Title: Multi-layer optical recording medium and method of manufacturing the same
Abstract: Preformatted areas in at least the most distal recording layer from an object lens among a plurality of recording layers in an optical disc include guard areas at both ends of the respective recording layer in the tracing direction. No data is recorded on the guard areas. The guard area length GL is determined to satisfy the following formula:
GL≧YL+T×(NA/n)/[1-(NA/n)2]1/2
where YL is a maximum allowable value of position deviation between the preformatted areas in the most distal recording layer and in another recording layer in the tracing direction; NA is the numerical aperture of the object lens; T is a distance between the most distal and the another recording layer; and "n" is an refraction index of a medium between the most distal and the another recording layers.
Patent Number: 7,006,427 Issued on 02/28/2006 to Yamamoto, et al.
| Inventors:
|
Yamamoto; Kaoru (Tsurugashima, JP);
Suga; Keiji (Tsurugashima, JP);
Shida; Noriyoshi (Tsurugashima, JP);
Iida; Tetsuya (Tsurugashima, JP)
|
| Assignee:
|
Pioneer Corporation (Tokyo, JP)
|
| Appl. No.:
|
674461 |
| Filed:
|
October 1, 2003 |
Foreign Application Priority Data
| Sep 12, 2000[JP] | 2000-276757 |
| Current U.S. Class: |
369/275.3; 369/275.4; 369/283; 428/64.4 |
| Current Intern'l Class: |
G11B 7/24 (20060101) |
| Field of Search: |
369/2752,275.3,275.4,275.1,277-279,283
428/644,641
264/133,106,107
425/810
|
References Cited [Referenced By]
U.S. Patent Documents
| 4644520 | Feb., 1987 | Lange.
| |
| 4795511 | Jan., 1989 | Wouters et al.
| |
| 5972250 | Oct., 1999 | Miyamoto et al.
| |
| 6532208 | Mar., 2003 | Nakajima.
| |
| Foreign Patent Documents |
| 10-172241 | Jun., 1998 | JP.
| |
Primary Examiner: Neyzari; Ali
Attorney, Agent or Firm: Drinker Biddle & Reath LLP
Parent Case Text
This application is a Divisional of application Ser. No. 09/948,785, filed on
Sep. 10, 2001, now U.S. Pat. No. 6,656,560.
Claims
What is claimed is:
1. A rewritable multi-layer optical recording medium having a plurality of recording
layers, wherein data recording areas are divided by preformatted areas in a tracing
direction in each of the plurality of recording layers,
wherein the preformatted areas in at least a most distal recording layer among
the plurality of recording layers from an object lens adapted to collect a radiated
light beam include guard areas located at both ends of the respective preformatted
areas in the tracing direction and having no data recorded thereon, and wherein
the length of the guard area GL satisfies;
GL≧YL+T×(
NA/n)/[1-(
NA/n)
2]
1/2
where,
YL: a maximum allowable value of position deviation between the preformatted
areas in the most distal recording layer and in another recording layer in the
tracing direction
NA: the numerical aperture of the object lens
T: a distance between the most distal recording layer and said another recording layer
n: a refraction index of a medium between the most distal recording layer and
said another recording layer.
2. A rewritable multi-layer optical recording medium according to claim 1, wherein
each of the plurality of recording layers includes a phase change medium for data
signal recording, and the length of the guard area GL satisfies the following formulas:
GL≧YL+R×[1-2
×VP×(
TA+TC)/|
TA-TC|]
R=T×(
NA/n)/[1-(
NA/n)
2]
1/2
Where,
TC: transmittance of a crystal portion of the phase change medium
TA: transmittance of an amorphous portion of the phase change medium
VP: a maximum allowable variation rate of intensity of the light beam.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-layer optical recording medium having
a plurality of recording layers, and more particularly to a multi-layer optical
recording medium having data recording regions divided by preformatted regions
and a method of manufacturing the recording medium.
2. Description of the Related Art
A multi-layer optical disc is recently known as a large capacity recording medium
that has an increased recording capacity per one side of the optical disc. Such
multi-layer optical disc has a structure in which a plurality of recording layers
are stacked at relatively small gaps. Another type of conventional multi-layer
optical disc is a rewritable multi-layer optical disc employing a recording material
or medium such as a phase change medium.
For simplicity of description, the following description deals with a two-layer
DVD (Digital Versatile Disc) having two recording layers in which each layer contains
the phase change medium. More particularly, the two-layer DVD has a structure in
which phase-change recording films are formed on both layers, that is, an upper
layer (or first recording layer) which is proximate to an object lens of an optical
pickup and a lower layer (or second recording layer). A laser beam is focused on
one of the recording layers and a signal is recorded on or reproduced from the
recording layer when information is recorded on or reproduced from the two-layer disc.
It should be assumed now that the laser beam is focused on the second recording
layer (hereinafter, simply referred to as "second layer") of the above described
two-layer DVD or the like upon recording or reproduction. In this case, the laser
beam is transmitted through the first recording layer (hereinafter, simply referred
to as "first layer") and is radiated on the second layer to record and/or reproduce
a data signal. Such recording and/or reproduction (hereinafter, simply referred
to as "recording/reproduction") is influenced by the first layer if an amount of
light reflected from the first layer and received by a light receiving unit varies
and/or if an amount of light transmitted to the second layer through the first
layer varies. An adverse effect caused by the variations in the amount of reflected
light from the first layer can be reduced by modifying a structure of a light detecting
system or other element(s). The variations in the amount of transmitted light through
the first layer, however, remain in the form of variations in intensity of the
recording light during the recording operation, and in the form of variations in
level of a reproduced signal during the reproducing operation. These adverse effects
are sometimes not negligible.
When a phase change medium such as germanium antimony tellurium (GeSbTe) is
used for the recording layer, optical transmittance of a crystal portion of the
medium differs from that of an amorphous portion; the former is lower than the
latter. Almost 100% of the areas of the phase change medium which have no data
recorded thereon are crystal portions, while crystal portions and amorphous portions
exist in the recorded areas in a mixed manner. Further, the transmittance for the
beam is an average value of the transmittance of the crystal portion and that of
the amorphous portion although the beam is not focused on the recorded area of
the first layer and the recorded signal is not reproduced therefrom. As a result,
upon reproduction of the second layer, the amount of received light (i.e., the
RF signal level during the reproducing operation) differs according to whether
the beam passes through the recorded area or the non-recorded area of the first layer.
If the ratio of the crystal area to the amorphous area is constant in the region
of the first layer through which the beam passes, the transmittance of the beam
does not change so that the amount of received light (i.e., RF signal level) does
not change.
A general rewritable multi-layer optical disc, however, is provided with a preformatted
area in which no data signal is recorded. Referring to FIGS. 1 and 2 of the accompanying
drawings, a DVD-RAM (Random Access Memory) will be taken as an example. The disc
3 has recording areas divided by preformatted areas
5 in a tracing
direction (i.e., circumferential or tangential direction of the disc) and a plurality
of data areas
6 are concentrically formed. A sector
7 is defined
by a preformatted area
5 and an adjacent data area
6.
FIG. 2 illustrates an enlarged view of the preformatted area and the neighboring
areas (portion "A" in FIG. 1) together with transmittance of these areas. Information
data such as an addresses is recorded in the form of embossed pits
8 within
the preformatted area
5. The data area
6 includes lands (L) and grooves
(G), and recorded marks
9 are formed on data recorded portions.
As illustrated in FIG. 2, the average transmittance T
D of the data
area
6 is greater than the transmittance T
P of the preformatted
area
5. Thus, the transmittance changes in the preformatted area
5
of the first layer and the recording beam intensity or reproduced signal intensity
changes when the recording operation or reproducing operation is performed for
the second layer. In order to avoid the adverse effect from occurring in the multi-layer
optical recording medium having the preformatted areas during information recording
and/or reproduction, the positions of the preformatted areas in the first layer
should be aligned with those of the preformatted areas in the second layer as shown
in FIG. 3. No adverse influence occurs during the recording and/or reproduction
operations if the preformatted areas of the second layer always lie below the preformatted
areas of the first layer that would reduce the amount of transmitted light. It
is, however, practically difficult to align the positions of the preformatted areas
with each other in a manufacturing process.
There is therefore a demand for a method of manufacturing an optical disc having
the preformatted areas of the first layer aligned with those of the second layer,
or an optical disc that has minimized location deviations of the preformatted areas
between the first and second layers. It is also necessary that the adverse effects
in recording/reproduction operations such as an S/N ratio (signal to noise ratio)
deterioration and reproduced RF signal variations resulting from the above described
transmittance variations are prevented even if the preformatted areas of the manufactured
disc are not aligned with each other between the recording layers.
OBJECT AND SUMMARY OF THE INVENTION
The present invention aims to solve the above described problems, and one of
the objects of the present invention is to provide a manufacturing method of an
optical disc that can reduce position deviation or alignment of the preformatted
areas between the recording layers.
Another object of the present invention is to provide a high-performance
rewritable multi-layer optical recording medium that ensures stable recording and
reproduction even if the positions of the preformatted areas are not aligned with
each other.
According to one aspect of the present invention, there is provided a rewritable
multi-layer optical recording medium having a plurality of recording layers, wherein
data recording areas are divided by preformatted areas in a tracing direction in
each of the plurality of recording layers, wherein the preformatted areas in at
least a most distal recording layer among the plurality of recording layers from
an object lens adapted to collect a radiated light beam include guard areas located
at both ends of the respective preformatted areas in the tracing direction and
having no data recorded thereon, and wherein the length of the guard area GL satisfies;
GL≧YL+T×(
NA/n)/[1-(
NA/n)
2]
1/2
where,
- YL: a maximum allowable value of position deviation between the preformatted
areas in the most distal recording layer and in another recording layer in the
tracing direction
- NA: the numerical aperture of the object lens
- T: a distance between the most distal recording layer and the another
recording layer
- n: an refraction index of a medium between the most distal recording
layer and the another recording layer.
According to another aspect of the present invention, there is provided
a method of manufacturing a rewritable and rotatable multi-layer optical recording
medium having a plurality of recording layers, wherein data recording areas are
divided by preformatted areas in each of the plurality of recording layers in a
tracing direction, which comprises the steps of:
- A) forming a projection of a circular shape on a first substrate such
that the projection is substantially coaxial to a rotation center of the first
substrate, the first substrate having at least one recording layer;
- B) forming a recess in a second substrate such that the recess is substantially
coaxial to a rotation center of the second substrate and adapted to engage with
the projection, the second substrate having at least one recording layer; and
- C) engaging the projection and the recess with each other to attach
the first and second substrates to each other.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates a view of a structure of an optical disc including
preformatted areas, data areas and sectors;
FIG. 2 schematically illustrates an enlarged view of the preformatted area and
the data areas together with transmittance of these areas;
FIG. 3 illustrates a cross sectional view of first and second layers of an optical
disc when positions of preformatted areas in the first and second layers are aligned
with each other;
FIG. 4 illustrates a cross sectional view of a structure of a two-layer optical
disc according to the present invention, taken in a tracing direction of the optical disc;
FIG. 5 schematically illustrates an enlarged view of the preformatted areas
and the data areas in the first and second layers in the vicinity of a boundary
between the preformatted and data areas, taken along the tracing direction, according
to a first embodiment of the present invention, together with the average transmittance
of the first layer and power variations of a reflected light beam from the second layer;
FIG. 6 illustrates a radius R of a light beam in the first layer when the light
beam is focused on the second layer;
FIG. 7 schematically illustrates an enlarged view of the preformatted and the
data areas in the first and second layers in the vicinity of a boundary between
the preformatted and data areas, taken along the tracing direction, according to
a second embodiment of the present invention, together with the average transmittance
of the first layer and power variations of a reflected light beam from the second layer;
FIG. 8 illustrates an eccentricity and a radial position deviation between the
first and second recording layers, which cause position deviation of the preformatted areas;
FIG. 9 illustrates a perspective view of a first substrate having a first recording
layer and a second substrate having a second recording layer according to a third
embodiment of the present invention;
FIG. 10 illustrates a cross sectional view of the first and second substrates
showing a manner of attaching the first substrate to the second substrate shown
in FIG. 9;
FIG. 11 illustrates a perspective view of a structure of an optical disc according
to a fourth embodiment of the present invention, and is useful to describe a manner
of attaching two substrates to each other;
FIG. 12 illustrates a cross sectional view of a structure of a dual-sided optical
disc according to a fifth embodiment of the present invention, and is useful to
describe a manner of attaching substrates to each other; and
FIG. 13 also illustrates a cross sectional view of the structure of the dual-sided
optical disc according to the fifth embodiment of the present invention, and is
useful to describe the manner of attaching the substrates to each other.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Embodiments of the present invention will now be described in detail
in reference to the accompanying drawings. It should be noted that similar reference
numerals are assigned to similar elements in different drawings.
First Embodiment
Referring to FIG. 4, schematically illustrated is a cross sectional view
of a structure of a two-layer optical disc according to the present invention,
taken along a tracing direction. The two-layer optical disc
3 includes a
first recording layer (upper layer)
11 and a second recording layer (lower
layer)
12 when viewed in a direction of a laser beam radiated to record
or reproduce an information data signal. The second layer is therefore a layer
distal from an object lens adapted to collect the laser beam.
The first recording layer (first layer)
11 includes preformatted areas
5 and data areas
6. The second recording layer (second layer)
12,
on the other hand, includes preformatted areas
5, data areas
6 and
guard areas
14. The guard areas are formed at both ends of each preformatted
area
5 in the tracing direction, and no data is recorded on the guard areas.
As illustrated in FIG. 4, the positions of the preformatted areas
5 in
the first layer
11 are offset from those of the preformatted areas
5
in the second layer
12 in the tracing direction. This offset or position
deviation (YL) is produced when the optical disc
3 is fabricated.
Each of the first and second layers
11 and
12 also includes a
phase-change recording medium or material such as germanium antimony tellurium
(GeSbTe). The phase-change recording medium is in an amorphous state when it is
formed and has low reflectance (i.e., high transmittance). If a laser beam is radiated
to a certain area prior to recording during an initializing process, the temperature
of the radiated area is raised. The radiated area becomes crystallized and has
low transmittance when the area is cooled after its temperature exceeds a crystallization
temperature. In order to perform the data recording, the laser beam is radiated
to a particular area from an optical pickup to raise the temperature of the area.
After its temperature exceeds a melting point, the area is quickly cooled to create
an amorphous mark of low reflectance and high transmittance.
There is provided a spacer layer
15 between the first and second layers
11 and
12 as an interlayer medium. The spacer layer
15 is
made from a material, such as an ultraviolet curing resin, having high transmittance
in a wavelength range of the laser beam, since the spacer layer
15 serves
as a light path for the laser beam.
Referring to FIG. 5, schematically illustrated is an enlarged view of a
boundary region between a preformatted area
5A and a data area
6A
in the first layer
11 and a boundary region between a preformatted area
5B and a data area
6B in the second layer
11. FIG. 5 also
shows a graph of the average transmittance of the first layer
11 and the
power variation of a reflected laser beam from the second layer
12 in the
tracing direction when the laser beam is focused on the second layer
12.
The power variation is normalized using the light power radiated on the data area
6B for data reproduction.
When the laser beam is focused on the second layer
12 to reproduce data
from the second layer
12, the average transmittance of the first layer
11
is higher in the data area
6A and the transmittance of the first layer
11
is lower in the preformatted area
5A. In addition, the average transmittance
gradually changes (i.e., decreases) as the laser beam moves from the data area
6A to the preformatted area
5A of the first layer
11 because
the laser beam has a certain span or diameter in the first layer
11. It
should be noted that the shape of the laser beam and the light intensity distribution
in the laser beam transmitting the first layer
11 are not considered for
simplicity of calculation, and the variation of the average transmittance is approximated
by the linear line. The light power from the second layer
12 changes in
accordance with the average transmittance variation of the first layer
11.
When the laser beam is focused on the second layer
12 to reproduce the
data from the second layer
12, an area which is subject to the influence
of the transmittance variation of the first layer
11 is expanded to an extent
determined by the radius R of the laser beam in the first layer
11 as shown
in the lower illustration of FIG. 5. The length GL of the guard area
14
in the tracing direction is therefore required to be extended by the laser beam
radius R from the position offset YL between the preformatted areas
5A and
5B. In other words, the length of the guard area
14 should satisfy
the following equation:
GL≧YL+R (1)
When the laser beam is focused on the second layer
12, the laser beam
radius R at the first layer
11 changes with the numerical apertures (NA)
of the object lens of the optical pickup system, a refractive index (n) of the
spacer layer
15 through which the laser beam passes, and an interval (T)
between the recording layers as illustrated in FIG. 6. If the angle of expansion
of the laser beam is given by θ, the laser beam radius R can be expressed
by the following formula:
R=T×tan θ (2)
where sin θ=
NA/n (3)
cos θ=[1-(
NA/n)
2]
1/2 (4)
tan θ=(
NA/n)/[1-(
NA/n)
2]
1/2 (5)
Consequently, the length of the guard area
14 (GL) should be
determined to satisfy the following equation:
GL≧YL+T×(
NA/n)/[1-(
NA/n)
2]
1/2 (6)
As long as this condition is satisfied, the data recording and reproduction can
be conducted for the data areas
6B of the second layer
12 without
being affected by the preformatted areas
5A of the first layer
11.
The position deviation or offset YL in the above equations may be set, for example,
to a maximum tolerance limit of the manufacturing process.
Second Embodiment
A second embodiment of the present invention will now be described in reference
to the accompanying drawings.
Referring to FIG. 7, schematically illustrated is an enlarged view of a
boundary area between the preformatted area
5A in the first layer
11
and the preformatted area
5B in the second layer
12. This drawing
also shows in its upper region a graph of the average transmittance of the first
layer
11 and power variations of the reflected laser beam from the second
layer
12 in the tracing direction when the laser beam is focused on the
second layer
12. The power variations of the reflected laser beam is normalized
using the light power radiated onto the data area
6B for data reproduction.
It should be noted that the solid line and single-dot chain line are drawn on the
assumption that the shape of the laser beam is square in the first layer
11
and the light intensity distribution of the laser beam is constant through the
first layer
11 for simplification the calculation. The two-dot chain line
and three-dot chain line indicate the average transmittance and the power variations
of the reflected laser beam from the second layer
12 where the laser beam
is assumed to have a circular shape and the light intensity distribution of the
laser beam is taken into account. The power variations in the graph is also normalized
using the light power radiated on the data area
6B for data reproduction.
In the first embodiment, the length of the guard area
14 is determined
such that the laser beam power from the second layer
12 does not change
until the laser beam reaches the guard area
14 of the second layer
12.
In an actual system design, however, the length of the guard area
14 can
be reduced from the value indicated in the first embodiment if the power change
is admitted to a certain extent.
As illustrated in the graph of FIG. 7, when the laser beam moves from the data
area
6A of the first layer
11 to the preformatted area
5A
and part of the laser beam reaches the preformatted area
5A, the laser beam
power starts decreasing. If the decrease tolerance limit of the laser beam power
is given by VP (e.g., VP=0.05 when the decrease tolerance limit is 5%), the transmittance
of the crystal portion of the phase-change medium is TC and the transmittance of
the amorphous portion is TA, then part of the laser beam can enter the preformatted
area
5A by the length L, which is expressed by the following equation:
L=2
×R×VP×(
TA+TC)/|
TA-TC| (7)
To derive the above equation, the laser beam configuration in the first layer
11 is assumed to be square and the beam intensity distribution is constant
in the first layer to simplify the calculation.
The length GL of the guard area
14 in the tracing direction is therefore
determined to satisfy the following formula:
GL≧YL+R-L=YL+R×[1-2
×VP×(
TA+TC)/|
TA-TC|] (8)
R=T×(
NA/n)/[1-(
NA/n)
2]
1/2 (9)
When the length GL of the guard area
14 is determined to satisfy the
above condition, it is possible to confine the laser beam power variations within
a predetermined allowance range and perform stable (reliable) recording and reproduction
operations even if there is influence of the preformatted areas
5A of the
first layer
11. Further, it is feasible to elongate the length L in the
equation (7) to a certain extent, depending upon the allowable power variation,
because the average transmittance varies as indicated by the two-dot chain line
in FIG. 7 when the laser beam shape and the intensity distribution of the laser
beam are taken into consideration. This further reduces the length required to
the guard area.
The above described embodiments deal with the two-layer optical disc, but the
present invention is applicable to an optical disc having a plurality of phase-change
recording layers. In such instance, the guard areas are provided for the preformatted
areas in the recording layer which is most distal, among a plurality of recording
layers, from the object lens adapted to collect the laser beam.
Third Embodiment
Before describing a third embodiment of the present invention, the offset
(position deviation) of the preformatted areas will be described. As depicted in
FIG. 8, the preformatted area position deviations are caused from a discrepancy
in the center position (i.e., eccentricity) and a discrepancy in the disc rotational
direction between the first recording layer and the second recording layer.
FIG. 9 is a perspective view of the third embodiment of the present invention
and illustrates a structure of a first substrate
31 having the first recording
layer and a second substrate
41 having the second recording layer. The first
substrate
31 has a circular (or an annular) projection
35 that is
substantially coaxial to the rotation center of the first substrate
31.
The second substrate
41 has a circular recess
45 that is substantially
coaxial to the rotation center of the second substrate
41 and is adapted
to receive the projection
35 of the first substrate
31. The second
substrate
41 also has a recess
47 near its periphery that engages
with a projection
37 formed on the first substrate
31. The recess
47 is formed at a position corresponding to the position of the projection
37. In other words, the recess
47 is formed at the position that
fits over the projection
37 when the first and second substrates
31
and
47 are engaged to each other, and the position of the recess
47
substantially alignes the preformatted areas of the first substrate
31 with
the preformatted areas of the second substrate
41.
Referring to FIG. 10, schematically illustrated is a cross sectional view
to describe the manner of attaching the first substrate
31 to the second
substrate
41 shown in FIG. 9. As mentioned above, the first substrate
31
includes the recording layer (i.e., first layer
38) and the second substrate
41 includes the recording layer (i.e., second layer
48). The mating
face
31A of the first substrate
31 is directed to the mating face
41A of the second substrate
41 when these two substrates are united.
When attaching the first substrate
31 to the second substrate
41,
the circular projection
35 of the first substrate
31 fits in the
recess
45 of the second substrate
41, as described earlier, so that
an amount of eccentricity is reduced or minimized.
The projecting portion
37 formed near the periphery of the first substrate
31 fits in the recess portion
47 formed in the second substrate
41.
As described above, when the projection
37 and the recess
47 are
engaged with each other, the preformatted areas of the first substrate
31
are substantially aligned with those of the second substrate
41 so that
the deviation in the rotation direction is also reduced or minimized.
Accordingly, the optical disc having the reduced eccentricity and rotational
deviation (i.e., reduced preformatted area position deviation) is obtained.
Although the above described embodiment deals with a configuration in which
the first substrate
31 has the projections
35 and
37 and the
second substrate
41 has the mating recesses
45 and
47, the
positions of the projections and recesses are interchangeable. For example, the
first substrate
31 may have the circular projection and peripheral recess
and the second substrate
41 may have the mating recess and projection. The
positions of the projections and recesses are arbitrary as long as the projections
and recesses do not obstacle the recording layers.
Fourth Embodiment
Referring to FIG. 11, schematically illustrated is a view to describe a
method of manufacturing the optical disc
3 according to a fourth embodiment
of the present invention. This embodiment is the same as the third embodiment in
that the first substrate
31 has the circular projection
35 and the
second substrate
41 has the recess
45 that engages with the projection
35. Engagement between the projection
35 and the recess
45
therefore also reduces the eccentricity in this embodiment.
In the fourth embodiment, the first substrate
31 has marks
39 ("+"
marks in the drawing) formed in the center area, peripheral area or peripheral
side portion of the first substrate
31 to indicate positions of the preformatted
areas in the recording layer of the first layer
31. Likewise, the second
substrate
41 has marks
49 ("+" marks in the drawing) formed at the
peripheral side portion of the second substrate
41 to indicate positions
of the preformatted areas in the recording layer of the second layer
41.
Affixing of the first substrate
34 onto the second substrate
41
is conducted such that the marks
39 and
49 are aligned with each
other. This reduces the deviation in the rotational direction of the optical disc.
It should be noted that the locations of the marks
39 and
49 unnecessarily
indicate the exact locations of the preformatted areas. In other words, it is satisfactory
as long as the relative relationship between the marks
39 and the preformatted
areas in the first substrate is the same as that between the marks
49 and
the preformatted areas in the second substrate. That is, it is satisfactory as
long as the positions of the preformatted areas in the first substrate are substantially
aligned with those in the second substrate as a result of matching the marks of
the first substrate to those of the second substrate and uniting the first substrate
to the second substrate. It should also be noted that any mark may be employed
for this purpose, such as those written during the signal recording and those created
during a process of fabricating the substrates (e.g., concave and/or convex portions
formed on the substrates).
Fifth Embodiment
The above described embodiments are concerned with a single-sided disc, but the
present invention can be applied to a dual-sided (double-sided) disc in a similar
manner. Referring to FIGS. 12 and 13, schematically illustrated is a cross sectional
view to describe a method of manufacturing the optical disc
3 according
to a fifth embodiment of the present invention.
The first substrate
31 having a recording layer (second layer)
38
is prepared as illustrated in FIG. 12, like the third embodiment. The first substrate
31 therefore possesses the circular projection
35 at its center and
the projection
37 near its edge.
Another substrate
51 that does not possess a recording layer and is
designed to be attached to the first substrate is then prepared. Like the second
substrate
41 in the third embodiment, the substrate
51 includes recesses
55 and
57, which engage with the projections
35 and
37
on the first substrate
31, on its face
51A that adheres to the first
substrate
31. The other adhesion face
61A of the substrate
51
opposite the face
51A also has an circular recess
65 at its center
and a recess
67 near its edge.
As in the third embodiment, the faces
31A and
51A are attached
to
each other. As illustrated in FIG. 13, the resulting substrate
61 is now
utilized as the second substrate having the recording layer
38 as in the
third embodiment. The substrate
61 has an circular recess
65 at its
center and a recess
67 near its edge on the face
61A, which recesses
are to be engaged with the center projection
35 and peripheral projection
37 on another first substrate
31 respectively. By attaching the first
substrate
31 onto the second substrate
61 having the recording layer
68, it is possible to obtain a dual-sided optical disc that has the reduced
eccentricity and deviation in the rotational direction, i.e., the reduced preformatted
area position deviation.
As described in the foregoing, the present invention can provide an optical disc
that has smaller position deviation between preformatted areas in one recording
layer and those in an adjacent recording layer. In addition, even if there is slight
position deviation between the preformatted areas of the adjacent recording layers,
the optical disc of the present invention can realize stable data recording and reproduction.
It should be noted that the illustrated and described embodiments are examples
of the present invention, and therefore suitable changes and modifications can
be made to the embodiments, and/or the embodiments can be combined with each other
without departing from the scope and spirit of the present invention.
As understood from the above description, the present invention provides a multi-layer
optical recording medium with which stable data recording and reproduction can
be assured. The present invention also provides an optical disc with reduced position
deviation between preformatted areas of adjacent recording layers.
The invention has been described with reference to the preferred embodiments
thereof. It should be understood by those skilled in the art that a variety of
alterations and modifications may be made from the embodiments described above.
It is therefore contemplated that the appended claims encompass all such alterations
and modifications.
This application is based on Japanese Patent Application No. 2000-276757 which
is hereby incorporated by reference.
*
