Magnetic Random-Access Memory

Visualize   By Tracy Staedter   July/August 2002

Take a tour through a magnetic random-access memory cell.

Your computer has a leak. The dynamic random-access memory (DRAM) technology inside it relies on electrons stored in microscopic cells. The electrons escape frequently, though, and the cells must be electrically recharged thousands of times per second to keep your electronic files intact. But a new kind of memory may end that. Magnetic random-access memory (MRAM) stores data in the spin of electrons inside tiny magnetic sandwiches (see “Computing’s New Spin,” TR January/February 2001). The sandwiches don’t lose their magnetism—or memory—even if the power goes out. What’s more, MRAM has the potential to store as much data as DRAM, write it faster and access it almost instantly—all while consuming less energy.

A magnetic random-access memory cell is made of a thin insulating layer sandwiched between two magnets. Depending on the way their electrons are spinning, the magnets can have fields that point in the same direction or in opposite directions. These two states correspond to the ones and zeroes of digital memory. Each cell sits at the intersection of perpendicular electrodes that run above and below it.

To write a bit, electric current must pass through two intersecting electrodes. At the cross point, the currents induce a magnetic field sufficient to alter the spins of electrons and therefore the cell’s magnetic orientation. To read the data, a lower-voltage current travels along the bottom electrode, through the specific memory cell, and out along the top electrode. If the two layers are magnetized in the same direction, their electrical resistance is low, indicating a one; if they are magnetized in opposite ways, resistance is high, indicating a zero. An electrical sensor at the end of the top electrode reads the resistance and determines the binary state of the cell that was read.

Motorola, IBM and Eden Prairie, MN-based NVE are developing the technology with funding that comes in part from the U.S. Defense Advanced Research Projects Agency. If they succeed, we could see MRAM devices as early as 2004.

Tracy Staedter is the managing editor at Technology Review.