One of the biggest challenges in spaceflight is how to deal with the effects of radiation on electronic components. Radiation-hardened (rad-hard) ICs are used in space applications to ensure the reliable performance of systems in these harsh environments. For chipmakers, this means special attention needs to be paid to the design, layout, manufacturing processes, and testing of these ICs. The demand for higher integration, smaller size, and better power efficiency also is contributing to new challenges in rad-hard IC development.
The most recent space program to test these mission-critical components is the Mars 2020 Perseverance rover. “Deep space is a challenging environment for spaceflight and Mars rover systems, particularly due to the intense radiation environment encountered in nearly all mission profiles,” said Josh Broline, director of marketing applications at Renesas Electronics Corp. “For product development, the biggest challenge is not necessarily the general performance of the IC but, rather, meeting that performance in a radiation environment.”
The highest levels of radiation hardness are required for high orbits and deep space as well as for the expected mission lifetime, said Eric Toulouse, senior vice president and general manager for IR HiRel, an Infineon Technologies AG company.
Space applications demand high-reliability power electronics that perform in the harshest environments, and they must withstand severe thermal, mechanical, and radiation conditions, he added.
The only way to provide components that are bulletproof with the highest level of radiation hardening is by optimizing each and every step of the process, starting with the wafer recipe itself, Toulouse said. “It’s not only about making sure you use the best processes, but it’s also making sure that you hit the sweet spot every time for those parts in terms of how they are fabricated, so there is very little tolerance for variation around the nominal specifications.”
Testing is also extensive, which includes stressing the device for extreme temperature and operating the device in full operational mode for an extensive amount of time, he said. “When we’re done and we think the lot is good enough because it meets those stringent standards, we go back and do it again.”
Both IR HiRel and Renesas are supplying components to NASA’s rover programs. Rad-hard ICs from both companies are onboard the Perseverance rover, launched from Cape Canaveral Air Force Station in Florida on July 30, 2020. Also hitching a ride with the rover for a trip to Mars’ Jezero Crater landing site is an innovative autonomous helicopter that NASA plans to flight-test. The rover is expected to reach the landing site in February 2021.
Integration, size, and efficiency
Demand for higher efficiency, smaller size, and higher integration typically translates into additional challenges in deep-space applications.
“Since we are always pushing the envelope on innovation by advancing items like IC feature set, integration, size, and power efficiency, this brings on new challenges in regard to optimal performance and functionality in a radiation environment,” said Broline.
This is even the case for best practices like selecting key process technologies, applying proven layout and design techniques, and manufacturing steps like burn-in and total dose testing to ICs, he continued. “It is a combination of utilizing new process technology size/nodes, lower- or higher-voltage process-level devices, and the new circuit topologies to drive innovation, among other things.
“For a given product development, the biggest challenge is not necessarily the general performance of the IC, but rather meeting that performance in a radiation environment,” he added.
The challenges are even more so for space applications, agreed Toulouse. “Keep in mind that part of the cost of launching a probe or a satellite in space has to do with the weight of the equipment, and that cost per pound or kilo is actually very high. You’re talking about tens of thousands of dollars, depending on which orbit you’re trying to launch to, and therefore, there is a lot of pressure to reduce weight. Reducing size is also a good thing. Typically, the way people try to resolve those weight and size issues has to do with improving energy efficiency, especially in the power system.”
So the call for higher efficiencies and smaller size is very relevant because that savings in space and weight can be used for more sensors for greater capability, and if you’re talking about a commercial satellite, for example, it can improve the revenue stream, Toulouse said.
But you can’t limit the efficiency discussion to the power semiconductor component; there is a lot more to it, he said.
“Our focus typically is on the large converter — several hundreds of watts — and what you find out when you do a budget analysis is that the losses, of course, occur in the power switches, silicon, or gallium nitride [GaN], but you also have losses everywhere else,” he continued. “There are losses in the substrate; there are losses in some of the passive components because their resistivity is not zero; and there are losses in the magnetics if you’re using an isolated type of architecture. At the end of the day, we need to find a way to optimize the whole system.”
To have a conversation about efficiency, it involves all of the subcomponents within that power converter, said Toulouse. “We’re trying to talk in terms of total system efficiency, not just in terms of what a component can do.”
Toulouse said that IR HiRel offers vertical integration, enabling them to build “whole applications.” In addition to developing components and ICs, the company also designs what they call “hybrids” that bring in more of the passive components, as well as full PCB power supply systems. The company offers standard, semi-custom, and custom design support.
“We’re learning a lot from doing this development,” he said. “What are the best tradeoffs and also what are the best components that can be used in conjunction with our semiconductors. So for a total solution, you end up with the best possible performance from an efficiency standpoint while maintaining the reliability aspect.”
While Toulouse admits that there is “a little bit of a hype” around GaN and silicon carbide (SiC) technologies for good reasons, there is still a lot of innovation happening in silicon-based rad-hard MOSFETs, which also enable low-risk upgrades. He teased that IR HiRel will release in late November a new rad-hard MOSFET that “brings an incredible improvement in overall system efficiency to the point that it’s raising the bar for the other technologies to demonstrate a superior level of efficiency.”
Onboard the rover
Marking the company’s fifth time supplying power electronics onboard a Mars rover, IR HiRel has supplied thousands of mission-critical rad-hard components, including space-grade MOSFETs, ICs, and other power control products in several rover subsystems. These include the flight computer, motor control, radar, robotic arm, and mission instrument suite.
They can be found in various scientific instruments, including Mastcam-Z (a mast-mounted HD camera with panoramic, stereoscopic, and zoom capabilities); SuperCam (a camera, laser, and spectrometers); Planetary Instrument for X-ray Lithochemistry (PIXL); Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC), otherwise known as a UV spectrometer; and the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE), an oxygen-producing instrument.
Renesas’s Intersil rad-hard ICs are deployed throughout the Perseverance rover and its seven instruments. These include voltage regulators and references, synchronous buck and LDO regulators, PWM controllers, MOSFET drivers, 16-channel multiplexer, SPST switch, RS-422 line transmitters and receivers, and microprocessor supervisory circuits. The ICs support subsystems for mission-critical applications in power management and distribution, inertial measurement units, precision data handling and processing, and navigation and flight entry, descent, and landing control.
There are also five Renesas Intersil-brand ICs onboard the Ingenuity Mars Helicopter, which launched with the Perseverance rover, including two RS-422 interface products, voltage reference, linear regulator, and a supervisor IC.
The autonomous aircraft is a 4-pound (2-kilogram) helicopter, designed from a combination of specially designed components and off-the-shelf parts. Travelling in the belly of the Perseverance rover, it charges from the rover’s power supply. But once deployed on Mars, the helicopter’s solar panel will provide power to the batteries.
Ingenuity is a technical demonstration and the first aircraft to attempt controlled flight on another planet. The flight challenges on Mars range from a thin atmosphere, which makes it difficult to achieve enough lift to the extreme cold down to –130°F (–90°C). The extreme temperatures will also challenge the reliability of many of the parts on the helicopter, including solar cells, batteries, and other components.
When the rover lands on Mars’ surface, NASA will release the helicopter and test it to distances of 980 feet and 10 to 15 feet off the ground for a maximum of 90 seconds. If successful, the tests will help engineers build the next-generation helicopter for the next mission to Mars.