Large-sized out-of-plane stretchable electrodes based on poly-dimethylsiloxane substrate

This paper describes a reliable fabrication method of stretchable electrodes based on polydimethylsiloxane (PDMS) substrate. The electrode traces and pads were formed in out-of-plane structures to improve the flexibility and stretchability of the electrode array. The suspended traces and pads were attached to the PDMS substrate via parylene posts that were located nearby the traces and under the pads. As only conventional micro-electro-mechanical systems techniques were used, the out-of-plane electrode arrays were clearly fabricated at wafer level with high yield and reliability. Also, bi-layer out-of-plane electrodes were formed through additional fabrication steps in addition to mono-layer out-of-plane electrodes. The mechanical characteristics such as the stretchability, flexibility, and foldability of the fabricated electrodes were evaluated, resulting in stable electrical connection of the metal traces with up to 32.4% strain and up to 360° twist angle over 25 mm. The durability in stretched condition was validated by cyclic stretch test with 10% and 20% strain, resulting in electrical disconnection at 8600 cycles when subjected to 20% strain. From these results, it is concluded that the proposed fabrication method produced highly reliable, out-of-plane and stretchable electrodes, which would be used in various flexible and stretchable electronics applications.