A Rapid and Straightforward Liquid Metal Patterning Technique on Paper Using Laser Printer for Soft Electronics

A gallium‐based liquid metal patterning for paper‐based soft electronics is reported. A method is proposed that is rapid and straightforward liquid metal patterning on a printing paper using selective wetting properties obtained by lyophilic and lyophobic coating. The paper is coated with a lyophilic waterproof agent followed by a lyophobic printing toner with a desired pattern in an inverse pattern. Then a sponge roller soaked with liquid metal is rolled and filled into the exposed waterproof agent coating to create the desired pattern. It is believed that this is one of the most convenient yet quite versatile liquid metal patterning methods. The minimum line pattern width, spacing, and patternable angle are 50 μm, 200 μm, and 3°, respectively. To demonstrate versatility, a university symbol and a map shape are coated with liquid metal. The bending, folding, cutting, pasting, and burning of the light‐emitting diode circuit on paper is also demonstrated. Additionally, the deposition of 3 μm Parylene on top of the liquid metal pattern works as a passivation layer, and no damage is noticed when the liquid metal pattern on the paper is repeatedly folded and bent. Finally, a pressure sensor using the proposed method by measuring resistance is demonstrated.