Design Of High Energy Efficiency 4H-SiC MESFET With Dual Channel

Because 4H-SiC material has excellent characteristics such as wide band gap,high electron saturation velocity,high critical electric field,and high thermal conductivity,it has broad prospects in the fields of high frequency,high temperature,high power,and radiation resistance.SiC-based metal semiconductor field effect transistors(MESFETs)have incomparable advantages over Si and Ga As devices in the microwave field,and have important applications in aerospace,microwave communications,electronic countermeasures,and large-capacity information processing.At present,most researches are based on simultaneously improving the AC and DC characteristics of the device.There is less research on improving the efficiency of the device,and lower efficiency means greater energy waste,so the design for efficiency is particularly important.In this thesis,a dual-channel MESFET device model is established in the ADS software,and the AC and DC parameters that affect the power added efficiency of the device are simulated and analyzed.The simulation results show that the threshold voltage,transconductance,and gate-source capacitance of dual-channel devices are more sensitive to power added efficiency.Among them,reducing the absolute value of the threshold voltage,gate-source capacitance,and transconductance helps to improve the power added efficiency.Because the dual-channel MESFET has low power added efficiency,therefore,the threshold voltage,gate-source capacitance,breakdown voltage and other AC and DC parameters of the device are improved by optimizing the thickness of the channel layer,thereby improving the power added efficiency.The analysis of the simulation results shows that when the thickness of the upper channel layer in the channel increases,the breakdown voltage increases,and the absolute value of the threshold voltage,gate-source capacitance,and transconductance decrease.When the thickness of the upper channel layer is 0.2?m,the power added efficiency is the largest.Compared with the original structure,the optimized dual-channel MESFET structure has increased the power added efficiency by48.95%.At the same time,the influence trend of drain-source voltage,input power,and frequency on the power added efficiency is simulated and analyzed.The simulation results show that the power added efficiency increases first and then decreases with the increase of drain-source voltage,input power,and frequency.PAE reaches its maximum value at the inflection point,that is,when the drain-source voltage is 16V,the input power is 30d Bm,and the frequency is 0.9GHz,the power added efficiency reaches the maximum value of71.03%.Following the design idea of dual-channel MESFET,a 4H-SiC MESFET structure with locally highly doped and undoped channel is proposed(LDUS MESFET).This structure is based on the partially undoped double recessed gate device structure(DRUS MESFET),and is formed by partially high doping under the lower gate and optimizing its undoped area.High doping under the lower gate can increase the transconductance and saturation current,while the undoped area between the drain side and the upper gate can increase the breakdown voltage and improve the gate-source capacitance.By designing the thickness and doping concentration of the highly doped region and optimizing the undoped region,a better power added efficiency can be achieved.Simulation results show,when the thickness of the highly doped region under the lower gate is 0.05?m,the doping concentration is 6×10¹⁷cm^-3,and the thickness of the undoped region is 0.05?m,the PAE of the device reaches the maximum value of 64.10%.Compared with DRUS MESFET,LDUS MESFET has a certain degree of improvement in saturation current,transconductance,threshold voltage,and gate-source capacitance.Therefore,LDUS MESFET has better AC and DC characteristics.Through ADS simulation,the PAE of LDUS MESFET is 85.80%higher than that of DRUS MESFET.Therefore,LDUS MESFET has certain advantages in terms of high energy efficiency.Through the optimization simulation of the dual channel 4H-SiC MESFET structure and LDUS 4H-SiC MESFET,the PAE is improved compared with the original structure,which verifies the proposed high energy efficiency design theory.Lay the device foundation for the design of high-efficiency and high-performance RF power amplifier.