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Page 4 of 32 Keum et al. Soft Sci 2024;4:34 https://dx.doi.org/10.20517/ss.2024.26

research in the areas of materials and structural designs for stretchable electrodes and interconnects is
introduced. For display applications, highly conductive electrodes and interconnection are required to
[21]
suppress the RC delay effect . Therefore, electrode materials with an electrical resistivity of several μΩ-cm
are typically used for active-matrix (AM) displays. Specifically, electrodes and interconnects utilizing metal
nanowires (MNWs) [22-27] , metallic particles (nano- or micro-scale) [28-33] , liquid metals (LMs) [34-38] , inorganic/
[40]
[39]
organic-based composites , carbon-based nanomaterials , and hybrid-type conductive materials [41-44] are
discussed. Figure 3 shows comparisons of different stretchable interconnect material types in terms of
[17]
stretchability, transparency, conductivity, cost competitiveness, and processing scalability . Additionally,
stretchable electrodes/interconnects obtained through 2D or 3D structural pattern designs are also
introduced, which typically utilize rigid inorganic or organic-based materials.

MNWs
Table 1 lists representative stretchable electrodes and interconnects reported recently, comparing the
stretchability, electrical conductivity (or sheet resistance), materials, and applications. Among various types
of conducting components, MNWs are the representative 1D-type nanomaterials that can exhibit low sheet
resistance and high optical transparency owing to their percolating network structure and high aspect
ratios . The percolating network of 1D metallic nanomaterials is advantageous for maintaining electrical
[22]
conductivity even under deformation conditions. Among them, silver nanowires (AgNWs) are most widely
used due to their superior sheet resistance (< 10 Ω·sq ), high optical transparency (≥ 89%), low-cost
-1
fabrication, and ease of patterning . Due to these unique properties, AgNWs have been utilized for
[14]
deformable electrodes in solar cells, sensors, and displays by depositing or coating them on flexible or
[24]
stretchable substrates . In this context, Cai et al. reported a stretchable electroluminescent (EL) display
using printed AgNW patterns as the electrodes [Figure 4A(i)]. The AgNW ink was patterned on a
[24]
biaxially pre-stretched polydimethylsiloxane (PDMS) substrate using a direct printing method. The
fabricated stretchable conductor could maintain the electrical conductivity up to 156% of the stretching
state. A stretchable EL device was demonstrated with parallelly printed AgNW electrodes assembled with a
phosphor composite in a crossbar structure. The fabricated EL display could operate under a 20% stretching
state [Figure 4A(ii)]. Similarly, Lin et al. reported high-resolution AgNW patterning into a PDMS substrate
[26]
using the screen printing method . The AgNW electrodes were patterned with high resolution (~50 μm)
and utilized in a large-size stretchable circuit and light-emitting diode (LED) array. Additionally, other types
[27]
[46]
[45]
of 1D-type nanomaterials, such as Au nanofibers , Cu meshes , and Cu nanowires , have also been
reported for use as stretchable electrodes and interconnects in functional electronic devices.
LMs
LMs are also considered as one of the most impressive candidates for stretchable conductors due to their
intrinsic characteristics of high electrical conductivity, extreme mechanical deformability, and possibility of
large-area patterning [34,37] . In the case of using LMs as interconnecting materials, issues such as relatively low
electrical conductivity and limited patternability should be resolved to implement in commercial-level
display panels. Additionally, LMs are typically deposited using solution-based fabrication methods;
therefore, appropriate process design is further required. As an example, Park et al. demonstrated a 4 × 4
[37]
stretchable AM micro-LED display using the LM-based interconnects [Figure 4B]. The display pixel
islands consisted of oxide TFTs and micro-LEDs. They fabricated oxide TFTs on a flexible polyimide (PI)
substrate and bonded the micro-LEDs onto the TFT backplane. Afterward, the pixel islands were
transferred onto a stretchable PDMS substrate and LM interconnect patterns were printed using a lift-off
process. The micro-LED displays using the LM interconnection were able to function under stretching up
to 24% without noticeable performance degradation. Furthermore, Liu et al. introduced a printable solid-
liquid biphasic Ga-In (BGaIn) that maintains a near-constant resistance under stretching states . The
[35]
BGaIn was produced by thermally treating eutectic gallium-indium (EGaIn) nano-particles to form a liquid-