Novel Structure And Model Of MOS Gate Pulse Power Devices

Pulse power systems compress low power energy into high power energy?MW to GW?within a very short time?ns or?s?,which are widely used in particle acceleration,electromagnetic catapult,mineral mining,environmental protection and so on.The pulse power switches are the key of the compression of low-power input and high-power output,which closely relate to the power level,shape and stability of the output pulse.The development of pulse power technology mostly determined by the update of the pulse power switches.Recently,the solid-state switches as replacement of traditional gas/spark switches in pulse power systems has been a trend,in which the research on high di/dt capability of solid-state switches is hotspot.Among the mainsteam solid-state switches,MOS-gate power devices that feature easily-drivering gate and integration are priority.However,the application of conventional MOS-gate power devices,such as insulated gate bipolar transistor?IGBT?and MOS oxide semiconductor field effect transistor?MOSFET?,in pulse power are limited,due to their low pulse current and poor di/dt characteristics??27?1000 A/?s?.The high-di/dt pulse current generating theory and high high-di/dt device technology are still to be developed.This dissertation,which aims at the urgent requirement of the next generation pulse power systems on high-di/dt MOS gate pulse power devices,studies the mechanism of high-di/dt conductivity modulation?CM?,novel device structure and improvement of di/dt capability.main innovations of this dissertation are summarized as“1 model,2structures and 1 technology”,which are described in detail as follows:?1?The model of high-di/dt conductivity modulation?di/dt-CM?.This model demonstrates the close link of high-di/dt pulse current and the strong conductivity modulation.By solving the equations of RLC pulse ring down circuit and pulse power device,the di/dt-CM model is established.The effect of the anode and cathode injection efficiency on the strong conductivity modulation is investigated,and then the implementation path of strong conductivity modulation MOS gate pulsed power device and high-di/dt pulse current generation is obtained.?2?Nevol NPT MOS gate thyristor with strong conductivity modulation.When being used in pulse power systems,conventional MOS-controlled thyristor?con-MCT?suffers from low-level conductivity modulation,negative gate voltage for sustaining blocking state and poor d V/dt immunity.Based on the proposed di/dt-CM model,this dissertation proposes cathode-short MCT?CS-MCT?and Schottky-barrier MCT?MCT?.The CS-MCT introduces cathode shunts,equipping normally-off characteristics and improved d V/dt immunity.At the same time,we imbed Schottky barrier in the cathode shunts,increasing the P-well potential and e n Hancing the cathode injection efficiency as well as the conductivity modulation.the SB-MCT features high-di/dt and improved repetitive pulse characteristics.Experimental results show that the CS-MCT exhibits 1600V breakdown voltage?BV?under V_G=0 V and d V/dt immunity over 16.2 k V/?s,demonstrating normally-off characteristics and improved d V/dt immunity.The SB-MCT performs performs a di/dt up to 120 k A/?s with peak current near 10 k A,increasing di/dt by about 20%than the CS-MCT.Simultaneously,the proposed SB-MCT continuously undergoes more than 20 000 shots.?3?4500 V FS MCT with high-effeciency injection anode?Hi A-MCT?.Based on the di/dt-CM model,this dissertation proposes high-effeciency injection anode for enhancing the conductivity modulation.High-concentration anode is used to increase the?35?N between N-FS layer and P⁺-anode;Thick anode layer is used to reduce the electron flowing out and increase the nonequilibrium carrier concentration??35?n=?35?p>>N_d,N_d is the concentration of N-drift layer?.Experimental results show that the proposed Hi A-MCT achieves di/dt up to 140 k A/?s and peak current of 20.6 k A within 200 ns.?4?di/dt capability improvement thechnique based on voltage coupling enhancement.It is found that,due to the gate-cathode voltage?V_G-V_C?coupling associated with the intrinsic gate-cathode capacitor(C_gc)and inevitable common-source-inductance?L_C?of MCT,the gate voltage?V_G?would oscillate with the cathode voltage V_C,which produces high gate-cathode voltage(V_GC)oscillation.This easily leads to device failure especially at high di/dt pulse condition.enhanced V_G-V_C coupling by increasing intrinsic C_gc can contribute to the close following of V_G against V_C,suppressing the transient gate overvoltage and improving the di/dt capability.Based on the mechinsm of V_G-V_C coupling enhancement,this dissertation proposed a di/dt capability improvement thechnique.By using a modified dummy gate MCT?DG-MCT?structure,the intrinsic C_gc is increased and the transient gate overvoltage is suppressed.Experimental results show that,the DG-MCT has a low gate overvoltage(V_GC-max)of 31.2 V,while the V_GC-max of conventional MCT is over 136.7 V at di/dt=17.2 k A/?s.