Richard Kullberg

Processes and materials for creating and maintaining reliable vacuum and other controlled atmospheres in hermetically sealed MEMs packages.

Many MEMs systems require controlled atmospheres or vacuum for successful operation. These atmospheres or vacuum must first be obtained and then maintained against degradation over the lifetime of the device. Vacuum and controlled atmospheres decay in quality over time due to various mechanisms including poor processing and outgassing. At the beginning of the MEMs era many researchers felt that these systems were immune to these degradation mechanisms due to their small sizes. As the technology has developed and moved in the application phase many groups have run into lifetime issues when they have tried to package their systems. Investigation demonstrated that the same problems that large-scale static vacuum systems suffer apply in the MEMs arena as well. The key to controlling this process of degradation is good processes and process control during the manufacturing phase and the introduction of gettering materials into the package to deal with long term outgassing of harmful species. The key steps of a successful generic process inclusive of getter use and activation will be discussed.

Vacuum maintenance in hermetically sealed MEMs packages

Packages for many high sensitivity MEM devices (Micro- Electro-Mechanical devices) such as accelerometers need to operate in a vacuum in order to obtain their full performance. This vacuum is destroyed by the outgassing of species such as hydrogen and water vapor from the surfaces of the package exposed to this vacuum. To control this outgassing a getter is needed. MEM packages are too small to accommodate traditional sintered porous getters. A solution has been developed using a high porosity thick film getter material. The getter consists of a highly porous, mechanically stable, getter coating on a metal substrate. This getter reacts with active gases such as water vapor, hydrogen, oxygen, nitrogen, and carbon monoxide that outgas from the inner surfaces of the package. The physical characteristics and performance of this material will be demonstrated per ASTM sorption testing. The results of this testing will be used to demonstrate the potential for vacuum performance in a real world MEM package.

New getter configuration at wafer level for assuring long-term stability of MEMS

The evolution from ceramic packages to wafer to wafer hermetic sealing poses tremendous technical challenges to integrate a proper getter inside the MEMs to assure a long term stability and reliability of the devices. The state of the art solution to integrate a getter inside the MEMs of the last generation consists in patterning the getter material with a specific geometry onto the Si cap wafer. The practical implementation of this solution consists in a 4” or 6” Si wafers with grooves or particular incisures, where the getter material is placed in form of a thick film. The typical thickness of these thick films is in the range of few microns, depending on the gas load to be handled during the lifetime of the device. The structure of the thick getter film is highly porous in order to improve sorption performances, but at the same time there are no loose particles thanks to a proprietary manufacturing method. The getter thick film is composed of a Zr special alloy with a proper composition to optimize the sorption performances. The getter thick film can be placed selectively into grooves without affecting the lateral regions, surrounding the grooves where the hermetic sealing is performed.