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State-of-the-art magnetoelectronics lab puts Ames Lab on thin-film fast track

Tucked away in a small laboratory space on the second floor of Metals Development is new, state-of-the-art research equipment that should help boost Ames Lab researchers David Jiles and John Snyder to the forefront of thin-film research and the newly emerging field of magnetoelectronics. The new equipment will take guesswork out of the formula when developing magnetic thin films and allow the research team to more quickly and easily create and perhaps more importantly, duplicate thin films with unprecedented control.

Nearly two years in development, the new Magnetoelectronics Laboratory was 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. Consisting of a vacuum chamber with myriad valves, hoses and dials standing behind a clear plastic curtain, the equipment allows atoms-thin layers of material to be deposited on a silicon-wafer substrate. As Snyder explains, 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 says. "Then the ion beam blasts the material, and a thin layer of particles, maybe only an atom or two thick, is deposited on the substrate. Based on the placement of the beam, we know where the particles 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). Obtaining high-purity materials is the easy part, thanks to Ames Lab's Materials Preparation Center. Achieving such high vacuum is time consuming it takes several hours, using both a mechanical vacuum pump and a cryogenic pump located behind a wall in the adjacent lab space. Noise was one factor for putting the pumps in the other room dust was the other. When laying down atoms-thin layers of material, even the smallest dust particles can cause irregularities or breaks in the film. Fans on the pumps could stir up dust.

"We had to create an industrial-class clean room," Jiles says. "That meant stripping everything out of the room, installing polyethylene ceiling tiles, and sealing the masonry. Filtered air is blown down from above so that we create positive pressure within the room. The plastic curtains also help prevent dust from settling on the equipment."

There was one small hitch in setting things up. When the equipment finally arrived, it was too large to fit through the door. Rather than disassemble the one-of-a-kind machinery, Jiles and Snyder opted to remove the door frame and repair the wall once the equipment was in place.

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

But Jiles and Snyder don't stop there. A second ion-beam gun allows etching of the substrate between layers so the researchers 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. All these variables should help in developing a basic understanding of how thin films behave.

"By subjecting the substrate to a variety of conditions, it may change how the material is deposited," Jiles says. "Particles may orient differently when exposed to a magnetic field or behave differently when heated or cooled. 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 how the film performs. 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 device to short out just like an extension 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, it is RAM that 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 says. "You wouldn't lose data, and the computer would come on instantly without having to go 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 film desirable for use on the read-heads on next-generation disks capable of storing 100-500 gigabits of data per square inch.

"It opens whole new areas of research," Jiles says of the facility, "and we hope to be able to use it as a lever to attract research funding and to build other projects around this basic work."


by Kerry Gibson


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