Wrinkled and cracked amorphous carbon film for high-performance flexible strain sensors

Due to the trade-off relationship between sensitivity and strain range (ε), it has been a lasting challenge to develop flexible strain sensors with both high sensitivity and excellent stretchability. Here, based on the mismatch of mechanical properties between hard amorphous carbon (a-C) films and soft polydimethylsiloxane (PDMS) substrates, we successfully fabricated a high-performance a-C/PDMS sensor by introducing wrinkled and cracked structure, with the facile direct-current magnetron sputtering technology. The sensor showed a maximum gauge factor of over 2300, high stretchability up to 50 % together with good linearity, rapid response (loading delay time τ1 = 125.4 ms and unloading delay time τ2 = 51.8 ms, 0–10 % strain) and excellent repeatability beyond 11,000 cycles. The combined in situ characterization of surface morphology and electrical potential revealed that increasing the applied strain would stimulate the formation of wrinkles and cracks in a-C films, which subsequently favor the cyclic break/contact changes in conductive areas in the surface and film growth direction. This continuous and rapid response of electric resistance would benefit the ultrasensitive and highly stretchable a-C/PDMS sensor. Current insights into the multi-scale and high-precision in situ characterization of a-C films will provide a new strategy to fabricate the flexible strain sensor by using the wrinkled and cracked structure engineering.