The Study On Fabrication And Properties Of Flexible Variable Gate Graphene Field Effect Strain Sensor

Graphene has attracted mucn attention as a kind of two-dimensional materials which possesses lots of outstanding properties including excellent electrical condctivity,transparency,flexibility and high carrier mobility.Rcently,some flexible electrical devices made of graphene are widly researched in the fileds of Biological electronic sensing equipment,wearable electronic devices due to its excellent electrical properties,simple fabrication,and flexiblility.An flexible graphene field effect strain sensor with variable gate is fabricated by the graphene,Ion Gel,and silvemanowires.The graphnene was grown on an ridge array by CVD and transferred to a flexible substrate which owned the same structure with graphene.The element is used to detect the pressure related to the contact area of gate and grphene changed by the movement of the grid.The model of the array was made on silicon by photolithography and etching technology.It was filled with TPU so that we could get the copper model by the way of electroplating on TPU.Finally,graphene grown on copper by CVD method and transferred onto PDMS substrate.The element was fabricated with the graphene,gate made by silver nanowires and ion gel as a dielectric layer.The graphene was characterized by the Raman in all steps of the experiment,including the growth of graphene by CVD,transferring graphehe onto PDMS substrate,and the deformation of the element.The graphene used in the experiment was a single layer graphene.It was hardly damaged seriously in the fabrication of the element.It still appeared excellent electrical properties after deformation.But the maximal strain of the gate moving must be controlled in 48%.The field effect of strain sensor is measured along the edge and the vertical direction.The maximum effective strain the element can withstand is 48%.As the strain increases,the variable current of the element increases in linear.When the grid voltage was fixed,field effect current in the vertical direction increases exponentially as the strain increaes until 48%and the speed of the current increasing becomes slowly when the strain is more than 36%.The maximum current change rate is 8.5%.As the same time,the field effect current in the horizontal direction increases linearily and the maximum current rate of change 12.7%.The structure model of the element has been established to study the relationship between strain and current of the element in theory when the gate was fixed.The simulation on the strain of the surface of the element was finished with Abaqus.There was almost compression strain on the surface of the edge so that strain could not destory graphene on it.After repeated deformation,the resistance of the sansor is almost unchanged so that the element has good flexibility and repeatability.The element fabricated in the paper can detect the strain by the way of changing the contact area between the gate and graphene.It means to change the channel width of the element.Compared to the graphene plane strain sensing element,the strain sensor with 3D structure should be able to withstand more strain.