SiC devices for space exploration: Venus Planet

In recent times, exploration of the neighboring planets has witnessed several technological advancements with about five rovers have been sent to Mars, the Perseverance rover being the latest. SiC devices for space exploration help scientists closely study the surface and atmosphere while also further preparing for human explorations of such planets. Mars is an icy cold planet with an average temperature of -70°C. Hence conventionally used silicon-on-insulator IC technology could be used in electronics for space rovers. These Si ICs have a maximum operating temperature of about 300°C above which they cannot be used for a long period of time.

Venus is considered to be the sister planet of Earth because it has a similar size and composition, and surface exploration of this planet is expected to provide valuable information about Earth’s history. The average temperature on the surface of Venus is about 400°C, which is way above the maximum limit of the functioning of conventional Si-based electronic devices. Previous explorations sent to Venus have proved that these ICs only survived about 2 hours in that environment. This is where SiC devices prove to be powerful candidates. These wide band gap devices are suitable to be used for high-power and high-temperature applications.

FIGURE 1: SILICON CARBIDE-BASED ELECTRONICS

SiC-based devices for space exploration

Venus’s atmosphere is extremely dense and is mostly made up of CO2 (96.5%), with a surface temperature of 450°C and 92 atm of surface atmospheric pressure. The Soviet Union’s prior Venus landers, Venera 7 (1970), which ran for 23 minutes, and Venera 13, which operated in 1982, both had short operational lifespans due to the extreme climatic conditions.

Landers used in space explorations are divided into three categories– short-term landers, long-term landers, and mobile surface platforms. Short-term landers are used for only a few hours to carry out the meteorological analysis of the rocks and the soil present on the planet. Because of short-term operation, Si-based devices along with optimum cooling mechanisms can be deployed in them. Long-term landers are deployed for an average of 120 days for analyzing the temperature, pressure, wind speed and direction, atmospheric chemistry, and seismicity of the planet. Whereas, mobile surface platforms conduct mineralogical analysis and take panoramic pictures of the planet’s surface. For long-term landers and mobile surface platforms, Si-based electronics cannot be used because they lose their semiconductor property above 300°C, hence SiC based alternatives are being researched for longer operations.

Along with the fact that the Silicon Carbide bandgap is three times wider than Silicon, the SiC can also keep its semiconductive properties up to 600°C while Si loses them above 300°C. (3.2eV versus 1.1eV ). In comparison to Si, SiC can withstand higher voltages, power, radiation, and off-state leakage currents thanks to its wider bandgap. SiC dissipates heat faster than other semiconductor materials due to its excellent thermal conductivity. SiC devices can therefore run at very high power levels while still dissipating the enormous amounts of excess heat they produce. SiC power devices have high-voltage blocking capabilities, low on-resistance, and high-temperature operation. This is because SiC has a ten times higher breakdown electric field and three times higher thermal conductivity as compared to Si.

Challenges in SiC-based devices for space exploration

SiC technology is still in the development phase and is technologically behind the Si-based technology in manufacturing. SiC technology is inferior in terms of wafer size, manufacturing cost, and transistor size. The channel length for the currently available SiC transistors is in the order of μm, which is comparable to the Si-based channel length in the 1980s. This will eventually lead to SiC electronics being slower as compared to Si to further limiting its functionality and application in complex electronic circuits that operate on higher frequencies.

The material’s properties present the biggest problem for SiC manufacturing. SiC takes more energy, longer, and higher temperatures for crystal growth and processing due to its extreme hardness (nearly diamond-like). Additionally, because of its great transparency and high refractive index, especially for the most commonly found crystalline structure (4H-SiC), it makes it challenging to analyze the material for surface flaws that can potentially influence epitaxial growth or final component yield.

Crystalline stacking faults, surface particles, micropipes, pits, scratches, stains, and crystalline stacking faults are the principal flaws that occur while manufacturing SiC substrates. Research has shown that these flaws are found more frequently in 150-mm wafers than in 100-mm. This could negatively affect the performance of SiC-based devices for space exploration. SiC’s manufacture presents difficult hurdles in terms of cycle time, cost, and dicing performance as it is the third-hardest composite material in the world and also very brittle. Due to the extremely low diffusion constants of impurities, the diffusion process is not practical for impurity doping in SiC.

Hence, the newer technologies have been developed in recent times to address both material development as well as processing problems in SiC manufacturing. Material development technologies include bulk and epitaxial growth for material manufacturing, in which 5-100µm thick, lightly doped layers are homoepitaxially grown by chemical vapour deposition (CVD) on off-axis SiC wafers. Process development technologies like ion-implantation and in-situ doping during growth are exclusively employed for SiC device fabrication.

Conclusion

Apart from Venus explorations various other high-power and high-temperature applications require the development of high-temperature withstanding electronic devices using SiC. These applications include naval vessels, aircraft engines, hybrid vehicles and charging facilities, traction equipment for railways, HVDC transmission and flexible AC transmission system (FACTS), solar PV power generation and wind power, smart grid, etc. In order to make these devices more efficient and the electronics more compact, SiC is the future. Recent developments have shown that SiC-based electronics can replace Si-based electronics in high-power and high-temperature applications in the coming years.

References

[1] H. Kim, J. Bagherzadeh and R. G. Dreslinski, “SiC Processors for Extreme High- Temperature Venus Surface Exploration,” 2022 Design, Automation & Test in Europe Conference & Exhibition (DATE), 2022, pp. 406-411, doi: 10.23919/DATE54114.2022.9774769.

[2] T. Kimoto, “SiC technologies for future energy electronics,” 2010 Symposium on VLSI Technology, 2010, pp. 9-14, doi: 10.1109/VLSIT.2010.5556137.

[3] Friedrichs, Peter. (2007). Technological challenges for manufacturing power devices in SiC. 2007 International Conference on Compound Semiconductor Manufacturing Technology, CS MANTECH 2007.