@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
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
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.