SU-8 for Microsystem Fabrication
SU-8 is a negative-tone photoresist that can be used to fabricate thick, high aspect ratio structures. The thickness of SU-8 structures ranges from several micrometers to several hundred micrometers or up to millimeters by direct spin coating or stacking of multiple layers of dry films. Being a negative resist, SU-8 can be used to fabricate complex three-dimensional structures such as sealed microchannels or tilted optical surfaces by multiple exposures. Another feature of SU-8 is that its properties can be controlled and modified during processes by the exposure doses, baking temperature, or even additives. This provides possibilities for novel device design and fabrication without complex fabrication processes. SU-8 has relatively low loss and absorption in the RF and visible spectral ranges, therefore, it has been used to fabricate various sensing, optical, and RF components and systems. This chapter summarizes the basic material properties and fundamental fabrication processes of SU-8. Examples of various structures, actuators, sensors, and fluidic/optical/RF components are presented to demonstrate the wide possibility of devices that can be implemented in SU-8.