A Tiny Silicon Clock

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Besides the advantage of size, SiTime's silicon oscillators are an appealing alternative because of their ability to be tuned to different frequencies. Unlike a quartz crystal, which is fabricated to resonate at a certain frequency throughout its lifetime, a silicon oscillator is capable of vibrating at many different frequencies, depending on the software controlling the circuit. This makes the manufacturing process less costly, according to Partridge, since when a quartz crystal is fabricated, it's designed to resonate at a single frequency throughout its lifetime. Changing the function of the quartz clock from one that operates a cell phone to one that runs a high-definition television, for example, requires fabricating an entirely different batch.

But SiTime's silicon resonators don't require frequency adjusting during fabrication, which makes them easier to manufacture. And when they're ready to be used, an engineer simply tunes to the desired frequency using software.

SiTime is one of a handful of new companies developing MEMS resonator technology, says Roger Howe, professor of electrical engineering at Stanford and chief scientist at Silicon Clocks, a University of California, Berkeley spin-off. The area is "ripe for commercialization," he says, thanks to a combination of maturing technologies in the MEMS industry and ultra-clean encapsulation techniques. As a result, a number of startups specializing in MEMS resonators have emerged, including Silicon Clocks and Mobius Microsystems, a University of Michigan spin-off.

SiTime has partnered with major manufacturers of quartz clocks, which will sell its silicon oscillators. But there is more work to be done. Partridge says that the products to ship at the end of the year will satisfy a few applications for quartz oscillators, such as simple microprocessor clocks. But they aren't good enough to replace, for example, quartz timing mechanisms in GPS devices. Future silicon clocks, he says, will have a higher precision, as his team learns to fine-tune the fabrication techniques.