| Graphene is a two-dimensional material with the thickness of only one single atom.Due to its high mechanical strength and ductility,graphene has been realized as an excellent sensing material for piezoresistive,piezoelectric,displacement-based,and resonant types of pressure sensors.Among those types of sensors,the resonant pressure sensors endow the properties of digital outputs,robust anti-electromagnetic interference,and excellent stability,which has become one of the research hotspots at present.The essential subjects for developing resonant pressure sensors are analyzing,fabricating,driving,and detecting the graphene-based resonator.Nevertheless,the graphene-based resonators derived from suspended graphene on the large size cavity face the difficulties of unreliably suspending graphene with a low yield.To settle the above problems in this thesis,the resonance characteristics of graphene were primarily analyzed through theoretical modeling and finite element modeling,followed by designing the fabrication procedures of the large-scale suspended graphene film based on an upside-down transfer method.A Fabry-Perot(F-P)graphene resonator was fabricated,while a photo-thermal driving and detecting subsystem was designed.After integrating the above resonator and subsystem,the graphene resonant pressure sensor prototype has been tested and verified.The research results of the thesis provide a theoretical and technical route for the design of photothermally drived graphene resonant pressure sensors.The main research contents of this paper are as follows:1.Modeling and analysis of graphene resonance characteristics.Aiming at calculating the resonant frequency of graphene resonator,the theoretical model of prestressed thin plate has been established.This model is used to calculate the resonant frequency of graphene resonator.Then,the results are compared with the finite element simulation results and the experimental results in the literature to verify the accuracy of the theoretical modeling.Further,the Q value changes of graphene resonator under different temperature and pressure has been analyzed by COMSOL.Finally,the resonant frequency changes under different pressure difference has been analyzed by COMSOL.2.Fabrication of fiber F-P graphene resonator.Based on the problem of low yield in the fabrication of large-size suspended graphene,we design and realize the fabrication method based on the inverted floating method.With the help of this method,6-8 layers of graphene(with a thickness of about2nm)are suspended in a circular cavity with a diameter of 125μm as the average yield has reached 80%.Aiming at fabricating the fiber F-P graphene resonator,precision displacement equipment and sample fixture system are designed and realized.The fiber F-P graphene resonator has been fabricated with this system.3.Graphene resonance pressure sensing prototype system integration.First,the overall plan and composition of the graphene resonance pressure sensing prototype system are introduced,and then the key components are optimized and experimentally analyzed.The length of the F-P cavity is set no more than 100 μm and is operated at the linear point.The air-tightness of the resonator is verified and the displacement sensitivity of the resonator is tested to be about 153nm/k Pa.Then a photothermal drive system of the resonator is designed and implemented.By this system,the displacement sensitivity of the resonator is tested to be approximately 633.3 μV/k Pa.Then,the optical F-P interference detection system is designed and realized.The relationship between detection light and the length of resonator F-P cavity was tested by the optical F-P interference detection system.The result was a little different from the theoretical value.Finally,the detection path was tested,and the results show that the noise level can meet the working requirements of the graphene resonance pressure sensing prototype system. |
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