A sacrificial-layer-free fabrication technology for MEMS transducer on flexible substrate

The authors report the fabrication of polymer MEMS transducers, without using any sacrificial layers, on flexible substrates. The elimination of sacrificial layers and the process overhead associated with them is achieved through maskless grayscale UV lithography of SU-8 photoresist, and results in a simplification of the overall fabrication process. Six batches, with a total of 60 cantilevers and 60 double- clamped beams, and three batches, with a total of 1500 circular membranes, have been fabricated on commercially available, 45 um Kapton ^® polyimide sheets coated with a 35um copper layer. The validation of the fabrication process has been done through functional characterization of the bi-directional electro-mechanical interface and robustness to mechanical bending. The test and measurement results of the fabricated microstructures validate a good design predictability (geometry error: <5%, dynamical performance error: <4%), high reproducibility (less than 4% normalized standard deviation between individual microstructures) and an acceptable robustness against temporary bending of the substrate (less than 3% behavior change before and after bending). The approach opens the path for simple fabrication of MEMS transducers and their hybrid integration with electronics in all-flexible microsystems.