Review of vacuum packaging and maintenance of MEMS and the use of getters therein

Abstract

Key types of microelectromechanical systems (MEMS) sensors need vacuum or other controlled ambients in order to operate properly. Examples include MEMS infrared sensors and sensitive MEMS gyros. Steps to attain and maintain the vacuum ambient include: (i) Proper processing to reduce trapped gasses in the package, (ii) hermetically sealing the package, and (iii) providing a means to pump away gasses that outgas into the package. Proper package processing and getter technology are key to success in this endeavor. Although many aspects of package processing and assembly are proprietary, the key items to control include leaks (i.e., obtaining a hermetic package) and outgassing from materials within the vacuum cavity. Once gas loads are minimized as much as possible, the actual service life of a package depends on pumping away any internal gases built up through outgassing, leaks, or permeation. This pumping is done by a class of materials called getters. Gettering technology is discussed in relation to vacuum-packaged MEMS/MOEMS. With proper materials and processes, controlled ambients to include vacuum can be obtained in MEMS/MOEMS packages. Not only can they be obtained, they can be maintained for the desired system lifetime.