How Many Atoms Does It Take To Store A Memory Bit?
January 13, 2012

How Many Atoms Does It Take To Store A Memory Bit?

Researchers at International Business Machines (IBM) have discovered how to store a bit of information in just 12 atoms, a process that usually requires the use of a million or more atoms.

The technique, reported in the journal Science, is based on ferromagnetism and could allow for even smaller, faster and more energy-efficient devices in the future.

“The chip industry will continue its pursuit of incremental scaling in semiconductor technology but, as components continue to shrink, the march continues to the inevitable end point: the atom,” Andreas Heinrich, lead investigator in atomic storage at IBM Research, told Kate Taylor of TG Daily. “We´re taking the opposite approach and starting with the smallest unit - single atoms - to build computing devices one atom at a time.”

Until now, it was unknown exactly how many atoms it would take to build a reliable magnetic memory bit.

Ferromagnets use a magnetic interaction between their constituent atoms that align all their spins — the origin of the atoms´ magnetism — in a single direction. While they have been used successfully for magnetic data storage in the past, miniaturizing this down to atomic dimensions hasn´t been possible because of the interaction of neighboring bits with each other.

The magnetization of one magnetic bit can strongly affect that of its neighbor as a result of its magnetic field. To harness magnetic bits at the atomic scale, it is necessary to control the interactions between the bits.

“Magnetic materials are extremely useful and strategically important to many major economies, but there aren´t that many of them,” Shan X. Wang, director of the Center for Magnetic Nanotechnology at Stanford University, told John markoff of the New York Times. “To make a brand new material is very intriguing and scientifically very important.”

The IBM Research team created the smallest possible unit of magnetic storage by meticulously arranging two rows of six iron atoms on a surface of copper nitride. Such closeness is possible because the cluster of atoms is ant antiferromagnetic -- a rare quality in which each atom in the array has an opposed magnetic orientation.

The team used a scanning tunneling microscope, which looks like a giant washing machine adorned with aluminum foil, to capture images of atoms and reposition them.

Although the research took place at a temperature near absolute zero, the scientists said the same experiment could be done at room temperature with as few as 150 atoms.

As part of their demonstration of the antiferromagnetic storage effect, the team created a computer byte, or character, out of an individually placed array of 96 atoms. They then used the array to encode the IBM motto “Think” by repeatedly programming the memory block to store representations of its five letters.

Moreover, Heinrich said, smaller groups of atoms begin to exhibit quantum mechanical behavior – simultaneously existing in both “spin” states, in effect 1 and 0 at the same time. In theory, such atoms could be assembled into Qbits – the basic unit of an experimental approach to computing that might one day exceed the capabilities of today´s most powerful supercomputers.

“If you do this with two atoms, then they behave more like a quantum mechanical object,” Dr. Heinrich told Markoff. “This is why science is interested in this work more than the technology.”

Computer industry analysts said the IBM effort gives other researchers a new direction for nanotechnology and that it might offer a route to new kinds of nanomaterials.

“Nanotechnology labs are going to begin asking, ℠What else is going on down there?´ ” Richard Doherty an electrophysicist who is director of Envisioneering, an industry consulting firm based in Seaford, N.Y., told the New York Times. “The information storage side of this is fantastic, but this truly changes our ideas of the behavior of materials at molecular levels.”

Antiferromagnetic materials are now implemented in two key areas of data storage. They are essential for the manufacture of recording heads used in today´s hard disk drives. They are also used in a new type of memory chip known as spin-transfer-torque RAM (STT-RAM), which some view as a future competitor for DRAM and Flash memory chips.

Heinrich noted that many research groups are exploring ways of designing novel materials using self-assembly methods, including mechanical and biological approaches.

Industry officials said that as the semiconductor industry draws closer to exhausting the ability to scale down today´s circuits, an intense international hunt is under way for a manufacturing technology beyond microelectronics.

“The nation that discovers the next logic switch will lead the nanoelectronics era and reap the economic rewards associated with it,” said Ian Steff, vice president for global policy and technology partnerships of the Semiconductor Industry Association.


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