A High Density Optical Recording Low to High Medium For Write Once Applications and A Method For Manufacturing The Same.
FIELD OF THE INVENTION
The present invention relates in general, relates to an optical recording medium and a method for its manufacturing ,and more particularly to a low to high optical recording medium for write once applications and its manufacturing method, that is adaptive for recording information at high density. The present invention also relates to a method for manufacturing high-density optical recording, write once blu ray(recordable) low to high discs, which includes phase change recording layer as a primary component, on which data can be recorded using a laser beam, having a wavelength of 405 nm. The present invention meets the current Blu ray disc (recordable) book specifications, of jitter and write power. BACKGROUND OF THE INVENTION
It is known in the art, that there are two different types of recording namely L2H, H2L. L2H refers to Low-to-High change, which essentially means transition of reflectivity from low to high, upon laser irradiation. Similarly, H2L refers to reflectivity transition from high-to-low after laser shining.
With the transition into the digital age, more and more data are being generated resulting in cropping up of need to store these ever increasing data, appropriately and safely. Hence, over the years, the need to increase the density of the storage devices, has kept on increasing. In optical recording elements, this increase in density is achieved, primarily by decreasing the feature size used for storing information. To accomplish this decrease in feature size, the laser wavelength is decreased and the numerical aperture of the focusing lenses is increased, to reduce the size of the read/write laser spots. One vital drawback, encountered in the aforesaid adaptation is that the capability of the storage medium, to support the small feature size is not guaranteed. For example, the recommended laser wavelength and numerical aperture for Blu-ray

disc are 405 nm and 0.85, respectively. The track pitch for the blu-ray disc is reduced to 0.32 micron and the smallest mark size (2T) is 0.16 micron. In the ablative type media, frequently, there is a rim around the ablative marks which physically prevents, small features from being made. In the Sb-ln-Sn phase-change alloys the noise increases, when the recorded crystalline marks become smaller. The mark formation in this recording material is hampered by arbitrary delays and decreased mark, especially the 2T marks, suggesting a low nucleation-site density in these alloy films. When the recording density increases, however, the marks become smaller and the probability of proper nucleation during the irradiation time of the writing laser, becomes smaller. Consequently, the recorded marks may become less uniform and the read back jitter increases. Doping oxygen (commonly-assigned U.S. Pat. No. 5,271,978), water, nitrogen, or methane (commonly-assigned U.S. Pat. Nos. 5,312,664 and 5,234,803) to Sb-ln-Sn alloys improves the situation somewhat, but not to satisfactory extent as the issue of small mark recording, still remains problematic.
Another shortcoming of the Sb-ln-Sn alloy is the high optical density of the alloys. For certain applications, it is desirable to construct a multi-layer structure and utilize optical interference to enhance recording performance or to change the polarity of the recorded signals. For example, one can use a three-layer structure comprising a phase-change recording layer, a dielectric layer, and a reflective layer; or a four-layer structure with an additional dielectric layer on the other side of- the phase-change recording layer. For the optical interference to work, a substantial amount of light has to transmit through the phase-change layer and, therefore, the thickness of the phase-change layer has to be small. The required thickness decreases, with increasing optical density of the phase-change layer. The Sb-ln-Sn alloys have high optical absorption, with the imaginary part of the optical constant, k, larger than 3.0 in the amorphous phase and it increases to even higher values when the material crystallizes. When a Sb-ln-Sn alloy thin film is used as the recording layer for a three-layer or four-layer recording

element, its thickness has to be so small, that concern arises with respect to the film's chemical stability. For operating at 650 nm wavelength, for example, the thickness of the phase-change recording layer needs to be less than 10 nm. The thickness of the dielectric layer also depends on the optical density of the phase-change layer. The thickness increases, as the optical density increases. Since the deposition rates for dielectric layers are smaller than those for alloys, the need for a relatively thick dielectric layer reduces the manufacturing throughput and increases product costs. The deposition process for dielectric layers are also hotter than that for alloys, long deposition time used for thick dielectric layers causes unwanted heating of the substrates. The high optical density of the Sb-In-Sn necessitates the use of thicker dielectric layer,as well. Hence, the aforesaid technologies known in the art, have not been able to meet the requirement of designing an optical recording medium, adapted to store information at high density and simultaneously ensuring, betterment of technical performance and cost effectiveness .
Accordingly, there was a long felt need to develop an optical recording medium and a method for its manufacturing , so as to ensure storing of information at high density and to„ simultaneously ensure, low jitter, betterment of technical performance and cost effectiveness . The present invention is directed, in general to achieve this long felt need.
At places throughout the specification including the claims, the term blu ray (recordable) low to high write once discs, have been referred to for the sake of understanding and application of the invention and is not limited to it, unless specifically mentioned to that effect. OBJECTS OF INVENTION
The prime object of the present invention is to provide a low to high optical recording medium for write once applications , adapted to store information at high density, simultaneously ensuring low jitter, betterment of technical performance and cost effectiveness .

It is a further object of the present invention to provide a method for manufacturing, low to high optical recording medium for write once applications, adapted to store information at high density and simultaneously ensuring low jitter,betterment of technical performance and cost effectiveness. It is a further object of the present invention to provide an improved low to high Blu ray(recordable) disc for write once applications, adapted to store information at high density and simultaneously ensuring low jitter, betterment of technical performance and cost effectiveness.
It is a further object of the present invention to provide a method for manufacturing an improved low to high Blu ray (recordable) disc for write once applications, adapted to store information at high density and simultaneously ensuring low jitter, betterment of technical performance and cost effectiveness. It is a further object of the present invention to provide a method for manufacturing high-density optical recording, write once blu ray(recordable) low to high discs, which includes phase change recording layer as a primary component, on which data can be recorded using a laser beam, having a wavelength of 405 nm.
It is a further object of the present invention to improve the overall performance of the disc, by ensuring better read stability, modulation and asymmetry. It is yet another object of the present invention to provide an optical recording medium having uniform recorded marks including lowest size 2T marks, which ensures low jitter,betterment of technical performance and cost effectiveness. Yet another object of the present invention is to develop inorganic L2H media using laser wavelength of 405 nm and having the normalized push-pull signal, meeting the book specifications.
How the aforesaid objects are achieved and the other aspects of the invention
*
will be clear from the following description, which is purely for the sake of understanding and not by way of any sort of limitation.

SUMMARY OF THE INVENTION
Accordingly, the present invention provides a low to high optical recording medium for write once applications , including a substrate, a reflective layer, dielectric layers , phase change material and a cover layer wherein said phase change material is a metal-ceramic combination comprising 80-99 at% (50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 80ZnS-20SiO2 ceramic, whereby said medium, gets adapted to store information at high density, simultaneously ensuring low jitter, betterment of technical performance and cost effectiveness . The present invention also provides a low to high optical recording medium for write once applications comprising :
(a)1.1 mm pre-grooved substrate
(b) 100-200 nm reflective layer
(c ) 5-20 nm first dielectric layer
(d) 40-80 nm second dielectric layer
(e) 6-18nm phase-change material sputtered from a metal-ceramic target comprising of80-99 at% (50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 80ZnS-20SiO2 ceramic to achieve smaller mark formation in high density optical recording and
(f) 100 D 5.0 micron a hard coated polycarbonate cover layer
In accordance with preferred embodiments :
-the substrate is made of polycarbonate, the dielectric layers are a mixture of ZnS and Si02) the reflective layer is a metallic layer, such as alloys of AI or Ag and the protective cover layer is made up of 100 micro meter thick polycarbonate film coated with pressure sensitive adhesive (PSA) on the bonding side and hard coating on the laser exposure side.
-which enables uniform recording of marks including lowest size 2T marks, which ensures low jitter,betterment of technical performance and cost effectiveness.

-said medium is a blu ray (recordable ) low to high disc.
-includes phase change recording layer as a primary component, on which data can be recorded using a laser beam, having a wavelength of 405 nm. The present invention also provides a method of manufacturing low to high optical recording medium for write once applications including forming a substrate, applying a reflective layer, dielectric layers and phase-change recording layer on said substrate and also forming a protective coating layer thereon wherein the said method comprises the step of changing the atomic structure of antimony-tin-indium alloy, doped with Zinc, Sulphur, Silicon, Oxygen recording phase- change material from amorphous state to crystalline state such tttat the phase change recording layer comprises a metal-ceramic combination having 80-99 at% (50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 8OZnS-2OSiO2 ceramic, whereby said medium, gets adapted to store information at high density, simultaneously ensuring low jitter, betterment of technical performance and cost effectiveness .
In accordance with preferred embodiments of the method of the present invention :
- changing the atomic structure of antimony-tin-indium alloy, doped with Zinc, Sulphur, Silicon, Oxygen recording phase- change material from amorphous state to crystalline state, is facilitated by applying blue laser of 405 nm wavelength.
-the thickness of the phase-change recording layer and the dielectric layers are selected, so as to optimize the recording performance and the recording contrast.
-said medium is a blu ray (recordable) low to high disc. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The nature and scope of the present invention will be better understood from the accompanying drawings of some preferred embodiments of the present invention , which are for the sake of understanding only and not by way of any sort of

limitation. In the accompanying drawings.
Fig1 is a schematic representation, in cross sectional view, of write once low to
high optical recording element that can be made in accordance with a preferred
embodiment of the present invention wherein the read /write laser beam is
illuminated from the front surface of the element
Fig 2 illustrates the signal to noise ratio for the 8T marks at 1X speed
Fig 3 illustrates the signal to noise ratio for the 8T marks at 2X speed
Fig.4 illustrates the signal to noise ratio for the 2T marks at 1X speed
Fig.5 illustrates the signal to noise ratio for the 2T marks at 2X speed
Fig 6 illustrates the eye pattern for the random marks at 1X speed.
Fig 7 illustrates the eye pattern for the random marks at 2X speed
DETAILED DESCRIPTION OF THE INVENTION
The following describes some preferred embodiments of the present invention,
which are purely for the sake of understanding and not by way of any sort of
limitation.
As stated before, the present invention aims at storing information in low to high
optical recording medium at high density for write once applications and
simultaneously, ensuring low jitter,betterment of technical performance and cost
effectiveness.
To achieve the aforementioned objects the present invention provides a phase-
change recording material of metal-ceramic combination consisting of 80-99 at%
(50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 80ZnS-20SiO2 ceramic
enabling 2T mark formation and lower jitter values.
The present invention also provides a write-once-read-many times (WORM) optical recording media for high density L2H recording comprising
(a) 1.1 mm pre-grooved substrate
(b) 100-200 nm reflective layer

(c) 5-20 nm first dielectric layer (d)40-80 nm second dielectric layer
(e) 6-18nm phase-change material sputtered from a metal-ceramic target comprising of80-99 at% (50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 80ZnS-20SiO2 ceramic to achieve smaller mark formation in high density optical recording and
(f) 100 D 5.0 micron a hard coated polycarbonate cover layer
The present invention also includes a process for preparing a write-once-read-many times (WORM) optical recording media characterized by the step of changing the atomic structure of antimony-tin-indium alloy, doped with Zinc, Sulphur, Silicon, Oxygen recording phase- change material from amorphous state to crystalline state using blue laser of 405 nm wavelength. The said phase-change material in combination with dielectric layer, and reflectance layer is used to meet the requirements of high-density recording. The doped material's particle size is selected to in such a way that it will meet the end requirements of low jitter and better 2T mark formation.
Thus according to the present invention the same is directed to an improved BDRL2H (Blu Ray Recordable Low to High) medium with better jitter, modulation and write power meeting the book specification by way of incorporated suitable particle size of dopants and method of adding during phase change target development.
The target making process ensures segregation of the ceramic phase at the grain boundaries of the metallic phase, which enables better 2T mark formation and improves the overall performance of the media.
Fig 1: is an illustration of a preferred embodiment of the WORM low to high optical recording element, made in accordance with the present invention It. comprises a substrate 1, a reflective layer 2, a dielectric layer 3, a phase-change

recording layer 4, a second dielectric layer 5 and a hard coated protective cover layer 6. The substrate 1 is made of polycarbonate and a guide groove on the surface where the reflective layer, dielectric layers and phase-change recording layer are applied. The dielectric layers 3,5 are a mixture of ZnS and Si02. The reflective layer 2 can be a metallic layer, such as alloys of Al or Ag. The protective cover layer 6 is made up of 100 micro meter thick polycarbonate film coated with Pressure Sensitive Adhesive (PSA) on the bonding side and hard coating on the laser exposure side. The thickness of the phase-change recording layer 4 and the dielectric layers 3 and 5 are selected to optimize the recording performance and the recording contrast.
Fig 2 and 3 illustrate the signal to noise ratio for the 8T marks are quite high and the I8 single tone jitter is very good both in 1X and 2X speed. This was achieved by selecting the suitable particle size of the dopants in the phase change materials and adopting appropriate write strategy. Fig:4 and 5 illustrate the signal to noise ratio for the 2T marks are quite high and the I2 single tone jitter is good both in !X and 2X speed and further improvement is possible with suitable composition and particle size of the phase change materials.
Fig:6 and 7 illustrate the eye pattern for the random marks for 1X and 2X The various results, as manifested in the aforesaid figures, unequivocally establish that, on application of the phase change recording material of metal-ceramic combination consisting of 80-99 at% (50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 80ZnS-20SiO2 ceramic , it is possible to design a low to high optical recording medium for write once applications , adapted to store information at high density, simultaneously ensuring low jitter, betterment of technical performance and cost effectiveness . This technical advancement as well as economic significance was hitherto, not achieved in the art , which makes the present invention unique in all respects.

The present invention has been described with reference to some drawings and preferred embodiments, which are purely for the sake of understanding and not by way of any limitation and the present invention embraces all legitimate developments within the scope of what has been described before and claimed in the claims hereinafter.

WE CLAIM
1.A low to high optical recording medium for write once applications , including a substrate, a reflective layer, dielectric layers , phase change material and a cover layer wherein said phase change material is a metal-ceramic combination comprising 80-99 at% (50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 8OZnS-20SiO2 ceramic, whereby said medium, gets adapted to store information at high density, simultaneously ensuring low jitter, betterment of technical performance and cost effectiveness .
2. A low to high optical recording medium for write once applications comprising :
(a)1.1 mm pre-grooved substrate
(b) 100-200 nm reflective layer
(c) 5-20 nm first dielectric layer
(d) 40-80 nm second dielectric layer
(e) 6-18nm phase-change material sputtered from a metal-ceramic target comprising of80-99 at% (50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 8OZnS-2OSiO2 ceramic to achieve smaller mark formation in high density optical recording and
(f) 100 □ 5.0 micron a hard coated polycarbonate cover layer

3. The low to high optical recording medium for write once applications as claimed in any preceding claim wherein the substrate is made of polycarbonate,the dielectric layers are a mixture of ZnS and Si02) the reflective layer is a metallic layer, such as alloys of Al or Ag and the protective cover layer is made up of 100 micro meter thick polycarbonate film coated with pressure sensitive adhesive (PSA) on the bonding side and hard coating on the laser exposure side.
4. The low to high optical recording medium for write once applications as claimed in any preceding claim which enables uniform recording of marks including lowest size 2T marks, which ensures low jitter,betterment of technical performance and cost effectiveness.

5.The low to high optical recording medium for write once applications wherein said medium is a blu ray (recordable ) low to high disc.
6.The low to high optical recording medium for write once applications as claimed in claim 5 which includes phase change recording layer as a primary component, on which data can be recorded using a laser beam, having a wavelength of 405 nm.
7.A method of manufacturing low to high optical recording medium for write once applications including forming a substrate, applying a reflective layer, dielectric layers and phase-change recording layer on said substrate and also forming a protective coating layer thereon wherein the said method comprises the step of changing the atomic structure of antimony-tin-indium alloy, doped with Zinc, Sulphur, Silicon, Oxygen recording phase- change material from amorphous state to crystalline state, such that the phase change recording layer comprises a metal-ceramic combination having 80-99 at% (50-70)Sb-(3-15)ln-(15-30)Sn alloy and 2-20 at% 80ZnS-20SiO2 ceramic, whereby said medium, gets adapted to store information at high density, simultaneously ensuring low jitter, betterment of technical performance and cost effectiveness .
8.The method of manufacturing low to high optical recording medium for write once applications as claimed in any preceding claim, wherein changing the atomic structure of antimony-tin-indium alloy, doped with Zinc, Sulphur, Silicon, Oxygen recording phase- change material from amorphous state to crystalline state, is facilitated by applying blue laser of 405 nm wavelength.
9.The method of manufacturing low to high optical recording medium for write once applications as claimed in any preceding claim wherein the thickness of the phase-change recording layer and the dielectric layers are selected, so as to optimize the recording performance and the recording contrast.

10. The method of manufacturing low to high optical recording medium for write once applications as claimed in any preceding claim wherein said medium is a blu ray (recordable) low to high disc.