2-D Strain Sensors Implemented on Asymmetrically Bi-Axially Pre-Strained PDMS for Selectively Switching Stretchable Light-Emitting Device Arrays

Crack phenomenon is one of the most well-known mechanisms to turn a conductive thin film into a strain sensor. However, there is a limitation that most of the crack-based strain sensors using elastomeric materials with high Poisson's ratio only allow uni-axial deformation because unintended cracks are easily formed into arbitrary directions even under low strain. Therefore, if directional crack formation can be engineered and thus a strain sensor only responds to a specific axial-direction strain, it can be used as an excellent trigger sensing deformation direction and will act an interesting role in various stretchable electronics fields. In this work, we introduce an anisotropic crack formation mechanism and implement micro-crack based strain sensors with silver thin films that are inkjet-printed on an asymmetrically pre-strained roughened poly(dimethylsiloxane) (PDMS) substrate. Anisotropic crack formation combined with the asymmetric buckling structure remarkably differentiates sensors' sensitivity to axial directions of the applied strain. We demonstrate a resolution-sustainable and 2-dimensionally stretchable LED array with feedback functionality between sensing strain directions and turning on corresponding axial LEDs by using two orthogonally arranged strain sensors. This work will provide an insight emphasizing a new role of strain sensors in stretchable electronics applications.