Pushing material boundaries for better electronics

Associate Professor Jeehwan Kim is exploring systems that could take over where silicon leaves off.

Undergrads, take note: The lessons you learn in those intro classes could be the key to making your next big discovery. At least, that’s been the case for MIT’s Jeehwan Kim.

A recently tenured faculty member in MIT’s departments of Mechanical Engineering and Materials Science and Engineering, Kim has made numerous discoveries about the nanostructure of materials and is funneling them directly into the advancement of next-generation electronics.

His research aims to push electronics past the inherent limits of silicon — a material that has reliably powered transistors and most other electronic elements but is reaching a performance limit as more computing power is packed into ever smaller devices.

Today, Kim and his students at MIT are exploring materials, devices, and systems that could take over where silicon leaves off. Kim is applying his insights to design next-generation devices, including low-power, high-performance transistors and memory devices, artificial intelligence chips, ultra-high-definition micro-LED displays, and flexible electronic “skin.” Ultimately, he envisions such beyond-silicon devices could be built into supercomputers small enough to fit in your pocket.

The innovations that have come out of his research are recorded in more than 200 issued U.S. patents and 70 research papers — an extensive list that he and his students continue to grow.

Kim credits many of his breakthroughs to the fundamentals he learned in his university days. In fact, he has carried his college textbooks and notes with him with every move. Today, he keeps the undergraduate notes — written in a light and meticulous graphite and ink — on a shelf nearest to his MIT desk, close at hand. He references them in his own class lectures and presentations, and when brainstorming research solutions.

“These textbooks are all in my brain now,” Kim says. “I’ve learned that if you completely understand the fundamentals, you can solve any problem.”

Fundamental shift

Kim wasn’t always a model student. Growing up in Seoul, South Korea, he was fixed on a musical career. He had a passion for singing and was bored by most other high school subjects.

“It was very monotonic,” Kim recalls. “My motivation for high school subjects was very low.”

After graduating high school, he enrolled in a materials science program at Hongik University, where he was lucky to met professors who had graduated from MIT and who later motivated him to study in the United States. But, Kim spent his first year there trying to make it as a musician. He wrote and sang songs that he recorded and sent to promoters, and went to multiple auditions. But after a year, he was faced with no call-backs, and a hard question.

“What should I do? It was a crisis to me,” Kim says.

In his second year, he decided to give materials science a go. When he sat in on his first class, he was surprised to find that the subject — the structure and behavior of materials at the atomic scale — made him want to learn more.

“My first year, my GPA was almost zero because I didn’t attend class, and was going to be kicked out,” Kim says. “Then from my second year on, I really loved every single subject in materials science. People who saw me in the library were surprised: ‘What are you doing here, without a guitar?’ I must have read these textbooks more than 10 times, and felt I really understood everything fundamental.”

Back to basics

He took this newfound passion to Seoul National University, where he enrolled in the materials science master’s program and learned to apply the ideas he absorbed to hands-on research problems. Metallurgy was a dominant field at the time, and Kim was assigned to experiment with high-temperature alloys — mixing and melting metallic powders to create materials that could be used in high-performance engines.

After completing his master’s, Kim wanted to continue with a PhD, overseas. But to do so, he first had to serve in the military. He spent the next two and a half years in the Korean air force, helping to maintain and refuel aircraft, and inventory their parts. All the while, he prepared applications to graduate schools abroad.
In 2003, after completing his service, he headed overseas, where he was accepted to the materials science graduate program at the University of California at Los Angeles with a fellowship.

“When I came out of the airplane and went to the dorm for the first day, people were drinking Corona on the balcony, playing music, and there was beautiful weather, and I thought, this is where I’m supposed to be!” Kim recalls.

For his PhD, he began to dive into the microscopic world of electronic materials, seeking ways to manipulate them to make faster electronics. The subject was a focus for his advisor, who previously worked at Bell Labs, where many computing innovations originated at the time.

“A lot of the papers I was reading were from Bell Labs, and IBM T.J. Watson, and I was so impressed, and thought: I really want to be a scientist there. That was my dream,” Kim says.

During his PhD program, he reached out to a scientist at IBM whose name kept coming up in the papers Kim was reading. In his initial letter, Kim wrote with a question about his own PhD work, which tackled a hard industry problem: how to stretch, or “strain,” silicon to minimize defects that would occur as more transistors are packed on a chip. 

The query opened a dialogue, and Kim eventually inquired and was accepted to an internship at the IBM T.J. Watson Research Center, just outside New York City. Soon after he arrived, his manager pitched him a challenge: He might be hired full-time if he could solve a new, harder problem, having to do with replacing silicon.

At the time, the electronics industry was looking to germanium as a possible successor to silicon. The material can conduct electrons at even smaller scales, which would enable germanium to be made into even tinier transistors, for faster, smaller, and more powerful devices. But there was no reliable way for germanium to be “doped” — an essential process that replaces some of a material’s atoms with another type of atom in a way that controls how electrons flow through the material.

“My manager told me he didn’t expect me to solve this. But I really wanted the job,” Kim says. “So day and night, I thought, how to solve this? And I always went back to the textbooks.”

Those textbooks reminded him of a fundamental rule: Replacing one atom with another would work well if both atoms were of similar size. This revelation triggered an idea. Perhaps germanium could be doped with a combination of two different atoms with an average atomic size that is similar to germanium’s.

“I came up with this idea, and right after, IBM showed that it worked. I was so amazed,” Kim says. “From that point, research became my passion. I did it because it was just so fun. Singing is not so different from performing research.”

As promised, he was hired as a postdoc and soon after, promoted to research staff member — a title he carried, literally, with pride.

“I was feeling so happy to be there,” Kim says. “I even wore my IBM badge to restaurants, and everywhere I went.”

Throughout his time at IBM, he learned to focus on research that directly impacts everyday human life, and how to apply the fundamentals to develop next-generation products.

“IBM really raised me up as an engineer who can identify the problems in an industry and find creative solutions to tackle the challenges,” he says.

Cycle of life

And yet, Kim felt he could do more. He was working on boundary-pushing research at one of the leading innovation hubs in the country, where “out-of-the-box” thinking was encouraged, and experimentally tested. But he wanted to explore beyond the company’s research portfolio, and also, find a way to pursue research not just as a profession but as a passion.

“My experience taught me that you can lead a very happy life as an engineer or scientist if your research becomes your hobby,” Kim says. “I wanted to teach this cycle — of happiness, research, and passion — to young people and help PhD students develop like artists or singers.”

In 2015, he packed his bags for MIT, where he accepted a junior faculty position in the Department of Mechanical Engineering. His first impressions upon arriving at the Institute?

“Freedom,” Kim says. “For me, free thinking — to compose music, innovate something totally new — is the most important thing. And the people at MIT are very talented and curious of all the things.”

Since he’s put down roots on campus, he has built up a highly productive research group, focused on fabricating ultra-thin, stackable, high-performance electronic materials and devices, which Kim envisions could be used to build hybrid electronic systems as small as a fingernail and as powerful as a supercomputer. He credits the group’s many innovations to the more than 40 students, postdocs, and research scientists who have contributed to his lab.

“I hope this is where they can learn that research can be an art,” Kim says. “To students especially, I hope they see that, if they enjoy what they do, then they can be whatever they want to be.”