Liquid metal-based paper electronics: Materials, methods, and applications

The liquid metals exhibit both the properties of liquids and metals and have a low melting point near room temperature. As a low-cost and easy-to-obtain flexible substrate, paper has significant advantages for large-area and multilayer flexible circuit fabrication. This has led to a growing interest in liquid metal-based paper electronics among both scientists and industry. In order to promote the development and application of liquid metal-based paper electronics, this review will summarize and analyze the progress from three perspectives, including liquid metal inks, printing methods, and their applications. A variety of liquid metal-based electronic inks are introduced, and their advantages and disadvantages are discussed. Then, a comparison of typical fabrication methods has been presented, including chemical interaction-based selective adhesion and surface roughness-based transfer printing. A number of emerging applications used and expected to be applied to liquid metal-based paper electronics have been demonstrated. Finally, paper electronics based on liquid metals are discussed along with their challenges and opportunities for the further development. In the future, further investigations and applications of paper electronics based on liquid metals are expected.