Ultrasound Powered Wetting and Filling of Liquid Metal into Ultrafine Channels for Flexible Electronics

Abstract

Liquid metals (LMs) that possess both metallic and fluidic properties at room temperature promise numerous benefits in flexible electronics. However, preparing fine LM circuits with complex architectures at the microscale and below poses great challenges due to large surface tension of LMs, hindering the development of flexible electronic devices with increased integration and/or complexity. Herein, we develop a facile strategy that employs ultrasonic stimulation to power the wetting and filling of LMs into non-wettable elastic microchannels for ultrafine LMs circuits fabrication. Taking advantage of ultrasound-induced asymmetrical acoustic pressure within LMs, rapid and complete filling of LMs into microchannels as fine as ~ 750 nm could be achieved within several seconds without destroying the soft substrate. Electromechanical investigations suggested that the LM-filled microchannels by ultrasound possessed excellent cyclic stability and robustness. Through ultrasonic filling and patterning ultrafine LM circuits, we created a miniaturized pressure sensor array capable of accurately sensing load pressure and spatial information. The sensitivity of the finger-wearable strain sensor was further enhanced by 22.6 times via introducing local microstructures and filling LM inside the microchannel. Finally, we demonstrated the efficient preparation of complex LM circuit patterns powered by ultrasound, e.g., integrated circuits, spiderman, and snowflake patterns with multiple interlaced branches, planar structures, blind holes as well as vertical architectures, all of which could hardly be achieved by conventional injection methods. This work presented an ultrasound-based fabrication method for versatile LMs circuits, providing a platform technology for the advancement of next-generation compact and integrated flexible electronics.