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New boot with MRAM
Sandia National Laboratories and Pacific Northwest National Laboratory developed a way to help next-generation computers to boot up instantly, making entire memories immediately available for use.
The technique eliminates the present-day hurdle of metal atoms clustering together into three-dimensional islands when deposited on oxide surfaces. These thick bumps of metal - similar to water beads on a waxed car - are a problem because they produce poorly crystallized metal films. These are relatively weak, require inefficiently large amounts of material, and produce more heat because more electricity is needed to produce variations in magnetic signals. Neal Singer, from Sandia National Laboratories, explains how the process works: "The findings may have the most immediate bearing on magnetic tunnel junctions, slated for use in magneto-resistive random access memory, or MRAM. MRAM will allow computers to store information in a nonvolatile fashion, meaning that the information is not lost when the computer is turned off. As a result, MRAM promises a day when computers would boot up instantly once turned on, rather than comparatively slowly while retrieving information from the hard drive. Major corporations have begun developing MRAM modules in hopes of generating robust nonvolatile memory in the next few years. But growing an atomically flat, ultrathin film of metal on top of any insulator material is a difficult feat. In a magnetic tunnel junction, an ultrathin layer of insulator, typically aluminum oxide with a thickness of less than or about 1 nanometer, is sandwiched between layers of magnetic metal, such as cobalt or nickel-iron. When current flows through the device, the magnetic orientation of the two metal layers can be switched, resulting in different values of the tunneling current. This creates an environment in which 'bits' of computer memory can be stored". Science magazine published in its latest issue the article of a team led by Scott Chambers (picture), a chief scientist at Pacific Northwest National Laboratory, which says that in 2000, Sandia solid-state theorist Dwight Jennison approached Chambers with a theory that the presence of hydroxyls - in effect, water fragments - would enhance the binding of metals to oxide surfaces. Jennison calculated that then certain metals would form flat films on sapphire (a phase of aluminum oxide). Using a special synthesis technique he created, Chambers and PNNL postdoctoral fellow Tim Droubay produced an atomically flat film of cobalt on hydroxylated sapphire. They found, as Jennison had suspected, that the cobalt accumulated in layer-by-layer fashion, rather than clustering to form islands. "Cobalt's interaction with oxide is so weak that it would normally ball up when deposited," says Jennison. "However, by changing the surface of the oxide, Scott discovered that cobalt atoms can cause the release of a hydrogen gas molecule and the cobalt atoms then become oxidized themselves - that is, they link up with the newly available oxygens and end up strongly bound within the top layer of the oxide. These are the anchors." These metal atoms, embedded at scattered points within the top layer of the oxide, amount to about one anchor for every ten oxygen atoms in the top layer. These anchoring atoms bind other metallic atoms to themselves and to each other just above the oxide surface, forming a crystalline metallic layer. Chambers says that the process uses equipment already in place in chip manufacturing plants, so " "For industry, a solution may be as simple as exposing the thin aluminum oxide films to a low pressure of water vapor before adding a final cobalt layer". The entire process may be done at room temperature, which is beneficial since it is often important to avoid high temperatures in manufacturing. Related news:
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The
technique is able to deposit flat ultrathin metallic layers on very
thin oxide layers. The thinness of the deposition reduces material
cost and requires less electricity to produce more rapid magnetic
effects in the service of computer memory. The inexpensive innovation
also may produce better, less expensive catalysts for chemical reactions,
better ceramic/metal seals, and lead to improved nanodevices.
