Highly Stretchable Strain Sensor with a High and Broad Sensitivity Composed of Carbon Nanotube and Ecoflex Composite

Wearable strain sensors with high and broad sensitivity, high stretchability and excellent mechanical endurance will be widely useful in smart wearable electronics. In this work, we developed a stretchable strain sensor fabricated with a simple stencil printing technique. The stretchable strain sensor was fabricated using a multi-walled carbon nanotubes (MWCNTs)-Ecoflex composite paste on an Ecoflex substrate. In particular, using IPA solvent, CNT particles were uniformly dispersed in the Ecoflex binder. The effect of the amount of Ecoflex resin on the stretchability and sensitivity of the sensor were also investigated. It was found that as the amount of Ecoflex resin increased, the stretchability of the sensor increased. The fabricated stretchable strain sensor showed a maximum stretchability of 1,000% with a wide sensitivity range from 3 to 12,287. The hysteresis tests indicated that the hysteresis of the fabricated stretchable strain sensor was very small, the electrical resistances of the sensors quickly returned to original value after tests. The strain sensor showed excellent mechanical durability during cyclic repeated tensile tests of 400,000 cycles. The results of the cross-cut adhesion tests indicated that the adhesion strength between the sensor composite layer and Ecoflex substrate was excellent. We also demonstrated the potential application of the stretchable sensor in wearable electronics by bending tests on a human finger and wrist.