More rad-hard gallium nitride devices are circling the planet.
Unlike silicon, requiring custom manufacturing processes and packaging to insulate semiconductors from radiation effects, gallium nitride (GaN) devices are largely resistant to damage caused by radiation due to physical characteristics and structure.
Those attributes can be leveraged in the design of satellites. Orbiting electronics must withstand the effects of gamma rays, neutrons and heavy ions. Protons make up 85 percent of space radiation, while heavier nuclei make up the remainder. Radiation can deteriorate, interrupt knock out satellite electronic components.
Degradation occurs in a variety of ways, including crystal disintegration. For example, traps created in the non-conduction zone or a cloud of electron-hole pairs can imbalance device functionality by short circuits. Because electron-hole pairs cannot be formed in GaN devices, energetic particles cannot induce a short circuit.
Alex Lidow, CEO of Efficient Power Conversion Corp., discussed the growing potential of radiation-resistant GaN devices for space applications with Power Electronics News.
PEN: Thermal management of electronic components and circuits is essential for ensuring reliable systems under all operating circumstances. Designers must grasp the challenges of wide-bandgap semiconductors like GaN in order to fully realize their promise. It is feasible to decrease passive components such as inductors and capacitors, constructing lighter and smaller systems by operating at greater switching frequencies and higher power density. What are the space-related considerations?
Lidow: The biggest driver of cost in satellites is weight. In a power system, weight is proportional to efficiency. The more efficient a system, the smaller it is and the less thermal management is required. GaN transistors are far more efficient than Si MOSFETs. They also enable higher-frequency designs, which reduce the size of passive components and therefore the weight of the system. GaN devices are also thermally more efficient, so not only do they generate less heat, but they also require smaller thermal management systems for cooling.
PEN: How would you compare the efficiency of GaN devices and silicon?
Lidow: Comparing a radiation-hardened GaN transistor with a rad-hard Si MOSFET illustrates the enormous performance gap between the two technologies. Let’s pick a specific example, the FBG20N18 GaN FET versus the IRHNA67260. Both are 200-V transistors with about the same [drain source on resistance]. However, the GaN device… is one-tenth the size and weight; has one-fortieth the capacitance required to switch; it has zero reverse recovery; it is much more radiation-resistant and has a price that is half that of the Si MOSFET.
PEN: What are some deployment examples?
Lidow: Two examples of systems that are in spatial orbits today are DC/DC converters, such as the one discussed above, and reaction wheel motor drives. Reaction wheels keep a satellite in a stable orientation, and thousands of these satellites are in orbit today using FBS-GAM02 hybrid modules from EPC Space. These modules include a half-bridge circuit with drive- and level-shift electronics that save space and are rad-hard. There are also many lidar systems in space that use GaN devices for the same reason that autonomous cars use GaN: It can generate high-current and extremely narrow pulses that drive lasers. These high-current and narrow pulses mean the lidar system can see farther and with greater resolution. The radiation-hardness of the GaN devices reduce any shielding requirements.
PEN: What are the challenges in terms of power supply for space?
Lidow: Rad-hard GaN transistors are available to replace most rad-hard Si MOSFETs. Customers are very happy with the performance, the reliability, and especially the low cost — about half the cost of a rad-hard Si MOSFET. We are getting many requests to expand our line of rad-hard products to integrated circuits so that the same degree of radiation-hardness can be extended to the rest of the system. We already have GaN-driving modules available…. In the fourth quarter of this year, we will launch a series of GaN IC drivers for GaN transistors. In the future, we will also offer rad-hard monolithic power stages like the commercial EPC2152. Beyond the power stages, we are planning to evolve our products into complete systems-on-a-chip that will be rad-hard.
PEN: GaN power transistors are widely used for power conversion applications in space. What are the challenges for achieving adoption for space applications? Where do you see significant opportunities for future expansion?
Lidow: Rad-hard Si MOSFETs are lower-performance, larger, weaker, and more expensive than rad-hard GaN devices. They also have extremely long lead times. [We] do not see any remaining barriers to adoption. The most challenging has been to get the first parts in space. Satellite designers are naturally conservative and therefore reluctant to try new things. The advantages of GaN have been so compelling that we were able to convince satellite designers to launch products starting about five years ago. Today, there are over 50,000 components in low-earth orbit to geosynchronous equatorial orbit, GEO being the most demanding in terms of reliability and radiation tolerance. Once legacy was established, designers started using our GaN products quickly.
The biggest opportunities will come from GaN power ICs. We can integrate motor drives and power supplies on just a few GaN chips — all of which are extremely rad-hard.
The key areas where GaN can be used are in both RF and power conversion. Because of its tiny form factor and excellent efficiency, a power supply designer could opt for a GaN transistor over a silicon transistor. In comparison with silicon devices with higher thermal management needs, GaN transistors waste less power and have higher thermal conductivity. The new power devices are also intrinsically rad-hard and can operate at temperatures up to 600˚C. Because the voltages needed in space missions are lower than typical AC line voltages, 200-volt and occasionally 300-volt devices are the best to utilize.
And in that range, GaN just outperforms silicon carbide, making it the preferable choice. Gallium nitride, as a lateral device, will also be easier to incorporate in the future.
Maurizio Di Paolo Emilio holds a Ph.D. in Physics and is a telecommunication engineer and journalist. He has worked on various international projects in the field of gravitational wave research. He collaborates with research institutions to design data acquisition and control systems for space applications. He is the author of several books published by Springer, as well as numerous scientific and technical publications on electronics design.