Review—Radiation Damage in Wide and Ultra-Wide Bandgap Semiconductors

Heavy-ion microbeams are employed for probing the radiation-sensitive regions in commercial silicon carbide (SiC) vertical double-diffused power (VD)-MOSFETs with micrometer accuracy By scanning the beam spot over the die, a spatial periodicity was observed in the leakage current degradation, reflecting the striped structure of the power MOSFET investigated Two different mechanisms were observed for degradation At low drain bias (gate and source grounded), only the gate-oxide (at the JFET or neck region) is contributing in the ion-induced leakage current For exposures at drain–source bias voltages higher than a specific threshold, additional higher drain leakage current is observed in the p-n junction region This provides useful insights into the understanding of basic phenomena of single-event effects in SiC power devices

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Heavy-Ion Microbeam Studies of Single-Event Leakage Current Mechanism in SiC VD-MOSFETs

Both experiments and simulations have shown that single-event burnout (SEB), a catastrophic event, occurs at less than half of the rated blocking voltage in commercial 4H-SiC power devices under a heavy-ion strike. The failure was shown to be due to significant impact ionization near the epi/substrate interface. Adding a buffer layer between the drift epi and substrate layers reduces the impact ionization effect and changes the thermal failure location. In this article, the SEB phenomenon in a 4H-SiC power MOSFET utilizing a buffer layer is investigated. Heavy-ion transport and 3-D electro-thermal transient simulations were performed to study the device response to a heavy-ion strike. In examining the time evolution of electric field profile, charge carrier dynamics, and thermal heat transfer, it is determined that the failure mode for this design is the location shift of the mesoplasma (or hot spot) to within the drift epi region, away from the high field area. A sensitivity analysis was conducted to identify the dominant electrical or thermal factors contributing to device failure due to second breakdown. From these simulations, it is found that the semiconductor thermal conductivity is the primary material parameter that influences the mesoplasma formation.

Ion-Induced Mesoplasma Formation and Thermal Destruction in 4H-SiC Power MOSFET Devices

In this article, the single-event response of the 1.2-kV silicon-carbide (SiC) power MOSFETs with varied buffer layer designs is investigated by the 2-D numerical simulations. The structural parameters of the buffer layers are compared and analyzed to understand the transient response after the heavy ion strike and the related physical mechanisms comprehensively. Simulation results reveal that an optimized single buffer structure can be acquired by using a relatively thicker buffer layer (T $\mu \text{m}$ ) and a moderate doping concentration (D cm−3). It demonstrates that the single-event-burnout (SEB) performance can be improved significantly under the worst case bias conditions [a drain bias voltage of 1.2 kV and a linear energy transfer (LET) of 1 pC/ $\mu \text{m}$ ]. In addition, the optimized structural combinations adopted in the dual or triple buffer layers can strengthen the SEB performance further. The simulation results show that a step electric field distribution is established inside the optimized dual or triple buffers, where the electric field peak is mitigated from 3 to 2.2 MV/cm. Moreover, the excess carrier generation is suppressed and the local temperature rise is weakened during the transient electrothermal process. Consequently, the structure with the optimal buffer layer designs can enlarge the SEB safe operating area (SOA) from 30%–50% to 100% rated breakdown voltage at high LET bias, which makes the SiC power MOSFETs used in aerospace and aviation power electronic systems become possible.

Impact of Varied Buffer Layer Designs on Single-Event Response of 1.2-kV SiC Power MOSFETs

Accelerated terrestrial neutron irradiations were performed on different commercial SiC power MOSFETs with planar, trench, and double-trench architectures. The results were used to calculate the failure cross sections and the failure-in-time (FIT) rates at sea level. Enhanced gate and drain leakage were observed in some devices which did not exhibit a destructive failure during the exposure. In particular, a different mechanism was observed for planar and trench gate MOSFETs, the first showing a partial gate rupture with a leakage path mostly between the drain and the gate, similar to what was previously observed with heavy ions, while the second exhibiting a complete gate rupture. The observed failure mechanisms and the postirradiation gate stress (PIGS) tests are discussed for different technologies.

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Impact of Terrestrial Neutrons on the Reliability of SiC VD-MOSFET Technologies

Heavy-ion data suggest that a common mechanism is responsible for single-event burnout (SEB) in 1200-V power MOSFETs and junction barrier Schottky (JBS) diodes. Similarly, heavy-ion data suggest a common mechanism is also responsible for leakage current degradation in both devices. This mechanism, based on ion-induced, highly localized energy pulses, is demonstrated in simulations and shown to be capable of causing degradation and SEB for both the MOSFETs and JBS diodes.

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Ion-Induced Energy Pulse Mechanism for Single-Event Burnout in High-Voltage SiC Power MOSFETs and Junction Barrier Schottky Diodes

Ion- and terrestrial neutron-induced single-event burnout (SEB) data indicate that a thicker, more lightly doped epitaxial (epi) region significantly increases the threshold at which ion-induced SEB occurs in silicon carbide (SiC) power MOSFETs and junction barrier Schottky (JBS) diodes. Simulations indicate that the reduction of power dissipation along the core of the ion track is responsible for the increased robustness of the devices that have higher breakdown voltage ratings. Implications for circuit design show that using a 3300-V power MOSFET provides a significant increase in SEB threshold margin compared to a 1200-V MOSFET, with minor impact on power dissipation during normal operation.

J. M. Hutson

Papers

Ion-Induced Energy Pulse Mechanism for Single-Event Burnout in High-Voltage SiC Power MOSFETs and Junction Barrier Schottky Diodes

Effects of Breakdown Voltage on Single-Event Burnout Tolerance of High-Voltage SiC Power MOSFETs