Research On The Electrical Characteristics And Analytical Model Of Tunneling Field Effect Transistors

Very large scale integration follow Moore's Law,with metal oxide semiconductor field effect transistors(MOSFETs)shrinking in size and increasing chip integration.When MOSFET size enters the nanometer scale,it is subject to secondary effects that lead to large off-state currents and static power consumption,and MOSFETs have a subthreshold swing(SS)limit of 60 m V/dec at room temperature.Tunneling field effect transistors(TFETs)using quantum tunneling mechanism on-state currents can break this theoretical limit of 60 m V/dec.With lower static power consumption and steeper switching characteristics than MOSFETs,TFETs have promising applications in lowpower integrated circuits.Researchers see them as one of the most promising alternatives to MOSFETs in the post-Moore era,however,the current analytical modeling of TFET devices is not well studied,and TFETs also suffer from the difficulties of low open-state currents due to low tunneling efficiency,the difficulties of double conduction,the difficulties of highly doped mutation junctions due to the physical structure of the device,and the difficulties of poor RF characteristics.Therefore,the development of physically based analytical models for TFETs is not only useful for guiding device design but also important for TFETs in circuit applications.In this thesis,an exponential surface energy band model from source to drain is developed for TFETs based on the two-dimensional Poisson equation,which takes into account the effect of doping concentration in the source and drain regions without any fitting parameters and without involving numerical iterations and correction processes.Based on the surface energy band model a model of the tunneling distance is derived which is in accordance with the operating principle of the TFET,the tunneling distance is an extremely important physical quantity to characterise the TFET device current.Based on the classical Kane theory,an approximate expression of the electric field strength is obtained by using the ratio of the forbidden band width to the tunneling distance,resulting in a model for the tunneling current of the TFET.Using the relationship between energy band and potential,a model of the device trench surface potential is developed based on the surface energy band model,and the alternating modulation effect of the gate voltage and drain voltage on the trench potential is portrayed.The carrier sources of the tunneling current and TFET device charge are analysed,and the channel carrier accumulation of the TFET device in different states is described,leading to a charge model and capacitance model for each end of the gate,source and drain.This thesis analyses the operating principle of electrically doped tunneling field effect transistors(CP TFETs)based on their electrical doping characteristics,fully considers the energy band landing in the uncovered electrode region of CP TFET devices,applies the TFET modelling method to CP TFET devices,and uses the two-dimensional Poisson equation to model the exponential surface energy band from source to drain for CP TFETs,taking into account the the effect of doping concentration in the source and drain regions,again without involving numerical iterations and correction processes.Based on the surface energy band model,a tunneling distance model is derived that is consistent with the operating principle of the CP TFET,and a CP TFET tunneling current model is developed using classical Kane current theory.The analytical device model in this thesis was validated using Sentaurus TCAD software and the fit was good.