News Release

New facility puts Ames lab on thin-film fast track

Peer-Reviewed Publication

DOE/Ames National Laboratory

AMES, Iowa -- When it comes to making magnetic thin films in the laboratory, chance has played a large role in whether a film has the characteristics that the researcher is seeking. But thanks to a new state-of-the-art lab facility, researchers at the U.S. Department of Energy's Ames Laboratory can now easily create and, perhaps more importantly, duplicate thin films with unprecedented control of the composition and nanostructure. That ability to control a number of variables will allow thin-film "recipes" to be developed and compared, resulting in a better understanding of how thin films work.

Nearly two years in development, the new Magnetoelectronics Laboratory is set to boost Ames Lab researchers David Jiles and John Snyder to the forefront of the newly emerging field of magnetoelectronics, a combination of microelectronics and magnetics. Potential uses of thin films include nonvolatile computer random access memory (commonly known as RAM) that would require no "boot-up" sequence and would not lose data in cases of power interruptions. Better multi-layer thin-film structures could also mean boosting data storage capacity by 10 to 50 times over conventional disk storage.

Funded by a $530,000 grant from the Roy J. Carver Charitable Trust, the centerpiece of the lab is a new, custom-built Indel ion-beam deposition system. As Snyder explained it, the system works like a well-placed break shot in a game of pool.

"To lay down a thin layer of a certain material, you place a piece of it on a target plate," Snyder said. "Then the ion beam blasts that target and a thin layer of the material, maybe only a few atomic layers thick, is deposited on the substrate, usually a silicon wafer. Based on the placement of the beam, we know where the atoms of the target material will wind up."

The material being deposited must be highly pure and the process must take place under extreme vacuum (10-7 Torr or better) and in a dust-free environment, since even microscopic dust could cause variations or breaks in the atoms-thin film. Obtaining high-purity materials is the easy part, thanks to Ames Lab's Materials Preparation Center. Clean-room air handlers control the dust. Achieving such high vacuum, however, is time consuming -- it takes several hours, using both mechanical and cryogenic pumps.

To speed up the process and minimize the possible introduction of oxygen, dust, or other contaminants, the new system has a turret with six target plates. This allows Snyder and Jiles to load up six different materials in advance without having to break and reestablish the vacuum within the deposition chamber. To change materials, the researchers simply rotate the desired target plate into position.

But Jiles and Snyder didn't stop there. A second ion-beam gun allows etching of the substrate between layers so they can remove excess material or "clean" the surface before the next layer is deposited. They also designed the chamber so they can heat and cool the deposition substrate, subject it to magnetic fields, and rotate the substrate table.

"By subjecting the substrate to a variety of conditions, we can change how the thin-film material grows," Jiles said. "Particles may orient differently when exposed to a magnetic field or grow differently when heated or cooled during deposition. The beauty of this equipment is that everything is computer-controlled so we can easily recreate a particular 'recipe' for any thin-film wafers we create."

Having that type of control is crucial because minute changes in layer thickness or particle orientation may change the film's properties. For example, magnetic tunnel junctions consist of a thin insulating film sandwiched between two magnetic films. The thinner you make the insulating layer, the less electrical resistance produced. However any gaps in the insulation will cause the structure to short out just like an electrical cord with frayed insulation.

Magnetic tunnel junctions could replace semiconductor technology now used for a computer's random access memory. When you run a software program, RAM keeps the application accessible and allows users to read data from memory and write new data into the memory. However, most semiconductor-based RAM is volatile, meaning that it requires constant electrical power to operate. If power is lost, so is the data being held in RAM.

"Magnetic tunnel junctions operate magnetically so they aren't affected by power interruptions," Jiles said. "You wouldn't lose data and the computer would come on instantly without going through the boot-up process."

Thin films can also possess giant magnetoresistive, or GMR, properties that allow them to undergo dramatic changes in their electrical resistance in response to relatively small changes in the magnetic field surrounding them. Its high sensitivity and small size would make such films desirable for use on the read-heads on next-generation disks capable of storing 100-500 gigabits of data per square inch.

"The research conducted for the DOE is focusing on the mechanisms of clean, multi-element film growth and the structuring of such films at the atomistic to nano-length scale," Jiles said. "It opens whole new areas of research and we hope to be able to use the facility as a lever to attract research funding and to build other projects around this basic work."

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Ames Laboratory is operated for the DOE by Iowa State University. The Lab conducts research into various areas of national concern, including energy resources, high-speed computer design, environmental cleanup and restoration, and the synthesis and study of new materials.

(Note: David Jiles is a senior physicist at Ames Laboratory. He is also an ISU professor of both materials science and engineering, and electrical and computer engineering. John Snyder is an associate scientist at Ames Laboratory and an ISU adjunct assistant professor of materials science and engineering.


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