Replacing well-established technology is always a tricky proposition. Researchers have been trying to displace quartz crystals with Micro-Electromechanical system (MEMS) resonators for more than 40 years. Based on a new wafer encapsulation approach, SiTime Corp. may finally have a viable solution. The company’s MEMS-First wafer-level encapsulation and packaging technology addresses the stability and low cost required for high-frequency oscillator applications.
Built in epitaxially sealed epipoly (epitaxially grown polysilicon) chambers buried under the wafer surface, the MEMS resonator structure is isolated from external contamination prior to packaging. A vacuum of approximately 10 mT seals out water and other high- vapor pressure contaminants at the wafer level. After dicing, the resonators are molded into standard plastic IC packages.
Testing showed a total frequency error of less than 100 ppb under a measurement noise floor of 200 ppb and a specified measurement error of 30 ppb. Measurements were made of the compensated frequency stability for the resonator in a plastic molded package as it was swept twice from 40 to +85C and back to 40C. The hysteresis was less than about 50 ppb. Over a one year timeframe, the MEMS resonator drifts less than 1ppm compared to typical small quartz crystals that drift 3- to 5ppm.
Specified in the frequency range of 1- to 125 MHz, initial production fixed frequency and programmable oscillators have a frequency tolerance of ±50 to ±100 ppm and aging of ±2ppm/year. The units are specified at ±150 psec of peak to peak jitter. Four-pin QFN type packaging options for the MEMS resonators include: 2.0 × 2.5 × 0.85 mm, 2.5 × 3.2 × 0.85 mm, 3.2 × 5.0 × 0.85 mm, and 5.0 × 7.0 × 0.85 mm packages.
For more information on SiTime oscillators, go to http://rbi.ims.ims.ca/4928-504.
Fabricating the MEMS mechanical resonator in a standard CMOS process allows the integration of additional circuitry on the surface to provide further system cost reduction and improved performance.
It won't be too much longer and hardware design, as we used to know it, will be remembered alongside the slide rule and the Karnaugh map. You will need to move beyond those familiar bits and bytes into the new world of software centric design.
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