Optimization And Simulation Of L-type TFET Devices

In recent years,the size of MOSFET devices has continuously decreased under the guidance of Moore's Law.With the ever-decreasing size of MOSFET devices,the effects of short-channel effects and quantum effects on device performance become more and more serious.Tunneling Field Effect Transistors?TFETs?can achieve a sub-threshold swing?SS:Sub-threshold Swing?lower than 60mV/dec due to freedom from Boltzmann distribution.Faster turn-on and turn-off and drastically lower device power consumption are considered the most powerful alternatives to MOSFETs.Compared with MOSFETs,TFETs have a lower sub-threshold swing?SS?,and a larger switching current ratio can be obtained at lower operating voltages.However,the traditional TFETs still have two major disadvantages:?1?its on-state The current is too small;?2?The reverse bipolar effect is obvious.Based on the L-type TFET,this paper optimizes the device structure so as to achieve the purpose of suppressing the bipolar effect without affecting the start-up characteristics.The main contents are as follows:First,the L-type TFET structure optimization:?1?the use of heterogenous gate dielectric structure makes the gate in the source region and near the drain of the channel region with different gate control capabilities,which effectively inhibit the reverse bipolar current.The simulation results show that,compared with the traditional LTFET,the LTFET with hetero-gate dielectric structure reduces the reverse bipolar current by three orders of magnitude,and the switching current ratio is increased by 100 times;?2?The introduction of lightly doped drain regions.When reverse tunneling occurs,the tunneling junction near the drain region has lower electric field intensity at the junction due to lower doping concentration,and the tunneling current decreases.The results show that when LTFET with lightly doped drain structure is used,V_ds=0.5V,the shutdown current is reduced to the order of 10^-15,and the switching current ratio is effectively improved;?3?The underlapped gate to drain structure reduces the effect of the gate voltage to the electric field at the reverse tunneling junction.As the simulation results shown,the reverse bipolar current of the device is reduced by about three orders of magnitude after the introduction of the underlapped gate to drain structure.Next,the Analog/RF characteristics of the above optimized structure were compared and analyzed.The simulation results show that the above optimized structure can effectively reduce the gate-drain capacitance of the device.When V_ds=1.8V,the gate-drain capacitance can be reduced to half of the traditional LTFET.Meanwhile,the transconductance of the device is basically not affected during the optimization process.As a result,the device characteristic frequency f_T and gain bandwidth product are significantly improved.Finally,the paper also analyzes the process implementation of LTFET and its optimized structure.Through the process simulation tool Sprocess in Sentaurus TCAD,all the process steps involved in the LTFET device are simulated in detail,and the electrical characteristics of the device structure obtained by Sprocess are performed simulation.The simulation results are in line with the expected results.In summary,this article has conducted in-depth research on the structure optimization and fabrication of traditional TFET devices.The results show that the introduction of hetero-gate dielectrics,lightly doped drain structures and underlapped gate to drain structure can effectively suppress the bipolar effect of TFET devices.The results of this study have guiding significance for the structural optimization and process implementation of TFETs.