KR100554070B1 - High-density optical storage medium - Google Patents

Abstract

An optical disc used in conjunction with a light beam for reading and writing information provides a substrate having a pre-formatted structure for storing information on one surface of the substrate, the substrate having a thickness that maintains a substantially flat shape. A thin film reflection layer on a surface that reflects an incident light beam used for writing or reading information, a recording layer overlying the thin film reflection layer and storing information, a thickness thicker than the depth of the preformatted structure of the substrate And a transparent first transparent layer having a first refractive index, a transparent second transparent layer overlying the first transparent layer and having a thickness of a second refractive index less than the first refractive index and the same order as that of the substrate, and A transparent third transparent layer overlying the second transparent layer and having a third refractive index close to the first refractive index and a thickness close to the second transparent layer. All. Therefore, the optical disk according to the present invention reaches the information recording area through the transmission layer having a relatively high refractive index and the transmission layer having a low refractive index to reach the information recording area, so that even if there are dust or surface defects Information can be recorded or read on. Incident light beams focused on the information recording area do not pass through the substrate. Therefore, there is no optical aberration caused by thinning the substrate for high density recording.

 high-density optical disk, dust, disk thickness

Description

High-density optical storage medium

1 is a view showing a single layer structure of a general optical disc,

2 is a view showing a monolayer structure of an optical disk according to the present invention;

3 is a view showing a single layer structure of an optical disk manufactured according to the present invention;

4 is a view for explaining the deformation of the spacer shown in FIG.

5A and 5B are views for explaining and comparing the optical disk and the conventional optical disk according to the present invention with respect to dust placed on the surface of the optical disk.

* Explanation of symbols for main parts of the drawings

20, 30: optical disk 21, 31: substrate

23: recording layer 25: first transmission layer

27: 2nd permeable layer 29: 3rd permeable layer

33: reflective layer 35: protective layer

36: spacer 37: air layer

39: transparent plate

The present invention relates to an optical storage medium used with a light beam for the writing and / or reading of information, and more particularly to an optical storage medium capable of writing and / or reading at high density.

1 shows a monolayer structure of a conventional optical disc used as an optical storage medium. In Fig. 1, reference numeral 10 is a substrate, 12 is a reflective layer, and 14 is a protective layer. A light beam, for example, laser light, used for reading information recorded on the optical disc shown in FIG. 1 is incident on the optical disc through the substrate 10. Feeds or grooves are formed on the surface of the substrate 10. The reflective layer 12 is formed on the surface of the substrate 10 in the form of pits or grooves, and the light beam reflected from the pits or grooves on which the reflective layer 12 is formed contains information recorded on the optical disc.

An optical disc of the rewritable type has a substrate, a recording layer, a reflective layer, and a protective layer. The recording layer is made of a material in which the crystalline and amorphous states are reversibly changed, and the portion heated by the light beam is changed to the amorphous state, whereby information is recorded.

The above-described optical discs are being developed to provide high-capacity recording and high-speed playback that can provide high definition television images. In order to achieve the goals of high capacity recording and high speed reproduction, it is necessary to increase the disk area or increase the number of rotations of the disk. However, an approach to increasing the disk area is not practical because of the increase in the size of the disk and the reproducing apparatus or the increase in production cost. Therefore, a method of increasing the recording density per unit area for high capacity recording and high speed power reproduction has been studied.

Since the size of the optical spot used for reading and / or writing to the optical disk is proportional to λ / NA, the optical disk can be reduced by reducing the wavelength of the light or by reducing the size of the optical spot by using an objective lens having a high numerical aperture (NA). Can increase the recording density. However, if the optical wavelength is reduced or the NA is increased, the coma increases as shown in Equation 1 below, resulting in poor signal recording and reproducing characteristics.

Coma ∝ NA ³ t / λ

Where NA is the numerical aperture of the objective lens, λ is the wavelength of the light beam used, and t is the thickness from the surface of the substrate on which the light beam is incident to the reflective layer.

As one method of improving the recording and reproducing characteristics of such signals, there is a method of reducing the thickness of the substrate.

However, there are other problems when the substrate thickness is made thin. That is, a substrate manufactured by injection molding does not become a completely flat substrate due to the characteristics of injection molding, but optical defects such as birefringence or mechanical defects such as warping or tilting occur, resulting in increased coma. Since optical defects and mechanical defects are more likely to occur as the thickness of the substrate becomes thinner, it is difficult to expect a coma reduction effect due to the reduction of the substrate thickness when manufacturing the optical disc through injection molding.

In addition, when the disk substrate becomes thin, the recorded information is obscured due to dust getting on the surface of the protective layer or scratching the surface of the protective layer, which causes an error when reading the information. Therefore, in order to correct such an error, the redundancy of the data with respect to the information to be recorded must be increased, resulting in a decrease in the capacity of the optical disc.

SUMMARY OF THE INVENTION In order to solve the above problems, it is an object of the present invention to provide an optical storage medium capable of high density write / read by reducing optical aberration caused by the mechanical properties of the substrate.

According to this invention, an optical disc used with a light beam for reading and writing information provides a pre-formatted relief for storing information on one surface of a substrate, while maintaining a substantially flat shape. A substrate having a; A thin film reflection layer placed on the one surface to reflect an incident light beam used to write or read information; A recording layer on the thin film reflection layer and storing information; A transparent first transmission layer overlying the thin film reflection layer and having a thickness and a first refractive index that is thicker than the depth of the preformatted structure of the substrate; A transparent second transparent layer overlying the first transparent layer and having a second refractive index less than the first refractive index and a thickness of the same order as the substrate; And a transparent third transmission layer overlying the second transmission layer and having a third refractive index close to the first refractive index and a thickness close to the second transparent layer.

In accordance with the present invention, a double-sided optical storage medium used in conjunction with a light beam for reading and writing information has both surfaces that provide a preformatted structure for storing information on each surface of the substrate and is substantially flat. A substrate having a thickness that maintains form; A thin film reflection layer placed on each surface to reflect an incident light beam used for writing or reading information; A recording layer on each of the thin film reflection layers and storing information; A transparent first transmission layer overlying each of the recording layers and having a thickness and a first refractive index that is thicker than the depth of the preformatted structure of the substrate; A transparent second transparent layer overlying each of the first transparent layers and having a second refractive index less than the first refractive index and a thickness of the same order as the substrate; And a transparent third transparent layer overlying each of the second transparent layers and having a third refractive index close to the first refractive index and a thickness close to the second transparent layer.

An optical disc used with a light beam for reading information includes a substrate having a thickness that maintains a substantially flat shape, providing a relief of a pre-formatted structure for storing information on one surface of the substrate; A thin film reflection layer disposed on the one surface and reflecting an incident light beam used to read information; A transparent first transmission layer overlying the thin film reflection layer and having a thickness and a first refractive index that is thicker than the depth of the preformatted structure of the substrate; A transparent second transparent layer overlying the first transparent layer and having a second refractive index less than the first refractive index and a thickness of the same order as the substrate; And a transparent third transmission layer overlying the second transmission layer and having a third refractive index close to the first refractive index and a thickness close to the second transparent layer.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

2 shows a monolayer structure of a rewritable optical disc according to the present invention. The optical disc 20 shown in FIG. 2 includes a substrate 21, a recording layer 23, a first transmission layer 25, a second transmission layer 27, and a third transmission layer 29. In the case of this optical disk 20, a light beam used for reading or writing information is incident on the third transmission layer 29.

Mechanical properties such as warpage, tilt and the like are determined by the substrate 21. Therefore, if the thickness of the substrate 21 is properly maintained, deterioration of mechanical characteristics can be prevented. In other words, it is possible to prevent the deterioration of mechanical properties that occur when the thickness of the substrate is reduced to reduce the coma. The thickness of the substrate 21 has a thickness within a range satisfying the recording / reproducing characteristics of the recording-only DVD (DVD-ROM) and the DVD-RAM, and the thickness ranges from 0.3 mm to 0.9 mm.

The substrate 21 has a relief, for example recording pits or grooves, of a pre-formatted structure on its upper surface, a reflective layer (not shown) is formed on the upper surface on which the recording pits or grooves are formed and on the recording layer. 23 is formed. Then, on the recording layer 23, a first transparent layer 25 which serves to protect the recording layer from corrosion is formed. The first transmission layer 25 needs to have a thickness such that the diffraction characteristics of the recording / reproducing light beam are not affected by the first transmission layer 25. In order to satisfy this condition, the first transparent layer 25 has a thickness larger than the depth of recording pits or grooves formed in the substrate 21, and the thickness is 100 m or less. The first transmission layer 25 is also transparent to the wavelength of the recording / reproducing light beam.

The first transparent layer 25 is not required for the optical disc of the write-once type such as the hole ablation method. This is because the write-once optical disc does not have a separate recording layer. For reference, the hole melting elimination method is a method of recording information by making a portion which does not reflect the light beam on the reflective layer of the optical disk.

When a light beam for reading or writing information is incident on the optical disc 20 through the third transmission layer 29, the optical aberration is affected by the third transmission layer 29. Therefore, when writing or reading information on the optical disk 20, an increase in aberration caused when using short wavelength light and a high numerical aperture (NA) optical head, as can be seen from the above equation (1), The thickness can be canceled by reducing the thickness of the three permeable layers 29. When the third transparent layer 29 has a larger refractive index than the second transparent layer 27, the second transparent layer 27 and the third transparent layer 29 may reduce the size of the incident light beam. The third transparent layer 29 has a refractive index of approximately 1.5 to 1.6, and the second transparent layer 27 has a refractive index much less than the third transparent layer 29, for example, a refractive index close to one. The third transmission layer 29 is made of a material which is transparent to the wavelength of the incident light beam and allows the birefringence generated in the third transmission layer 29 to be within a range that does not affect recording and reproduction, and the thickness thereof is 0.1 to 0.5. has a range between mm. The second transparent layer 27 has a thickness in the range of 0.1 mm to 0.9 mm. The sum of the thicknesses of the second permeable layer 27 and the third permeable layer 29 is such that dust on the outer surface of the third permeable layer 29 and defects in the third permeable layer 29 are written or read. It is in the range of 0.4 to 1.2mm to reduce the effect on the signal.

3 shows a read-only optical disc embodying the present invention. In the optical disc 30 shown in Fig. 3, the lower substrate 31 is ejected using a stamper having a minimum recording mark of 0.25 mu m, modulated using a track pitch of 0.37 mu m, an 8 to 14 modulation plus (EFM +). Produced by molding. The lower substrate 31 has a thickness of 0.6 mm. The reflective layer 33 overlying the substrate 31 is formed by applying aluminum (Al) using a sputtering method. The protective layer 35 serving as the first transparent layer 25 is formed by applying an ultraviolet curable resin using spin coating, and has a thickness of about 10 μm and a refractive index of about 1.5 to 1.60.

As can be seen from the description with reference to FIG. 2, the second transparent layer 27 needs to have a much lower refractive index than the third transparent layer 29 having a refractive index of approximately 1.5. Therefore, the optical disc 30 has an air layer 37 serving as a second transmission layer, which is formed by a spacer 36 installed on the inner and outer circumferences of one surface of the optical disc 30. do. The thickness of the air layer 37, that is, the distance between the protective layer 35 and the upper transparent plate 39 serving as the third transparent layer is 0.3 mm. The spacer 36 is provided at a position not including the information recording area of the optical disc 30, and has a size within a range in which mechanical characteristics of the substrate 31 are not deteriorated.

The spacer 36 may be manufactured integrally with the transparent plate 31 or the substrate 39. In this case, the spacer 36 includes spacer members 36a and 36b protruding from surfaces located at the inner and outer peripheral portions of the transparent plate 31 or the substrate 39. 4 shows spacer members 36a and 36b integrated with the substrate 31.

In order to match the center of the substrate 31 and the spacer 36, the outer diameter of the spacer member 36a located on the outer circumferential surface of the substrate 31 and the spacer member 36b located on the inner circumferential surface of the substrate 31. The inner diameter of is made to match with the outer diameter and the inner diameter of the board | substrate 31, respectively. In the case of a DVD, the spacer member 36a of the outer circumference is provided in a portion having a diameter range of 116 to 120 mm, and the spacer member 36b of the inner circumference is provided in a portion having a diameter range of 15 to 40 mm. The spacer member 36b of the inner circumference is installed to include the disk clamping region to prevent deterioration of mechanical properties. The transparent plate 39 is made of polycarbonate or glass having a refractive index of approximately 1.5 to 1.6, and has a thickness of 0.3 mm.

The spacer 36 having the configuration shown in FIG. 4 can be transformed into another spacer composed of a plurality of protrusions. In this case, the protrusions constituting the spacer have a shape protruding with respect to all of the inner and outer surfaces of the lower substrate 31 or the transparent plate 39, and integrally with the substrate 31 or the transparent plate 39. Is produced.

The spacer 36 shown in FIG. 3 or FIG. 4 and the spacer modified from this can also be manufactured separately from the board | substrate 31 and the transparent plate 39. In this case, the spacer is coupled to the substrate 31 and the transparent plate 39 through assembly.

When producing a rewritable optical disc or magneto-optical disc according to the present invention, a reflective layer, a dielectric layer, a recording layer, a dielectric layer, and a protective layer are sequentially applied to one surface of the optical disc onto which the light beam is incident. Then, the transparent plate serving as the air layer and the third transmission layer is sequentially placed on the protective layer.

When manufacturing a double-sided optical disc according to the present invention, the substrate has a thickness of 0.4 mm, the thickness of each air layer is 0.1 mm, and the thickness of the transparent plate is 0.3 mm. Reflective layers, recording layers, protective layers, etc., which are disposed between the air layer and the substrate are obvious to those skilled in the art of the optical storage medium, and thus detailed description thereof will be omitted.

5A and 5B are views for comparing and comparing an existing optical disc with an optical disc according to the present invention. The conventional optical disc shown in FIG. 5A has a recording layer 52 and a protective layer 53 formed on the substrate 51, and the light beam focused by the objective lens 50 is recorded through the protective layer 53. To form a beam spot. Existing optical disks having such a structure are disclosed in US Pat. No. 5,202,880. 5b shows an optical disc according to the invention. The optical disc shown in FIG. 5B includes a substrate 55, a recording layer 56, an air layer 57, and a transparent plate 58. When dust is on the surface of the optical disc, the light beam focused by the objective lens 50 is covered by the dust, so that information cannot be read from the existing optical disc shown in FIG. 5A. However, the optical disc according to the present invention shown in FIG. 5B includes an air layer 57 and a transparent plate having a higher refractive index than the air layer. That is, a transparent layer 58 having a high refractive index and an air layer 57 having a low refractive index are provided between the objective lens 50 and the recording layer 56. Therefore, information can be read from the optical disc with respect to the dust of the same size.

As described above, in the optical disk according to the present invention, since the light beam focused by the objective lens reaches the information recording area through the transmission layer having a relatively high refractive index and the transmission layer having a low refractive index, there is no dust or surface defects. Even in this case, information can be recorded or read on the optical disc. Incident light beams focused on the information recording area do not pass through the substrate. Therefore, there is no optical aberration caused by thinning the substrate for high density recording.

Claims (13)

In an optical disc used with a light beam for reading and writing information, A substrate having a thickness that maintains a substantially flat shape, the relief of a preformatted structure for storing information on one surface of the substrate; A thin film reflection layer placed on the one surface to reflect an incident light beam used to write or read information; A recording layer on the thin film reflection layer and storing information; A transparent first transmission layer overlying the thin film reflection layer and having a thickness and a first refractive index that is thicker than the depth of the preformatted structure of the substrate; A transparent second transparent layer overlying the first transparent layer and having a second refractive index less than the first refractive index and a thickness of the same order as the substrate; And And a transparent third transmission layer overlying the second transmission layer and having a third refractive index close to the first refractive index and a thickness close to the second transparent layer. The optical disc of claim 1, wherein the substrate has a thickness in a range of 0.3 mm to 0.9 mm. The optical disc of claim 1, wherein the first transparent layer has a refractive index of about 1.5 to 1.60. The optical disc of claim 1, wherein the first transparent layer has a thickness of 100 μm or less. The optical disc of claim 1, wherein the second transparent layer is an air layer and comprises a spacer spaced apart from the first transparent layer and the third transparent layer to provide the air layer. The optical disc of claim 5, wherein the spacer is installed on an inner circumference and an outer circumference of the optical disc. The optical disc of claim 6, wherein the spacer is integrated with one of the substrate and the third transmission layer. The optical disc of claim 1, wherein the third transparent layer has a thickness in a range of 0.1 mm to 0.5 mm. 6. The optical disc of claim 5, wherein the sum of the thicknesses of the air layer and the third transparent layer is in the range of 0.4 to 1.2 mm. In double-sided optical storage media used with light beams for reading and writing information, A substrate having both surfaces having a pre-formatted structure for storing information on each surface of the substrate, the substrate having a thickness that maintains a substantially flat shape; A thin film reflection layer placed on each surface to reflect an incident light beam used for writing or reading information; A recording layer on each of the thin film reflection layers and storing information; A transparent first transmission layer overlying each of the recording layers and having a thickness and a first refractive index that is thicker than the depth of the preformatted structure of the substrate; A transparent second transmission layer overlying each of the first transmission layers and having a second refractive index less than the first refractive index and a thickness of the same order as the substrate; And And a transparent third transmission layer overlying each of the second transmission layers and having a third refractive index close to the first refractive index and a thickness close to the second transparent layer. The double-sided optical storage medium of claim 10, wherein the second transparent layer is an air layer and comprises a spacer spaced apart from the first transparent layer and the third transparent layer to provide the air layer. In a read-only optical disc used with a light beam for reading information, A substrate having a thickness that maintains a substantially flat shape, the relief of a preformatted structure for storing information on one surface of the substrate; A thin film reflection layer disposed on the one surface and reflecting an incident light beam used to read information; A transparent first transmission layer overlying the thin film reflection layer and having a thickness and a first refractive index that is thicker than the depth of the preformatted structure of the substrate; A transparent second transparent layer overlying the first transparent layer and having a second refractive index less than the first refractive index and a thickness of the same order as the substrate; And And a transparent third transmission layer overlying the second transmission layer and having a third refractive index close to the first refractive index and a thickness close to the second transparent layer. 13. The optical disc of claim 12, wherein the second permeable layer is an air layer and comprises a spacer spaced apart from the first permeable layer and the third permeable layer to provide the air layer.

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