| With the rapid development of new power systems,electrical transportation,aerospace,defense,and military fields,the requirements and demands for core components of high-voltage high-power semiconductor devices are also higher.With the advancement of wide band semiconductor such as silicon carbide,gallium nitride,and other material technologies,semiconductor devices are developing to higher voltage level with shorter turn-on and turn-off time and higher repetition frequency.Therefore,the package insulation of semiconductor devices is subjected to extreme operating conditions with extremely high voltage change rate,extremely high repetition frequency,and extremely high temperature.Silicone elastomers are widely used in packaging insulation because of their high overall performance.However,the unique degradation mechanism and early failure mechanism of silicone elastomers under pulsed electric fields are not yet clear and need to be studied in depth.Therefore,in this paper,the electrical tree degradation characteristics,microscopic degradation mechanism,and macroscopic degradation mechanism of silicone gel and silicone rubber under pulsed electric field are investigated and the effect of semiconductor operating conditions is analyzed.First,the electrical tree degradation characteristics under thermal coupled pulsed electric field are studied.An experimental platform of electrical tree under thermal coupled pulsed electric field is built.The effects of pulse edge time,repetition frequency,and temperature on the onset voltage,intuitive development morphology,fractal dimension,accumulated damage area,and expansion coefficient of electrical tree are investigated respectively.It is found that silicone rubber has higher insulation strength,while silicone gel has certain self-recovery performance.The increase of repetition frequency,the decrease of edge time,and the increase of temperature all contribute to the initiation and growth of electrical tree from different angles and degrees,making the electrical tree transform between fine,dendritic,clumped,and loose tree.Then,the degradation mechanisms of electric tree are studied at two scales,the microscopic and macroscopic scales,respectively.For the microscopic deterioration mechanism,the study is mainly carried out from the phenomenon of charge-exciting molecular vibration.The charge distribution and molecular vibration test platform under thermal coupled pulsed electrical field are built.The theoretical relationship between charge and molecular chain segment motion is connected through the molecular chain segment dynamics equation.The effects of edge time,pulse amplitude,frequency,temperature,and pressurization time on molecular vibration are investigated experimentally.The evolution mechanism of molecular vibration is analyzed by combining molecular vibration theory and charge distribution changes.The molecular vibration amplitude is linearly related to the rate of voltage change,quadratically related to the pulse amplitude,and less affected by the repetition frequency,but closely related to the pulse edge frequency component.As the temperature increases,the amplitude of silicone gel increases while that of silicone rubber increases and then decreases.The molecular amplitude of both increases gradually with pressurization time.The effects of molecular vibrations on insulation degradation are analyzed from three aspects:mechanical,energy and long-term effects.For the macroscopic deterioration mechanism,the study is mainly carried out from the bubble discharge phenomenon.The two-dimensional plasma simulation model of bubble discharge under pulsed electrical field is constructed.The discharge process is analyzed and the effect of operating conditions on breakdown voltage,discharge current,and ozone molecule number is focused.The discharge mainly occurs at the edge of the pulse,where the bubble breaks through and generates a high discharge current and rapid ozone generation.The decrease of the edge time makes the breakdown voltage increase slightly,but discharge current increase significantly,and the number of ozone molecules increase.The increase of the repetition frequency makes the breakdown voltage and discharge current decrease,and the number of ozone molecules increase in a certain time.The increase of the temperature makes the breakdown voltage decrease and the discharge current increase,but the number of ozone molecules decrease.The mechanism of the effect of bubble discharge on deterioration through discharge current and ozone and the effect of operating conditions are analyzed theoretically. |
