Fabrication And Characterization Of Pressure Sensor Based On Laser Induced Graphene

With the development of health monitoring and electronic skin,flexible wearable pressure sensors are attracting widespread attention.However,it is still a huge challenge to manufacture high-performance pressure sensors reliably,cost-effectively and efficiently.Graphene is a very strong material with good elasticity.Its Young’s modulus is 1.0TPa,and its tensile strength is130GPa.Based on the excellent performance of graphene,this thesis studies the graphene flexible pressure sensor applied to the human body’s tiny signals.In the thesis,screen printing and laser direct writing techniques are used to prepare flexible pressure sensors,and the piezoresistive properties of sensors prepared in different ways are studied.In both methods,an asymmetric double-layer structure is used to control the initial resistance.First,the graphene flexible pressure sensor is prepared by screen printing technology.The screen printing technology is simple,efficient,low-cost,and has a wide range of printability.The surface microstructure of the sensor electrode is constructed by screen printing.During the screen printing process,the surface morphology of the sensor electrode is changed by adjusting the viscosity of the ink and the mesh number of the screen,which affects the sensitivity of the sensor.The flexible pressure sensor fabricated based on screen printing has high sensitivity(～1.86 k Pa^-1,ranging from 3.4 to 150 Pa),with a response time of only 4 ms,and can remain stable even in more than 2,000 cycle tests.The sensor also performs well in practical application.In the monitoring of pulse,the principal pulse,tide pulse and dicrotic pulse are clearly recorded.When performing voice recognition,the frequency spectrum of the entire song is also well reflected.Later,a flexible pressure sensor composed of multi-walled carbon nanotubes（MWCNTs）and laser-induced graphene（LIG）was developed.The key piezoresistive material,MWCNTs/LIG,was prepared using a simple,convenient and efficient laser direct writing technology.By virtue of this designed three-dimensional crosslinked structure,MWCNTs/LIG hybrid endows the asymmetric pressure sensor with combined excellent characteristics of a high sensitivity(2.41 k Pa^-1 ranging from 0 to 200 Pa),prominent detectable limit（～1.2 Pa）,very responsive recovery（2 ms）,and remarkable durability（>2?000 cycles）.This high-performance MWCNTs/LIG asymmetric pressure sensor can clearly detect various subtle human motions（such as breath,vocal vibration,finger movement,and wrist pulse）in real time.Moreover,the prepared 3×3 MWCNTs/LIG sensor array can accurately identify different pressures at different points.Benefit from its outstanding sensing performances,the as-fabricated pressure sensor has vital inspiration for widespread practical applications in human monitoring of physiological activities,electronic skin,and other wearable fields.