Gradient Modulus Strategy for Alleviating Stretchable Electronic Strain Concentration

The island-bridge structural design is a common strategy for imparting stretchability to flexible electronic devices. In this structure, the low modulus regions bear most of the deformation, while the rigid islands, which house the electronic components, undergo minimal deformation. However, due to the modulus differences that can be several times or even several orders of magnitude larger, severe strain concentration occur at the edges of the rigid islands in high modulus regions. This strain concentration caused by rigid constraints not only reduces the stretchability of the soft substrate but also degrades the mechanical performance of the interconnected structures, thereby significantly affecting the overall stability of the device. Starting from finite element simulations, this paper introduces modulus gradient regions and optimizes geometric parameters, significantly alleviating the strain concentration at the edges of the rigid islands. Serpentine-shaped circuits are then transferred to a substrate with strain isolation, which demonstrates better stretchability stability under 20% elongation compared to traditional strain isolation strategies. In addition, the stretchable light emitting diode (LED) system with gradient modulus has better stretchability compared to the system with conventional strategy. This suggests that this strategy has great potential in maintaining the stability of stretchable systems.