WO2006036123A1

WO2006036123A1 - A recording medium

Info

Publication number: WO2006036123A1
Application number: PCT/SG2004/000315
Authority: WO
Inventors: Xiang Hu; Luping Shi; Xiangshui Miao
Original assignee: Agency For Science, Technology And Research
Priority date: 2004-09-27
Filing date: 2004-09-27
Publication date: 2006-04-06
Also published as: TW200611269A

Abstract

A recording medium utilising metallic glass is described according to embodiments of the invention. The state of the metallic glass is variable between a low optical density state and a high optical density state when irradiated with a laser beam having a wavelength of not more than 800 nm. This optical property variability enables the recording medium to be used preferably with conventional read-write laser beam systems. Additionally, the metallic glass recording layer enables the recording medium to achieve high data recording density, high data transfer rate and improved long-duration storage reliability.

Description

A RECORDING MEDIUM

Field Of Invention

The present invention relates generally to a recording medium. In particular, the invention relates to a recording medium having a metallic glass recording layer for providing a recordable optical media having high-density, high data transfer rate and improved long-duration storage reliability.

Background Various optical recording media, for example compact disk (CD) and digital versatile disk (DVD), have been widely used as recording media for recording digital data, audio and video data, and high definition images and movies. These optical recording media are typically categorized into read-only media, for example CD-ROM, DVD- ROM and the like non-writeable and non-rewriteable media, recordable optical media, for example CD-R, DVD±R and the like writeable but non-rewriteable data media, and rewriteable optical media, for example CD-RW, DVD-RAM, DVD±RW and the like rewriteable data media.

It is well known that a ROM-type optical media uses pits (or prepits) formed in the substrate for recording data, while a rewriteable optical media uses changes in an optical characteristic caused by phase change of phase change materials.

A variety of methods and devices exist for optical recording. In a first example, laser ablative recording is achieved when pulsed laser beam is used for creating physical pits in a recording layer. This method requires an air-sandwiched structure to maintain the flatness on the surface of a recording disk during pit formation therein, which results in production cost elevation. In addition, it is difficult to apply a contact protection layer to the medium used for laser ablative recording. In a second example, a laser beam is used to cause either chemical interaction between several layers or fusion of the several layers into a unitary layer, which requires the use of a high power laser. In a third example, organic dyes such as cyanine dyes, phthalocyanine dyes, and azo dyes are used in recordable optical media by utilizing changes in optical characteristics caused by chemical changes to the organic dye which is usually accompanied by physical deformation. However, since organic dyes degrade due to self-sensitization and easily undergoes photo- deterioration when exposed to sunlight, it is difficult to sustain long-duration storage reliability for media wherein an organic dye is used as a material for the recording layer.

Additionally, although organic dyes have been successfully used in CD-R disks, they suffer from strong wavelength dependency. For example, a DVD system using a laser diode of 650 nm is not able to write onto a CD-R disks which is designed to work at a wavelength of 780 nm.^' Conventionally, this problem is circumvented by use of an optical system in which information is independently recorded and reproduced by two separate and characteristically different laser beams, for example, a laser beam with a wavelength of 780 nm and a laser beam with a wavelength of 650 nm. However, this naturally leads to increased production cost.

In a third example, phase change-based recording is used. Unlike conventional rewriteable phase change media, a recording medium is designed for recording data via laser crystallization of an amorphous phase material. These materials are designed such that it is practically impossible to reverse an already laser-crystallized state of a phase change material back into an amorphous state. Example for such materials, or more specifically alloys, are described in United States Patent 3,971874 which describes a phase change recording layer of TeOx-Te composition (where 0<x<2), and United States Patent 4,774,170 which describes a phase change recording layer made from Sb-Sn-Zn alloys. However, these phase change materials and alloys produces a phase change recording layer that suffer from small optical constants and low reflectance, and therefore requires a complicated multi-layered structure. The slow crystallization speed of these materials also limits application in high speed recording.

Hence, this clearly affirms a need for an improved recordable optical media with high data recording density, high data transfer rate and improved long-duration storage reliability.

Summary

Described hereinafter is a recordable optical medium with metallic glass alloy in the recording layer. The metallic glass material allows usage of a laser beam with a wavelength between 300 and 800 nm and is capable of meeting the requirements of high recording capacity and high data transfer rate with excellent readout stability.

Therefore, in accordance with a first aspect of the invention, there is disclosed a recording medium comprising: a recording layer comprising metallic glass, the recording layer having a first face and a second face outwardly opposing the first face, at least a portion of the recording layer having an optical density being variable for optical recording of data thereby, wherein the metallic glass being formed from at least two metallic elements, has a disordered structure when cooled and a crystalline structure when heated.

In accordance with a second aspect of the invention, there is disclosed a recording medium comprising: a recording layer comprising metallic glass and having a first face and a second face outwardly opposing the first face, the recording layer having a plurality of recording locations, each of the plurality of recording locations having an optical density being variable through at least two states for indicating a data value, the metallic glass being formed from at least two metalloid elements, has a disordered structure when cooled and a crystalline structure when heated; and a substrate stacked adjacent to the recording layer for structurally supporting the recording layer, wherein a write laser beam is directable towards one of the plurality of recording locations of the recording layer for varying the optical density thereof through the at least two states, and wherein a processed beam having a beam property is processed from a read laser beam directed towards one of the plurality of recording location of the recording layers, the laser beam being processed by the corresponding one of the plurality of recording locations with one of the at least two states thereof determining the beam property, the beam property of the processed beam being indicative of the data value of the corresponding one of the plurality of recording locations.

Brief Description Of The Drawings

Embodiments of the invention are described hereinafter with reference to the following drawings, in which:

FIG. 1 shows a partial front sectional elevation of a recording medium having a substrate stacked adjacent to a recording layer according to a first embodiment of the invention;

FIG. 2 shows a ternary composition diagram of palladium (Pd), phosphorous (P) and one of nickel (Ni) and copper (Cu) for the recording layer of the recording medium of FIG. 1 ;

FIG. 3 shows a partial front sectional view of the recording medium of FIG. 1 with a reflective layer stacked adjacent to the recording layer according to a second embodiment of the invention;

FIG. 4 shows a partial front sectional view of the recording medium of FIG. 1 with a dielectric layer stacked adjacent to the recording layer according to a third embodiment of the invention;

FIG. 5 shows a partial front sectional view of the recording medium of FIG. 3 with the recording layer interfacing a first dielectric layer and a second dielectric layer according to a fourth embodiment of the invention; FIG. 6 shows a partial front sectional view of the recording medium of FIG. 1 with the substrate being positionally replaced by a cover layer and the recording layer interfacing the cover layer and the substrate according to a fifth embodiment of the invention;

FIG. 7 shows a partial front sectional view of the recording medium of FIG. 4 with the substrate being positionally replaced by a cover layer and the dielectric layer interfacing the cover layer and the recording layer according to a sixth embodiment of the invention;

FIG. 8 shows a partial front sectional view of the recording medium of FIG. 3 with the substrate being positionally replaced by a cover layer and substrate being stacked adjacent to the reflective layer according to a seventh embodiment of the invention;

FIG. 9 shows a partial front sectional view of the recording medium of FIG. 5 with the substrate being positionally replaced by a cover layer and the substrate being stacked adjacent to the reflective layer according to a eighth embodiment of the invention;

FIG. 10 shows the carrier-to-noise ratio (CNR) and peak-to-peak amplitude performance of the recording medium of FIG. 4 in a first example; and

FIG. 11 shows the carrier-to-noise ratio (CNR) and peak-to-peak amplitude performance of the recording medium of FIG. 7 in a second example.

Detailed Description

A recording medium is described hereinafter for addressing the foregoing problems.

A first embodiment of the invention, a recording medium 20, is described with reference to FIG. 1, which shows a partial front sectional elevation of the recording medium 20. The recording medium comprises a recording layer 22 and a substrate 24 stacked adjacent thereto and for structurally supporting the recording layer 22. The recording layer 22 has a first face 26 and a second face 28 outwardly opposing the first face 26. Additionally, the recording layer 22 has a plurality of recording locations 30 (shown only in FIG. 1) with each recording location 30 having an optical density being variable between two states, a substantially crystalline state and a substantially amorphous state, for indicating a data value.-

Preferably, the substrate 24 has a plurality of grooves 40 (shown only in FIG. 1) formed therein for forming and defining at least one land segment 42 (also shown only in FIG. 1) therebetween. Each recording location 30 is adjacent to and opposes either or both of one land segment 42 and one groove 40. The plurality of grooves 40 is for tracking and addressing the recording locations 30 of the recording layer 22. The substrate 24 and the plurality of grooves 40 therein are formed preferably by one of injection molding and extrusion molding f a resin, for example, polycarbonate.

The substrate 24 is preferably made from one of polycarbonate, polymethyl methacrylate (PMMA), amorphous polyolefϊn, carbonate-type resin, ultraviolet curable resin, ceramic, and glass.

Preferably, the recording layer 22 comprises metallic glass. Generally, metallic glass is formed from at least two metallic elements, has a disordered structure when cooled and a crystalline structure when heated. Therefore, metallic glass is known in the art as a material which contains no long range structural order but can contain short range structure and chemical ordering. Preferably, the recording layer 22 further comprises at least palladium (Pd) and at least one of Pt, Pr, Mn, Fe, Al, Hf, Zr, Ti, Cu, Ir, Nd, Ag, Ge, Ga, Sn, Sb, Te, Bi, Pb, In, Zn, Se, As, B, C, P, and Si. The recording layer 22 has a thickness within one of a range of 5 to 400 nm and a range of 15 to 200nm.

Alternatively, the recording layer 22 comprises a Pd-M-X alloy, wherein M comprises at least one of Pt, Ag, Cu, Ni, Pr, La, Hf, Ir, Ag, and X comprises at least one of B, Si, C, N, and O. Further alternatively, the material composition of the recording layer 22 is graphically defined as being within at least one of a trapezoidal boundary 44 and a rectilinear boundary 46 in a ternary composition diagram 48 of Pd, phosphorous (P) and one of nickel (Ni) and copper (Cu). The composition diagram 48 is shown in FIG. 2.

In the composition diagram 48 of FIG. 2, the trapezoidal boundary 44 is defined by vertices A, B, C, and D while the rectilinear boundary 46 is defined by vertices E, F, G, and H.

A write laser beam 50 is directable towards one recording location 30 of the recording layer 22 for varying the optical reflectivity 32 from the amorphous state to the crystalline state to thereby record data thereonto.

The recorded data is retrievable by directing a read laser beam 52 towards the one recording location 30 and obtaining a processed beam 54 therefrom. The processed beam 54 has a beam property and is processed by the optical density of the one recording location 30. The optical density determines the optical reflectivity of the one of the recording location 30 to thereby vary the beam property, for example magnitude, of the processed beam 54 with the beam property being indicative of the recorded data.

Each of the write laser beam 50 and the read laser beam 52 has a wavelength that does not exceed 800nm and is directed initially through the substrate 24 and subsequently onto the recording layer 22.

The Pd based recording layer 22 with the above described composition comprising phosphorous and one of Ni and Cu has a crystallization temperature of substantially 350" C, which is much higher than the 12O⁰ C crystallization temperature of conventional chalcogenide alloys, for example, Ge₂Sb₂Te_S. The Pd-based material composition of the recording layer 22 provides the recording layer 22 and recording medium 20 with high thermal stability and consequently high readout stability. Furthermore, the recording layer 22 enables the recording medium 20 to have good resistance to light and corrosion. Both Ni and Cu can alternatively co-exist in the composition of the recoding layer 22.

A second embodiment of the invention, a recording medium 60 as shown in FIG. 3, comprises two main elements: a recording layer 22 and a substrate 24. The descriptions in relation to the structural configurations of and positional relationships between the recording layer 22, the substrate 24 and the plurality of recording locations 30 corresponding with the recording layer 22 with reference to the first embodiment of FIG. 1 and the material composition of the recording layer 22 in accordance with the composition diagram of FIG. 2 are incorporated herein.

The recording medium 60 further comprises a reflective layer 62 stacked adjacent to the recording layer 22. The substrate 24, recording layer 22 and the reflective layer 62 are arranged such that the second face 28 of the recording layer 22 opposes the reflective layer 62 and the first face 26 of the recording layer 22 opposes the substrate 24. The reflective layer 62 is for dissipating excessive accumulation of heat generated by at least one of the write laser beam 50 and the read laser beam 52 during application thereof to the recording layer 22.

Preferably, the reflective layer 62 is made from at least one of Au, Al, Ag, Ti, Cr, Cu, Pd, W, and Pt, and has a thickness within one of a range of 20 to 200 nm and a range of 50 to 150 nm.

A third embodiment of the invention, a recording medium 64 as shown in FIG. 4, comprises two main elements: a recording layer 22 and a substrate 24. The descriptions in relation to the structural configurations of and positional relationships between the recording layer 22, the substrate 24 and the plurality of recording locations 30 corresponding with the recording layer 22 with reference to the first embodiment of FIG. 1 and the material composition of the recording layer 22 in accordance with the composition diagram of FIG. 2 are incorporated herein. The recording medium 64 further comprises a dielectric layer 66. The dielectric layer

66 is stacked adjacent to the recording layer 22 with the dielectric layer 66 interfacing the substrate 24 and the recording layer 22.

The dielectric layer 66 is made from at least one of oxide, nitride, chalcogenide, fluoride, and a carbide of a metal. Preferably, the dielectric layer 66 is made from at least one of SiO₂, SiO, Al₂O₃, GeO₂, In₂O₃, TeO₂, TiO₂, Ta₂O₅, MoO₃, WO₃, Si₃N₄, AlN, BN, TiN, ZnS, CdS, CdSe, ZnTe, AgF, PdF₂, and SiC.

The dielectric layer 66 has a refractive index of at least 1.5 and is for enhancing reflectance, modulation and recording sensitivity of the recording medium 64. The dielectric layer 66 preferably has a thickness within a range of 10 to 200nm.

A fourth embodiment of the invention, a recording medium 70 as shown in FIG. 5, comprises three main elements: a recording layer 22, a substrate 24 and a reflective layer 62. The descriptions in relation to the structural configurations of and positional relationships between the recording layer 22, the substrate 24, the reflective layer 62 and the plurality of recording locations 30 corresponding with the recording layer 22 with reference to the second embodiment of FIG. 3 and the material composition of the recording layer 22 in accordance with the composition diagram of FIG. 2 are incorporated herein.

The recording medium 70 further comprises a first dielectric layer 72 and a second dielectric layer 74. The first dielectric layer 72 is stacked adjacent to the recording layer 22 with the first dielectric layer 72 interfacing the substrate 24 and the recording layer 22. The second dielectric layer 74 is also stacked adjacent to the recording layer 22 with the second dielectric layer 74 interfacing the recording layer 22 and the reflective layer 62. Each of the first dielectric layer 72 and the second dielectric layer 74 is made from at least one of oxide, nitride, chalcogenide, fluoride and a carbide of a metal. Preferably, each of the first dielectric layer 72 and the second dielectric layer 74 is made from at least one of SiO₂, SiO, Al₂O₃, GeO₂, In₂O₃, TeO₂, TiO₂, Ta₂O₅, MoO₃, WO₃, Si₃N₄, AlN, BN, TiN, ZnS, CdS, CdSe, ZnTe, AgF, PdF₂, and SiC.

Each of the first dielectric layer 72 and the second dielectric layer 74 has a refractive index of at least 1.5 and is for enhancing reflectance, modulation and recording sensitivity of the recording medium 70. The first dielectric layer 72 and the second dielectric layer 74 are preferably made from the same material. However, the first dielectric layer 72 and the second dielectric layer 74 are alternatively made from different materials. Specifically, the second dielectric layer 74 is further for conditioning the temperature of the recording medium 70 and for protecting the substrate 24 and the recording layer 22 from heat damage.

Alternatively in the fourth embodiment of the invention, only one of the first dielectric layer 72 and the second dielectric layer 74 exist in the recording medium 70 of FIG. 5. For example, the first dielectric layer 72 is stacked adjacent to the recording layer 22 with the recording layer 22 interfacing the first dielectric layer 72 and the reflective layer 62. Again for example, the second dielectric layer 74 is stacked adjacent to the recording layer 22 with the recording layer 22 interfacing the second dielectric layer 74 and the substrate 24.

A fifth embodiment of the invention, a recording medium 80 as shown in FIG. 6, comprises two main elements: a recording layer 22 and a substrate 24. The descriptions in relation to the structural configurations of and positional relationships between the recording layer 22, the substrate 24 and the plurality of recording locations 30 corresponding with the recording layer 22 with reference to the first embodiment of FIG. 1 and the material composition of the recording layer 22 in accordance with the composition diagram of FIG. 2 are incorporated herein The recording medium 80 further comprises a cover layer 82 stacked adjacent to the recording layer 22. In the recording medium 80 of FIG. 6, the cover layer 82 opposes the first face 26 of the recording layer 22, the substrate 24 opposes the second face 28 of the recording layer 22 and the recording layer 22 interfaces the cover layer 82 and the substrate 24.

Preferably, the cover layer 82 is made from at least one of polycarbonate, cellulose triacetate and polydicyclopendadiene, (methyl)methacrylate and

(methyl)propylacrylate, and has a thickness within one of a range of 10 to 400 um and a range of 15 to 150 um.

The cover layer 82 is preferably formed by one of solvent casting, polymerization- casting, spin coating, die coating and pressure-based lamination, and has a surface roughness of preferably 2 um. The cover layer 82 preferably has a transmittance of at least 80%.

In recording medium 80 of FIG. 6, each of the write laser beam 50 and the read laser beam 52 has a wavelength that does not exceed 500nm and is directed initially through the cover layer 82 and subsequently onto the recording layer 22.

A sixth embodiment of the invention, a recording medium 84 as shown in FIG. 7, comprises two main elements: a recording layer 22, a substrate 24 and a dielectric layer 66. The descriptions in relation to the structural configurations of and positional relationships between the recording layer 22, the substrate 24 and the plurality of recording locations 30 corresponding with the recording layer 22 with reference to the third embodiment of FIG. 4 and the material composition of the recording layer 22 in accordance with the composition diagram of FIG. 2 are incorporated herein

The recording medium 84 further comprises a cover layer 86 stacked adjacent to the dielectric layer 66. In the recording medium 84 of FIG. 7, the cover layer 86 opposes the first face 26 of the recording layer 22, the substrate 24 opposes the second face 28 of the recording layer 22 and the dielectric layer 66 interfaces the cover layer 86 and the recording layer 22.

Preferably, the cover layer 86 is made from at least one of polycarbonate, cellulose triacetate and polydicyclopendadiene, (methyl)methacrylate and

The cover layer 86 is preferably formed by one of solvent casting, polymerization- casting, spin coating, die coating and pressure-based lamination, and has a surface roughness of preferably 2 um. The cover layer 86 preferably has a transmittance of at least 80%.

In recording medium 84 of FIG. 7, each of the write laser beam 50 and the read laser beam 52 has a wavelength that does not exceed 500nm and is directed initially through the cover layer 86 and subsequently onto the recording layer 22.

• A seventh embodiment of the invention, a recording medium 90 as shown in FIG. 8,' comprises three main elements: a recording layer 22, a substrate 24 and a reflective layer 62. The descriptions in relation to the structural configurations of and positional relationships between the recording layer 22, the substrate 24, the reflective layer 62 and the plurality of recording locations 30 corresponding with the recording layer 22 with reference to the second embodiment of FIG. 3 and the material composition of the recording layer 22 in accordance with the composition diagram of FIG. 2 are incorporated herein.

In the seventh embodiment of the invention, the substrate 24 of FIG. 3 is positionally replaced with a cover layer 92 in the recording medium 90. Instead, the substrate 24 is stacked adjacent to the recording layer 22 with the reflective layer 62 interfacing the recording layer 22 and the cover layer 92. Positionally, the cover layer opposes the first face 26 of the recording layer 22. Preferably, the cover layer 92 is made from at least one of polycarbonate, cellulose triacetate and polydicyclopendadiene, (methyl)methacrylate and

In recording medium 90 of FIG. 8, each of the write laser beam 50 and the read laser beam 52 has a wavelength that does not exceed 500nm and is directed initially through the cover layer 92 and subsequently onto the recording layer 22.

A eighth embodiment of the invention, a recording medium 100 as shown in FIG. 9, comprises five main elements: a recording layer 22, a substrate 24, a reflective layer 62, a first dielectric layer 72 and a second dielectric layer 74. The descriptions in relation to the structural configurations of and positional relationships between the recording layer 22, the substrate 24, the first dielectric layer 72, the second dielectric layer 74, the reflective layer 62 and the plurality of recording locations 30 corresponding with the recording layer 22 with reference to the fourth embodiment of FIG. 5 and the material composition of the recording layer 22 in accordance with the composition diagram of FIG. 2 are incorporated herein.

In the eighth embodiment of the invention, the substrate 24 of FIG. 5 is positionally replaced with a cover layer 102 in the recording medium 100. Instead, the substrate 24 is stacked adjacent to the recording layer 22 with the reflective layer 62 interfacing the substrate 24 and the second dielectric layer 74, and the first dielectric layer 72 interfacing the recording layer 22 and the cover layer 102. Positionally, the first face 26 of the recording layer 22 opposes the cover layer 102.

Preferably, the cover layer 102 is made from at least one of polycarbonate, cellulose triacetate and polydicyclopendadiene, (methyl)methacrylate and

(methyl)propylacrylate, and has a thickness within one of a range of 10 to 400 um and a range of 15 to 150 um. In recording medium 100 of FIG. 9, each of the write laser beam 50 and the read laser beam 52 has a wavelength that does not exceed 500nm and is directed initially through the cover layer 102 and subsequently onto the recording layer 22.

The different layers, excluding the substrate, forming the recording medium in any of the abovedescribed eight embodiments are formed preferably by one or a combination of sputtering, and evaporative and chemical vapor depositions.

The following examples demonstrate certain aspects of the invention, the recording medium, and should not be taken as limiting the scope thereof.

In a first example, a first sample disk was prepared with in accordance with the structural configuration of the recording medium 64 of Fig. 4. The substrate 22 is made from polycarbonate and has a thickness of 0.6 mm, a diameter of 120 mm and a track pitch was 0.74 μm.

The dielectric layer 66 has a thickness of 120 nm and contains a mixture of ZnS (80at%) and SiO2 (20at%). The recording layer 22 contains Pd as a primary component and has a thickness of 50 nm. Both the recording layer 22 and the dielectric layer were sequentially formed on the polycarbonate substrate using conventional sputtering methods. The dielectric layer 66 was deposited by RF magnetron sputtering while the recording layer 22 was prepared by DC magnetron sputtering in an argon atmosphere at a pressure of 0.5 Pa. The substrate 24 with the dielectric layer 66 and the recording layer 22 formed thereon was subsequently bonded to a dummy substrate with UV resin using a spin coating method. Compared with blue laser recordable optical media that uses a dye as a recording material and need a time intensive spin-coating and drying treatment as described in United States Patent Applications US 2003/0203147 Al and US 2003/0082331 Al, fabrication duration is substantially shortened for the recording medium 64 due to the formation of all the component layers thereof using only sputtering methods. Recording performance of the recording medium 64 was evaluated using a dynamic tester (ShibaSoku DVD TESTER LM330A) with a laser diode of 650 nm in wavelength and a numerical aperture of 0.60. Carrier to noise ratio (CNR) measurement was carried out to record a single signal of 2.9MHz at a rotation velocity of 6.3 m/s. The pulse waveform used for recording was a pulse train that was modulated between a peak power of 8 mW and a bias power of 1 mW with the channel clock duration being 17.125 ns. Under these conditions, recording of a 1OT signal train was performed in an unrecorded track only once and a reading power of 1 mW was used to reproduce the signal. CNR was measured using a spectrum analyzer. A CNR value of 45 dB was obtained for the recording medium 64 in the first example. This signal was read using a reading power of 1 mW for 1 hour. Variations in the peak-to-peak value and CNR value of the signal were observed as shown in Fig. 10.

In a second example, a second sample disk was prepared with in accordance with the structural configuration of the recording medium 84 of Fig. 7. The substrate 22 is made from polycarbonate and has a thickness of 1.1 mm, a diameter of 120 mm and a track pitch was 0.32 μm with a depth of 26nm.

The dielectric layer 66 has a thickness of 120 nm and contains a mixture of ZnS (80at%) and SiO2 (20at%). The recording layer 22 contains Pd as a primary component and has a thickness of 50 nm. Both the recording layer 22 and the dielectric layer were sequentially formed on the polycarbonate substrate using conventional sputtering methods. The dielectric layer 66 was deposited by RF magnetron sputtering while the recording layer 22 was prepared by DC magnetron sputtering in an argon atmosphere at a pressure of 0.5 Pa. The cover layer 86 is subsequently formed by a polycarbonate sheet of 75 μm bonded to the substrate 22, recording layer 22, and dielectric layer 66 structure with UV resin using a spin coating method. Recording performance was evaluated using a dynamic tester (PULSTEC Blu-ray

Disk Tester DDU-1000) with a laser diode having a 405 nm wavelength and a numerical aperture of 0.85. The pulse waveform used for performing data recording was a pulse train modulated between a peak power of 4.3 mW and a base power of 1.3 mW with the channel clock duration being 15.15 ns. Under these conditions, recording of a single signal of 4.12 MHz was performed at a disk rotational velocity of 5.28 m/s in an unrecorded track only once. A reading power of 0.3 mW was used to reproduce the signal. A CNR value of 50 dB was then obtained using a spectrum analyzer. This signal was read using a reading power of 0.3 mW for a duration of 1 hour. Again, only a minor variation in the peak-to-peak value and CNR value of the signal was observed, as shown in Fig. 10.

In the foregoing manner, a recording medium is described according to eight embodiments of the invention for addressing the foregoing disadvantages of conventional recording mediums. Although only eight embodiments of the invention are disclosed, it will be apparent to one skilled in the art in view of this disclosure that numerous changes and/or modification can be made without departing from the scope and spirit of the invention.

Claims

1. A recording medium comprising: a recording layer comprising metallic glass, the recording layer having a first face and a second face outwardly opposing the first face, at least a portion of the recording layer having an optical density being variable for optical recording of data thereby, wherein the metallic glass being formed from at least two metallic elements, has a disordered structure when cooled and a crystalline structure when heated.

2. The recording medium as in claim 1, further comprising metallic glass containing: at least palladium (Pd), the recording layer comprising a plurality of recording locations having the optical density, the optical density of each of the plurality of recording locations being variable between two states for indicating a data value.

3. The recording medium as in any of claims 1 and 2, a write laser beam being directable towards one of the plurality of recording locations of the recording layer for varying the optical density thereof from one to the other of the two states, and a processed beam having a beam property being processable from a read laser beam directed towards one of the plurality of recording locations of the recording layers, the read laser beam being processed by the corresponding one of the plurality of recording locations with one of the at least two states thereof determining the beam property, the beam property of the processed beam being indicative of the data value of the corresponding one of the plurality of recording locations, wherein each of the read laser beam and the write laser beam having a wavelength with a range of 400nm and 800nm, and the write laser beam having a magnitude to one of the two states of each of the plurality of recording locations.

4. The recording medium as in any of claims 2 and 3, the two states of each of the plurality of recording locations being a substantially crystalline state and a substantially amorphous state, wherein each of the two states of each of the plurality of recording locations corresponds with the optical reflectivity of the corresponding one of the plurality of recording locations.

5. The recording medium as in any of claims 1 to 4, the recording layer further comprising metallic glass containing at least one of Pt, Pr, Mn, Fe, Al, Hf, Zr, Ti, Cu, Ir, Nd, Ag, Ge, Ga, Sn, Sb, Te, Bi, Pb, In, Zn, Se, As, B, C, P, O and Si.

6. The recording medium as in any of claims 1 to 4, the recording layer further comprising metallic glass having a composition within at least one of a trapezoidal boundary and a rectilinear boundary in a ternary composition diagram of Pd, phosphorous (P) and one of nickel (Ni) and copper (Cu), the composition diagram being:

P

wherein the trapezoidal boundary is defined by vertices A, B, C and D, and the rectilinear boundary is defined by vertices E, F, G and H therein.

7. The recording medium as in claim 1, the recording layer further comprising a

Pd-M-X alloy, wherein M comprises at least one of Pt, Ag, Pr, La, Hf, Ir, and X comprises at least one of B, Si, C, N, and O.

8. The recording medium as in any of claims 1, the recording layer is for data recording thereto and data retrieval therefrom using laser having one of a plurality of wavelengths.

9. The recording medium as in any of claims 1 to 8, the recording layer having a thickness within one of a range of 5 to 400 nm and a range of 15 to 200nm.

10. The recording medium as in any of claims 1 to 9, further comprising: a substrate stacked adjacent to the recording layer for structurally supporting the recording layer.

11. The recording medium as in claim 10, the substrate having a plurality of grooves formed thereon for forming and defining at least one land segment, each of the plurality of recording locations being adjacent to and opposing at least one of the at least one land segment and one of the plurality of grooves, wherein data recording on the recording layer spatially corresponds with at least one of the at least one land segment and one of the plurality of grooves.

12. The recording medium as in claim 10, the substrate being made from one of polycarbonate, polymethyl methacrylate (PMMA), amorphous polyolefin, carbonate type resin, ultraviolet curable resin, ceramic, and glass.

13. The recording medium as in any of claims 1 to 12, each of the write laser beam and the read laser beam having a wavelength not exceeding 800nm and being directed initially through the substrate and subsequently onto the recording layer.

14. The recording medium as in any of claims 1 to 13, further comprising: a reflective layer stacked adjacent to the recording layer, the reflective layer opposing the second face of the recording layer and the substrate opposing the first face of the recording layer.

15. The recording medium as in claim 14, the reflective layer being made from at least one of Au, Al, Ag, Ti, Cr, Cu, Pd, W and Pt.

16. The recording medium as in any of claims 14 and 15, the reflective layer having a thickness within one of a range of 20 to 200 nm and a range of 50 to 150 nm.

17. The recording medium as in any of claims 1 to 12, further comprising: a cover layer stacked adjacent to the recording layer, the cover layer opposing the first face of the recording layer and the substrate opposing the second face of the recording layer.

18. The recording medium as in claim 17, the cover layer having a thickness within one of a range of 10 to 200 um and a range of 15 to 150 um.

19. The recording medium as in any of claims 17 and 18, the cover layer is made from at least one of polycarbonate, cellulose triacetate and polydicyclopendadiene, (methyl)methacrylate and (methyl)propylacrylate.

20. The recording medium as in any of claims 17 to 19, each of the write laser beam and the read laser beam having a wavelength not exceeding 500nm and being directed initially through the cover layer and subsequently onto the recording layer.

21. The recording medium as in any of claims 17 to 20, further comprising: a reflective layer stacked adjacent to the substrate, the reflective layer opposing the second face of the recording layer.

22. The recording medium as in claim 21, the reflective layer being made from at least one of Au, Al, Ag, Ti, Cr, Cu, Pd, W, and Pt, and having a thickness within one of a range of 20 to 200 nm and a range of 50 to 150 nm.

23. The recording medium as in any of claims 1 to 22, further comprising at least one of: a first dielectric layer stacked adjacent to the recording layer, the first dielectric layer interfacing the substrate and the recording layer; and a second dielectric layer stacked adjacent to the recording layer, the recording layer being disposed between the substrate and the second dielectric layer.

24. The recording medium as in claim 23, each of the first dielectric layer and the second dielectric layer being made from at least one of oxide, nitride, chalcogenide, fluoride, and a carbide of a metal.

25. The recording medium as in claim 23, each of the first dielectric layer and the second dielectric layer being made from at least one of SiO₂, SiO, Al₂O₃,

GeO₂, In₂O₃, TeO₂, TiO₂, Ta₂O₅, MoO₃, WO₃, Si₃N₄, AlN, BN, TiN, ZnS, CdS, CdSe, ZnTe, AgF, PdF₂, and SiC.

26. The recording medium as in any of claims 24 to 25, each of the first dielectric layer and the second dielectric layer having a thickness within one of a range of 1 to 250 nm and a range of 10 to 150 nm.

27. The recording medium as in any of claims 23 to 26, each of the recording layer, reflective layer, cover layer, first dielectric layer, and second dielectric layer being formed by one of sputtering, evaporation, and chemical vapor deposition.

28. The recording medium as in any of claims 23 to 26, the cover layer being formed by one of solvent casting, polymerization-casting, spin coating, die coating and pressure-based lamination.

29. The recording medium as in any of claims 23 to 28, the substrate being formed by one of injection molding and extrusion molding.

30. A recording medium comprising: a recording layer comprising metallic glass and having a first face and a second face outwardly opposing the first face, the recording layer having a plurality of recording locations, each of the plurality of recording locations having an optical density being variable through at least two states for indicating a data value, the metallic glass being formed from at least two metallic elements, has a disordered structure when cooled and a crystalline structure when heated; and a substrate stacked adjacent to the recording layer for structurally supporting the recording layer, wherein a write laser beam is directable towards one of the plurality of recording locations of the recording layer for varying the optical density thereof through the at least two states, and wherein a processed beam having a beam property is processed from a read laser beam directed towards one of the plurality of recording location of the recording layers, the laser beam being processed by the corresponding one of the plurality of recording locations with one of the at least two states thereof determining the beam property, the beam property of the processed beam being indicative of the data value of the corresponding one of the plurality of recording locations.

31. The recording medium as in claim 30, the recording layer further comprising metallic glass containing palladium (Pd).

32. The recording medium as in any of claims 30 and 31 , the at least two states of each of the plurality of recording locations of the recording layer being at least two crystallinity levels.

33. The recording medium as in any of claims 30 to 32, the at least two states of each of the plurality of recording locations comprising a substantially crystalline state and a substantially amorphous state.

34. The recording medium as in any of claims 30 to 33, each of the at least two states of each of the plurality of recording locations corresponding with the optical reflectivity of the corresponding one of the plurality of recording locations.

35. The recording medium as in claim 30, the optical density of each of the plurality of recording locations being variable between a substantially crystalline state and a substantially amorphous state with the at least two crystallinity levels extending and forming graduations therebetween, wherein varying a portion of the recording layer between the substantially crystalline state and the substantially amorphous state varies optical reflectance of the portion of the recording layer.