Performance Analysis Of U-gate Tunneling Field-Effect Transistors

With the rapid development of integrated circuit process technology,the feature size of MOSFET is gradually decreasing and getting closer to the physical limit.At this time,the appearance of short channel effects has seriously affected the performance of traditional MOSFET.Through theoretical and experimental research,it has become increasingly difficult to use methods of size reduction to improve device performance,and at the same time it faces serious power consumption problems.To solve these problems,a tunneling field effect transistor?TFET?based on band-to-band tunneling?BTBT?mechanism has been proposed.TFETs not only can effectively inhibit the short channel effects,but also can break the limit of the traditional MOSFET subthreshold swing?SS?which can not be lower than60 mV/decade,thus greatly reducing the switching power consumption of the device.Therefore,TFET is considered to be one of the most promising ultra low power devices.TFETs are still facing the difficulties to achieve the on-state current comparable with that of MOSFETs.To solve this problem,researchers mainly improve the structure or material of the device.Improvements in materials can use narrow bandgap materials such as III-V compound families and Germanium-Tin?GeSn?materials with direct tunneling.Structural improvements include multi-gate or ring-type gate structures to enhance gate-to-channel control.These methods could partly improve the device performance,but also bring some corresponding problems at the same time.In this paper,a U-gate TFET structure is proposed with a lightly doped spacer layer between a channel layer and a drain region,which can effectively suppress the Off-state current.This paper studies the influence of structural parameters and materials on the electrical properties of U-gate TFETs based on Sentaurus TCAD.?1?Working mechanism and electrical characteristics of U-gate TFET.Ge based U-gate enhanced p-channel TFETs?PTFETs?were designed and characterized.By analyzing the energy band diagram and band to band tunneling generation rate(G_BTBT),it is found that On-state current and Off-state current can be controlled by BTBT and source-drain tunneling?SDT?mechanisms,respectively.It is found that with the increase of the spacer layer thickness(T_sp),the Off-state leakage current of the device is significantly reduced,and the subthreshold swing characteristic is improved.In addition,by reducing the thickness of the channel layer?TC?or increasing the gate length?Lg?,the On-state current of the device is improved.By increasing the source-drain voltage|V_DS|,the on-state current and off-state current of the device increase.?2?Electrical characteristics and parameter optimization of GeSn/SiGeSn II heterojunction U-gate TFETs.GeSn based TFETs have become a hot spot in the research of microelectronics.The band gap of GeSn alloys at?point is continuously tuned from 0 to0.8 eV.As the Sn composition increases up to 6.5¹1%,GeSn can be changed from the indirect bandgap material to the direct band.Based on these material properties,GeSn TFETs have demonstrated the improved electrical performance compared to other group IV alloys devices and even III-V TFETs.By tuning the alloy compositions,type-II heterostructure and lattice matching can be obtained at GeSn/SiGeSn interface.U-gate GeSn/SiGeSn hetero-TFETs achieve a significant improvement in electrical performance compared to the GeSn homo transistors.By increasing the thickness of the spacer layer,reducing the thickness of the channel layer,and increasing the gate length,the electrical performance of the U-gate TFET device can be improved.In addition,it is found that as the Sn composition increases,the On-state current of the device is improved,but the Off-state characteristics are deteriorated.By optimizing the spacer layer and forming a heterojunction between the spacer layer and the channel layer,a higher performance U-gate hetero-TFET can be obtained.