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A site-selective integration strategy for microdevices on conformable substrates

Nature Electronics volume 7, pages 383–395 (2024)Cite this article

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Abstract

Microdevices can be integrated on conformable substrates to create high-performance and multifunctional human–machine interfaces. However, existing integration schemes often use unpatterned, thick and rigid adhesive layers that can increase the flexural rigidity and compromise mechanical compliance. Here we report the site-selective and anisotropically conductive integration of microdevices on conformable substrates. An adhesive precursor is selectively deposited on high-density arrays of microdevices using a velocity-controlled dip-transfer coating method. This technique suppresses capillary action and unwanted coating between devices, thereby minimizing the extent of bonding areas that degrade the inherent compliance of polymeric substrates. Ferromagnetic particles in the adhesives are magnetically self-assembled into well-defined anisotropic chains, resulting in a low contact resistance without electrical interference between fine-pitch terminals. We use the approach to additively integrate multiscale, die-level microdevices on various flexible and stretchable substrates. We show that it can be used to assemble microscale light-emitting diodes and a microcontroller die on a flexible circuit to create a skin-attachable device capable of detecting and displaying temperature.

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Fig. 1: S-ACI for highly conformable microelectronics.
Fig. 2: Velocity-controlled dip-transfer coating for selectively patterning epoxy composites onto high-density microdevices.
Fig. 3: Electrical characteristics of magnetically self-assembled S-ACI.
Fig. 4: Mechanical characteristics of S-ACI-based conformable systems.
Fig. 5: Compatibility of the S-ACI scheme across various substrates and electrodes.
Fig. 6: Skin-attachable microelectronic systems integrating die-level microdevices onto an FPCB.

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Data availability

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

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Acknowledgements

This research was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under project no. SRFC-IT1801-07.

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Authors and Affiliations

  1. Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center (ISRC), Seoul National University, Seoul, Korea

    Hyungsoo Yoon, Sujin Jeong & Yongtaek Hong

  2. Department of Chemical Engineering, Stanford University, Stanford, CA, USA

    Byeongmoon Lee

Authors
  1. Hyungsoo Yoon
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Contributions

H.Y., B.L. and Y.H. conceived the idea and designed the experiments. H.Y. and S.J. performed the device fabrication and characterization of S-ACI performance. H.Y. and S.J. carried out the FEA in discussion with B.L. H.Y., S.J., B.L. and Y.H. demonstrated the miniaturized micro-LED display and temperature-indicating system. H.Y., B.L. and Y.H. wrote the paper. All authors discussed the results and revised and approved the paper.

Corresponding authors

Correspondence to Byeongmoon Lee or Yongtaek Hong.

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Nature Electronics thanks Ravinder Dahiya and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 FEA of the effect of dip-transfer velocity on the capillary rise of the epoxy composite between two microdevices.

a, Schematic illustration of the dip-transfer coating of the epoxy composite for two microdevices separated by 30 µm. The withdrawing velocity of microdevices from the epoxy composite is considered a \({v}_{{\rm{dt}}}\) for FEA. b, Calculated y-component fluid position (\({p}_{{\rm{f}}}\)) (left) and fluid velocity (\({v}_{{\rm{f}}}\)) (right) of the epoxy composite at the centre of the meniscus. c, FEA results visualizing the y-component fluid velocity for various \({v}_{{\rm{dt}}}\) values from 1 to 50 mm min-1. d, Magnified FEA results visualizing the y-component fluid velocity and arrows representing the fluid velocity vectors. The left result shows the meniscus rising at a lower \({v}_{{\rm{dt}}}\) of 5 mm min-1. The right result shows the meniscus separating at a higher \({v}_{{\rm{dt}}}\) of 20 mm min-1.

Supplementary information

Supplementary Information

Supplementary Figs. 1–46 and Tables 1–12.

Supplementary Video 1

Flexible micro-LED display.

Supplementary Video 2

Velocity-controlled dip-transfer coating of epoxy composite to microdevices.

Supplementary Video 3

Miniaturized, die-level micro-LED display.

Supplementary Video 4

Real-time detection and visualization of water temperature flowing into a metal straw.

Supplementary Video 5

Skin-attachable, miniaturized temperature-indicating system.

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Yoon, H., Jeong, S., Lee, B. et al. A site-selective integration strategy for microdevices on conformable substrates. Nat Electron 7, 383–395 (2024). https://doi.org/10.1038/s41928-024-01159-3

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