Application of Liquid-Metal GaIn Alloys to Soft-matter Capacitance and Related Stretchable Electronics

Stretchable electronics is an exciting new field of developing technology, allowing devices to undergo large deformations such as, bending, twisting, stretching and compression. As such, they can be easily interfaced with the human body, conforming to its contours and enabling a range of advances in electronic skins. Creating stretchable circuits, however, is not straight forward, as most electrically conductive materials are rigid. Because of this, researchers have developed a number of methods in which conductive materials can support deformation. These include deterministic architectures (e.g. wavy circuits), polymer composites, and electrically conductive fluids. The focus of this work is the latter technique, utilizing highly conductive gallium-indium (GaIn) metal alloys. Since they are liquid at room temperature, these metals are inherently deformable with no defined shape, and can create highly stretchable electronics when encapsulated within an elastomer. Using these materials, we target stretchable capacitance and related technologies, with capacitive elements playing a vital role in modern electronics and sensors. A family of highly stretchable microfluidic planar capacitors and inductors are introduced, which can be elongated by at least 200% of their initial length. The capacitance-strain response is examined using kinematic modeling and through experiment, and shows that these devices are viable as softmatter strain gauges. Next, new fabrication methods are introduced that incorporate freezing of the GaIn alloys. This enables the creation of tall, 3D circuit features that can be used to tune the capacitance of a given device. Additionally, freezing improves the ease with which the metal can be handled, manipulated, and altered. Conductive materials can be incorporated into polymers, creating composites with improved permittivity, which in turn will improve capacitance. By using GaIn alloys as the iv conductive inclusion and forming liquid metal embedded elastomers, highly stretchable dielectric materials can be fabricated. These composites can be elongated to as high as 600% strain and with dielectric improvements of over 400%. Continued advances of GaIn based technology can enable inherently compliant electronic skins and soft capacitive sensor arrays that can be incorporated into stretchable bio-compatible devices or bio-mimetic robots.