Timing Is Everything

Read about a senior member's work on a stable silicon timing device that does not rely on quartz crystals

6 May 2010

IEEE Senior Member Michael McCorquodale has managed a feat that vexed engineers for decades: He has built a stable silicon timing device that does not rely on quartz crystals. Now his invention is poised to challenge quartz timing as the status quo.

Timing devices—also known as oscillators, frequency references, and clock generators—enable electronics to “talk” to one another. They’re inside most digital devices and generate constant, repetitive frequencies by which data can be exchanged via circuit paths, USB, wireless, and other interfaces. For example, the iPhone uses seven quartz frequency references.

All-silicon timing has been attempted since the 1960s, but no one has been able to match or improve upon the stability and accuracy of frequencies generated by vibrating quartz crystals. Silicon is more temperamental and suffers from sensitivity to temperature, power supply variations, humidity, and other environmental fluctuations. But an all-silicon clock would provide a cheaper, smaller product with enormous market potential, and one that’s less sensitive to outside mechanical vibration.

“Billions of quartz crystal units are shipped every year,” McCorquodale says. “It’s the de facto frequency reference in the world.” He has found a way to get quartz-level stability with silicon oscillators—first at Mobius Microsystems, his former 6-year-old start-up that began shipping silicon oscillators in 2006, and continuing at Integrated Device Technology (IDT), the global semiconductor giant headquartered in San Jose, Calif., that acquired Mobius in January. IDT put McCorquodale in charge of its Silicon Frequency Control Business Unit, where he continues to refine his silicon oscillator technology, as well as oversee the unit’s operations, including sales and marketing.

McCorquodale is scheduled to present a paper in June on his latest creation, which IDT announced April 29: a stand-alone silicon oscillator that can be assembled with other silicon components—enabling smaller, thinner, more compact products—at the IEEE International Frequency Control Symposium, in Newport Beach, Calif.

An unpackaged timing reference is unique. All quartz references are encased in expensive metal or ceramic packages to increase their stability by protecting them from the environment. Until now, McCorquodale’s silicon oscillators were encased in less expensive plastic for the same reasons. But the new silicon oscillator is bathed in a proprietary coating—which allows companies to combine it with other silicon chips into their own custom packages, essentially assembling the frequency reference in nearly any manner they choose. It took awhile for McCorquodale’s team to find a coating that protected the circuitry and ensured the oscillator’s stability by blocking interference from external electromagnetic fields.

In September, the work done at Mobius earned McCorquodale awards from his two alma maters, the 2009 Recent Engineering Graduate Award from the College of Engineering at the University of Michigan, Ann Arbor, and the 2009 Young Alumni Achievement Award from the electrical and computer engineering department at the University of Illinois, Urbana-Champaign.

McCorquodale’s silicon oscillator, which is approximately a fifth of a cubic millimeter, allows for new kinds of products impossible with quartz crystals, which are typically some 80 times larger in volume than what he has developed.

Moreover, quartz components cannot be assembled and integrated with the same processes as silicon. For example, silicon makes it possible to embed a frequency source into a phone SIM card, allowing for greater memory storage and for data on the card to be transferred to another phone or computer. Right now, most data is stored in the phone itself and lost when the SIM card is switched to another phone. A quartz crystal is too large to fit on a SIM card.

“Quartz is great, but the rest of the electrical engineering world operates in silicon,” McCorquodale says. “The technical community has wanted to achieve this for a long time, but the accuracy, until now, has been poor. Quartz-timed products are stable to 0.005 percent, meaning that the frequencies they generate vary no more than 0.005 percent over all conditions. Our initial silicon oscillators were stable to 1 percent. However, after six years of development, we are currently making products that are stable to 0.01 percent, and can sample products that are accurate to 0.0025 percent, but these products are not yet production-worthy.

“Our objective is to drive the technology to the ultimate limit of frequency stability—or as small a frequency variance as possible. We don’t know yet what that is. It’s an entirely new technology.”

McCorquodale, who grew up in Naperville, Ill., got interested in electronics while playing electric guitar in a rock band in high school. “Electronics improve the quality of music,” he says. For his senior high school project, he built a sound-effects board around a digital signal processor that produced reverberation and other effects when he played. “It works to this day,” he says.

He earned a bachelor’s degree in EE from the University of Illinois in 1997, then spent a year working on oscillator circuits at Hughes Space and Communications (now part of Boeing) in El Segundo, Calif., where he got interested in timing and frequency generation. From there, he went to the University of Michigan and earned a master’s degree in 2000 and Ph.D. in 2004, both in EE. He began tinkering with silicon oscillators at Michigan.

McCorquodale launched Mobius in Ann Arbor in 2004 to commercialize his research, which he relentlessly pursued. “Every day since, I’ve been wondering when I’ll get to nap,” he says. In 2006, armed with US $10 million in venture capital, McCorquodale kept Mobius’ Ann Arbor office but opened a new headquarters in Sunnyvale, Calif., where the semiconductor industry talent pool was larger. IDT first contacted McCorquodale in 2007 and began serious talks about merging eight months ago. By its merger, Mobius had shipped more than 10 million silicon timing devices to customers but had yet to break even.

“Any entrepreneur starts thinking about maintaining a stand-alone business, but given the market reality and the country’s financial crisis, I became very pragmatic,“ he says. ”It feels like every other company in Silicon Valley is shutting down. The fact that we were acquired and continue to build the products initially designed at Mobius is a huge success.”

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