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Japanese Satellite First to Use Magnetic Memory

SpriteSat mission combines magnetoresistive random access memory (MRAM) with a silicon integrated circuit to read, write and store information about Earth's magnetic field



Courtesy of Freescale Semiconductor, Inc.

When Japan's SpriteSat research satellite launches in October on its three-year mission to study Earth's magnetic field, it will be equipped with a special type of computer memory that will allow it to operate despite extreme temperatures and radiation in Earth's upper atmosphere.

The magnetoresistive random access memory (MRAM) made by Freescale Semiconductor, Inc., in Austin, Tex., (and integrated into the satellite built by the Ångström Aerospace Corporation) is smaller, leaving more space for transponders and other signal transmitters and receivers. The reason: thanks to its speed, capacity and durability, MRAM can do the job of both flash memory and static random access memory (SRAM) that normally are part of a satellite's electronics.

"MRAM has the storage capabilities of flash and the speed and endurance of SRAM," says Saied Tehrani, a Freescale fellow and director of analog and mixed signal technologies.

He says that MRAM's role is novel, because it marks the first time that magnetic materials that store information are being combined with the silicon circuitry that reads and writes the information. He notes that it's also a lot quicker, more efficient and durable than flash. "We are programming the memory in 35 nanoseconds—five or six orders of magnitude faster than flash—and the number of times we reprogram is unlimited," Tehrani says, noting that flash takes microseconds to program, milliseconds to erase and can be reused about 100,000 times. He adds that MRAM performs nearly as fast as SRAM.

The four-megabit Freescale MRAM device is part of Uppsala, Sweden–based Ångström's Tohoku-ÅAC MEMS Unit (TAMU), a magnetometer subsystem that will be sent into space aboard SpriteSat, which was built by Tohoku University in Sendai, Japan, and takes its name from the role it will play monitoring the effects of "sprites" (a type of high-altitude lightning) in Earth's upper atmosphere. The satellite is set to monitor the phenomenon from an orbit about 500 miles (800 kilometers) above the planet.

The integration of MRAM and TAMU comes about a year after Johan Åkerman, a professor of material physics and applied spintronics at the Royal Institute of Technology in Stockholm and a former Freescale researcher, first suggested that Ångstrom consider Freescale's new technology to provide space-saving memory technology for its satellites. "If you have an MRAM, you can replace one-time programmable memory and SRAM," he says. MRAM does this while hosting the software that operates the satellite's navigation systems as well as detects any radiation problems that the satellite encounters.

"If this flight is successful, I would expect this MRAM would pop up on all small satellites [less than 220 pounds, or 100 kilograms] in the world," says Fredrik Bruhn, Ångstrom's vice executive chairman and CEO. "We are trying to standardize the different interfaces on all satellites."

Ångstrom, along with Honeywell International, Inc., and other technology makers are currently adapting MRAM for use in space and by the military. Freescale also envisions it as potentially useful to automakers and other terrestrial industries. Cars could use MRAM, for instance, to collect data from systems that control air bag deployment, engine function and stereo sound systems. Tehrani says that Freescale is proving that MRAM can function in some of the harshest environments: space, for one, but also on the ground, under a car hood, where temperatures range from –67 to 257 degrees Fahrenheit (–55 to 125 degrees Celsius).

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