Encapsulation layers keep carbon nanotube transistors stable in open air
Individual transistors made from carbon nanotubes are faster and more energy efficient than those made from other materials. Going from a single transistor to an integrated circuit full of transistors, however, is a giant leap.
“A single microprocessor has a billion transistors in it,” said Northwestern Engineering’s Mark Hersam. “All billion of them work. And not only do they work, but they work reliably for years or even decades.”
When trying to make the leap from an individual, nanotube-based transistor to wafer-scale integrated circuits, many research teams, including Hersam’s, have met challenges. For one, the process is incredibly expensive, often requiring billion-dollar cleanrooms to keep the delicate nano-sized components safe from the potentially damaging effects of air, water, and dust. Researchers have also struggled to create a carbon nanotube-based integrated circuit in which the transistors are spatially uniform across the material, which is needed for the overall system to work.
Now Hersam and his team have found a key to solving all these issues. The secret lies in newly developed encapsulation layers that protect carbon nanotubes from environmental degradation.
Supported by the Office of Naval Research and the National Science Foundation, the research appears online in Nature Nanotechology on September 7. Tobin J. Marks, the Vladimir N. Ipatieff Research Professor of Chemistry in the Weinberg College of Arts and Sciences and professor of materials science and engineering in the McCormick School of Engineering, coauthored the paper. Michael Geier, a graduate student in Hersam’s lab, was first author.
“One of the realities of a nanomaterial, such as a carbon nanotube, is that essentially all of its atoms are on the surface,” said Hersam, the Walter P. Murphy Professor of Materials Science and Engineering. “So anything that touches the surface of these materials can influence their properties. If we made a series of transistors and left them out in the air, water and oxygen would stick to the surface of the nanotubes, degrading them over time. We thought that adding a protective encapsulation layer could arrest this degradation process to achieve substantially longer lifetimes.”
Hersam compares his solution to one currently used for organic light-emitting diodes (LEDs), which experienced similar problems after they were first realized. Many people assumed that organic LEDs would have no future because they degraded in air. After researchers developed an encapsulation layer for the material, organic LEDs are now used in many commercial applications, including displays for smartphones, car radios, televisions, and digital cameras. Made from polymers and inorganic oxides, Hersam’s encapsulation layer is based on the same idea but tailored for carbon nanotubes.
To demonstrate proof of concept, Hersam developed nanotube-based static random-access memory (SRAM) circuits. SRAM is a key component of all microprocessors, often making up as much as 85 percent of the transistors in the central-processing unit in a common computer. To create the encapsulated carbon nanotubes, the team first deposited the carbon nanotubes from a solution previously developed in Hersam’s lab. Then they coated the tubes with their encapsulation layers.
Using the encapsulated carbon nanotubes, Hersam’s team successfully designed and fabricated arrays of working SRAM circuits. Not only did the encapsulation layers protect the sensitive device from the environment, but they improved spatial uniformity among individual transistors across the wafer. While Hersam’s integrated circuits demonstrated a long lifetime, transistors that were deposited from the same solution but not coated degraded within hours.
“After we’ve made the devices, we can leave them out in air with no further precautions,” Hersam said. “We don’t need to put them in a vacuum chamber or controlled environment. Other researchers have made similar devices but immediately had to put them in a vacuum chamber or inert environment to keep them stable. That’s obviously not going to work in a real-world situation.”
Hersam imagines that his solution-processed, air-stable SRAM could be used in emerging technologies. Flexible carbon nanotube-based transistors could replace rigid silicon to enable wearable electronics. The cheaper manufacturing method also opens doors for smart cards — credit cards embedded with personal information to reduce the likelihood of fraud.
The Latest on: Carbon Nanotube Integrated Circuits
via Google News
The Latest on: Carbon Nanotube Integrated Circuits
- Scientists make chip using carbon nanotubes instead of siliconon September 4, 2019 at 4:10 am
“In particular, carbon nanotube field-effect transistor-based digital circuits promise substantial energy-efficiency ... nanotubes has precluded the realization of very-large-scale integrated systems.
- The world’s most advanced nanotube computer may keep Moore’s Law aliveon August 30, 2019 at 11:09 am
Carbon nanotubes could be the perfect solution. Not only are nanotube transistors faster than silicon ... the first are semiconductors that are perfect for creating integrated circuits, but the second ...
- Carbon nanotube 16-bit microprocessor takes computing beyond siliconon August 28, 2019 at 10:17 pm
Ever since Robert Noyce produced the first integrated circuit (IC) on a silicon chip in 1959 ... possible to demonstrate the modern microprocessor built entirely out of carbon nanotube field-effect ...
- Biggest carbon-nanotube chip yet says ‘Hello, World!’on August 28, 2019 at 10:10 am
Some researchers hope that carbon ... using clever circuit design to mitigate for natural defects in the tubes that cause some to be metallic rather than having the semiconducting properties needed to ...
- Modern microprocessor built from complementary carbon nanotube transistorson August 28, 2019 at 10:06 am
In particular, carbon nanotube field-effect transistor (CNFET)-based digital circuits promise substantial energy-efficiency ... nanotubes has precluded the realization of very-large-scale integrated ...
- Semiconducting Carbon Nanotubes Can Reduce Noise In Carbon Nanotube Interconnectson November 17, 2017 at 9:25 am
Downscaling of component size in integrated circuits (ICs) to nanometer scale coupled with high density integration makes it challenging for researchers to maintain signal integrity in ICs. There are ...
- Realizing Carbon Nanotube Integrated Circuitson September 6, 2015 at 5:00 pm
Individual transistors made from carbon nanotubes are faster and more energy efficient than those made from other materials. Going from a single transistor to an integrated circuit full of transistors ...
- Researchers test carbon nanotube-based ultra-low voltage integrated circuitson June 22, 2012 at 8:22 am
What do you think about this particular story? Your feedback will go directly to Science X editors.
- First successful operation of carbon nanotube-based integrated circuits manufactured on plastic substrateson February 7, 2011 at 4:00 pm
(Nanowerk News) As part of NEDO's Industrial Technology Research Grant Japan-Finland collaborative project, Professors Yutaka Ohno from Nagoya University in Japan and Esko I. Kauppinen from Aalto ...
- Complex Integrated Circuits Made of Carbon Nanotubeson December 16, 2009 at 4:00 pm
The Stanford group is currently working to make ever more complex integrated circuits. “So far as complexity is concerned, there is fundamentally no barrier” on carbon nanotubes, says Mitra. Materials ...
via Bing News