WO2009038331A2

WO2009038331A2 - Recording method of optical recording medium

Info

Publication number: WO2009038331A2
Application number: PCT/KR2008/005478
Authority: WO
Inventors: Sun Hee Kim; Keum Cheol Kwak; Chang Ho Lee
Original assignee: Lg Electronics Inc.
Priority date: 2007-09-21
Filing date: 2008-09-17
Publication date: 2009-03-26
Also published as: KR20090030858A; WO2009038331A3

Abstract

A recording method of an optical recording medium which includes a reproducing layer applying super-resolution is disclosed, the method which includes forming marks on a recording layer, and performing post curing to remove marks formed on the reproducing layer during the mark forming operation.

Description

Description RECORDING METHOD OF OPTICAL RECORDING MEDIUM

Technical Field

[1] The present invention relates to a recording method of an optical recording medium, and more particularly, to a recording method of an optical recording medium, capable of recording a mark or a pit sized under a diffraction limit by including a reproducing layer generating super-resolution. Background Art

[2] Optical discs according to the current technologies include a digital versatile disc

(DVD) using red laser and a blue-ray disc (BD) using blue laser. The DVD has a capacity of about 4.7GB whereas the BD has a capacity of about 25GB.

[3] In order to store signal flows of a high-definition digital video as data, a data storage medium is required to have a greater than 20GB capacity and a greater than 25Mbps data transfer rate. Furthermore, afterwards, it will be required a technology for recording data with a capacity of greater than 100GB or even a terabyte -range.

[4] In such various multimedia environments, a variety of multifunctional data storage technologies have been developed, among which an optical recording technology is capable of storing large capacity data while being detachably applied. Moreover, due to its reliability in data storage and random access, which is indispensable in the multimedia environments, and low cost, the optical recording technology is being spotlighted most.

[5] The capacity of an optical recording medium can be increased by reducing the size of a mark or a pit recorded in the medium. For this, it is required to redvce the size of an incident laser beam. The laser beam size is proportional to a wavelength of the laser and inverse-proportional to a numerical aperture (NA) of an object lens. Therefore, in order to increase the capacity of the optical recording medium, the wavelength needs to be reduced or the NA needs to be increased. To this end, a recording medium for recording and reproducing data using a short- wavelength laser has been studied as a high-density recording medium. Logically, however, the technology for accomplishing svch high density by the short- wavelength laser (405 nm of BL) and an object lens with high NA (0.85) is now limited. Therefore, a new technology for a greater storage capacity is in increasing demand.

[6] According to svch a demand, development and research are undergoing for an optical disc using super-resolution, as an optical memory enabling compatible use with existing CD and DVD reprodudng devices and also enabling high-density storage with a capacity hundreds of times higher than 650MB, that is, the capacity of the first stage CD. Such a super-resolution optical disc technology is expected to increase the storage density by considerably redudng the size of recording marks though still using an existing laser optical pickup system.

[7] However, the super-resolution optical disc uses a great level of laser power to open an aperture of a reprodudng layer during data reproduction, thereby causing deterioration of the reproducing layer and increasing noise of a lens. In addition, during the data recording operation in the super-resolution optical disς recording marks may be formed even on the reprodudng layer not only on the recording layer, thereby causing noise and deteriorating the reprodudng stability. Disclosure of Invention Technical Problem

[8] An object of the present invention devised to solve the problem lies on a recording method of an optical recording medium, capable of preventing deterioration of a reprodudng layer, redudng noise during the reproduction, and guaranteeing stable reproduction. Technical Solution

[9] The object of the present invention can be achieved by providing a recording method of an optical recording medium which includes a reprodudng layer applying super- resolution, the method comprising forming marks on a recording layer, and performing post curing to remove marks formed on the reprodudng layer during the mark forming operation.

[10] The post curing may be performed by projecting a laser beam having 2.5mW to 3.5mW power to the reprodudng layer.

[11] The recording layer may include a first recording layer formed of at least one of S,

Ge, Sn and C, and a second recording layer formed mainly of Ag.

[12] The second recording layer may include at least one of Ti, Sb, Te, Cu, Mg, Bi, Ge,

S, Sn and Co, as an additive.

[13] Here, the second recording layer may contain the additive by 50 at.% or less.

[14] The first recording layer may include at least one of Cu, Zn, B, Bi, Mg, Mn, Fe, Ga,

Zr and Te, as an additive.

[15] The first recording layer may contain 1 to 50 at.% of the additive .

Advantageous Effects [16] In accordance with a recording method of an optical recording medium according to an exemplary embodiment of the present invention, deterioration of a recording layer can be prevented while reduing reproduced noise by removing recording marks generated during the data recording. Also, the reproducing stability can be guaranteed. Brief Description of the Drawings

[17] The accompanying drawings, which are included to provide a further understanding of the invention, illustrate exemplary embodiments of the invention and together with the description serve to explain the principle of the invention.

[18] In the drawings :

[19] Fig. 1 is a schematic sectional view of an optical recording medium according to an exemplary embodiment of the present invention;

[20] Fig. 2 schematically shows a recording layer after the data recording operation;

[21] Fig. 3 schematically shows a reproducing layer after the data recording operation;

[22] Fig. 4 is a graph analyzing a spectrum during the data reprodudng operation in an optical recording medium according to a comparative example of the present invention;

[23] Fig. 5 is a graph analyzing a spectrum of the data reprodudng operation in an optical recording medium according to an experimental example of the present invention;

[24] Fig. 6 is a graph illustrating reprodudng stability in accordance with post curing powers;

[25] Fig. 7 and Fig. 8 are graphs showing RF and EQ properties of before and after the post curing, respectively, performed after a 75nm mark is formed; and

[26] Fig. 9 and Fig. 10 are graphs showing RF and EQ properties of before and after the post curing, respectively, performed after a 50nm mark is formed. Best Mode for Carrying Out the Invention

[27] In the following description, while generally known terms are selected as possible, in some cases specific terms are employed by the applicant, and definitions of the terms are explained herein in detail. In this case, therefore, it is required that the terms be understood by the specific meanings not simply by general meanings.

[28] An optical recording medium cited herein refers to any medium in which certain data is optically recorded or capable of recording data therein, for example, an optical disc. In addition, when something is described as disposed "on" another thing, this may also mean that yet another thing is interposed between the two, as well as that the something is directly on the another thing. Finally, since like reference numerals refer to like elements throughout the drawings, description of the same part once explained will not be repeated.

[29] Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[30] Fig. 1 is a schematic sectional view of an optical recording medium according to an exemplary embodiment of the present invention, more specifically, a write-once read- many (WORM) optical recording medium including a recording layer and being capable of recording data only once. Referring to Fig. 1, the optical recording medium includes a substrate 100, a reflection layer 110, a recording layer 120, a reprodudng layer 130, and a light transmitting layer 140. Additionally, first through third dielectric layers 150, 160 and 170 are further included to protect the recording layer 120 and the reprodudng layer 130.

[31] The substrate 100 has a disc form with about 0.6 to 1.1mm thickness to secure thickness of the optical recording medium. On a surface of the substrate 100, a groove and a land for guiding laser are spirally formed from the center to the outer circumference or in the opposite direction. The substrate 100 may be formed of various materials including glass, ceramiς and resin. Especially, it is preferred that polycarbonate (PQ having low weight, excellent injectability, and low birefringence during incidence of laser is employed for the substrate 100 so as to increase the carrier- to-noise ratio (CNR). Also, preferably, the substrate 100 is formed through injection molding using a stamper. However, other methods can also be used, sirh as a pho- topolymer method.

[32] The reflection layer 110 reflects the laser beam being incident from the light transmitting layer 140 back to the light transmitting layer 140. The reflection layer 110 may be formed of any material among Mg, Al, Ti, Cr, Fe, Co, M, Cu, Zn, Ge, Ag, Pt and the like. Especially, Al, Au, Ag, Cu or an alloy containing any of them is preferably employed since having high reflectivity. By including the reflection layer 110, the optical recording medium is able to guarantee predetermined reflectivity, and thereby secure a high CNR after the optical recording is completed.

[33] In addition, the reflection layer 110 has an effect of absorbing heat generated from the recording layer 120, as well as the general optical effect. Therefore, marks formed at the recording layer 120 can be uniformly maintained without spreading, thereby improving the signal quality.

[34] If the reflection layer 110 has lower than 5 ran thickness, the above expected effects of the reflection layer 110 can hardly be obtained. If the thickness is greater than 300nm, on the other hand, the surface property of the reflection layer 110 is deteriorated. Also, since the deposition rate is elongated, productivity is deteriorated. Therefore, the reflection layer 110 is formed within a range of 5 to 300nm in thickness, more preferably within a range of 20 to 200nm.

[35] On the recording layer 120, irreversible recording marks are formed such that recording and reprodudng of data can be achieved by the difference of reflectivity between the marks formed by a proper recording power and the other parts not applied with the laser.

[36] As shown in the drawings, the recording layer 120 includes a couple of layers, that is, a first recording layer 120a and a second recording layer 120b. When a certain part on the recording layer 120 is irradiated with the laser having a predetermined power, two elements of the respective recording layers 120a and 120b at the laser applied part are partially or wholly mixed, thereby producing the marks. Thus, the reflectivity difference is generated between the marks and the other parts not applied with the laser, thereby enabling the data recording and reprodudng.

[37] The first recording medium 120a mainly includes any one of S, Ge, Sn and C, and may further include, as an additive, at least one among Cu, Zn, B, Bi, Mg, Mn, Fe, Ga, Zr and Te. Being not indispensable, the additive may be contained by 50 at.% or less with respect to the whole component of the first recording layer 120a.

[38] The second recording layer 120b mainly includes Ag. In addition, another material having relatively low thermal conductivity can be added to the second recording layer 120b. Such an additive helps reduce the recording power, control shapes of the marks more easily, and improve the recording property. At least one among Ti, Sb, Te, Cu, Mg, Bi, Ge, S, Sn and Co may be employed for the additive. The additive may oxupy 1 to 50 at.% with respect to the whole component of the second recording layer 120b.

[39] Thickness of the recording layer 120 is not specifically defined but preferably within a range of 1 to 30nm to be appropriate for restricting a noise level of reproduced signals and securing enough recording sensitivity and enough variation of the reflectivity before and after the data recording.

[40] Although the recording layer 120 is disposed between the substrate 100 and the reprodudng layer 130 according to Fig. 1, the present invention is not limited to this configuration. For example, the recording layer 120 may be disposed between the reprodudng layer 130 and the light transmitting layer 410.

[41] The reprodudng layer 130 may be formed of a material capable of achieving super- resolution. For example, a non-linear optical material, a phase change material, or a thermochromic material of which optical property varies according to temperature distribution can be used for the material achieving super-resolution. Especially a GeSbTe- based phase change material can be employed for the reproducing layer 130.

[42] Although thickness of the reprodudng layer 130 is not specifically defined, it is preferred that the reprodudng layer 130 has 3 to 200nm thickness to achieve the super- resolution and optical change rate as desired.

[43] The light transmitting layer 140 constitutes a surface for receiving the laser beam, while functioning as a path of the laser beam. The light transmitting layer 140 may have 100/M to 0.6mm thickness. A material having relatively high optical transmittance in the wavelength region of the laser beam, sirh as an acryl-based or epoxy -based UV- curable resin, is employed for the light transmitting layer 140. Also, a light transmissive resin sheet of various types of adhesive can be used for the material of the light transmitting layer 140.

[44] According to the exemplary embodiment of the present invention, the optical recording medium may further include the first and the second dielectric layers 150 and 160 for protecting the reprodudng layer 130. In detail, the first and the second dielectric layers 150 and 160 physically and chemically protect the reprodudng layer 130 mounted therebetween, also effectively preventing deterioration of the recorded data.

[45] The material for the first to the third dielectric layers 150, 160 and 170 is not specifically defined as long as being a dielectric material transparent in the wavelength region of the laser beam. For example, an oxide, a sulfide, a nitride, or a compound of the above may be used for the dielectric layers 150, 160 and 170.

[46] More specifically, in order to prevent thermal deformation of the substrate 100 and protect the reprodudng layer 130, the dielectric layers 150, 160 and 170 preferably include an oxide, a sulfide, and a nitride of Al, S, Ce, Ti, Zn and Ta, such as A12O3, AlN, ZnO, ZnS, GeN, GeCrN, CeO2, SO, SO2, S3N4, SC, La2O3, TaO, TiO2 and so on. A compound of the above may also be used.

[47] Especially, it is preferred to use a compound of ZnS and SO2 for the dielectric layers 150, 160 and 170. In this case, the ZnS to SO2 ratio can be set to 80:20. Also, the first to the third dielectric layers 150, 160 and 170 may be all formed of the same material or respectively different materials.

[48] When thickness of the dielectric layers 150, 160 and 170 is less than 3nm, the expected effect can hardly be obtained. When the thickness is greater than 200nm, the deposition rate is elongated and the productivity would be deteriorated. Furthermore, cracks may be generated according to stress of the respective dielectric layers 150, 160 and 170. Accordingly, the dielectric layers 150, 160 and 170 preferably have the thickness within a range of 3 to 200nm. However, the present invention is not restricted in this preferred range.

[49] The reflection layer 110, the reproduing layer 130, the recording layer 120, and the dielectric layers 150, 160 and 170 may be manufactured by sputtering or vacuum vapor-deposition. Especially the sputtering is preferred.

[50] According to this exemplary embodiment, the optical recording medium may be formed in a disc shape having an outer diameter of about 120mm and thickness of about 1.2mm. Additionally, the optical recording medium is a write-once type medium which records and reproduces data by irradiating the recording layer 120 with the laser beam of a 230 to 450nm wavelength, more preferably about 405 nm, from a light receiving surface which is the surface of the light transmitting layer 140.

[51] When reproducing the data with respect to the optical recording medium, an object lens having the NA greater than 0.7, preferably 0.85 NA, may be applied. According to this, a beam spot of the laser beam on the recording layer 120 may be about 0.4/M.

[52] Hereinafter, the data recording method of the optical recording medium according to the exemplary embodiment of the present invention will be explained in detail.

[53] In order to record data according to this exemplary embodiment, an optical recording medium having a reprodudng layer applying super-resolution, such as the above- described optical recording medium, may be employed. However, any other optical recording medium is applicable as long as having a super-resolution reproducing layer.

[54] Fig. 2 schematically shows the recording layer at the time of reprodudng recorded data. First, more particularly, marks 210 are formed by irradiating the recording layer with a laser beam having a predetermined recording power. In case that the recording layer includes two layers as described above, elements of the two layers are partially or totally mixed at the laser- applied part, thereby forming the marks 210. Here, the marks 210 formed on the recording layer may be sized under the diffraction limit.

[55] As shown in the drawings, while reproducing the data, a super-resolution region 220 is generated at a part of a reprodudng beam 200 being projected to the reprodudng layer, the super-resolution region 220 wherein the temperature distribution and optical properties are varied.

[56] Fig. 3 schematically shows the reprodudng layer when the recorded data is being reproduced. As aforementioned, the reprodudng layer of the super-resolution optical recording medium may be formed of a GeSbTe-based phase change material. Referring to Fig. 3, when using the phase change material for the recording layer, during the data recording, the recording marks may be formed even at the reproducing layer as well as the recording layer. In this case, the reproduced noise and the reprodudng stability may be affected.

[57] As shown in Fig. 3, a laser transmitting region on the reprodudng layer may include three regions, that is, a first region which overlaps an aperture 240, a second region not overlapping the aperture 240 within a region of the mark 230 formed during the recording, and a third region where only the reproducing beam is transmitted, not overlapping the mark 230 nor the aperture 240.

[58] The mark 230 formed on the reproducing layer during the data recording is read simultaneously with a mark of the recording layer during the data reproduction, thereby greatly affecting RF signals. Furthermore, melting and cooling are repeated at boundaries between the first and the second regions and between the first and the third regions, and accordingly there oxurs a difference of thermal sensitivity between a crystalline and an amorphous substance. Therefore, deterioration may start from the boundaries.

[59] Accordingly, by performing post curing after the recording, the phase can be evened while the marks 230 are removed from the reprodudng layer. Accordingly, during the data reproduction, degree of freedom of the phase change of the reprodudng layer is decreased, thereby redudng the deterioration. Meanwhile, the reproduction quality is improved since only the marks on the recording layer are reproduced.

[60] During the post curing, if the laser power is less than 2.5mW, the reprodudng stability is deteriorated since the reprodudng layer is not completely removed. If the laser power exceeds 3.5mW, recrystallization is performed in the reprodudng layer, thereby deteriorating evenness of the phase. Accordingly, the reprodudng stability is deteriorated.

[61] Therefore, preferably, the post curing is performed by projecting a laser beam having power of 2.5mW to 3.5mW onto the reprodudng layer. However, the present invention is not limited to this, but the laser power for the post curing may be varied according to the materials and the structure of the optical recording medium.

[62] Hereinafter, the present invention will be described in greater detail through an experimental example. Snce this is only by way of example, the present invention is not limited to the following exemplary embodiment.

[63] Experimental Example

[64] After manufacturing the optical recording medium structured as in Fig. 1 and forming marks, a reproducing beam is projected. The first recording layer is made of S while the second recording layer is made of Ag mainly and a GeSbTe -based substance additionally. The first recording layer is 7 ran thick. The second recording layer, being simultaneously formed through sputtering, is 5 ran thick. In addition, the GeSbTe-based phase change material is deposited by 7 ran as the reproducing layer.

[65] After marks of 75ran and 50ran (2T-2T) are sequentially recorded, the post curing is performed using a dynamic tester according to the power. Specifically, the post curing is performed with laser powers of OmW, 2mW, 2.5mW, 3.OmW, 3.5mW, and 4mW. The wavelength of the laser is 405ran, the NA is 0.85 and the linear velocity is 2.5m/sec.

[66] Comparative Example

[67] As a comparative example, an optical recording medium having the same structure as the experimental example is formed. Then, marks are formed under the same condition and a reproducing beam is projected. However, the post curing is omitted.

[68] Fig. 4 and Fig. 5 are graphs analyzing a spectrum during the data reproduction in the optical recording medium according to the comparative example and the experimental example of the present invention, respectively. It can be understood from the graphs that the noise level is lower in the experimental example than in the comparative example.

[69] Fig. 6 shows the reproducing stability in accordance with the laser powers during the post curing. When the power is less than 2.5mW, the reproducing stability is unsatisfactory since the power is insufficient for completely removing the marks from the reproducing layer. When the power is greater than 2.5mW and equal to or less than 3.5mW, the CNR is not decreased in some section according to the number of data reproducing operations. When the power is greater than 3.5mW, recrystallization occurs at the reproducing layer, thereby deteriorating evenness of the phase and the reproducing stability.

[70] Fig. 7 and Fig. 8 graphs showing RF and EQ properties of before and after the post curing with a 75ran mark, respectively. Fig. 9 and Fig. 10 are graphs showing RF and EQ properties of before and after the post curing with a 50ran mark, respectively. The jitter is 12% in Fig. 7 and 9% in Fig. 8. In Fig. 10, the jitter is 15%. Since the marks recorded on the reproducing layer are removed after the post curing and the phase is evened, the RF signals become clean while the jitter property and the reproducing stability are improved.

[71] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. [72]

Claims

[1] A recording method of an optical recording medium which includes a reproducing layer applying super-resolution, the method comprising: forming marks on a recording layer; and performing post curing to remove marks formed on the reproducing layer during the mark forming operation. [2] The method of claim 1, wherein the post curing is performed by irradiating the reproducing layer with a laser beam having 2.5mW to 3.5mW power. [3] The method of claim 1, wherein the recording layer includes a first recording layer formed mainly of at least one of S, Ge, Sn and C, and a second recording layer formed mainly of Ag. [4] The method of claim 3, wherein the second recording layer includes at least one of Ti, Sb, Te, Cu, Mg, Bi, Ge, S, Sn and Co, as an additive. [5] The method of claim 3, wherein the second recording layer contains the additive by 50 at.% or less. [6] The method of claim 3, wherein the first recording layer includes at least one of

Cu, Zn, B, Bi, Mg, Mn, Fe, Ga, Zr and Te, as an additive. [7] The method of claim 3, wherein the first recording layer contains 1 to 50 at.% of the additive.