Creating a Carbon-based Electronics Future

Pictured is a cross section through a graphene field-effect transistor during operation. This image, rendered by Alex Jerez of Beckman's Visualization Laboratory, earned the cover of the current issue of NANOLetters.

Beckman Institute researcher Eric Pop is taking on the problem of power dissipation in electronics through the use of carbon nanomaterials. Pop is a member of Beckman's Nanoelectronics and Nanomaterials group.

Sometimes stars get their start at college radio stations, but that usually doesn’t happen with scientists. Beckman Institute researcher Eric Pop is a former college disc jockey who didn’t go on to a career in show business, but he is fast becoming a star in scientific circles.

Just three-and-a-half years into a professorship at Illinois, Pop has already won some of the most coveted awards out there for a young science and engineering researcher. A professor in the Department of Electrical and Computer Engineering and member of the Nanoelectronics and Nanomaterials group at Beckman, Pop has earned the National Science Foundation CAREER Award and Young Investigator awards from DARPA and the Navy and Air Force research offices. And, just last month, Pop won the Presidential Early Career Award for Scientists and Engineers (PECASE), which is the highest honor given by the United States government for science and engineering professionals in the early stages of their independent research careers.

Pop has traversed a somewhat unusual path for a career in science: moving to Los Angeles from his native Romania at age 17 equipped with only, he says, “rudimentary” English skills, which made his experiences in high school and in college the reverse of most students.Paradoxically, for me college at MIT was in a way easier than high school because my English was getting better.”    

From there it was on to Stanford for a Ph.D. in electrical engineering, and postdoctoral work in chemistry studying carbon nanotubes. Pop’s stay in the Bay Area also included a gig as a disc jockey.

“It was just at the Stanford student-run radio station, but it was heard all over the San Francisco Bay area so theoretically there were seven million listeners,” Pop said with a smile. “I was an electrical engineer, so I favored electronic music. I guess it was fitting.”

Pop eventually became the station’s general manager, a position which he says prepped him for his current role as research group leader.

“It was a good experience for what I’m right doing now,” he said. “In fact, I mentioned it during my interview here. I told the dean, ‘I managed a group of about 50-60 volunteers’ when asked how I was going to manage a group of five student researchers.”

Pop’s research group is actually about four times that size; the PopLab at Illinois numbers around 20 graduate, undergraduate, and postdoctoral researchers exploring nanotechnology topics in the areas of nanoscale energy transport, low-power carbon nanotube and graphene devices, and novel non-volatile memory. To quote from his lab’s website, “We take a ‘bottom-up’ approach to this issue, looking at electrical and thermal transport in nanoscale devices, interconnects, and material interfaces.”

Pop says that his research islooking at power dissipation problems” that arise in ultra-dense integrated circuits.

“My group is focused on two fundamental bottlenecks in nanoelectronics: one is the memory problem and the other is the power problem,” Pop said. “Starting about five years ago these two issues began to limit the progress of electronics and Moore’s Law.

“When microprocessors reached a few gigahertz, the memory and the hard drive could no longer keep up. At the same time, the high frequencies led to microprocessors getting very, very hot, so you would have 100-watt processors distributing this heat into a piece of silicon the size of a postage stamp. Even today, five years later, we are still limited by the speed of memory and the heat dissipated by the processor.”

Pop’s proposed solution focuses on finding alternatives to silicon-based electronics problems using carbon nanotubes (CNTs) and graphene because of their excellent conducting and semiconducting capabilities. For low-power memory, the Pop group investigates phase change materials like the germanium antimony telluride used to store information optically in DVDs. They are creating nanoscale phase-change bits that are programmable with CNT interconnects. Pop said that his research in these areas is “tied together through one basic material, which is carbon.

“I tell people ‘in a sense, we’re trying to replace both silicon and copper with carbon.’ Carbon is very abundant, like silicon, and it is faster for electronics. Like any new technology, it obviously has problems, but that is why it’s such a good research topic.”

Pop published a paper in late 2008 demonstrating an avalanche process for driving semiconducting CNTs that resulted in a nearly twofold increase in current from what was previously thought possible. Pop said the small scale of CNTs and their excellent conducting properties make them ideal for providing the same amount of computational power as silicon, but with lower dissipation.

“Our work isn’t just carbon,” Pop said. “For memory we use these phase change materials, which have been around since the ‘60s, and it’s only in the last 10 years that people have started using them for memory elements. Since the ‘80s they’ve been used for re-writeable DVDs, and right now we’re using them for very low power memory. In fact, it would be the memory used to replace what’s inside your iPod.”

Pop said germanium antimony telluride is an excellent phase change material for memory elements because it switches at low power and low voltage.

“The only thing that it didn’t do is switch at low current,” he added. “So the progress we’ve made in my lab is that we’ve gotten it to switch at very low current, which means low power consumption in general. This issue of finding the absolute lower limits of power dissipation in these materials is a big component of my group’s efforts right now.”

Pop gets excited when discussing the potential of electronics based on CNTs, graphene, and phase change materials.

“There are no fundamental laws of physics limiting us from making electronics a hundred times more energy efficient than they are today,” Pop said. “So, perhaps we will have laptops with six-month battery life, or with a hundred times more functionality for the same battery life.”

I tell people ‘in a sense, we’re trying to replace both silicon and copper with carbon.’ Carbon is very abundant, like silicon, and it is faster for electronics. Like any new technology, it obviously has problems, but that is why it’s such a good research topic.
– Eric Pop

Pop joined Beckman soon after coming to Illinois because he found himself interacting and collaborating with many faculty members who had appointments here.  

“A lot of my ECE colleagues are in Beckman, a lot of my colleagues in Materials Science and Mechanical Engineering are in Beckman, and I found myself always meeting with them at the Beckman (Café) discussing ideas,” Pop said. “At some point (Beckman faculty member) Jean-Pierre Leburton said ‘you should be an affiliate here, so we would see you more often.’ It was natural, it found me.”

The awards have also found Pop. The PECASE Award means a trip to the White House and a ceremony with President Barack Obama.

“It’s great, as I’ve never been to the White House before,” Pop said. “It is also a really nice recognition for the work the students in my group have been doing.”

Pop’s dream when he first went to MIT was to become an astrophysicist. He studied and had research jobs in that area but became more interested in electronics. His career path began to veer away from astrophysics during an internship with IBM working in microelectronics.

“I learned about semiconductors and I realized this field was both fun and practical,” he said. “As a teenager, I had my eyes on things in the sky and in high energy physics, and now I work on very small things and really low-energy physics, so it’s completely the opposite. Often, you never know until you get into it if you’re going to like something or not.

“That’s what I tell a lot of freshman and undergraduates, you’ve got to try things out. Don’t wait until you are a senior to do a research project,” Pop added. “The bottom line is, get involved in research your freshman year. I know a lot of students shy away from this because they think they have no experience, but you have to keep trying until you find a fitting project. Any self-taught computer programming skills or hands-on skills are very useful. We have freshmen in my lab, and we like undergraduates who want to know how things work, who take apart their bikes or computers and put them back together. Those kinds of skills are very important, and no formal training is required.”

Pop says it is ultimately the students and postdoctoral researchers who are critical to making research happen.

“What I really want people to know is that the only way our research works and the only way we get the results we do is because of very good students and postdocs,” he said. “That’s where the University of Illinois and Beckman are top-rate in terms of attracting this kind of talent. We can talk about low-power electronics but we have to have very good student researchers who are shaping this and coming up with their own ideas and challenging mine which, let’s face it, often fail. Continual and collaborative refinement of ideas is what really pushes this field forward.”