The Diverse Behaviours of Discharged Degradation at Varied Interfaces of Silicone Gel/Ceramic Substrates Under High-Frequency Square Wave Voltage

Because of the harsh serving conditions of insulated gate bipolar transistor (IGBT) packaged by silicone gel with high voltage and high frequency, it is crucial to reveal the developing characteristics and inhibiting method of discharged degradation at the interface of silicone gel/ceramic substrates. This study investigates and compares the discharge channel development at the interfaces of three kinds of silicone gel/ceramic substrate combinations under bipolar square wave voltage with frequencies from 10 to 30 kHz. The results showed that the discharge channels at the interfaces of silicone gel/Al₂O₃, silicone gel/AlN and silicone gel/Si₃N₄ exhibited fast development followed by stagnation, continuous propagation and gradual growth with bubbles, respectively. These characteristics were indicated by the spatial distribution of in situ luminescence and fluorescent imaging. Besides, light emitted by discharge channels was concentrated in the same ultraviolet (UV) range except for the light with a wavelength of 296 nm found only at the interface of silicone gel/AlN. Elements of C and Si were accumulated, whereas the amount of Al decreased in discharge channels. The luminescent behaviours, partial discharge at the rising/falling edge of bipolar square wave voltage, conductivity in channels and behaviour of space charges contributed to the discharge channel development simultaneously. It is also demonstrated that doping UV absorbers into silicone gel can inhibit discharge channel propagation at the interface of silicone gel/ceramic substrates.