Design Of IGBT New Structure With Low Miller Capacitance

IGBT combines the advantages of MOSFET devices and bipolar transistors.As the core device of energy conversion and power transmission systems,IGBTs are widely used in consumer electronics,transportation,defense technology and other fields covering personal life and national development.Affected by market demand,researchers have been exploring and researching in the direction of reducing IGBT switching losses,increasing IGBT operating frequency and improving IGBT reliability.Improving the contradictory relationship between IGBT turn-on loss and electromagnetic interference noise has become a hot spot and nodus for designers at home and abroad.Reducing the Miller capacitance of IGBT is one of the important directions to improve this trade-off.Based on this direction,the thesis proposes a new structure that can effectively reduce the Miller capacitance of the IGBT,and further improve the electrical performance of the IGBT.The main research contents of this thesis are as follows:1.A trench gate IGBT structure（Poly silicon Diodes Gate structure for trench gate IGBT,PDG-TIGBT）with a polysilicon diode gate structure is proposed.This structure introduces a P⁺POLY gate as a buffer layer and a P^-POLY gate for realizing a poly silicon diode structure between the N⁺POLY gate and the bottom of the trench gate.The P^-POLY silicon gate can be mutually depleted with the N^-drift region of the IGBT to form a depletion capacitance in the gate,which reduces the Miller capacitance of the device and raises the potential Vacc near the trench gate at a higher collector voltage.The simulation results show that,compared with the traditional FS-TIGBT,when the gate resistance is 80Ω and the collector voltage is 600 V,the Miller capacitance decreases by 70.7% and the bottom potential of the trench gate increases by 146%.The improvement of two electrical parameters,Miller capacitance and initial potential near the trench gate,further optimizes the trade-off relationship between the turn-on characteristics and the EMI noise characteristics of the IGBT.The simulation results show that during the turn-on transient of the device,The potential growth rate at the bottom of the trench gate decreases by 23.5%,collector current rate of change maximum value decreased by 45.8%,and on the premise that Eon remained the same,maximum value of the collector current change rate of PDG-TIGBT decreased by 84.2%,maximum value of anode voltage change rate of freewheel diode dropped by 44.4%.2.Design process and layout for PDT-TIGBT.On the basis of the traditional process,combined with the characteristics of the proposed structure,an appropriate process was established,and several key process parameters such as the thickness and resistivity of the N^-drift region,the implantation dose of the P^-type base region,the depth of the trench gate,the thickness and resistivity of the FS layer,and the implantation dose of the P⁺collector region are simulated and optimized,obtaining a set of cell process parameters that meet the design indicators of IGBT breakdown voltage,threshold voltage and forward voltage drop.On this basis,the design of the terminal of the proposed structure is realized by the combination of the equipotential ring,the field limit ring and the field plate,and the ring spacing is adjusted to meet the withstand voltage requirements of the terminal.Finally,the layout design of PDG-TIGBT is completed.