New Structure And Current Transport Mode Of MOS Gate-controlled High Voltage Power Devices

The MOS gate-controlled power devices as fully voltage-controlled device act as the core components in the application of power switching,drive circuits,and control systems,because of their advantages of high input impedance and simple driving circuits.Then the MOS gate-controlled power devices have the largest market share in discrete power devices.The key design targets of MOS gate-controlled power devices are to achieve low power consumption,high breakdown voltage（BV）,as well as high power density.As the core component of Smart Power IC（SPIC）,the power LDMOS encounters the“Silicon Limit”relationship between the BV and specific on-resistance(R_on,sp)in the form of R_on,sp∝BV ^2.5.The RESURF technology and Superjunction（SJ）technology are usually adopted to reduce the R_on,sp without compromising the BV,by introducing additional P-type region into the drift region to enhance the depleting effect and then increase the doping concentration（N_d）of N-drift region.The R_on,sp is still seriously dependent on the N_d for the two methods mentioned above.Moreover,the introduced P-type region in the N-drift region will occupy part of the current path,which is detrimental to decrease the R_on,sp.IGBT is the core component of power conversion and transmission device.The conductivity modulation effect in the drift region allows the IGBT device to achieve low on-state voltage drop(V_on),which in turn increases the turning off loss(E_off).In this dissertation,in order to address the fundamental issues of MOS-gated power devices mentioned above,the power LDMOS and IGBT based on novel current transport mode and new structures have been researched in order to realize high voltage and low power consumption.1.New structure of high voltage thin SOI LDMOS with ultralow specific on resistance and better temperature characteristicAiming at the“Silicon Limit”relationship between the BV and R_on,sp,and the“hot spot”problem for thin SOI devices,two novel new structures are proposed and investigated by simulations in this thesis,including AEG SOI LDMOS with accumulation-mode current transport and JFP SOI LDMOS with conductance enhanced mode.The AEG（Accumulation-mode Extended Gate）structure and JFP（Junction Field Plate）structure assist depleting the N-drift region and then increase the doping concentration（N_d）while not occupy the current transport path,which is conductive to decrease the R_on,sp.Furthermore,the AEG structure could form high density electron accumulation layer in the N-drift surface and establish an ultralow resistance current transport path in the N-drift,which decreases the R_on,sp significantly.Based on the novel accumulative current transport mode,the new AEG SOI LDMOS could eliminate the“hot spot”effect at the source side and relieve the strong dependence of R_on,sp on N_d.Compared with the conventional VLD SOI LDMOS,the AEG SOI LDMOS and JFP SOI LDMOS decrease the R_on,sp by 65%and 36%,and improve the FOM(Figure of merit,FOM=BV²/R_on,sp)value by 223%and 82%,respectively.In the conduction state with the same power density,the surface temperature difference（?T）of VLD SOI LDMOS is as high as 78K,while the JFP SOI LDMOS decreases?T value to 26K,and the AEG SOI LDMOS almost achieves even surface temperature distribution with?T=1K.2.New structure of high voltage bulk-Si LDMOS with conductance-enhancedTo address the“Silicon Limit”relationship,we proposed two novel structures,named as AEG NFL LDMOS and JFP NFL LDMOS,which feature the N+floating layer（NFL）in the P-type substrate and the AEG/JFP structure above the N-drift region,respectively.These two new devices retain the advantages of AEG structure and JFP structure in increasing the N_d and reducing the R_on,sp.Combined with the modulation effect of linearly doped AEG/JFP structure on the surface lateral electric field and the optimized distribution effect of NFL layer on the equipotential lines in the device body,JFP NFL LDMOS and AEG NFL LDMOS not only achieve high BV values,but also obtain a better tradeoff relationship between the BV and R_on,sp.Compared with the conventional bulk-Si LDMOS,the BV values of JFP NFL LDMOS and AEG NFL LDMOS are both increased by over 60%,and the R_on,sp values are decreased by 43.7%and 67.1%,respectively.What’s more,this thesis has also experimentally proved the operation mechanisms of the JFP/AEG structure and NFL on improving the BV and R_on,sp.The experimental results also prove the feasibility and advancement of accumulative current transport mode induced by the AEG structure.3.Novel structure of RC-IGBT with high speed and low power lossAiming at the snapback phenomenon and the contradictory relationship between the E_off and V_on in RC-IGBT devices,we proposed a novel 1200V-class RC-IGBT with a Controllable trench gate（CTG）in the collector side.By controlling the gate voltage V_RCC between the CTG and the collector electrode,in the forward conduction state,the CTG together with the hole inversion layer around it allows the proposed device to not only eliminate the snapback effect in a small cell pitch by increasing the distributed resistance,but also achieve a low forward conduction voltage drop by increasing the equivalent length of P+collector.In the reverse conduction state,the electron accumulation layer around the CTG extends the equivalent length of N+collector,then the novel device could obtain a low reverse conduction voltage drop.In the blocking state,the CTG together with the electron accumulation layer act as an equivalent N-buffer layer to terminate the electric field and sustain high voltage.During the turning off process,flipping the voltage potential of V_RC prior to turning off the device,the P+collector is shorted to the N+collector through the electron accumulation layer around the CTG and then it stops injecting holes into the N-drift region,which means less carriers needed to be extracted during turning off period.In the end,the proposed device turns off like a unipolar MOS device without tail current and decreases the E_off significantly.Compared with conventional RC-IGBT,the novel CTG RC-IGBT decreases the V_on by 34%at the same E_off and decreases the E_off by 74%at the same V_on respectively.4.New structure of integratable MCSA LIEGT with high speed and low power lossA novel 600V-class integratable LIEGT with MOS-controlled shorted anode（MCSA）has been proposed in his thesis.By controlling the g voltage V_AG between the anode trench gate（ATG）and the anode electrode,in the forward conduction state with the ATG turned off,the N+anode is full shielded by the ATG and P-well region,and then the new device exhibits snapback-free without degrading the on-state voltage drop(V_on).In the blocking state with the ATG turned on,the novel MCSA LIEGT achieves a MOS breakdown mode since the N+anode is shorted to the N-buffer through the turned on channel around the ATG,which relieving the contradictory relationship between the BV and V_on on the doping concentration of P+anode.During the turning off process,the ATG is turned on prior to turning off the device,then the P+anode,N+anode and the N-buffer are shorted through the turned on channel around the ATG.Hence,the P+anode stops injecting holes into the N-drift region and less carriers needed to be extracted during the turning off period.Therefore,the MCSA LIEGT turns off as fast as a unipolar MOS device without long tail current and its E_off is dramatically decreased.Compared with conventional LIEGT,the novel MCSA LIEGT decreases the E_off by 88%at the same V_on value.