Design And Research Of TFET With Field Plate Structure

Under the guidance of Moore's Law,the gate length of MOS devices in integrated circuits is decreasing,and has been reduced to about 10 nm.As the critical dimensions of integrated circuits continue to decrease,many problems caused by small size begin to appear.For example,the increase of static power consumption caused by the increase of off-state leakage current has become one of the main bottlenecks restricting the continued development of integrated circuits.In order to continue Moore's Law,researchers have made a series of efforts,including finding new devices that can replace MOS devices.The TFET based on the quantum tunneling principle has attracted great interest from researchers due to its extremely low off-state leakage current and subthreshold swing of less than 60mV/dec at room temperature.With the in-depth development of TFET study,researchers have focused on improving the structure of TFETs to achieve larger on-state currents and lower subthreshold swings.A variety of novel TFET structures have been proposed,such as the use of a narrow bandgap material in the tunneling region.By reducing the electron tunneling barrier by this method,the tunneling probability can be effectively increased,thereby increasing the tunneling current,but this method also causes a significant increase in the off-state leakage current of the TFET.Another method is to use a vertical channel,such as a U-shaped gate or an L-shaped gate structure,to significantly increase the tunneling area without increasing the device area,but this method leads to a significant increase in the process difficulty of fabricating a TFET.A more effective way to increase the on-state current is to enhance the electric field in the tunneling region.Based on this idea,a new TFET structure using field plate structure to enhance the electric field of the tunneling region of the TFET is proposed.The main research contents of this thesis are as follows:In order to study the main causes of TFET performance degradation,the tunneling mechanism when applying different bias voltages on the TFET gate is simulated and analyzed.It is found that the concentration of the electric field at the sharp corners of the source region of the vertical TFET causes the tunneling at the sharp corners to open early,resulting in a significant step in the current-voltage curve of the TFET,the threshold voltage of the device is significantly reduced,the subthreshold swing is increased,and the turn-off window is reduced even causing the device cannot be turned off.In order to analyze the influence of various structural parameters and process parameters on the electrical properties of the GFP-TFET proposed in this paper,the effects of device size,doping concentration,epitaxial region doping type,metal electrode work function and dielectric relative permittivity on device performance parameters were simulated.It is found that the electric field distribution of the epitaxial region and the intrinsic region can be adjusted by changing the dielectric relative permittivity and the work function of the metal electrode,thereby achieving the purpose of suppressing tunneling at the sharp corners of the source region.In view of some of the problems in GFP-TFET,two effective solutions are proposed in this paper.The problem of the early opening of tunneling at the sharp corner of the source region,which is prevalent in vertical TFETs,can be avoided by using a corner-cut TFET structure.The use of SiGe materials in the epitaxial region can effectively increase the on-state current and achieve a lower average subthreshold swing,while having little effect on the ambipolar current.