Title:  All-soft and 3D-integrated Multifunctional Microsystems Enabled by Liquid Metal and Soft Lithography

Committee: 

Dr. Brand, Advisor       

Dr. Ghovanloo, Chair

Dr. Inan

Abstract:

The objective of the proposed research is to explore all-soft and 3D-integrated multifunctional microsystems enabled by gallium-based liquid metal (eutectic gallium-indium alloy, EGaIn) and soft lithography. Lightweight, flexible, and stretchable wearable electronics have gained significant attention for various sensing applications ranging from entertainment to healthcare, but the mechanical mismatch between soft biological skins and conventional rigid and bulky electronic materials often limits the ultimate usability and leads to hard-soft material interface failure. To circumvent this limitation, the use of conducting liquid, such as EGaIn, has great potential because of its non-toxicity, low melting temperature, and excellent electrical and mechanical properties. However, EGaIn patterning challenges, particularly regarding minimum feature sizes, size-scalability, uniformity, and residue-free surfaces, have limited the demonstration of high-density, soft microelectronic devices. This research investigates an advanced EGaIn thin-film patterning based on soft lithography and a compatible vertical integration technique, which enable size-scalable and high-density EGaIn-based soft microelectronics. The proposed patterning technique overcomes the current limitation in EGaIn fabrication by demonstrating uniform and residue-free EGaIn thin lines with width from single micrometers to several millimeters at room temperature and under ambient pressure. Also, vertical integration using EGaIn-filled soft vias facilitates high-density integration as well as system-level flexibility and stretchability. By combining the scalable fabrication process and vertical integration approach, two types of all-soft and 3D-integrated microsystems are demonstrated: i) a finger-mountable strain sensing microsystem with reduced temperature sensitivity and ii) wireless and battery-free chemical microsystems for liquid- and gas-phase volatile organic compound (VOC) sensing.