Study Of Fast Switching And Low Loss MOS-gated Power Devices

In the field of power semiconductor devices,a kind of devices controlled by MOS gates is called a fully-controlled device,which has the advantages of high input impedance,easily drived,and small driving power.Among them,LIGBT is a lateral power MOS gate-controlled bipolar device.LIGBT forms conductivity modulation effect by injecting holes from anode and electrons from channel,which causes the advantages of high breakdown voltage and low on-voltage drop at the same time.It is also easy to integrate in the power circuit.There is a serious tail current nevertheless when the device turns off,which leads to high turn-off loss,and needs solving the trade off between V_on and E_off.Another important kind of MOS gate-controlled devices is power MOSFETs,where conventional trench-gated VDMOS has large gate-to-drain capacitance(C_GD),resulting a high product of Q_GD×R_DS（on）and poor dynamic characteristics.In order to solve the above problems of MOS gate-controlled devices and further realize the low power consumption of MOS gate-controlled devices,a new structure of fast turn-off LIGBT and a new structure of split gate MOSFET are proposed.1.An LIGBT structure with self-biased n-MOS is proposed.The new structural features an anode trench gate,p-layer region in the anode region to form an embedded n-MOS.When the device turns on,the p-layer region acts as electron barrier to hinder the electron current being collected by the N+anode,thereby controls the anode current distribution and effectively controls the transformation of conduction mode,and eliminates the snapback effect.When the device turns off,n-MOS self-opened at the high anode voltage,providing a low-resistance extraction channel for the extracting electrons stored in the drift region and reducing the E_off.In the blocking state,the self-biased n-MOS opens to collect the electron leakage current,and then the P+anode/N-drift region junction cannot be opened to inject holes,suppressing the triggered of the parasitic PNP transistor,and obtaining a breakdown voltage value as high as that of PN junction.An improved structure is proposed,in which a cathode trench is introduced,which acts as not only a barrier to holes to enhance electron injecting,but also as the bypass path for hole to improve the V_on and expand the safe working area.Compared with the traditional LIGBT structure with the same V_on,the simulation results show that the E_off of the new device is reduced by up to 43%and the breakdown voltage is increased by 11%.In addition,the embedded n-MOS realizes self-biased in each state,eliminating the need for additional control circuits and strategies to save design costs.2.Propose a split gate MOSFET structure with a HK dielectric.The structural features a split gate structure while with a high K dielectric as a shield gate dielectric.Compared with SiO₂ gate dielectric,the high-k dielectric helps to accumulate high concentration electrons on the sidewall of the shielding gate as the current low-resistance layer in the on-state,which reduces the on-resistance.In the blocking state,the high-K dielectric assists depleting the drift region,which allows the expansion of the depletion area.In the switching,the split-gate enhances the shielding effect to C_GD by the strong coupling effect of high-k dielectric,further reducing C_GD.Lower C_GDD combined with rapid depletion of the drift region by high-k dielectric achievies fast turn-on and turn-off,then reduced switching losses for the new structure.The simulation results show that compared with the traditional split-gate VDMOS,the Q_GDD and the on-resistance of the new device is reduced by 69%and 12%,respectively;the switching loss and and the final figure of merit Q_GD×R_DS（on）is reduced by 31%and 72%,respectively.