A versatile and flexible low-temperature full-wafer bonding process of monolithic 3D microfluidic structures in SU-8

We present a versatile fabrication process for the precise fabrication of embedded three-dimensional microfluidic structures in SU-8 photoresist. The full-wafer bond process based on a polyester (PET) handling layer enhances the previous low-temperature bonding technology. We achieved an extremely high bond strength of 45 MPa while requiring only small anchoring structures. Small channel structures with an aspect ratio >2 as well as wide membranes with an aspect ratio <0.02 were successfully bonded to realize precisely defined channel structures. Furthermore, the developed process features high yields (>80%) and enables the integration of microelectronics. The flexibility of the fabrication process is presented in two contrary applications. A completely freestanding and transparent SU-8 foil with a thickness of 225 µm featuring embedded 3D microchannels was fabricated. Also, high quality ink-jet dispensers were successfully fabricated whereas the dispenser quality mainly depends on the channel quality.