"This achievement shows that we're on track to producing products by the year 2000 that will contain 10 billion bits of data per square inch of disk surface, or nearly 20 times the areal data density of today's most advanced disk drives," says Robert A. Scranton, Manager of Storage Systems and Technology at IBM's Almaden Research Center here and also Advanced Technology Director for the Storage Systems Division (SSD), the IBM unit that develops, manufactures and sells a wide range of magnetic and optical data storage products. "These products should permit our customers to meet their future data storage needs. With the advent of the information superhighway, for example, many people and companies will want to have access to huge amounts of data at both the sending and receiving ends."
Called a "spin-valve" head, the new sensor is already five times more sensitive than today's best commercially available disk-drive sensor. This capability is due to the "giant magnetoresistive" (GMR) effect, which was discovered less than six years ago. IBM's spin valve is the first high-density recording head design to take advantage of the GMR effect.
"We are determined to move important scientific discoveries, such as GMR, from our laboratories into products as rapidly as we can," Scranton adds. "This should help us maintain our technology leadership in the data storage industry."
The scientists performed this work at IBM's Almaden Research Center as part of the Advanced Magnetic Recording Laboratory (AMRL) joint program between Almaden and SSD. The scientists used the sensor to read data bits written onto a magnetic hard disk at a density of 1 billion bits (a gigabit) per square inch.
"We could have easily used a higher density, but we wanted to compare these results with those from our 1989 world-record 'gigabit per square inch' demonstration, which used a traditional magnetoresistive (MR) head," says Virgil S. Speriosu, manager of magnetic thin films at Almaden. "The spin valve's electrical signal -- one thousandth of a volt per micron of track width -- was five times greater than that of our best MR sensor available in today's products. This result is especially encouraging because we expect to improve it substantially in the future as we become more familiar with the spin-valve design's characteristics."
The spin valve's stronger signal gives disk-drive designers the option of packing more bits into a given area of disk surface -- thus increasing the data capacity of the disk drive -- or relaxing other design constraints to increase performance, such as faster data rate (by spinning the disk faster) or ruggedness and reliability (by flying the head farther from the disk). Much of the data-density increases would come from a six-fold decrease in the magnetic bit track width -- from 3 to 0.5 microns -- that the spin-valve design would permit, in conjunction with necessary improvements in other critical areas.
Ching Tsang of Almaden will present these technical results on Monday (June 20) at the 6th Joint Magnetism and Magnetic Materials (MMM)/Intermag Conference in Albuquerque, New Mexico. Co-authors on the technical report are Robert E. Fontana, Bruce A. Gurney, Speriosu and Mason L. Williams of Almaden and David E. Heim and Tsann Lin of SSD.
Technical background
A recording head serves two functions in a hard-disk drive: it writes data onto a disk as well as reads back that data. Until recently, all recording heads used electrical induction for both reading and writing. To write, an electrical current sent through a coil induced a magnetic field within the head that was projected through a small gap onto a spinning disk. To read, the process was reversed: the magnetic fields on the disk were picked up by the gap, inducing a current in the head's coil. This reading process becomes much more difficult as the size of the data bit shrinks because it produces an ever-weaker induced current. Moreover, since the same coil and gap are used for both writing and reading, inevitable design compromises further limit the inductive head's overall performance.
IBM made a leap in disk-drive technology in 1991 when it introduced the first hard-disk drive that used an MR reading sensor, which is made of several thin layers of a magnetic material, that changes its electrical resistance in a magnetic field. Only about 300 angstroms thick overall, or 3,000 times thinner than a human hair, the MR sensor is placed within or near the gap of the write element and gives a much stronger signal when reading data at comparable densities and data rates. Moreover, the inductive coil and gap could now be optimized solely for writing.
Today, IBM is still the only company currently shipping disk drives with MR recording heads in volume. MR technology is the chief reason that IBM drives now boast the industry's top areal density (564 Mbits/inch) and reliability (up to 750,000 hours, or more than 85 years mean time before failure). Whereas IBM's 2.5-inch, 270MB drive has one disk, competitors need two or more. IBM is also the only company shipping 2.5-inch drives with capacities as high as 810 MB.
GMR occurs in multi-layer structures of even thinner films (5-100 angstroms each). GMR was discovered in France in 1988 in perfect-crystal samples exposed to very high magnetic fields (20,000 Oersted, which is 40,000 times the earth's magnetic field and 1,000 times than that used in disk drives.) Almaden's Stuart Parkin opened the door for affordable applications in 1989 when he showed that more-easily-made sputtered, polycrystalline multilayers also showed the spectacular GMR effect. Speriosu then led a research effort to find structures that would exhibit GMR in external magnetic fields weak enough to be useful in a recording head. That research led to the spin-valve design unveiled today.