Investigation On Physical Mechanism And Optimal Design Of Electrically Doped Tunneling Field Effect Transistor

With the development of integrated circuit,the core device of VLSI technology is still the field effect transistors(FET)based on the physical mechanism of drift-diffusion.However,with the reduction of the device's characteristic size,the existence of short channel effect,gate oxygen tunneling effect and other non-ideal effects make its subthreshold swing(SS)higher than 60mV/dec at room temperature,thus increasing part of the static power consumption of the integrated circuit.For this reason,researchers have proposed tunneling field effect transistors(TFET)in recent years.Based on the mechanism of carrier tunneling,the theoretical SS of TFET can be lower than 60mV/dec.However,there are still some problems in the practical application of TFET,such as the tunneling junction between the source region and the channel.That needs mutation to improve the on-state current.The low tunneling probability of the carrier makes the on-state current insufficient,and the ambipolar current exists under the reverse gate voltage.In view of the unsatisfactory electrical characteristics of TFET,this paper optimizes structural design for traditional TFET,and analyzes the physical mechanism and current change trend of different structures.In order to avoid the physical doping of the traditional TFET structure,the researchers proposed the TFET based on electrical doping.In this paper,a new type of electrically doped line tunneling FET which combines the advantages of TFET structure optimization and electrical doping is proposed.Through the optimization of the gate structure,the line tunneling of carriers can increase the on-state current.The basic contents of this paper are as follows:(1)Based on the traditional TFET research,the classification and research of electrically doped TFETs are conducted,and the physical mechanism of electrical doping based on charge plasma(CP)is studied.(2)In view of the unsatisfactory on-state current,the growth of the device's on-state current under different gate overlapping source structure and the influence of different device parameters on its on-state current are studied through optimizing the gate structure.Based on the inherent ambipolar current of TFET,the ambipolar current suppression of TFET under different gate structures and drain doping types are studied.At the same time,considering the structure of Gaussian doping drain region TFET,the trend of different structure parameters for ambipolar current suppression is further discussed.(3)In view of the need of physical doping to realize the abrupt junction in TFET,the charge plasma TFET(CP TFET)is investigated.CP TFET can form the active region of TFET in the lightly doping or doping-less semiconductor channel via covering the metal with specific work function in the source and drain region.In order to solve the shortage of on-state current in CP TFET,the symmetrical double gate structure in traditional CP TFET to the asymmetrical double gate structure is optimized.As a result,a new type of charge plasma line tunneling field effect transistor(CP LTFET)is obtained.CP LTFET can achieve larger line tunneling area and tunneling probability under the same device size,thus improving the on-state current.The physical mechanism and structural parameters of the CP LTFET are simulated and analyzed.It is found that the on-state current of the CP LTFET is improved and it is not easy to be limited by the device materials and parameters,and its electrical characteristics are improved compared with traditional structure.In addition,we changed the traditional junctionless channel into a PN junction and proposed the CP source region tunneling field effect transistor(CPS TFET)based on the PN junction channel region.The CPS TFET reduces the type of deposited metal by doping the drain region,and optimizes the gate structure,which improves the on-state current and suppresses the ambipolar current.In conclusion,based on the research of TFET,the physical mechanism of electrical doping based on CP is studied.In view of the electrical characteristics of TFET,the effects of different gate structures extending on the increase of device on-state current and the suppression of ambipolar current are studied.Moreover,the device structures that can enhance the on-state current and effectively reduce the ambipolar current of TFET are proposed.Finally,a new device structure which can generate carrier line tunneling in the CP TFET based on the electrical doping and the optimized TFET structure is put forward.The simulation tools are used to analyze the device parameters' influence on the electrical characteristics of the different structures,and to optimize the device performance in several ways.Through replacing the undoped channel in the CP TFET with a PN junction and optimizing the gate structure,a CP source line tunneling field effect transistor(CPS LTFET)based on the PN junction channel region is obtained.In general,the research on electrically doped TFETs provides certain guidance for the further relevant studies.