Porous Thin Film Packaging for Wafer Level Vaccum Encapsulation

Description

Concept of Porus Packaging

With a nano-porous thin film as an encapsulation shell in thin film packaging of surface-micromachined MEMS devices, fast removal of the sacrificial material (yellow layer in figures above) can be achieved, while the penetration of the sealing material into the package during the sealing process can be minimized.

An encapsulated microbridge on a MUMPS

An encapsulated Pirani Gauge

Top solid polysilicon sealing layer and bottom porous polysilicon layer

We have developed a novel on-chip vacuum encapsulation technique, which turns a thick polysilicon layer porous, by electrochemical etching, "after" deposition on sacrificial material, so that the process is fully compatible with typical polysilicon surface micromachining process. Once the polysilicon shell layer is deposited over the top sacrificial PSG layer and turned porous, the thick porous layer, with pore size less than 10nm, allows for fast removal of sacrificial PSG (in 1 minute) underneath, but not the penetration of sealing materials during subsequent vacuum sealing. The pressure inside the sealed package, measured by an encapsulated polysilicon Pirani gauge, was around 200 mTorr and showed no detectable leaks over 12 months. The proposed encapsulation idea was also demonstrated through the common MUMPs foundry service.

Current Members:

Rihui He

Past Members:

Publications

"On-Chip Hermetic Packaging Enabled by Post-Deposition Electrochemical Etching of Polysilicon",
R. He, and C. -J. Kim,
Proceedings of IEEE MEMS 2005, Jan 30 -Feb 3, Miami, Florida, pp. 544-547
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"Post-deposition porous etching of polysilicon: fabrication and characterization of free-standing structures",
R. He, and C.-J. Kim,
Proceedings of IMECE2004 2004 ASME International Mechanical Engineering Congress and Exposition, November 13-19, 2004, Anaheim, California
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"Porous Polysilicon Shell Formed by Electrochemical Etching for On-Chip Vacuum Encapsulation",
R. He, L. Fan, M.C. Wu, and C.-J. Kim,
Solid-State Sensor, Actuator and Microsystems Workshop (HH'04), Hilton Head Island, South Carolina, June 6-10, 2004, pp.332-5
PDF format