Patent ID: 7943411

Claim:
A method of bonding a MEMS device wafer to a second wafer, the method comprising: forming an aluminum layer on the MEMS device wafer; forming a germanium layer on the second wafer; bringing the aluminum layer on the device wafer into contact with the germanium layer on the second wafer; heating the aluminum layer and the germanium layer, heating at least in part causing the aluminum layer and germanium layer to form a eutectic material, heating being initiated either before or after the aluminum layer is in contact with the germanium layer; and cooling the wafers to form a plurality of hermetic seal rings between the wafers, wherein at least one of the seal rings has varying concentrations of aluminum, germanium, or aluminum/germanium eutectic, the region of the seal ring adjacent to the device wafer having a higher concentration of aluminum than the region of the seal ring adjacent to the second wafer, the region of the seal ring adjacent to the second wafer having a higher concentration of germanium than the region of the seal ring adjacent to the device wafer.