Design And Simulation Of 4H-SiC MESFET With High Efficiency

Along with the maturity of the third generation semiconductor gradually,and the improvement in 4H-SiC MESFET fabrication,the advantages of 4H-SiC MESFET device has become manifest signally.It is rapidly expected to be the best candidate in the microwave power semiconductor,which gets the researcher's attention.Due to the excellent material properties and device performance,4H-SiC MESFET is more and more applied to high temperature,high voltage,high frequency,high radiation,high power and other harsh environment.4H-SiC MESFET is the ideal choice among numerous microwave power semiconductor devices.In recent years,some remarkable achievements on 4H-SiC MESFET has been made at home and abroad,but there is a contradiction in the power-frequency to ensure high saturation drain current and high breakdown voltage simultaneously.The improvement in DC characteristics always causes the deterioration in RF characteristics.All of these issues are needed to be worked out.A novel structure named 4H-SiC metal semiconductor field effect transistor with double upper gate and recessed p-buffer(DURP MESFET)is proposed in this paper for the first time,which ensures high saturation drain current and high breakdown voltage simultaneously.And the radio frequency characteristic has been improved by the decrease in the gate-source capacitance greatly.The thickness of channel layer under the gate is increased by the upper gate near source and drain side,which makes an increase in the carrier in the channel,further obtains greater saturation drain current.The potential in the channel is no longer only focused on the gate corner near drain side,because of a new peak electric field at the left of drain upper gate introduced by upper gate,which weakens the electric field at the gate corner near the drain side,the electric distribution becomes more uniform,thus optimizing the breakdown characteristic.The distance between the upper gate and channel surface is larger due to the double upper gate,which will make the depletion region around the gate extend toward to the channel surface and achieve a decrease in the area of the depletion region.On the one hand,the area of valid channel increases,further the drain current becomes great.On the other hand,RF characteristics is achieved to be improved by a distinct decrease in the gate-source capacitance.Unfortunately,the trans-conductance is diminished because of the large distance between the upper gate and channel bottom,that is to say,the ability of the gate to control the channel drops.Hence,a recessed p-buffer is employed to decrease the distance to improve trans-conductance.The height of upper gate,the depth and length of recessed p-buffer and the location of recessed p-buffer are optimized to gain the optimal size parameters.The relationship between the performance parameters of device and the efficiency of power amplifier is analyzed,which may give the new way for device design.The simulated results indicate that when the height of upper gate is 0.1?m,the depth and length of recessed p-buffer are 0.05?m and 0.35?m respectively,the performance of DURP MESFET are the most outstanding.Compared to DR MESFET with the same structure parameters,the maximum saturation drain current(drain-source voltage is 40 V,gate-source voltage is 0V)of the new structure is increased by 22.5%.The breakdown voltage is grown from 109 V to 129.3V,enlarged by 17.9%.The maximum output power density is 8.24W/mm,increased by 43.6%.Meanwhile,the radio frequency characteristic is improved by 8.9%.The saturation drain current and breakdown voltage of the new structure are enhanced simultaneously.DURP MESFET has superior DC performance and RF characteristic comprehensively.In this paper an improved clival gate 4H-SiC MESFET with recessed drain drift region and recessed p-buffer layer(RDRP-CG MESFET)is proposed.The recessed p-buffer near source side makes the thickness of the channel thicken and ensures a great saturation drain current.However,the increase in the thickness of channel always leads to the reduction in breakdown voltage.In order to avoid the decrease in breakdown voltage caused by thicker channel,a recessed drift region near drain side is introduced,which can reduce the thickness of channel,and make the distribution of electric field in the channel layer more uniform,thus improving the breakdown voltage.The simulated results show a 51.8% increment in breakdown voltage for RDRP-CG MESFET in comparison with CG MESFET which presents the same size parameters.The radio frequency performance shows a slight reduction,which doesn't affect the application in high frequency.In this paper,there is qualitative analysis about the influence of channel thickness on drain current and breakdown voltage,there is no optimization for the size parameters of recessed drain drift region and recessed p-buffer.