NU 2017-148

INVENTORS
Mark Hersam*
Ethan Secor
Alexander Cook
Christopher Tabor

SHORT DESCRIPTION
A method to achieve robust electrical contacts between conventional and liquid metals using an interfacial conductive barrier

BACKGROUND
Gallium-based liquid metal alloys (GaLMAs) are often connected directly to conventional metals, resulting in alloying. While certain metals show slow alloying (e.g., tungsten), this strategy does not provide long-term stability and can result in mechanical embrittlement at the interface. Moreover, these alternative metals are not compatible with liquid-phase processing, limiting the possibilities for practical implementation in a low-cost, scalable manner.  Liquid metals offer metallic conductivity with the mechanical properties of a liquid, and therefore have great potential for stretchable, wearable, or reconfigurable electronics. While mercury is a prototypical liquid metal, its toxicity prevents many applications. Gallium-based alloys overcome this limitation, but lead to unstable interfaces with conventional metals.

ABSTRACT
Northwestern researchers have developed a strategy that offers a route to integrate Ga-based liquid metal alloys with conventional metals in a stable, reliable configuration.  They achieve robust electrical contacts between conventional and liquid metals using an interfacial conductive barrier fabricated from a pristine graphene ink. With a thin layer of graphene between eutectic Gallium Indium (eGaIn) and silver, alloy formation is effectively suppressed, offering a low-resistance junction with excellent chemical, thermal, and mechanical stability. By realizing a suite of desirable properties using scalable, liquid-phase patterning methods, this strategy offers a practical route to the reliable integration of liquid metals with conventional electronic materials and systems.  While these liquid metals are widely researched for a range of applications (e.g., stretchable interconnects, reconfigurable circuits, sensors), their practical use requires integration with conventional metal interconnects and circuits. Having a simple and reliable method to stabilize this interface is therefore valuable for ongoing development of liquid metal electronics.

APPLICATIONS  

• Stretchable/wearable electronic devices
• Flexible electronic devices
• Reconfigurable electronics
• Soft robotics
• Self-healing electronics

ADVANTAGES  

• Prevents alloy formation between GaLMAs and conventional metal interconnects
• Offers improved reliability and long-term stability
• Provides desirable chemical, thermal, and mechanical stability for a variety of demanding applications    

PUBLICATIONS
Secor E, Cook A, Tabor C and Hersam M (2017) Wiring up Liquid Metal: Stable and Robust Electrical Contacts Enabled by Printable Graphene Inks.  Advanced Electronic Materials.  4:  1700483.

IP STATUS
A US patent application has been filed.