Minority Carrier Charge Regulation Mechanism And New Structure Of MOS Gate-Controlled Power Devices

MOS gate-controlled power devices mainly include IGBTs and power MOSFETs,which are the key components of power conversion,drive,and control systems.Low-loss IGBTs and power MOSFETs can improve the efficiency of energy conversion and transmission in power systems.When the IGBT is turned on,the minority carrier charge produces conductance modulation effect,which makes it have low on-state voltage drop and large current handling capability.However,due to the need to extract the minority carrier charge when it is turned off,excessive minority carrier charge always lead to a large turn-off loss;When the power MOSFET utilizes body diode reverse freewheeling,the minority carrier charge produces conductance modulation effect so that it has a low forward voltage drop,but because the minority carrier charge needs to be extracted when it is turned off,excessive minority carrier charge always causes a large reverse recovery charge and loss.Therefore,minority carrier charges cause a contradictory relationship between conduction loss and switching loss in MOS gate-controlled power devices.To improve the performance of MOS gate-controlled power devices,this dissertation researches the mechanism of minority carrier charge regulation of MOS gate-controlled power devices and proposes new structures of low-loss MOS gate-controlled power devices based on this mechanism.The specific contents are as follows:1.Elucidate the mechanism of minority carrier charge regulationFor the hard switching application loss of MOS gate-controlled power devices caused by minority carrier charges,this dissertation explores the qualitative relationship between the minority carrier charge and the on-state voltage drop/turn-off loss of IGBT,and clarifies the minority carrier charge regulation mechanism to achieve the low loss in IGBT by optimizing the minority carrier charge distribution and reducing the effective doping concentration in the depletion region;explores the qualitative relationship between minority carrier charge and power MOSFET body diode forward voltage drop/reverse recovery charge,and clarified the minority carrier charge regulation mechanism to achieve low-loss in power MOSFET by reducing minority carrier injection or reducing minority carrier storage,which points out the direction for the design of low loss MOS gate-controlled power devices.2.Propose new structures of low turn-off loss IGBTAiming at the problem of high turn-off loss due to the slow extraction speed of minority carrier charges when the IGBT is turned off,according to the minority carrier charges regulation mechanism,a new structure of IGBT with an optimized distribution of minority carrier charges is proposed,that is,the self-regulated potential lateral IGBT.It can first operate in the thyristor conduction mode and then enter the lateral IGBT conduction mode when turns on,thereby enhancing the injection of majority carriers,optimizing the minority carrier distribution,and improving the minority carrier extraction speed during turn-off,so that the turn-off loss is 79.1% lower than that of the conventional lateral IGBT with the same on-state voltage drop;a new IGBT structure with a low effective doping concentration in the depletion region is proposed,that is,an IGBT with an inner primary blocking junction.It reduces the effective doping concentration of the depletion region by introducing opposite doping in the drift region,thereby accelerating the expansion of the depletion region,increasing the extraction speed of minority carriers,and reducing the turn-off loss by 79.7%,besides,the introduction of opposite doping has almost no effect on the on-state voltage drop.3.Propose new structures of low reverse recovery charge super junction VDMOSAiming at the problem of high loss of super junction VDMOS in power MOSFET due to high reverse recovery charge,according to the mechanism of minority carrier charge regulation,a new structure of super junction VDMOS with weak minority carrier storage is proposed,that is,super junction VDMOS with reduced hole barrier,which reduces the hole barrier caused by the high-concentration substrate by introducing a Schottky contact on the drain side,thereby weakening the minority carrier storage and reducing the reverse recovery charge by 64.6%;proposes a new structure of super junction VDMOS with low minority carrier injection,that is,super junction VDMOS with P-type Schottky diode and MOS channel diode,which uses a P-type Schottky diode to suppress the conduction of the Pi N body diode,and at the same time uses a MOS channel diode to freewheel,thereby reducing minority carrier injection and reducing the reverse recovery charge by 84%.4.Propose a new structure of low-loss reverse conducting lateral IGBTThe reverse conducting IGBT that integrates the IGBT and Pi N diode monolithically needs to balance the relationship between the on-state voltage drop and the turn-off loss of IGBT caused by the minority carrier charge during forward conduction,and the forward voltage drop and reverse recovery charge relationship of the body diode caused by the minority carrier charge during reverse conduction.However,since the forward and reverse conduction paths of the reverse conducting IGBT overlap each other,the optimization of the forward and reverse performance is limited.To solve this problem,this dissertation proposes a new reverse-conducting lateral IGBT structure with separated forward and reverse conduction paths,that is,a reverse-conducting lateral IGBT with embedded PPN diodes in the oxide trench.It uses an oxide trench to separate the forward and reverse conduction paths and optimizes the minority carrier charge distribution and concentration according to the different requirements of the forward and reverse conduction characteristics on minority carrier charges,reducing the turn-off loss by57.1%,reducing the forward voltage drop of the body diode 25.4% and reducing the reverse recovery charge by 68.9%,so its forward and reverse conduction both achieve low loss.