Design Of 1200V FS-IGBT With Thin Wafer And High Breakdown Robustness

Insulated Gate Bipolar Transistor(IGBT)has the advantages of small on-state voltage drop,high current density,high breakdown voltage,fast switching speed and good thermal stability.It has been widely used in power electronic systems.Field Stop IGBT(FS-IGBT)with thin wafer has become the mainstream of current design due to its low loss,but it has the problem of low breakdown robustness.This thesis aims to address the issue of low breakdown robustness of 1200V FS-IGBTs with thin wafer.Firstly,the operating principle of FS-IGBT,preparation process flow,as well as the basic information of the sample chips were introduced.Secondly,the breakdown characteristics of the sample chips were tested and found that the existing FS-IGBT chips failed when the breakdown current reached 1mA.In this thesis,the failure mechanism was studied in depth and found that the breakdown failure of FS-IGBTs occurred mainly in the transition-terminal region and cell region.The reason for the failure in the transition-terminal region of IGBTs is that the local electric field concentration effect which occurred at the bottom of deep trench in transition region and junction bend position of field limiting ring in terminal region results in forming weak points of breakdown.The failure in the cell region is mainly due to the serious breakdown negative resistance characteristics of IGBTs,which lead to current concentration effect.Thirdly,the thesis designed and optimized an FS-IGBT with high breakdown robustness,the transition-terminal structure with zero-potential deep P-ring is optimized to eliminate the breakdown points of FS-IGBT,the cell structure of an Electric Field Modulation IGBT(EFM-IGBT)with a heavily doped N-type layer at the bottom of the trench gate is optimized,which improves the trade-off between the IGBT breakdown negative resistance characteristic and the on-state voltage drop,so as to reduce the conduction loss of the device and improve the breakdown robustness of the device at the same time.Finally,the test results show that the breakdown voltage of optimized IGBT device is 1250V,the on-state voltage drop is 1.478V at the current density of 100A/cm~2,and the breakdown failure current is more than 8mA.All the parameters reach the design indicators.