3D Micro Architectures Using Intrinsic Stress in SU-8 Photoresist

It is commonly acknowledged that for SU-8 photoresist, a thermal stress is generated during a post bake induced cross-linking process. For decades, numerous of literature considered it as a side effect and tried to diminish or even overcome this problem. Here, conversely, we use this heat induced intrinsic stress to make 3D micro architectures. SU-8 photoresist is patterned on a pre-deposited sacrificial layer on Si wafers. Then most of the sacrificial layer is etched away, with only a tiny part holding down the structure. The structure is subsequently immersed in water with heat energy. Then, the thermal-induced stress causes the SU-8 to curve from 2D patterns to 3D architectures, such as tubes, rings, books, springs, and out of plane structures with different patterns on them. By intentionally controlling the exposure energy at different positions on the SU-8 surface, more complicated 3D structures can be made. Taking advantage of photolithography techniques, thousands of 3D microstructures can be integrated on a wafer with a self-assembly process that takes less than 30 seconds. Moreover, this assembly process allows the integration of 2D materials into the 3D structures, which enables the realization of 2D material-based 3D microstructures. This fabrication technique may promote further development of complex micro robotics, 3D sensors, and 3D passive elements.