WO2006049452A1

WO2006049452A1 - Multi-layer disc

Info

Publication number: WO2006049452A1
Application number: PCT/KR2005/003712
Authority: WO
Inventors: Jin Yong Kim; Kyung Chan Park
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2004-11-05
Filing date: 2005-11-04
Publication date: 2006-05-11
Anticipated expiration: 2007-05-05
Also published as: KR101106596B1; CN101053028A; CN101053028B; KR20060040764A

Abstract

A multi-layer disc is disclosed which includes a plurality of recording layers, as in a dual layer blu-ray disc. In the multi- layer disc, the tolerance of a transparent substrate thickness from a surface of a cover layer to each recording layer is set to be different from those of transparent substrate thicknesses to other recording layers within a range in which no degradation in the characteristics of recording and reproduction signals for each recording layer occurs. Accordingly, it is possible to more efficiently manufacture multi -layer discs, to achieve an improvement in the manufacturing yield of multi-layer discs, and to achieve a reduction in the manufacturing costs of multi-layer discs.

Description

D E S C R I P T I O N

MULTI-LAYER DISC

I . Technical Field

The present invention relates to a multi-layer disc, and more particularly to a multi-layer disc in which the tolerance of a thickness from a surface of a cover layer to each recording layer in the disc is set to be different from those of thicknesses to other recording layers.

2. Background Art

High-density optical discs capable of recording or reproducing a large quantity of high-quality video and audio data, such as blu-ray discs (BDs) , have been developed, and are expected to be made commercially available. Generally, such optical discs have a multi-layer structure in which a plurality of recording layers are formed on a single disc substrate, in order to achieve an increase m recording capacity.

Referring to FIG. 1, a single layer BD 100 is illustrated. The single layer BD 100 has a laminated disc structure including a substrate 10, a recording layer 11, and a cover layer 12.

Typically, the single layer BD 100, which has the above-mentioned disc structure, has a total thickness Dt of 1,200 μm. The cover layer 12 has a thickness of 100 μm when the radial position corresponding to a radius of 22 to 23 mm is set as a reference position, under the condition m which the cover layer 12 has a refractive index of, for example, 1.6. Since the cover layer 12 has a thickness tolerance of +5 μm, the thickness from an exposed surface of the cover layer 12 to the recording layer

II, LOt, ranges from 95 μm to 105 μm. Referring to FIG. 2, a dual layer BD 200 is illustrated. The dual layer BD 200 has a laminated disc structure including a substrate 20, a first recording layer 21, a space layer 24, a second recording layer 23, and a cover layer 22. Typically, the dual layer BD 200 has a total thickness Dt of 1,200 μm. The cover layer 22 has a thickness of 75 μm when the radial position corresponding to a radius of 22 to 23 mm is set as a reference position, under the condition in which the cover layer 22 has a refractive index of, for example, 1.6. Since the cover layer 22 has a thickness tolerance of ±5 μm, the thickness from an exposed surface of the cover layer 22 to the second recording layer 23, Lit, ranges from 70 μm to 80 μm.

Also, the thickness to the first recording layer 21, LOt, corresponds to the sum of the thickness of the cover layer 22, second recording layer 23 (Ll), and space layer 24, and ranges from 95 μm to 105 μm, as m the single layer BD.

Typically, either the single layer BD 100 or the dual layer BD 200 is designed to satisfy a thickness tolerance of ±2 μm. In order to satisfy this thickness tolerance, it is necessary to achieve an increased disc manufacture accuracy. However, this causes great degradation in manufacturing yield under the currently given manufacture conditions, thereby resulting in a great increase in disc manufacturing costs. On the other hand, when the thickness tolerance is undesirably increased, degradation in signal characteristics occurs. In this case, errors may be generated during recording and reproducing operations.

3. Disclosure of Invention Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a multi-layer disc which is capable of achieving an enhancement in manufacture efficiency without causing degradation in signal characteristics in recording and reproduction operations.

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a multi-layer disc comprising: a plurality of recording layers, wherein a thickness from a surface of a cover layer of the disc to each of the recording layers has a tolerance determined such that a tolerance of the thickness associated with the recording layer more distant from the cover layer is larger than a tolerance of the thickness associated with the recording layer closer to the cover layer.

The thickness associated with an arbitrary recording layer may correspond to a thickness of the cover layer, or to a sum of the thickness of the cover layer, thicknesses of recording layers closer to the cover layer than the arbitrary recording layer, and thicknesses of space layers, while being closer to the cover layer than the arbitrary recording layer, formed between two recording layers.

The thickness associated with the recording layer more distant from the cover layer may have a tolerance of ±3 μm. The thickness associatedwith the recording layer closer to the cover layer may have a tolerance of ±2 μm. The thickness tolerance may be determined under conditions in which a radial position of the disc corresponding to a radius of 33 to 34 mm is set as a reference position, and the cover layer has a refractive index of 1.6.

In accordance with another aspect, the present invention provides a multi-layer disc having a laminated disc structure comprising a substrate, a first recording layer, a space layer, a second recording layer, and a cover layer, wherein the cover layer has a thickness tolerance of ±2 μm when the cover layer has a thickness of 75 μm, and a sum of thicknesses of the cover layer, the second recording layer, and the space layer has a tolerance of ±3 μm when the thickness sum is 100 μm.

The tolerance of the sum of the thicknesses of the cover layer, the second recording layer and the space layer may be determined to satisfy a minimal limited equalizer (LEQ) jitter value of 6 5 %, and a LEQ jitter value of not more than 10% at a radial tilt of ± 0.6 degree, in associated with the first recording layer. The tolerance of the thickness of the cover layer may be determined to satisfy a minimal LEQ jitter value of 6.5 %, and a LEQ jitter value of not more than 10% at a radial tilt of ± 0.6 degree, in associated with the second recording layer.

4. Brief Description of Drawings

The accompanying drawings, which are included to provide a further understanding of the invention, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the present invention.

FIG. 1 is a schematic view illustrating a general single layer blu-ray disc (BD) ; FIG. 2 is a schematic view illustrating a general dual layer BD;

FIG. 3 is a schematic view illustrating a dual layer BD according to the present invention;

FIG. 4 is a schematic view illustrating a procedure for manufacturing the dual layer BD according to the present invention;

FIG. 5 is a graph depicting limited equalizer (LEQ) jitter characteristics of a first recording layer in the dual layer BD according to the present invention; and FIG. 6 is a graph depicting limited equalizer (LEQ) jitter characteristics of a second recording layer in the dual layer BD according to the present invention.

Features, elements, and aspects of the invention that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects in accordance with one or more embodiments.

5. Modes for Carrying out the Invention

Hereinafter, preferred embodiments of a multi-layer disc according to the present invention will be described m detail with reference to the annexed drawings.

The present invention is applicable to multi-layer discs of various types in which a plurality of recording layers are laminated over a single substrate.

Referring to FIG. 3, a dual layer blu-ray disc (BD) 300 is illustrated. The dual layer BD 300 has a laminated disc structure including a substrate 30, a first recording layer 31 (LO) , a space layer 34, a second recording layer 33 (Ll), and a cover layer

32

The dual layer BD 300 has a total thickness Dt of 1,200 μm.

The sum of the thicknesses of the cover layer 32, second recording layer 33 and space layer 34, which corresponds to the thickness from an exposed surface of the cover layer 32 to the first recording layer 31, namely, a thickness LOt, is 100 μm with a tolerance of ±3 μm when the radial position corresponding to a radius of 33 to 34 mm is set as a reference position, under the condition m which the cover layer 32 has a refractive index of, for example, 1.6.

The thickness of the cover layer 32, which corresponds to the thickness from the exposed surface of the cover layer 32 to the second recording layer 33, namely, a thickness Lit, is 75 μm with a tolerance of +2 μm when the radial position corresponding to the radius of 33 to 34 mm is set as the reference position, under the condition in which the cover layer 32 has a refractive index of, for example, 1.6

That is, the first recording layer 31 more distant from the cover layer 32, has a relatively large thickness tolerance of +3 μm, whereas the second recording layer 33 closer to the cover layer 32, has a relatively small thickness tolerance of ±2 μm. Hereinafter, the procedure for manufacturing the dual layer BD in which the recording layers have different thickness tolerances, as described above, will be described in detail.

FIG. 4 illustrates a procedure for manufacturing the dual layer BD according to the present invention.

In the disc manufacturing procedure, a pit array is first formed on the substrate 30 which may be injection-molded. A reflective film is then coated over the pit array formed on the substrate 30 in accordance with a sputtering process, to form the first recording layer 31 (SlO) . An ultraviolet (UV) resin is pressed on the first recording layer 31, to form the space layer 34 (SIl) .

Thereafter, a stamper 40, which has a pit array, is accurately positioned on the space layer 34 (S12) . A pressure is then applied to the stamper 40, thereby causing the stamper 40 to form a pit array on the space layer 34 (S13) . In this case, the thickness of the space layer 34 is maintained to be 20 to 30 μm.

Subsequently, UV rays are irradiated onto the substrate 30.

The stamper 40 is then removed. Thereafter, a reflective film is coated over the pit array formed on the space layer 34 in accordance with a sputtering process, to form the second recording layer 33 (S14) .

Next, a cover sheet is attached to the second recording layer 33 using a UV resin, and is then fixed to the second recording layer 33 by irradiating the UV resin with UV rays, and thus, curing the UV resin (S15) . In this case, the cover layer 32 has a thickness of about 75 μm including the thickness of the UV resin.

In the above-described disc manufacturing procedure, the first recording layer 31 is first formed, the space layer 34 having the thickness of 20 to 30 μra is formed, the second recording layer 33 is formed, and the cover layer 32 having the thickness of about 75 μra is finally formed. In this case, the 5 tolerance of the thickness from the exposed surface of the cover layer 32 to the first recording layer 31, namely, the thickness LOt (100 μm) , results from the accumulation of the thickness tolerance of the space layer 34 and the tolerance of the thickness from the exposed surface of the cover layer 32 to the second

10 recording layer 33, namely, the thickness Lit (75 μm) .

In this regard, the tolerance of the thickness LOt associated with the first recording layer 31, for example, a tolerance DO, the tolerance of the thickness Lit associated with the second recording layer 33, for example, a tolerance Dl, and

15 the tolerance of the thickness of the space layer 34, for example, a tolerance S, have a relation expressed by "|Dθ|=Vi)I² +S² " .

Referring to this relation, it can be seen that the tolerance of the thickness LOt associated with the first recording layer 31, namely, the tolerance DO, is larger than the

20 tolerance of the thickness Lit associated with the second recording layer 33, namely, the tolerance Dl.

Meanwhile, FIG. 5 illustrates a variation in limited equalizer (LEQ) jitter characteristics depending on a variation in the thickness LOt associated with the first recording layer

25 31 (LO) when the first recording layer 31 has a storage capacity of 25 GB. When the thickness LOt associated with the first recording layer 31 is 100 μm, and has a tolerance ranging within +3 μm, the condition, in which the minimal LEQ jitter value should be less than 6.5 %, is satisfied, as shown in FIG. 5. Also, the

30 LEQ jitter value is not more than 10% at a radial tilt of ± 0.6 degree. Accordingly, a desired margin of signal reproduction characteristics can be secured. However, referring to FIG. 5, it can be seen that, when the thickness LOt has a tolerance of +4 μra, it is impossible to satisfy the condition in which the minimal LEQ jitter value should be less than 6.5 %.

Thus, the first recording layer 31 can satisfy required signal characteristics so long as the thickness LOt associated with the first recording layer 31 has a tolerance of ±3 μm.

FIG. 6 illustrates a variation in limited equalizer (LEQ) jitter characteristics depending on a variation in the thickness Lit associated with the second recording layer 33 when the second recording layer 33 (Ll) has a storage capacity of 25 GB. When the thickness Lit associated with the second recording layer 33 is 75 μm, and has a tolerance ranging within +2 μm, the condition, in which the minimal LEQ jitter value should be less than 8.5 %, is satisfied, as shown in FIG. 6. Also, the LEQ jitter value is not more than 10% at a radial tilt of ± 0.6 degree. Accordingly, a desired margin of signal reproduction characteristics can be secured. However, referring to FIG. 5, it can be seen that, when the thickness LOt has a tolerance of ±3 μm, it is impossible to satisfy the condition in which the minimal LEQ jitter value should be less than 8.5 %.

Thus, the second recording layer 33 can satisfy required signal characteristics so long as the thickness Lit associated with the second recording layer 33 has a tolerance of ±2 μm. As apparent from the above description, in accordance with the present invention, it is possible to more efficiently manufacture a multi-layer disc by setting the tolerance of the thickness from the exposed surface of the cover layer to each recording layer in the disc to be different from those of thicknesses to other recording layers. Accordingly, it is possible to achieve an enhancement in disc manufacturing yield, and thus, a reduction in disc manufacturing costs.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A multi-layer disc comprising: a plurality of recording layers, wherein a thickness from a surface of a cover layer of the "> disc to each of the recording layers has a tolerance determined such that a tolerance of the thickness associated with the recording layer more distant from the cover layer is larger than a tolerance of the thickness associated with the recording layer closer to the cover layer. 0

2. The multi-layer disc as set forth in claim 1, wherein the thickness associated with an arbitrary recording layer corresponds to a thickness of the cover layer, or to a sum of the thickness of the cover layer, thicknesses of recording layers 5 closer to the cover layer than the arbitrary recording layer, and thicknesses of space layers, while being closer to the cover layer than the arbitrary recording layer, formed between two recording layers .

0 3. The multi-layer disc as set forth in claim 1, wherein the thickness associated with the recording layer more distant from the cover layer has a tolerance of ±3 μm, and the thickness associated with the recording layer closer to the cover layer has a tolerance of +2 μm. 5

4. The multi-layer disc as set forth in claim 1, wherein the thickness tolerance is determined under conditions in which a radial position of the disc corresponding to a radius of 33 to 34 mm is set as a reference position, and the cover layer has 0 a refractive index of 1.6.

5. The multi-layer disc as set forth in claim 1, wherein the multi-layer disc is a blu-ray disc having a first recording layer and a second recording layer.

6. The multi-layer disc as set forth in claim 5, wherein, under conditions in which a radial position of the disc corresponding to a radius of 33 to 34 mm is set as a reference position, and the cover layer has a refractive index of 1.6, the thickness associated with the first recording layer has a tolerance of +3 μm, and the thickness associated with the second recording layer has a tolerance of +2 μm.

7. A multi-layer disc having a laminated disc structure comprising a substrate, a first recording layer, a space layer, a second recording layer, and a cover layer, wherein the cover layer has a thickness tolerance of ±2 μm when the cover layer has a thickness of 75 μm, wherein a sum of thicknesses of the cover layer, the second recording layer, and the space layer has a tolerance of ±3 μm when the thickness sum is 100 μm.

8. The multi-layer disc as set forth in claim 7, wherein the tolerance of the sum of the thicknesses of the cover layer, the second recording layer and the space layer is determined to satisfy a minimal limited equalizer (LEQ) jitter value of 6.5 %, and a LEQ jitter value of not more than 10% at a radial tilt of + 0.6 degree, in associated with the first recording layer.

9. The multi-layer disc as set forth in claim 7, wherein the tolerance of the thickness of the cover layer is determined to satisfy a minimal limited equalizer (LEQ) jitter value of 6.5 %, and a LEQ jitter value of not more than 10% at a radial tilt of + 0.6 degree, in associated with the second recording layer.