Single-Event Radiation Effects in Silicon Carbide Power MOSFETs

Abstract

In this research, the radiation induced single event effects (SEE) observed in silicon carbide (SiC) power MOSFETs have been studied. Heavy ions, terrestrial neutrons and protons were selected as radiation environments to be investigated, as representative of space, avionics and high-energy accelerator applications. SEE tests and electrical analysis were performed in order to identify the modes and mechanisms of failure, and to assess the reliability of commercial SiC MOSFET technologies. The research initially focused on the non-catastrophic SEEs induced by heavy-ion irradiation, which represent a significant risk for the part reliability in space applications. The broad-beam and microbeam results pave the way to the understanding of the degradation mechanism, named single event leakage current (SELC). Two types of degradation are described in this work, involving different parts of the SiC MOSFET structure depending on the applied voltage during the operation. At low bias the SELC is observed in the region under the gate oxide, whereas for voltages over a certain threshold a second mechanism involving the p-n junction is newly added. Heavy-ion latent damage effects were also studied through radiation tests and scanning electron microscopy (SEM) analysis of the damaged site. Two mechanisms were observed, involving the gate oxide and the SiC crystal lattice. Finally, the heavy-ion SEEs are summarised as function of the operational bias and linear energy transfer (LET). The second part of this work focused on SiC MOSFET reliability when exposed to proton and terrestrial-neutron environments. Accelerated single event burnout tests were performed using devices with different architectures. Electrical analysis of the damaged devices was carried out to investigate the failure mechanism. The results provide useful information about the reliability of the commercial SiC MOSFET technologies for avionic and high-energy accelerator applications. This project was carried out in the framework of a collaboration between the Physics Department at the University of Jyväskylä, the radiation to electronics (R2E) project at the European Council for Nuclear Research (CERN), and the Advanced Power Semiconductor (APS) Laboratory at ETH Zürich. Keywords: silicon carbide, power MOSFETs, radiation effects, Single Event Effects, SELC, SEB, SEGR, latent damage