Hermetic packaging is used for the encapsulation of MEMS structures in order to protect them from environmental effects. Aging effects on sensors and actuators are thereby reduced and slowed down. The housing cavity is typically filled with an inert gas (e.g. Nitrogen). Using appropriate measurement techniques, we can determine the leak rate for a given gas, and extrapolate the theoretical lifetime of the system.
The hermetically packaged cavity sits between a silicon substrate and a glass substrate. Through dry etching (DRIE), cavities and vias are built into the silicon substrate. The cavity is sealed using a thermo-compressive low temperature bonding process. To this end, two microstructured gold thin films are pressed against each other at a temperature of 300 °C, and thus bonded. In the same process, vertical electrical feed-throughs are realized. These feed-throughs are the electrical contacts between the meander structures inside the cavity, and the devices on the outside.
- Contact resistance of the vias: 0.4 ± 0.05 Ω
- Standard leak rate: 4.3x10-10atm cm3/s
- Cavity dimensions: 10 x 10 mm
- Cavity depth: 200 µm
- Via radius: 500 µm
- Aspect ratio of the vias: 1