Highly stretchable multilayer electronic circuits using biphasic gallium-indium

Abstract

Stretchable electronic circuits are critical for soft robots, wearable technologies and biomedical applications. Development of sophisticated stretchable circuits requires new materials with stable conductivity over large strains, and low-resistance interfaces between soft and conventional (rigid) electronic components. To address this need, we introduce biphasic Ga–In, a printable conductor with high conductivity (2.06 × 106 S m−1), extreme stretchability (>1,000%), negligible resistance change when strained, cyclic stability (consistent performance over 1,500 cycles) and a reliable interface with rigid electronics. We employ a scalable transfer-printing process to create various stretchable circuit board assemblies that maintain their performance when stretched, including a multilayer light-emitting diode display, an amplifier circuit and a signal conditioning board for wearable sensing applications. The compatibility of biphasic Ga–In with scalable manufacturing methods, robust interfaces with off-the-shelf electronic components and electrical/mechanical cyclic stability enable direct conversion of established circuit board assemblies to soft and stretchable forms.

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Fig. 1: bGaIn for SCBAs.
Fig. 2: Material characteristics of bGaIn.
Fig. 3: Electromechanical characteristics of bGaIn.
Fig. 4: Integration with rigid electronic components.
Fig. 5: Printable patterns and stretchable VIAs.
Fig. 6: Applications of SCBAs.

Data availability

Source data are provided with this paper. Other data supporting the findings of this study are available upon request from the corresponding author.

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Acknowledgements

We acknowledge R. A. Bilodeau, M. C. Yuen and S. Y. Kim for their valuable comments on the manuscript; S. Wang for drawing the illustrations in Fig. 1e and Fig. 2a; L. Wang for access to the Zygo Nexview 3D Optical Profiler at the Yale West Campus Cleanroom; and M. Li for access to the scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction instruments at the Yale West Campus Materials Characterization Core and his advice on data analysis. S.L. was supported by the National Science Foundation (CAREER Award 1454284). D.S.S. was supported by a NASA (US National Aeronautics and Space Administration) Space Technology Research Fellowship (80NSSC17K0164).

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Authors

Contributions

S.L., D.S.S. and R.K.-B. conceived the project and planned the experiments. S.L. conducted all the experiments. D.S.S. programmed the PIC microcontroller for the signal conditioning circuit board demonstration. All authors participated in drafting and editing the manuscript. All authors contributed to, and agree with, the content of the final version of the manuscript.

Corresponding author

Correspondence to Rebecca Kramer-Bottiglio.

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The authors declare no competing interests.

Additional information

Peer review information Nature Materials thanks Jaehong Lee, Tsuyoshi Sekitani and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Notes 1–4, Tables 1–2, Figs. 1–18 and refs. 1–12.

Supplementary Video 1

Supplementary Video 1 shows the solid side of the bGaIn film breaking into flakes when stretched, while the biphasic portion fills in the cracks, maintaining connection between the solid particles, which allows the bGaIn film to remain thin and continuous on the substrate during stretching.

Supplementary Video 2

Supplementary Video 2 shows a ‘YALE’ LED array with bGaIn electrical interconnects; 33 LEDs are pick-and-place assembled on a VHB tape, which is stretched to 250% strain, showing no perceptible diminishing of the LED brightness.

Supplementary Video 3

Supplementary Video 3 shows a summing amplifier circuit that is stretched up to 400% strain, showing negligible changes in the output signal.

Supplementary Video 4

Supplementary Video 4 shows a stretchable multilayer LED display with bGaIn electrical interconnects—25 LEDs and 25 VIAs on a silicone elastomer—that can be stretched along all in-plane directions.

Supplementary Video 5

Supplementary Video 5 shows a stretchable multilayer signal conditioning circuit board measuring a capacitive strain sensor on the surface of a user’s shirt sleeve.

Source data

Source Data Fig. 2

Source data for Fig. 2e.

Source Data Fig. 3

Source data for Fig. 3a–d.

Source Data Fig. 4

Source data for Fig. 4a–c,f,g.

Source Data Fig. 5

Source data for Fig. 5b,c,f,g.

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Liu, S., Shah, D.S. & Kramer-Bottiglio, R. Highly stretchable multilayer electronic circuits using biphasic gallium-indium. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-00921-8

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