Bonding of SU-8 films onto KMPR structures for microfluidic, air-suspended photonic and optofluidic applications

We present a method to bond unstructured and structured SU-8 films down to sub-micron thicknesses onto microchannels fabricated in KMPR using a flexible polydimethylsiloxane (PDMS) stamp. By exploiting differently casted PDMS stamps, 3D microfluidic channel networks, air-suspended photonic devices and optofluidic structures have been fabricated. First, microchannels of KMPR are patterned by photolithography and an SU-8 film is spin coated onto a prepared PDMS stamp. The stamp is then placed on top of the KMPR microchannels and the SU-8 layer is cross-linked by applying sufficient heat and pressure. After peeling off the PDMS stamp, the SU-8 layer remains bonded on the KMPR. In our experiments, we demonstrate the bonding of approximately 0.5 μm thick structured SU-8 films onto KMPR microchannels of about 500 μm width and 25 μm height. Bond strength tests demonstrated that such thin layers can withstand pressures up to 1100 hPa. The laminated SU-8 layers can enable various functionalities, e.g. sealing of microfluidic channels, realization of air-suspended photonic structures or optofluidic devices. Most importantly, the combination of fluid handling in the microchannels and air-suspended photonic structures realized in the laminated SU-8 layer enables research towards a large range of applications, such as optofluidics, biosensors, chemical and biomedical analysis, environmental investigations, and renewable energy.