JPH0973661A - Optical information recording medium and optical recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information recording medium with which the recording taking advantage of a current compact disk technique as far as possible or the erasure of the record is possible. SOLUTION: This optical information recording medium is constituted by forming a recording layer for recording the information modulated in mark length by detecting optical changes on a substrate provided with concentric or spiral grooves and is so constituted as to record the information in these grooves. At this time, the reflectivity of the parts where there are no grooves is 15 to 40%. The push-pull intensity PP after the recording defined by the following equation (1) is 0.12 to 0.25. PP=111-121/Itop (where value at the time of an offset of 0.1μm in a radial direction)...(1) equation. In the equation, 111-121 is the difference of the light quantity of the bisected photodetectors, Itop is the top level at the time of reproducing the longest mark signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recordable or recordable optical information recording medium which makes the best use of the current compact disc technology.

[0002]

2. Description of the Related Art Optical discs include a read-only type, an optical recordable type, and a rewritable type.
It has already been put to practical use as an audio disk, and even as a large-capacity computer disk memory. Among them, compact discs (CDs) are widely used as disc memories for audio reproduction of music and the like and computers.

A compact disc (CD) is a CD-formatted EFM (Eight to Four).
(Teen Modulation) signal hole (pit)
Is transferred to a substrate made of plastic, and a reflective film and a protective layer made of metal such as aluminum are provided thereon. The reading of information from a CD is performed by irradiating a semiconductor laser beam from the substrate side and irradiating the optical disc, and by changing the reflectance depending on the presence or absence of pits, C
The D format signal or the like is read.

Further, the wavelength of the laser used is shortened and the NA is increased.
It is being studied to further increase the capacity by increasing the capacity and reducing the substrate thickness. However, these reproduction-only discs cannot record / edit or rewrite information. software,
CD for data files, files such as still images
Optical recording / erasable optical discs for ROM (Read only memory) or CD-I (interactive) are desired.

On the other hand, typical examples of the optical recordable type are the hole punching / deforming type, the magneto-optical type and the phase change type. A recording layer made of a low melting point metal such as Te or a dye is used as the perforation / deformation type, and is locally heated by laser light irradiation,
Holes or recesses are formed. The magneto-optical type performs recording and erasing according to the direction of magnetization of the recording layer and reproduces by the magneto-optical effect, and therefore has a reproducing principle different from that of a CD drive that utilizes the difference in reflectance.

As a disc for recording a CD format signal, an optical disc having a recording layer made of a dye or a polymer containing the dye on a substrate, and an optical information recording method using the optical disc have been proposed (Japanese Patent Laid-Open Publication No. Sho. No. 61-237239, 61-233943), these optical disks cannot be rewritable.

On the other hand, the phase-change type utilizes the fact that the reflectance changes before and after the phase change, and is common to the CD in that the reproduction is performed by the difference in reflectance without the need for an external magnetic field. There is. Further, there is an advantage that recording / erasing can be performed only by modulating the power of laser light, and one-beam overwriting in which erasing and re-recording are simultaneously performed with a single beam is also possible.

Therefore, the rewritable medium of the CD is preferably a phase change type, and it is preferable to determine the push-pull signal or the like under conditions advantageous for the phase change medium. In the one-beam overwritable phase change recording method, it is general that the recording film is made amorphous to form a recording bit and is crystallized to erase.

As a recording layer material used in such a phase change recording system, a chalcogen alloy thin film is often used. For example, Ge-Te system, Ge-Te-Sb
System, In-Sb-Te system, Ge-Sn-Te system, Ag-
In-Sb-Te type alloy thin film etc. are mentioned. In order to use the phase change medium as a rewritable CD, it is a standard of CD, which is a recordable compact disk.
Systems Part II: CD-WO Ve
Standards for version 2.0 (Editor: Sony Cor
p. & N.K. V. A media design according to Philips, January 1994) is preferred.

However, since the phase change medium has a low reflectance in many cases, it is necessary to take measures such as increasing the reproducing laser power as compared with the conventional CD drive. Signal characteristics other than reflectance, that is, values such as modulation, push-pull signal, and radial contrast can be adapted to the Orange Book standard.

[0011]

However, it has become clear that inconvenience occurs when the signal characteristics other than the reflectance of the phase change medium are adapted to the Orange Book standard.
In particular, when the push-pull signal strength is adjusted to the standard value, signal deterioration due to repeated recording is severe.

That is, it was experimentally clarified that deterioration phenomena such as increase in jitter and decrease in reflectance due to repeated recording are related to the push-pull signal strength. In order to reduce signal deterioration due to repeated recording, it is necessary to make the push-pull signal strength larger than the standard value. The groove shape of the substrate greatly affects these signal characteristics.

For example, when the groove depth is smaller than λ / (8n) (n is the substrate refractive index), the push-pull signal increases as the groove depth increases. As for the groove width, there is a groove width value at which the push-pull signal strength increases. The groove width and the groove depth similarly affect the radial contrast, the reflectance and the like.
The groove width and the groove depth are also related to the phenomenon that the reflectance gradually decreases due to repeated recording.

[0014]

According to the present invention, at least a recording layer for recording information by detecting an optical change is provided on a substrate provided with concentric circles or spiral grooves. In an optical information recording medium for recording information on
The reflectivity at the non-groove portion is 15 to 40%, and the push-pull strength PP after recording defined by the following formula (1)
Is 0.12 to 0.25, which is an optical information recording medium.

PP = | I1−I2 | / Itop (however, value at offset of 0.1 μm in radial direction) (1) where | I1−I2 | is the difference between the light amounts of the two photodetectors. , Itop are at the top level at the time of reproducing a long bit signal.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Reading of an optical groove is carried out by a servo photodetector divided into two in the radial direction of an optical disc which receives the reflected light of a light spot which moves integrally with a head or a pickup. The output I1 of the photodetector and the output I2 of the second photodetector are processed in the signal processing circuit.

When the focus position of the beam deviates from the tracking center, the push-pull signal output shows a corresponding curve. Itop is the top level when reproducing a long bit signal. Recordable Compact Di
sk Systems Part II: CD-WO
Version 2.0 Standards (Editor: Sony Co
rp. & N.K. V. Philips, January 1994), the push-pull signal strength ranges from 0.04 to 0.09.

However, in a disk in which the push-pull signal strength falls within this range, deterioration of jitter and reduction of reflectance due to repetitive recording are severe. The reason for this is not always clear, but the push-pull signal strength is greatly affected by the groove shape, and is probably related to the groove shape. When the groove depth is relatively shallow, the push-pull signal strength decreases as the groove depth decreases.

If the groove is too shallow, the jitter will increase remarkably due to repeated recording. Regarding the groove width, if the width is too wide, the jitter will increase remarkably due to repetitive recording, and if the groove width is too narrow, the reflectance will decrease remarkably due to repetitive recording.
As a result, only when the push-pull signal strength was larger than the standard value, a comprehensively excellent repeated recording characteristic was obtained.

The push-pull signal strength is preferably 0.12 or more, particularly preferably 0.19 or more. If there is a large difference in push-pull signal strength, the drive cannot support it, so the upper limit is preferably 0.25 or less. When the push-pull signal strength is large, it is advantageous when the density is increased, such as narrowing the track pitch.

When the track pitch is narrowed, the maximum value of | I1-I2 | when the beam is removed from the track center becomes smaller than that when the track pitch is wide. Therefore, if the push-pull signal strength is increased as in the present invention, it becomes easy to deal with higher density. In some cases, a phenomenon in which the medium reflectance gradually decreases due to repeated recording may be observed.

The cause of this phenomenon is not always clear because it does not correspond to the deterioration of jitter, but it becomes remarkable when the groove width is narrow experimentally. When the groove width is less than 0.5 μm, the reflectance is likely to be significantly reduced. Therefore, in consideration of the decrease in reflectance in addition to the repeated recording characteristics, it is most preferable to add the condition that the groove width is 0.5 μm or more to the limitation of the push-pull signal.

Expressed in terms of groove width and groove depth, the groove pitch is 1.
In the case of 5 to 1.7 μm, the groove depth is preferably 25 to 60 nm and the groove width is 0.5 to 0.8 μm. It is not always necessary to change the standard value for radial contrast. The radial contrast standard defines the relationship between the groove reflectance and the land reflectance.

According to the standard, the reflectance of the groove must be smaller than the reflectance of the land to some extent, and it is sufficiently possible to meet the radial contrast standard within the value range of the push-pull signal having excellent repetitive recording characteristics. is there. Considering the utilization of the CD technology, it is preferable not to change the radial contrast standard.

Regarding the reflectance, it becomes difficult to obtain a disk having a high contrast of recording signals when the reflectance of the groove-free portion (mirror surface portion) of the disk exceeds 40%.
On the other hand, if the reflectance is small, it means that all the signal intensities are small. Therefore, the reflectance must not be too small.
Therefore, the mirror surface reflectance is preferably 15 to 40%, and 2
0 to 35% is particularly preferable.

The material of the recording layer is G from the viewpoint of rewriting characteristics.
The eSbTe type and AgInSbTe type are particularly preferable. It is known that these materials can be overwritten by one beam. For example, Sb is added to the composition on the GeTe-Sb ₂ Te ₃ line in several at. % Added is excellent in writing and erasing characteristics.

Optically, a composition closer to GeTe tends to have a larger signal amplitude. Rewriting characteristic is Sb ₂ T
It is better to increase the content rate of e ₃ . As a layer structure, it is general that a dielectric protective layer, a phase transition type optical recording layer, a dielectric protective layer, and a reflective layer are laminated in this order on a substrate. The dielectric protective layer material used in the present invention has a refractive index, a thermal conductivity,
It is determined by paying attention to chemical stability, mechanical strength, adhesion, etc.

Generally, M, which is highly transparent and has a high melting point,
g, Ca, Sr, Y, La, Ce, Ho, Er, Yb,
Ti, Zr, Hf, V, Nb, Ta, Zn, Al, S
oxides, sulfides, nitrides such as i, Ge, Pb, Ca, M
g, a fluoride such as Li can be used. These oxides, sulfides, nitrides, and fluorides do not always need to have a stoichiometric composition, and it is also effective to control the composition for controlling the refractive index and the like, or to use a mixture.

Considering the repetitive recording characteristics, the high refractive index dielectric is preferably a mixture of a plurality of dielectrics based on ZnS.
The reflective layer is preferably made of a material having a high reflectance, such as Au, Ag,
Cu, Al, etc. are used, and Ta, for controlling thermal conductivity, etc.
A small amount of Ti, Cr, Mo, Mg, V, Nb, Zr or the like may be added.

As the substrate of the recording medium in the present invention,
It may be any of glass, plastic, glass provided with a photocurable resin, etc., but a polycarbonate resin is preferable from the viewpoint of CD compatibility. Considering that the technology of CD is utilized, it is preferable to record in the groove. Therefore, a U-shaped groove having a flat recording portion is preferable.

The recording layer, the dielectric layer and the reflective layer are formed by a sputtering method or the like. It is desirable to form a film using an in-line apparatus in which a target for a recording film, a target for a protective film, and if necessary, a target for a reflective layer material are installed in the same vacuum chamber, from the viewpoint of preventing oxidation and contamination between layers. It is also excellent in terms of productivity.

[0032]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 12 (ZnS) ₈₀ (SiO ₂ ) ₂₀ layers were formed on a disk substrate.
0 nm, Ge ₁₂ Sb ₃₆ Te ₅₂ (at.%) Layer 30n
m, (ZnS) ₈₀ (SiO ₂ ) 20 layer 20 nm, Al
A disc was prepared by sequentially stacking alloy layers of 200 nm by magnetron sputtering.

The push-pull signal strength PP of this disk after recording was measured by an optical disk evaluation device (laser wavelength 780 nm, NA 0.55) and found to be 0.23. The reflectance of the mirror surface portion was 31%, and the radial contrast RCa was 0.46.

This disk was E at 1.4 m / s, a writing laser power of 12 mW and an erasing laser power of 6 mW.
The mark jitter increase of the 3T signal after overwriting the FM random signal 1000 times was 6 ns. The groove width and the groove depth of the substrate were obtained by using the interference light intensity of the HeNe laser. The result was that the groove width was 0.67 μm and the depth was 57 n.
m, and the groove pitch was 1.6 μm.

Example 2 12 (ZnS) ₈₀ (SiO ₂ ) ₂₀ layers were formed on a disk substrate.
0 nm, Ge ₁₂ Sb ₃₆ Te ₅₂ (at.%) Layer 30n
m, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 200 nm were sequentially laminated by a magnetron sputtering method to prepare a disk.

The push-pull signal strength PP of this disc after recording was measured using an optical disc evaluation apparatus (laser wavelength 780 nm, NA 0.55) and found to be 0.15. The specular reflectance was 31% and the radial contrast RCa was 0.36.

This disk was E at 1.4 m / s, a writing laser power of 12 mW and an erasing laser power of 6 mW.
The mark jitter increase of the 3T signal after overwriting the FM random signal 1000 times was 9 ns. The groove width and the groove depth of the substrate were obtained by using the interference light intensity of the HeNe laser, and the result was that the groove width was 0.65 μm and the depth was 30 n.
m, and the groove pitch was 1.6 μm.

Example 3 12 (ZnS) ₈₀ (SiO ₂ ) ₂₀ layers were formed on a disk substrate.
0 nm, Ge ₁₂ Sb ₃₆ Te ₅₂ (at.%) Layer 30n
m, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 200 nm were sequentially laminated by a magnetron sputtering method to prepare a disk.

The push-pull signal strength PP of this disc after recording was measured using an optical disc evaluation apparatus (laser wavelength 780 nm, NA 0.55) and found to be 0.12. The specular reflectance was 31% and the radial contrast RCa was 0.44. This disc is 1.4
The increase in mark jitter of the 3T signal after overwriting the EFM random signal 1000 times at m / s, writing laser power of 12 mW, and erasing laser power of 6 mW was 9
It was ns. The groove width and the groove depth of the substrate were obtained using the interference light intensity of the HeNe laser, and the result was a groove width of 0.39 μm.
m, depth 30 nm, and groove pitch 1.6 μm.

Comparative Example 1 12 (ZnS) ₈₀ (SiO ₂ ) ₂₀ layers were formed on a disk substrate.
0 nm, Ge ₁₂ Sb ₃₆ Te ₅₂ (at.%) Layer 30n
m, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 200 nm were sequentially laminated by a magnetron sputtering method to prepare a disk.

The push-pull signal strength PP of this disc after recording was measured by an optical disc evaluation apparatus (laser wavelength 780 nm, NA 0.55) and found to be 0.11. The reflectance of the mirror surface portion was 31% and the radial contrast RCa was 0.23.

This disk was E at 1.4 m / s, a writing laser power of 12 mW and an erasing laser power of 6 mW.
3 after overwriting the FM random signal 100 times
The increase in the mark jitter of the T signal was as large as 14 ns.
The groove width and the groove depth of the substrate were obtained by using the interference light intensity of the HeNe laser, and the result was that the groove width was 1.12 μm and the depth was 26 n.
m, and the groove pitch was 1.6 μm.

Comparative Example 2 12 (ZnS) ₈₀ (SiO ₂ ) ₂₀ layers were formed on a disk substrate.
0 nm, Ge ₁₂ Sb ₃₆ Te ₅₂ (at.%) Layer 30n
m, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ layer having a thickness of 20 nm and an Al alloy layer having a thickness of 200 nm were sequentially laminated by a magnetron sputtering method to prepare a disk.

The push-pull signal strength PP of this disc after recording was measured by an optical disc evaluation apparatus (laser wavelength 780 nm, NA 0.55) and found to be 0.07. The specular reflectance was 31% and the radial contrast RCa was 0.33.

This disk was E at 1.4 m / s, writing laser power of 12 mW and erasing laser power of 6 mW.
The increase in mark jitter of the 3T signal after overwriting the FM random signal 1000 times was as large as 13 ns. The groove width and the groove depth of the substrate were obtained by using the interference light intensity of the HeNe laser, and the result was a groove width of 0.36 μm and a depth of 1
It was 7 nm and the groove pitch was 1.6 μm.

[0046]

By using the optical recording medium of the present invention, it is possible to obtain a rewritable optical information recording medium having excellent repetitive recording characteristics by utilizing the existing compact disc technology. Therefore, if a read-only type optical disc that matches the optical information recording medium of the present invention is used, it becomes easy to manufacture a drive capable of playing both a read-only type and a rewritable type. Further, in consideration of high density, the optical information recording medium of the present invention is more advantageous than the conventional CD standard.

Claims (8)

[Claims] 1. A substrate provided with concentric circles or spiral grooves is provided with at least a recording layer for recording information whose mark length is modulated by detecting an optical change, and information is recorded in the grooves. The optical information recording medium to be recorded has a reflectance of 15 to 40% at a portion having no groove.
The push-pull strength PP after recording defined by the equation is 0.
An optical information recording medium characterized by having a size of 12 to 0.25. PP = | I1-I2 | / Itop (however, value at the time of 0.1 μm offset in the radial direction) (1) where | I1-I2 | is the difference between the light amounts of the photodetectors divided into two, and Itop is Set to the top level when playing the longest mark signal. 2. The optical information recording medium according to claim 1, wherein RCa> 0.2 for the radial contrast defined by the following equation (2). RCa = 2 * (Il-Ig) / (Il + Ig) (2) Here, Il is the average reflectance of the land portion, and Ig is the average reflectance of the groove portion, which is a measured value after recording. 3. The optical information recording medium according to claim 1, wherein the information is recorded by an EFM modulated signal. 4. The optical information recording medium according to claim 2, wherein the recording layer is a phase change recording layer. 5. The phase-change recording layer is an alloy thin film containing Ge, Sb, and Te as main components, or A
The optical information recording medium according to claim 3, which is an alloy thin film containing four elements of g, In, Sb, and Te as main components. 6. The optical information recording medium according to claim 5, wherein at least a protective layer, a recording layer, a protective layer, and a reflective layer are provided in this order on the substrate. 7. The optical information according to claim 6, wherein the groove shape has a depth of 25 to 60 nm, a groove width of 0.5 to 0.8 μm, and a groove pitch of 1.5 to 1.7 μm. Recording medium. 8. An optical recording method, wherein recording / reproducing is performed on the optical information recording medium according to claim 6 at a linear velocity of 1.2 to 6.0 m / s.