25, 2019
Updated: Monday, February 25, 2019
The properties of folded, bent and twisted graphene at nanoscale are difficult to study theoretically and experimentally. In his dissertation, however, Oleg Kit utilized symmetry, a time-worn concept of theoretical physics, to develop an effective method to run computer experiments on nanostructures under complex deformations.

The new method allows explorations of folding, bending and twisting in more diverse ways than previously. Information about nanostructure properties is obtained by modeling only a few atoms, instead of simulating the whole structures. As the research utilized the laws of quantum mechanics, the method provided also information about changes in the electronic structure of graphene.

The advantage of the technique is that it makes possible studies of structures with millions of atoms that lack traditional symmetries. It enabled simulations which predict that carbon nanotubes can be made by twisting graphene.

Tags:  Carbon Nanotubes  Graphene  Oleg Kit  University of Jyväskylä 

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Drilling speed increased by 20% – yet another upgrade in the oil & gas sector made possible by graphene nanotubes

Posted By Graphene Council, The Graphene Council, Friday, January 25, 2019
Updated: Friday, January 25, 2019

56% of drilling tool failures in the oil extraction industry are caused by low durability of the rubber stator – one of the most important elements in a screw drill. In China, annual losses from the failure of drilling tools are estimated to be more than $40,000 per oil well. Equipment manufacturers are thus always looking for ways to improve the rubber used in screw drilling tools, to reduce these financial losses for oil-extracting companies.

One of the largest Chinese producers of PDM drilling tools, Orient Energy & Technology Ltd., has completed laboratory testing of nitrile butadiene rubber (NBR) containing TUBALL graphene nanotubes, produced by OCSiAl. Just 1.7 wt.% of graphene nanotube concentrate introduced into NBR was found to increase the tensile modulus by 30%.

“Improving the modulus of elasticity is the most valuable advantage of graphene nanotubes in our industry, because that leads to a 30% increase in output torque of our products. With that, the drilling speed can also be increased by more than 20%, resulting in a shortened drilling cycle, reduced energy consumption and less environmental pollution, greatly improving China’s drilling technology,” said Mr. Hu, a rubber engineer at Orient Energy & Technology. At the same time, the graphene nanotubes result in a reduction of abrasion by 20% without increasing the Mooney viscosity of rubber, whereas other additives such as multi wall carbon nanotubes increase viscosity, which is unacceptable for injecting.



Graphene nanotubes are one of the allotropic forms of carbon, where each tube can be considered to be a rolled-up sheet of graphene. This universal additive is already on duty protecting the oil & gas industry, where it is widely applied as a conductive additive in fiberglass pipes for permanent and uniform conductivity, as well as 15% reinforcement. Another example is anti-static fiberglass tanks for storing and transporting easily combustible materials, where these nanotubes ensure permanent and stable resistivity of less than 10^6 Ω·cm, without “hot spots” and independent of humidity.

Orient Energy & Technology is continuing to test TUBALL graphene nanotubes, in particular by studying their effects on other types of rubber, such as HNBR and FKM. Meanwhile, the first industrial prototype of a TUBALL-enhanced NBR stator for a screw drill is undergoing industrial trials.

Tags:  Carbon Nanotubes  Graphene  TUBALL 

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Novel Production Technique Offers Start-up New Approach to Markets

Posted By Dexter Johnson, IEEE Spectrum, Thursday, December 20, 2018

California-based NTherma is leveraging a proprietary graphene production method based on the unzipping of multiwalled carbon nanotubes into graphene nanoplatelets or nanoribbons.

The backgrounds of NTherma’s co-founders Cattien V. Nguyen, President & CEO, and Thuy Ngo, VP Business Developments & Investor Relations, cover both the science of graphene as well as its business development. Nguyen’s background contains some of the heavy hitters in nanomaterials research over the last 20 years: IBM Almaden Research Center and Stanford University.

With their manufacturing process offering a high degree of customization, NTherma is targeting applications that exploit this inherent flexibility that other manufacturing techniques can’t so easily deliver on.

As a new Corporate Member of The Graphene Council, we got the opportunity to ask them about how they are approaching the market with their novel manufacturing technique, some of the challenges they are facing and how they plan to overcome them.

 Q: Could you provide us more details about your method for producing graphene? It appears from your website that it may be a bottom-up approach. Is it a CVD-enabled process or direct chemical synthesis? And what kind of graphene does it produce?

Our graphene production method is different from the two current production processes.  We don't produce graphene by CVD of single layer directly on a metal substrate and we don't produce graphene by exfoliating graphite.  Both of these production methods have a number of tradeoffs including cost, purity, and control of structural parameters.

NTherma's unique approach to the production of graphene starts with our patent-pending method of producing carbon nanotubes (CNTs) that have high purity and high degree control of lengths and diameters, and most importantly a much lower production cost.  NTherma's graphene is then derived by the chemical conversion of high quality CNTs. 

Depending on the degree of chemical oxidation process, the produced graphene can be nanoplatelets or nanoribbons, or a combination of the two types.  Our ability to control the CNT length and their high purity together translates to high quality graphene at a much lower cost.  Of particularly importance is the availability of graphene nanoribbons at a large scale with controlled length, high purity, and much lower cost. This will open up a number of applications not currently feasible with commercially available graphene.

Could you let us know what applications you are targeting for your graphene? And can you tell us a bit about how you came to target these applications?

We are currently focusing on the following applications:

1.  Graphene for Oil Additives:  These reduce engine friction, improved fuel efficiency and lower emissions.  We differentiate our graphene as an oil additive in that our graphene forms a stable dispersion in oil with a demonstrated shelf life of greater than 12 months.

2.  Coatings:  There are many coating applications employing graphene and currently we are working with a few partners to integrate our graphene products.  We are also focusing on applications such as touchscreen and display as well as smart windows that other graphene materials have not been able to effectively address. 

3.  Lithium-ion (Li-ion) Batteries:  Preliminary test results are positive.  We're looking for partners to continue developing and testing the process. 

Because of our unique customization ability, we can alter length, layers and uniformity of our graphene per customers' requests.  Realizing that our high quality and consistent materials can unlock previous bottlenecks that other graphene products couldn't resolve, we chose these applications in the order provided as we see these applications and markets having the highest potential and where our technology will have the highest impact.

You are also producing multi-walled carbon nanotubes (MWCNTs). How do you see this fitting with your graphene production?

We produce MWCNTs for several other applications such as thermal management and also carbon nanotube yarns in development with a commercial partner. 

We also produce our graphene by the chemical conversion of MWNTs.

Is your strategy to remain a graphene and MWCNT producer, or do you see yourself moving further up the value chain to make devices from these materials?

We will focus on scaling up the production of high quality MWCNTs and graphene for the near future.  At the same time, we are developing, or have plans to develop, other applications and markets by ourselves or with partners in order to add more value to our business by strategically positioning our unique technology in a variety of verticals.

What do you see as the greatest challenge for your business in making an impact the commercialization of graphene, i.e. customer education, lack of standards, etc.? And what do you believe can be done to overcome these challenges?

The greatest challenges as a business for us have been our efforts to work with the end users and to understand as well as to educate the potential customers of our unique graphene products for any particular applications and product development processes.  Not all graphene products are the same in their purity, structural parameters such as size and number of layers, and cost.  These facts have to be made known to the end users and have to match with the end user's specific application.

Additionally, we also have to overcome clients' negative experiences with using other producers' inconsistent quality products.  We have to resolve these issues by continuing to work closely with our potential customers and partners by helping them to understand the materials and also optimizing and testing products for specific applications ourselves to provide clients with testing procedures and data (both in a lab environment and in real life).

Tags:  carbon nanotubes  coatings  CVD  Li-ion batteries  lubricants 

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2D Fluidics Pty Ltd created to launch the Vortex Fluidic Device (VFD)

Posted By Terrance Barkan, Friday, June 22, 2018

 

Advanced materials company, First Graphene Limited (“FGR” or “the Company”) (ASX: FGR) is pleased to announce the launch of its 50%-owned associate company, 2D Fluidics Pty Ltd, in collaboration with Flinders University’s newly named Flinders Institute for NanoScale Science and Technology

 

The initial objective of 2D Fluidics will be the commercialisation of the Vortex Fluidic Device (VFD), invented by the Flinders Institute for NanoScale Science and Technology’s Professor Colin Raston. The VFD enables new approaches to producing a wide range of materials such as graphene and sliced carbon nanotubes, with the bonus of not needing to use harsh or toxic chemicals in the manufacturing process (which is required for conventional graphene and shortened carbon nanotube production). 

 

This clean processing breakthrough will also greatly reduce the cost and improve the efficiency of manufacturing these new high quality super-strength carbon materials. The key intellectual property used by 2D Fluidics comprises two patents around the production of carbon nanomaterials, assigned by Flinders University. 

 

2D Fluidics will use the VFD to prepare these materials for commercial sales, which will be used in the plastics industry for applications requiring new composite materials, and by the electronics industry for circuits, supercapacitors and batteries, and for research laboratories around the world.

 

2D Fluidics will also manufacture the VFD, which is expected to become an in-demand state-of-the-art research and teaching tool for thousands of universities worldwide, and should be a strong revenue source for the new company. 

 

Managing Director, Craig McGuckin said “First Graphene is very pleased to be partnering Professor Raston and his team in 2D Fluidics, which promises to open an exciting growth path in the world of advanced materials production. Access to this remarkably versatile invention will complement FGRs position as the leading graphene company at the forefront of the graphene revolution.” 

 

Professor Colin Raston AO FAA, Professor of Clean Technology, Flinders Institute for NanoScale Science and Technology, Flinders University said “The VFD is a game changer for many applications across the sciences, engineering and medicine, and the commercialisation of the device will have a big impact in the research and teaching arena,” Nano-carbon materials can replace metals in many products, as a new paradigm in manufacturing, and the commercial availability of such materials by 2D Fluidics will make a big impact. It also has exciting possibilities in industry for low cost production where the processing is under continuous flow, which addresses scaling up - often a bottleneck issue in translating processes into industry.

Tags:  2D Fluidics  batteries  Carbon Nanotubes  circuits  Composites  electronics  First Graphene  Graphene  Plastics  research laboratories  supercapacitors  Vortex Fluidic Device (VFD) 

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MIT's Michael Strano turns plants into chemical detectors

Posted By Terrance Barkan, Monday, October 31, 2016

Scientists have transformed the humble spinach plant into a bomb detector.

Source: MIT

By embedding tiny tubes in the plants' leaves, they can be made to pick up chemicals called nitro-aromatics, which are found in landmines and buried munitions. Real-time information can then be wirelessly relayed to a handheld device.

The MIT (Massachusetts Institute of Technology) work is published in the journal Nature Materials. The scientists implanted nanoparticles and carbon nanotubes (tiny cylinders of carbon) into the leaves of the spinach plant. It takes about 10 minutes for the spinach to take up the water into the leaves.

To read the signal, the researchers shine a laser onto the leaf, prompting the embedded nanotubes to emit near-infrared fluorescent light. This can be detected with a small infrared camera connected to a small, cheap Raspberry Pi computer. The signal can also be detected with a smartphone by removing the infrared filter most have.

Co-author Prof Michael Strano, from MIT in Cambridge, US, said the work was an important proof of principle. "Our paper outlines how one could engineer plants like this to detect virtually anything," he told the BBC News website.

Prof Strano's lab has previously developed carbon nanotubes that can be used as sensors to detect hydrogen peroxide, TNT, and the nerve gas sarin. When the target molecule binds to a polymer material wrapped around the nanotube, it changes the way it glows. "The plants could be use for defence applications, but also to monitor public spaces for terrorism related activities, since we show both water and airborne detection," said Prof Strano.

"Such plants could be used to monitor groundwater seepage from buried munitions or waste that contains nitro-aromatics." Using the set-up described in the paper, the researchers can pick up a signal from about 1m away from the plant, and they are now working on increasing that distance.

Source: BBC News

Tags:  Carbon Nanotubes  Michael Strano  MIT  Sensors 

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