Pushing the limits of photo-curable SU-8-based superparamagnetic polymer composites

We present a facile method to extend the particle-induced exposure depth limitation in SU-8-based superparamagnetic polymer composites (SPMPCs) by adding H-Nu 470 photo initiator (PI). While superparamagnetic magnetite particles strongly absorb i-line radiation required to crosslink SU-8, H-Nu 470 expands the photosensitivity of the resist towards the visible spectrum, where the composite is more transparent. Using the g-line emission of a mercury short-arc lamp we are able to increase the exposure depth from 5.3 μm to 11.6 μm for a 5 %vol composite and for the first time expose a 10 %vol composite with a depth (thickness) of 5.6 μm. In comparison to i-line sensitive SPMPCs, the proposed PI enables crosslinking films with a 2.2-fold magnetization while maintaining a homogeneous particle distribution.