  For the advancement of highly-integrated stretchable electronics, the
development of scalable sub-micrometer conductor patterning is required.
Eutectic gallium indium EGaIn is an attractive conductor for stretchable
electronics, as its liquid metallic character grants it high electrical
conductivity upon deformation. However, its high surface energy precludes
patterning it with (sub)-micron resolution. Herein, we overcome this limitation
by reporting for the first time the electrodeposition of EGaIn. We use a
non-aqueous acetonitrile-based electrolyte that exhibits high electrochemical
stability and chemical orthogonality. The electrodeposited material led to
low-resistance lines that remained stable upon (repeated) stretching to a 100
percent strain. Because electrodeposition benefits from the resolution of
mature nanofabrication methods used to pattern the base metal, the proposed
bottom-up approach achieved a record-high density integration of EGaIn regular
lines of 300 nm half-pitch on an elastomer substrate by plating on a gold seed
layer pre-patterned by nanoimprinting. Moreover, vertical integration was
enabled by filling high aspect ratio vias. This capability was conceptualized
by the fabrication of an omnidirectionally stretchable 3D electronic circuit,
and demonstrates a soft-electronic analogue of the stablished damascene process
used to fabricate microchip interconnects. Overall, this work proposes a simple
route to address the challenge of metallization in highly integrated (3D)
stretchable electronics.
