Design of porous partition elastomer substrates for the island-bridge structures in stretchable inorganic electronics

Stretchable inorganic electronics are of growing interest over the past decades due to their various attractive potential applications. The island-bridge structure is the most widely used structural design, where rigid inorganic devices (islands) and interconnects (bridges) are attached onto an elastomer substrate, and large deformations in the structure are accommodated by the large stretchability of the interconnects and the elastomer underneath them. Due to the large modulus mismatch of more than five orders of magnitude between the rigid island and elastomer substrate, there is a severe stress and strain concentration at the interface between the island and the substrate during large deformations, which may cause the interface fracture and delamination. In this work, the analytical solution of the interfacial shear and peel stress between the island and the substrate is derived to reveal the mechanism of interface fracture and agrees well with finite element analysis (FEA) results. A simple porous partition substrate design strategy is proposed to alleviate this stress and strain concentration at the boundary of the interface, where the porous region can undergo larger deformation due to the reduced stiffness of the material. FEA obtains the key parameters affecting the pore layout. The digital image correlation (DIC) experiment verifies the design strategy. The results show that, compared to the solid substrate, the porous partition substrate strategy can significantly reduce the maximum normal strain of the substrate around the island, thus effectively reducing the risk of structural interface failure.