JP2002269855A - Optical recording medium - Google Patents

Abstract

(57) [Problem] To provide a flexible optical recording medium without permanent deformation that adversely affects recording and reproduction by the Bernoulli method. An optical recording medium having a metal reflective layer, a first protective layer, an optical recording layer, and a second protective layer in this order on a flexible substrate, wherein each of the layers is formed by sputtering in a vacuum, and When the accumulated electric energy of the sputtering is 2
An optical recording medium having a power of 7 kWs or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible optical recording medium in which information storage layers are formed on a flexible substrate without giving much heat damage to the substrate.

[0002]

2. Description of the Related Art Conventionally, as an information recording disk commercialized by forming a recording layer on a flexible substrate, Japanese Patent No.
For example, there is a magnetic disk contained in a hard cartridge shown in, for example, Japanese Patent No. 607577. As an example of application to an optical disk, there is Japanese Patent No. 2942430 and the like. According to the present invention, a flexible substrate is rotated at a high speed on a Bernoulli surface, and an air bearing is formed by the generated air flow to suppress surface deviation during rotation to perform good recording / reproduction. An optical disk is formed by forming a pre-groove by sputtering or the like, and forming each layer for information storage thereon by sputtering or the like. For this flexible optical disk, recording and reproduction are performed by using a Bernoulli stabilizing device as disclosed in Japanese Patent Application Laid-Open No. 5-114227 to reduce surface shake and condensing light.

[0003] However, the stabilization by the Bernoulli stabilizing device is effective for a large umbrella-shaped warpage of a disk because of the use of an air bearing, but it completely removes a small period of a few millimeters. Is difficult. Patent No. 294
In No. 2430, the surface runout is reduced by increasing the rigidity of the outer peripheral portion of the disk, but the method of increasing the rigidity of the outer peripheral end is effective for large-period surface runout and warpage, but is effective for small-period warpage. Is not effective. In order to perform stable recording and reproduction without being affected by the small period warpage, it is necessary to improve the response of the focus servo of the optical pickup on the high-speed side, which is not easy. There is a demand for producing a flexible optical disk having a small warpage without permanent deformation. However, since the flexible substrate is vulnerable to temperature rise and easily wrinkles during film formation, it is necessary to suppress the temperature rise during film formation.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a flexible optical recording medium free from permanent deformation that adversely affects the recording and reproduction by the Bernoulli method.

[0005]

Means for Solving the Problems The above problems are as follows:
The invention is solved by the invention 7) (hereinafter referred to as Inventions 1 to 7). 1) An optical recording medium having a reflective layer, a first protective layer, a recording layer, and a second protective layer in this order on a flexible substrate, wherein each of the layers is formed by sputtering in a vacuum, and integration of the sputtering is performed. An optical recording medium having an electric power of 27 kWs or less. 2) the second protective layer is 1 characterized in that a mixture of GeS ₂ or GeS ₂ and an inorganic oxide), wherein the optical recording medium. 3) The optical recording medium according to 2), wherein the second protective layer is made of a mixture of GeS ₂ and SiO ₂ . 4) The optical recording medium according to 2), wherein the second protective layer is made of a mixture of GeS ₂ and Nb ₂ O ₃ . 5) The optical recording medium according to any one of 1) and 4), wherein the reflective layer is mainly composed of Ag. 6) The optical recording medium according to 5), wherein the first protective layer does not contain sulfide and mainly contains oxide, nitride, or carbide. 7) The first protective layer is made of SiC, ZnO-Al
₂ O ₃ , SiAlxNy (x and y are arbitrary numbers), In ₂
The optical recording medium according to 6), wherein any one of O ₃ -SnO ₂ is a main component.

Hereinafter, the present invention will be described in detail. In the flexible optical disk of the present invention, when forming each layer for information storage by sputtering in a vacuum, the integrated discharge power of the sputtering cathode per disk is set to 27 kWs or less, and the temperature rise during film formation is suppressed. This suppresses the thermal deformation of the substrate and reduces the warpage of a small cycle. Therefore, it is desirable to select and use a material having high sputtering efficiency for the reflective layer and the protective layer. For the reflective layer, use a material containing Ag as a main component, and for the second protective layer, which is the thickest protective layer, a sputtering efficiency. Good G
It is preferable to use eS ₂ material. FIG. 1 shows a cross-sectional structure of a flexible optical disk of the present invention. A reflective layer, a first protective layer, a recording layer, and a second protective layer are formed on a flexible substrate. The flexible substrate is formed of a sheet or film of polyester, polyimide, polycarbonate, or the like.

FIG. 2 shows the relationship between the integrated discharge power and the amount of warpage of a flexible disk when a pure Ag film is formed on a disk-shaped polyester sheet having a diameter of 120 mm and a thickness of 70 μm. Specifically, a single-wafer sputtering apparatus for forming a disk medium thin film having a diameter of 120 mm is provided with a diameter of 2 mm.
The stationary opposing sputtering was performed by attaching a pure Ag target of 00 mm, and the removed flexible disk was rotated at 3600 rpm by a drive, and the runout was evaluated by a laser displacement meter. Even if the flexible disk is largely warped before rotation, a large amount of warp can be removed by rotation due to centrifugal force and air resistance. However, since a permanently deformed flexible disk does not have a large surface deviation even when rotated, a film must be formed so as not to be permanently deformed. If the accumulated power exceeds 27 kWs, permanent deformation is suddenly caused and warpage is increased. If a substrate material with good heat resistance such as polyimide is used, the integrated power can be increased.However, considering that the material cost is high and that the pregroove is formed by thermal transfer, the heat resistance is too high as a substrate material if possible. Preferred are polyester and polycarbonate. In addition, it is preferable that each layer for information storage can be formed without applying heat as much as possible.

When a multilayer film is formed, the film is not formed with one cathode. For example, in the case of a four-layer structure, if the substrate is in close contact with the substrate holder during the movement time between chambers, heat escapes and cools down. Therefore, in the case of 4 cathodes, 27
No deformation of the sheet occurred up to about kWs. However, a dielectric is generally used for the first and second protective layers,
Because of the hardness, the sputter rate is low, and the integrated power amount is large. In response to this problem, among the sulfides having relatively high rates, the rate of the GeS ₂ material is particularly high,
It was found that the recording / reproducing characteristics were also good.
The integrated electric energy of the layer could be reduced to 27 kWs or less.
Further, since the Ag-based reflective layer is deteriorated by sulfuration, sulfide cannot be used for the first protective layer. However, in the present invention, SiC, ZnO-Al ₂
O ₃ , SiAlxNy (x and y are arbitrary values), In ₂ O
With ₃ -SnO _2, small thermal damage to the substrate can be a direct current sputtering, and oxides These include nitrides have also found that high relatively sputter rate in the carbide.

[0009]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples. The flexible optical disk was rotated at 3600 rpm, and the amount of runout was measured at a position with a radius of 55 mm using a laser displacement meter. In addition, laser wavelength 405 nm, NA
Using a 0.85 optical head, 1-7 modulated random data was recorded, and the recording / reproducing characteristics were evaluated by observing jitter. The recording density is 0.26 μm / bit.

EXAMPLE 1 A spiral groove having a track pitch of 0.66 μm, a groove width of 0.33 μm, and a depth of 30 nm was formed on a polyethylene terephthalate (PET) film having a diameter of 120 mm and a thickness of 30 μm by thermal transfer. Each layer for information storage was formed on this film using a single-wafer sputtering apparatus in the following order. First, a 30 nm-thick pure Ag reflective layer was formed under the conditions of an argon pressure of 5 mbar, a sputtering power of 1 VDC, a discharge of 3 seconds, and an integrated power of 3 kWs. At the next cathode, an argon pressure of 2 mba
The first protective layer of SiC having a thickness of 6 nm was formed under the following conditions: r, sputtering power = DC 1 kW, discharge 6 seconds, integrated power amount 6 kWs. At the next cathode, a thickness of 1 was obtained under the conditions of an argon pressure of 3 mbar, a sputtering power of 0.5 VDC, a discharge of 1.8 seconds, and an integrated power of 0.9 kWs.
A phase change recording layer made of AgInSbTeGe having a thickness of 0 nm was formed. At the next cathode, argon pressure 3m
bar, sputtering power = high frequency 2 kW, discharge 1.
Under the conditions of 3 seconds and an integrated power amount of 2.6 kWs, the thickness is 30 nm.
A second protective layer of GeS ₂ was formed. The above integrated power amount is very small, that is, 12.5 kWs in total for four layers. In particular, the sputtering rate of GeS ₂ used for the second protective layer is several times higher than that of ZnS—SiO ₂ generally used in a phase-change recording medium, and is therefore extremely effective in reducing thermal damage. is there. Next, an ultraviolet curable resin was applied on the second protective layer by a spinner and cured to form a protective layer having a thickness of 4 μm. This flexible optical disk is loaded at a linear velocity of 2
m / s, laser feed 20 μm / rotation, laser power 500 mW, laser beam diameter = minor axis 3 μm, major axis 100
Initial crystallization was performed with a laser beam of μm. The drive used for the evaluation has an elliptical Bernoulli guide with a short diameter of 15 mm and a long diameter of 35 mm on the surface facing the optical pickup with the flexible optical disk interposed therebetween. The minor axis of the Bernoulli guide was made to coincide with the radial direction of the flexible optical disk, and the flexible optical disk was mounted on the drive, and rotated on the Bernoulli guide. At this time, the optical head was evacuated, and a dynamic displacement during rotation near the focal point of the optical head was measured by a laser displacement meter. Although the flexible disk was warped by several millimeters or more in the stationary state, the runout was almost eliminated by the Bernoulli stabilization, and the maximum value of the runout was a good value of 10 μm. Also, the recording power peak 8 mW,
When recording and reproduction were performed at an erasing power of 3.3 mW and a reproducing power of 0.3 mW, the jitter was 10% or less.
After 500 repetitive rewrites, the jitter increased to 15%.

Example 2 A spiral groove having a track pitch of 0.66 μm, a groove width of 0.33 μm and a depth of 30 nm was formed by thermal transfer on a polyethylene terephthalate (PET) film having a diameter of 120 mm and a thickness of 30 μm. Each layer for information storage was formed on this film using a single-wafer sputtering apparatus in the following order. First, a 30 nm-thick pure Ag reflective layer was formed under the conditions of an argon pressure of 5 mbar, a sputtering power of 1 VDC, a discharge of 3 seconds, and an integrated power of 3 kWs. At the next cathode, an argon pressure of 2 mba
The first protective layer of SiC having a thickness of 6 nm was formed under the following conditions: r, sputtering power = DC 1 kW, discharge 6 seconds, integrated power amount 6 kWs. At the next cathode, a thickness of 1 was obtained under the conditions of an argon pressure of 3 mbar, a sputtering power of 0.5 VDC, a discharge of 1.8 seconds, and an integrated power of 0.9 kWs.
A phase change recording layer made of AgInSbTeGe having a thickness of 0 nm was formed. At the next cathode, argon pressure 3m
bar, sputtering power = high frequency 2 kW, discharge 1.
Under the conditions of 6 seconds and an integrated power amount of 3.2 kWs, the thickness is 30 nm.
A second protective layer of GeS ₂ —SiO ₂ (molar ratio of SiO ₂ 20%) was formed. The above integrated electric energy is 4 layers total 1
Very low at 3.1 kWs. In particular, G used for the second protective layer
Although the sputtering rate of eS ₂ —SiO ₂ is lower than that of GeS ₂ , Zn which is generally used in a phase-change optical recording medium is used.
It is very effective to reduce the heat damage from a high-speed several times more than that of the S-SiO _2. Next, an ultraviolet curable resin was applied on the second protective layer by a spinner and cured to form a protective layer having a thickness of 4 μm. This flexible optical disk is fed at a linear velocity of 2 m / s and a laser feed of 20 μm.
/ Rotation, laser power 500mW, laser beam aperture =
Initial crystallization was performed using laser light having a minor axis of 3 μm and a major axis of 100 μm. The drive used for the evaluation is a short diameter of 15 m on the opposite surface of the optical pickup with the flexible optical disk in between.
m, an elliptical Bernoulli guide having a major axis of 35 mm. The minor axis of the Bernoulli guide was made to coincide with the radial direction of the flexible optical disk, and the flexible optical disk was mounted on the drive, and rotated on the Bernoulli guide. At this time, the optical head was evacuated, and a dynamic displacement during rotation near the focal point of the optical head was measured by a laser displacement meter. Although the flexible disk was warped by several millimeters or more in the stationary state, the runout was almost eliminated by the Bernoulli stabilization, and the maximum value of the runout was a good value of 12 μm. When recording and reproduction were performed at a recording power peak of 8 mW, an erasing power of 3.3 mW, and a reproducing power of 0.3 mW, the jitter was 9% or less. After repeated rewriting 500 times jitter has increased to 10%, but the deterioration of the repetitive than for GeS ₂ only the second protective layer is reduced. This is probably because the film became amorphous and became tough.

Example 3 A spiral groove having a track pitch of 0.66 μm, a groove width of 0.33 μm and a depth of 30 nm was formed by thermal transfer on a polyethylene terephthalate (PET) film having a diameter of 120 mm and a thickness of 30 μm. Each layer for information storage was formed on this film using a single-wafer sputtering apparatus in the following order. First, under the conditions of an argon pressure of 5 mbar, a sputtering power of 1 kW DC, a discharge of 3 seconds, and an integrated power amount of 3 kWs, a 30 nm-thick Ag-2 mol% Cu
Was formed. In the next cathode, a 6 nm thick Z was formed under the conditions of an argon pressure of 2 mbar, a sputtering power of 1 kW DC, a discharge of 4 seconds, and an integrated power amount of 4 kWs.
to form a first protective layer of _{nO-Al 2} O 3 (molar ratio 5% _Al 2 _{O 3).} At the next cathode, a thickness of 1 was obtained under the conditions of an argon pressure of 3 mbar, a sputtering power of 0.5 VDC, a discharge of 1.8 seconds, and an integrated power of 0.9 kWs.
A phase change recording layer made of AgInSbTeGe having a thickness of 0 nm was formed. At the next cathode, argon pressure 3m
bar, sputtering power = DC 2 kW, discharge 1 second,
GeS ₂ with a thickness of 30 nm under the condition of an integrated power amount of 2 kWs
Was formed -Nb ₂ O ₃ second protective layer (molar ratio of 20% _Nb 2 _{O 3).} The above integrated power amount is 9.9 kW in total for four layers.
Very small with s. In particular, GeS ₂ -N used for the second protective layer
Since b ₂ O ₃ has conductivity in the target and can be sputtered by direct current, the sputter rate is high, and the thermal damage to the substrate is small as compared with the high frequency. In this embodiment, since all the sputtered films can be formed by direct current, the film forming apparatus can be simplified, which is extremely useful. Next, an ultraviolet curable resin was applied on the second protective layer by a spinner and cured to form a protective layer having a thickness of 4 μm. This flexible optical disk is supplied at a linear velocity of 2 m / s and a laser feed of 20 μm.
m / rotation, laser power of 500 mW, laser beam diameter = short diameter 3 μm, and long-term diameter 100 μm. The drive used for the evaluation has a short diameter of 15 mm on the opposing surface of the optical pickup with the flexible optical disk in between.
mm and an elliptical Bernoulli guide having a major axis of 35 mm. The short axis of the Bernoulli guide was made to coincide with the radial direction of the flexible optical disk, and the flexible optical disk was mounted on the drive, and rotated on the Bernoulli guide. At this time, the optical head was evacuated, and a dynamic displacement during rotation near the focal point of the optical head was measured by a laser displacement meter. Although the flexible disk was warped by several millimeters or more in the stationary state, the runout was almost eliminated by the Bernoulli stabilization, and the maximum value of the runout was a good value of 10 μm. When recording and reproduction were performed at a recording power peak of 9 mW, an erasing power of 3.6 mW, and a reproducing power of 0.3 mW, the jitter was 7% or less. After repeated rewriting 500 times increased the jitter of 8%, but the deterioration of the repetitive than for GeS ₂ only the second protective layer is reduced. This is probably because the film became amorphous and became tough.

Example 4 A spiral groove having a track pitch of 0.66 μm, a groove width of 0.33 μm and a depth of 30 nm was formed on a polyethylene terephthalate (PET) film having a diameter of 120 mm and a thickness of 30 μm by thermal transfer. Each layer for information storage was formed on this film using a single-wafer sputtering apparatus in the following order. First, under the conditions of an argon pressure of 5 mbar, a sputtering power of 1 kW DC, a discharge of 3 seconds, and an integrated power of 3 kWs, a 30 nm-thick Ag-0.7 mol%
A reflective layer of Pd-0.5 mol% Cu was formed. At the next cathode, gas (mixed gas of argon + 30% nitrogen by volume) pressure 2 mbar, sputtering power = DC 1
kW, discharge 3 seconds, integrated power 3kWs, thickness 6
nm SiAlxNy (x and y are arbitrary values, Si and Al
(The molar ratio of Si is 80%). At the next cathode, a 10 nm-thick AgInS under the conditions of an argon pressure of 3 mbar, a sputtering power of 0.5 kW DC, a discharge of 1.8 seconds, and an integrated power of 0.9 kWs.
A phase change type recording layer made of bTeGe was formed. At the next cathode, argon pressure 3 mbar, sputtering power = DC 2 kW, discharge 1 second, integrated power 2 kWs
Under the conditions described above, a GeS ₂ —Nb ₂ O ₃ (Nb
(Molar ratio of ₂ O ₃ 20%) was formed. The above integrated power amount is very small, that is, 8.9 kWs in four layers. In particular, GeS ₂ —Nb ₂ O ₃ used for the second protective layer has conductivity in the target and can be sputtered with direct current, so that the sputtering rate is high, and the thermal damage to the substrate is small as compared with the high frequency. In this embodiment, since all the sputtered films can be formed by direct current, the film forming apparatus can also be simplified,
Extremely useful. Next, an ultraviolet curable resin was applied on the second protective layer by a spinner and cured to form a protective layer having a thickness of 4 μm. This flexible optical disk was initially crystallized with a laser beam having a linear velocity of 2 m / s, a laser feed of 20 μm / rotation, a laser power of 500 mW, a laser beam diameter of 3 μm, and a major axis of 100 μm. The drive used for the evaluation has a short diameter of 15 mm and a long diameter of 35 mm on the opposing surface of the optical pickup with the flexible optical disk interposed therebetween.
Has an elliptical Bernoulli guide. The minor axis of the Bernoulli guide was made to coincide with the radial direction of the flexible optical disk, and the flexible optical disk was mounted on the drive, and rotated on the Bernoulli guide. At this time, the optical head was evacuated, and a dynamic displacement during rotation near the focal point of the optical head was measured by a laser displacement meter. The flexible disk was warped by several millimeters or more in the stationary state, but the runout was almost eliminated by Bernoulli stabilization, and the maximum value of the runout was 1
The value was as good as 0 μm. Further, a peak recording power of 8 mW, an erasing power of 3.1 mW, and a reproducing power of 0.3 mW.
As a result, the jitter was 10% or less. After 500 repetitions, the jitter is 10
%.

Example 5 A spiral groove having a track pitch of 0.66 μm, a groove width of 0.33 μm and a depth of 30 nm was formed by thermal transfer on a polyethylene terephthalate (PET) film having a diameter of 120 mm and a thickness of 30 μm. Each layer for information storage was formed on this film using a single-wafer sputtering apparatus in the following order. First, a 30 nm-thick pure Ag reflective layer was formed under the conditions of an argon pressure of 5 mbar, a sputtering power of 1 VDC, a discharge of 3 seconds, and an integrated power of 3 kWs. At the next cathode, an argon pressure of 2 mba
r, sputtering power = DC 1 kW, discharge 3.5 seconds,
Under the condition of an integrated power amount of 3.5 kWs, In ₂ having a thickness of 6 nm
A first protective layer of O ₃ —SnO ₂ (40% by mole of SnO ₂ ) was formed. At the next cathode, an argon pressure of 3
mbar, sputtering power = DC 0.5 kW, discharge 1.8 seconds, integrated power amount 0.9 kWs, thickness 10
A phase change type recording layer made of AgInSbTeGe with a thickness of nm was formed. At the next cathode, an argon pressure of 3 mb
ar, sputtering power = high frequency 2 kW, discharge 1.3
Sec, under the condition of integral power consumption 2.6KWs, to form a second protective layer of GeS ₂ thick 30 nm. The above integrated power amount is very small, that is, 10 kWs in total for four layers. Next, an ultraviolet curable resin was applied on the second protective layer by a spinner and cured to form a protective layer having a thickness of 4 μm. This flexible optical disk is fed at a linear velocity of 2 m / s and a laser feed of 20 μm.
/ Rotation, laser power 500mW, laser beam aperture =
Initial crystallization was performed using laser light having a minor axis of 3 μm and a major axis of 100 μm. The drive used for the evaluation is a short diameter of 15 m on the opposite surface of the optical pickup with the flexible optical disk in between.
m, an elliptical Bernoulli guide having a major axis of 35 mm. The minor axis of the Bernoulli guide was made to coincide with the radial direction of the flexible optical disk, and the flexible optical disk was mounted on the drive, and rotated on the Bernoulli guide. At this time, the optical head was evacuated, and a dynamic displacement during rotation near the focal point of the optical head was measured by a laser displacement meter. Although the flexible disk was warped by several millimeters or more in the stationary state, the runout was almost eliminated by the Bernoulli stabilization, and the maximum value of the runout was a good value of 10 μm. When recording and reproduction were performed at a recording power peak of 8 mW, an erasing power of 3.3 mW, and a reproducing power of 0.3 mW, the jitter was 10% or less. After 500 repetitive rewrites, the jitter increased to 14%.

Comparative Example 1 A spiral groove having a track pitch of 0.66 μm, a groove width of 0.33 μm and a depth of 30 nm was formed by thermal transfer on a polyethylene terephthalate (PET) film having a diameter of 120 mm and a thickness of 30 μm. Each layer for information storage was formed on this film using a single-wafer sputtering apparatus in the following order. First, a 30 nm thick Al-1 wt% Ti reflective layer was formed under the conditions of an argon pressure of 5 mbar, a sputtering power of DC 2.5 kW, a discharge of 3 seconds, and an integrated power of 7.5 kWs. At the next cathode,
Argon pressure 2 mbar, sputtering power = RF 1 kW, discharge 2.9 seconds, under conditions of integrated electricity 2.9KWs, forming a first protective layer having a thickness of 6nm _ZnS-SiO 2 (molar ratio of SiO ₂ 20%) did. At the next cathode, the argon pressure was 3 mbar, the sputtering power was 0.5 kW DC, the discharge was 1.8 seconds, and the accumulated power was 0.9 kWs.
Under these conditions, a phase-change recording layer made of AgInSbTeGe and having a thickness of 10 nm was formed. At the next cathode,
Under the conditions of argon pressure 3 mbar, sputtering power = high frequency 2 kW, discharge 15 seconds, integrated power amount 30 kWs,
To form a second protective layer of ZnS-SiO ₂ having a thickness of 30 nm. Note that a 30 kWs discharge at a stretch was obviously too large in thermal stress, so that three cathodes were used and five seconds of film formation were divided into three times. The above integrated power amount is 41.3k in four layers
Ws. Next, an ultraviolet curable resin was applied on the second protective layer by a spinner and cured to form a protective layer having a thickness of 4 μm. However, after film formation, the run-out was measured by stabilizing Bernoulli in the same manner as in the example, but a residual run-out of 50 μm or more remained. Occasional noise which occasionally slides with the guide was also generated, and it was judged that the recording / reproduction was not endurable.

Comparative Example 2 A reflective layer, a first protective layer, and a reflective layer were formed in the same manner as in Comparative Example 1 except that a polycarbonate film having a thickness of 70 μm was used.
Although the phase-change recording layer and the second protective layer were laminated, the flexible optical disc after film formation was clearly permanently deformed, and was in a state that could not withstand spin coating of an ultraviolet curable resin.

[0017]

According to the first aspect of the present invention, it is possible to reduce the thermal damage in producing a flexible optical disk by forming each information storage layer on a flexible substrate by sputtering, thereby preventing permanent deformation of the substrate. It is possible to reduce the warpage and surface runout to the extent that recording and reproduction are possible by stabilizing Bernoulli, and it is possible to record and reproduce stably without extending the high frequency band of the focus servo. Further, according to the second aspect of the present invention, the sputter rate of the second protective layer is high,
Sputtering power can be reduced, and thermal damage can be reduced. According to the third aspect of the present invention, in addition to the above effects, Ge
Strong protective layer is obtained for the thermal stress repeatedly rewritten a tough than S ₂ alone. According to the fourth aspect, in addition to the above effects, the second protective layer can also be formed with a direct current, so that all the layers can be formed with a direct current, and the film forming apparatus is simplified. According to the fifth aspect of the present invention, Ag has a high sputter rate, can reduce sputtering power, and can reduce thermal damage.
According to the sixth aspect, it is possible to prevent the Ag reflective layer from being degraded by sulfurization. According to the seventh aspect of the present invention, furthermore, direct current sputtering can be performed and thermal stress can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross section of a flexible optical disk of the present invention.

FIG. 2 is a diagram illustrating a relationship between an integrated power amount and a warp amount of a flexible sheet.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/24 534 B41M 5/26 X (72) Inventor Hidenori Ito 1-3-3 Nakamagome, Ota-ku, Tokyo No. 6 Inside Ricoh Company, Ltd. (72) Inventor Yuji Ito 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Inside Ricoh Company (72) Shozo Murata 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Company Ricoh F-term (reference) 2H111 FA01 FA12 FA14 FA23 FA25 FA27 GA03 5D029 KA01 KA30 LA11 LA12 5D121 AA01 AA02 AA03 EE01 EE03 EE30

Claims (7)

[Claims] 1. An optical recording medium having a reflective layer, a first protective layer, a recording layer, and a second protective layer in this order on a flexible substrate, wherein each of the layers is formed by sputtering in a vacuum, and Integrated power of sputtering is 27kW
s or less. Wherein said second protective layer, GeS ₂ or GeS
_2. The optical recording medium according to claim 1, comprising a mixture of ₂ and an inorganic oxide. 3. The method according to claim 1, wherein the second protective layer is formed of GeS ₂ and SiO _2.
The optical recording medium according to claim 2, comprising a mixture of the following. 4. The method according to claim 1, wherein the second protective layer is formed of GeS ₂ and Nb ₂ O.
_3. An optical recording medium according to claim 2, wherein said optical recording medium comprises a mixture of ( ₃ ). 5. The optical recording medium according to claim 1, wherein the reflection layer is mainly composed of Ag. 6. The optical recording medium according to claim 5, wherein the first protective layer does not contain sulfide and contains oxide, nitride or carbide as a main component. 7. The first protective layer is made of SiC, ZnO-A.
l ₂ O ₃ , SiAlxNy (x and y are arbitrary values), In
₂ O ₃ The optical recording medium according to claim 6, wherein the one of -SnO ₂ as a main component.