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Hard Disk Drive Technology

2001-12 (Vol.37, No.2)

2001-12 (Vol.37, No.2) Contents

1. Preface (29 KB): ---[Ichiro Komura, Group President Storage Products Group. ]

2. Information Storage for the Broadband Network Era (324 KB): As the network-computing infrastructure expands around the world, information storage systems are becoming key elements of information technology (IT). The amount of original information created in 2000 has been estimated at about 5 EB, and there is now a worldwide information stock of about 100 EB. Commercial models of hard disk drives (HDDs) now have 18 million times the magnetic recording density of the world's first hard disk drive and are the only candidate solution for storing the bulk of the world's information stock. In this paper, we analyze the size of the information stock and the future capacity of HDD media. We also describe Fujitsu's breakthrough technology of synthetic ferrimagnetic media (SFM), which can extend the recording limit to up to 300 Gbit/in² ---[Yoshimasa Miura ]

Hard disk drives in production

3. 3.5-inch High-Performance Disk Drives for Enterprise Applications: AL-7 Series (477 KB): Fujitsu offers the new AL-7 series of high-performance SCSI drives for server applications. The series consists of a 73G-byte, 10 000 rpm model and a 36G-byte, 15 000 rpm model. This paper describes how the mechanisms of these drives were improved to reduce their power consumption and make them fast, highly reliable, and acoustically quiet. We describe how the non-repeatable run-out (NRRO) was reduced by stabilizing the internal airflow and reducing resonance in the spindle motor. Next, we describe the new lightweight, rigid actuator and servomechanisms we developed to increase the access speed and the steps that were taken to reduce the drives' acoustic noise and increase their reliability. Finally, we present the results of some benchmark tests we conducted on these drives. ---[Keiji Aruga ]

4. 2.5-inch Hard Disk Drives for Mobile Applications: Hornet-15L (116 KB): Fujitsu has developed the Hornet series of 2.5-inch compact hard disk drives (HDDs). These drives are suitable for use in mobile applications such as notebook personal computers. This paper introduces the Hornet-15L (MHR2xxx) drives, which are our latest 2.5-inch super-slim HDDs. The HN-15Ls feature an areal recording density of 56.5 Mbit/mm² (36.4 Gbit/in²), which makes them the highest density drives in the world. This paper introduces the head, medium, mechanical, and electronic technologies of the Hornet drives. ---[Akihiko Makita ]

Advanced media technology

5. Synthetic Ferrimagnetic Media (272 KB): The thermal stability and read-write performance of longitudinal magnetic recording media with antiferromagnetically coupled layers were investigated. The thermal stability is strongly dependent on the interaction between layers and the anisotropy energy of the stabilizing layer or layers. For media with two coupled layers, the energy barrier is increased by 30% to 80% of the anisotropy energy of the stabilizing layer, depending on the strength of the interaction. Although the total thickness is larger compared to a conventional medium with the same remanence magnetization and thickness product M_rδ , the resolution is higher and depends on the difference in thickness between the layers. With these "synthetic ferrimagnetic" structures, thermally stable, low M_rδ and high-resolution media are made possible with an areal density advantage of at least 1.75 times that of conventional longitudinal recording media. ---[E. Noel Abarra, B. Ramamurthy Acharya, Akihiro Inomata, Antony Ajan, Iwao Okamoto ]

6. Perpendicular Magnetic Recording Using Magneto-Optical Media (279 KB): TbFeCo perpendicular magnetic recording media were developed by employing an NiP underlayer to control the magnetic properties of the TbFeCo magnetic layer. With the NiP underlayer, the magnetization reversal changed from wall motion to the rotation mode. The dynamic write-read characteristics of a single-layer medium were examined using a conventional merged-type GMR head with a write core width of 1 µm that was designed for longitudinal magnetic recording. A clear magnetic pattern of 450 kFCI, high media SNR, and acceptable overwrite properties were obtained. It was shown that the thermal stability of the TbFeCo medium is sufficient for practical applications. A double-layer medium with a soft-magnetic backlayer exhibited practical overwritability for a narrow track pitch of 0.4 µm. ---[Koji Matsumoto]

Advanced head technology

7. High-Performance Write Head Design and Materials (254 KB): The rapid increase in areal recording density means that a stronger writing field without side erasure is required. However, the increase in the data transfer rate makes write head optimization difficult. Moreover, it has become very important to minimize the write pole size tolerance because of the reduction in write track width. We have designed a new head throat shape with a deep gap depth that is formed with SiO₂ thin film. Our head has an advantage in gap depth tolerance as well as in write track width tolerance. We also developed soft magnetic FeCoAlO films with a saturation magnetic flux density (Bs) of 2.4 T for improving the overwrite (O/W) performance without worsening the side erasure characteristics. It was found that the O/W becomes less than -30 dB when the writing field is larger than the dynamic coercivity Hc0 of the medium. The side erasure was characterized by investigating the maximum tolerance field against di-bit signal degradation on the adjoining track. ---[Ikuya Tagawa, Shoji Ikeda, Yuji Uehara ]

8. Advanced Spin-Valve GMR Head (125 KB): Information and communication systems increasingly handle huge amounts of data, placing heavy demands on hard disk storage capacity and performance. Progress in the development of giant magnetoresistive (GMR) spin-valve materials and highsensitivity spin-valve read heads has allowed a continuous increase of areal recording density in hard disk drives. This paper describes our advanced spin-valve head technology. This technology features a bottom type synthetic ferrimagnet spin-valve with low magnetostriction. It comprises a magnetic layer, Ru interlayer, and magnetic layer sandwich as a pinned layer. It also has a specular spin-valve with specular reflection layers consisting of a layer of natural oxide or another oxide material. The synthetic ferrimagnet spin-valve and the specular spin-valve enable increased readback output of the spin-valve head. This paper also describes our demonstration of over 100 Gbit/in² technologies at areal recording densities achieved by a high-sensitivity, double-specular spin-valve head on synthetic ferrimagnet media. ---[Hitoshi Kanai, Kenji Noma, Jongill Hong ]

9. Low-Resistance Ferromagnetic Tunnel Junction (451 KB): To develop the next-generation magnetic read head, we investigated ferromagnetic tunnel junctions (MTJs) with a low resistance and a high magneto-resistance (MR) ratio, the MTJs were fabricated by Ultra High Vacuum (UHV) magnetron sputtering with various Al layer thicknesses and oxidization conditions. The MR ratio dependencies on the RS (junction resistance x area) values were studied. By optimizing the barrier thickness and oxidization conditions, we fabricated an MTJ with a 0.9 nm Al-O barrier layer that has an MR ratio of 20% and an RS of 7.8 Ωµm². When the thickness of the Al-O barrier layer in the MTJ was less than 0.9 nm, RS was below about 10 Ωµm². However, the MR ratio and the breakdown voltage decreased when RS was decreased. We found that the decreases in MR ratio and the breakdown processes at a low RS were caused by pinholes in the barrier layer. Therefore, to obtain an MTJ with a low RS and a high MR ratio for the next-generation magnetic read head, we will optimize the deposition conditions and find materials for making a thinner barrier layer without pinholes. ---[Hideyuki Kikuchi, Masashige Sato, Kazuo Kobayashi ]

10. CPP Operational Mode of GMR Head (207 KB): We have investigated the magneto-resistance (MR) properties of spin-valves (SVs) operating in the current perpendicular to plane (CPP) mode. These SVs are strong candidates for ultra-high-density recording heads because of their low resistance and high sensitivity. By adding an oxide layer to a CPP element consisting of a conventional single SV film, we changed its resistance-change area product ΔRA from 0.6 mΩµm² to 34 mΩµm² and its MR ratio from 0.5% to 2%. These dramatic changes may have been achieved because the oxide layer narrowed the current-flow area. Micromagnetics simulation revealed that a moderate-impedance CPP head such as an SV film with an oxide layer shows several advantages compared with low-impedance heads, for example, a higher output voltage and signal-to-noise ratio, less influence from the magnetic field of the sense current, and a narrower core width. We believe the CPP-SV head will play an important role in the read heads of future hard disk drives (HDDs). ---[Keiichi Nagasaka, Yoshihiko Seyama, Reiko Kondo, Hirotaka Oshima, Yutaka Shimizu, Atsushi Tanaka ]

Advanced head-disk interface technology

11. Advanced Stiction-Free Slider and DLC Overcoat (266 KB): The demand for higher areal densities in hard disks requires a lowering of the magnetic spacing between heads and media. To achieve this, the flying height of the slider and the thickness of the slider and media overcoats must be lowered. To fly a slider stably at low altitude, the media surface must be as smooth as possible. However, some degree of surface roughness is beneficial because it keeps the head from adhering to the disk when at rest. Reducing the contact area between the head and disk is the most suitable way of lowering the stiction force. This can be achieved by adding contact pads to the air-bearing surface, resulting in what we call a stiction free slider (SFS). On the other hand, overcoat thickness must be reduced while maintaining the durability and anti-corrosion properties. In this paper, we first focus on the material and tribological properties of sputtered hydrogenated amorphous carbon films, which are currently used for the overcoats of thin film media. Then, we describe the PCVD technique for the next generation of overcoats. Finally, we describe a tetrahedral amorphous carbon overcoat deposited by filtered cathodic arc deposition, which will be used in the future. ---[Takayuki Yamamoto, Yoshiharu Kasamatsu, Hiroyuki Hyodo ]

Advanced mechanical technology

12. Development of Shear-Mode Piezoelectric Microactuator for Precise Head Positioning (213 KB): We have developed a novel piezoelectric micro-actuator for dual-stage actuator systems in magnetic disk drives. This microactuator is based on the shear deformation of piezoelectric elements and drives the head suspension assembly. The actuator is suitable for thin devices and is easily manufactured because of its simple stack configuration. We installed the microactuator in one of Fujitsu's 3.5-inch commercial drives to evaluate the servo system of a dual-stage actuator. The dual-stage actuator system achieved a non-repeatable position error (NRPE) 3σ of 0.036 µm. The dual-stage servo system reduced the NRPE by 35% compared with the conventional single actuator system, even in HDDs with a high rotational speed of 10 000 rpm. ---[Shinji Koganezawa, Takeyori Hara ]

13. Servo Track Writing Technology (181 KB): To achieve an ultra high track density in hard disk drives, the track-following performance should be improved by using micro-actuators and other new technologies. For practical use of an ultra high-density drive, it is essential to develop a new servo track writer. This paper introduces the high-precision, high-efficiency, low-priced servo track writers we have developed that use a newly developed sheet scale. ---[Yukihiro Uematsu, Masanori Fukushi ]

14. A Numerical Simulation of Unsteady Airflow in HDDs (441 KB): In this paper, using aerodynamic numerical analysis, we investigate the mechanisms causing disk flutter in hard disk drives. A computer simulation model of three stacked disks was calculated using the finite-difference method with the LES model of turbulence. As a result, secondary airflows were found to move upward and downward though the shroud gap around the outer edge of the disk. The inference from this discovery is that a phase difference of spatial pressure patterns between the top and bottom surfaces of a disk causes disk flutter. ---[Masayuki Tatewaki, Naozumi Tsuda, Tsugito Maruyama ]

Advanced measurement technology

15. Wide-Bandwidth Scanning Kerr Microscope for Measurement of Write Head Dynamics (183 KB): We have developed a wide-bandwidth scanning Kerr microscope to diagnose magnetic heads using an optical sampling technique. Using an externally triggerable pulse diode laser, the temporal response and frequency dependence of the write head magnetization behavior can be easily evaluated. The developed system has a 5 GHz measurement bandwidth and a 0.2 µm spatial resolution. ---[Shin-ichi Wakana, Toshiaki Nagai, Yuji Sakata, Hidenori Sekiguchi ]

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