Design And Characteristic Research Of New Trench SiC MOSFET

SiC materials have outstanding characteristics such as wide band gap,high critical breakdown electric field strength,high power,high thermal conductivity and high saturated electron drift velocity,which make them have better development prospects in high voltage,high temperature and high frequency fields compared with Si materials.SiC MOSFET power devices have attracted much attention and active research from the industry due to their characteristics of high breakdown voltage,high working frequency and being easy to drive.Since SiC MOSFET devices are often used in bridge circuits,inverter applications and other power management systems,there is a demand for reverse conduction function.Therefore,the reverse recovery characteristics is an important indicator to evaluate its performance.And by integrating MOS-channel diodes to achieve reverse conduction,both better reverse recovery characteristics can be obtained and bipolar degradation effect can be avoided.In response to the above problems,thesis proposes two new SiC MOSFET structures with integrated MOS-channel diodes to improve the reverse recovery characteristics of the devices,and explores the working mechanism and electrical characteristics of the two new structures through simulation.The main work content of this thesis is as follows:1.A new type of SiC MOSFET device MT MOS with integrated MOS-channel diode is proposed.The MOS-channel diode can realize conduction function when it works in reverse conduction mode by turning on MOS-channel diode which reduces reverse conduction voltage drop（V_F）and effectively suppresses body diode conduction eliminating bipolar degradation effect;double trench structure is adopted which modulates electric field through P-type region under source trench reducing electric field peak at silicon dioxide corner at bottom of gate trench.MT MOS has obvious advantages in both forward and reverse characteristics.MT MOS’s V_F compared with DT MOS decreased by 38.2%.When I_load=700 A/cm²,MT MOS’s reverse recovery charge Q_rr compared with DT MOS decreased by 58.7%.At the same time,T MOS retains same forward conduction and blocking characteristic advantages as DT MOS.Compared with ST MOS structure,the proposed MT MOS increased the breakdown voltage by 22.9%,and decreased the specific on-resistance R_on,sp by 18.2%.2.A new split-gate SiC MOSFET device MSG MOS with integrated MOS-channel diode is proposed,which integrates the MOS-channel diode and provides another reverse conduction path different from the body diode to reduce the reverse conduction voltage drop V_F,while suppressing body diode conduction to avoid bipolar degradation effects.With a composite split gate structure,the gate-to-drain capacitance C_gd of the device can be effectively reduced.The reverse conduction voltage drop V_F of the MSG MOS device is 35.2%lower than that of the T MOS device.In terms of dynamic characteristics,when I_load=700 A/cm²,the reverse recovery charge of the MSG MOS device is 1.61μC/cm2,which is 77.29%lower than the Q_rr of 7.09μC/cm² for the T MOS device;The switching loss E_switch of MSG MOS device was 2.607 m J/cm2,which is decreased by 66.6%compared with E_switch=7.806 m J/cm² of the T MOS.