Reducing wrinkles and cracks of metal films on PDMS substrate by hexane extraction and oxygen plasma etching

• We focused on the reduction of the wrinkles and cracks of metal films on PDMS.
• The PDMS was treated by hexane extraction after etching in an oxygen plasma.
• The surface roughness, surface free energy and wettability of PDMS were studied.
• The dry electrode provided ECGs that was comparable to the standard gel electrode.

Metal films deposited on polydimethylsiloxane (PDMS) substrates frequently exhibit wrinkles and cracks, which is a problem in fabricating flexible electronics. Here, we present the result of a study investigating the influence of the PDMS surface roughness, surface free energy and wettability on the quality of metal films and explored methods to reduce those wrinkles and cracks. Initially, the low molecular weight chains (LMW) in PDMS substrate were extracted by hexane solution. After extraction, the PDMS was etched in an oxygen plasma and the metal was deposited. Both surface roughness measurements and microscopic photographs demonstrated that Cu film deposited on the pretreated PDMS substrate exhibited less wrinkles and cracks than on native PDMS substrate. Finally, to demonstrate the effectiveness of the wrinkle improvement, a flexible dry electrode with micro domes was fabricated and used for Electro Cardio Gram (ECG) recording. The results showed that the fabricated dry electrode with reduced wrinkles produced good ECG signals with distinct P, QRS, and T waves.

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