Structural Design And Performance Optimization Of Novel Gate-All-Around Tunneling Field-Effect Transistors

Over the years,with the rapid development of integrated circuits,the process size of transistors has shrunk from the micron level to the nanometer level.This reduction in process size has led to increased integration and improved performance of integrated circuits.However,as the process size shrinks,secondary effects such as short-channel effect,narrow-channel effect,and drain introduction barrier reduction effect become more and more obvious in metal-oxide-semiconductor field-effect transistors(MOSFETs),which not only affect the performance of transistors,but also hinder the continuation of Moore's law.Therefore,researchers at home and abroad have started to study new transistors,expecting that these problems can be solved.Tunnelling field-effect transistors(TFETs)are one of the most promising new devices for next-generation integrated circuits because of their low power consumption,ability to break the Boltzmann limit of 60mV/dec,and high switching current ratio based on the band-and-band tunneling operation principle.However,TFETs devices have the disadvantages of bipolar effect,low open-state current,and unstable subthreshold slope.To address the drawbacks of TFETs,the following studies are conducted in this thesis.First,this thesis proposes a novel TFET device:the germanium-around-source gate-all-around tunneling field-effect transistor(GAS GAA TFET).Three devices,GAS GAA TFET,silicon source gate-all-around TFET(Si GAA TFET)and germanium source gate-all-around TFET(Ge-source GAA TFET),are simulated by Sentaurus TCAD.The experimental results show that the on-state current of the GAS GAA TFET reaches the same level as that of the Ge-source GAA TFET,which is about 104 times that of the Si GAA TFET,while the off-state current of the GAS GAA TFET is reduced to one-fifth that of the Ge-source GAA TFET.In addition,the variance of the subthreshold slope of the GAS GAA TFET is the smallest among the three devices,proving that the subthreshold slope of the GAS GAA TFET is more stable than the other two devices.Thus,the GAS GAA TFET has the two advantages of high on-state current and stable subthreshold slope,and has a low off-state current.Then,this thesis investigates the effect of gate work function on the bipolar effect of GAS GAA TFETs and mitigates the bipolar effect of GAS GAA TFETs by a gate work function of 4.4eV.Then,the processing flow of GAS GAA TFETs is designed based on the processing process of nanotube MOSFETs.Next,two devices,O-GAS GAA TFET and P-GAS GAA TFET,are proposed in this thesis.It is found that the Overlap structure in the O-GAS GAA TFET can suppress the electric field at the device channel and drain contact locations.the off-state current of the O-GAS GAA TFET with an Overlap length of 6nm is about 17.8%of that of the GAS GAA TFET,so the Overlap structure can reduce the off-state Therefore,the Overlap structure can reduce the off-state current of TFETs devices,and O-GAS GAA TFETs have the advantage of low off-state current.P-GAS GAA TFETs are designed to increase the probability of band-tunneling by adding an n-type Pocket at the source-channel contact,which bends the source valence band downward and closer to the channel conduction band.The open-state current of P-GAS GAA TFETs with a Pocket doping concentration of 1018cm-3 is increased by 3.9%compared to that of GAS GAA TFETs.Therefore,the Pocket structure can increase the open-state current of TFETs devices,and P-GAS GAA TFETs have the advantage of high open-state current.Finally,this thesis designs the processing flow of O-GAS GAA TFET and P-GAS GAA TFET based on the GAS GAA TFET processing flow,respectively.