March 29, 2014

SiTime SiT8008 - MEMS oscillator : weekend die-shot

SiTime SiT8008 is a programmable MEMS oscillator reaching quartz precision but with higher reliability and lower g-sensitivity. Also SiTime is one of companies who received investments from Rosnano - Russian high-tech investment fund.

Photo of MEMS die puzzled us for quite some time. Is it some sort of integrated SAW/STW resonator?

The trick is that to reach maximum Q-factor (up to ~186'000 according to patents) MEMS resonator must operate in vacuum. So they package resonator _inside_ the die in hydrogen atmosphere, then anneal it in vacuum so that hydrogen escapes through silicon. So we see here only a cap with contacts to "buried" MEMS resonator. We were unable to reach the resonator itself without x-ray camera or ion mill.

MEMS die size - 457x454 µm.

Thankfully relevant patents were specified right on the die : US6936491 US7514283 US7075160 US7750758 :)

Digital die contains LC PLL and digital logic for one-off frequency programming and temperature compensation.
Die size - 1409x1572 µm.

Poly level:

Standard cells ~250nm techology.