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UIC Engineers Square the Ring in Magnetic Memory Research

A team of University of Illinois at Chicago electrical and computer engineers has demonstrated that nanometer-sized permalloy rings, shaped into tiny rectangles, can store and access data almost instantly. The finding brings closer by one step the commercial reality of a promising form of memory called MRAM.

Magnetic Random Access Memory is a contemporary spin on decades-old core memory technology that uses magnetic fields rather than electrical charges to reliably store and randomly access data.

Square-shaped magnetized memory rings may be the key to making MRAM work.

"With MRAM, you don't have to refresh the memory," said Vitali Metlushko, associate professor of electrical and computer engineering at UIC. "You store it, recall it and it's there. It's non-volatile."

With the more conventional DRAM (dynamic random access memory), information is stored as electrical charges. It must be constantly refreshed, Metlushko said.

"If your battery dies, you lose information. But with MRAM, even if your battery dies, your magnetized layer of memory stays magnetized and the data stays there, hopefully, forever."

Metlushko and his graduate students Vidhyashankar Baskaran, Dwarakanath Geerpuram and Anand Subra Mani report on their research into square rings used for MRAMs in the October issue of Nanotechnology, a journal published by the London-based Institute of Physics.

While Metlushko originally investigated the memory properties of circular rings, he found that square and rectangular-shaped rings sitting on nano-scale memory cells proved to be a more reliable design for storing data, keeping data stable and for switching the magnetic field, making it possible to retrieve information.

But the technology remains largely in the development phase with improvements needed in patterning the magnetic material so the square rings are uniform down at sizes below 50 nanometers. Presently MRAM square ring cells that work well as a circuit are comparatively large -- often as big as 500 nanometers.

"Everything is determined by shape, and small variations in the shape of magnetic material leads to drastic changes in switching properties," said Metlushko. "You want all of your memory elements, all these MRAM cells, switching exactly together. We have to be able to control it more precisely."

The UIC researchers are part of a larger international team of university scientists and researchers, as well as researchers at the Argonne and Los Alamos national laboratories, among others, trying to advance the state of the art of nano-scale MRAM. Corporations such as Motorola and Hitachi also are engaged in substantial MRAM research projects.

Unlike with everyday DRAM memory chips used in personal computers and other consumer electronic devices, MRAM holds the promise of providing instant access memory without the boot-up delays now common after turning a device's power on. Also, MRAM is not prone to memory loss caused by radiation particles, so it may prove to be the memory storage device of choice in future spacecraft electronics, such as space probes, launch vehicles, laboratories and earth-orbiting satellites.

Metlushko said MRAM is an alternative form of memory that will someday rank high among low-power nanoelectronic components, but he said it is hard to predict when.

"Look how much time it took for the transistor to enter consumer electronics after its invention. MRAM will happen, but I wouldn't bet it would be tomorrow. Nanoscience is unpredictable," he said. "That's part of the beauty of it."

For more information about UIC, visit www.uic.edu

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