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SCIENCE CHINA Materials, Volume 62, Issue 7: 982-994(2019) https://doi.org/10.1007/s40843-018-9400-2

Semi-liquid metal and adhesion-selection enabled rolling and transfer (SMART) printing: A general method towards fast fabrication of flexible electronics

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  • ReceivedDec 10, 2018
  • AcceptedJan 29, 2019
  • PublishedFeb 27, 2019

Abstract

Recent breakthrough in eutectic gallium-indium alloy has revealed its great potential in modern electronic engineering. Here, we established a general method towards super-fast fabrication of flexible electronics via semi-liquid metal and adhesion-selection enabled rolling and transfer (SMART) printing on various substrates. Based on the semi-liquid metal and its adhesion-difference on specifically designed target materials, we demonstrated that the rolling and transfer printing method could serve to rapidly manufacture a wide variety of complicated patterns with high resolution and large size. The process is much faster than most of the currently existing electronic fabrication strategies including liquid metal printing ever developed, and the cost either in time or consumption rate is rather low. As illustrated, a series of functional flexible and stretchable electronics such as multiple layer and large area circuits were fabricated to show their superior merit in combination with electrical conductivity and deformability. In addition, it was also demonstrated that the electronics fabricated in this way exhibited good repeatablity. A most noteworthy advantage is that all the fabrication processes could be highly automatic in the sense that user-friendly machines can thus be developed. This method paves a practical way for super-fast soft electronics manufacture and is expected to play an important role in the coming industry and consumer electronics.


Funded by

the National Natural Science Foundation of China Key Project(91748206)

Dean’s Research Funding and the Frontier Project of the Chinese Academy of Sciences.


Acknowledgment

This work is partially supported by the National Natural Science Foundation of China Key Project (91748206) and Dean’s Research Funding and the Frontier Project of the Chinese Academy of Sciences.


Interest statement

The authors declare no conflict of interest in this research.


Contributions statement

Guo R and Liu J conceived this work and wrote the article. Guo R performed all the experiments and interpreted the results. All authors joined the research and discussed the results. Liu J supervised the work.


Author information

Rui Guo received his BE degree in biomedical engineering from Tsinghua University in 2016. Now he is a PhD candidate majored in biomedical engineering in Tsinghua University. His interest focuses on gallium-based liquid metal flexible and wearable electronics.


Jing Liu is a jointly appointed professor of Tsinghua University and Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. He also performs visiting research at both Purdue University and Massachusetts Institute of Technology. His research on liquid metal soft machines, biomaterials, printed electronics, and chip cooling has initiated many game changing technologies.


Supplement

Supplementary information

Supporting data are available in the online version of the paper.


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  • Figure 1

    (a) The periods of various methods in preparing flexible electronics. (b) The schematic diagram of semi-liquid metal rolling and transfer printing method. (c) The photographs about the preparation process of rolling and transfer printing method.

  • Figure 2

    (a) Photographs of Ni-EGaIn with different contents of micro Ni particles. (b) The conductivity of Ni-EGaIn with different contents of micro Ni particles. (c) The schematic diagram about the adhesion mechanism of Ni-EGaIn on PU glue and toners. (d) The contact angle of Ni-EGaIn on toners, PU glue and ecoflex substrates. (e) The adhesion force of Ni-EGaIn on toners, PU glue and ecoflex substrates. (f) The images of Ni-EGaIn on toners, PU glue and ecoflex substrates in the obliquity experiments (scale bar=2 mm). (g) The photograph of Ni-EGaIn printed on the thermal transfer paper by a brush, while not the toners.

  • Figure 3

    The SEM image of the PU glue and its cross-section image (a), the printed toners on PU glue (b), the ecoflex substrate (c), the Ni-EGaIn line rolling printed on PU glue (d), the Ni-EGaIn line transfer printed on ecoflex (e). (f) The cross-section images of the Ni-EGaIn line printed on PU glue and the Ni-EGaIn transferred on Ecoflex. (g) The photograph and SEM image of the small chip resistor attached with the Ni-EGaIn line. (h) The photograph of folded paper and the SEM image of the bending part showing continuous state of Ni-EGaIn lines.

  • Figure 4

    The electrical tests of the Ni-EGaIn lines printed on thermal transfer paper and the stretchable lines transfer printed on ecoflex. (a) The resistance of Ni-EGaIn lines with different widths (length of 5 cm, width of 0.1, 0.3, 0.5, 1, 3, and 5 mm, respectively). (b) The resistance of Ni-EGaIn lines with different widths during the bending process (bending angle from −180° to 180°). (c) The relationship between bending cycles and the resistances of Ni-EGaIn lines with different widths. (d) The IV curves of the Ni-EGaIn lines with LED under different bending conditions (bending angle from −180° to 180°). (e) The resistance of Ni-EGaIn lines with different widths under various strains. (f) The relationship between stretching cycles and the resistances of Ni-EGaIn lines with different widths. (g) The resistance curve of the Ni-EGaIn lines stretched to different lengths (30%, 60% and 90%). (h) The IV curves of the Ni-EGaIn lines with LED under various strains (strain 0% to 100%). (i) The photographs of the LED lights packaged in ecoflex stretched vertically and distorted.

  • Figure 5

    The applications of flexible electronics based on rolling printing method. (a) The LED array flexible paper circuit. (b) The detail and working pictures of the LED array flexible paper circuit. (c) The schematic diagram about the connection of Ni-EGaIn on two paper layers. (d) The photographs of the double layer paper circuit. (e) The double layer paper LEDs array served as display.

  • Figure 6

    A series of large area conductive patterns on paper. (a) The large area solenoid coil patterns. (b) The conductive Taiji patterns. (c) The Ni-EGaIn rolling printed on paper with colored toners. (d) The large area Chinese calligraphy conductive pattern.

  • Figure 7

    (a) The photographs of the stretchable LED array circuit. (b) The resistance of the Ni-EGaIn strain sensor under various strains. (c) The resistance of this strain sensor under various bending angles of the wrist joints. (d) Responsive signal of Ni-EGaIn strain sensor during cyclic bending-unbending motion of the wrist.

  • Figure 8

    (a) The photographs of the recycle process of Ni-EGaIn printed on PU glue. (b) The photograph of the gathered Ni-EGaIn droplet. (c) The photographs of the burnt process of Ni-EGaIn.

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