Resonators: silicon challenges quartz
01 January 2007
A company founded in 2004 has set its sights on the $3billion quartz and clock market that is by introducing resonators, oscillators and timing MEM devices, replacing the quartz element.
SiTime (www.sitime.com) has introduced the SiT0100 SiRES 5.1MHz resonator to replace quartz ones. The MEMs devices are produced in SOI wafers, using glass layers in a CMOS process for 1.4mm x 1.4mm chips and 2mm x 2.5mm SIPs (system in packages). The package is pincompatible with the smallest quartz oscillator available today, claims the company.
The resonator can be placed on the die, explains Markus Lutz, co-inventor and co-founder, SiTime. Circuit adjustments can be made to the die for it to drop in without being connected to an external device.
The phase noise performance of the SiT0100 is –115dBc/Hz at 10kHz, which makes it suitable for use in most consumer, automotive and industrial frequency control applications. Initial target applications are notebook PCs, mobile phones, digital still cameras and portable media players. The device is passive and consumes no power and can exhibit a similar power consumption to quartz devices with similar Q ratings when the MEMs is combined with an oscillator circuit.
According to internally produced tables, the SiRES quartz crystal has a 1,000:1 ratio advantage over quartz crystal and operates at 5.1MHz. This will graduate to 20MHz with the next-gen silicon crystal due to be available in the middle of this year and around 40 to 45MHz with the generation after that, to compete with quartz crystal’s 30MHz frequency performance.
It is the stability levels of silicon quartz that attracts interest, with a 0.15ppm (parts per million) /year, over 25 years, compared to 3ppm with quartz crystal and 100 failure in thousand (FIT) for quartz surpassed by SiRES’s five FIT statistic.
The resonator is produced with proprietary processes MEMS first and EpiSeal. MEMS First, using SOI wafers can produce thousands of resonators on a single wafer, improving the reliability of quartz.
The EpiSeal process encapsulates the resonator in a clean, high vacuum cavity. This cavity allows the single crystal bean to resonate in a clean environment, without risk of contamination. The process is claimed to yield a part that ages less than 0.15ppm/year for 25 years with no detectable thermal hysteresis. This rate eliminates frequency error sources that are impossible to calibrate, says Lutz. A single point temperature calibration will yield a resonator that is better than ±
As the MEMs oscillators are not directly compatible with quartz resonators, the company has prepared a design-in kit, the SiT0100DK which has an 0.18ìm CMOs drive circuit and datasheet/documentation.
Packaging is industry standard plastic, as opposed to the expensive vacuum ceramic required by quartz crystal. A future option, speculates SiTime’s vice president, sales and marketing, John McDonald, could be to integrate the resonator with digital circuitry to expand further on the 9billion units, $3billion quartz and clock market.
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