IEEE Awards Booklet - 2020 - 3


THE ROAD TO FINFET: Chenming Hu joined the faculty of the
University of California, Berkeley, in 1976 [bottom left]. His early
research at Berkeley included hybrid cars, like the gas-electric car
he presented at the University of California Board of Regents meeting in 1980 [above]. In his lab in 1997 [top left], Hu was deep in
the development of the FinFET, with the help of a DARPA grant.

fellow Berkeley faculty member, Jeffrey Bokor, who, in turn, had
heard about it while windsurfing with a DARPA program director. So Hu quickly met with Bokor and another colleague, Tsu Jae
King, and confirmed that the team would pull together a proposal
within a week. On a plane trip to Japan a day or two later, he
sketched out the two designs, faxing his sketches and a description
of his technical approach back to Berkeley when he arrived at his
hotel in Japan.The team submitted the proposal, and DARPA later
awarded them a four-year research grant.
Ideas similar to FinFET had been described before in theoretical
papers. Hu and his team, however, actually built manufacturable
devices and showed how the design would make transistors 25 nm
and smaller possible. "The others who read the papers didn't see it
as a solution, because it would be hard to build and may or may not
work. Even the people who wrote the papers did not pursue it,"
says Hu. "I think the difference was that we looked at it and said,
we want to do this not because we want to write another paper, or
get another grant, but because we want to help the industry.We felt
we had to keep [Moore's Law] going.
"As technologists," Hu continues, "we have the responsibility to
make sure the thing doesn't stop, because once it stops, we're losing
the biggest hope for us to have more abilities to solve the world's
difficult problems."
Hu and his team "were well-poised to develop the FinFET because of the way he trains his students to think about devices," says
Elyse Rosenbaum, a former student of his and now a professor at
the University of Illinois at Urbana-Champaign."He emphasizes big
picture, qualitative understanding. When studying a semiconductor
device, some people focus on creating a model and then numerically
solving all the points in its 3D grid. He taught us to step back, to try
to visualize where the electric field is distributed in a device, where
the potential barriers are located, and how the current flow changes
when we change the dimension of a particular feature."
Hu felt that visualizing the behavior of semiconductor devices
was so important, Rosenbaum recalls, that once, struggling to teach
his students his process, he "built us a model of the behavior of an
MOS transistor using his kids' Play-Doh."
"These things looked like a lightning invention," said Fari
Assaderaghi, a former student who is now senior vice president

of innovation and advanced technology at NXP Semiconductors.
"But his team had been working on fundamental concepts of what
an ideal device should be, working from first principles of physics
early on; how to build the structure comes from that."
By 2000, at the end of the four-year grant term, Hu and his team
had built working devices and published their research, raising immediate, widespread interest within the industry. It took another
decade, however, before chips using FinFETs began rolling off of
manufacturing lines, the first from Intel in 2011.Why so long?
"It was not broken yet," Hu explains, referring to the industry's
ability to make semiconductor circuits more and more compact.
"People were thinking it was going to break, but you never fix
anything that's not broken."
It turned out that the DARPA program managers were prescient-they had called the project the 25-nm Switch, and FinFETs
came into play when the semiconductor industry moved to sub25-nm geometries.
FDSOI, meanwhile, also progressed and is also being used in
industry today. In particular, it's found in optical and RF devices,
but FinFETs currently dominate the processor industry. Hu says he
never really promoted one approach over the other.
In FinFET's dormant years, Hu took a three-year break from
Berkeley to serve as chief technology officer of semiconductor
manufacturer TSMC in Taiwan. He saw that as a chance to pay
back the country where he received his initial education. He returned to Berkeley in 2004, continuing his teaching, research in
new energy-efficient semiconductor devices, and efforts to support
BSIM. In 2009, Hu stopped teaching regular classes, but as a professor emeritus, he still works with graduate students.
Since Hu moved back to Berkeley, FinFET technology has swept
the industry. And Moore's Law did not come to an end at 25 nm,
although its demise is still regularly predicted.
"It is going to gradually slow down, but we aren't going to have
a replacement for MOS semiconductors for a hundred years," Hu
says. This does not make him pessimistic, though. "There are still
ways of improving circuit density and power consumption and
speed, and we can expect the semiconductor industry to keep giving people more and more useful and convenient and portable devices.We just need more creativity and a big dose of confidence." ■



IEEE Awards Booklet - 2020

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