Intrinsically Stretchable Biphasic (Solid–Liquid) Thin Metal Films

Abstract

Liquid metals, encapsulated in soft materials, have therefore attracted much attention in recent years [2a,8] to manufacture soft conductors with metallic conductivity, high stretchability and reconfigurability. [9] Gallium-based alloys, rather than toxic mercury, are widely used. The high surface tension and the passivating oxide skin that spontaneously forms on the surface of these liquids hinder their patterning using conventional techniques. Alternative methods focus on injection into channels, molding and printing for rapid manufacturing of highly conductive and stretchable metal networks but none of these patterning techniques offer high-resolution batch processing over large (wafer-scale) surface areas. [10] Based on these observations, we developed a new class of stretchable electronic conductors formed of biphasic solidliquid thin metal films. A bilayer metallization sequence starting with the sputtering of an alloying gold film followed by the thermal evaporation of liquid gallium (that displays a melting point of 29.8 °C [11] ) results in a heterogeneous film composed of clusters of the solid intermetallic alloy AuGa 2 and supercool liquid gallium forming a continuous network and dispersed bulges [11b,12] (Figure 1a-c). We designed and engineered the biphasic metallic films to be compatible with large-area and standard microfabrication. Figure 1d,e shows examples of fine patterns produced at wafer scale on elastomeric substrates. Multilayered stretchable circuits can be readily integrated by covalently bonding membranes hosting patterned biphasic conductors connected through soft vias. Figure 1e displays a 4 × 4 wafer-sized hybrid array of surface mounted light emitting diodes interconnected with a two-level network of biphasic solid-liquid conductors. The array withstood demanding multiaxial inflation cycles, constantly delivering power to the optoelectronic devices (Movie S1, Supporting Information).To prepare the stretchable biphasic solid-liquid thin metal films, a two-step process was developed in which liquid gallium was evaporated on a substrate preliminarily coated with a wetting and alloying thin film. We selected poly(dimethylsiloxane) (PDMS), a silicone, as the soft carrier substrate and a gold film sputtered on the PDMS as the alloying layer. However, our process is not limited to those materials ( Figure S1 and S2, Supporting Information). Non-noble metals may be used, provided the alloying thin film is not oxidized.The high surface tension of the liquid metal prevented the formation of an evaporated continuous liquid metal film on bare silicone substrates. Instead, the surface of the elastomer was covered with a nonconducting arrangement of liquid gallium microdroplets ( Figure S3, Supporting Information). In contrast, evaporating gallium on an alloying metal film, first deposited on the silicone surface, overcame the cohesive forces Stretchable conductors are the foundation of soft electronic circuits. [1] Manufacturing elastic wiring networks to distribute and carry electrical pote...

Untethered soft robotics

“…Recent work has demonstrated fast and accurate filling of complex microchannel geometries via a vacuum 104 ( Fig. 4g), as well as the fabrication of biphasic thin films by sputtering gold and thermally evaporating liquid gallium 105 (Fig. 4h).…”

“…4h). Several techniques have also focused on forming liquid-metal interconnects between IC devices 105 .…”

Liquid Metal Phagocytosis: Intermetallic Wetting Induced Particle Internalization

“…For liquid metals (LMs), such problem becomes very important and also challenging due to the uniqueness of the base liquids rising from their surface tension, passivity, and many other aspects 4, 5, 6, 7. The combination of fluidity and metallic nature of LMs makes them appealing for applications where excellent heat conductivity, electrical conductivity, and flexibility are required 8, 9, 10. Up to now, the search for safe‐handling room‐temperature LMs only narrows down to gallium‐based LMs, a group of alloys consisting gallium and other metals like indium, tin, etc.…”

Engineering reversible elasticity in ductile and brittle thin films supported by a plastic foil

“…Elastic electronic materials display stable and reliable electrical properties upon repeated and multi-axial deformations [3,4]. An alternative approach to produce stretchable devices and circuits out of non-elastic materials is the patterning of strain-relief motifs in the form of serpentines, to minimize local mechanical stress in the most fragile materials [5,6].…”