Magneto-optical recording medium

Details Magneto-optical recording medium Magneto-optical recording medium

1998-06-01

2003-07-01

Neyzari, Ali (Department: 2655)

Dynamic information storage or retrieval

Storage medium structure

Optical track structure

C369S013350, C369S288000, C428S064100

Reexamination Certificate

active

06587427

ABSTRACT:

TECHNICAL FIELD
This invention relates to optical data storage, and more particularly to recordable magneto-optical storage media for use in a near field system.
BACKGROUND
A variety of optical storage media and technologies exist. These include media which may not be recorded on by the user (often referred as read-only memory (ROM) as in CD-ROM). Also included are user recordable media (frequently designated as write-once-read-many WORM) and user re-recordable media. One area of user recordable and/or re-recordable media involves magneto-optical technology. A typical magneto-optical disk drive features a magnetic recording head and at least one laser. Bits of information are recorded in discrete locations (“domains”) along the lengths of tracks spirally spanning the disk. In one form, the information is read via light from a read laser reflected by the disk. The nature of the reflected light is influenced by particles within the disk. To record a bit of information at a particular domain, a write laser may heat the domain to a condition wherein the magnetic head may apply a field to the domain to align the particles in that domain in a particular orientation corresponding to the state of the associated bit. Subsequently, with the particles frozen in the desired state, the read laser may be used to read the state of the bit.
FIG. 1
shows one conventional magneto-optical disk
20
. The bulk of the disk
20
may be formed by a substrate
22
such as a polycarbonate disk. The flat upper surface
24
of the substrate
22
forms the upper surface of the disk. The surface
24
is in close facing proximity to the underside
28
of the head
30
as is described in further detail below. For reference, unless specified to the contrary, the “upward” direction
500
shall refer to the local direction from the media to the head when the head is in position to read or write data from or to the media. It is understood that the media and head may be placed in a variety of absolute orientations.
The lower surface
32
of the substrate may be formed with a series of alternating spiral grooved and ungrooved areas
34
and
36
, respectively. A first dielectric layer
38
may be applied to the lower surface
32
of the substrate
22
. A magneto-optical layer
40
may be applied to the lower surface
42
of the first dielectric layer. A second dielectric layer
44
may be applied to the lower surface
46
of the magneto-optical layer. A reflective layer
48
may be applied to the lower surface
50
of the dielectric layer. A protective layer
52
may be applied to the lower surface
54
of the reflective layer. The portions of the magneto-optical layer
40
below the grooved areas
34
define the tracks
56
on which bits of information may be recorded.
In operation, the disk
20
is rotated at high speed about its central axis (not shown). The magneto-optical head
60
, which does not rotate with the disk, may be reciprocated approximately radially relative to the disk's central axis to access the various tracks on the disk.
A common head design for data storage systems is the “flying head”. With a flying head, the relative motion between the disk and head caused by the rotation of the disk produces a flow of air between the head and the upper surface of the disk. The flow of air prevents the head from colliding with the disk and allows the head to maintain its close facing relationship with the upper surface of the disk. This is achieved by providing the lower surface of the head with appropriate air bearing surfaces
62
.
The inconsistent spacing between the air bearing surfaces and the disk presents a number of difficulties. First, the stability of the head may be affected as the head moves across the disk. Second, the interaction of the head with the disk is harder to computationally model than with a uniformly flat upper disk surface. Such modeling is important if it is desired to economically alter the properties of the head, the geometry of the size and spacing of the tracks, or the rotational speed of the disk.
Accordingly, in one aspect, the invention is directed to a magneto-optical recording medium in a near-field optical storage system. A flying optical medium is suspended over the medium by a cushion of gas. The head includes a magneto-optical recording layer having at least one recording track for magneto-optical recording of information. At least one tracking feature is associated with the track. An upper transparent dielectric layer is provided with an upper surface which is substantially planar over a recordable area of the medium above the recording track and the tracking feature. A reflector layer is positioned below the magneto-optical layer above a base substrate. The upper dielectric layer has an upper surface which is substantially flat for presenting the flying optical head with a substantially uniform cushion of air between the upper surface of this dielectric layer and the air bearing surface of the flying optical head.
Implementations of the invention may include one or more of the following features. A lower transparent dielectric layer may be positioned below the magneto-optical recording layer and above the reflector layer. An upper surface of the recording track and the upper transparent dielectric layer may be separated by a distance between approximately 100 and 1 &mgr;m. The medium may be a disk. The reflector layer may be metallic.
The recording track and the tracking feature may each include annular features. The tracking feature may include a depression formed in an upper surface of at least one of: the substrate; the reflector layer; the lower transparent dielectric layer; and the magneto-optical recording layer. The depression may be formed by a groove in an upper surface of the substrate, the groove propagating the depression upward through the reflector layer, the lower transparent dielectric layer and the magneto-optical recording layer.
Either the upper or the lower dielectric layer may include a high index dielectric material, where the other of the layers includes a first sublayer of low index dielectric material and a second sublayer of high index dielectric material.
The high index dielectric material may be silicon nitride. The low index dielectric material may be silicon oxide. The magneto-optic layer may be made of a rare earth-transition metal compound including TbFeCo.
The groove has a groove width and a groove separation, a ratio of the groove width to groove separation may be less than about 7:15. The groove width may be less than about 0.175 &mgr;m.
In another aspect, the invention is directed to a near-field magneto-optical storage system. The system includes an optical head having an air-bearing surface, a laser for emitting a beam of light having a wavelength less than about 1 &mgr;m, a lens, a drive motor, and a magneto-optical storage disk.
The disk has an upper surface having a flat portion for interacting with the optical head via a substantially uniform cushion of air between the flat portion and the air bearing surface of the optical head. A magneto-optical recording layer is formed below the upper surface and includes at least one recording track for magneto-optical storage of information, which information is readable by the laser. The upper surface along the track is separated by a distance smaller than the wavelength from the lens. At least one tracking feature is associated with the recording track. A reflector layer is formed below the magneto-optical recording layer, below which is a substrate.
Implementations of the invention may include one or more of the following. An operational distance between the lens and the upper flat surface along the track is less than about 150nm.
In another aspect, the invention is directed to a medium in an optical storage system where a flying optical head is suspended over the medium by a cushion of gas. The medium includes a data layer having at least one track for storing information, at least one tracking feature associated with the at least one track, a dielectric layer having an upp

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