Research On Model Of Two Dimensional Materials Based High-frequency Nanoelectromechanical Resonators

High frequency nanoelectromechanical resonators have broad potenial applications in the fields of high quality factor devices,high sensitivity sensors,single molecular detectors and macro quantum effect detections.Due to the nanoscale physical size,two-dimensional physical structure,excellent mechanical and electrical properties of two-dimensional materials,such as graphene and molybdenum disulphide,high frequency nanoelectromechanical resonators made of two-dimensional materials have unique advantages in critical technologies such as device fabrication,excitation and detection.Thus,they are currently the focus of nanoelectromechanical system?NEMS?research.The two-dimensional material based nanoelectromechanical resonator model plays an important role in optimizing device structure,performance and NEMS system design.Due to the semiconductor properties of two-dimensional materials such as graphene and molybdenum disulfide,the nanoelectromechanical resonator is also called as resonant channel transistor?RCT?.However,different from the traditional high frequency field effect transistor,the two-dimensional material suspended above the substrate simutenously acts as a carrier transport and a mechanical vibrator.Thus,the traditional transistor model cannot describe the unique characteristics of RCT,such as mechanical resonance,electromechanical coupling,and mechanical nonlinearity.Therefore,in this thesis,the equivalent circuit model is studied for the high frequency two-dimensional based nanoelectromechanical resonator.The main research includes:1.Reserch on small signal equivalent circuit model of high frequency graphene nanoelectromechanical resonator.Due to electromechanical coupling induced by the mechanical vibration of the high frequency nanoelectromechanical resonator,a transconductance(g_mm)depicting the mechanical resonance characteristics is added based on the traditional field-effect transistor small signal equivalent circuit topology,and then high frequency equivalent circuit model of the nanoelectromechanical resonator is builded.Furthermore,to solve the problem of inaccurate phase description at the resonant point of the model,the phase drift introduced by the interaction of mechanical resonant signal and excitation signal is considered in the g_mm model,which improves the phase accuracy of the model.Finally,because of the iterative calculating problem of the mechanical resonant frequency with the interaction of electrostatic force and graphene stress,a calculation method based on the capacitance between gate electrode and channel?C_g?is proposed,and an iterative compution is carried out by using the objective optimization function of bias correlation.The results show that root-mean-square?RMS?error of the small signal model is less than 4%,and the resonance frequency error is less than 3%within the range of large bias voltage?-20V²0V?.2.Reserch on nonlinear model of high frequency two-dimensional based nanoelectromechanical resonator.Due to the absence of electromechanical coupling in traditional semiconductor field-effect transistor model,this thesis improves the parameter variation caused by mechanical resonance in I-V and nonlinear capacitance models,and proposes a gate capacitance C_g model including electromechanical coupling effect with channel vibriating.Furthermore,considering that the suspended channel stress of the nanoelectromechanical resonator is related to the ambient temperature,the temperature parameter of the material is added in the stress calculation in this thesis.As a result,the applicable temperature range of the model can cover125K³00K.Due to the bandgap of monolayer molybdenum disulphide,which is different from graphene,we build graphene-based and molybdenum disulphide-based nanoelectromechanical resonator model,respectively.Finally,because of the mechanical nonlinear effect,the vibration displacement,obtained by solving the nonlinear vibration equation,is embedded to the gate capacitance model,and a high frequency nanoelectromechanical resonator model including mechanical nonlinear effect is developed.Validation results show that,under different bias conditions,the high frequency nanoelectromechanical resonator model can well predict linear scattering?S?parameters and nonlinear fundamental component,second harmonic and third harmonic components,and the third order intermodulation response,as well as the mechanical nonlinear resonance produced by the beam"hardening"and"softening",which can prove the accuracy of the model.