All-Flexible And Stretchable Capacitive Pressure Sensor Arrays Based On Liquid Metal Droplet/Film Electrodes

In recent years,flexible pressure sensing has drawn broad attention from scientists and researchers.Highly sensitive,accurate,and fast responding pressure sensors have been widely developed and applied onto wearable devices,soft robots,decentralized healthcare,intelligent housing,and many other areas.However,the tradeoff between electrical performance and mechanical stretchability limits the development of materials fabrication methods for flexible pressure sensing,which remains a great challenge in this field.Among the conductive materials,gallium-based liquid metal,which features low Young's modulus and high metallic conductivity,is a great candidate for stretchable electronic devices.My thesis starts with a brief review of the development of flexible electronic materials and their latest applications in wearable pressure sensors.I propose to develop capacitive pressure sensor arrays based on all-flexible materials for the optimal performance in both electronics and mechanics.My thesis includes the developments of two types of devices.In the first part,I introduce the design,fabrication,and performance evaluation of a capacitive pressure sensor based on liquid metal droplets.By using the liquid metal droplet as the electrode of the sensor,this design features a sensitive capacitive responsiveness derived from the electrode deformation induced by the external mechanical load.I have developed a protocol to prepare flexible circuits by patterning the liquid metal particles followed by mechanical sintering.Through this method,an array of liquid metal droplet-based sensors has been fabricated and evaluated preliminarily.In the second part,I introduce a different design to fabricate the capacitive pressure sensor arrays based on dome-structured liquid metal film electrodes.The film electrodes are prepared on elastic membranes by directly spraying of liquid metal through a stencil.The dome structures are created by applying a negative pressure,assisted with a mold.The as-prepared all-flexible electrodes can deform dramatically under the mechanical loads,thus improving the sensitivity to the pressure.The fabrication procedure of this kind of sensors is straightforward,cost-effective,highly producible,and suitable for scaled-up production.The sensor is capable of detecting pressure on curved surfaces,and is robust enough to endure repeated tensile strains up to 94%.Benefiting from the unique dome structure of the liquid metal film electrodes,accurate pressure detection can be maintained under 45%tensile strainThe applications of the sensor array have been demonstrated in pressure distribution mapping and identification of cervical postures.By calculating the pressure of each sensing unit,profiles of different external load sources can be distinguished.In addition,the sensor can be mounted on the neck of a volunteer for potential applications of force monitoring in rehabilitation.I have successfully demonstrated identification of different cervical postures by real-time pressure distribution tracking.In summary,I have designed two liquid metal-based capacitive flexible and stretchable pressure sensors,and performed the evaluation and the proof-of-concept demonstration of force mapping.These devices developed in my thesis promises wide applications in wearable electronics integrating sensitive and highly stretchable pressure sensing units.