Study On Mechanism And New Structures Of Reverse Blocking IGBT

The symmetric blocking ability allows reverse blocking insulated gate bipolar transistor?RB-IGBT?cut down the components,power loss and redundancy of application system,which can improve the energy efficiency and system reliability in application of the T-type and matrix converters.With a long drift region,the non punch through?NPT?IGBT can obtain a bidirectional blocking ability.However,the NPT IGBT has large on-state voltage drop(V_on)and turn-off energy loss(E_off).The field stop?FS?IGBT wins a superior V_on-E_off tradeoff,owing to the existence of N-buffer layer.The FS IGBT doesn't possess the bidirectional blocking ability nevertheless.In order to address above problems,this thesis will propose and investigate two RB-IGBT devices by simulations.1.A RB-IGBT with shorted collector field plate?SCFP?is proposed?SCFP FS RB-IGBT?.The novel device has three strcuture features:Shorted Collector Field Plate?SCFP?,discontinuous N2 layer;and highly doped N1 in emitter side.In the forward blocking process,the trenches make the depletion region expand laterally and vertically under the N1 layer and enhance the E-field in thr drift region,and shield the high E-field from the J1 junction?p-body/N1?,avoiding premature breakdown at J1.The device obtains a high forward breakdown voltage?BV_F?.In the reverse blocking process,the SCFP helps the depletion boundary extend laterally and vertically between the discontinuous N2,which enhances the E-field in the drift region and avoids premature breakdown at J2.Finally,the E-field is stopped by the N1 together with trenches,a high reverse breakdown voltage?BV_R?is obtained.High doping N1 plays a role as carrier storage layer to increase the carrier concentration and make carriers distribution more uniform.Thus the device gains a low V_on.During turn-off process,the electrons are extracted by the low resistance channel formed below the N2 layer by the SCFP.Therefore,a low E_off and a good V_on-E_off tradeoff are achieved.E_off is reduced 49%and67.2%compared with those of BEFE FS RB-IGBT and NPT RB-IGBT,respectively.2.A RB-IGBT with a collector assisted trench gate?CAG?is proposed.It features a spilt gate and a high doping N1 layer in emitter side,and Collector Assisted trench Gate,?CAG?.In the forward conduction state,when a negative voltage is applied to the CAG,hole injection efficiency is enhanced.Moreover,N1 acts as carrier stored layer and stores the holes.Consequently,a low V_on is obtained.In the forward blocking state,a positive voltage is applied to the CAG to attract electrons around the CAG,forming an equivalent N-buffer layer to stop E-field.Thus a high BV_F is obtained.Compared with FS IGBT,the BV_R of the CAG RB IGBT is not restricted by the high doping N-buffer in the reverse blocking state.In the turn-off process,the spilt gates shorten the turn-off delay.The voltage applied to CAG is switched to positive to form electrons accumulation layer in advance,forming a low resistance path for extraction electron,leading to a low E_off.The simulation results show that the proposed RB-IGBT realize much smaller V_on and E_off than NPT RB-IGBT,E_off is reduced 52%and 85%compared with those of SJ SCT RB-IGBT and BEFE RB-IGBT,respectively.