Study On The Degradation And Failure Mechanisms Of SiC MOSFET Devices Under Gate And Body Diode Coupling Conditions

In recent years,the demand for high-performance power electronics devices has grown significantly in industries such as new energy vehicles,aviation and power transmission.As a result,power semiconductor devices have gained increased attention as key components of such equipments.Currently,Silicon(Si)semiconductors are the most widely used in the market due to their stable characteristics,mature manufacturing processes,and low prices.However,the material characteristics of Si devices have reached a bottleneck and are proving difficult to overcome.Silicon Carbide(SiC),a wide bandgap semiconductor,has a wide application space due to its high-temperature,high-voltage resistance,high-frequency capability,and high-power density.Despite its advantages,SiC devices are still facing challenges due to the immaturity of the manufacturing process,which poses significant reliability issues under severe operating conditions.The reliability of SiC MOSFET devices in the third quadrant is one of the key concerns.When SiC MOSFET devices working in the third quadrant with inductive loads,reliable external inverse parallel diode are typically used for current continuation.As the manufacturing process matures,the body diodes of SiC MOSFET devices are expected to replace external inverse parallel diode,reducing packaging difficulty and cost.Nevertheless,under severe working conditions,the body diode may be exposed to surge currents,and large energy shocks can cause device failure,leading to severe economic losses.A highly reliable device can effectively dissipate surge energy without failure,providing a higher security for the power system.Therefore,reliable applications in the third quadrant of SiC MOSFET devices are critical.However,the body diode and the gate of SiC MOSFET devices are coupled due to the body effect.Thus,studying reliability of body diode,gate,and coupling of the two is the basis for a deeper investigation into the third quadrant reliability of SiC MOSFET devices.The main research contents and innovative achievements of this paper are as follows:Gate degradation mechanism of SiC MOSFET devices:A high-temperature gate bias test technique is proposed to monitor the threshold voltage and gate leakage current at same time,and a corresponding test platform is established.The effect of electrical-thermal stress on threshold voltage and gate leakage current is revealed,and the degradation mechanism of the threshold voltage and gate leakage current is explained.Based on the test results,the actual impact of threshold voltage shift on the circuit is analyzed,the gate leakage current decreases mechanism is revealed,and recommendations for the selection of the gate leakage current failure reference value in reliability testing are given.Eventually,the coupling relationship between threshold voltage and gate leakage current under electrical-thermal stress is revealed.Degradation and failure mechanism of external anti-parallel diodes under surge current:A novel surge current testing technique is proposed that allows for the simultaneous monitoring of voltage,current,junction temperature,and package characteristics.Futhermore,a corresponding test platform is established.The voltage curve and I-V characteristics curve of the diode under surge current are studied.The temperature curve of the diode under surge current is analyzed in relation to the power consumption,and the failure temperature is identified.In addition,the package characteristic change process is recorded.The relationship between electrical,thermal,and package characteristics is constructed,and the connection between I-V characteristic curves and metal layer melting process is revealed.Finally,the degradation and failure mechanism of the diode under surge current is explained.The degradation and failure mechanism of SiC MOSFET devices under surge current:Data related to electrical,thermal,and package characteristics during degradation and failure of the body diode are recorded.The relationship between the package characteristics and the electrical characteristics of the body diode is revealed.The failure temperature of the body diode under surge current is identified.The effect of package characteristics on electrical parameters is decoupled.The influence of gate turn-off voltage on surge current capabilities is explained.The mechanism of gate degradation under surge current is studied.Furthermore,the degradation and failure mechanism under gate and body diode coupling conditions is explored.Finally,the mechanisms under different failure modes are discussed.Novel gate degradation characterization method:A gate degradation characterization method based on the coupling relationship between the gate and the body diode is proposed,termed as the "body effect threshold voltage(VTH(body))"method.A theoretical model is established to describe the relationship between VTH(body)and gate degradation.A method is proposed to obtain VTH(body)from the "body diode voltage-gate voltage" curve during gate voltage switching.The influence of test parameters on VTH(body)is revealed,and a high-temperature gate bias test technique is proposed for VTH(body)measurement.The practical application value of VTH(body)was confirmed.Additionally,the measurement capability under non-constant temperature environment is verified,and the performance of VTH(body)is compared with other gate degradation characterization electrical parameters.