Abstract
This review surveys advances in the fabrication of functional microdevices by multi-photon lithography (MPL) using the SU-8 material system. Microdevices created by MPL in SU-8 have been key to progress in the fields of micro-fluidics, micro-electromechanical systems (MEMS), micro-robotics, and photonics. The review discusses components, properties, and processing of SU-8 within the context of MPL. Emphasis is focused on advances within the last five years, but the discussion also includes relevant developments outside this period in MPL and the processing of SU-8. Novel methods for improving resolution of MPL using SU-8 and discussed, along with methods for functionalizing structures after fabrication.
Highlights
This review surveys advances in the fabrication of functional microdevices by multiphoton lithography (MPL) using the SU-8 material system
The name MPL is preferred because (a) higher-order nonlinear processes, and not just 2PA, commonly occur in the PIs and sensitizer used in MPL, and (b) while MPL is typically enabled by multi-photon absorption (MPA)-based photopolymerization, MPA-based micro-fabrication is possible via other photochemistries such as 2PA-assisted reduction [3,20,21,22] or 2PA-assisted patterning of chalcogenide films [4,23,24,25]
Kuebler et al reported that this procedure causes irreversible shrinkage and distortion in SU-8 micro-lattices fabricated by MPL because as the ethanol solution of ethylenediamine infuses and swells the structure, it can react with unpolymerized oligomers and wash them away, causing irreversible distortion (Figure 13b) [83]
Summary
MPL is an increasingly versatile technique for fabricating 3D micro- and nanostructures based on multi-photon absorption (MPA) activated with a tightly focused pulsed laser. MPL has been performed with a wide range of materials, including photopolymers, chalcogenide glasses, as well as ceramic/polymer and metal/polymer composites [1,2,3,4]. MPL using SU-8 has enabled significant advances in micro-device fabrication, due to the novel properties of SU-8 and its ability to be activated by MPA. The non-linear optical response of the photoresist strongly confines photochemical activation within the 3D volume of the material to a region centered around the focal spot. Non-linear chemical response of the material to the local irradiance profile confines the material transformation and enables high-resolution 3D patterning
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