A Strategy Reducing Interfacial Stress by Placing Pores Around Serpentine Electrodes for Highly Durable Stretchable Electronics

The development of stretchable electronic devices has brought great attention to next-generation wearable devices such as electronic skins (E-skins) and electrical tattoos.^[1] In the field of wearable technology, there is a growing demand for soft electronics in health monitoring and various types of applications such as the Internet of Things and soft actuators, VR/AR.^[2-3] The stretchable functional electronics has been adopted for increasing durability under stretching by using intrinsically stretchable materials and structural dynamics designs. Especially, many research about gaining stretchability through structural designs such as serpentine interconnects and kirigami structure have been reported.^[4-6] Among the various structural designs of stretchable electronics, the "island-leg" design represents a widely used strategy, and bridge-modified interconnects in the middle area (i.e., trenches) between non-stretchable elements such as islands provide stretchability and flexibility. However, these devices are susceptible to mechanical failure such as fatigue breakdown of ductile materials and brittle material destruction, and peeling of adhesive interfaces. A delamination occurs due to mechanical mismatch (i.e., modulus, stretchability) between the serpentine and the elastomer substrate. Therefore, device stretchability is reduced because the material can reach the limit locally in smaller macro variants. Here, pores near the serpentine electrode can be proposed to effectively improve stretchability and durability of stretchable electronic system. The system configuration includes a serpentine and a pore with a convex oval design around it. The serpentine electrode made of the designed polyimide reduces the von mises stress between the interface and the electrode. The T-shaped pores in the substrate absorb the stress concentration near the serpentine electrode, which is prone to microcracking. The pores presented in this study have an effect of reducing stress by about four times compared to electrodes without pores. Experimental measurements and finite element analysis (FEA) on island bridge designs using interconnects between serpentine electrode and substrates confirm the validity of substrate pore strategies. Furthermore, the various applications such as heater, display, and e-skin are demonstrated.<br/><br/>1. N. Qaiser, A. N. Damdam, S. M. Khan, S. Bunaiyan, M. M. Hussain, Design criteria for horseshoe and spiral-based interconnects for highly stretchable electronic devices. Adv. Funct. Mater. 31, 2007445 (2021).<br/>2. S. Y. Hong, M. S. Kim, H. Park, S. W. Jin, Y. R. Jeong, J. W. Kim, Y. H. Lee, L. Sun, G. Zi, J. S. Ha, High-sensitivity, skin-attachable, and stretchable array of thermo-responsive suspended gate field-effect transistors with thermochromic display. Adv. Funct. Mater. 29, 1807679 (2018).<br/>3. J. O. Kim, J. S. Hur, D. Kim, B. Lee, J. M. Jung, H. A. Kim, U. J. Chung, S. H. Nam, Y. Hong, K. S. Park, J. K. Jeong, Network structure modification-enabled hybrid polymer dielectric film with zirconia for the stretchable transistor applications. Adv. Funct. Mater. 30,<br/>1906647 (2020).<br/>4. C. A. Silva, J. lv, L. Yin, I. Jeerapan, G. Innocenzi, F. Soto, Y. G. Ha, J. Wang, Liquid metal based island-bridge architectures for all printed stretchable electrochemical devices. Adv. Funct. Mater. 30, 2002041 (2020).<br/>5. R. Xu, Y. Zhang, K. Komvopoulos, Mechanical designs employing buckling physics for reversible and omnidirectional stretchability in microsupercapacitor arrays. Mater. Res. Lett. 7, 110–116 (2019).<br/>6. A. J. Bandodkar, J.-M. You, N.-H. Kim, Y. Gu, R. Kumar, A. M. V. Mohan, J. Kurniawan, S. Imani, T. Nakagawa, B. Parish, M. Parthasarathy, P. P. Mercier, S. Xu, J. Wang, Soft, stretchable, high power density electronic skin-based biofuel cells for scavenging energy from human sweat. Energ. Environ. Sci. 10, 1581–1589 (2017).