Development, fabrication and characterization of textured substrates for stretchable electronics

Abstract

Stretchable electronics technologies have recently garnered increasing interest by enabling the fabrication of electronic devices compatible with applications in fields such as wearable technology and healthcare. In particular, this area has underscored the significance of surface roughness which, when properly engineered, can lead to highly promising results. This thesis aimed to develop, fabricate, and characterize textured substrates for stretchable electronics. Using tensile samples in PDMS cured in 3D-printed molds and covered with gold, the focus was on generating various 2D out-of-plane roughness profiles to isolate and quantify the impact of the three roughness parameters defined by the H-H correlation method on specimen electrical behavior. The study began with a commercial LED-LCD printer and progressed to the characterization and use of a custom printer to produce molds with more detailed and accurate surface features. The results highlighted key trends, starting with the stabilizing effect of surface roughness which reduces resistance variation under tensile strain compared to flat samples. The RMS roughness and correlation length of the surface profile showed opposite effects combined through the ratio correlation length/RMS roughness : lower ratios correlate with lower resistance variation under tensile deformations. A non-linear influence of the RMS roughness was however suggested by the results. In addition, high surface fractality led to a real plateau of stable electrical properties during tensile tests while staircase-like profiles promoted overall stabilization and increased critical strain. During custom printer’s characterization, interesting results were also obtained with the smaller the desired feature in the XY plane, the higher the required UV light intensity for a complete polymerization but also the more challenging it becomes to achieve a significant height without compromising lateral resolution. Nanometric surface roughness was attainable by increasing UV intensity, exposure time, and introducing pixel movement during printing.