Source: https://patents.google.com/patent/JP3566743B2/en
Timestamp: 2020-08-09 19:14:50
Document Index: 244909179

Matched Legal Cases: ['art 41', 'art 41', 'art 61', 'art 61', 'art 41', 'art 410', 'art\n5']

JP3566743B2 - Optical recording medium - Google Patents
JP3566743B2
JP3566743B2 JP34181893A JP34181893A JP3566743B2 JP 3566743 B2 JP3566743 B2 JP 3566743B2 JP 34181893 A JP34181893 A JP 34181893A JP 34181893 A JP34181893 A JP 34181893A JP 3566743 B2 JP3566743 B2 JP 3566743B2
JP34181893A
JPH07169094A (en
亮 稲葉
徳彦 繁田
1993-12-13 Application filed by Ｔｄｋ株式会社 filed Critical Ｔｄｋ株式会社
1993-12-13 Priority to JP34181893A priority Critical patent/JP3566743B2/en
1995-07-04 Publication of JPH07169094A publication Critical patent/JPH07169094A/en
2004-09-15 Publication of JP3566743B2 publication Critical patent/JP3566743B2/en
239000002609 media Substances 0.000 title claims description 70
238000005280 amorphization Methods 0.000 claims description 26
238000004544 sputter deposition Methods 0.000 description 13
The present invention relates to an optical recording medium that records and erases information by utilizing a change in the crystal structure of a recording layer, and more particularly to an optical recording medium that can increase track density and linear recording density.
In recent years, attention has been focused on optical recording media capable of high-density recording and capable of erasing and rewriting recorded information. Among the rewritable optical recording media, phase change optical recording media change the crystal structure of the recording layer by irradiating laser light, and detect the change in reflectivity of the recording layer. is there. In the phase change type optical recording medium, recording or erasing can be arbitrarily selected by changing the intensity of the light beam at the time of recording light irradiation, so that apparent overwrite recording using a single light beam is possible, Further, since the optical system of the driving device is simpler than that of the magneto-optical recording medium, it has been attracting attention.
Further, the phase change type optical recording medium can form a small and sharp recording mark without changing the optical system of the driving device due to a so-called self-sharpening effect. In the phase change type optical recording medium, the temperature near the center of the recording light beam spot on the surface of the recording layer is high and the heat is easily diffused, so that the cooling rate is high. On the other hand, in the vicinity of the end of the beam spot, the temperature is low and the cooling rate is slowed by thermal diffusion from near the center of the beam spot. Therefore, by setting the recording light power to an appropriate value, only the vicinity of the center of the beam spot can be made amorphous. Thereby, a small and sharp recording mark can be formed without shortening the wavelength of the recording light, and high-density recording is possible. Such an effect is usually called a self-sharpening effect. On the other hand, for example, in the magneto-optical recording medium, since the recording layer temperature at the time of recording is as low as 200 ° C. or less, it is impossible to make a small recording mark using the difference in the cooling rate in the recording light irradiation section.
Optical recording media are capable of high-density recording, but in recent years, higher-density recording is required for recording images and the like. In order to increase the recording density per unit area, there are a method of narrowing the pitch of recording tracks and a method of increasing the linear recording density by reducing the interval between recording marks. In an optical recording medium, a groove is usually provided on a substrate surface for tracking, and a recording mark is formed in the groove. When the track pitch is narrowed, the groove width is also narrowed, but when the optical system of the recording apparatus is not changed, the diameter of the beam spot of the recording light becomes larger than the groove width, so that the recording mark spans the land between the grooves. It will be. When reproducing light with a large beam spot diameter is used to reproduce an optical recording medium on which such recording has been performed, noise increases due to the influence of reflected light from the land, so the groove depth is reproduced. As 1/8 to 1/6 of the light wavelength, a method of reducing the influence of reflected light from the land by interference action is employed. However, in this method, since the groove becomes deep and the reflectance is lowered, the signal intensity is lowered and high C / N cannot be obtained. On the other hand, in the method of reducing the bit interval, if the beam spot diameter of the reproduction light in the recording layer is the same as before, the information of the recording mark adjacent in the scanning direction is expanded and this becomes noise. / N will decrease.
In order to prevent C / N reduction in reproduction of an optical recording medium having a high track density or linear recording density, it is only necessary to reduce the beam spot diameter of the reproduction light. Increasing the numerical aperture of the lens is effective. However, these are technically difficult. Therefore, there is a need for a method that can improve C / N regardless of shortening the wavelength of the reproduction light or increasing the numerical aperture.
Further, when recording a digital image or the like having a large amount of information, it is necessary to record for a long time with high density. When recording for a long time, it is necessary to lower the relative linear velocity of the medium with respect to the recording light. However, when forming a long recording mark, the irradiation end region is continuously affected by the influence of the adjacent irradiation part. Since it is heated, it will be in a slow cooling state. For this reason, uniform amorphization is not achieved and good C / N cannot be obtained, and good repeated recording characteristics cannot be obtained. Under such circumstances, it is required to prevent a C / N drop in recording at a low linear velocity.
An object of the present invention is to obtain a high C / N by a method other than shortening the numerical aperture and reproduction wavelength of an objective lens system of a reproducing apparatus when reproducing an optical recording medium having a high recording density. The objective is to prevent C / N degradation in recording at low linear velocities.
Such purposes are as follows (1) to (16This is achieved by the present invention.
(1) having a mask layer, an intermediate dielectric layer, a recording layer and a reflective layer on a transparent substrate;
The recording layer contains a recording material capable of recording information by changing the crystal structure by recording light irradiation,
The mask layer includes a mask material whose light transmittance is improved when melted, and the complex refractive index (n of the mask layer when the mask material is amorphous or microcrystalline)0 -Ik0 ) Real part n0 Reduction amount is 0.7 or less, and the imaginary part k0 An optical recording medium characterized in that the amount of decrease is 0.45 to 0.80.
(2) When the minimum value of the relative linear velocity that becomes amorphous or microcrystalline after irradiation with a light beam is defined as the amorphization linear velocity, the amorphization linear velocity of the mask layer becomes the amorphization of the recording layer. The optical recording medium according to (1), wherein the optical recording medium is faster than the linear velocity.
(3) Mask materials are A (A is Ag and / or Au), B (B is In), C (C is Te and / or Se), MI (MI Is Sb and / or Bi) and MII(MIIIs at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Mn, W and Mo), and the atomic ratio of each element in the mask material is represented by the following formula:(1) or (2)Optical recording media.
Formula {(Aa Bb C1-ab )c MI 1-c }1-d MII d
0.01 ≦ a <0.50,
0.01 ≦ b <0.50,
0.30 ≦ c ≦ 0.70,
0.001 ≦ d ≦ 0.20
(4) (1) to (1) above, wherein the mask layer contains a dielectric material.(3)Any of the optical recording media.
(5) In the mask layer, the dielectric material / (mask material + dielectric material) is 25% by volume or less.(4)Optical recording media.
(6) Recording materials are A (A is Ag and / or Au), B (B is In), C (C is Te and / or Se), MI (MI Is Sb and / or Bi) and MII(MIIIs at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Mn, W and Mo), and the atomic ratio of each element in the recording material is represented by the following formula: (1) ~(5)Any of the optical recording media.
Formula {(Ae Bf C1-ef )g MI 1-g }1-h MII h
0.01 ≦ e <0.50,
0.01 ≦ f <0.50,
0.30 ≦ g ≦ 0.70,
0.001 ≦ h ≦ 0.20
(7) The above recording layer contains a dielectric material(6)Optical recording media.
(8) In the recording layer, the dielectric material / (recording material + dielectric material) is 25% by volume or less.(7)Optical recording media.
(9) The thickness of the mask layer is from 7 to 100 nm (1) to(8)Any of the optical recording media.
(10) The thickness of the intermediate dielectric layer is 10 to 200 nm (1) to(9)Any of the optical recording media.
(11) (1) to (1) having a lower dielectric layer between the transparent substrate and the mask layer.(10)Any of the optical recording media.
(12) The wavelength of the reproduction light is λR And the refractive index of the lower dielectric layer is nThree When the thickness of the lower dielectric layer is
{ΛR / (2nThree )} ± 50nm
Above is(11)Optical recording media.
(13) (1) to (1) having an upper dielectric layer between the recording layer and the reflective layer.(12)Any of the optical recording media.
(14) (1) to (1) having a protective layer containing an organic substance on the reflective layer(13)Any of the optical recording media.
(15) (1) to (1) in which the unrecorded area of the recording layer is crystalline and the recording mark is amorphous or microcrystalline.(14)Any of the optical recording media.
(16) (1) to (1) in which the unrecorded area of the recording layer is amorphous or microcrystalline, and the recording mark is crystalline.(14)Any of the optical recording media.
As shown in FIG. 1, the optical recording medium of the present invention has a mask layer 4 and a phase change type recording layer 6 with an intermediate dielectric layer 5 interposed therebetween. Recording light and reproducing light are irradiated from the mask layer 4 side.
The present invention is also applicable to an optical recording medium (hereinafter referred to as a first type) of a type in which a crystalline unrecorded portion is changed to amorphous or microcrystalline to form a recording mark. The present invention can also be applied to an optical recording medium (hereinafter referred to as a second type) of a type in which the unrecorded portion is changed into crystalline to form a recording mark, but is particularly suitable for the first type.
The first type of recording, reproduction and erasure will be described.
First, the recording layer 6 that is amorphous immediately after formation is melted using a DC laser beam or the like, and then cooled to crystallize. Thus, when the recording layer 6 is crystallized, the mask layer 4 is also crystallized. This crystallization is so-called initialization. At this time, it is not necessary to crystallize the entire surface of each layer, and at least the recording target region of the recording layer 6 and the region immediately below the region of the mask layer 4 may be crystallized. When the mask layer 4 is crystalline, it is substantially opaque to reproduction light.
FIG. 2 is a schematic diagram for explaining the operation during recording. In recording, recording light having a power capable of melting the mask layer 4 and the recording layer 6 is used. In the recording light irradiation part, the mask layer 4 is melted, and the melting part 41 becomes substantially transparent to the recording light. Then, the beam spot of the recording light passes through the melting part 41 of the mask layer 4 and reaches the recording layer 6, and the recording layer 6 is melted to form a melting part 61. Since the recording layer 6 is in contact with the reflective layer 8 having high thermal conductivity, directly or through the thin upper dielectric layer 7, the recording layer 6 has a rapid cooling structure. On the other hand, one surface of the mask layer 4 is in contact with the intermediate dielectric layer 5, and the other surface is in contact with the lower dielectric layer 3 or the transparent substrate 2, and each dielectric layer and the transparent substrate have low thermal conductivity. The mask layer 4 has a slow cooling structure. For this reason, after the beam spot of the recording light passes, the melting part 61 of the recording layer 6 is rapidly cooled to form the amorphous or microcrystalline recording mark 62 shown in FIG. On the other hand, since the mask layer 4 has a low cooling rate, the melted portion 41 is gradually cooled to return to crystalline again.
Since the beam spot of the recording light has an intensity distribution in the irradiation surface, the mask layer 4 and the recording layer 6 near the center of the beam spot are melted. Therefore, a recording mark having a desired size and smaller than the beam spot diameter can be formed by using recording light having an appropriate power. In FIG. 3, the recording mark is formed on the bottom surface of the groove 63 of the recording layer 6, but the recording mark may extend over the land 64 of the recording layer 6.
FIG. 3 shows a schematic diagram for explaining the operation during reproduction. At the time of reproduction, reproduction light having a power sufficient to melt only the mask layer 4 and not the recording layer 6 is used. As shown in the figure, the melted portion 41 of the mask layer 4 is smaller than the beam spot diameter of the reproduction light. Since the light transmittance is improved in the melting part 41, the reproduction light is filtered through the melting part and irradiated to the recording marks 62 of the recording layer 6. At this time, a schematic view of the vicinity of the recording mark viewed from the lower side (transparent substrate 2 side) is also shown in FIG. The region X shown in the figure is the recording mark 62, the region Y is the crystalline region of the recording layer 6, and the region Z is the crystalline region of the mask layer 4. Both are reflected images of the reproduction light transmitted through the transparent substrate and each layer. Is schematically represented. The melted portion 41 formed by the reproduction light has a smaller diameter than the beam spot, and the mask layer immediately returns to crystalline after passing through the beam spot of the reproduction light, thereby preventing the influence of crosstalk noise due to the adjacent recording mark. be able to.
The mask layer 4 in the present invention has a complex refractive index (n0 -Ik0 ) Imaginary part k0 Changes, but the real part n0 Hardly changes, the phase of the reproduction light transmitted through the melting portion 41 hardly changes. Therefore, the difference between the reflectance of the region Y and the reflectance of the region Z is small, and only the reflectance of the region X is low, so that accurate reading can be performed. For this reason, C / N is high and jitter is small. On the other hand, n in the melting part 410 Is greatly changed, the phase of the reproduction light transmitted through the melting portion 41 is greatly changed, and the reflectance of the region Y is lowered. As a result, the difference in reflectance between the region Y and the region Z becomes large, and the difference in reflectance between the region Y and the region X becomes small. Therefore, the reproduction apparatus misidentifies the region Y as a recording mark, and noise or jitter. Increase.
2 and 3 are schematic diagrams, and the shape and dimensions of the melted region and recording mark of each layer are not limited to the illustrated examples.
At the time of erasing, erasing light having a power lower than that at the time of recording and higher than that at the time of reproducing is irradiated. By irradiating the erasing light, the mask layer 4 is melted, and the erasing light raises the temperature of the recording layer 6. Since the temperature reached by the recording layer 6 during erasing is lower than that during recording, the cooling rate of the recording layer 6 is lower than during recording. For this reason, the recording layer 6 becomes crystalline after irradiation with erasing light.
In the first type, the constituent materials of both layers are selected so that the amorphization linear velocity of the mask layer is higher than that of the recording layer. The amorphized linear velocity is the lowest relative linear velocity at which amorphous or microcrystals are formed, and large crystals grow at a linear velocity lower than this. The relative linear velocity of the medium with respect to the recording light is set to be equal to or higher than the amorphization linear velocity of the recording layer and lower than the amorphization linear velocity of the mask layer. Thereby, an amorphous or microcrystalline recording mark can be formed in the recording layer, and the mask layer can be crystallized.
In the first type, the intensity of the laser light is modulated so that it has the power required for recording, playback, and erasing, so that recording, playback, and erasing can be performed with a single light beam. It is.
Next, the second type in which the recording mark is crystalline will be described. In the second type, the mask layer and the recording layer are melted at the time of recording. In this type, the cooling rate of the recording layer is decreased by increasing the thickness of the upper dielectric layer 7 or reducing the thickness of the reflective layer 8. A material having a relatively high crystal transition rate is used for the recording layer, and the recording layer is crystallized after melting. In this specification, the crystal transition rate means the rate at which amorphous or microcrystals grow into coarse crystals. At the time of reproduction, the recording mark is read out in the same manner as in the first type. In the second type, a phase change from crystalline to amorphous or microcrystalline is necessary to erase the recording mark of the recording layer 6. Therefore, in order to increase the cooling speed at the time of erasing, it is necessary to irradiate a high-power laser beam as erasing light. For this reason, since the adjacent recording marks are likely to be affected during erasure, the recording marks are practically used as write once optical recording media. Thus, although rewriting is difficult with the second type, it is not necessary to initialize the recording layer.
In the second type, the amorphization linear velocity of the mask layer and the recording layer is not particularly limited. That is, in this type, the linear velocity may be selected so that both layers are crystallized during recording, and the linear velocity may be lower than the amorphizing linear velocity of the mask layer during reproduction.
In a preferred embodiment of the present invention, {(Aa Bb C1-ab )c MI 1-c }1-d MII d Further, a predetermined amount of dielectric material is added to the mask layer. Thereby, the complex refractive index change of a mask layer can be easily made into the said range.
In a preferred embodiment of the present invention, in the first type, a recording material having the same composition as the mask material is used for the recording layer. This recording material has a low crystal transition rate, that is, a material that is relatively difficult to crystallize even when the cooling rate is low. For this reason, it is possible to suppress a decrease in C / N which becomes a problem when a long recording mark is formed at a low linear velocity. Therefore, good C / N can be obtained in high-density long-time recording. Also, matching with the above mask material, which requires a lower linear velocity for recrystallization, is good. As described above, since the recording layer is close to the reflective layer, the cooling rate is faster than that of the mask layer. Therefore, even when a recording material having a crystal transition rate equivalent to that of the mask material is used, the recording layer is made amorphous. Since the speed is slower than that of the mask layer, it is possible to form amorphous recording marks and recrystallize the mask layer.
By the way, the mask material and the recording material are (Ag, Au) In (Te, Se) using a chalcopyrite type compound.2 -(Sb, Bi) series. Chalcopyrite type compounds have been extensively studied as compound semiconductor materials and applied to solar cells and the like. Chalcopyrite type compounds can be obtained from Ib-IIIb-VIb using the chemical periodic table.2And IIb-IVb-Vb2 And has a structure in which two diamond structures are stacked. The structure of a chalcopyrite type compound can be easily determined by X-ray structural analysis, and its basic characteristics are described in, for example, Monthly Physics vol. 8, no. 8, 1987, pp-441, and electrochemistry vol. 56, no. 4, 1988, pp-228, and the like.
Among these chalcopyrite type compounds, especially AgInTe2 Is known to be usable as a recording layer material for an optical recording medium having a linear velocity of about 7 m / s by diluting with Sb or Bi (Japanese Patent Laid-Open Nos. 3-240590 and 3-99884). No. 3-82593, No. 3-73384, etc.). Specifically, JP-A-3-240590 discloses (AgInTe2 )1-a Ma (M is Sb and / or Bi, 0.30 ≦ a ≦ 0.92) as a main component, and AgInTe2 An information recording medium having a recording layer that is a mixed phase of a phase and an M phase has been proposed. This publication mentions improvements in laser writing sensitivity, erasing sensitivity, recording-erasing repetition performance, erasing ratio, and the like. However, conventionally, there has been no proposal to use the mask material as described above by controlling the complex refractive index change of the chalcopyrite type compound.
In JP-A-5-89511, JP-A-5-109117, and JP-A-5-109119, the reflectance varies depending on the temperature on a transparent substrate on which optically readable recording pits are formed. An optical disc having a material layer formed thereon is disclosed. These optical discs are read-only optical discs in which information is carried in phase pits. The material layer is for obtaining a high resolution exceeding the limit due to the reproduction light wavelength λ and the numerical aperture NA of the objective lens by substantially the same action as the mask layer in the present invention.
However, these publications do not mention the change in complex refractive index when the material layer is melted. In JP-A-5-89511, Sb2 Se3 In an optical disk having a structure in which a phase change material layer is sandwiched between two dielectric layers, a reproduction power of 9 mW and a linear velocity of 3 m / s are reproduced to obtain a C / N of 25 dB.2 Se3 When C is used as the material layer, it is difficult to obtain a C / N higher than this. Sb2 Se3 Has a complex refractive index of about 1/10 of that of a normal phase change material, and in order to exhibit a sufficient effect as a mask layer, a thickness greatly exceeding 100 nm is required. When the mask layer is made thick in this manner, the refractive index is low near the center of the melted portion formed by light beam irradiation, and high at the peripheral portion, and acts as a concave lens. For this reason, the light beam diameter increases due to the diffusion action, and high C / N cannot be obtained. In addition, the phase change material exemplified in each of the above publications cannot obtain the same C / N improvement effect as that of the present invention because the complex refractive index change amount at the time of melting is out of the scope of the present invention.
Japanese Patent Application Laid-Open No. 2-96926 describes a record carrier having a layer of nonlinear optical material that achieves super resolution. In this publication, a layer of phase change material is cited as an example of a layer of nonlinear optical material, which exhibits substantially the same operation as the mask layer in the present invention. The publication also discloses a configuration in which a writable information layer having a phase change material and a nonlinear layer having a phase change material are combined. However, this publication does not disclose the technical idea of suppressing the change in the complex refractive index of the layer of the nonlinear optical material within a certain range. For example, the publication discloses GaSb and InSb as examples of the phase change material used for the nonlinear layer, and describes that sufficient complex refractive index change is caused by light irradiation with an intensity that does not cause a phase change. However, in these phase change materials, the real number part of the complex refractive index greatly changes as the transmittance is improved, so that the above-described problem occurs unlike the present invention. FIG. 17 of the same publication shows a combination in which a phase change material is used for both the information layer and the nonlinear layer. However, since the information layer and the nonlinear layer are in close contact with each other, each layer is amorphous. It is difficult to control the linearization speed.
[Specific configuration]
Hereinafter, a specific configuration of the present invention will be described in detail.
A configuration example of the optical recording medium of the present invention is shown in FIG. The illustrated optical recording medium 1 has a lower dielectric layer 3, a mask layer 4, an intermediate dielectric layer 5, a recording layer 6, an upper dielectric layer 7, a reflective layer 8, and a protective layer 9 on a transparent substrate 2.
<Transparent substrate 2>
Since the recording light and the reproduction light are applied to the recording layer 6 through the transparent substrate 2, the transparent substrate 2 can be made of a material that is substantially transparent to the light beam used, for example, resin or glass. preferable. Of these, resins are preferred because they are easy to handle and inexpensive. Specifically, various resins such as acrylic resin, polycarbonate, epoxy resin, and polyolefin may be used. The shape and dimensions of the transparent substrate are not particularly limited, but are usually disc-shaped, and the thickness is usually about 0.5 to 3 mm and the diameter is about 50 to 360 mm. On the surface of the transparent substrate, a predetermined pattern such as a groove is provided as necessary for tracking or addressing.
<Lower dielectric layer 3>
A lower dielectric layer 3 is preferably provided on the transparent substrate 2. The lower dielectric layer 3 prevents thermal deformation of the transparent substrate 2. When recording, reproducing and erasing, the mask layer 4 is melted. When the transparent substrate 2 is made of a resin having low heat resistance, the transparent substrate 2 may be thermally deformed by heat when the mask layer 4 is melted. The lower dielectric layer prevents such thermal deformation of the transparent substrate. Further, the lower dielectric layer has an effect of controlling the cooling rate of the mask layer 4.
The constituent material of the lower dielectric layer may be appropriately selected from various dielectric materials mentioned in the description of the mask layer 4.2 And SiO2 A mixture of ZnS and ZnS, so-called LaSiON containing La, Si, O and N, so-called SiAlON containing Si, Al, O and N, SiAlON containing Y, NdSiON, etc. may be used. In consideration of heat resistance at the time, ZnS-SiO2 It is preferable to use a mixture or LaSiON.
The thickness of the lower dielectric layer is not particularly limited, and may be appropriately determined so that thermal deformation of the transparent substrate can be suppressed. However, the wavelength of the reproduction light is λR And the refractive index of the lower dielectric layer is n3 When the thickness of the lower dielectric layer is
{ΛR / (2n3 )} ± 50nm
3, the difference in reflectance between the region X and the region Y shown in FIG. 3 can be increased, and the difference in reflectance between the region Y and the region Z can be reduced. It can be selectively lowered and noise can be reduced.
The lower dielectric layer is preferably formed by a vapor deposition method such as sputtering or vapor deposition.
<Mask layer 4>
The mask layer includes a mask material that improves light transmittance when melted. Complex refractive index of mask layer 4 when mask material is amorphous or microcrystalline (n0 -Ik0 ) Changes in real part (refractive index) n0 Decrease of 0.7 or less, imaginary part (extinction coefficient) k0 The amount of decrease is 0.45 to 0.80. These reduction amounts are based on the complex refractive index when the mask layer is crystalline. n0 If the amount of decrease is too large, noise and jitter will increase for the reasons described above. k0 If the decrease amount is too small, the difference in reflectance between the region X and the region Y in FIG. 3 becomes small, and high C / N cannot be obtained. k0 If the reduction amount is too large, the mask layer must be thinned. In this case, the amorphization linear velocity of the mask layer becomes slow, and recrystallization becomes difficult.
The complex refractive index of the mask layer can be obtained, for example, by forming the mask layer alone on a glass substrate and measuring the spectral transmission coefficient at each wavelength. In the present invention, the amount of change in the complex refractive index is obtained with reference to the case where the mask layer is crystalline. In this specification, the difference between crystalline and amorphous or microcrystalline is the transmission electron microscope (TEM). ). In the TEM image, in the case of amorphous or microcrystalline, the mask layer is slightly dark overall, and almost no crystal grains having a grain size of about 5 nm or more are seen, whereas in the case of crystalline, about 5 nm or more. However, when a dielectric material is included in the mask layer as will be described later, small-sized crystal grains having an average grain size of about 10 to 50 nm can be easily obtained. It is possible to obtain such a small-diameter crystal grain as a real part n of the complex refractive index.0 The extinction coefficient k0 It is thought that it contributes to selectively changing.
The complex refractive index when the mask material is amorphous or microcrystalline is substantially the same as the complex refractive index when the mask material is melted. This can be confirmed by measuring the reflected light from the medium when the mask material is amorphous or microcrystalline and examining the characteristics.
The complex refractive index of the mask layer may be changed as described above in the wavelength of the reproduction light to be used. In the optical recording medium of the present invention, the wavelength range of the reproduction light is not particularly limited, and may be appropriately selected from the range of, for example, 400 to 850 nm. Usually, the usable reproduction light wavelength is in the range of 460 to 850 nm. In the present invention, it is preferable that the change amount of the complex refractive index as described above is realized in such a wavelength range.
In the first type described above, the mask layer needs to return to crystalline after recording light irradiation, while the recording layer needs to change from crystalline to amorphous or microcrystalline by recording light irradiation. The amorphization linear velocity of the layer is made faster than the amorphization linear velocity of the recording layer described later. The amorphization linear velocity of the mask layer is preferably 4.5 to 7.0 m / s, more preferably 5.0 to 6.0 m / s. When the amorphization linear velocity of the mask layer is too slow, the difference from the amorphization linear velocity of the recording layer becomes small, and the linear velocity range in which high density reproduction can be performed becomes narrow. On the other hand, if it is too fast, fine crystals are generated in the melted portion of the mask layer during reproduction, which causes scattering and increases noise. The amorphization linear velocity of the mask layer and the recording layer is such that the mask layer and the recording layer are melted by irradiating a DC laser beam having the same power as the recording light while gradually decreasing the linear velocity of the medium. It can be determined by confirming the highest linear velocity for crystallization, or by confirming the lowest linear velocity that becomes amorphous or microcrystalline while increasing the linear velocity.
In this specification, the amorphized linear velocity is the minimum linear velocity required for the mask material or recording material to be amorphous or microcrystalline in the mask layer or recording layer existing in the medium. It is. The linear velocity is a relative linear velocity of the medium with respect to the beam spot of recording light or reproducing light.
The mask material is not particularly limited as long as the complex refractive index exhibits the above change, but preferably A (A is Ag and / or Au), B (B is In). , C (C is Te and / or Se), MI (MI Is Sb and / or Bi) and MII(MIIIs at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Mn, W and Mo), and a mask material in which the atomic ratio of each element is represented by the following formula is used. Is preferred.
A, B and C are the stoichiometric composition of the chalcopyrite type compound, ie ABC2 However, it may be biased as shown in the above formula. However, if a or b is out of the above range, the transmittance change accompanying the phase change becomes small. Further, when c is less than the above range, it is difficult to set the complex refractive index change amount within the above range, and when c exceeds the above range, the change in transmittance accompanying the phase change becomes small, and noise is generated during reproduction. And jitter will increase.
MIIWhen d representing the content of is less than the above range, it is difficult to make the complex refractive index change amount within the above range, and in the first type described above, the reliability after repeated overwriting deteriorates. When d exceeds the above range, it becomes difficult to control the phase change rate. Note that V and Ti are good in improving the reliability under adverse conditions such as high temperature and high humidity, and V has a particularly high reliability improving effect. Therefore, one or more of Ti and V, especially V is MIIIt is preferable to occupy 80 atomic% or more, particularly 100 atomic% of the whole.
MI There is no restriction | limiting in particular in the ratio of Sb in the inside.
In addition to the above elements, the mask layer may contain other elements such as Cu, Ni, Zn, Fe, O, N, and C as trace impurities. The total content is preferably 0.05 atomic% or less.
The mask layer preferably includes a dielectric material in addition to the mask material. The dielectric material contained in the mask layer is not particularly limited, for example, SiO2 Such as silicon oxide and Si3 N4 Various transparent ceramics such as silicon nitride such as ZnS, zinc sulfide such as ZnS, or a mixture thereof may be used, and various glasses may be used. For example, so-called LaSiON containing La, Si, O and N, so-called SiAlON containing Si, Al, O and N, or SiAlON containing Y can be preferably used. Among these, for example, those having a refractive index of 1.4 or more in the wavelength range of 400 to 850 nm are preferable, and those having a refractive index of 2 or more are particularly preferable. The above wavelength range includes 780 nm, which is the wavelength used by current CD players, and is a wavelength range preferably used for the optical recording medium of the present invention. Specifically, the dielectric material used is ZnS and SiO.2 Mixture of ZnS and Si3 N4 A mixture of ZnS and Ta2 O5 And a mixture such as LaSiON are preferred. In the mask layer, the dielectric material / (mask material + dielectric material) is preferably 25% by volume or less, more preferably 10 to 22% by volume. If the ratio of the dielectric material is too low, the extinction coefficient k of the mask layer0 Becomes larger and the mask layer has to be made thinner, and the amorphization linear velocity becomes slower. On the other hand, if the ratio of the dielectric material is too high, the extinction coefficient k of the mask layer0 Becomes too small, and the difference in reflectance between the region X and the region Y in FIG. 3 becomes small.
In the mask layer, when the mask material melts, the dielectric material usually does not melt.
Refractive index n of the mask material in the aforementioned wavelength range0 Is about 4.0 to 5.5 when crystalline, and about 3.0 to 4.5 when microcrystalline or amorphous.0 Is about 0.75 to 3.0 when crystalline, and about 0.50 to 2.0 when microcrystalline or amorphous. In the mask layer of mask material / dielectric material = 3/1 (volume ratio), n0 Is about 4.0 to 4.5 when crystalline, and about 3.4 to 3.8 when microcrystalline or amorphous, the extinction coefficient k0 Is about 1.00 to 1.50 when crystalline, and about 0.50 to 0.75 when microcrystalline or amorphous.
In the present invention, in addition to the composition represented by the above formula, for example, Ge2 Sb2 Te5 Can be used as a mask material, but in this case, in order to make the complex refractive index change within the scope of the present invention, it is essential to include a dielectric material in the mask layer.
The thickness of the mask layer is preferably 7 to 100 nm, more preferably 10 to 100 nm, and still more preferably 15 to 50 nm. If the mask layer is too thin, the mask effect is insufficient, and if it is too thick, the phase change of the reproduction light transmitted through the melted portion of the mask layer becomes large, and the difference in reflectance between the region X and the region Y in FIG. End up.
The method for forming the mask layer is not particularly limited, and may be appropriately selected from sputtering and vapor deposition. However, when a dielectric material is included in the mask layer, a multi-source sputtering method using a plurality of targets should be used. Is preferred. In this case, a mask material target and a dielectric material target are usually used. Then, the targets are arranged so as to face the transparent substrate, and sputtering is performed while rotating the transparent substrate relative to each target. At this time, the relative rotation speed of the transparent substrate with respect to the target is preferably 1 to 10 rpm. If the rotation speed is too low, the dispersion of both materials in the mask layer becomes non-uniform. On the other hand, if the rotational speed is too high, the degree of dispersion becomes too good and the crystal growth during crystallization is hindered. Note that the present invention is not limited to such a method, and a composite target of a mask material and a dielectric material may be used.
In the mask layer formed by using the sputtering method, the dielectric material particles are usually dispersed in the mask material, and this structure can be confirmed by a transmission electron microscope or the like. The particle size of the dielectric material in the mask layer is usually about 10 to 50 nm.
<Intermediate dielectric layer 5>
The intermediate dielectric layer 5 is provided to separate the mask layer 4 and the recording layer 6. The constituent material of the intermediate dielectric layer is not particularly limited. For example, the intermediate dielectric layer may be composed of at least one of the dielectric materials mentioned in the description of the mask layer 4, and the mask layer and the recording layer above and below the intermediate dielectric layer. Is a dielectric material that is as resistant to thermal shock as possible, such as ZnS-SiO.2 Mixture, LaSiON, AlN-ZnS-SiO2 Etc. are preferably used.
The thickness of the intermediate dielectric layer is preferably 10 to 250 nm, more preferably 80 to 250 nm, and still more preferably 100 to 200 nm. If the intermediate dielectric layer is too thin, it will not be able to endure thermal shock, and the number of times overwriting can be repeated will decrease.If it is too thick, the recording layer will generate heat due to melting of the mask layer during recording in the second type described above. The recording sensitivity is lowered due to insufficient use.
The intermediate dielectric layer is preferably formed by a vapor phase growth method such as sputtering or vapor deposition.
<Recording layer 6>
The recording layer 6 contains a recording material capable of recording information by changing the crystal structure by irradiation of recording light, that is, a phase change recording material.
The amorphization linear velocity of the recording layer is preferably 2.4 to 4.5 m / s. If the amorphization linear velocity of the recording layer is too slow, the erasure rate at the time of overwriting deteriorates, resulting in an increase in noise. On the other hand, if it is too fast, the recording state is not stabilized, the reflectance difference is small in the case of the first type described above, and the crystalline recording mark formed is large in the case of the second type. This causes distortion in the signal waveform.
The recording material used in the present invention is not particularly limited, and various ordinary phase change recording materials can be used. However, as described above, good C / N and repetitive characteristics can be obtained at a low linear velocity. It is preferable to use a recording material having a composition represented by the formula.
A, B and C are the stoichiometric composition of the chalcopyrite type compound, ie ABC2 However, it may be biased as shown in the above formula. However, when e or f is out of the above range, the change in reflectance accompanying the phase change becomes small. When g is less than the above range, the crystal transition speed is increased, and in the first type described above, sufficient C / N cannot be obtained at a low linear speed, and the repeated recording characteristics are also poor. If g exceeds the above range, the change in reflectance accompanying the phase change becomes small, and a sufficient difference in reflectance cannot be secured.
MIIWhen h representing the content of s is less than the above range, the crystal transition speed becomes too fast, so that when recording a 11T signal having a long signal length at a slow linear speed, good C / N cannot be obtained, and repetitive recording is performed. The characteristics are also poor. If h exceeds the above range, the recording characteristics become poor and the relative signal intensity cannot be obtained. The effect of lowering the crystal transition rate is MIIOf these, Ti and V, particularly Ti, are high. In addition, V and Ti are good in improving the reliability under adverse conditions such as high temperature and high humidity, and V has a particularly high reliability improving effect. Therefore, one or more of Ti and V, especially V is MIIIt is preferable to occupy 80 atomic% or more, particularly 100 atomic% of the whole.
In addition to the above elements, the recording layer may contain other elements such as Cu, Ni, Zn, Fe, O, N, and C as trace impurities. The total content is preferably 0.05 atomic% or less.
The recording layer may include a dielectric material in addition to the recording material. In the recording layer, the dielectric material / (recording material + dielectric material) is preferably 25% by volume or less, more preferably 10% by volume or less, and still more preferably 8% by volume or less. The dielectric material allows the recording layer to be thickened by reducing the extinction coefficient of the recording layer. This increases the interference effect and provides high modulation. When such an effect is required, the ratio of the dielectric material is preferably 2% by volume or more. If the ratio of the dielectric material in the recording layer is too high, the extinction coefficient of the recording layer becomes too small, the difference in reflectance due to phase change becomes small, and the modulation decreases.
In addition to this, (Ge2 Sb2 Te5 )x Sb1-x The amorphization linear velocity of the recording layer containing this as a main component can be controlled by Sb, but the reliability decreases as the Sb amount increases. Also, (Ge2 Sb2 Te5 )x Sb1-x Is difficult to control the amorphization linear velocity as compared with the preferable recording material described above.
The thickness of the recording layer is not particularly limited, but in order to obtain high reflectivity and high modulation, it is usually preferably 10 to 200 nm, particularly preferably 15 to 150 nm.
The recording layer may be formed in the same manner as the mask layer described above.
<Upper dielectric layer 7>
An upper dielectric layer 7 is preferably provided on the recording layer 6. The upper dielectric layer 7 prevents thermal deformation of the reflective layer 8 accompanying heating of the recording layer 6. Further, the upper dielectric layer has an effect of controlling the cooling rate of the recording layer. The constituent material of the upper dielectric layer is not particularly limited, and may be appropriately selected from the same dielectric materials as those for the intermediate dielectric layer described above. However, in order to enhance the cooling effect, a material having a relatively high thermal conductivity is preferable. Moreover, since the thermal shock is repeatedly applied to the upper dielectric layer, it is preferable that the upper dielectric layer is not easily deformed or broken by the thermal shock. As such a dielectric material, ZnS-SiO2 AlN-Zn-SiO2 Etc.
The thickness of the upper dielectric layer is preferably 8 to 30 nm, more preferably 15 to 25 nm. If the upper dielectric layer is too thin, it may be destroyed by repeated thermal shocks during recording. If it is too thick, the cooling rate of the recording layer will slow down, making it impossible to form good recording marks. C / N cannot be obtained.
The upper dielectric layer is preferably formed by a vapor deposition method such as sputtering or vapor deposition.
<Reflection layer 8>
The reflective layer 8 mainly has an effect as a heat dissipation layer that increases the cooling rate of the recording layer 6, but also exhibits an effect of increasing the amount of light reflected to the transparent substrate 2 side. The material of the reflective layer 8 is not particularly limited, and may usually be composed of a high reflectivity metal such as a simple substance such as Al, Au, Ag, Pt, or Cu, or an alloy containing one or more of these. The thickness of the reflective layer is preferably 30 to 150 nm. If the thickness of the reflective layer is less than the above range, the cooling rate of the recording layer becomes insufficient, and it becomes difficult to form an amorphous or microcrystalline recording mark. Moreover, it becomes difficult to obtain sufficient reflectance. Even if the thickness of the reflective layer exceeds the above range, the improvement in reflectance is small, which is disadvantageous in cost. The reflective layer is preferably formed by a vapor phase growth method such as sputtering or vapor deposition.
<Protective layer 9>
The protective layer 9 is provided for improving scratch resistance and corrosion resistance. The protective layer is preferably composed of various organic substances, and in particular, it is preferably composed of a substance obtained by curing a radiation curable compound or a composition thereof by radiation such as electron beam or ultraviolet ray. . The thickness of the protective layer is usually about 0.1 to 100 μm and may be formed by a usual method such as spin coating, gravure coating, spray coating, dipping or the like.
The recording light is preferably irradiated in the form of pulses. By recording one signal by at least two irradiations, heat storage in the recording region is suppressed, and swelling (tear drop phenomenon) at the rear end of the recording region can be suppressed, so that C / N is improved. In addition, the erasure rate is improved by the pulsed irradiation.
The specific values of the recording light power, the reproduction light power, and the erasing light power may be determined experimentally.W Is 12-20mW, reproduction light power PR Is 3 to 6 mW, and the erasing light power PE Is PW And PR Between.
In the optical recording medium of the present invention, the relative linear velocity with respect to the light beam spot at the time of recording, reproduction, and erasing is not particularly limited, and may be set as appropriate so that the above-described recording, reproduction, and erasure can be performed. The relative linear velocity with respect to the recording light and the reproducing light may be less than the amorphization linear velocity of the mask layer.
Hereinafter, specific examples of the present invention will be shown to describe the present invention in more detail.
A lower dielectric layer 3, a mask layer 4, an intermediate dielectric layer 5, a recording layer 6 and an upper dielectric are formed on the surface of a disk-shaped polycarbonate transparent substrate 2 having a diameter of 133 mm and a thickness of 1.2 mm, on which grooves are simultaneously formed by injection molding. The layer 7, the reflective layer 8, and the protective layer 9 were sequentially formed to produce an optical recording disk sample having the configuration shown in FIG. The pitch of the grooves was 1.0 μm.
The lower dielectric layer 3 is a ZnS-SiO having a thickness of 130 nm.2 And the intermediate dielectric layer 5 is ZnS-SiO having a thickness of 180 nm.2 The upper dielectric layer 7 has a thickness of 20 nm of ZnS-SiO.2 Both were formed by sputtering. ZnS-SiO2 ZnS: SiO in2 (Molar ratio) was set to 0.85: 0.15. ZnS-SiO at a wavelength of 780 nm2 The refractive index of was 2.3.
The mask layer 4 had a thickness of 30 nm and the recording layer 6 had a thickness of 20 nm, both of which were formed by sputtering. Table 1 shows the composition of each layer. As the target, an Sb target surface with Ag, In, Te, and V chips attached thereto was used. In the sample containing a dielectric material in the layer, in addition to the target, the target used for forming the dielectric layer was used, and the layer was formed by sputtering while rotating the transparent substrate at 5 rpm. The dielectric material target was RF sputtering, and the other targets were DC sputtering. Table 1 shows the volume ratio of the dielectric material in each layer. Further, the complex refractive index (n0 -Ik0 ) Change amount (n at a wavelength of 780 nm)0 Reduction amount and k0 ), And the amorphization linear velocity of the mask layer and the recording layer were measured. These results are shown in Table 1.
The reflective layer 8 was formed by sputtering using Au as a target, and the thickness was 100 nm. The protective layer 9 was formed by applying an ultraviolet curable resin by spin coating and then curing by ultraviolet irradiation. The thickness of the protective layer after curing was 5 μm.
Next, the amorphous mask layer and the recording layer were each irradiated with 10 mW laser light to crystallize the mask layer and the recording layer.
Next, while rotating the sample at a linear velocity of 2.8 m / s, a 3 MHz signal and a 5 MHz signal were recorded, and the C / N of each reproduced signal was measured. The power P of the recording lightW Is 18mW, power P for erasing lightE Is 6.0 mW, power P of the reproduction lightR Was 5.4 mW. The wavelength of each light was 780 nm. Further, a reference sample was prepared in the same manner as each sample except that the mask layer and the intermediate dielectric layer were not provided, and C / N was also measured for these samples. Table 1 shows the amount of increase in C / N for each sample relative to the corresponding reference sample. In the reference sample, the C / N of the 3 MHz signal was about 10 dB, and the C / N of the 5 MHz signal was about 1 to 2 dB.
From the results shown in Table 1, the effect of the present invention is clear. That is, when the reduction amount of the complex refractive index when the mask layer is melted is within the range of the present invention, an extremely high C / N is obtained. On the other hand, sample no. 4 is n0 C / N is poor because the amount of decrease in C is too large.
Even when at least a part of Sb of the mask material and / or the recording material was replaced with Bi, the same effect was observed. Further, when at least a part of V was replaced with Ti, an equivalent effect was observed. When at least a part of Ag was replaced with Au, the amorphization linear velocity of the recording layer was slightly higher than that of Ag alone, but by increasing the amount of V added, results equivalent to those of Ag alone were obtained. It was. The effect of the present invention was also observed when at least part of V was replaced with one or more of Zr, Hf, Nb, Ta, Mn, W, and Mo.
Further, the sample of the present invention shown in Table 1 and a comparative sample to which V was not added were stored under conditions of 80 ° C. and 80% RH, and the deterioration of the recording layer was examined. As a result, the sample of the present invention to which V was added showed no change for 200 hours or more, whereas the comparative sample showed deterioration in the recording layer in 20 hours. Specifically, crystallization occurred in the recording portion in the amorphous state, and a tendency to approach the reflectance in the unrecorded state (crystalline state) was observed.
The above example is of the first type described above, but high C / N was obtained even when the present invention was applied to the second type for forming a crystalline recording mark.
The effects of the present invention are apparent from the results of the above examples.
FIG. 1 is a partial cross-sectional view showing a configuration example of an optical recording medium of the present invention.
FIG. 2 is a partial cross-sectional view for explaining the operation during recording of the optical recording medium of the present invention.
FIG. 3 is a partial cross-sectional view for explaining the operation during reproduction of the optical recording medium of the present invention.
1 Optical recording media
3 Lower dielectric layer
41 Melting part
5 Intermediate dielectric layer
6 Recording layer
61 Melting zone
62 Record mark
7 Upper dielectric layer
8 Reflective layer
Having a mask layer, an intermediate dielectric layer, a recording layer and a reflective layer on the transparent substrate;
The mask layer includes a mask material whose light transmittance is improved when melted, and the real part n 0 of the complex refractive index (n 0 −ik 0 ) of the mask layer when the mask material is amorphous or microcrystalline. The optical recording medium is characterized in that the decrease amount of the imaginary part k 0 is 0.45 to 0.80.
When the minimum value of the relative linear velocity that becomes amorphous or microcrystalline after light beam irradiation is defined as the amorphization linear velocity, the amorphization linear velocity of the mask layer is higher than the amorphization linear velocity of the recording layer. The optical recording medium according to claim 1, which is faster.
The mask material is A (A is Ag and / or Au), B (B is In), C (C is Te and / or Se), M I (M I is Sb And / or Bi) and M II (M II is at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Mn, W and Mo), and in the mask material the optical recording medium according to claim 1 or 2 atomic ratio of each element is represented by the following formula.
Formula {(A a B b C 1-ab ) c M I 1-c } 1-d M II d
One of the optical recording medium according to claim 1 to 3 in which the mask layer contains a dielectric material.
5. The optical recording medium according to claim 4 , wherein the dielectric material / (mask material + dielectric material) is 25% by volume or less in the mask layer.
The recording material is A (A is Ag and / or Au), B (B is In), C (C is Te and / or Se), M I (M I is Sb And / or Bi) and M II (M II is at least one element selected from Ti, Zr, Hf, V, Nb, Ta, Mn, W and Mo) in the recording material one of the optical recording medium according to claim 1 to 5 in which the atomic ratio of each element is represented by the following formula.
Formula {(A e B f C 1-ef ) g M I 1-g } 1-h M II h
The optical recording medium according to claim 6 , wherein the recording layer contains a dielectric material.
8. The optical recording medium according to claim 7 , wherein the dielectric material / (recording material + dielectric material) is 25% by volume or less in the recording layer.
One of the optical recording medium according to claim 1-8 thickness of the mask layer is 7～100Nm.
One of the optical recording medium according to claim 1-9 thickness of the intermediate dielectric layer is 10 to 200 nm.
One of the optical recording medium according to claim 1-10 having a lower dielectric layer between the transparent substrate and the mask layer.
When the wavelength of the reproduction light is λ R and the refractive index of the lower dielectric layer is n 3 , the thickness of the lower dielectric layer is {λ R / (2n 3 )} ± 50 nm.
The optical recording medium according to claim 11 .
One of the optical recording medium of claim 1 to 12 having an upper dielectric layer between the recording layer and the reflective layer.
One of the optical recording medium according to claim 1 to 13 having a protective layer containing a substance of organic on the reflective layer.
Unrecorded area of the recording layer is crystalline, either optical recording medium according to claim 1-14 recording mark is amorphous or microcrystalline.
Unrecorded area of the recording layer is amorphous or microcrystalline, one of the optical recording medium according to claim 1-14 recording mark is crystalline.
JP34181893A 1993-12-13 1993-12-13 Optical recording medium Expired - Fee Related JP3566743B2 (en)
US08/340,340 US5470628A (en) 1993-12-13 1994-11-14 Optical recording medium
JPH07169094A JPH07169094A (en) 1995-07-04
JP3566743B2 true JP3566743B2 (en) 2004-09-15
JP34181893A Expired - Fee Related JP3566743B2 (en) 1993-12-13 1993-12-13 Optical recording medium
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1994-11-14 US US08/340,340 patent/US5470628A/en not_active Expired - Lifetime
JPH07169094A (en) 1995-07-04
US5470628A (en) 1995-11-28
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