Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2000-07-21
2002-07-02
Neyzari, Ali (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S047100
Reexamination Certificate
active
06414935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording medium on which a data signal, an address signal, and the like are recorded by wobbling groove side wall, and a method for producing a recording medium master used for producing such a recording medium.
2. Description of the Prior Art
As shown in
FIG. 1
for example, on a surface of an optical disc, a concavo-convex pattern is formed according to a data signal or the like. More specifically, in a signal recording area where a data signal is to be recorded, a groove
100
which is an indentation and a land
101
which is a protrusion are formed on one surface of a disc substrate made from an optically transparent plastic material. The groove
100
is provided in a spiral state with a predetermined track pitch p. Here, the track pitch p is assumed to be approximately 0.7 &mgr;m to 1.6 &mgr;m. In the optical disk shown in
FIG. 1
, a recording layer is formed on its surface so as to enable recording and reproduction of a data signal.
For example, in the most of the phase-change type recordable optical discs or the magneto-optical disks, the signal recording area is occupied by the land
101
as a recording area and the groove
100
as the light reflection area for tracking. In these optical discs, a phase-change film or a magnetic film as a recording layer and a light reflection film or the like are formed on a signal recording plane on which the groove
100
or the like is formed.
Moreover, a shown in
FIG. 2
, in most of the optical discs dedicated for reproduction, a string of pits
102
on a signal recording plane is used as a recording area and a diffraction grating for tracking. It should be noted that a light reflection film and the like are also formed on the signal recording plane.
When carrying out a recording/reproduction to/from an optical disk as has been described above, the optical disc is rotated and a laser beam is applied from a beam source provided in an optical pickup, to a surface opposite to the substrate surface on which the groove and pit are formed.
Here, in the optical disc capable or recording a data signal, a data is written by the laser beam in the recording layer on the land
101
and the written data is read out by reflection of the laser beam. In this data signal recording and reproduction, the laser beam for recording or reproduction is controlled by a tracking control so that the laser beam is always applied onto a predetermined track, for example, by detecting a reflected beam from the groove.
On the other hand, in the optical disc dedicated for reproduction, a data reading and tracking control are carried out by applying a laser beam onto the signal recording plane and detecting a diffraction light reflected from the signal recording plane having the string of the pits
102
.
Thus, the concavo-convex pattern on the surface of an optical disc determines the performance as a data recording medium. Consequently, when producing an optical disc, it is necessary to produce a disc substrate on which a concavo-convex pattern is formed with a high accuracy.
Description will now be directed to a method for producing such a disc substrate.
For producing a disc substrate, firstly, it is necessary to prepare a glass master substrate whose surfaces are sufficiently polished and washed. On this master substrate, about 0.1 mm thickness of photo-resist is painted which becomes alkali-soluble by exposure to light.
Next, a laser beam is focused via an objective lens onto the surface of the photo-resist. For this, the glass master substrate is rotated and the laser beam is fed in the radius direction by an identical distance for each turn. By this application of the laser beam, a latent image of a groove is formed in the photo-resist at a predetermined interval p in a spiral state. At this time, if the laser beam is applied intermittently, it is possible to generate a latent image of a pit string in the photo-resist for each track pitch.
Next, this glass master substrate is developed with an alkaline developing solution, so as to remove the portions which have been exposed to the laser beam in the aforementioned step. Thus, in a recordable optical disc, a continuous groove is formed in the photo-resist to define a convex land left between the continuous groove in the radius direction of the glass master substrate. In an optical disc dedicated for reproduction, a convex pit string is formed in the photo-resist.
Next, the glass master substrate is plated with Ni so as to prepare a stamper on which the groove or the continuous pit string of the photo-resist is transferred.
Next, the concavo-convex pattern formed on this stamper is transferred to a plastic material of an optical disc substrate by way of injection molding or the like, so as to complete a disc substrate on which the groove and the land or the pit string are formed.
As for the recordable optical disc, when preparing this disc substrate, a recording film and a reflection film are formed on the concave-convex pattern having the groove on the disc substrate. As for the optical disc dedicated for reproduction, a reflection film and a protection film are formed on the concavo-convex pattern having the pit string on the substrate.
For the optical disc provided with such a disc substrate, there are two recording methods: a land recording method in which a data signal is recorded only on the land; and groove recording method in which a data signal is recorded only in the groove. Furthermore, in order to increase a recording density in future, there has been suggested a land/groove recording method in which the width of the land is formed almost identical to the width of the groove and a signal is recorded both on the land and in the groove.
Moreover, such a disc substrate has not only the groove configuration as a signal recording area but also contains address signals recorded in advance such as a track address signal for accurately recording/reproducing a data signal recorded and a clock generation signal for controlling the disc rotation velocity.
There are two types of methods to record these address signals: emboss forming for recording the address signals and groove side wall wobbling for recording the address signals.
FIG. 3
shows the emboss pit forming method for recording an address signal. An address signal is recorded by emboss pits
102
forming a concavo-convex pattern in a signal recording area. In this emboss pit method using the emboss pits
102
for recording an address signal, a predetermined area is occupied by address signals, where no data signal can be recorded. The address signal area in which the emboss pits
102
are formed for recording the address signals occupies about 20 positions in one round of the disc substrate. Consequently, this decreases the signal recording area, i.e., decreases the data signal recording capacity.
On the other hand,
FIG. 4
shows the groove side wall wobbling method for recording an address signal. As shown in the figure, the groove side walls are meandered according to an address signal to be recorded, by wobbling the laser beam spot applied onto the photo-resist formed on the glass master substrate, and this wobbling is detected at reproduction. In this method, in comparison to the aforementioned emboss pit method, the signal recording area is not partially occupied by the address signals, enabling to use the entire signal recording area for recording data signals. Consequently, this method enables to increase a data signal recording capacity.
As has been described above, as means for realizing a high density in the future, it is considered to use the land/groove recording in combination with the address data recording by way of wobbling.
However, in the conventional wobbling method as shown in
FIG. 4
, the configuration of the land
101
is defined by the meandering configuration of the adjacent groove(s)
100
and it is impossible to assign an inherent address signal.
Here, a one-sided wobbling method has been suggested as shown in
FIG. 5
, in which on
Masuhara Shin
Yamamoto Masanobu
Neyzari Ali
Rader & Fishman & Grauer, PLLC
Sony Corporation
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