Research On Surface Structure Of Novel MOS-controlled Bipolar Devices

As a typical representative of MOS-controlled bipolar device,the Insulated Gated Bipolar Transistor(IGBT)has been widely used in green industries such as smart grids,new energy sources,electric vehicles,and high-speed rails.With the continuous development and application of the wafer thinning technology and injection enhancement technology,a greatly improvement have been achieved in terms of the key performances of IGBT.These key performances include on-state voltage,switching loss,electromagnetic interference noise and short circuit safe operating area.However,the on-state voltage of IGBT is still much higher than that of the thyristor-based devices.Although the on-state voltage of IGBT could be reduced by introducing a heavily doped carrier stored layer.However,as the concentration of the carrier stored layer increases,the breakdown voltage of IGBT will be severely degraded.Increasing the effective electron channel density could also help to reduce the on-state voltage of IGBT,but it would increase the saturation current and the Miller capacitance.Nowadays,the turn-on loss of IGBT is close to or even exceeds to its turn-off loss.How to improve the turn-on characteristics of IGBT has become the focus of researchers.On the other hand,MOS-controlled thyristor devices typically have a lower on-state voltage,but their safe operating areas are often inferior to IGBT.In response to the above problems,guided by Professor XingBi Chen,the author carried out a series of research work through researching and reading a large number of references.The innovation work of this paper mainly includes:1.A MOS-controlled bipolar device with diode-clamped P-region is proposed.By introducing a diode-clamped P-region at the bottom of the IGBT trench gate,the trade-off relationships between the doping concentration of the carrier stored layer and the breakdown voltage are completely eliminated,thereby greatly reduced on-state voltage is obtained.In addition,the saturation current is also reduced,hence the short circuit safe operating area of the proposal is improved.The simulation results of a 1200 V IGBT show that the doping concentration of the carrier stored layer of the proposal can be increased by 4 orders of magnitude and the on-state voltage could be reduced by more than 0.5 V without affecting the breakdown voltage.While the saturation current can be reduced by more than 60%,which results in nearly 6 times increase in the short circuit safe operating time.Obviously,this concept could also be used to MOS-controlled thyristor devices.2.A MOS-controlled bipolar device with a self-biased pMOS clamped P-region is proposed.Although the MOS-controlled bipolar device with the diode-clamped P-region shows excellent performance,the manufacturing process is relatively complicated.In order to simplify the manufacturing process,a MOS-controlled bipolar device with a self-biased pMOS clamped P-region is proposed.An integrated diode-connected self-biased pMOS is formed by introducing a P-region at the bottom of the trench gate and by connecting a portion of the trenches to the Emitter electrode.The pMOS is capable to clamp the potential of the P-region through proper design.The manufacturing process of the proposal is fully compatible with current IGBT manufacturing processes and does not require any additional lithography mask.Applying this concept to IGBTs can also completely eliminate the trade-off relationships between the doping concentration of the carrier storage layer and breakdown voltage,and reduce saturation current at the same time.The simulation results show that under the same voltage class of 1200 V,the on-state voltage of the proposed one can be reduced by more than 0.6 V,the saturation current can be reduced by more than 47%,and hence the short circuit safe operating time can be increased by nearly 4 times.The performances of the MOS-controlled thyristor device with the proposed concept could be more excellent than that of CIGBT(Cluster Insulated Gated Bipolar Transistor).3.The turn-on characteristics of IGBT with floating P-region are analyzed in detail.Based on those analyses,it is found that the turn-on characteristics of the IGBT could be improved by suppressing the rise rate of the potential of the floating P-region.Thus,an IGBT with floating N-region is proposed.The floating N-region has a higher barrier to holes,and during the turn-on transient,only a very small number of holes can enter and accumulate in the floating N-region,thereby suppressing the rapid rise of the potential of the floating N-region.The simulation results show that the introduction of the floating N-region does not affect the other characteristics of the device such as the dynamic and static breakdown voltage,on-state voltage and so on.However,the turn-on characteristics are improved significantly.The rise rate of potential of the floating region could be reduced by 63%,and the lower limit of the maximum reverse recovery dV/dt of the freewheeling diode could be reduced by about 85%.Furthermore,it also enhances the controllability of the gate resistance over the turn-on dI/dt and dV/dt of IGBT.4.An IGBT with emitter-embedded gate is proposed.By introducing an oxide isolated emitter electrode into the trenches,the input capacitance of IGBT is increased without affecting the Miller capacitance,and hence the ratio of the Miller capacitance to the input capacitance is reduced.In this way,the turn-on characteristics of the IGBT is improved,in particular,the effect of the floating P-region on the turn-on characteristics of the IGBT and the turn-on loss of IGBT at a certain maximum dV/dt noise can be reduced.The simulation results show that the turn-on loss of proposed one could be reduced by 63% when the maximum reverse recovery dV/dt of the freewheeling diode is 10 kV/?s.In addition,the lower limit of the maximum reverse recovery dV/dt of the freewheeling diode could be reduced by about 91%.In addition,the controllability of the gate resistance over the turn-on dI/dt and dV/dt of IGBT is also improved.