Residual Compressive Stress Enabled 2D-to-3D Junction Transformation in Amorphous Carbon Films for Stretchable Strain Sensors

Usually, two-dimensional (2D) flexible strain sensors based on cracks have very high sensitivities but small measuring ranges, while the three-dimensional (3D) ones behave in the opposite way. Here, by utilizing the large residual compressive stress of an amorphous carbon (a-C) film and the flexibility of polydimethylsiloxane (PDMS), we developed a facile and economic strategy to fabricate a high-sensitive a-C/PDMS stretchable strain sensor. Results showed that for the first time, the a-C film ranging from 25 nm to 1 μm changed the shape and orientation of conductive scales, as well as made a one-step 2D-to-3D electrical junction transformation in integrated sensors. In particular, the sensor with a 1 μm thick a-C film exhibited the best comprehensive performance, displaying a maximum gauge factor of 746.7 and strain range up to 0.5. However, the linearity decreased slightly as the strain range went beyond 0.43. Additionally, the sensor showed a satisfactory repeatability for 5000 cycles, together with excellent time and temperature drift performances at zero position of 75 ppm full scale (FS) and 25 ppm FS·°C^-1 in the range of -20 to 155 °C, respectively. The sensor has large potentials for wearable devices used in the monitoring of various human motions and physiological signals.