Research On Models And New Structures Of Insulate-Gate Power Devices With High Voltage And Low Loss

IGBTs and LDMOSFETs are popular insulated-gate controlled power devices.Both aim to achieve low loss,high breakdown voltage(BV)and high power density.IGBTs have the largest share of the discrete power device market rated above 600V,owing to the low conduction loss and high current capability.It is often the most important work for the upgrade of IGBT products to improve the two trade-off relationships:the ON-state voltage versus the turn-off loss,the turn-on loss versus the Electro-Magnetic Interference noise(EMI).For the LDMOSFETs,low specific ON-resistance(R_on,sp)often requires high drift region concentration and shortened drift region length,which nevertheless induce degraded BV.Consequently,The essential method to realize low-loss LDMOSFETs is to improve the trade-off relationship between R_on,sp and BV.In this dissertation,new device structures are proposed to achieve high BV and low loss for both IGBTs and LDMOSFETs,and their mechanisms and models are studied.Three new IGBT structures are investigated and discussed in chapter 2,chapter 3 and chapter 4,respectively.A new LDMOSFET structure is proposed and experimented in chapter 5.All the device structures proposed in this thesis are demonstrated with reduced energy loss.1.Injection enhanced LIGBT on thin SOI layerA Lateral Injection Enhanced Insulated Gate Bipolar Transistor(LIEGT)on thin SOI layer is proposed and investigated to reduce the ON-state voltage.The LIEGT features a recessed trench at the Emitter side of the drift region,of which the sidewalls and bottom are covered by the extended gate.The recessed trench suppresses holes being extracted and enhances the electron injection,thus contributing to very low loss in the ON-state.The saturation current of the LIEGT is 1.4 times that of the conventional LIGBT and the ON-state voltage(V_ON)is reduced by 24%at current density of200A/cm².The LIEGT exhibits improved trade-off between V_ON and turn-off loss(E_OFF).For the same E_OFF,the V_ON is decreased by 20%compared with that of the conventional LIGBT.2.A novel trench IGBT with voltage-clamping for turn-on overshoot suppressionA novel Insulated Gate Bipolar Transistor(IGBT)with improved turn-on transient characteristics is proposed and investigated.The proposed IGBT features a built-in voltage clamping structure.The floating p-region adjacent to the trench gate is clamped at an appropriately high voltage before turn-on.This slows down the hole accumulation process in the floating p-region during turn-on transient,and the self-charging displacement current through the gate capacitance is reduced.As a result,the proposed IGBT achieves a 23% decrease in collector current(I_C)overshoot and 14%decrease in d I_C/dt,when compared to the conventional IGBT with the same turn-on loss(E_on).3.New RC IGBT structures with low turn-off lossTwo similar RC IGBT structures are proposed to eliminate the Snapback effect and reduce the turn-off loss:one with alternating n/p buffers(AB RC IGBT)and the other with discontinuous field-stop layer(DFS RC IGBT).Both eliminate snapback effect with very small cell pitches by increasing the distributed resistance at the collector region.Compared with the conventional RC IGBT,the turn-off losses of the AB RC-IGBT and the DFS RC IGBT are reduced by 20%and 30%,respectively,at the same forward on-state voltage drop.4.Accumulation-type LDMOSFET with reduced specific ON-resistanceA novel Lateral Double-Diffused MOSFET(LDMOSFET)with ultra-low resistance is investigated.The proposed LDMOSFET features an extended gate field plate consisting of two back-to-back diodes.In the ON state,the electron accumulation layer is formed below the field plate and provides a low-resistance current conduction path.In the blocking state,the drift region is depleted by the step-doped p region in the field plate and thus the BV is increased.The R_on,sp and BV of the fabricated prototype device are 70 m??cm² and 680 V,respectively.The R_on,sp of the proposed LDMOSFET is decreased by 50%compared with the LDMOSFET without accumulation effect.