MIT researchers have adopted gallium nitride for applications like Venus exploration due to its resilience in temperatures over 500 degrees Celsius.
Venus’s surface temperatures reach 480 degrees Celsius—hot enough to melt lead—making it too hostile for humans and conventional machines. This has prevented scientists from deploying rovers, as silicon-based electronics fail under extreme conditions.
Researchers from MIT have recently adopted gallium nitride for high-temperature applications, such as exploring Venus, due to its ability to withstand temperatures exceeding 500 degrees Celsius. While gallium nitride is already employed in earth-based electronics, such as phone chargers and cell phone towers, there is still limited understanding of how this material performs beyond 300 degrees, the maximum operational threshold for traditional silicon electronics.
Turning up the heat
The researchers utilized MIT.nano facilities to construct gallium nitride devices known as transfer length method structures, consisting of a series of resistors to measure material and contact resistance. They applied ohmic contacts using two common techniques: one involving metal deposition on gallium nitride followed by annealing at 825 degrees Celsius for 30 seconds, and a team at Ohio State, which removes portions of gallium nitride to replace with highly doped gallium nitride that facilitates enhanced current conduction.
A comprehensive approach
In their research, devices underwent two testing methods: short-term at Rice University using a hot chuck at 500 degrees Celsius for immediate resistance measurements, and long-term at MIT with a specialized furnace assessing resistance changes over 72 hours. Advanced microscopy at MIT.nano and the Technology Innovation Institute further analyzed the effects of high temperatures on gallium nitride and ohmic contacts at the atomic level.
Findings indicated that contact resistance remained stable at 500 degrees for 48 hours, and performance improved with the regrowth process. However, material degradation began after 48 hours in the furnace. Efforts to enhance long-term durability, such as adding protective insulators, are ongoing. These insights are crucial for developing high-temperature gallium nitride transistors.
