It’s about time

It's been over 10 years since the push for commercial silicon-based MEMS resonators began. Early players like Discera and SiTime believed that, eventually, MEMS-based components would not only be able to replace other types of oscillators, but would actually be built onto logic chips as a normal part of IC fabrication; no longer would external components like quartz crystals be need for timing. While that still could happen someday, it hasn't yet.

Many of the devices that MEMS oscillators were designed to compete with have also improved with time, and are still being used today. As C.S.Lam, Director, Product Development & Marketing at Epson Electronics America, noted in “Let’s talk oscillators,” “Unknown to many, quite a few quartz crystal (and SAW) components are being manufactured with some MEMS processing steps — double-side photolithography, non-planar metallization, etch through, sacrificial layer deposition and removal, Au etch protection, etc.” The constant improvement has allowed those components to continue to compete quite successfully with silicon MEMS oscillators. But as Lam also noted elsewhere, “The quartz crystal and crystal oscillator industry needs to continue monitoring the development efforts of the MEMS oscillator and all silicon oscillator. Evidence is clear that oscillator circuitries especially those based on PLLs will get better and better as time progresses.” SiTime’s MEMS oscillators are based on fractional-N PLLs.

In the last month, SiTime introduced a device, the SiT1542 32 kHz MEMS oscillator, aimed at the commercial heart of the quartz-crystal market today: smartphones and tablets. In introducing the new product, Rajesh Vashist, CEO of SiTime, said that because of the his company's silicon MEMS and analog technology, they were able to “deliver innovative timing solutions that leapfrog decades of quartz industry development.…Now, we are bringing these exceptional benefits to the booming mobile market.”

Among the claimed benefits versus quartz for the MEMS device is that it:
• Uses 70% less board area than the smallest quartz package sampling today, and eliminates the need for load capacitors.
• Uses 50% less power than an equivalent quartz solution.
• At 0.55 mm, is the thinnest available device.
• Provides frequency stability of ±20 ppm at room temperature and ±100 ppm over -40° to 85°C range.
• Is 30 times more robust than quartz.
• Offers more robust system startup in extreme temperatures.
• Has an MTBF of 500 million hours, 15 times better than quartz.
Of course, the device still comes in a separate package, but perhaps the day when MEMS oscillators are actually built alongside complex commercial CMOS analog and digital devices on the same substrates isn't that far off.