Study On Surface Acoustic Wave Devices With Graphene Electrode

Surface acoustic wave（SAW）devices have been widely used in many applications such as radar,electronic warfare,wireless communication,fiber-optic communication and bio-sensor,bio-medical,microfluidics,lab on chip due to its unique advantages.Traditional surface acoustic wave（SAW）devices utilize metal（Al,Au,etc.）interdigital electrode（IDT）,which could produce quality load effect and enhance the parasitism of the device.What's more,metal material is visible which is unable to be applied in transparent devices.Graphene is a new material that is super thin and near zero mass.In this paper,a novel SAW device based on graphene IDT is designed and fabricated.The structure and performance of the SAW device are analyzed by the simulation and experimental results.Graphene is a potential candidate for SAW device electrodes because of its high electron mobility and near zero mass.This paper mainly focuses on the study of application of graphene in SAW device electrodes.Through a serious of simulation and experiments,grapheme is proved to be suitable for SAW devices.Based on the analysis,we fabricated SAW device based on graphene electrode with excellent performance.This thesis include:1.First of all,the paper discusses the theory of the excitation and propagation of SAW and the working principle of IDT.COM model of the IDT is established,based on the model typical parameters of the SAW device are simulated.Among what the influence of resistance of IDT on the device characteristics is studied mainly.In this part,theoretical feasibility of grapheme working as electrodes is proved.2.Wet transfer technique of graphene is studied and optimized,single layer and multi-layer（two,three,four）graphene with large area is transferred successfully.Raman spectrometer,AFM,four-point probe and UV spectrophotometer are used for characterization following.Properties of different layer graphene are analyzed.With the layer increase from single to four,surface roughness increases and square resistance decreases from 250Ω/□to 76.6Ω/□successively.Visible light transmittance reduced from97.7%to 90.3%.3.SAW devices with IDT on LiNbO₃ substrate are fabricated,and their feature parameters with different layer graphene are measured.With the increase of graphene layer,electromechanical coupling coefficient of SAW device increases,and insertion loss decreases,signal amplitude enhances.Four-layer graphene SAW device show the best performance.A typical center frequency of a SAW device is 91.65MHz with transmission signal amplitude of 20dB and electromechanical coupling factor k of 2.8%.And also,temperature and humidity sensing properties are measured.The results show excellent potential to applied as temperature and humidity sensors.4.Transparent SAW devices with Glass/ZnO/Graphene structure are fabricated,and their performance is tested.For the substrate,piezoelectric layer and electrodes are all transparent,the transmittance of the whole device could reach to above 80%.The novel device has great potential in invisible field.Temperature and humidity sensing properties of the device are tested,based on what transparent SAW breath sensor is made.Breathe frequency and body state can be detected by the as-made sensor.