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MEMS pioneer draws up technology's course

Posted: 16 Aug 2007 ?? ?Print Version ?Bookmark and Share

Keywords:MEMS technology? SiTime sensors? silicon resonators? micromachining?

Petersen: By 2010, the MEMS resonator and timing-chip markets will total over $7.5 billion!that's enough for us.

Kurt Petersen has been called a "founding father of MEMS" because of his pioneering research work on MEMS at IBM Corp. in the 1970s. He has co-founded four MEMS startups, the most successful of which, NovaSensor Inc., has delivered hundreds of millions of MEMS sensors worldwide.

Petersen also pioneered the fusion of MEMS and microfluidic technology in a biological detection system made at another of his startups, Cepheid Inc. It's now used by the U.S. Postal Service to screen mail for possible anthrax contamination.

Petersen's most recent startup, SiTime Corp., plans to substitute MEMS and CMOS chips for all the billions of bulky quartz-crystal oscillator cans that maintain time bases for everything from watches to the electronics on PCBs. In this interview with EE Times, he recalls the technology's early roots and discusses where MEMS is headed in the future.

EE Times: Your work in the 1970s resulted in the seminal IEEE paper "Silicon as a Mechanical Material." What first got you started in MEMS?
Kurt Petersen: In a word, Stanford University. I had just finished my Ph.D. in electrical engineering from the Massachusetts Institute of Technology and was interviewing in the San Francisco Bay area. I went to the Xerox Palo Alto Research Center to interview. But this was in 1975 and they didn't have any labs yet, so they were doing most of their work in Stanford's labs. During the interview, they took me over to Stanford, where I saw a poster from visionary professor Jim Angell's group. It showed a gas chromatograph on a wafer done by Steve Terry. That's when it hit me!you can use silicon as a mechanical material.

I ended up joining IBM in San Jose, and within about four months was doing micromachining. We built a little fab and began dealing with MEMS-specific issues such as various applications, stiction and stress.

And what types of devices were you working on?
Back then we were trying to do optical MEMS. The first silicon-dioxide beams we made were to deflect light and were very, very flat. That made me think, "Wow, this really works." But on the second try, the beams got all curled up like potato chips. So we discovered that we had a lot of issues to deal with at the beginning, just to get consistent results.

What do you see as the milestones that have been passed since you presented that paper in 1982?
I think the paper helped bring people together and defined MEMS as an independent research field. There was no volume production at that time because the big companies had not gotten heavily involved yet. But by 1985, MEMS pressure sensors were in volume production at Motorola. Then the automotive applications took off at Delco before industrial applications caught on at Foxboro, then at National Semiconductor. And lots of research was done at IBM.

Didn't you start your own initial MEMS company around that time? What was the biggest obstacle for your first startup?
Yes, I started Transensory Devices Inc. with Jim Knutti, Henry Allen and Joe Brown, who joined me there from IBM. The biggest obstacle was definitely the fab. In those days, there were no foundries, so the first thing we had to do was build our own fab from the ground up. It was small, but it gave us control over all aspects of our development work.

Your own fab? That must have been incredibly expensive for a startup.
Well, we were just doing applied research. In those days, we weren't yet taking into account the production, testing or packaging issues. Most of our revenue was from R&D contracts, but I wanted to make products. So when I met Janusz Bryzek and Joe Mallon, who were very experienced in traditional pressure sensors, I left to help start NovaSensor, which has since been acquired by GE Industrial Systems. We had MEMS pressure sensors in production just six months after founding.

How did you get a fab up and running so quickly?
We would rent time on the third shift at other people's fabs and make our sensors there in the middle of the night. The amazing thing was that we took our first order for 50,000 chips before we even had a product then delivered them in 10 weeks. Not only did they work, they had tighter specs and worked much better than the traditional sensor parts they were replacing.

What types of structures were you building then?
At NovaSensor, we were using several technologies that are commonplace today but were revolutionary in those days. For instance, building reproducible piezoresistors on the same chip with the MEMS structures was very tricky, but we solved the problems by using ion implantation. We also started using silicon nitride for use in pressure sensors, as well as electrochemical etch stops to accurately define the thickness of the diaphragm.

So did you go directly from NovaSensor to found SiTime?
No. I stayed at NovaSensor for 11 years, but I wanted to start a company that actually made end-user products, so I founded Cepheid. That company used MEMS in microfluidics devices to do rapid DNA analysis.

So Cepheid's microfluidic devices identify medical maladies by their DNA?
Yes, but the post office is actually Cepheid's largest customer now. For medical tests, you can tolerate as much as a one-percent false-positive rate, but to identify anthrax in letters for the post office, they run millions of tests. Every time you have a false positive, it's a huge deal. It costs them millions of dollars to shut down a facility, bring in the Federal Bureau of Investigation and the Centers for Disease Control and Prevention, and test all the employees, so they demanded a false-positive rate of better than one in 500,000.

How did you go from making microfluidic devices to making MEMS resonators for SiTime?
One day, Brown came to me and told me about this great process that Robert Bosch GmbH had to make resonators. And I told him, "Come on, Joe, people have been trying to perfect resonators for 30 years!it's just too hard a problem." But he convinced me to take a look at their process, and I came away convinced that Bosch had finally developed a process that was good enough.

So will silicon resonators replace quartz crystals in all applications?
I always say no to that question because it's a very big marketplace. We divide the market into three segments. The low end is like the crystals in your watch!very low-cost with a precision of about 200ppm. The middle billion dollars is CE, with a precision of about 50ppm. Then you have the top billion dollars composed of high-precision parts such as oven-controlled crystal oscillators for cellphone base stations and temperature-compensated crystal oscillators, with a precision of about 1ppm. Today, our parts are aimed at the middle billion-dollar CE market, but we have two more resonators in development: one that will move upward into the top $1 billion tier and another that goes into the bottom $1 billion tier.

Do you have any plans to make any other MEMS devices besides resonators and oscillators?
By 2010, the resonator and timing-chip markets will total over $7.5 billion!that's enough for us. SiTime will be directly attacking about one-third to one-half of this CE market.

- R. Colin Johnson
EE Times

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