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Commercialization of World's First Hard Disk Drive Equipped with GMR Head

The recording density and capacity of hard disk drives were dramatically improved by innovative GMR head and perpendicular magnetic recording technologies.

Commercialization of World's First Hard Disk Drive Equipped with GMR Head

To improve the recording density of a hard disk drive (HDD), a high-sensitivity head to read the weak magnetic field of the tiny recording bits is essential. The realization of a large rate of change in the magnetoresistance effect (referred to as the MR ratio) by a magnetic field is also important. In 1988, a major increase in the rate of change in resistance was achieved in Europe using an artificial lattice with alternately laminated layers of ultra-thin iron and chromium, which attracted considerable attention.

Toshiba responded to this situation by assembling a task force of personnel who had been working on video recorder heads and other devices, with the objective of developing a magnetic head, and in 1992 started research and development of a giant magnetoresistive (GMR) head. Rather than simply competing to attain a higher MR ratio, we focused our efforts on a spin valve configuration with two magnetic layers. The MR ratio was slightly smaller compared with that of a multilayer structure, but a good linear response was obtained that was suitable for detection of the reproduced signal. We then consolidated the basic design using an iridium-manganese (IrMn) alloy as a special magnetic layer with a magnetization fixed specifically for the spin valve configuration, and a cobalt-iron (CoFe) alloy that made it possible to control the crystal orientation so that a large MR ratio was produced even in a weak magnetic field.

Next we entered the phase of verifying a prototype of the head. The facilities available at the time were insufficient for this purpose, but with the understanding of management we introduced expensive equipment such as a stepper and accelerated the development work. As a result, at the end of 1997 we were able to issue a press release announcing the world's first practical HDD equipped with a GMR head, offering a recording density of 3 Gbit/in2. After that, HDDs began to be installed not only in PCs but also many other products such as portable music players, DVD players, and so on.

Concurrently with this development work, we also initiated research on perpendicular recording using a medium with perpendicular magnetic anisotropy that was made of cobaltchromium (CoCr)-based metallic magnetic material, aiming at the achievement of higher recording density. Although perpendicular recording was considered to be a superior technology in theoretical terms, at that stage nobody had been able to demonstrate its ability to provide performance significantly exceeding that of conventional longitudinal recording. A turning point came when a certain physical phenomenon, in which recording magnetization is attenuated by thermal fluctuations, became more conspicuous in longitudinal recording. In the case of perpendicular recording, on the other hand, it was understood that the higher the density, the greater the intensification of the adjacent magnetization. Moreover, the volume of magnetic particles could be increased. This meant that perpendicular recording would have a very high tolerance of thermal fluctuations.

Around 1994, we were working on the development of cobaltplatinum oxide (CoPtO)-based magnetic materials with high magnetic anisotropy, aiming at the realization of a longitudinal recording medium with a high tolerance of thermal fluctuations, when this development work had an unexpected outcome. The magnetic particle structure that we were investigating, in which CoPt crystal with high magnetic anisotropy served as a core surrounded by an amorphous layer with a high concentration of oxygen, was a unique configuration developed by our company. We embarked on the introduction of oxygen, which was considered to be taboo for metal films because of the fear of oxidation, but, as an outcome of this, were able to realize the ideal characteristics for perpendicular magnetization. The amorphous grain boundary containing a high oxygen concentration maintained the exchange coupling between the grains, and the material was found to have an excellent ability to maintain its magnetic characteristics from low to high temperatures.

In 1997, while engaged in a study to enhance the performance of magnetic film, we also found that ruthenium (Ru) was an excellent base material for crystal growth control. Through the combination of these discoveries—namely, the CoPtO-based magnetic material, grain boundary separation by an oxide, and the use of Ru as the base material for crystal growth—the design concept of the magnetic characteristics and recording material of the perpendicular recording medium became clear and the research and development work rapidly progressed. At a technological exhibition held at the Ome Works (currently the Ome Complex) in January 2002, a PC equipped with a perpendicular recording HDD was shown to the press for the first time in the world, and received an enthusiastic response. In 2005, we shipped the world's first perpendicular recording HDD products. These products had a recording density of 133 Gbit/in2, the highest HDD recording density in the world, as well as excellent environmental robustness. They led the way in a major shift in the field of recording systems, the first such shift to have occurred in the history of magnetic recording.

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