Characterization of the onset of carrier multiplication in power devices by a collimated radioactive alpha source

摘要

The quantitative characterization of charge multiplication in reverse biased junctions is mandatory to design robust power devices, as well as to define their safe operating area. This applies especially for failure mechanisms like single event burnout, where the charge generated by ionizing radiation is transported and eventually multiplied by the internal electric field of the reverse-biased device. Because of their limited sensitivity, DC techniques detect charge multiplication as an increase of the reverse current of the junction once the breakdown already occurred. Optical and particle beams with dedicated test structures have been exploited to improve the sensitivity at lower electric field. However, the latter solutions cannot be simply applied to real devices. Furthermore, they just deliver averaged values of the multiplication factor.In this paper, single alpha particles from a collimated radioactive source are used to generate controlled charge bursts in the close vicinity of the reverse-biased junction of a power diode. The fast reverse current pulse arising to the drift of the initial charge burst is collected by a dedicated spectrometry chain. The acquired data are processed to obtain the probability distribution of the multiplication factor under consideration of the stochastic nature of the impact ionization process. The results of the measurements are compared with the multiplication values obtained by analytical models and by Monte Carlo simulation. The technique is demonstrated based on a commercial 1.2 kV-70A power diode in the reverse bias range from 700 V to 1250 V. Finally, detailed information is provided about the proposed hardware solutions, which can easily be implemented under usual laboratory conditions.