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Electrical characterizations are used to understand power MOSFETs failure mechanisms after heavy ion irradiation. Results indicate that both bias levels and impact localization of heavy ion are important parameters for SEGR triggering or latent defect formation. This work addresses the limits of the post-irradiation gate stress relevance used for Power MOSFETs space qualification.

A methodology for power MOSFET radiation hardness assurance is proposed. It is based on the statistical analysis of destructive events, such as gate oxide rupture. Examples of failure rate calculations are performed.

Heavy ion-induced Power MOSFET's reliability degradation has been studied. Irradiations were realized at low and high energy with the same electronic stopping power at the surface of the die. For both energies, a decrease of the charge to breakdown has been observed after irradiation. However, an enhanced degradation of the oxide layer reliability is observed at low energy. The lifetime reduction at high energy is correlated to local disorder along the ion track that can act as precursor damage. On the other hand, the most important reliability degradation at low energy is attributed to a synergy effect between ionizing and non-ionizing processes. Clusters of defects can indeed be formed, adding an additional wear-out mechanism. These results may be significant in the frame of Single Event Testing

We present results on the effects of ELDRS at dose rates of 10, 5, 1, and 0.5 mrad(Si)/s for a variety of commercial, radiation hardened, and ELDRS-free devices. We observed low dose rate enhancement below 10 mrad(Si)/s in several different part types. The magnitudes of the low dose rate enhancement varied substantially. The most notable case showed dose rate sensitivity in the functional failures for a commercial voltage regulator, with initial failures occurring after 10 krad(Si) for the parts irradiated at 0.5 mrad(Si)/s. Radiation hardened and ELDRS-free devices also showed ELDRS at the ultra-low dose rates. An ELDRS-free high power regulator showed a low dose rate enhancement factor of ×33 after 10 krad(Si) for parts irradiated at 0.5 mrad(Si)/s. The enhanced degradation at the ultra-low dose rates present challenges for hardness assurance.

This paper reports on the impact of single event gate rupture and post-irradiation gate stress on Power MOSFETs switching ability. A dedicated setup has been developed and presented in this paper. The data showed that devices can switch after Single Event Gate Rupture. Failure of energy conversion system does not depend on gate current of the device but its associated external circuitry. Moreover, the data showed that devices having a gate layout constituted of parallel stripes are less sensitive than hexagonal shape when electrical constraints are applied after failure. It was also observed that the sensitivity of SEGR can be enhanced by X-ray irradiation but enhanced degradation is not observed during the switching operation.

This paper reports on the different responses observed during heavy ion irradiation and the Post-irradiation-Gate-Stress test on radiation-hardened Power MOSFETs. The data show a correlation between IG gate current during irradiation and different behaviors observed during the post-irradiation test. This work addresses the relevance of the post-gate stress test used in space qualification of power MOSFETs.

Charge collection is used as a non-destructive technique to analyze the statistical response of vertical power MOSFETs and their single-event burnout (SEB) rate as a function of the incident ion energy. Two effects are observed at either low or high energy. At low energy, the collected charge significantly decreases because of the limited ion range and energy straggling in the thick epitaxial layer. Because of this limited range effect, using low energy ions for SEB testing can significantly underestimate the SEB rate. At high energy, the presence of thick source bond wires, which partially cover the die area, as typically encountered in power MOSFETs, induce a large shadowing effect. When crossing the bond wires, high energy ions loose energy and can have a higher LET (but still a significant range) when they reach the active die. As a result, they can deposit more charge in the thick sensitive epitaxial layers of the transistors than the primary beam. A significant probability of high collected charge events is then observed at high energy. Contrary to the low energy (range) effect, the shadowing at high energy contributes to overestimating the SEB rate. General rules for the SEB radiation hardness assurance, related to the ion energy versus the power MOSFET voltage rating, are provided to avoid both range and shadowing effects.