Vacuum packaging technology using localized aluminum/silicon-to-glass bonding

A glass vacuum package based on localized aluminum/silicon-to-glass bonding has been successfully demonstrated. A constant heat flux model shows that heating can be confined locally in the dielectric layer underneath a microheater as long as the width of the microheater and the thickness of silicon substrate are much smaller than the die size and a good heat sink is placed underneath the silicon substrate. With 3.4 W heating power, ~ 0.2 MPa applied contact pressure and 90 min wait time before bonding, vacuum encapsulation at 25 mtorr (~ 3.33 Pa) can be achieved. Folded-beam comb drive [micro]-resonators are encapsulated and used as pressure monitors. Long-term testing of vacuum-packaged [micro]-resonators with a Quality Factor (Q) of 2500 has demonstrated stable operation after 69 weeks. A [micro]-resonator with a Q factor of ~ 9600 has been vacuum encapsulated and shown to be stable after 56 weeks. [686] Index Terms--Localized heating, MEMS packaging, microresonators, vacuum encapsulation, wafer level packaging.