Vacuum encapsulation of resonant devices using permeable polysilicon

This paper reports on a novel manufacturable, in situ vacuum micropackaging technology. Permeable polysilicon etch-access windows enable rapid removal of sacrificial material from beneath the shell (e.g., 1 mm wide shells cleared of PSG within 2 minutes) and practically eliminate internal deposition of the sealing film. Inside the vacuum encapsulation shells were lateral microresonators. These devices were selected for packaging because they are well characterized vacuum probes. Measured mechanical quality factors four months after sealing have been shown to be above 3000. These quality factors indicate a cavity pressure near 600 mTorr four months after vacuum encapsulation.