Fabrication And Properties Of Flexible Strain Sensor Based On Plasma Treatment Reduced Graphene Oxide

Flexible wearable sensors are used to realize real-time human body signal acquisition under various conditions,playing a vital role in the modern society as the rapid development of Internet of Things.Modern flexible mechanical sensors based on graphene have been widely reported,with various optimization schemes and preparation methods for different application scenarios.To realize the fabrication of flexible graphene strain sensor with excellent performance,we treated graphene oxide（GO）with H₂-N₂plasma for simultaneous reduction and surface modification,by which the electrochemical performance of graphene can be improved.Also,micro-patterning scheme and microstructure feature for the sensing layer were employed as optimal design of the device,achieving better strain response range,reliability and sensitivity.Here,a novel fabricating method of high-performance flexible strain sensor based on graphene with environmental friendliness and high efficiency is described.The morphology of prepared sensors were characterized,and the mechanical and electrical properties were studied.Besides,an application for detecting human physiological signals has been realized by prepared sensors.The study on performance of fabricated devices shows that the Nitrogen-doped reduced graphene oxide（N-rGO）prepared by plasma treatment possesses good mechanical and electrical properties and fewer surface defects,and can be applied to the reduction preparation of micro-patterned graphene thin films.The GF（Gauge Factor）of N-rGO thin films prepared by vacuum filtration transfer combining with plasma treatment can reach～44-100 under 0.25%-1%strain.Micro-structured PDMS stamps were obtained by photoetching,dry etching and reverse molding of the silicon template for micro-contact printing process.With plasma treatment reduction,a complete neet rectangular-grid-shape N-rGO film with thickness of about 2μm and line width of 10μm was successfully prepared.Raman characterization proved that the graphite structure of N-rGO treated by H₂-N₂ plasma was restored during reduction.The mechatronic test shows that the strain sensor based on micro-patterned graphene has better sensitivity（GF～8-23,0.1%-0.25%strain）under small deformation,comparing with that of the sensor based on N-rGO film without micro-pattern of similar thickness,and can work stably under 0.25%strain.Graphene flexible sensors based on microstructure was prepared by filling graphene nanosheets into the surface microstructure of PDMS substrate by brush coating and blade coating method.The performance testing results show that the introduction of designed microstructure effectively optimizes the tensile properties of stress sensor and broadens its application range.GF reaches～13-21 under 1%-10%strain and～95 under 20%strain.The sensor is assembled into a dual-channel multi-state strain sensor.The optimized structure of the sensor was obtained through testing and analysis,and the sensor was applied to monitoring of human hand movements.Distinguishing of force under complex conditions（including wrist bending,clenching fist,external force pressing,palm stretching,etc.）was realized,and the working principle was analyzed.