In the pursuit of ambitious space exploration, NASA’s technology roadmap underscores the critical need for advancements in power and energy storage. Driven by the imperative to support extended missions to Mars and beyond, NASA’s objectives demand cutting-edge solutions.

The threat of radiation-induced failures in power semiconductor devices poses a significant challenge. In an interview with EE Times, CoolCAD Electronics co-founder and CTO Akin Akturk stressed this issue, noting the importance of robust technologies to withstand space radiation hazards. CoolCAD is pioneering the development of semiconductor devices based on silicon carbide (SiC), engineered for resilience in extreme environments.

CoolCAD’s mission aligns with NASA’s goals to develop next-generation radiation-hardened (rad-hard) devices capable of withstanding solar and cosmic radiation. These devices promise compactness to enable substantial reductions in spacecraft mass. By addressing operating voltage and frequency limitations, CoolCAD aims to simplify circuit designs and enhance reliability.

This collaborative effort signifies a leap forward in space power technology. Future space missions demand rad-hard semiconductor power devices resistant to cosmic radiation, compact advanced power systems to reduce spacecraft mass and discrete devices capable of higher voltages and frequencies. These systems must withstand intense acceleration forces and extreme temperature ranges from –270°C to 400°C, addressing critical challenges in space technology.

Understanding space radiation hazards

Space radiation presents diverse threats across different orbits and regions. In low Earth orbit (LEO), protons and heavy ions affect satellites and spacecraft electronics. Above LEO, the Van Allen radiation belt and the South Atlantic Anomaly pose substantial risks to astronauts and spacecraft, necessitating protective measures. Further out in space, a broad spectrum of cosmic and solar radiation, including high-energy heavy ions, threatens spacecraft and human missions. Understanding and mitigating these hazards is critical for the safety and success of future space exploration endeavors.

According to Akturk, semiconductor devices used in space encounter significant risks from cosmic radiation, which comprises high-energy particles and electromagnetic waves. Akturk outlined three primary radiation-induced failure modes affecting these devices:

* Single-event effects arise from heavy-ion impacts that dislodge electrons from their covalent bonds, generating electron-hole pairs within the semiconductor material. This can result in transient plasma and instantaneous failures like latch-ups, burnouts and gate ruptures. Single-event burnouts and single-event gate ruptures manifest as sudden, catastrophic high-current states induced by radiation.

* Total ionizing dose (TID) causes gradual failures due to a cumulative buildup of charge defects in the insulating oxide layer. Over time, this alters device performance, particularly in threshold voltage, rendering devices non-operational. In MOSFETs, absorbed radiation can create electron-hole pairs in the oxide layer and within the bulk of the material.

* Displacement damage results from high-kinetic-energy particles colliding with semiconductor atoms, dislodging them from their positions and degrading the material’s electrical properties, notably increasing leakage and decreasing breakdown voltage.

Single-event effects lead to immediate failures due to ionization trails, while TID gradually erodes device performance, especially in higher-voltage applications. Displacement damage further exacerbates semiconductor degradation, affecting critical electrical parameters. Awareness of these radiation-induced failure modes is essential for designing robust semiconductor devices capable of withstanding the harsh conditions of space. Over time, these phenomena can significantly affect material properties and the electrical performance of devices. While shielding is commonly used to lessen radiation damage, it comes with the drawback of added cost, volume and mass.

Limitations

The limitations of present voltage capabilities impact the design and performance of power systems for space missions by necessitating larger and heavier payloads to deliver increased power. To address this, according to Akturk, current strategies involve using modular multilevel converters (MMCs), which stack multiple lower-voltage components in series to achieve higher voltages and power levels. However, MMCs have drawbacks, such as complex gate driver designs requiring isolation for each component, intricate circuit complexity wherein all components must synchronize, compromised reliability due to single component failures affecting the entire system, and significant increases in system size and weight that negatively affect mission payload mass and volume.

According to Akturk, current constraints on voltage ratings for rad-hard power devices in space applications limit devices to 200 V, with NASA aiming for a 300-V threshold. This limitation for rad-hard high-voltage and high-current power devices necessitates stacking multiple low-voltage devices for higher voltages, adding complexity and weight to spacecraft systems like the ISS. Advancements in rad-hard technology to achieve 300 V and beyond are crucial. Such devices would streamline power system design, enabling high-power electric propulsion and higher-voltage solar arrays, reducing mission payload weights significantly.

However, upcoming long-range space missions demand increased resilience against radiation damage, requiring a 50% derating factor. Future power devices must endure radiation testing at bias voltages of 600 V or more to ensure reliability under extreme conditions. This shift underscores the critical need for advancements in semiconductor technology to meet the demands of NASA’s ambitious space exploration goals.

CoolCAD’s approach

According to Akturk, CoolCAD’s approach to rad-hard semiconductor design leverages the key advantages of SiC power devices for space applications. Although not immune to radiation degradation, these devices can be hardened to achieve radiation tolerance at elevated bias voltages, presenting significant advantages over conventional technologies. CoolCAD has successfully designed and rigorously tested its rad-hard SiC MOSFETs, demonstrating the capability to withstand high-energy radiation up to 900 V or more, even with a 50% derating factor that qualifies them for voltages up to 450 V.

The benefits of these advancements cascade throughout the system. Eliminating the need for component stacking simplifies circuit design, enhances reliability and reduces system size and weight. Notably, increasing the voltage rating from 100 V to 300 V can reduce the weight of harness cables by a factor of 9.

“In comparison, GaN-based power devices, while capable of being radiation-hardened, are limited to approximately 200 V,” Akturk said. “Achieving higher voltages and greater power using GaN technology often requires stacking multiple GaN devices, which adds size, weight and complexity to the system.”

Akturk noted that CoolCAD has optimized design parameters and fabrication processes to enhance the radiation resilience of its semiconductor devices by drawing upon its profound understanding of semiconductor technologies and vast experience in SiC device design. The company’s specialized techniques include a design- and process-oriented strategy tailored for radiation-hardening SiC power devices. Through the adept use of advanced modeling and simulation tools, CoolCAD optimizes semiconductor designs, driving the development and implementation of patented technology and proprietary fabrication techniques.

CoolCAD’s commitment to quality management and meticulous adherence to manufacturing process controls have yielded extraordinary results, producing SiC MOSFETs that avert burnout and achieve a radiation tolerance threshold nearing 1,000 V. This achievement underscores CoolCAD’s leadership in advancing rad-hard semiconductor technology for critical space applications.

Advancements in space power systems

According to Akturk, innovations in power technology are poised to revolutionize spacecraft design and efficiency. Breakthroughs in boosting power semiconductor devices’ catastrophic damage threshold voltage promise significant enhancements in efficiency and reliability for future space missions. These developments not only increase power availability but also reduce payload mass and volume, critical for extended missions to Mars and lunar bases. Additionally, essential power equipment like microgrids and thrusters will become simpler and more compact.

Looking ahead, CoolCAD aims to lead in space electronics with SiC rad-hard MOSFET devices. Its goal is to enhance radiation tolerance, reliability, and efficiency not only for space applications but also for terrestrial power systems. This progress will benefit various sectors, from aviation to nuclear power plants, by improving semiconductor technology’s performance and longevity.

By: DocMemory
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