Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2002-02-19
2004-03-09
Mulvaney, Elizabeth (Department: 1772)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064500, C428S064600, C430S270130
Reexamination Certificate
active
06703098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns an information recording medium for use in optical disks.
2. Description of Related Art
For recording information on thin films (recording films) by irradiation of a laser beam, various principles have been known. Among them, those utilizing the change of the arrangement of atoms by the irradiation of a laser beam such as phase change of the film material (also referred to as phase transfer and phase transformation) scarcely cause deformation of the thin films and, accordingly, have an advantage capable of obtaining an information recording medium of a both side disk structure by directly bonding two sheets of disk members.
Usually, the information recording medium described above has a constitution comprising a protective layer, a recording film such as made of a GeSbTe series material, a protective layer and a reflective layer formed on a substrate.
In this specification, the term “phase change” includes not only the phase change between a crystalline state and an amorphous state but also includes phase change between melting (change to liquid phase) and recrystallization, as well as phase change between a crystalline state and another crystalline state. Further, “mark-edge recording” means a recording system of corresponding an edge area of a recording mark to signal “1” and inter mark and intra mark areas to signal “0”. In this specification, the optical disk means a disk containing information that can be regenerated by the irradiation of light and/or a device for regenerating information by the irradiation of light.
In a rewritable optical disk such as DVD-RAM, a recording track comprises a pre-formatted area in which address pits are disposed and a user-data area having a tracking groove for recording and conducts information writing or reading after confirming the address and detecting clocks or synchronization signals.
However, since deformation formed by stresses exerting between stacked films and a substrate is different between the pre-formatted area and the user-data area, the recording track is bent relative to the pre-formatted area. This may cause a situation the address data in the pre-formatted area can not be read, assuming a case of push-pull tracking relative to the tracking groove, at a high recording track density with a recording track width of 0.62 &mgr;m or less for an optical spot diameter represented by &lgr;/NA of about 0.96 &mgr;m. This may also cause offset in a recording area to partially erase data of adjacent tracks when tracking offset is corrected so as to situate at a normal position relative to the pre-formatted area.
It is considered that the deformation is different between the pre-formatted area in which address pitch are disposed and the user-data area for recording because the user-data area has tracking grooves and the inclined portion of the grooves undergoes force and tends to deform. Further, as another problem caused by the stresses exerting between the stacked films and the substrate, when a number of tracks are rewritten by overwriting for multi-cycles, the substrate of the surface tends to thermally expand and deform by during recording and the tracking grooves are bent in the direction of undergoing the force by the stress exerting from the stacked films to the substrate. Bending occurs remarkably toward the vicinity of the center for the multi-time recording area for 500 cycles or more.
In view of the above, this invention intends to overcome such problems and provide an information recording medium with no deformation of tracking grooves caused by stresses between stacked films and a substrate upon high density writing/reading, capable of possessing favorable writing/reading characteristics, having large process margin, capable of using a manufacturing apparatus at a reduced cost, excellent in view of material cost and mass productivity and with less stresses.
SUMMARY OF THE INVENTION
For overcoming the foregoing problems, the information recording medium according to this invention adopts the following countermeasures. That is, the temperature of the substrate is kept as low as possible. When the temperature of the substrate rises during film preparation and the film is deposited in an expanded state and then cooled, the stress from the substrate to the films changes in the direction of increasing the compressive stress. This invention intends to prevent occurrence of stresses by keeping the temperature of the substrate from rising.
Specifically, this invention provides multi-time rewritable information recording media as described below.
(1) A multi-time rewritable information recording medium conducting writing by the change of arrangement of atoms under the irradiation of light, comprising a substrate of a thickness of 0.7 mm or less, a lower protective layer of a thickness of 20 nm to 60 nm, a recording film, an upper protective layer and a reflective layer from the light-incident side, with the interval between tracks being 0.62 &mgr;m or less.
(2) A multi-time rewritable information recording medium conducting writing by the change of arrangement of atoms under the irradiation of light, comprising a substrate of a thickness of 0.7 mm or less, a lower protective layer of a thickness of 20 nm to 60 nm, a recording film, an upper protective layer and a reflective layer from the light-incident side, in which
90 atomic % or more for the material of the reflective layer comprises any one of Cr, Cr—Al, Cr—Ag, Cr—Au, Cr—Ge, or a Cr alloy as a main ingredient, an Al alloy such as Al—Ti, Al—Cr, Al—Co as a main ingredient, or Ge—Cr, Ge—Si, Ge—N, Co, Ni, Mo, Pt, W, Ge, Sb, Bi, Ag, Au or Cu.
(3) A multi-time rewritable information recording medium conducting writing by the change of arrangement of atoms under the irradiation of light, comprising a substrate of a thickness of 0.7 mm or less, a lower protective layer of a thickness of 20 nm to 60 nm, a recording film, an upper protective layer and a reflective layer from the light-incident side, in which
90 atomic % or more for the material of the lower protective layer comprises any one of oxides of:
ZnS—SiO
2
, ZnS—Al
2
O
3
, ZnS—Ta
2
O
5
, ZnS—SnO
2
, ZnS—In
2
O
3
, ZnS—TiO
2
, ZnS—Cr
2
O
3
, ZnS—ZnO or ZnO, SiO
2
, Al
2
O
3
, Ta
2
O
5
, SnO
2
, In
2
O
3
, TiO
2
, SnO
2
—In
2
O
3
, Cr
2
O
3
, ZnO—SiO
2
, Al
2
O
3
—SiO
2
, Ta
2
O
5
—SiO
2
, SnO
2
—SiO
2
, In
2
O
3
—SiO
2
, TiO
2
—SiO
2
, SnO
2
—In
2
O
3
—SiO
2
, Cr
2
O
3
—SiO
2
, ZnO—Al
2
O
3
, Ta
2
O
5
—Al
2
O
3
, SnO
2
—Al
2
O
3
, In
2
O
3
—Al
2
O
3
, TiO
2
—Al
2
O
3
, SnO
2
—In
2
O
3
—Al
2
O
3
and Cr
2
O
3
—Al
2
O
3
,
a mixture of the materials described above and the material formed by partially or entirely substituting the material described above with a nitride.
(4) A multi-time rewritable information recording medium conducting writing by the change of arrangement of atoms under the irradiation of light, comprising a substrate of a thickness of 0.7 mm or less, a lower protective layer of a thickness of 20 nm to 60 nm, a recording film; an upper protective layer and a reflective layer from the light-incident side, in which
90 atomic % or more for the material of the lower protective layer comprises any one of ZnO—In
2
O
3
, SnO
2
, SnO
2
—In
2
O
3
, ZnO—SiO
2
, SnO
2
—In
2
O
3
—SiO
2
.
(5) A multi-time rewritable information recording medium conducting writing by the change of arrangement of atoms under the irradiation of light, comprising a substrate of a thickness of 0.7 mm or less, a lower protective layer of a thickness of 20 nm to 60 nm, a recording film, an upper protective layer and a reflective layer from the light-incident side, in which
90 atomic % or more for the material of the upper protective layer comprises any one of oxides of:
ZnS—SiO
2
, ZnS—Al
2
O
3
, ZnS—Ta
2
O
5
, ZnS—SnO
2
, ZnS—In
2
O
3
, ZnS—TiO
2
, ZnS—Cr
2
O
3
, ZnS—ZnO or ZnO, SiO
2
, Al
2
O
3
, Ta
2
O
5
, SnO
2
, In
2
O
3
, TiO
2
, SnO
2
—In
2
O
3
, Cr
2
O
3
, ZnO—SiO
2
, Al
2
O
3
—SiO
2
, Ta
2
O
5
—SiO
2
, SnO
2
—SiO
2
, In
2
O
3
—SiO
2
, TiO
2
—SiO
2
, SnO
2
—In
2
O
Andoo Keikichi
Anzai Yumiko
Hirotsune Akemi
Minemura Hiroyuki
Miyamoto Makoto
LandOfFree
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