INSULATED GATE BIPOLAR TRANSISTOR’S AGEING AND ITS IMPACTS ON THE ELECTROMAGNETIC CONDUCTED EMISSIONS

Insulated Gate Bipolar Transistors (IGBTs) have become key electronic components in many applications, including life critical or mission critical products. The understanding of the failing mechanisms and the reliability aspects of the IGBT have become important to semiconductor manufacturers and application engineers, to provide reliable solutions especially in enhanced lifetime (thirty to forty years) applications. Since the IGBT is employed at elevated power scenarios, its substructures can be prone to multiple failure mechanisms which can lead to the general IGBT failure. The IGBT’s failure mechanisms can be mainly divided into two categories: die-related failure mechanisms and package-related failure mechanisms. These will contribute to gate oxide degradation, bond-wire lift-off, bond-wire cracks, bond-wire ruptures, solder delamination, solder cracking, and the degradation of the metallization layers. The presented work tried to address the current gap in knowledge, by studying the relationship between specific degradation within the IGBT (primarily the degradation of the die-attach layer and the gate’s oxide contamination), the static and dynamic operation of the IGBT, and hence the consequential influence this degradation has, on the EM conducted disturbances. For this purpose, accelerated ageing was conducted on commercially available 600V, 16A IGBTs. This was achieved through the development of a power cycling accelerated ageing system (PCAS), which subjects the IGBT to thermo-electrical overstress. The degree of the inflicted degradation was analyzed through X-Ray inspection. Moreover, the static electrical parameters of tested IGBTs, were characterized before, during and after accelerated ageing, noting significant changes. Consecutively the switching transients of the aged IGBTs were studied, by developing a Double-Pulse characterization system. This evidenced that the employed accelerated ageing, contributed to significant slow down of the IGBT’s turn-off transients, while producing minimal changes in the IGBT’s turn-on transients. This led to the modelling of the IGBT’s switching transients’ evolution with ageing, effectively evidencing that the die-attach degradation together with the monitored contamination of the gate’s oxide, were contributing to a more pronounced turn-off “tail current”, and changes in the IGBT’s parasitic elements predominantly the Miller capacitance. Finally, an EM conducted emissions experimental setup was developed, where it was determined that there is a direct correlation between the inflicted degradation, the switching transients, predominantly the collector current (Ic) turn-off transient, and the measured decrease in the EM conducted disturbances.