Dielectric-layer for magneto-optic storage media structures

Details Dielectric-layer for magneto-optic storage media structures Dielectric-layer for magneto-optic storage media structures

1994-04-07

2001-04-10

Kiliman, Leszek (Department: 1773)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S690000, C428S690000, C428S690000, C428S690000, C428S690000, C428S900000, C501S056000, C501S059000, C501S061000, C501S062000, C501S066000, C501S067000

Reexamination Certificate

active

06214482

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to magneto-optic storage media and specifically relates to adjustment of the refractive index, density and chemical durability of the dielectric layers used in a magneto-optic storage medium. Quite specifically, the invention relates to the use of compound oxide glasses of SiO
2
—MO
2
, SiO
2
—M
2
O
3
or SiO
2
—M
2
O
5
and combinations thereof as the dielectric layer, where M is selected from but not limited to Zr, Ti, Al, Nb, Y, Sn, In, Ta and Sb.
Magneto-optic recording media refer to a storage medium or memory element which corresponds to radiant energy permitting the use of such energy sources as laser beams for both recording and reading. The media modify the character of an incident polarized light beam so that the modification can be detected by an electronic device such as a photodiode. Magneto-optic recording media have several advantages over known magnetic recording media: the spacing between the medium and the recording head is greater thereby reducing the potential for contact between the two and use of a pulsed laser beam as the writing implement results in very high density data storage. The use of magneto-optic storage media and the manner of writing data onto and reading data from the medium are both well-known to those skilled in the art.
Rare earth-transition metal amorphous alloys constitute a class of magnetic materials which are magneto-optically active, have large coercivity and magnetic anisotropy values at room temperature, and thus hold promise as an active media for a reversible storage technology based on optical recording. In a typical disk storage media structure, the active magneto-optic layer is sputter-deposited on a grooved substrate on which a first thin dielectric layer has previously been deposited and then a second thin dielectric layer is deposited on the magneto-optic layer, thereby sandwiching the magneto-optic layer between a pair of thin dielectric layers. The dielectric layers provide appropriate refractive index matching to maximize optical coupling into the magneto-optical media, thermal isolation and environmental stability for the magneto-optic layer.
Dielectric layers containing simple oxides such as ZrO
2
, SiO
2
, Al
2
O
3
, Ta
2
O
5
and Nb
2
O
3
have been tried but as a class these materials have generally not been adequate to provide acceptable signal enhancement and environmental protection. This is due to their tendency in some cases to crystallize during thermal cycling and/or allow penetration of atmospheric contaminants to the magneto-optic layer. Other compounds such as nitrides, oxynitrides and amorphous carbon likewise exhibit shortcomings when used as dielectric layers in a magneto-optic storage media due to a variety of factors such as unacceptable stress levels in the films and poor surface coverage. Also, in these latter cases the compounds used provide only discrete index of refraction values and the optical design of the magneto-optic storage disk must be predicated upon that discrete value.
U.S. Pat. No. 4,680,742 describes a magneto-optic recording element comprising a substrate, a magnetic layer and a dielectric layer, the dielectric layer being formed by deposition of a composition comprising Si
3
N
4
and a refractive index-improving agent such as Al
2
O
3
or Y
2
O
3
. Such a nitride containing medium is sensitive to residual gas impurities in the vacuum system during deposition. For example, if oxygen is in the reaction chamber in sufficient quantity a silicon oxynitride may be formed in the dielectric layer which will greatly reduce the refractive index of the dielectric layer.
U.S. Pat. No. 4,569,881 describes a magneto-optic storage media comprising at least one dielectric layer to enhance the coupling of a read/write laser light into the magneto-optic material. The dielectric layers comprise an oxide or nitride. There is no mention of any adjustment of index of refraction or the degree of environmental protection provided by the dielectric layers.
SUMMARY OF THE INVENTION
In accordance with the present invention, in order to overcome the limitations found in the described magneto-optic storage media and to achieve improved signal-to-noise ratio and environment stability, the dielectric layer comprises a compound oxide glass. The preferred glass has the chemical formula SiO
2
—MO
2
or SiO
2
—M
2
O
3
and SiO
2
—M
2
O
5
where M is selected from but not limited to Zr, Ti, Al, Nb, Y, Sn, In, Ta or Sb and preferably is Ti, Zr or Al. A principal object of the present invention is therefore, the provision of a magneto-optic storage medium exhibiting stable, protective, high, and precisely controllable and adjustable index of refraction dielectric layers for magneto-optic storage.
Another object of the present invention is the provision of a magneto-optic storage medium including at least one dielectric layer comprising a compound oxide glass.
A further object of the present invention is the provision of a magneto-optic storage medium including at least one dielectric layer comprising a compound oxide glass, where the compound oxide glass has the chemical formulation SiO
2
—MO
2
or SiO
2
—M
2
O
3
or SiO
2
—M
2
O
5
and combinations thereof where M is selected from but not limited to Zr, Ti, Al, Nb, Y, Sn, In, Ta and Sb.
Further and still other objects of the present invention will become more clearly apparent when the following description is read in conjunction with the accompanying drawings.


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Nogami, “Glass Preparation of the ZrO2-SiO2System by the Sol-Gel Process from Metal Alkoxides”, J Non-Crys. Solids, 69, 1985, 415-423.
Asano et al, “Magneto-Optical Recording Media with New Protective Films”, Intermag '87, Paper CG-10.
Patents Abstracts of Japan, vol. 10, N. 169, P. 468, (2225), Jun. 14, 1986.

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