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Zou et al. Soft Sci 2024;4:19 https://dx.doi.org/10.20517/ss.2024.13 Page 3 of 10

Figure 1. Strategies toward the fabrication of deformable Micro-LEDs, including substrate removal (A-C), micro-assembly (D-F), and
mechanical design (E-I). Schematics for the substrate removal methods, including (A) laser lift-off, (B) chemical lift-off, and (C)
mechanical lift-off [35] ; Representative transfer methods for Micro-LED integration on curvilinear substrates reported recently, including
[11]
(D) ballon-shaped stamp transfer [60] , (E) roller transfer , and (F) photosensitive tape-assisted transfer [17] ; Typical mechanical
structure designs for improved stretchability of Micro-LED devices, including (G) island-bridge design [61] , (H) buckling structures [16] ,
[9]
and (I) Kirigami structures . Figure 1A-C reproduced under the terms of the CC-BY Creative Commons Attribution 4.0 International
license [35] ; Figure 1D adapted with permission from ref. [60] . Copyright 2021 Springer Nature; Figure 1E reproduced under the terms
[11]
of the CC-BY Creative Commons Attribution 4.0 International license ; Figure 1F reproduced under the terms of the CC-BY
Creative Commons Attribution 4.0 International license [17] ; Figure 1G reproduced under the terms of the CC-BY Creative Commons
Attribution 4.0 International license [61] ; Figure 1H adapted with permission from ref. [16] . Copyright 2009 AAAS; Figure 1I adapted with
[9]
permission from ref. . Copyright 2022 Wiley-VCH. Micro-LED: Micro-scale light-emitting diode.
Micro-assembly
System-scale flexibility can be partially enhanced by micro-assembling Micro-LEDs onto soft
substrates [35,54-56] . With shrinking the Micro-LED size and thickness into the micro-scale regime, fast and
accurate manipulation of Micro-LEDs in a reliable manner becomes a critical challenge. Several micro-
assembly techniques have been established to partially address this issue, including the pioneering stamp
transfer printing methods [15,16,56,57] , where an elastic polydimethylsiloxane (PDMS) stamp picks up the
microscale device from the source wafer and then releases it to a receiver. To assist the transfer, Micro-LEDs
are commonly patterned in a manner such that they are weakly suspended on the growth substrate by using
anchors or undercut microstructures . Other popular methods include laser-based [6,58] or fluid-assisted
[7]
micro-assembly [55,59] , which have competing advantages in terms of the transfer speed. While most of them
do work for transfer printing microscale devices to planar surfaces, some present poor combability for