Poisson Effect Assisted Replication Lithography and its Applications for Rapid Fabrication of 3D Microstructures

With the surge in demand for integrated circuits that are smaller and more efficient, as well as the demand for micro/nano-scale precision components in various fields such as optics, sensors, and MEMS, the importance of ultra-precision manufacturing technology capable of intricately fabricating microstructures is becoming increasingly prominent. Imprint lithography technology has enabled the replication of micro/nano-scale structures using relatively inexpensive equipment and a simple process, facilitating high-efficiency fabrication. Furthermore, recent advancements in the development of large-area molds and roll-to-roll processes have further enhanced the fabrication efficiency of the imprint-based lithography. However, due to inherent limitations in the process principle, which involves mechanically contacting the mold to the replication resin and then curing and demolding it, only relatively simple 2D or 2.5D structures can be replicated. Thus, replicating 3D microstructures with closed-loops or significant overhangs remains a challenge. On the other hand, by utilizing the direct laser writing technology based on two-photon polymerization, it's possible to fabricate almost any complex micro/nano-scale structure by curing photo-curable resin with a femtosecond laser in a freeform manner, similar to 3D printing. While this method has gained widespread attention among researchers due to its ability to easily create intricate microstructures, its slow fabrication speed limits its application primarily to laboratory-level research samples. In this study, we introduce Poisson effect-assisted replication lithography technique leveraging the Poisson effect and examples of its application. By utilizing the three-dimensional deformation of a soft mold caused by the Poisson effect, replication of 3D microstructures with closed-loops can be achieved. A master mold created through 2PP-based laser lithography is used to replicate an elastomer soft mold. The prepared soft mold undergoes a specific normal compressive strain, inducing the assembly of the target 3D microstructure's cavity. After curing the replication resin inside the cavity, the normal compressive strain is removed, allowing the cured 3D microstructure to be intactly demolded from the soft mold through shape recovery of the elastomeric material. Considerations and limitations for successful replication including mold design principle, soft mold material, pattern tiling, etc. are discussed. Applications of the working principle to replication of various 3D microstructures, photolithographically prepared master mold for large-area replication, roll-to-roll system for continuous fabrication are also investigated. Since the replication process is almost the same as conventional soft lithography except the intentional deformation of the soft mold, PEARL can also be applied to a continuous microfabrication system such as roll-to-roll, with an additional pressurizing module. Further research on the PEARL technology promises effective fabrication of intricate microstructures and devices including microrobots, metamaterials, 3D scaffolds, and various functional surfaces, paving the way for their commercialization.