FABRICATION: Maintaining Vacuum in Sealed MEMS.

Nonevaporable getters have been proposed for use in maintaining vacuum inside hermetically sealed MEMSs that rely on vacuum for proper operation. A vibratory microgyroscope is an example of such a MEMS. The proposed getters could also be used in such vacuum components as cathode ray tubes, microwave tubes, conventional electron tubes, plasma display devices, particle accelerators and colliders, vacuum-thermal insulation, ultrahigh vacuum systems for processing semiconductors, x-ray tubes, lamps, and field emission display devices. Work on this proposal was done by Rajeshuni Ramesham of Caltech for NASA's Jet Propulsion Laboratory (Tel: 818/354-2577).

The need for getters arises as follows. Over time, the vacuum inside a sealed MEMS (or inside any other sealed vacuum device) is degraded by outgassing of common atmospheric gases and packaging material vapors from the surfaces of the vacuum chamber, and by diffusion and/or microleaking of these and other gases. Getters are materials that help maintain vacuum by chemically sorbing gases. Getters have been used in vacuum electron devices since the early years of electronic technology; but until now, there has been little systematic effort to incorporate them into MEMS.

The proposed getters would be components of the MEMS vacuum packaging in which they would be installed. They could be fabricated in simple planar shapes or in more complex three-dimensional shapes. They would be made from Zr-Al-Fe, Zr-V- Fe, or other suitable materials. They would be made highly porous to facilitate access of gases and to provide high active surface area for sorption. The getters would be required to be ...