Size‐Scalable and High‐Density Liquid‐Metal‐Based Soft Electronic Passive Components and Circuits Using Soft Lithography

The use of conducting liquids with high electrical conductivity, such as eutectic gallium–indium (EGaIn), has great potential in electronics applications requiring stretchability and deformability beyond conventional flexible electronics relying on solid conductors. An advanced liquid metal thin‐line patterning process based on soft lithography and a compatible vertical integration technique are presented that enable size‐scalable and high‐density EGaIn‐based, soft microelectronic components and circuits. The advanced liquid metal thin‐line patterning process based on poly(dimethylsiloxane) (PDMS) substrates and soft lithography techniques allows for simultaneous patterning of uniform and residue‐free EGaIn lines with line width from single micrometers to several millimeters at room temperature and under ambient pressure. Using this fabrication technique, passive electronic components and circuits are investigated under elastic deformations using numerical and experimental approaches. In addition, soft through‐PDMS vias with high aspect ratio are demonstrated for multilayer interconnections in 2.5D and 3D integration approaches. To highlight the system‐level potential of the patterning technique, a chemical sensor based on an integrated LC resonance circuit with a microfluidic‐tunable interdigitated capacitor and a planar spiral inductor is fabricated and characterized. Finally, to show the flexibility and stretchability of the resulting electronics, circuits with embedded light emitting diodes (LEDs) are investigated under bending, twisting, and stretching deformations. An advanced EGaIn thin‐line patterning process based on soft lithography and a vertical integration technique are presented that enable size‐scalable and high‐density eutectic gallium–indium (EGaIn)‐based, soft microelectronic components and circuits. The proposed fabrication technique enables size‐scalable, high‐resolution, uniform, and residue‐free EGaIn patterns for passive components and circuits. Also, microfluidic integration for chemical sensing applications and multilayered integration using soft vias are demonstrated.