Research On Self-consistent Modeling Method Of Graphene FET Large Signal Equivalent Circuit

The rapid advancement of modern information technology has led to the continuous improvement of circuit integration.Traditional devices based on silicon-based materials have approached their physical limits and cannot meet today’s needs for miniaturization and high performance.Graphene has attracted a lot of research from scholars at home and abroad because of its excellent performance,in order to continue to promote the development of Moore’s law.Because the band gap of undoped graphene is zero,the on-state current of undoped graphene field effect transistor（GFET）,which is directly used as channel material,shows bipolar characteristics.The switching ratio is small,it is difficult to turn off completely,and it is difficult to reach saturation.Therefore,this paper studies the large signal modeling method of doped GFET.The main contents include the following:（1）Based on the two-dimensional density of states（DOS）and drift-diffusion equation of undoped graphene,the main parameters involved in the modeling of undoped GFET are physically analyzed.According to the working principle of undoped GFET,a large signal model suitable for the whole working region is proposed.The model considers the contribution of holes and electrons to the total drain current,and can accurately describe the asymmetric conduction behavior of undoped GFET.The accuracy of the undoped GFET large signal model is verified by comparing the I_DS-V_GS and I_DS-V_DS of the large signal model with the measured data.The analysis process of large signal modeling of undoped GFET provides a theoretical basis for large signal modeling of B/N doped GFET.（2）The non-zero band gap of graphene was induced by four different concentrations of B/N substitution doping.Through the physical analysis of the main parameters involved in the modeling,it is found that Q_sh and C_q are multiple logarithmic functions that depend entirely on the channel potential V_ch.Therefore,Newton-Raphson iteration method（NR）is used to solve Q_sh,C_q and V_ch self-consistently to obtain accurate potential-charge relationship,and a large-signal self-consistent model of B/N doped GFET is established.The simulation data of the model are in good agreement with the measured data,which verifies the accuracy of the model.The B/N doped GFET completely suppresses the bipolar characteristics and the switching ratio is significantly improved,and the current reaches saturation.Therefore,B/N doped GFETs meet the requirements in digital and analog/RF applications.（3）Based on the self-consistent model of B/N doped GFET and the channel charge density Q_sh,the charge expression of each port is derived by using the Ward-Dutton charge distribution scheme.The intrinsic circuit model is written in Verilog-A language in ADS,and the external parasitic circuit is built to establish the large signal equivalent circuit model of B/N doped GFET.The circuit simulation data are basically consistent with the measured data,which verifies the effectiveness of the self-consistent modeling research on the large-signal equivalent circuit of B/N doped GFET in this paper.