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Cited by 187Nanomaterials and Printing TechnologiesNanofabrication and Lithography TechniquesAdvancements in Photolithography Techniques

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Nanofabrication for all-soft and high-density electronic devices based on liquid metal

Open access
Kim, Min-gu, Brown, Devin K., Brand, Oliver·2020·Nature Communications
DOI 10.1038/s41467-020-14814-yPMC PMC7035367
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Abstract

Innovations in soft material synthesis and fabrication technologies have led to the development of integrated soft electronic devices. Such soft devices offer opportunities to interact with biological cells, mimicking their soft environment. However, existing fabrication technologies cannot create the submicron-scale, soft transducers needed for healthcare and medical applications involving single cells. This work presents a nanofabrication strategy to create submicron-scale, all-soft electronic devices based on eutectic gallium-indium alloy (EGaIn) using a hybrid method utilizing electron-beam lithography and soft lithography. The hybrid lithography process is applied to a biphasic structure, comprising a metallic adhesion layer coated with EGaIn, to create soft nano/microstructures embedded in elastomeric materials. Submicron-scale EGaIn thin-film patterning with feature sizes as small as 180 nm and 1 μm line spacing was achieved, resulting in the highest resolution EGaIn patterning technique to date. The resulting soft and stretchable EGaIn patterns offer a currently unrivaled combination of resolution, electrical conductivity, and electronic/wiring density.

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Fig. 1 Nanofabrication process based on hybrid lithography for submicron-scale EGaIn patterning. a Hybrid lithography process combining electron-beam lithography and soft lithography for fabrication of submicron-scale, soft electronic devices based on EGaIn. b Patterned Au (top) and EGaIn on Au (bottom) structures. Scale bars indicate 40 μm. c Patterned EGaIn square-shaped dot arrays with various dot dimensions from 50 μm down to 500 nm, and d soft material encapsulation and release process of the EGaIn structures.
Fig. 1 Nanofabrication process based on hybrid lithography for submicron-scale EGaIn patterning. a Hybrid lithography process combining electron-beam lithography and soft lithography for fabrication of submicron-scale, soft electronic devices based on EGaIn. b Patterned Au (top) and EGaIn on Au (bottom) structures. Scale bars indicate 40 μm. c Patterned EGaIn square-shaped dot arrays with various dot dimensions from 50 μm down to 500 nm, and d soft material encapsulation and release process of the EGaIn structures.CC BY · PubMed Central
Fig. 2 Patterned EGaIn nano/microstructures. a SEM images of EGaIn lines with widths from 10 µm to 500 nm and close-up of EGaIn lines with 1 µm and 500 nm width. Scale bars indicate 2 μm. b 3D images and cross-sections of EGaIn lines with width of 10 µm, 5 µm, 1 µm, and 500 nm. The blue symbols represent the measured profile, while the dashed yellow line indicates the designed cross-section. c Measured thickness of fabricated EGaIn lines as a function of line width. The x- and y-error bars represent the standard deviation. The thickness of the PMMA film (1 µm) is shown as dashed red line for reference.
Fig. 2 Patterned EGaIn nano/microstructures. a SEM images of EGaIn lines with widths from 10 µm to 500 nm and close-up of EGaIn lines with 1 µm and 500 nm width. Scale bars indicate 2 μm. b 3D images and cross-sections of EGaIn lines with width of 10 µm, 5 µm, 1 µm, and 500 nm. The blue symbols represent the measured profile, while the dashed yellow line indicates the designed cross-section. c Measured thickness of fabricated EGaIn lines as a function of line width. The x- and y-error bars represent the standard deviation. The thickness of the PMMA film (1 µm) is shown as dashed red line for reference.CC BY · PubMed Central
Fig. 3 Characterization of patterned EGaIn nano/microstructures. a Measured cross-sectional area of EGaIn lines (symbols) with widths from 10 µm to 500 nm, compared to the designed cross-sectional area (solid line), as a function of the line width. The y-error bars represent the standard deviation. b Calculated (symbols) and measured resistance of 200-µm-long EGaIn lines as a function of line width. The y-error bars represent the standard deviation. The dashed line accounts for the resistance of the EGaIn film only while the dot-dashed line assumes a theoretical parallel circuit of the EGaIn film and the underlying Au adhesion layer. c, d EGaIn patterning characterization using different metallic adhesion layers, namely Au and Cu. c Patterned Au structures after lift-off process without EGaIn stamping and stamped and patterned EGaIn structures on Au. d Patterned Cu structures after lift-off process without EGaIn stamping and stamped and patterned EGaIn structures on Cu. Scale bars in c and d indicate 40 μm.
Fig. 3 Characterization of patterned EGaIn nano/microstructures. a Measured cross-sectional area of EGaIn lines (symbols) with widths from 10 µm to 500 nm, compared to the designed cross-sectional area (solid line), as a function of the line width. The y-error bars represent the standard deviation. b Calculated (symbols) and measured resistance of 200-µm-long EGaIn lines as a function of line width. The y-error bars represent the standard deviation. The dashed line accounts for the resistance of the EGaIn film only while the dot-dashed line assumes a theoretical parallel circuit of the EGaIn film and the underlying Au adhesion layer. c, d EGaIn patterning characterization using different metallic adhesion layers, namely Au and Cu. c Patterned Au structures after lift-off process without EGaIn stamping and stamped and patterned EGaIn structures on Au. d Patterned Cu structures after lift-off process without EGaIn stamping and stamped and patterned EGaIn structures on Cu. Scale bars in c and d indicate 40 μm.CC BY · PubMed Central
Fig. 4 EGaIn patterning performance. a SEM images of EGaIn structures with designed line widths of 1 µm, 500 nm, and 100 nm on Si wafer as well as 3D profile of 100 nm EGaIn line fabricated using 1-µm PMMA thickness. Scale bars indicate 3 μm. b Patterned EGaIn test structures on Si wafer to evaluate achievable line spacing. c 3D cross-sectional profile of EGaIn line with designed 100-nm line width using 1 µm PMMA thickness. d Measured thickness of fabricated EGaIn lines as a function of designed EGaIn width for different PMMA thicknesses from 1 µm down to 300 nm. The x- and y-error bars represent the standard deviation. e Measured aspect ratio (AR) of EGaIn lines as a function of designed AR for PMMA thicknesses from 1 µm to 300 nm. f Measured 3D cross-section of EGaIn line with a designed width of 100 nm in the case of 300 nm PMMA thickness. The inset shows an SEM image of a fabricated 180-nm-wide EGaIn line.
Fig. 4 EGaIn patterning performance. a SEM images of EGaIn structures with designed line widths of 1 µm, 500 nm, and 100 nm on Si wafer as well as 3D profile of 100 nm EGaIn line fabricated using 1-µm PMMA thickness. Scale bars indicate 3 μm. b Patterned EGaIn test structures on Si wafer to evaluate achievable line spacing. c 3D cross-sectional profile of EGaIn line with designed 100-nm line width using 1 µm PMMA thickness. d Measured thickness of fabricated EGaIn lines as a function of designed EGaIn width for different PMMA thicknesses from 1 µm down to 300 nm. The x- and y-error bars represent the standard deviation. e Measured aspect ratio (AR) of EGaIn lines as a function of designed AR for PMMA thicknesses from 1 µm to 300 nm. f Measured 3D cross-section of EGaIn line with a designed width of 100 nm in the case of 300 nm PMMA thickness. The inset shows an SEM image of a fabricated 180-nm-wide EGaIn line.CC BY · PubMed Central
Fig. 5 Fabricated all-soft electronic devices. a Resistive sensor arrays fabricated on a Si wafer with 500 nm line width and 1 µm spacing, and 1 µm line width and 1 µm spacing; Encapsulation with soft elastomeric material, such as PDMS, and release of soft resistive sensor array from the Si wafer. Scale bars indicate 5 μm. b Strain sensor array with straight-line resistors having 500 nm and 1 µm line widths and c measured and simulated relative resistance changes ΔR/R of the resistive strain sensors as a function of the bending radius. The y-error bars represent the standard deviation. d Interdigitated capacitors with 5 μm line width and spacing and e measured capacitance as a function of frequency (top) for different numbers of interdigitated electrodes (IDE) as well as measured and simulated capacitance as a function of the number of IDE (bottom). The y-error bars represent the standard deviation. f Microelectrode array with 100 electrodes (scale bar, 100 μm) and g measured relative resistance change as a function of the number of bending and twisting cycles (bending was performed around a cylinder with 7.5 mm radius, and twisting was performed to a 180˚ angle). h Fabricated soft circuit with three embedded LEDs under mechanical stretching and folding deformation.
Fig. 5 Fabricated all-soft electronic devices. a Resistive sensor arrays fabricated on a Si wafer with 500 nm line width and 1 µm spacing, and 1 µm line width and 1 µm spacing; Encapsulation with soft elastomeric material, such as PDMS, and release of soft resistive sensor array from the Si wafer. Scale bars indicate 5 μm. b Strain sensor array with straight-line resistors having 500 nm and 1 µm line widths and c measured and simulated relative resistance changes ΔR/R of the resistive strain sensors as a function of the bending radius. The y-error bars represent the standard deviation. d Interdigitated capacitors with 5 μm line width and spacing and e measured capacitance as a function of frequency (top) for different numbers of interdigitated electrodes (IDE) as well as measured and simulated capacitance as a function of the number of IDE (bottom). The y-error bars represent the standard deviation. f Microelectrode array with 100 electrodes (scale bar, 100 μm) and g measured relative resistance change as a function of the number of bending and twisting cycles (bending was performed around a cylinder with 7.5 mm radius, and twisting was performed to a 180˚ angle). h Fabricated soft circuit with three embedded LEDs under mechanical stretching and folding deformation.CC BY · PubMed Central
Fig. 6 Liquid metal patterning technologies. Comparison of resolution (minimum line width) and film thickness of published liquid metal (eutectic gallium-indium alloy, EGaIn) patterning technologies as well as proposed nanofabrication technique based on hybrid lithography for submicron resolution.
Fig. 6 Liquid metal patterning technologies. Comparison of resolution (minimum line width) and film thickness of published liquid metal (eutectic gallium-indium alloy, EGaIn) patterning technologies as well as proposed nanofabrication technique based on hybrid lithography for submicron resolution.CC BY · PubMed Central

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Metadata

Authors
Kim, M.-G., Brown, D. K., & Brand, O.
Affiliations
Georgia Institute of Technology (US)
Corresponding author
Brand, Oliver
ORCID
Venue
Nature Communications
Publisher
Springer Science and Business Media LLC
Published
2020-02-21
Volume
11
Issue
1
Pages
1002-1002
ISSN
2041-1723 (ISSN-L)
DOI
10.1038/s41467-020-14814-y
PMC
PMC7035367
OpenAlex
W3008821181
Cited by
186
References
56
Citations by year
2026: 17 · 2025: 33 · 2024: 40 · 2023: 33 · 2022: 33 · 2021: 21 · 2020: 9
FWCI
8.24
Type
journal article
Language
en
Open access
Licence
Locations
  • Nature Communications (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • RePEc: Research Papers in Economics (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • National Science Foundation (1711259, 1542174)
  • Georgia Institute of Technology (ECCS-1542174)
  • Division of Electrical, Communications and Cyber Systems (1542174, ECCS 1542174, 1711259)
Topics
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Nanomaterials and Printing Technologies
  • Physical Sciences › Materials Science › Surfaces, Coatings and Films › Nanofabrication and Lithography Techniques
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Advancements in Photolithography Techniques
Keywords
eutectic gallium-indium alloy, liquid metal electronics, soft electronics, nanofabrication, submicron patterning, elastomeric substrates, stretchable electronics, high-density electronics
MeSH terms
Alloys, Electric Conductivity, Electronics, Equipment Design, Gallium, Indium, Metals, Printing, Surface Properties, Elastomers, Nanotechnology, Electrical Equipment and Supplies, Manufacturing Industry

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