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 mu m 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 mu m 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.degrees C1 in the range of -20 to 155 degrees C, respectively. The sensor has large potentials for wearable devices used in the monitoring of various human motions and physiological signals.