MEMS Device Sealing in a High Vacuum Atmosphere Achieving Long Term Reliable Vacuum Levels

Abstract

Microeletromechanical Systems (MEMS) require encapsulation of delicate microelements in a controlled atmosphere or vacuum environment. In order to achieve proper device operation and protection from harsh environments, these packages must be hermetically sealed and the internal atmosphere must be maintained to prevent degradation of the device over it's lifetime. Controlled atmospheres and vacuum levels can change over time due to improper consideration of material and their outgassing characteristics. Packaging of MEMS has been and continues to be a major challenge unless all of the materials comprising of a sealed package are evaluated at the initial design phase. This paper will address the issues related to a ceramic package with a gold metallization seal ring, the importance of using low outgassing sensor attach materials, incorporating a getter material to be sealed in the package cavity, and the proper handling of the hermetic lid. In order to achieve the best and highest entrapped vacuum in the package, materials must be prepared before processing. This will involve proper vacuum baking and activating the getter film prior to sealing the MEMS device. By controlling the vacuum levels with aggressive bake outs, fully activating the getter, addressing all material out gassing rates, and optimizing the high vacuum sealing process profile a MEMS device with a controlled vacuum level can be obtained.