Oscillators: MEMS or Quartz
May 24, 2012, MEMS Business Forum, Santa Clara, CA—Harmeet Bhugra from IDT talked about the emerging market for MEMS passive capacitor oscillators. He detailed the arguments for MEMS oscillators and tried to explain why there is a preference for a lower-grade quartz technology.
Currently, most users consider piezoelectric oscillators over passive capacitive oscillators. Partly this is due to availability, and partly to various concerns and misconceptions about MEMS oscillators. The interesting aspect is that quartz oscillators have a fairly high zero-time failure rate, between 10 and 100 ppm. In comparison, MEMS oscillators cost less and have higher reliability than the standard quartz devices and always turn on when powered up in circuit.
One concern is that MEMS need to be protected from the environment. If you cap the MEMS before dicing, the micro-encapsulation allows for stacked die and plastic package assembly. The packaging depends upon the application and product, the I/O types and interfaces can call for different package types.
MEMS oscillators are available in many standard configurations and packages. The designs can be temperature compensated with many techniques, with the highest accuracy coming from active tuning of the oscillator.
MEMS oscillators have good long-term stability, specified at less than +/-2ppm at 25°C over a time frame of about 2 years with actual values of 0.5ppm. Quartz runs closer to +/-5ppm. The MEMS can survive over MIL-Spec 70k Gs acceleration, a level that requires special packaging for the more fragile quartz devices.
Even though the MEMS devices are more robust and accurate, the industry still favors quartz oscillators for precision frequency generation. The total market for oscillators of all types is about $4B, and MEMS are projected to capture about 10 percent of that market by '16.