Bucklable 2D Microstructures as Building Blocks for Stretchable Electronics
Wearable electronics is an important trend for personal electronics and long-term remote health monitoring. The key challenge is that the system must accommodate not only bending but also extensive stretching to accommodate the curved, soft, and elastic surfaces of biological objects, which is hard to achieve with traditional microelectronics technology with its strength in 2D patterning. With the combined approach in advanced mechanical simulation and experimental design, we developed a lithographically defined 2D hierarchical serpentine structure that can buckle into 3D layouts and adapt to high levels of tensile strain. Traditional planar electronics can then be reconstructed with this structure as interconnects and transform to stretchable electronics, both on the device level and system level.
Stretchable Lithium-ion Batteries
We have demonstrated the materials and integration schemes for a type of lithium ion battery that utilizes island-bridge layouts and deformable electrical interconnects in hierarchical serpentine geometries. The resulting devices offered biaxial stretchability up to strains of 300%, with a surface filling ratio of 50% and energy densities of ~1.1 mAh/cm2, and little loss in capacity for up to 20 cycles of recharging. The design also allowed integration of stretchable, magnetic resonant coils to enable wireless recharging through external supplies without the need for physical connections. In addition, an ordered unraveling mechanism of the hierarchical interconnects was unveiled both theoretically and experimentally, which provided theoretical references for future highly stretchable electronic devices.
Mechanically invisible multifunctional epidermal health monitoring patches
Conventional non-invasive health monitoring devices typically involve electrode pads that affix to the skin with adhesive tapes and/or use conductive gels to minimize contact impedances; this approach has strong clinical utility but limited value in everyday life due to discomfort and loss of adhesion.
A promising alternative is a wearable health monitoring system. Our recent progress includes a flexible device patch that integrates commercial off-the-shelf (COTS) surface mounted chips with silicone elastomer substrates, which can adhere directly to the skin via van der Waals forces alone. The result was a natural interface that is capable of accommodating the motions of the skin without any mechanical constraints, thereby establishing not only a robust, non-irritating skin/electrode contact but also the basis for intimate integration of diverse classes of electronic and sensor technologies directly with the human body. The demonstrated system achieved reversible stretchability up to 100% and was capable of wireless powering, multi-channel biological signal sensing (e.g. electrophysiological potential, temperature, and motion), and RF communication to the backend receiver.
S. Xu, Y.H. Zhang, L. Jia, K.E. Mathewson, K.I. Jang, J.H. Kim, H.R. Fu, X. Huang, P. Chava, R.H. Wang, S. Bhole, L.Z. Wang, Y.J. Na, Y. Guan, M. Flavin, Z.S. Han, Y.G. Huang, J. A. Rogers, Soft Microfluidic Assemblies of Sensors, Circuits, and Radios for the Skin, Science, 344, 70 (2014) [pdf]
K.-I. Jang, S.Y. Han, S. Xu, K.E. Mathewson, Y.H. Zhang, J.-W. Jeong, G.-T. Kim, R.C. Webb, J.W. Lee, T.J. Dawidczyk, R.H. Kim, Y.M. Song, W.-H. Yeo, S. Kim, H.Y. Cheng, S.I. Rhee, J.H. Chung, B.G. Kim, H.U. Chung, D.J. Lee, Y.Y. Yang, M.G. Cho, J.G. Gaspar, R. Carbonari, M. Fabiani, G. Gratton, Y.G. Huang and J.A. Rogers, Rugged and Breathable Forms of Stretchable Electronics with Adherent Composite Substrates for Transcutaneous Monitoring, Nature Communications, 5, 4779 (2014) [pdf]
S. Xu, Y.H. Zhang, J. Cho, J.H. Lee, X. Huang, L. Jia, J. Fan, Y.W. Su, J. Su, H.G. Zhang, H.Y. Cheng, B.W. Lu, C.J. Yu, C. Chuang, T.I. Kim, T. Song, K. Shigeta, S. Kang, C. Dagdeviren, I. Petrov, P.V. Braun, Y.G. Huang, U. Paik and J.A. Rogers, Stretchable Batteries with Self-Similar Serpentine Interconnects and Integrated Wireless Recharging Systems, Nature Communications, 4, 1543 (2013) [pdf]