Radiation-hardened electronics advance with emerging standards and expanding markets.
BY Skyler Frink
Space is one of the most difficult environments for electronics, and the systems that contain these electronics must last for years without any maintenance. Unlike an aircraft or underwater vehicle, which enters harsh environments as well, radiation-hardened electronics often are placed on satellites where, once the system is launched and operating, it will not receive any maintenance at all.
This means radiation-hardened electronics need to be completely fail-proof for their inclusion on systems on which lives often depend. These space systems are becoming more and more common for defense and consumer purposes, from military imaging satellites to consumer communication satellites. Highlighting the importance of space systems is the number of countries that are attempting to gain a presence in space.
Even with the shrinking U.S. defense budget, the radiation-hardened electronics industry is seeing a larger market than ever and systems designers that are requesting equipment to fit systems both new and old.
|Older satellite constellations, such as the Boeing 601 MEASAT satellite, are currently being replaced.|
There are satellites in orbit that have been up for dozens of years; these systems, while functioning, are not expected to last forever. While new systems ideally would replace them, some systems designers are simply looking for products that match legacy systems for form and performance. "Right now, systems designers are not doing a lot of research and development, but they are keeping legacy systems alive," says Peter Milliken, semicustom product manager at Aeroflex Inc. in Colorado Springs, Colo. "They are looking for parts for systems that were designed up to 10 or 15 years ago. The time it takes to requalify systems can take years. In legacy systems, they want form, fit, and function equivalents; which saves months, if not years, and millions of dollars."
With the recent defense budget cuts, keeping legacy systems up and running has been an effective alternative to designing entirely new systems. Many older systems that have begun to fail are being replaced, such as the Landsat remote-sensing satellite. Landsat 8 was launched this year for the sole purpose of keeping the Landsat system from falling into disrepair, and a new launch, Landsat 9, is already being planned to keep the system running beyond Landsat 8's design life.
Commercial and military
The consumer market has a major effect on the military market, with electronics that often are higher performing but less reliable. "I think the radiation-hardened electronics market is in two bands, typically based on the type of customer and the orbit they're in," says Simon Wainwright, vice president and general manager of the Microsemi Hi-Rel Group in Lawrence, Mass. "The commercial guys with communication satellites and stuff like that, they tend to be closer to the Earth. Then you have the military guys who tend to be the Geostationary orbits (GEO)."
Because of their use of low-Earth orbits, most consumer electronics can afford to be less tolerant of radiation, as they are exposed to far less radiation than satellites in Geostationary orbits.
Still, the military is looking at commercial products whenever possible. "Customers are looking at commercial solutions and products and looking at what they can get away with," says Microsemi's Wainwright. "Is it possible to use it in an aerospace or defense application?" Less rugged electronics can be used in launch gear, in particular, where the system only needs to last for a matter of minutes or hours before falling away from the primary system.
Risk and reward
With shrinking budgets, aerospace and defense systems designers have been watching the commercial mar- ket more closely for possible innova- tions. "There used to be higher reliability across the board," says Microsemi's Wainwright. "Now we're seeing it split up into different levels of risk. The commercial guys take more risks; they place fewer demands on electronics. They may have a radiation-level requirement that is slightly lower than the military guys. The military has much more stringent qualification levels. Iridium is considering plastic products; GPS 3 will not be using plastic products."
The major risky move the consumer market has made is the consideration of plastic products in communication satellites. If the products are a success, they may end up making their way on temporary, or less important, military systems.
Wainwright says the idea of using plastic parts is simply part of a cycle. "Every 10 to 15 years, people start toying with the idea of using non-hermetics and plastics in space," he says. "They have failures in their programs when they do it."
|The UT90 hardened-by-design standard cell uses 90-nanometer transistors and features 30,000,000 usable equivalent gates with a 1.0-volt Core using standard cell architecture.|
As with all electronics, superior performance and faster speeds are a primary concern. "The trends in designing have been smaller and better," explains Microsemi's Wainwright. "We're seeing more high-speed interfaces. Customers are trying to move a lot more data faster between boxes or between subassemblers in the electronics. If you have video, imagine a satellite taking the picture and having to process and stream that information. Compressing it, managing it, and transmitting it is where the direction is headed." Data processing is so important because of the increasing sensitivity of sensor payloads on satellites.
"The changes have been driven primarily by the sensor," says Aeroflex's Milliken. "We're trying to penetrate to the ground, use radar, take images. The sensor is responsible for collecting a lot of data. What we're seeing over the years is that the sensor's ability to collect more data improves.
"What we end up with is more data that needs to be moved from one satellite to another or back down to the ground, or it needs to be processed by the satellite itself," Milliken explains. "We need more powerful algorithms, more logic, in a smaller space. We are also concerned about power, because a satellite has to generate its power with solar cells. We've got power issues, thermal issues, and a payload that needs to crunch a lot of data and make a decision or send it to the ground. What we have seen is just an increase in the amount of data."
As the volume of data a satellite can gather increases, so too does the necessity of having the processing power to make that raw data useful. Not only is there more to process, but there is a need to process this information while using as little power as possible.
One response to the demand for superior electronics with greater efficiency has been shrinking the size of transistors. "Ninety-nanometer technology is a response to the requirement of more gates per unit area. The 90-nanometer refers to the size of the base transistors; we're building circuits with transistors that are, at a minimum, 90 nanometers," says Aeroflex's Milliken.
"Our systems designers require a particular logic density, and then our systems designers also require specific operating frequency, and they request a certain power. Those things result in physically smaller size transistors," Milliken mentions.
Nintey-nanometer technology may not be new to electronics, but the ability to have transistors of that size and still survive the space environment is. This results in not only superior processing, but also power savings. It does bring up new problems with how the electronics survive radiation, as lower voltages are more susceptible to radiation interference.
"Shrinking tech means you're lowering the voltage," says Milliken, "so the signal-to-noise ratio has gotten worse. The challenge is how do I get smaller and lower voltage and still get the same radiation tolerance."
The challenge of developing electronics that can not only ignore radiation, but also survive in an environment where they are exposed to it is what causes the radiation-hardened market to lag behind other electronics.
|The SVR series DC-DC converters and EMI filters from VPT are TOR qualified and designed for the harshest radiation environments.|
While radiation-hardened electron- ics typically rely on mature technol- ogies, the industry has been branching out to meet systems designers' demands for efficient and faster computing. One way this has manifested itself is in the industry's consideration of wide-bandgap technologies. Wide bandgap semiconductors feature electronic band gaps that are significantly larger than one electron volt, which gives them an advantage in higher temperature environments as well as higher efficiency. "The wide bandgap technologies provide improvement in terms of switching," explains Microsemi's Wainwright. "They lend themselves to much better efficiencies in, say, power supplies. When you use wide bandgap technologies in converters you can get between 3 and 10 percent increases in efficiencies."
Wide bandgap technologies are not a mature technology for the radiation-hardened industry, where products need to be extremely well tested and reliable to pass muster. "The military tends to be a lot more cautious when it comes to wide band gap technology," says Wainwright. "These technologies are in their infancy at this point and we still have a lot of work to do to say that they're reliable. We feel that they have potential and that we can get there. We just need to do the testing."
Wide bandgap technologies show promise for radiation-hardened electronics, and as the technology matures, it will likely become widespread in the industry with its higher efficiency and possible operating temperature.
As space becomes more important, the aerospace and defense industry has begun to test more and more frequently and design products based on the new testing. Effective testing for radiation effects is still relatively new and as research is done, testing changes. "I think the challenges are in trying to understand the different types of radiation effects that there are to withstand," says Microsemi's Wainwright. "The effects we're trying to characterize are total dose, a constant bombardment of radiation, and low dose rate effects that actually can have different effects on semiconductors. The difference there is that we expose the products to lower rates of radiation and we're finding out that even though the radiation is the same, there's actually a different performance when you lower the rate. We have to try to understand the effects as we go forward. We're always looking to do experimentation to understand where the worst effects occur."
With more information being uncovered all the time, the design of certain products has seen itself changing to become more rugged in high-radiation environments. "At the moment, we've been highly active in redesigning bipolar transistors to enhance the survivability over the low dose and high dose radiation spectrums," says Microsemi's Wainwright. "You can have different dose rates or a total dose, and a bipolar is more susceptible to a low dose rate that you'd see in space. We're designing some of our parts to make sure we have a higher resistance to the low dose environments."
The redesign of bipolar transistors comes after the discovery that consistent, low doses of radiation cause existing components issues. Different components react differently to dosage rates and total dose levels.
The emerging TOR standard
Previously, MIL-PRF-38534 Class K was considered the most stringent standard for radiation-hardened electronics. Anything above Class K was simply called Class K+ and was not standardized. This changed with Aerospace TOR, which refers to reports developed by the Aerospace Corp. and flowed down as requirements on space asset procurements that cover technical requirements on electronic parts, mechanical parts, materials, and processes involved in the manufacture of components used on space-based systems. The requirements include guidance on analysis, part deratings, prohibited part types, and part element evaluation and screening that exceeds the requirements of MIL-PRF-38534 Class K.
"TOR is a new requirement that has been growing with the industry," says Monty Pyle, vice president of sales and marketing for VPT Inc. in Everett, Wash. "Even in the tight-knit space industry, everyone is aware of it but nobody can define it unless you're knee deep in it. This continuing, growing requirement is constantly in a state of flux."
The TOR requirements are meant to give military and aerospace systems designers a better idea of requirements for programs that would have previously been Class K+, and companies have already begun designing electronics that fit the current requirements.
"The TOR standard has actually been reviewed and discussed for the past 5 years, and it has gone through many revisions," explains Microsemi's Wainwright. "They're trying to develop a standard that makes sense.
"Over the last couple years, they are trying to be more cost effective; they seem to be making changes that are less expensive for us to meet. We're actually looking at designing our products with the TOR requirements," Wainwright adds.
The TOR requirements take into account not only the needs of defense and aerospace systems designers, but also the needs of the industry. TOR requirements have made it easier for military and aerospace systems designers to communicate with the companies that produce radiation-hardened electronics by providing a common ground.
"As painful as it is, TOR has helped [high-reliability] programs kind of migrate in a general direction to a general point," says VPT's Pyle. "Instead of having various systems designers come in and talk about Class K+ in different ways-there's almost this feeling out and learning process every time-TOR has brought that vagueness more into a gray circle; it helps bring people to the point faster on what's really realistic and available. We can point to a spec now. There's a commonality there; it's not a start from ground zero."
Space has become more open than ever, with governments and their militaries jumping on the chance to get satellites into orbit. "The space market is definitely growing," says Microsemi's Wainwright. "Every time we turn around, there is a different country going into space. It used to be the U.S. was dominant, and then Europe jumped in; now countries all over the world are getting involved. Everybody wants to put a satellite in orbit."
Not only has space become more accessible, but legacy systems are growing obsolete, and some are even failing. "Satellites are not forever things," says Aeroflex's Milliken. "You have a lot of satellite capacity up there that's aging." Legacy systems are already being replaced, and many companies are looking to maintain the status quo, creating a large market for legacy parts.
These factors have made radiation-hardened electronics providers optimistic about the future of the industry, even after the past few years of relatively small growth.
"We believe that this is a market that we want to be in," says Microsemi's Wainwright. "We believe that we see growth in this specific market. We are completely dedicated to investing in it."
Aeroflex Inc. Plainview, N.Y. 516-694-6700
Aeroflex Colorado Springs, Colorado Springs, Colo. 719-531-0800
Aitech Chatsworth, Calif. 818-700-2000
Atmel San Jose, Calif. 408-441-0311
BAE Systems Electronic Solutions Nashua, N.H. 603-885-4321
Crane Interpoint Redmond, Wash. 425-882-3100
Curtiss-Wright Controls Embedded Computing Ashburn, Va. 703-779-7800
Honeywell Microelectronics Plymouth, Minn. 877-841-2840
International Rectifier El Segundo, Calif. 310-726-8000
Intersil Corp. Milpitas, Calif. 408-432-8888
Linear Technology Corp. Milpitas, Calif. 408-432-1900
Maxwell Technologies San Diego, Calif. 858-503-3300
Microelectronics Research Development Corp. Colorado Springs, Colo. 719-531.0805
Micropac Industries Garland, Texas 972-272-3571
Microsemi SoC Mountain View, Calif. 800-713-4113
Modular Devices Inc. Shirley, N.Y. 631-345-3100
MS Kennedy Corp. Liverpool, N.Y. 315-701-6751
Peregrine Semiconductor Corp. San Diego, Calif. 858-731-9400
Semicoa Corp. Costa Mesa, Calif. 714-979-1900
STMicroelectronics Geneva, Switzerland +41 22 929 29 29
Synova Inc. Melbourne, Fla. 321-728-8889
Teledyne Microelectronic Technologies Los Angeles, Calif. 310-822-8229
Texas Instruments Dallas, Texas 972-995-2011
3D-Plus McKinney, Texas 214-733-8505
TRAD Lebarge, France +33 (0)5 61 00 95 60
Triad Semiconductor Winston-Salem, N.C. 336-774-2150
Ultra Communications Inc. Vista, Calif. 760-652-0011
VPT Inc. Everett, Wash. 425-353-3010
Xilinx Inc. San Jose, Calif. 408-559-7778