3D-Integrated and Multifunctional All-Soft Physical Microsystems Based on Liquid Metal for Electronic Skin Applications

This paper presents 3D-integrated and multifunctional all-soft physical microsystems, which are composed of a soft sensor, a soft interconnector, and a soft readout circuit. The microsystems utilize gallium-based liquid metal (eutectic gallium-indium alloy, EGaIn) and poly(dimethylsiloxane) (PDMS) and are fabricated using an advanced EGaIn thin-line patterning technique based on soft lithography. Combining the scalable fabrication process and a vertical integration approach using EGaIn-filled soft vias, two types of all-soft physical microsystems are investigated using analytical, numerical, and experimental approaches and demonstrated to highlight high-density integration, multifunctional sensing capability, as well as system-level flexibility and stretchability: (i) a finger-mountable strain sensing microsystem with reduced temperature sensitivity and (ii) a fingertip microsystem for simultaneous proximity, touch, and pressure sensing. The demonstrated fabrication and integration approaches provide a path towards all-soft and highly integrated wearable physical microsystems for human-machine interfaces, soft robotics, and healthcare applications.