Transfer printing via a PAA sacrificial layer for wrinkle-free PDMS metallization

Polydimethylsiloxane (PDMS) metallization has been extensively used in varieties of micro- and nanosystem technologies. However, the deposited metal film on the PDMS surface is prone to wrinkling because of a large thermal mismatch stress, which may cause difficulties in some applications. In this work, a simple transfer printing method via a poly(acrylic acid) (PAA) sacrificial layer for PDMS metallization is presented. A PAA film was spin-coated on the silicon substrate, metal patterns were fabricated on the PAA film based on photolithography techniques, and a PDMS sheet was put on the surface of metal patterns and separated with metal patterns from the silicon substrate by dissolving the PAA film in room-temperature water. Au patterns with a variety of shapes and sizes were successfully transferred on the PDMS sheet, and there were no wrinkles in Au patterns. As a demonstration, a PDMS-based tunable diffraction grating with a line width of 2 µm and an initial period of 4 µm was fabricated. The grating displayed excellent diffraction efficiencies, and the period could be tuned by simply stretching the grating.