Fabrication of Large-Area Three-Dimensional Microstructures on Flexible Substrates by Microtransfer Printing Methods

This paper presents two robust microtransfer printing methods, namely, multiple transfer printing and peeling microprinting methods, to fabricate three-dimensional (3-D) and high-aspect-ratio microelectromechanical systems (MEMS) structures over large areas on flexible polydimethylsiloxane (PDMS) substrates. These techniques enable conformal wrapping of 3-D microstructures, initially fabricated in two-dimensional (2-D) layouts with standard fabrication technology onto a wide range of surfaces with complex and curvilinear shapes. The processes exploit the differential adhesive tendencies of the microstructures formed between a donor and a transfer substrate to accomplish an efficient release and transfer process. Experimental and theoretical studies show that the MEMS structures with a wide variety of pattern densities can be conformally transferred to bendable device substrates while keeping the structural integrity and density intact. Quantitative stress analysis on the micromechanics of such a curvilinear system suggests that the stress induced by wrapping the complete structure onto a cylinder is mostly in the flexible PDMS substrate, while the MEMS structures experience little stress.