Featured Research

from universities, journals, and other organizations

Engineers perfecting carbon nanotubes for highly energy-efficient computing

Date:
June 14, 2012
Source:
Stanford School of Engineering
Summary:
Carbon nanotubes represent a significant departure from traditional silicon technologies and offer a promising path to solving the challenge of energy efficiency in computer circuits, but they aren't without challenges. Now, engineers have found ways around the challenges to produce the first full-wafer digital logic structures based on carbon nanotubes.

An electron microscope image showing carbon nanotube transistors (CNTs) arranged in an integrated logic circuit.
Credit: Stanford University School of Engineering

Energy efficiency is the most significant challenge standing in the way of continued miniaturization of electronic systems, and miniaturization is the principal driver of the semiconductor industry. "As we approach the ultimate limits of Moore's Law, however, silicon will have to be replaced in order to miniaturize further," said Jeffrey Bokor, deputy director for science at the Molecular Foundry at the Lawrence Berkeley National Laboratory and Professor at UC-Berkeley.

Related Articles


To this end, carbon nanotubes (CNTs) are a significant departure from traditional silicon technologies and a very promising path to solving the challenge of energy efficiency. CNTs are cylindrical nanostructures of carbon with exceptional electrical, thermal and mechanical properties. Nanotube circuits could provide a ten-times improvement in energy efficiency over silicon.

Early promise

When the first rudimentary nanotube transistors were demonstrated in 1998, researchers imagined a new age of highly efficient, advanced computing electronics. That promise, however, is yet to be realized due to substantial material imperfections inherent to nanotubes that left engineers wondering whether CNTs would ever prove viable.

Over the last few years, a team of Stanford engineering professors, doctoral students, undergraduates, and high-school interns, led by Professors Subhasish Mitra and H.-S. Philip Wong, took on the challenge and has produced a series of breakthroughs that represent the most advanced computing and storage elements yet created using CNTs.

These high-quality, robust nanotube circuits are immune to the stubborn and crippling material flaws that have stumped researchers for over a decade, a difficult hurdle that has prevented the wider adoption of nanotube circuits in industry. The advance represents a major milestone toward Very-large Scale Integrated (VLSI) systems based on nanotubes.

"The first CNTs wowed the research community with their exceptional electrical, thermal and mechanical properties over a decade ago, but this recent work at Stanford has provided the first glimpse of their viability to complement silicon CMOS transistors," said Larry Pileggi, Tanoto Professor of Electrical and Computer Engineering at Carnegie Mellon University and director of the Focus Center Research Program Center for Circuit and System Solutions.

Major barriers

While there have been significant accomplishments in CNT circuits over the years, they have come mostly at the single-nanotube level. At least two major barriers remain before CNTs can be harnessed into technologies of practical impact: First, "perfect" alignment of nanotubes has proved all but impossible to achieve, introducing detrimental stray conducting paths and faulty functionality into the circuits; second, the presence of metallic CNTs (as opposed to more desirable semiconducting CNTs) in the circuits leads to short circuits, excessive power leakage and susceptibility to noise. No CNT synthesis technique has yet produced exclusively semiconducting nanotubes.

"Carbon nanotube transistors are attractive for many reasons as a basis for dense, energy efficient integrated circuits in the future. But, being borne out of chemistry, they come with unique challenges as we try to adapt them into microelectronics for the first time. Chief among them is variability in their placement and their electrical properties. The Stanford work, that looks at designing circuits taking into consideration such variability, is therefore an extremely important step in the right direction," Supratik Guha, Director of the Physical Sciences Department at the IBM Thomas J. Watson Research Center .

"This is very interesting and creative work. While there are many difficult challenges ahead, the work of Wong and Mitra makes good progress at solving some of these challenges," added Bokor.

Realizing that better processes alone will never overcome these imperfections, the Stanford engineers managed to circumvent the barriers using a unique imperfection-immune design paradigm to produce the first-ever full-wafer-scale digital logic structures that are unaffected by misaligned and mis-positioned CNTs. Additionally, they addressed the challenges of metallic CNTs with the invention of a technique to remove these undesirable elements from their circuits.

Striking features

The Stanford design approach has two striking features in that it sacrifices virtually none of CNTs' energy efficiency and it is also compatible with existing fabrication methods and infrastructure, pushing the technology a significant step toward commercialization.

"This transformative research is made all the more promising by the fact that it can co-exist with today's mainstream silicon technologies, and leverage today's manufacturing and system design infrastructure, providing the critical feature of economic viability," said Betsy Weitzman of the Focus Center Research Program at the Semiconductor Research Corporation

The engineers next demonstrated the possibilities of their techniques by creating the essential components of digital integrated systems: arithmetic circuits and sequential storage, as well as the first monolithic three-dimensional integrated circuits with extreme levels of integration.

The Stanford team's work was featured recently as an invited paper at the International Electron Devices Meeting (IEDM) as well as a "keynote paper" in the IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems.

"Many researchers assumed that the way to live with imperfections in CNT manufacturing was through expensive fault-tolerance techniques. Through clever insights, Mitra and Wong have shown otherwise. Their inexpensive and practical methods can significantly improve CNT circuit robustness, and go a long way toward making CNT circuits viable," said Sachin S. Sapatnekar, Editor-in-Chief, IEEE Transactions on CAD. "I anticipate high reader interest in the paper," Sapatnekar noted.


Story Source:

The above story is based on materials provided by Stanford School of Engineering. The original article was written by Andrew Myers. Note: Materials may be edited for content and length.


Cite This Page:

Stanford School of Engineering. "Engineers perfecting carbon nanotubes for highly energy-efficient computing." ScienceDaily. ScienceDaily, 14 June 2012. <www.sciencedaily.com/releases/2012/06/120614131202.htm>.
Stanford School of Engineering. (2012, June 14). Engineers perfecting carbon nanotubes for highly energy-efficient computing. ScienceDaily. Retrieved October 24, 2014 from www.sciencedaily.com/releases/2012/06/120614131202.htm
Stanford School of Engineering. "Engineers perfecting carbon nanotubes for highly energy-efficient computing." ScienceDaily. www.sciencedaily.com/releases/2012/06/120614131202.htm (accessed October 24, 2014).

Share This



More Matter & Energy News

Friday, October 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

IKEA Desk Converts From Standing to Sitting With One Button

IKEA Desk Converts From Standing to Sitting With One Button

Buzz60 (Oct. 24, 2014) IKEA is out with a new convertible desk that can convert from a sitting desk to a standing one with just the push of a button. Jen Markham explains. Video provided by Buzz60
Powered by NewsLook.com
Ebola Protective Suits Being Made in China

Ebola Protective Suits Being Made in China

AFP (Oct. 24, 2014) A factory in China is busy making Ebola protective suits for healthcare workers and others fighting the spread of the virus. Duration: 00:38 Video provided by AFP
Powered by NewsLook.com
Real-Life Transformer Robot Walks, Then Folds Into a Car

Real-Life Transformer Robot Walks, Then Folds Into a Car

Buzz60 (Oct. 24, 2014) Brave Robotics and Asratec teamed with original Transformers toy company Tomy to create a functional 5-foot-tall humanoid robot that can march and fold itself into a 3-foot-long sports car. Jen Markham has the story. Video provided by Buzz60
Powered by NewsLook.com
Police Testing New Gunfire Tracking Technology

Police Testing New Gunfire Tracking Technology

AP (Oct. 24, 2014) A California-based startup has designed new law enforcement technology that aims to automatically alert dispatch when an officer's gun is unholstered and fired. Two law enforcement agencies are currently testing the technology. (Oct. 24) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins