Laser-Driven Transfer Printing of Hyper-Stretchable Liquid Metal Electronics

Liquid metal (LM) alloys can conform to large deformations for flexible and stretchable electronics. The high surface energy and low wettability of LM hinder the binding with flexible substrates, making it difficult to precisely pattern LM-only electronic devices. Herein, a laser lift-off-and-fuse (LLOF) process is proposed for transfer printing LM onto flexible substrates with a patterning resolution of hundreds of microns. Liquid metal nanoparticles (LM NPs) from the donor substrate are transferred and subsequently activated on the receiver substrate by laser pulses, resulting in uniform, conductive patterns with arbitrary designs. Specifically, the LLOF method involves two steps: a transferring step by high-fluence laser pulses and an in situ activation step by low-fluence laser pulses. The LLOF method is additive and free of thermal or chemical damage to soft substrates. It brings superior quality and processability for high-precision LM flexible devices on stretchable substrates. Multiphysics numerical simulations provide a detailed demonstration of the transient vaporization of LM NPs and reveal a dynamic vapor-driven droplet transfer process. Finally, LM flexible devices with high conductivity, large ultimate strain, excellent fatigue resistance, and controllable strain conductivity are demonstrated, respectively.