Space is an area of interest to many power companies at the moment. The space industry has evolved from individual satellites working in high orbits to constellations of lower orbiting satellites that operate together as a single entity. These constellations can have tens of thousands of satellites communicating with each other to provide complete coverage over the surface of the earth. Satellites operating in low earth orbits (LEO), also known as new space, do not need as much radiation protection as those that operate further from the earth, which lowers the barrier to entry for suppliers. LEO satellites are cheaper, and can almost be thought of as disposable, as when one satellite fails, then the constellation is reconfigured to repair the network and restore full coverage.
LEO constellations may be the way that the majority of the industry is heading, however, that is not the full story. In many cases, for example, in the military and other critical applications, full radiation protection must be guaranteed, whatever orbit is chosen. Failures cannot be tolerated. Very few companies are able to target these applications because of their strict demands. Microchip has supplied the space industry with a wider variety of products for decades, and now, the company has added another capability, thanks to its new rad-hard power MOSFET family, which has been designed to meet the MIL-PRF-19500/746 slash-sheet specification, and includes the JANSF2N7587U3, 100V N-channel MOSFET with JANSF qualification to 300 Krad (Si) Total Ionizing Dose (TID).
The rad-hard power devices come in voltage ranges from 100–250V to 100 Krad (Si) TID, with the family expanding to higher Radiation Hardness Assurance (RHA) levels. The JANS RH MOSFET dies are available in multiple package options, including a plastic package for cost-effective new space and LEO applications, and a hermetically sealed ceramic package developed for total dose and Single-Event-Environments (SEE). The power MOSFETs have been designed to be the primary switching elements in power conversion circuits with low RDS(ON) and a low total gate charge.
PSD – Why are there so few suppliers for MOSFETs that meet these specifications?
Jim LeClare (JL), Senior Marketing Product Manager, High-Reliability Solutions at Microchip – Components are easy to make if you don't put them in a radiated environment. Once that happens, they collapse quickly. You need a lot of expertise to develop these types of product. That's kept this area very exclusive, and why we think that our new family of MOSFETs are a big deal. To get here, we have had to control every part of the process - design, fabrication, packaging and test. Multiple companies have tried to get into this market, but have given up.
PSD – Why have you succeeded when others failed?
JL - We have built components to Army and Navy specifications for around 50 years, and worked with aerospace companies for over a decade longer. That means we understand not only how to make the die, but how to package the parts and how to test them. In space applications, it's one thing to make be able to make the die, but it’s another to be able to package it and have it survive. Microchip has had decades of experience designing radiation-tolerant (RT) and radiation-hardened (RH) solutions for aerospace and defense, including MCUs, FPGAs, Ethernet PHYs, RF products, and timing solutions, as well as power devices. We supply the industry with everything from bare dies to system modules.
The difficulty in designing MOSFETs and other analogue parts for these applications is due to their oxide trapping charge. The oxide is under constant radiation, which builds up, reducing gain. To protect the devices, you need to move those charges around in nanoseconds. There's a lot of expertise required to accomplish this, and it takes very senior radiation design engineers.
One of the most important aspects of designing for space applications is testing. You have to test all the right parameters. When we first released these parts, we also went to independent sources, such as NASA and the Jet Propulsion Labs, and gave them parts to thoroughly test, right down to where the epoxy meets the die itself.
The testing is also what differentiates the parts. All of our parts start with dies that we would expect to make it right the way through the hardest environmental testing, but that costs a lot of money. So, for example, in our new space plastic package version, we have throttled down the testing. What's nice about this strategy is that if you have an end customer who wants the device to last two years, they can just use it as it is, but if they need a guarantee of a longer operational lifetime, they can add the extra screening themselves to get devices that will last 5 years, or 15 years.
You also have to be in a position to to supply the components when needed. In the consumer industry, customers might order millions of components each month for the next year. In these types of space application, an order may be a thousand pieces now, and then another thousand parts five years later. It's hard to replicate parts that you make one time, then make more years later.
That's why we have to keep everything in-house - so that we can control the quality, and that means high reliability in extreme conditions, which is the area where we think that we differentiate ourselves. When I say extreme conditions, I mean designing parts that can fly around in a LEO for five years, go all the way out to Jupiter, or can survive near man-made nuclear events.
PSD - Is it a completely new design?
JL - We based the family on an existing MOSFET range that is proven to perform in extreme conditions. These are newer versions of these parts with protection from 100k TID to 300k TID.
PSD – 300k TID seems a lot?
JL- Once you go to 300k TID, the demand is very selective, and mainly for countries and companies that work with the US government for strategic reasons, so they're very tightly controlled. The 100k TID versions are fine for companies or organizations such as NASA for weather satellites. They get used in new space applications for telecommunications or imaging companies, where they want to ensure the power supply is working at all times. If you get a glitch in digital logic, you can reset that digital side of the circuit, but you can't reset the power - it always has to work. 30K TID is usually sufficient for new space, but more normally 50k TID. 300K TID is mainly for deterrent strategic programs that have no room for any failure under any condition
https://www.microchip.com/en-us/solutions/aerospace-and-defense
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