Silicon MEMS Technology Expected to Replace Traditional Quartz Resonators

SiTime, a privately held Silicon Valley startup, has announced the availability of engineering samples of its SiT1xxx fixed frequency and SiT8002 programmable oscillator families based on its proprietary MEMS First™ and EpiSeal™ CMOS compatible processes. The SiTime silicon resonator is an electro-statically driven mechanical device that has ppm performance similar to consumer grade quartz products and orders of magnitude better than today's best silicon clock oscillators. The company expects that the availability of these devices will quickly replace the existing quartz technology, which currently dominates the market for a majority of electronic timing and frequency generation "clock" applications. The SiTime SiRes™ SiT1xxx and SiT8002 oscillator families generate frequencies between 1 to 125 MHz with excellent temperature and jitter performance and are packaged in tiny industry standard IC packages, which provide a significant cost advantage.

SiTime oscillators sampling today address more than 80% of the unit volume of quartz resonators and oscillators. Key target applications are digital still cameras, portable media players, notebook computers, and high reliability applications. However, MEMS oscillators will benefit any quartz application where small size and reliability are valued.
Robert Bosch, GmbH researchers Markus Lutz and Dr. Aaron Partridge in partnership with Prof. Tom Kenny of Stanford University discovered and developed a series of inventions definitively solving the temperature/frequency hysteresis, long-term stability, and packaging cost problems, which have previously prevented the commercialization of MEMS resonators. SiTime, under exclusive license from Robert Bosch, GmbH, was formed to productize this technology on 200 mm standard CMOS wafers.
SiTime resonators are 1000x smaller then equivalent quartz resonators and have shown remarkable performance when compared to commercial quartz devices. For example, long-term stability or aging is typically measured at 0.050 ppm, which is at the current limit of SiTime test equipment. On the other hand, quartz devices are typically specified at +/-2 to +/-5 ppm first year aging and +/-10 to +/-15 ppm aging over 10 years. Worse still are the non-MEMS silicon clock oscillators with frequency tolerances in the 2,500 to 25,000 ppm range. Temperature vs. frequency error hysteresis at temperature ramp rates in excess of 4 degrees C per minute is much less than 1 ppm as compared to +/-2 ppm for quartz devices. SiTime resonators are combined with a CMOS drive circuit to form extremely small high-performance SiRes™ oscillators.
SiTime's MEMS resonators are etched on a silicon wafer in low-cost CMOS fabs with 0.18um tooling. The deep reactive ion etch "DRIE or Bosch Process" results in a tiny and extremely tough mechanical structure that is free to vibrate when driven by an electrical signal. The vibration efficiency is measured in Q. The Q of the MEMS First™ resonators is approximately 80,000. The mechanical resonators measure 300um across with more than 50,000 per 200 mm wafer, which results in a high-performance and cost-effective resonator.

The silicon mechanical resonator is then encapsulated in a tiny and ultra-clean vacuum chamber formed directly on the wafer by SiTime's EpiSeal(TM) CMOS compatible process. The EpiSeal™ frees SiTime's resonators from the costly constraints of custom ceramic packages by enabling the use of any standard IC packaging technology. SiTime's first product families use QFN-type technology modified slightly to meet the quartz oscillator and resonator footprints. The QFN-type package contains a CMOS driver IC and MEMS resonator, which together form a complete oscillator in product footprint of only 2.0 mm (w) x 2.5 mm (l) x 0.85 mm (h).
Due to the extremely small size of the resonator beam, the ultra-clean encapsulation chamber, and the process consistency of today's modern CMOS fabs SiTime oscillators reduce or eliminate many reliability issues associated with quartz. Among these common quartz reliability issues are cracking, thermal sensitivity, over drive damage, shock and vibration sensitivity, custom packaging and footprints, inconsistent start-up, thermal hysteresis, ESD damage, and aging.

On the other hand, Quartz resonators require two load capacitors and often a shunt resistor for proper operation; as a result SiTime oscillators require 30% less PCB circuitry area for the same package size, reduce BOM cost, and require 3 less components per frequency source. In addition to the many performance and reliability improvements, SiTime oscillators are priced at less than $0.50 on a solution basis in high volume and are more cost competitive than quartz products with comparable features and package sizes.
Kurt Petersen, CEO and Co-Founder of SiTime and a MEMS industry veteran stated, "SiTime's introduction of SiRes(TM) oscillators represents a fundamental transformation of the timing industry. One of the last hold-outs of common electronic circuit components to be integrated onto silicon is the quartz crystal. Finally, a smaller, more reliable and cost-effective alternative is available to circuit designers, the SiRes™ oscillator."
SiTime's SiRes™ SiT1xxx oscillator family is available in more than 173 frequencies. The SiRes™ SiT8002 programmable oscillator family is a value-added solution for fast-turn, rapid prototypes, custom frequencies or low-volume production and is form, fit, and function compatible with the SG-8002 and similar quartz-based programmable oscillators while offering lower power and smaller package options at more competitive prices. Both families are available from 1.000 MHz to 125.000 MHz at optional frequency tolerances of +/-50 ppm or +/-100 ppm in industrial (-40 to 85 degrees C) or commercial (0 to 70 degrees C) temperature ranges. Also, 4 packages sizes from 5.0 mm x 7.0 mm x 0.85 mm down to 2.0 mm x 2.5 mm x 0.85 mm are available. Engineering samples are available now with full-production slated for September 2006.
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