A planar self-sacrificial multilayer SU-8-based MEMS process utilizing a UV-blocking layer for the creation of freely moving parts

This work presents the first-reported freely moving parts, including out-of-plane hinges and rotating parts, fabricated in SU-8 that require no post-development bonding step. The technology used is a PolyMUMPs-like SU-8 process developed by the authors, called the planar self-sacrificial multilayer SU-8 (PSALMS) process. The PSALMS process allows the independent patterning of planar SU-8 layers, so that the SU-8 acts as both the structural and sacrificial material. Each layer is a bilayer consisting of a standard SU-8 layer below a layer of SU-8 modified to heavily absorb UV by the addition of SC1827 resist. The use of this bilayer structure creates a greatly increased processing window, in which an exposure can expose the uppermost bilayer without affecting underlying bilayers. The ability to independently pattern layers allows for the creation of overhanging structures and freely moving parts. So far the PSALMS process has incorporated four structural layers, which allows for the creation of structures such as gears and out-of-plane hinges. A description of the underlying fabrication principle and processing details is presented in this paper. Also presented are gears and hinges that have been fabricated and display proper functionality.