Research On Carrier Lifetime Control Of High Voltage FSRD

Fast and Soft Recovery Diode(FSRD)is usually used in anti-parallel with main switching devices such as Insulated Gate Bipolar Transistor(IGBT)and Integrated Gate Commutated Thyristor(IGCT)to provide a freewheeling loop for the load inductance.With the continuous improvement of the performance of the main switching device,the performance requirements for the anti-parallel diode are also improved.There are two ways to improve the performance of FSRD,one is through the improvement of device structure,and the other is through carrier lifetime control.At present,with the continuous development of carrier lifetime control technology,the effect of carrier lifetime control on the improvement of diode characteristics is becoming greater and greater.Taking the 4.5kV FSRD as an example,the influence of different carrier lifetime control methods on the diode characteristics was studied in this thesis from the perspective of improving device characteristics and improving reliability.Sentaurus-TCAD software was used to simulate the characteristics of the diode,and the different carrier lifetime control diodes were analyzed and studied from the internal mechanism and external characteristics.The main research contents and results are as follows:Firstly,the static and dynamic characteristics of the high-voltage FSRD and the principle of carrier lifetime control technology are analyzed,and the dependence of various properties on the carrier lifetime is studied,laying a theoretical foundation for subsequent research.Secondly,the influence of single carrier lifetime control on high-voltage FSRD was studied.The overall lifetime control was studied by setting different lifetime values from 0.1?s to 30?s.Then,the single-sided local lifetime control was studied by setting the positions of different low lifetime regions and their low lifetime values.The result shown that single-sided local lifetime control can achieve a good compromise between on-state,cut-off and reverse recovery characteristics.Thirdly,the influence of composite carrier lifetime control on high-voltage FSRD was studied.The composite carrier lifetime control had been studied through the overall and local composite lifetime control,and the double-sided local lifetime control.The result shown that the two types,of composite carrier lifetime control can shorten the current tailing time and suppress the dynamic avalanches.Finally,the advantages and disadvantages of different carrier lifetime control methods were compared and analyzed,and single-sided local carrier lifetime control was finally selected as the final solution,which can achieve fast and soft recovery characteristics,and reduce the reverse recovery time from 355ns to 314ns.The softness factor was increased from 0.60 to 1.68,and the dynamic avalanche on the cathode side was eliminated;at the same time,the leakage current at high temperature(400K)was almost unchanged,but the forward voltage drop slightly increased,from 1.25V to 1.68V under the rated current density of 100A/cm2.The research results of this thesis provide a certain engineering reference for the research and development of high-voltage fast soft recovery diodes.