Description: As new WBG high voltage semiconductors and transistor topologies are developed, identification of failure modes and the conditions that initiate them are becoming increasingly important to ensure reliable use for space based applications. Issues with performance degradation and failure of Si power devices attributable to cosmic radiation has been observed in the use of these device in both space and high altitude applications. Although fewer and lower energy cosmic rays reach the Earths surface, this phenomenon is an increasing concern for terrestrial applications of power devices. Studies have shown that cosmic-ray-induced effects can strongly influence the voltage derating necessary for the safe and long term use of Si MOSFETs and IGBTs, directly affecting their adoption and use in various applications. Cosmic-ray-induced errorsmainly due to neutrons--will only worsen as circuit size continues to shrink. Proposals will need to establish and compare the influence of cosmic radiation on SiC MOSFETs and Si IGBTs under identical conditions in regards to cosmic radiation events. The effects will need to be analyzed to determine the long term reliability and performance of these technologies. Through these results, designers will be able to make better choices in the use of either Si or SiC for different applications. Additionally, semiconductor developers will be better equipped to develop design solutions once their reliabity has been established. Ultimately, the acceptance of WBG devices can result in dramatic energy savings across a broad spectrum of applications including switched-mode power supply, motor control, traction, solar and aerospace industries.
The high energy particles in cosmic rays are known to damage high voltage Si power devices such as diodes, IGBTs, MOSFETs and thyristors resulting in single-event upsets (SEUs) such as single event burnout (SEB) and single event gate rupture (SEGR). SEB is caused by the initiation of destructive avalanching due to drain-source filamentation resulting from activation of parasitic thyristors and-or bipolar transistors present in all devices except diodes. SEB in diodes is simply due to excessive leakage current induced by high energy particles while the device is biased at a high voltage. In MOSFETs and IGBTs, SEGR can occur due to the generation of a high transient field across the gate oxide and subsequent discharge of accumulated holes through the gate oxide. As a consequence of these issues, typical Si devices are limited to approximately 50% of their rated voltage in characteristic usage. Although these devices are likely to be more robust against cosmic ray damage due to the very poor gain of parasitic npn BJTs in SiC power MOSFETs, gate rupture may still occur.
Although initial work has demonstrated the ruggedness of SiC power MOSFETs, more in-depth fundamental experiments are needed [5-7]. The typical testing method, designed to quickly obtain information, is to irradiate devices with high energy neutrons (50-80 MeV, ~104 n-cm2). This method accelerates the failures to enable gathering the necessary data within weeks, but it is expensive and requires access to a high energy neutron beam facility. Another method (called the real-time terrestrial method) is easier to implement but requires a substantial number of devices (>100) for testing. The proposal for this subtopic should be to bias a large number of devices at high voltage and room temperature with a series resistance to limit the current and observe failures over a few months. The devices should be mounted flat to increase the flux of cosmic-rays impinging on the devices. The bias across the devices should be varied from 50- 100% of the rated voltage in stepped increments and readings should be taken at each bias point for an established period of time (e.g. 10 weeks). The goal of this subtopic will be to compare commercially available high voltage Si IGBTs and SiC MOSFETs devices to establish their resistance to radiation effects.