Direct Physical Vapor Deposition of Liquid Metal on Treated Metal Surface

Liquid metal has garnered significant interest as a potential stretchable wiring material for next-generation stretchable electronics. The operation of substrates within these electronics necessitates adherence to three primary criteria for the wiring of electronic substrates to facilitate the integration of stretchable circuits in society. First, the wiring’s top surface must remain exposed to allow for the straightforward attachment of electronic components following the wiring fabrication. Second, the design of the wiring pattern should not be subject to significant constraints. Third, the substrate’s top surface needs to be clean and devoid of excess conductive material to mitigate the risk of unintended short-circuits. Previous studies have not introduced a liquid metal patterning method that meets all of these criteria. Physical vapor deposition (PVD) is commonly employed for depositing hard metals on nonstretchable substrates such as silicon and glass. However, when subjected to direct PVD, liquid metal forms independent nanoparticles, losing conductivity due to its exceptionally high surface tension and the presence of surface oxide films. Consequently, the direct deposition of liquid metals without subsequent physical stimulation, such as the application of pressure, has been deemed challenging. In our study, we enhanced the substrate surface’s wettability by treating it with copper chloride, thereby facilitating the direct deposition of liquid metals onto the substrate surface. The oxide film on the liquid metal’s surface is disrupted upon contact with the copper chloride-treated substrate, enabling the nanoparticles to coalesce and establish electrical connectivity, thereby preserving conductivity even when stretched. The resultant stretchable wiring exhibited a fine line width of approximately 50 μm and a thin film thickness of approximately 1 μm, ensuring a robust bond with the substrate surface. Consequently, this wiring technique supports diverse patterning designs when combined with processing methods such as photolithography.