Interfacial and surface analysis of parylene C-modified PDMS substrates for soft bioelectronics

Parylene C-modified polydimethylsiloxane (PDMS) substrates such as parylene C-deposited PDMS and parylene C-filled PDMS have been developed for the microfabrication of soft electronic devices with mechanically and electrically stable metal patterns. In previous studies, we performed oxygen plasma etching to etch parylene C away from the PDMS surface of parylene C-deposited PDMS to maximize the benefits of soft and stretchable properties of PDMS. However, the resultant parylene C-filled PDMS exhibited microcracks during thin film metal patterning as the etching time increased. In this study, to analyze this cracking phenomenon precisely, the penetration depth of parylene C into PDMS was quantitatively investigated according to the thickness of deposited parylene C, and the amount of parylene C on the surface as well as in the interfacial region formed by parylene C and PDMS was analyzed depending on the etching time. It was observed that residual parylene C remained in the PDMS pores even after parylene C was etched away from the PDMS surface. In addition, we confirmed that only the amount of parylene C on the PDMS surface was reduced by excessive etching, and parylene C inside the PDMS pores was not significantly affected. From these results, we could confirm that the optimal condition to fabricate the parylene C-filled PDMS substrate was to etch parylene C just from the surface of PDMS without over-etching. The parylene C-filled PDMS substrate would enable the wafer-scale high-yield fabrication of soft bioelectronics for diverse applications.