Vacuum packaging for microsensors by glass-silicon anodic bonding

Vacuum packaging by the glass-silicon anodic process is studied. The residual gas generated during the anodic binding process and that desobed from the silicon and glass surface increase the pressure in a sealed cavity. In order to fabricate a vacuum sealed cavity, two methods are proposed to eliminate the residual gas; (i) the residual gases are evacuated through a small opening after bonding and then the opening is plugged by depositing a material in vacuum, (ii) the residual gases are absorbed by a getter inside the sealed cavity. A non-evaporable getter (NEG) is used for the second method. A vacuum sealing of tens of Torr is obtained by the firat method. The second method and a combnation of the two methids enables vacuum sealing at a pressure lower than 10^-5Torr. A prototype of a capacitive vacuum sensor is fabricated by using the second method.