Releasable SU-8 structures for various microfabrication processes using a water-soluble sacrificial layer

A promising release technique for SU-8 using a water-soluble sacrificial layer based on germanium oxide is developed. The relatively high etching rate of germanium oxide in water and its high etching selectivity make it suitable as a sacrificial layer for the release of SU-8 structures. Moreover, a water-soluble sacrificial layer causes no damage to either the structural materials or SU-8 because it can be etched under much milder conditions. To demonstrate the effectiveness of a water-soluble sacrificial layer for releasing SU-8 structures, a large-area SU-8 structure is released using this approach. In addition, various microfabrication processes are demonstrated using releasable SU-8 structures: a metal lift-off process using SU-8 as a lift-off mask, fabrication of thick metal microstructures using SU-8 as a mold, and fabrication of a free-standing SU-8 micromixer.