Research ArticleMATERIALS SCIENCE

High-resolution, reconfigurable printing of liquid metals with three-dimensional structures

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Science Advances  21 Jun 2019:
Vol. 5, no. 6, eaaw2844
DOI: 10.1126/sciadv.aaw2844
  • Fig. 1 High-resolution printing of liquid metals.

    (A) Schematic illustration of a printing system. (B) SEM image of 2D and 3D high-resolution EGaIn patterns. Scale bar, 100 μm. Inset: Magnified SEM image of the 3D structures. Scale bar, 100 μm. (C) AFM image and cross-sectional profile of printed EGaIn line. Scale bar, 2 μm. (D) SEM image of 1.9-μm-wide EGaIn patterns. Scale bar, 10 μm. (E) SEM image of 3D patterns of EGaIn on a PET film and epoxy (SU-8). Scale bar, 10 μm. (F) Photograph of printed high-resolution EGaIn patterns in (B). Scale bar, 1 cm. (G) Photograph of interconnect patterns of EGaIn. Inset: Top-view photograph. Scale bars, 5 mm. (H) Optical micrographs of printed EGaIn lines according to printing velocities. Scale bar, 40 μm. (I) The plot of line widths versus printing velocities. (J) The plot of line widths versus inner diameters of nozzles. Error bars in (I) and (J) indicate the SD. (Photo credit: Young-Geun Park, Yonsei University).

  • Fig. 2 Reconfiguration of liquid metals into 3D structures.

    (A) Schematic illustrations of each step of reconfiguration. (B) Schematic illustration of two adhesion forces during reconfiguration. (C) Photograph of lift-off (left) and cutoff (right) of EGaIn from the substrate. Scale bar, 100 μm. (D) The plot of the state of line versus the nozzle lift-off velocity. (E) Optical micrographs of reconfiguration. The printed horizontal line (left) is lifted off and reconfigured (right). Scale bars, 200 μm. (F) SEM images of reconfigured square coils. The end of the inner line in the square coil (left) is lifted and reconfigured (right). Scale bars, 200 μm. (G) SEM images of 3D bridges of EGaIn. Scale bar, 500 μm. Inset: Magnified SEM image of 3D bridge. Scale bar, 200 μm. (H) Plots of the applied biases and responding current densities in EGaIn. (Photo credit: Young-Geun Park, Yonsei University).

  • Fig. 3 The electrical contact of direct-printed and reconfigured liquid metals.

    (A) Schematic illustrations of direct printing (left) and reconfiguration (right). (B) Dependence of total resistance on the length of the channel. Error bars represent the SD. (C) Current-voltage characteristics between Ag pads and direct-printed EGaIn. (D) Current-voltage characteristics between Ag pads and reconfigured EGaIn. (E and F) SEM images of EGaIn on an Ag pad after 7 hours of direct printing. (G and H) SEM images of EGaIn after 7 hours of reconfiguration. Scale bars, 200 μm.

  • Fig. 4 3D reconfiguration of liquid metals for electronics.

    (A) Schematic illustrations of the reconfigurable antenna. (B) Schematic illustrations of two concentric antennas (top) and the SEM image of the disconnected region (bottom). Scale bar, 300 μm. (C) Schematic illustrations of two concentric antennas that are electrically connected (top) and the SEM image of connected lines by reconfiguration (bottom). Scale bar, 300 μm. (D) Measured scattering parameters of the printed antenna in disconnected and connected states. (E) Schematic illustrations of the reconfiguration process for dynamic switching of LEDs. (F) Colorized SEM image of three LED pixels and EGaIn interconnects. The red, green, blue, and yellow colors correspond to red, green, and blue LEDs and EGaIn, respectively. Scale bar, 1 mm. (G) Photograph of three LED pixels and EGaIn interconnects. Scale bar, 1 mm. (H) Schematic illustrations of reconfiguration and photographs of LED working. Scale bars, 5 mm. (Photo credit: Young-Geun Park, Yonsei University).

  • Fig. 5 MicroLED array with 3D liquid metal interconnects.

    (A) Schematic illustration of the microLED array with reconfigured 3D interconnects. (B) Colorized SEM image of the microLED array and EGaIn interconnects. Blue and yellow colors correspond to microLED and EGaIn, respectively. Scale bar, 300 μm. (C) Colorized SEM image of 3D interconnects. The blue and yellow colors correspond to the microLED and EGaIn, respectively. Scale bar, 300 μm. (D) Photographs of light emission of the microLED array. Scale bars, 1 cm. (E) Current-voltage characteristics of microLED with reconfigured interconnects under flat or bent condition. (Photo credit: Young-Geun Park, Yonsei University).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/6/eaaw2844/DC1

    Fig. S1. SEM images of the kinked or bent regions of the printed EGaIn filaments.

    Fig. S2. The lift-off or cutoff state of line versus the nozzle lift-off velocity.

    Fig. S3. Photograph of lift-off of EGaIn during reconfiguration.

    Fig. S4. Formation of kink- or arc-shaped 3D structures by reconfiguration.

    Fig. S5. Electrical breakdown test of EGaIn.

    Fig. S6. Heat resistance of EGaIn 3D structures.

    Fig. S7. SEM images of soft encapsulation of EGaIn by parylene.

    Fig. S8. Contact angle between EGaIn and Au.

    Fig. S9. The efficiency of interconnection through 3D printing.

    Table S1. Comparison with conventional 3D printing techniques of conductive materials in the aspect of printable materials, resolution, reconfigurability, processing temperature, and conductivity.

    Table S2. Comparison with published results of liquid metal patterning in the aspect of line width, the free-standing 3D structure, reconfigurability, and the used substrate.

    Movie S1. Reconfiguration of the square coil antenna.

    Movie S2. Multiple reconfigurations of the EGaIn filament.

    Movie S3. Reconfiguration of EGaIn that connects about a 650-μm step.

    Movie S4. Formation of kink-shaped 3D structure by reconfiguration.

    Movie S5. Formation of arc-shaped 3D structure by reconfiguration.

    Movie S6. Breakdown procedure of EGaIn under increasing dc bias.

    Movie S7. Breakdown procedure of EGaIn under increasing ac bias (120 Hz).

    Movie S8. Lift-off and relocation of 3D interconnect for LED switching circuit.

    Movie S9. Light emission from the RGB LED array.

    Movie S10. Light emission from selected pixels in the 4 × 4 microLED array.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. SEM images of the kinked or bent regions of the printed EGaIn filaments.
    • Fig. S2. The lift-off or cutoff state of line versus the nozzle lift-off velocity.
    • Fig. S3. Photograph of lift-off of EGaIn during reconfiguration.
    • Fig. S4. Formation of kink- or arc-shaped 3D structures by reconfiguration.
    • Fig. S5. Electrical breakdown test of EGaIn.
    • Fig. S6. Heat resistance of EGaIn 3D structures.
    • Fig. S7. SEM images of soft encapsulation of EGaIn by parylene.
    • Fig. S8. Contact angle between EGaIn and Au.
    • Fig. S9. The efficiency of interconnection through 3D printing.
    • Table S1. Comparison with conventional 3D printing techniques of conductive materials in the aspect of printable materials, resolution, reconfigurability, processing temperature, and conductivity.
    • Table S2. Comparison with published results of liquid metal patterning in the aspect of line width, the free-standing 3D structure, reconfigurability, and the used substrate.
    • Legends for movies S1 to S10

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). Reconfiguration of the square coil antenna.
    • Movie S2 (.avi format). Multiple reconfigurations of the EGaIn filament.
    • Movie S3 (.avi format). Reconfiguration of EGaIn that connects about a 650-μm step.
    • Movie S4 (.avi format). Formation of kink-shaped 3D structure by reconfiguration.
    • Movie S5 (.avi format). Formation of arc-shaped 3D structure by reconfiguration.
    • Movie S6 (.avi format). Breakdown procedure of EGaIn under increasing dc bias.
    • Movie S7 (.avi format). Breakdown procedure of EGaIn under increasing ac bias (120 Hz).
    • Movie S8 (.avi format). Lift-off and relocation of 3D interconnect for LED switching circuit.
    • Movie S9 (.avi format). Light emission from the RGB LED array.
    • Movie S10 (.avi format). Light emission from selected pixels in the 4 × 4 microLED array.

    Files in this Data Supplement:

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