ORTLAND, Ore.—Micro-electro-mechanical system (MEMS) resonators can now be integrated inside a semiconductor vendor's own plastic packages, eliminating the need for an external time base like a quartz crystal for real-time clocks. The world's first MEMS resonator for real-time clocks is being offered as a bare-die to CMOS chip makers by SiTime Corp.
"Semiconductor makers can wirebond our resonator die to their own chip inside a plastic package," said Piyush Sevalia, vice president of marketing at SiTime (Sunnyvale, Calif.). "We eliminate the need for an external quartz crystal for real-time clocks."
The quartz resonator market already tops $2 billion, according to SiTime, which claims that chip makers use them to create real-time clocks for microprocessors, microcontrollers, low power radios, sensor nodes, watches, SmartCards and application-specific standard products for portable, handheld and other consumer applications.
SiTime's novel MEMS resonator can be wirebonded to any CMOS die inside its package to eliminate external quartz crystals.
SiTime claims the low price and ten-times smaller size of its resonators will enable nearly any application using a quartz crystal for a real-time clock today to replace it with a cheaper, easier-to-use MEMS resonator that can be incorporated inside existing chip packages, thereby reducing a chip count. SiTime supplies all the necessary intellectual property (IP) for the amplification and compensation circuitry that conditions the raw resonator output for five parts-per-million (5 ppm) accuracy.
"Quartz requires all sorts of special tooling and packaging techniques making it more and more expensive if you integrate it with a plastic package," said Sevalia. "But for MEMS an inexpensive heterogeneous plastic package works just fine—our resonators is just another silicon die."
SiTime now markets MEMS resonators, oscillators and complete clock generator chips. The company has no announced customers yet, but claims to have already formed key partnerships with semiconductor makers for its new SiT1052 resonator.
The SiT1052 uses a basic clock frequency of 524 kHz that it divides by 16 to achieve a standard 32.768 kHz real-time resonator that can be combined with an SoC, ASIC or ASSP using wire-bonding or flip-chip plastic packaging. The half-millimeter square die—supplied on wafers with a known-good-die map—can withstand shocks 10-times greater than quartz crystals, according to SiTime, namely 70 Gs of vibration and up to 50,000 Gs of shock.
5 ppm (parts-per-million) accuracy is a significant improvement. The ppm of Good watch crystals have 20 - 30 ppm accuracy and cheap ones 100 ppm. 20-30 ppm is about 3 seconds per day.
Typically a watch oscillator crystal can be manufactured by depositing the resonator material on the silicon chip surface utilizing a photolithographic process, that is similar to the way integrated circuits are made.
Can this easy-to-use MEMs resonator be incorporated on the same die? Unless it's integrated on the same watch chip die I don't see a significant cost savings.
The general trend in a variety of semiconductor devices is to integrate as much as possible into the package. Historically it was thought that this would provide considerable cost savings over individual packages. For years this proved not to be true and is still true for many applications even today. However, it does serve as an excellent value-add marketing tool and in many cases provides an excellent incentive to your customers. It's one less thing for them to worry about or have to deal with and they can concentrate on their core competency. This is especially true for smaller companies and for start-ups. They typically have a specific niche and anything that helps them eliminate non-core competencies is a benefit. - Keith Schaub
@no.name_#4 & @KeithSchaub: good comments! I am not sure what processes SiTime's MEMS are fabricated with, so it is hard to judge whether it is possible to integrate on the same substrate with other circuits. There are many sensors that use CMOS processes so eventually there is a path to an universal MEMS CMOS process.
Multichip packages can provide a cost reduction if done right. Besides cost, there is the real estate premium now a days that will dictate more integration in a package, laterally or vertically.
Dr. MP Divakar