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Technique for storing data into molecules unveiled

29 Jan 2013

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Just yesterday, we had published a story about how scientists have managed to store and retrieve several files into DNA, error-free. Today, we discover that an international team of researchers at MIT have developed a technique for storing data into individual molecules.

An experimental technology called molecular memory, which would store data in individual molecules, promises another 1,000-fold increase in storage density. But previous schemes for molecular memory have relied on physical systems cooled to near absolute zero. The research team led by Jagadeesh Moodera, a senior research scientist in the MIT Department of Physics and at MIT's Francis Bitter Magnet Laboratory, describes a new molecular-memory scheme that works at around the freezing point of water—which in physics parlance counts as "room temperature."

Moreover, where previous schemes required sandwiching the storage molecules between two ferromagnetic electrodes, the new scheme would require only one ferromagnetic electrode. That could greatly simplify manufacture, as could the shape of the storage molecules themselves: because they consist of flat sheets of carbon atoms attached to zinc atoms, they can be deposited in very thin layers with very precise arrangements.

The storage molecules were developed by chemists at the Indian Institute of Science Education and Research in Kolkata. The Indian chemists believed that the molecules could be useful for the type of experimental devices studied by Moodera's group, which use "spin," a property of tiny particles of matter, to represent data.

Half a sandwich

Under Moodera's supervision, Karthik Raman, then a PhD student in MIT's Department of Materials Science and Engineering and now a scientist at IBM's Research Lab in India, and Alexander Kamerbeek, a visiting student from the University of Groningen, deposited a thin film of the material on a ferromagnetic electrode and added a second ferromagnetic electrode on top—the standard structure for magnetic memories. The idea is that a relative change in the electrodes' magnetic orientations causes a sudden jump in the device's conductivity. The two states of conductivity represent the 1s and 0s of binary logic.

To their surprise, however, the MIT researchers measured not one but two jumps in conductivity. That implied that the electrodes were changing the device's conductivity independently. "According to the common knowledge, this shouldn't happen," Moodera says.

To confirm their intuition, the researchers performed the experiment again, but instead of using two ferromagnetic electrodes, they used one ferromagnetic electrode and one ordinary metal electrode, whose only purpose was to read the current passing through the molecule. Indeed, they found that the jump in conductivity still occurred.

MIT molecular memory

The new molecules are known as 'graphene fragments,' because they largely consist of flat sheets of carbon (which are attached to zinc atoms). That makes them easier to align during deposition, which could simplify the manufacture of molecular memories.

As Moodera explains, the ability to alter the molecules' conductivity with only one electrode could drastically simplify the manufacture of molecular memory. The bottom electrode of a memory cell can be deposited in a perfectly flat layer and the storage molecules layered on top of it. But if the next layer to be deposited is the top electrode, its molecules will tend to mingle with the storage molecules. If the electrode is magnetic, that mingling can compromise the performance of the cell; if it's metallic, it won't.

In an alternate design, the top electrode is a tiny tip, like the tip of an atomic force microscope, positioned less than a nanometre above the storage molecules. But again, a magnetic electrode poses problems—in this case, by limiting how densely the storage cells can be packed. If they're too close together, a magnetic tip might change the magnetic orientation of cells adjacent to the one it's intended to address. That's not a concern with nonmagnetic tips.

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