The Study On Modeling For Schottky-barrier Surrounding Gate NMOSFET

In addition to the introduction of new materials and new technologies,it is also an important link to improve the device structure for the purpose of further improving the performance of MOSFET.The surrounding gate and schottky barrier source/drain structures are two alternatives which have more potential for the improvement of the device structure.And the schottky barrier-surrounding gate MOSFET(SB-SG MOSFET),which combines the surrounding gate and schottky barrier source/drain structures,is one of the potential devices of MOSFET in recent years.However,there were scarce studies on its theoretical models due to the complexity of the SB-SG MOSFET's structure and physical mechanisms.Many physical characteristics were often studied by the simulations and experiments.Starting from the structure and physical mechanisms of the SB-SG NMOSFET,the paper systematically studied the threshold voltage,drain-induced barrier thinning(DIBT)effect,drain-source current,transconductance,capacitance and frequency based on the basic device physical equations,the main research work and achievements obtained are as follows:1.The threshold voltage and DIBT effect of the SB-SG NMOSFET have been studied.The source electron enter the channel in the form of the field emission is verified as a threshold voltage conditionby analyzing the physical mechanism of the drain-source current.The surface potential distribution of the SB-SG NMOSFET was obtained by solving the two-dimensional poisson equation in the cylindrical coordinate system while the image force barrier loweringeffect and radialquantum effect under the small size were introduced as the perturbed items.The threshold voltage model was established through associating the minimum surface potential with the threshold voltage condition,and the simulation results of the threshold voltage model were compared with the Sentaurus TCAD simulation results to verify its rationality.The DIBT model was established based on the threshold voltage model at the same time.According to the results obtained,the paper analyzed the relationships between the channel length,electronic intrinsic schottky barrier height,drain-source voltage,channel radius,channel doping concentration and the threshold voltage,DIBT effect under different channel length respectively as well as the physical mechanisms,comparing the DIBT effect of the SB-SG NMOSFET and the drain-induced barrier lowering(DIBL)effect of the DSD SG NMOSFET,thus obtaining the corresponding evolution rules.The results show that the DIBT effect of the SB-SG NMOSFET is lower than the DIBL effect of the DSD SG NMOSFET.2.The drain-source current and transconductance of the SB-SG NMOSFET have been studied.Starting from the current equations of different mechanisms and threshold voltage,the drain-source current models based on the current mechanism which on the basis of analyzing the composition and influencing factors of the drain-source current in the 2.2.1 of the chapter 2 and threshold voltage in the 3.1.2 of the chapter 3 were established respectively.The higher accuracy of the drain-source current model based on the threshold voltage contrast tothe drain-source current model based on the current mechanism was verified through the simulation analysis carried out by the Sentaurus TCAD.Subsequently,the corresponding transconductance model was established based on the threshold voltage-based drain-source current model.The relationships between the electronic intrinsic schottky barrier height,bias voltage,channel length,channel radius,channel doping concentration and drain-source current,transconductance as well as the physical mechanisms were studied respectively,which is of great value for the analysis and research on the device.At the same time,the drain-source current and transconductance characteristics of the SB-SG NMOSFET were compared with those of the DSD SG NMOSFET.The results show that the important factor to determine the drain-source current and transconductance of the SB-SG NMOSFET is the electronic intrinsic schottky barrier height,and the schottky barrier with low barrier height shall be selected for the source/drain of the device.3.The capacitance and frequency characteristics of the SB-SG NMOSFET have been studied.According to the normalized inversion charge areal density model in the 4.2.3 of the chapter 4,the total gate capacitance and gate-drain capacitance models were established first,then the cut-off frequency and maximum oscillating frequency models were obtained based on the capacitance models and transconductance model,the feasibility of the above models were verified through the Sentaurus TCAD simulation analysis.The influence of the electronic intrinsic schottky barrier height,gate-source voltage,drain-source voltage,channel length,channel radius and channel doping concentration on the capacitance and frequency as well as the physical mechanisms were analyzed respectively,considering the design optimization of the frequency characteristics.The capacitance and frequency characteristics of the SB-SG NMOSFET and DSD SG NMOSFET under the same conditions were compared respectively at the same time.The results show that the capacitance and frequency characteristics of the SB-SG NMOSFET are better than those of the DSD SG NMOSFET,and the electronic intrinsic schottky barrier height is the important factor to improve the frequency characteristics of the SB-SG NMOSFET.The works of the paper lay a theoretical foundation for the in-depth study and analysis of the SB-SG NMOSFET.