Soft electronic vias and interconnects through rapid three-dimensional assembly of liquid metal microdroplets | Nature Electronics

Nature Electronics (2024)Cite this article

Metrics details

The development of soft electronics requires methods to connect flexible and stretchable circuits. With conventional rigid electronics, vias are typically used to electrically connect circuits with multilayered architectures, increasing device integration and functionality. However, creating vias using soft conductors leads to additional challenges. Here we show that soft vias and planar interconnects can be created through the directed stratification of liquid metal droplets with programmed photocuring. Abnormalities that occur at the edges of a mask during ultraviolet exposure are leveraged to create vertical stair-like architectures of liquid metal droplets within the photoresin. The liquid metal droplets in the uncured (liquid) resin rapidly settle, assemble and then are fully cured, forming electrically conductive soft vias at multiple locations throughout the circuit in a parallel and spatially tunable manner. Our three-dimensional selective stratification method can also form seamless connections with planar interconnects, for in-plane and through-plane electrical integration.

This is a preview of subscription content, access via your institution

Access Nature and 54 other Nature Portfolio journals

Get Nature+, our best-value online-access subscription

$29.99 / 30 days

cancel any time

Subscribe to this journal

Receive 12 digital issues and online access to articles

$119.00 per year

only $9.92 per issue

Buy this article

Prices may be subject to local taxes which are calculated during checkout

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Mack, C. A. Fifty years of Moore’s law. IEEE Trans. Semicond. Manuf. 24, 202–207 (2011).

Article MATH Google Scholar

Lancaster, A. & Keswani, M. Integrated circuit packaging review with an emphasis on 3D packaging. Integration 60, 204–212 (2018).

Article Google Scholar

Gambino, J. P., Adderly, S. A. & Knickerbocker, J. U. An overview of through-silicon-via technology and manufacturing challenges. Microelectron. Eng. 135, 73–106 (2015).

Article Google Scholar

Hensleigh, R. et al. Charge-programmed three-dimensional printing for multi-material electronic devices. Nat. Electron. 3, 216–224 (2020).

Article MATH Google Scholar

Rich, S. I., Wood, R. J. & Majidi, C. Untethered soft robotics. Nat. Electron. 1, 102–112 (2018).

Article Google Scholar

Truby, R. L., Katzschmann, R. K., Lewis, J. A. & Rus, D. Soft robotic fingers with embedded ionogel sensors and discrete actuation modes for somatosensitive manipulation. In Proc. 2019 2nd IEEE International Conference on Soft Robotics (RoboSoft) (ed Ren, H.) 322–329 (IEEE, 2019).

Bhattacharya, S. et al. A chest-conformable, wireless electro-mechanical e-tattoo for measuring multiple cardiac time intervals. Adv. Electron. Mater. 9, 2201284 (2023).

Article MATH Google Scholar

Kim, D.-H. et al. Epidermal electronics. Science 333, 838–843 (2011).

Article MATH Google Scholar

Guo, R. et al. Ni-gain amalgams enabled rapid and customizable fabrication of wearable and wireless healthcare electronics. Adv. Eng. Mater. 20, 1800054 (2018).

Article Google Scholar

Yao, D. et al. Achieving the upper bound of piezoelectric response in tunable, wearable 3D printed nanocomposites. Adv. Funct. Mater. 29, 1903866 (2019).

Article Google Scholar

Zhang, H. & Rogers, J. A. Recent advances in flexible inorganic light emitting diodes: from materials design to integrated optoelectronic platforms. Adv. Opt. Mater. 7, 1800936 (2019).

Article Google Scholar

Park, S., Vosguerichian, M. & Bao, Z. A review of fabrication and applications of carbon nanotube film-based flexible electronics. Nanoscale 5, 1727–1752 (2013).

Article MATH Google Scholar

Sekitani, T. et al. Stretchable active-matrix organic light-emitting diode display using printable elastic conductors. Nat. Mater. 8, 494–499 (2009).

Article MATH Google Scholar

Slee, D., Stepan, J., Wei, W. & Swart, J. Introduction to printed circuit board failures. In Proc. 2009 IEEE Symposium on Product Compliance Engineering, PSES 2009 (ed Nix, D.) 1–8 (IEEE, 2009).

Kim, T. W., Lee, J. S., Kim, Y. C., Joo, Y. C. & Kim, B. J. Bending strain and bending fatigue lifetime of flexible metal electrodes on polymer substrates. Materials 12, 2490 (2019).

Article MATH Google Scholar

Byun, J. et al. A single droplet-printed double-side universal soft electronic platform for highly integrated stretchable hybrid electronics. Adv. Funct. Mater. 27, 1701912 (2017).

Article Google Scholar

Shamkhalichenar, H., Bueche, C. J. & Choi, J. W. Printed circuit board (PCB) technology for electrochemical sensors and sensing platforms. Biosensors 10, 159 (2020).

Article MATH Google Scholar

Zhang, Y., An, M., Yang, P. & Zhang, J. Recent advances in electroplating of through-hole copper interconnection. Electrocatalysis 12, 619–627 (2021).

Article MATH Google Scholar

Dow, W.-P. et al. Through-hole filling by copper electroplating. J. Electrochem. Soc. 155, D750 (2008).

Article Google Scholar

Khoshmanesh, K. et al. Liquid metal enabled microfluidics. Lab Chip 17, 974–993 (2017).

Article MATH Google Scholar

Bartlett, M. D. et al. High thermal conductivity in soft elastomers with elongated liquid metal inclusions. Proc. Natl Acad Sci. USA 114, 2143–2148 (2017).

Article MATH Google Scholar

Dickey, M. D. et al. Eutectic gallium-indium (egain): a liquid metal alloy for the formation of stable structures in microchannels at room temperature. Adv. Funct. Mater. 18, 1097–1104 (2008).

Article MATH Google Scholar

Veerapandian, S. et al. Hydrogen-doped viscoplastic liquid metal microparticles for stretchable printed metal lines. Nat. Mater. 20, 533–540 (2021).

Article Google Scholar

Zheng, Y. et al. Lignin-based encapsulation of liquid metal particles for flexible and high-efficiently recyclable electronics. Adv. Funct. Mater 34, 2310653 (2024).

Article Google Scholar

Dickey, M. D. Stretchable and soft electronics using liquid metals. Adv. Mater. 29, 1606425 (2017).

Article MATH Google Scholar

Wang, X. & Liu, J. Recent advancements in liquid metal flexible printed electronics: properties, technologies, and applications. Micromachines 7, 206 (2016).

Article MATH Google Scholar

Chen, S., Cui, Z., Wang, H., Wang, X. & Liu, J. Liquid metal flexible electronics: past, present, and future. Appl. Phys. Rev. 10, 21308 (2023).

Article MATH Google Scholar

Ford, M. J., Patel, D. K., Pan, C., Bergbreiter, S. & Majidi, C. Controlled assembly of liquid metal inclusions as a general approach for multifunctional composites. Adv. Mater. 32, 2002929 (2020).

Article Google Scholar

Haque, A. T. et al. Electrically conductive liquid metal composite adhesives for reversible bonding of soft electronics. Adv. Funct. Mater. 34, 2304101 (2023).

Article MATH Google Scholar

Lee, W. et al. Universal assembly of liquid metal particles in polymers enables elastic printed circuit board. Science 378, 637–641 (2022).

Article MATH Google Scholar

Wu, D. et al. Fast and facile liquid metal printing via projection lithography for highly stretchable electronic circuits. Adv. Mater. 36, 2307632 (2024).

Article Google Scholar

Liu, S. et al. Ultrasonic-enabled nondestructive and substrate-independent liquid metal ink sintering. Adv. Sci. 10, 2301292 (2023).

Article Google Scholar

Yun, G. et al. Electro-mechano responsive elastomers with self-tunable conductivity and stiffness. Sci. Adv. 9, eadf1141 (2023).

Article Google Scholar

Kim, M. G., Alrowais, H., Pavlidis, S. & Brand, O. Size-scalable and high-density liquid-metal-based soft electronic passive components and circuits using soft lithography. Adv. Funct. Mater. 27, 1604466 (2017).

Article Google Scholar

Ren, P. & Dong, J. Direct fabrication of via interconnects by electrohydrodynamic printing for multi-layer 3d flexible and stretchable electronics. Adv. Mater. Technol. 6, 2100280 (2021).

Article Google Scholar

Marques, D. G., Lopes, P. A., de Almeida, A. T., Majidi, C. & Tavakoli, M. Reliable interfaces for egain multi-layer stretchable circuits and microelectronics. Lab Chip 19, 897–906 (2019).

Article Google Scholar

Liu, S., Shah, D. S. & Kramer-Bottiglio, R. Highly stretchable multilayer electronic circuits using biphasic gallium-indium. Nat. Mater. 20, 851–858 (2021).

Article Google Scholar

Hirsch, A. et al. Intrinsically stretchable biphasic (solid-liquid) thin metal films. Adv. Mater. 28, 4507–4512 (2016).

Article MATH Google Scholar

Yoon, J. et al. Design and fabrication of novel stretchable device arrays on a deformable polymer substrate with embedded liquid-metal interconnections. Adv. Mater. 26, 6580–6586 (2014).

Article MATH Google Scholar

Franssila, S. Introduction to Microfabrication (Wiley, 2010).

Patel, D. K. et al. Highly stretchable and UV curable elastomers for digital light processing based 3D printing. Adv. Mater. 29, 1606000 (2017).

Article Google Scholar

Qi, D., Zhang, K., Tian, G., Jiang, B. & Huang, Y. Stretchable electronics based on PDMS substrates. Adv. Mater. 33, 2003155 (2021).

Article Google Scholar

Llerena Zambrano, B. et al. Soft electronics based on stretchable and conductive nanocomposites for biomedical applications. Adv. Healthc. Mater. 10, 2001397 (2021).

Article Google Scholar

Bartlett, M. D. et al. Stretchable, high-k dielectric elastomers through liquid-metal inclusions. Adv. Mater. 28, 3726–3731 (2016).

Article MATH Google Scholar

Style, R. W. et al. Stiffening solids with liquid inclusions. Nat. Phys. 11, 82–87 (2015).

Article MATH Google Scholar

Markvicka, E. J., Bartlett, M. D., Huang, X. & Majidi, C. An autonomously electrically self-healing liquid metal–elastomer composite for robust soft-matter robotics and electronics. Nat. Materials 17, 618–624 (2018).

Article Google Scholar

Ford, M. J. et al. A multifunctional shape-morphing elastomer with liquid metal inclusions. Proc. Natl Acad. Sci. USA 116, 21438–21444 (2019).

Article MATH Google Scholar

Baum, D. et al. High-throughput segmentation of tiled biological structures using random-walk distance transforms. Integr. Comp. Biol. 59, 1700–1712 (2019).

Article MATH Google Scholar

Cheng, N.-S. Simplified settling velocity formula for sediment particle. J. Hydraul. Eng. 123, 149–152 (1997).

Article MATH Google Scholar

Bogatin, E. Essential principles of signal integrity. IEEE Microw. Mag. 12, 34–41 (2011).

Article MATH Google Scholar

Liu, Y. et al. Synthesis and applications of low dielectric polyimide. Resour. Chem. Mater. 2, 49–62 (2023).

MATH Google Scholar

Barron III, E. J., Williams, E. T., Wilcox, B. T., Ho, D. H. & Bartlett, M. D. Liquid metal-elastomer composites for water-resilient soft electronics. J. Polymer Sci. https://doi.org/10.1002/pol.20230616 (2023).

Download references

D.H.H. and M.D.B. acknowledge support from the Office of Naval Research Young Investigator Program (ONR YIP) (grant no. N000142112699) and the National Science Foundation CAREER award (grant no. 2238754). C.H. and L.L. acknowledge support from Virginia Polytechnic Institute and State University through the COE Faculty Fellowship. C.H. and L.L. also thank D. Baum for the kind assistance in using random-work distance transforms for quantitative microCT analysis.

Dong Hae Ho

Present address: Department of Energy Science and Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Republic of Korea

Chenhao Hu & Ling Li

Present address: Department of Materials Science and Engineering, University of Pennsylvania, Pennsylvania, PA, USA

Department of Mechanical Engineering, Soft Materials and Structures Lab, Virginia Tech, Blacksburg, VA, USA

Dong Hae Ho & Michael D. Bartlett

Macromolecules Innovation Institute, Virginia Tech, Blacksburg, VA, USA

Dong Hae Ho & Michael D. Bartlett

Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA, USA

Chenhao Hu & Ling Li

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

D.H.H. and M.D.B. conceived and designed research. D.H.H. conducted research. C.H. and L.L. contributed to measurement and analysis of the microCT scan data. M.D.B. supervised the work. D.H.H. and M.D.B. wrote the paper with contributions from all the authors.

Correspondence to Michael D. Bartlett.

M.D.B. and D.H.H. are inventors on a patent application (US Patent Application no. 63/535,919) on the fabrication approach. The other authors declare no competing interests.

Nature Electronics thanks Wedyan Babatain, Sujgjune Park and Nanjia Zhou for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary Notes, Figs. 1–21 and Videos 1–6.

Reconstructed microCT images of LM-STAIR vias.

LM-STAIR ultrasonic activation.

Real-time fabrication of LM-STAIR vias inside the photoresin.

Reconstructed microCT images of planar interconnect.

Circuit adhesion demonstration.

Magnetic field interface circuit demonstration.

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and permissions

Ho, D.H., Hu, C., Li, L. et al. Soft electronic vias and interconnects through rapid three-dimensional assembly of liquid metal microdroplets. Nat Electron (2024). https://doi.org/10.1038/s41928-024-01268-z

Download citation

Received: 13 November 2023

Accepted: 26 September 2024

Published: 24 October 2024

DOI: https://doi.org/10.1038/s41928-024-01268-z

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative