Study Of Novel Nitride-based Tunneling Field Effect Transistors

As process critical dimension continues to shrink,the power consumption has become one of the core problems which restricts the improvement of chips performance and applications.Developing next generation device of low power consumption is one of the effective ways to solve this issue.In recent years,tunneling field effect transistors(TFETs)are becoming one of the research hotspots in the field of ultra-low power consumption electronics.Compared with traditional MOSFET devices,TFETs have many advantages which is significant for the reduction in power consumption,such as lower off-state leakage current,steeper subthreshold swing(SS<60 m V/decade)and stronger immunity to short-channel effects,leading to great application potential.Innovative research work has been carried out in this thesis,aiming at three main bottlenecks faced in the development of TFETs devices,namely,low on-state current(I_ON),ambipolar current,and random dopant fluctuations(RDF).To solve these problems,four new types of TFETs are proposed based on the excellent characteristics of III-Nitride materials.For each proposed device,the working mechanism is deeply explored and the circuit-level simulation is analyzed.Based on these works,some research results and laws are obtained,which can provide a guidance for practical application.The main research results of this thesis are summarized as follows:1.An In Ga N TFET with polarization-doped source and drain as well as an In N interlayer(PD-IL TFET)was proposed and studied.The proposed device could achieve polarization doping in active area by using polarization effect of the In_xGa_1-xN material with a graded In composition,which avoids the RDF problems effectively.In addition,an In N insertion layer is adopted to enhance the electric field in tunneling junction,which greatly improved the I_ON and subthreshold characteristics.The simulation results show that the average subthreshold swing(SS_avg)of PD-IL TFET is as low as 1m V/dec,and the switch current ratio(I_ON/I_OFF)reaches 1×10¹³.2.A novel vertical In N/In Ga N heterojunction TFET with hetero T-shaped gate as well as polarization-doped source and drain region(In N-Hetero-TG-TFET)is studied.On the one hand,the proposed device could achieve the polarization doping in active area with the help of the polarization effect in the In Ga N/In N heterojunction,which avoids the RDF problems effectively.On the other hand,the method which can adjust the channel energy band and improve the electrical characteristics of the device by setting up a hetero T-type gate is proposed.At the same time,this thesis deeply analyzes the correlation between device characteristics and structure.The simulation results show that the I_ON>10^-4A/?m when V_DS=0.5V and V_overdrive=1V,and the I_ON/I_OFF reaches 1×10¹³.3.A vertical junctionless In Ga N TFET with trench electrodes(MSM-JLTFET)is first proposed and the conduction mechanism is discussed in detail.This device adopts the line tunneling mechanism which enhance the I_ON effectively.The simulation results show that the I_ON of MSM-JLTFET reaches 4.34×10^-4A/?m when V_DS=0.5V and V_overdrive=1V,and the I_ON/I_OFF reaches 1×10¹².4.Based on the MSM-JLTFET,an L-shaped junctionless In N TFET with trench electrodes and hetero gate(LMSM-JLTFET)is proposed.Compared with the MSM-JLTFET,the active region material of LMSM-JLTFET has a narrower band gap and smaller electron effective mass,which is more suitable for TFETs.Besides,LMSM-JLTFET can be fabricated by a simpler manufacturing process and get a better performance in circuit application compared to MSM-JLTFET.The simulation results show that the pull-down transmission delay(T_{p HL})is 0.2ps,and the power delay product reaches 25ps×n W in circuit application.