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

Abstract 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.