MANUFACTURING METHOD THEREFOR Field of Invention
The present invention relates in general to an optical storage medium such as a DVD and to a manufacturing method therefor and in particular, to a thin optical storage medium having a modified design, wherein structural changes are effected, so that the storage medium is compatible with the current disc players, aids in the printing process, provides a more robust design and consequently, reduces the tracking and focusing error. Baclcground of the Invention
It is traditionally known that optical media constitutes a very important tool in the field of data storage technology. Optical media comes in formats like CD-ROM/ CD-R/CD-RW/ DVD-ROM/ DVD-RW/DVD+RW/DVD-RAM Digital Video Disc or Digital Versatile Disc (DVD) is an optical storage medium for read-only, recordable and rewritable applications, DVD is considered to be an enhanced version of a compact disc (CD). They denote unified set of standards for high-density optical disc.
DVD-ROM comprises a circular disc, 120mm in diameter with a hub in center. Like CD, data is recorded on the disc in a spiral trail of tiny pits, (of finite lengths), and the discs are read by means of laser beams.
It is common knowledge that unlike CD, a DVD is a bonded disc, made of two substrates joined together (active and dummy). Thickness of each such substrate may vary between 0.5mm and 0,7mm. The active substrate, stores all the information and the dummy substrate, provides mechanical stability, so that tracking error (hereinafter referred to as TE) and focusing error (hereinafter referred to as FE) are kept within the acceptable limits. A stacking ring is provided at a predetermined distance, from the central region. Each substrate includes polycarbonate plastic, coated with a much thinner reflective layer of aluminum or gold. Usually, the two discs are glued together to form an approximately 1.4 mm disc that can be designed to read from one side (single sided) or both sides (double sided). The substrates are half as thick as a CD,

thereby making it possible to apply a lens, with a higher numerical aperture and hence, facilitates using smaller pits and narrower tracks. As explained aforesaid, polycarbonate resin forms a major component of the structural composition of these discs, particularly those of the active and dummy substrates. This substantially increases the cost of production. However, unless minimum amount of polycarbonate components are applied, the standard moment of inertia( hereinafter referred to as Ml) required, during rotation of the disc is not adequately achieved, resulting in substantial TE and FE, causing the tracking and the focusing servo to break lock. This results in read failure. Over the years, attempts have been made to optimize the application of polycarbonate components, in manufacturing optical storage media such as DVDs however, all such designs had some serious technical drawbacks. For example, a very common design known In the art comprises only data substrate and no supporting substrate. However, these discs are able to play back with great difficulty as the TE and FE are substantial, due to reasons as explained in the preceding paragraph. Furthermore, such discs, due to the manufacturing defects, rotate considerably faster during Fast Forward/Reverse of the discs, thereby resulting In failing of the unbalanced discs, due to disc vibration. Accordingly, there was a long felt need to optimize the application of polycarbonate components, to substantially reduce the cost of manufacturing of the discs and simultaneously ensure, that the technicalities such as Ml, TE, FE as discussed aforesaid, are maintained during functioning of the discs. The present invention meets the aforesaid long felt need. All through out the specification including the claims, reference has been made to DVDs for the sake of understanding only and not by way of limitation and the present invention embraces all relevant items in the field of optical storage media, as may be understood by persons skilled in the art.
Objects of the invention
It a principal object of the present invention to provide a cost-effective and technically sound optical storage medium such as a DVD.

It is a further object of the present invention to provide an optical storage
medium such as a DVD having only the active substrate, the dummy substrate
being removed, said medium being adapted to compensate for the loss of inertia,
due to the removal of the dummy substrate.
It is another object of the present invention to provide a thin optical storage
medium that is compatible with the existing drives.
It is a further object of the present invention, to alleviate the traclting and focusing
error, generated due to the thin size of the optical media due to disc fluttering.
It is a still another object of the present invention to reduce the overall quantity of
polycarbonate material applied and hence the cost of manufacturing.
It is a further object of the present invention to provide an optical storage medium
such as a DVD which is adapted to have oniy the active substrate and to
maintain the standard MI during rotation of the disc, thereby ensuring TE and FE
within acceptable limits.
It is yet another object of the present invention to provide a DVD, including only
the active substrate having a specific geometric configuration, such that the
standard Mi is maintained during operation and consequently, the TE and FE
are kept within acceptable limits.
It is yet another object of the present invention, to provide a DVD including only
the active substrate having a specific geometric configuration, whereby standard
Ml is maintained during the Fast Fonward/Reverse operation of the disc, hence
preventing failing of the unbalanced discs, due to disc vibration.
It is yet another object of the present invention to provide a method of
manufacturing a cost-effective and technically sound optical storage medium
such as a DVD.
The foregoing objects and the other aspects of the present invention will be clear
from the following description, which is purely by way of understanding and not
by way of any sort of limitation.

Summary of the invention
Accordingly the present invention provides an optical storage medium including a central hub, a stacking ring and an active substrate, wherein the configuration of the active substrate is modified at its top surface, whereby optimization of the application of polycarbonate components, to substantially reduce the cost of manufacturing of the discs Is achieved and simultaneously, the technicalities such as Ml, TE, FE are maintained during functioning of the discs.
In accordance with preferred embodiments of the optical storage medium of the
present invention:
-said modification comprises, at least one rod like feature at the top surface of
said active substrate.
-said modification comprises, varying the thickness of the active substrate at
predetermined positions.
-said modification includes increasing the thickness of said active substrate,
over the periphery of the inner hub of said storage medium.
-the thickness of said active substrate varies between 0.6mm+/-0.1mm.
-an additional element is provided over the periphery of inner hub of optical
storage medium.
-an additional element Is provided over the data side of the Inner hub of said
storage medium
-an additional element is provided over the optic side of the Inner hub of said
storage medium.
-said active substrate comprises at (east one continuous or discontinuous
reinforcing element.
-said reinforcing element comprises at least a continuous ring positioned any
where between the hub and the outermost periphery.
-said continuous rlng{s) Is (are) positioned at a 45mm radius.
-a plurality of reinforcing elements are provided in the form of substantially
equidistant ribs extending .radially from said stacking ring to the outer radius of
said medium.
-said ribs are substantially mutually perpendicular to each other, -thickness of said central bub, varies between 0.3mm and 1.40mm.

-said medium lacks dummy substrate and is a DVD.
-said modification comprises incorporation of both rod like feature{s) and ring like feature(s) on the top surface of said active substrate.
The present invention also provides a method of manufacturing an optical storage medium having a central hub, a stacking ring and an active substrate, including dyeing and sputtering wherein said method involves modifying the configuration of the top surface of the active substrate whereby, optimization of the application of polycarbonate components, to substantially reduce the cost of manufacturing of the discs is achieved and simultaneously, the technicalities such as Ml, TE, FE are maintained during functioning of the discs. In accordance with a preferred embodiment of the method of the present invention it involves, varying the thickness of the active substrate at predetermined positions.
Brief description of the accompanying drawings
The nature and scope of the present invention will be better understood from the accompanying drawings, which are by way of Illustration of some preferred embodiments and not by way of any sort of limitation.
In the accompanying drawings:
Figure 1 illustrates a conventional optical storage medium.
Figure 2 illustrates a preferred embodiment of an optical storage medium in
accordance with the present invention with the dummy substrate removed.
Figure 3 illustrates another preferred embodiment of the optical storage medium
according to the present invention.
Figures 4(a) and 4(b) illustrate two further preferred embodiments of the optical
storage medium in accordance with the present invention.
Figure 5 illustrates another preferred embodiment of the optical storage medium
according to the present invention.
Figure 6 illustrates another preferred embodiment of the optical storage medium
according to the present invention.

Figure? illustrates another preferred embodiment of the optical storage medium according to the present invention.
Figure 8 illustrates a further preferred embodiment of the optical storage medium according to the present invention.
Figures 9(a) and 9(b) illustrate cross sectional views of a typical disc and a finished disc respectively.
Detailed description of the instant invention
As stated aforesaid, a typical DVD-ROM structure is made of two substrates of 0.5 mm to 0.7mm thickness, each made up of Polycarbonate resin having an annular structure with outer diameter upto approximately 120 mm and inner diameter upto approximately 15 mm. The two substrates are usually joined by a UV cured resin, so that the overall thickness of the disc is upto approximately 1.2 mm.
A disc typlcaUy comprises upto 4.7 GB of data. The second substrate, called the dummy substrate, is primarily there to provide mechanical support to the disc, so that the discs, residual Tracking and Focusing errors are in control to ensure wide playback compatibility while rotating. Excessive Tracking and Focusing Errors (called TE and FE respectively) cause the tracking and the focusing servo to break lock, resulting in read failure.
As explained before, the dummy substrate is intended to provide mechanical support only. However, with rising Polycarbonate prices, calculation has shown that at least 60% of the total cost price of a DVD-ROM disc is taken up by Polycarbonate price. A DVD -ROM rotates, while being played back at 3.5m/s so that, the standard Moment of Inertia (hence forth to be designated as Ml) of a jointed disc is adequate for reducing TE and FE.
A very common design known In the art, to optimize the solution of polycarbonate material comprises only data substrate and no supporting substrate. However, these discs are able to play back with great difficulty as the TE and FE are substantial. Furthermore, such discs, due to the manufacturing defects, rotate

considerably faster dunng Fast Fonward/Reverse of the discs, thereby resulting in failing of the unbalanced discs, due to disc vibration.
The present invention optimizes the application of polycarbonate components, to substantially reduce the cost of manufacturing of the discs and simultaneously ensures, that the technicalities such as Ml, TE, and FE as discussed aforesaid, are maintained, during functioning of the discs. To ensure this, the present invention provides an optical storage medium such as a DVD which has no dummy substrate but has a data substrate vi/hich, unlike the conventional designs, Is not plain on top but has specific geometrical features. This technical advancement and/or economic significance were hitherto unknovi/n and not conceivable to persons skilled in the art.
In brief, the present invention discloses an optical storage medium including a central hub and a stacking ring and an active substrate, the structure of the active substrate being modified by varying the thickness of the active substrate at predetermined positions, for improving drive compatibility and /or alleviating the tracking error/ focusing error,
The optical storage medium of the present invention does not include a dummy substrate and the thickness of the active substrate varies between 0.6mm±0.1mm.
In order to enhance the robustness and stability of the optical storage medium and to reduce the tracking error and focusing error due to the removal of the dummy substrate, at least one reinforcing element is provided, vi/hich may be continuous or discontinuous. This reinforcing element may be at least a continuous ring, positioned at the outer periphery of the medium. Alternatively, it may be a continuous ring positioned at 45mm radius. However, this position may vary from anywhere between the hub and the outermost periphery. The optical storage medium may comprise a plurality of reinforcing elements, in the form of ribs extending radially, from the stacking ring to the outer radius, which are equidistant from one another. The reinforcing elements may be mutually perpendicular to one another.

The thickness of the active substrate is varied, by increasing its thickness over the periphery of the inner hub of said storage medium or over the data side of the inner hub of said storage medium or over the optic side of the inner hub of said storage medium.
The thickness of the active substrate is varied by providing an additional element over the periphery of inner hub of said storage medium or over the data side of the inner hub of said storage medium or over the optic side of the inner hub of said storage medium.
However, in order to have better manufacturing process and to optimize the design of the hub, the hub thickness is adjusted vi/ith the minimum raised hub thickness restricted to a vaiue of approximately 0.3 mm and with the maximum raised hub thickness restricted to a value of approximately 1.40. This is because, minimum thickness drives have difficulty in sensing the discs and with maximum thickness, it becomes too difficult to mould the Discs. The preferable thickness of the central hub is between 1.0 mm to 1.40 mm
Unlike CD, as shown in figure 1, a DVD is a bonded disc, made of two substrates joined together (active and dummy). The active substrate (1) stores all the information and the dummy substrate (2) is provided to give the disc a mechanical stability. A stacking ring (3) is provided at a predetermined distance from the central region. The substrates are polycarbonate plastic coated with a much thinner reflective layer of aluminum or gold. Two such discs are glued together to form a 1,4 mm disc that can be designed to read from one side (single sided) or both sides (double sided). The substrates are half as thick as the CD, to make it possible to use a lens with a higher numerical aperture and therefore use smaller pits and narrower tracks.
Optical storage devices store information in the form of pits and lands. The drives read the pits and lands by using a laser and sensor. The drive's laser scans the underside of the disc, searching for specific pits and lands that correspond to the command, the drive has received. A double-layered DVD has another layer of pits and lands, embedded below the top layer. The drive simply refocuses its laser, slightly in order to read the other layer.

Figure 2 illustrates a storage medium in accordance with the present invention, where the dummy substrate (2) has been removed and the thin optical medium comprises of only the active substrate (1). Due to removal of the dummy substrate (2) there is a loss of inertia, which is compensated by physical changes, in the structure of the optical medium. Also, to improve drive compatibility and to minimize the tracking error / focusing error, due to removal of the dummy substrate, modifications have to be made to the design of the optical storage medium.
All the conventional drives are designed for a 1.4mm thick disc. An optical disc with only the active layer will not be read. The clamping mechanism of the drive is not suitable for a 0.6mm±0.1 disc. Accordingly, the optical disc in accordance with the instant invention, is made compatible to be read by the drive. The optical pick up units of all drives, clamp a disc from both sides. Therefore, a thinner disc would not be held tightly and would not be read by the drive. This is because the clamping heads or the pins, which hold the disc, expect a 1.4mm thick disc. This would lead to drive compatibility problem and the disc would fail in many drives.
As shown in the Figure 3, in order to make the disc more robust and simultaneously improve the drive compatibility, the thickness of the active layer is varied by increasing its thickness over the periphery of the inner hub of said storage medium.
In a preferred embodiment, as illustrated in Figure 4, an additional element (5) is provided over the periphery of inner hub of optical storage medium or over the data side of the inner hub of said storage medium (as shown in Fig.4a) or over the optic side of the inner hub of said storage medium( as shown in Fig. 4b). Figure 5 illustrates a preferred embodiment, wherein in order to make the disc more robust and simultaneously improve the drive compatibility, a reinforcing element in the form of a continuous ring (4) is positioned, at the outer periphery of the medium. This figure also shows the stacking ring (3) and the centra! hole da)

As shown in another embodiment Illustrated by Figure 6, in order to make the disc more robust and simultaneously improve the drive compatibility, a plurality of reinforcing elements is provided in the form of ribs (5). These ribs extend radially from the stacking ring (3) to the outer radius of the medium and are equidistant from one another.
In the preferred embodiment shown In Figure 7, the reinforcing element (4) is a continuous ring positioned at a 45mm radius. However, this position can vary from anywhere between the hub and the outermost periphery.
Figure 8 shows a preferred embodiment of the present invention, wherein the plurality of ribs (5) which, extend radially from the stacking ring to the outer radius, are mutually perpendicular to one another.
In brief, to eliminate the danger of failure and simultaneously to reduce the
consumption of Polycarbonate, the present invention discloses a DVD-ROM
media having no dummy but only a data substrate, which, unlike conventional
media Is not plain on top but has specific geometrical features.
How the present invention overcomes the problems of prior art and why plane
single substrate, is not able to overcome the drawbacks is meticulously explained
below.
Ideally, a DVD-ROM substrate is an annular disc having a center hole of finite
Inner diameter and a finite outer diameter. The appearance of a typical disc has
been Illustrated in Fig 9(a). The appearance of a finished disc has been
Illustrated In Fig 9(b).
The Ml of a single substrate is calculated as follows.
If M Is the mass of a single substrate, then Ml is given by lsub= - M(R|^ + R ^ j „.
1
Let us now consider a case, where thin rods like features are present on the top of the substrate. The thickness of the rod may vary between 0 and 0,5mm. If m is the mass of the individual rods, whose radius Is very small, as compared to their length, then the Ml of each rod, about the center of the disc Is


Because of the additional term in eq 5, these types of media have additional Ml, which prevents deterioration of TE and FE, during faster rotation of the disc, thus ensuring reliable operation. N can be chosen suitably, so that deterioration is eliminated.
Let us now consider a case where thin ring like features, are present on the top of the substrate. The height of the rings may vary between 0 and 0.5mm.

This feature consists of thin rings of mass m, distributed within the annulus.
If three rings are considered with one having radius Ra, one at the center and another at the outermost radius (R1) then the Ml of the entire disc will be given by the following :

•mod ~ 'sub

, 2m
1 +
M

+

mR}

(6)

Because of the additional term in eq 5, these types of media have additional Ml which prevents flutter during faster rotation of the disc, thus ensuring reliable operation. N can be chosen suitably, so that flutter is eliminated. m and N can be varied, depending upon the requirements so as to achieve a suitable Ml, to prevent flutter. Same effect can be achieved and same derivation will hold good, if ring and rod features, are combined on a single disc. Equations 1, 5 and 6 may be applied to calculate numerical values, of Ml of discs, under different circumstances:
Ml of a normal half substrate: M=8 gm
Ri= 60 mm
R2=7.5 mm Then by eq 1 Mi= 14625 gm.mm^
Ml of a full disc: M=8 gm
Ri=60mm
R2=7.5 mm
Then by eq 1 Ml= 29250 gm.mm^
Ml of disc having 1 thin rod: N= 1

m= 0.0178 gm
Then by eq 5 Ml= 14645 gm.mm^
Ml of disc having 4 thin rods: N=4 m= 0,0178 gm
Then by eq 5 Ml= 14706 gm.mm^
Ml of disc having 1 ring at the center
m= 0.064 gm
Then by eq 6 Ml= 14639.4 gm.mm^
Ml of disc having 3 rings one at the inner diameter, one at the center and one at the edge:
m= 0 .064 gm
Then by eq 6 Ml= 14873.4 gm.mm^
Thus, any optical media will work as per the above principle, whose thickness varies between the ranges as aforesaid.
If the Ml of the half disc lies between 14639.4 gm.mm^ and 14706 gm.mm^ ^^"^ disc will work satisfactorily, othen/vise not.
Because of the additional term as shown in eq 5, these types of media have additional Ml, which prevents degradation of TE and FE during faster rotation, of

the disc thus ensuring reliable operation. N can be chosen suitably so that degradation is avoided.
m and N can be varied depending upon the requirements so as to achieve a suitable Ml, for prevent degradation. The same effect can be achieved and same derivation holds good, if ring and rod features are combined on a single disc.
Any method of manufacturing, which applies the principle as stated aforesaid, reduces the TE and FE of the discs.
Thus, the present invention optimizes the application of polycarbonate components in the manufacturing of an optical storage medium such as DVDs, to substantially reduce the cost of manufacturing of the discs and simultaneously ensure, that the technicalities such as Ml, TE, FE as discussed aforesaid, are maintained during functioning of the discs.
The present invention has been described vi/ith reference to some drawings and preferred embodiments, purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described hereinbefore and what has been claimed hereinafter.

We Claim:
1. An optical storage medium including a central hub, a stacking ring and an active substrate, wherein the configuration of the active substrate is modified at its top surface whereby optimization of the application of polycarbonate components to substantially reduce the cost of manufacturing of the discs is achieved and simultaneously, the technicalities such as Ml, TE, FE are maintained during functioning of the discs.
2. The optical storage medium as claimed in claim 1 wherein said modification comprises, at least one rod like feature at the top surface of said active substrate.
3. The optical storage medium as claimed in claim 1 wherein said modification comprises, varying the thickness of the active substrate at predetennined positions.
4. The optical storage medium as claimed in claim 3 wherein said modification
includes increasing the thickness of said active substrate, over the periphery
of the inner hub of said storage medium.
5. The optical storage medium as claimed in any preceding claim, wherein the thickness of said active substrate varies between 0.6mm+/-0.1mm.
6. The optical storage medium as claimed in any one of claims 3, 4 or 5, wherein an additional element is provided over the periphery of inner hub of optical storage medium.
7. The optical storage medium as claimed in any one of claims 3, 4 or 5, wherein an additional element is provided over the data side of the inner hub of said storage medium
8. The optical storage medium as claimed in any one of claims 3, 4 or 5, wherein an additional element is provided over the optic side of the inner hub of said storage medium.

9. The optical storage medium as claimed in claims 1 to 5 wherein said active
substrate comprises at least one continuous or discontinuous reinforcing
element.
10. The optical storage medium as claimed in claim 9 wherein said reinforcing
element comprises at least a continuous ring positioned any where between the
hub and the outermost periphery.
11. The optical storage medium as claimed in claim 10 wherein said continuous ring(s) is (are) positioned at a 45mm radius.
12. The optical storage medium as claimed in claim 9 wherein a plurality of reinforcing elements are provided in the form of substantially equidistant ribs extending .radially from said stacking ring to the outer radius of said medium.
13. The optical storage medium as claimed in claim 12 wherein said ribs are substantially mutually perpendicular to each other.
14. The optical storage medium as claimed in any preceding claim wherein thickness of said central hub, varies between 0.3mm and 1.40mm.
15. The optical storage medium as claimed in any preceding claim wherein said medium lacks dummy substrate and is a DVD.
16. The optical storage medium as claimed in claim 1 wherein said modification comprises incorporation of both rod like feature{s) and ring like feature(s) on the top surface of said active substrate.
17. A method of manufacturing an optical storage medium having a central hub, a stacking ring and an active substrate, including dyeing and sputtering wherein said method involves modifying the configuration of the top surface of the active substrate whereby, optimization of the application of polycarbonate components, to substantially reduce the cost of manufacturing of the discs is achieved and simultaneously, the technicalities such as Ml, TE, FE are maintained during functioning of the discs.

18. The method of manufacturing an optical storage medium as claimed in claim 17, wherein said method Involves varying the thickness of the active substrate at predetermined positions.