Photo-hardenable and patternable PDMS/SU-8 hybrid functional material: A smart substrate for flexible systems

Abstract

The fabrication of flexible electronics and systems, using rigid and brittle materials directly produced on stretchable substrate, leads to some issues and incompatibilities. These include rigidity for processing and modular flexibility for applications, macroscopic flexibility, and local rigidity to shield components from strain, compatibility with technological steps, and at the same time allowing patterning and machining. The development of smart substrate materials which meet such needs is therefore a promising route for flexible systems. Here, we demonstrate that by mixing polydimethylsiloxane (PDMS) and SU-8 photoresist, we obtain both a photo-hardenable and patternable stretchable hybrid material. A set of PDMS/SU-8 and baking process combinations have been tested to determine an effective photo-sensitive mixture. A standard photolithographic approach has been used on tensile test samples demonstrating a local hardening of millimeter-sized ultraviolet exposed features and a local strain reduction reaching 35%. In addition, surface topography analysis and wet-etching techniques have been used to demonstrate a light-induced molding process and a selective etching of micrometer-sized ultraviolet exposed patterns. The combined functional properties of the following material, its simplicity of implementation, and the well-known assets of PDMS and SU-8 make the PDMS/SU-8 material very interesting and promising for various applications, especially stretchable systems. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1281–1291