Room-Temperature Sealing of Microcavities by Cold Metal Welding

Wafer-Level Vacuum Packaging Enabled by Plastic Deformation and Low-Temperature Welding of Copper Sealing Rings With a Small Footprint

“…The low-temperature welding is based on large-scale plastic deformation of Cu at the bonding interface, thus making this method insensitive to surface roughness. A similar approach has been proposed earlier where protruding Au rings on both wafers were used for cavity sealing [36]. However, this caused considerable problems of breakage of the outer rings due to resulting shear stresses.…”

“…However, the reported sealing rings feature relatively large widths, ranging from 60 µm to 200 µm [33], [34], [39], and bonding layers with granular materials [35] or smoothed surfaces [39] have to be prepared by specialized processes. The high ductility of Au enables vacuum sealing based on cold welding of the Au sealing structures [36]- [38]. However, the proposed sealing techniques either rely on reinforcement of the bond strength by additional materials such as epoxy underfill [36], or solder patches [37], or the process is based on wafer bonding in combination with sealing of vent-holes by plastic deformation of Au plugs [38].…”

“…The high ductility of Au enables vacuum sealing based on cold welding of the Au sealing structures [36]- [38]. However, the proposed sealing techniques either rely on reinforcement of the bond strength by additional materials such as epoxy underfill [36], or solder patches [37], or the process is based on wafer bonding in combination with sealing of vent-holes by plastic deformation of Au plugs [38].…”

Hermetic integration of liquids in MEMS by room temperature, high-speed plugging of liquid-filled cavities at wafer level

“…We have also shown cold welding of overlapping gold sealing rings with negatively-sloped sidewall angles [5]. Both these methods seal the liquid in the cavity during wafer bonding and require additional mechanical stabilisation afterwards.…”

“…This can be as low as 37 • C for sensitive or living materials in for instance life-science applications. In traditional wafer-level integration schemes the liquid is hermetically sealed inside the cavity during the wafer bonding process [4,5,6]. This forces the cavity formation and sealing.…”