Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
1999-11-03
2002-04-30
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013530, C428S064200
Reexamination Certificate
active
06381200
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the recording, storage, and reading of information utilizing magneto-optical (MO) media, particularly rotatable MO storage media, such as in the form of thin film disks, and a protective overcoat/lubricant topcoat layer system for contact with cooperating transducer and/or sensor heads or devices.
BACKGROUND OF THE INVENTION
In recent years, much research and development of MO recording media for use as high density/high capacity memory devices has been carried out. Such media typically comprise a suitable substrate, e.g., of glass, polymer, metal, or ceramic material, coated with a perpendicularly magnetizable film used as a recording medium. Information is recorded within the medium by switching the direction of magnetization of desired portions (i.e., domains) of the perpendicularly magnetizable film. More specifically, for recording information, the recording medium is first initialized by applying to the medium a magnetic field from an externally positioned magnetic field generation device (i.e., external magnetic bias), thereby making the direction of the perpendicular magnetization uniformly upwardly or downwardly facing. A first laser beam of sufficiently high power or intensity from a suitable source, e.g., a laser diode, is then irradiated on desired recording portions of the recording medium in the presence of an externally applied magnetic bias field. As a consequence of the laser beam irradiation, the temperature of the irradiated portions (domains) of the recording medium rises, and when the temperature reaches or exceeds the Curie point of the vertically magnetizable film or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. When this state is achieved at the desired recording portions of the medium, and in the presence of the externally biased magnetic field, the direction of the perpendicular magnetization is switched, e.g., from upwardly facing (=digital logic 1 or 0) to downwardly facing (=digital logic 0 or 1, respectively) or vice versa, so as to be aligned with that of the external magnetic field. At the end of a write pulse (i.e., laser pulse), the temperature of the heated recording domain then decreases and eventually returns to room temperature by cessation of the laser beam irradiation thereof Since the alignment direction of magnetization of the recording media effected by the laser pulse heating to above the Curie temperature is maintained at the lowered temperature, desired information can thus be recorded in the magneto-optical media.
For reading the information stored in the MO media according to the above-described method, the recorded portions of the media are irradiated with a second, linearly polarized laser beam of lower power or intensity than the one used for recording, and light reflected or transmitted from the recorded portions is detected, as by a suitable detector/sensor means. The recorded information is read out by detecting the Kerr rotation angle of the polarization plane of light reflected from the recording layer or the Faraday rotation angle of the polarization plane of light transmitted through the recording layer. More particularly, since the rotation angle of the polarization plane varies depending upon the direction of magnetization of the recorded portions of the media according to the Kerr or Faraday effect, information stored within the media can be read out optically by a differential detector which decodes the polarization-modulated light beam into bits of information.
Conventional MO recording technology typically utilizes a transparent substrate and the polarized, lower intensity laser beam is transmitted through the recording medium layers for reception by the detector/sensor means for measurement of the rotation angle of the transmitted polarized light via the Faraday effect, as explained supra. However, in first surface magneto-optical (FSMO) recording systems, polarized, lower intensity laser beam light is reflected from the MO medium for measurement of the amount of rotation of the plane of the polarized laser light via the Kerr effect, again employing a suitable detector/sensor means. The FSMO type system is advantageous in that, inter alia, opaque substrate materials, e.g., polymers, can be utilized, and dual-sided media are readily fabricated. In addition, FSMO-type media can advantageously utilize such less expensive polymeric substrates with a pre-formatted servo pattern easily formed on the surface thereof by a masking and injection molding process, therefore not requiring electronic servo as in conventional hard disk drive technology.
In addition to the abovementioned advantages, the direct irradiation of the MO layer(s) via the front side also results in several other advantages vis-à-vis through-the-substrate illumination, e.g., FSMO systems can utilize head sliders flying over the disk surface by forming the optical and magnetic components integral with the slider, whereby the laser beam is irradiated through the slider body and directly focussed on the MO read-write layer. However, conventional overcoat layers and materials, e.g., sputtered SiN
x
films, are brittle and exhibit poor reliability during head loading, i.e., frequent head crashing when utilized in FSMO-type configurations, as explained in more detail below.
Such MO recording media, when fabricated in disk form for rotation about a central axis, can be adapted for use in conventional Winchester, or hard drive, devices as are employed with conventional magnetic recording media. Hard drives typically employed for such disk-shaped media utilize flying heads for mounting transducer/sensor devices, etc., thereon, for close positioning thereof adjacent the surface of the recording media. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined small distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Therefore, as in the case of magnetic disks, a protective overcoat layer and a lubricant topcoat layer are typically applied to the disk surface for minimizing scratching and abrasion of the sensor/transducer head and the recording media surface, which can result in an undesirably high wear rate of the head and recording media surface.
However, in the case of portable MO recording devices, the use of a lubricating oil, e.g., a fluorocarbon-based oil, is problematic in that it is difficult to maintain the lubricating oil on the surface of the MO media, thereby increasing surface scratching and wear. In addition, MO disks produced without lubricating oil on their surface by some manufacturers are not necessarily compatible with similar media produced with lubricating oil by other manufacturers.
In another approach for minimizing abrasion, scratching, and wear of transducer heads, a solid lubricant is applied to the bottom surface of the flying head which comes into contact with the surface of the MO recording medium. However, such solid lubricant applied to the bottom surface of the flying head must have a durability many times greater than lubricant applied to the MO recording medium. As a consequence, application of solid lubricant only to the flying head is not sufficient for adequately reducing abrasion, scratching, and wear.
An additional difficulty encountered in the development of wear-resistant, lubricated MO recording media and Winchester-type drives therefor, is the requirement imposed by the impetus for achieving ever-higher density recording, which necessitates further reduction in the disk-transducer/sensor spacing. The head-to-disk interface (HDI) becomes very critical as hea
Dinh Tan
McDermottt, Will & Emery
Seagate Technology LLC
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