Scalable Electrodeposition of Eutectic Indium Gallium from an Acetonitrile-Based Electrolyte for Integrated Stretchable Electronics

Abstract: 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.