SU-8 Gray Lithography

We are working on a novel technique for the fabrication of 3D polymer (SU-8) structures using Grayscale Lithography. Process is implemented through a Maskless Lithography system (SF-100, Intelligent Micropatterning, US) using a software generated mask.  Process achieves structure over-hangings and undercuts in a one-step batch exposure compared to a) multi-step exposure or b) serial techniques currently available such as Ebeam, Laser or normal photolithography with Multi-layer processes and one final developing step.
Fabrication process is based on photolithography and achieves its goal by varying the light-energy dose one shines on a targeted area. As it is known how stresses in the final polymer structure are mainly dependent on post exposure bake (PEB) times and how such stresses become more important as geometry size increases, we must optimize PEB times to be short enough to guarantee full development of undercut spaces without causing structure to peel from substrate (by reducing internal stresses) but long enough to allow polymer to fully cross-link after exposure.
Optimized PEB time allow the samples to be immersed in developer long enough (up to 26 hours) to permit the etching of all undercuts.
Proposed applications include:

Fluidic networks: A network of covered channels and chambers can be coupled to access ports for microfluidic applications. Additional features, such as electrodes, could also be incorporated.

Insulator Dielectrophoresis (iDEP): Polymer posts can be embedded in a channel towards an iDEP device. While a uniform electric field E is induced in the whole channel by external electrodes, posts introduce spatial non uniformities in E generating areas with electric field gradients. Such gradients attract or repel certain bioparticles allowing for a particle separation device without the need of antibody-coupled magnetic beads or fluorophores.

Molds: Relatively inexpensive 3D templates, sacrificial perhaps, for forming selected materials could be rapidly fabricated.

Precursor for novel carbon structures: Pyrolysis of certain polymers transforms them into carbon with a degree of isometric shrinkage. Such technique could be used to achieve carbon cantilevers, bridges, 3D molds, etc.