Facile and Rapid Method for Fabricating Liquid Metal Electrodes with Highly Precise Patterns via One‐Step Coating

Abstract

Gallium‐based alloys, which are virtually non‐toxic liquid metals at room temperature, are considered highly promising electrode materials for state‐of‐the‐art electronics with new form factors. Herein, a facile and rapid method to fabricate liquid metal electrodes with highly precise patterns via a one‐step coating is presented. For this work, polymeric stencil masks with dual structures, comprising upper and lower structures for injecting and molding the liquid metal, respectively, are used for direct patterning of the liquid metal via spray deposition for few seconds, enabling the formation of complex and minute patterns including long thin lines and hollow forms. This method can be adapted to 3D substrates of various materials without any surface treatment, owing to the intrinsic adhesive and flexible properties of the polymeric masks ensuring conformal contact with non‐flat surfaces, and is also expected to be applicable to sub‐micron patterns. In addition, a number of highly flexible/stretchable electronic applications, exhibiting no change in electrical conductivity upon consecutive structural deformations, are demonstrated on various substrates including human skin. It is anticipated that these results will not only spur the further development of flexible/stretchable electronics, but also significantly contribute to the innovative on‐site fabrication of wearable electronics with high durability.

Applications of liquid metals in nanotechnology

“…LM wires formed by 3D printing remain in the micro range (B2 mm in width), while the direct patterning of LMs can, in theory, achieve sub-micron resolution. 154,155 To date, sub-micron scale EGaIn patterns were achieved with features as small as B180 nm using a hybrid electron-beam and soft lithography method. 156 In comparison, sub 10 nm LM nanodroplets have been reported using mechanical agitation methods.…”

Flexible and Stretchable Liquid Metal Electrodes Working at Sub-Zero Temperature and Their Applications

“…Changes in the electrical resistances upon lateral stretching are shown in Figure 4a. At room temperature, the electrical resistances of both materials slightly increased with the stretching ratios, which is possibly originating from structural deformation [26]. At the temperature of −10 °C, the cracks were generated inside the EGaIn film upon the lateral stretches (see Figure 4b), leading to significant reduction in the film continuity.…”

“…Although Galinstan shows outstanding properties including flexibility and stretchability even under cold conditions, its high surface tension and rapid oxidation rate hinder the fabrication of desirable patterns for electronic devices and circuits in comparison with other functional materials [13][14][15]. Various methods for Galinstan patterning thus have been developed and enhanced, including microfluidic injection [16][17][18][19][20][21], photolithography [22,23], stencil lithography [24][25][26][27], imprint lithography [28], microcontact printing [29,30], and composite material synthesis [31]. Each of these methods has individual advantages (i.e., high processability, high resolution limits, high stability, or cost-effective fabrication); however, integrating all the advantageous elements is still a challenge.…”

Stretchable Conductors Fabricated by Stencil Lithography and Centrifugal Force-Assisted Patterning of Liquid Metal

“… 16 , 19 A broad range of manufacturing methods have been developed for structuring liquid gallium alloys at micrometer or submicrometer scale by taking advantage of its moldability. For example, liquid gallium alloys can be structured at the micrometer scale by using picosecond laser ablation, 20 printing directly on substrates via nozzles, 19 , 21 injecting into microfluidic channels, 22 , 23 screen printing 24 or spray deposition via stencils, 25 or using PDMS stamps to transfer patterns. 26 , 27 Although using PDMS stamps to transfer liquid metal patterns shows promising results, the substrate has to be molded to have desired channels, which prevents this approach to be applied on a wide range of substrate materials.…”