Design And Simulation Of A New 4H-SiC MESFET With Ultrahigh Upper Gate For High Efficiency

With the continuous improvement and development of semiconductor materials and devices fabrication technology,4H-Si C MESFET shows more excellent characteristics of high power,high frequency,high temperature and high pressure resistance,and has great potential and competitiveness in the field of microwave power devices applications.With the development of green development concept,the design of 4H-Si C MESFET structure with high efficiency has become a new research direction and trend.However,many new 4H-Si C MESFET structures are proposed to improve the DC and RF characteristics of devices.Therefore,in order to respond to the development trend of high efficiency devices,on the basis of ensuring that 4H-Si C MESFET has good DC and RF characteristics,we should also pursue the high efficiency characteristics of device structure.In this paper,the structure model of 4H-Si C MESFET with ultrahigh upper gate(UUMESFET)is established in ADS software,and an improved UU-MESFET structure with high efficiency(IUU-MESFET)is proposed.The effects of saturation drain current,threshold voltage,trans-conductance and breakdown voltage on power added efficiency(PAE)are simulated by using the UU-MESFET structure model.According to the simulation results,it can be concluded that increasing the saturation drain current,threshold voltage,trans-conductance and breakdown voltage of the UU-MESFET structure is beneficial to the improvement of the PAE.Based on these simulation results,the distance H from upper gate to channel surface in UU-MESFET structure is optimized by ISE TCAD software simulation.The simulation results show that increasing the distance H from the upper gate to the channel surface can improve the saturation drain current and breakdown voltage of the device structure,and reduce the threshold voltage,trans-conductance and gate-source capacitance of the device.This is because increasing the distance H from the upper gate to the channel surface in the device structure can increase the effective channel thickness,reduce the size of the depletion layer under the gate,and modulate the electric field distribution in the channel.However,changing the distance H from the upper gate to the channel surface in UU-MESFET structure cannot simultaneously improve the saturation drain current,threshold voltage,trans-conductance and breakdown voltage.Therefore,the influence of distance H from upper gate to channel surface on PAE in UU-MESFET structure is simulated by ADS.The results of ADS simulation show that when the distance H from the upper gate to the channel surface in UU-MESFET structure is 0.1 um,the PAE of the device reaches its peak value,and then the PAE of optimized UU-MESFET structure is 70.99%.The DC and RF characteristics of the IUU-MESFET structure are also simulated and compared with those of the UU-MESFET structure in this paper.The simulation results of ISE TCAD software show that the saturation drain current of IUU-MESFET and UUMESFET are 530.2 m A/mm and 549.3 m A/mm,respectively.Compared with UU-MESFET,the saturation drain current of IUU-MESFET is reduced by 3.5%.The threshold voltages of the two structures are-9.16 V and-9.82 V,respectively.The threshold voltage of the IUUMESFET structure is 6.7% higher than that of the UU-MESFET structure.For the two structures,the breakdown voltages are 143 V and 156 V,while the trans-conductance is 57.84 m S/mm and 55.93 m S/mm,respectively.Compared with the UU-MESFET structure,the breakdown voltage of the IUU-MESFET structure decreases by 8.3%,while the transconductance increases by 3.4%.All the above simulation results show that the IUUMESFET structure not only has high PAE,but also has good DC and RF characteristics.