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Applications of Polymer, Composite, and Coating Materials
Soft Elastomers with Programmable Stiffness as Strain-Isolating Substrates for Stretchable Electronics Min Cai, Shuang Nie, Yipu Du, Chengjun wang, and Jizhou Song ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 19 Mar 2019 Downloaded from http://pubs.acs.org on March 19, 2019
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ACS Applied Materials & Interfaces
Soft Elastomers with Programmable Stiffness as Strain-Isolating Substrates for Stretchable Electronics Min Cai ‡, Shuang Nie ‡, Yipu Du ‡, Chengjun Wang, Jizhou Song* Department of Engineering Mechanics, Soft Matter Research Center, and Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, 310027 Hangzhou, China ‡These
*To
authors contributed equally to this work.
whom correspondence should be addressed.
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ABSTRACT
Stretchable electronics are of rapidly increasing interests due to their unique ability to function under complex deformations. Strain isolation of stiff functional components from the substrate represents a key challenge in the development of stretchable electronics since their mechanical mismatch may yield undesirable strains to degrade the device performance. The results presented here report an approach to develop a soft strain-isolating polymer substrate with programmable stiffness by spatio-selective ultraviolet (UV) exposure for stretchable electronics. The approach compatible with the well-established lithographic process reduces the fabrication complexity significantly and offers a simple yet robust strain isolation mechanism to ensure the system stretchability of over 100%. Combined experimental and numerical studies reveal the fundamental aspects of the design, fabrication, and operation of the strain-isolating substrate. Demonstration of this concept in a stretchable inorganic metal-based resistive temperature sensor and a stretchable organic photodiode array with unusually high performance shows the simplicity of the approach and the robustness in strain isolation in both component and device levels. This type of strain isolation design not only creates promising routes for potential scalable manufacturing of stretchable electronics but also engineering opportunities for stretchable electronics involving the integration of various functional components, which require the quantitative control of the strain levels to achieve optimal performance.
KEYWORDS stretchable electronics, soft elastomer, strain isolation, programmable stiffness, spatio-selective ultraviolet exposure
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ACS Applied Materials & Interfaces
1. INTRODUCTION
Stretchable electronics are of rapidly increasing interests due to their ability to function under complex deformations and yield numerous important applications such as wearable electronics1-6, curvilinear electronics7-11 and bio-integrated real-time health monitoring devices12-14. To realize stretchable electronics, strain isolation/protection of stiff functional components from external deformations represents the most effective design strategy15-21. Delicate designs of the heterogeneous substrate with spatio-controlled stiffness including embedding stiff platforms within the soft substrate22-24, introducing stiff patterns on the soft substrate25,
26,
introducing
ultrasoft material on the surface of soft substrate27, and introducing liquid-filled cavities in the soft substrate28 have been explored to enable the strain isolation/protection of functional components. However, all these designs either involve non-compatible fabrication processes with the wellestablished lithographic process or require complex optimization schemes to achieve a large stretchability. The above unresolved challenges greatly hinder the commercialization of stretchable electronics. The recent work by introducing the spatially confined oxidation of thiolacrylate-based polymer to increase stiffness provided a highly effective way to bypass these challenges for potential manufacturing in a commercial setting29 but with a limited stretchability (
