JP3506621B2 - Optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a recording layer which changes into two states, amorphous and crystalline, in accordance with the output of a light beam such as a laser beam to be irradiated. In addition, the present invention relates to a rewritable optical recording medium for recording and reproducing digital information by utilizing a difference in light reflectance of recording pits in the two states. 2. Description of the Related Art FIG. 1 is a partial sectional view of a conventional rewritable optical recording medium M utilizing a phase transition (hereinafter referred to as a medium M). In the figure, 1 is a disk-shaped transparent substrate made of resin such as polycarbonate, glass or the like, and 2 is Zn
The first transparent dielectric layer made of S-SiO ₂ or the like, 3 GeT
e, etc., a recording layer capable of phase-change into two states of amorphous-crystalline, 4 is a second transparent dielectric layer made of ZnS-SiO ₂ or the like, 5 is a reflective layer made of a high reflectivity material such as Al. It is. In such a rewritable medium M, the recording layer 3 has a different light reflectivity between the crystalline state and the non-crystalline state. Generally, the crystalline state has a higher reflectivity. . The operating principle of the medium M is as follows. First, all the recording pits of the recording layer 3 are crystallized. That is, initialization is performed in a state where the reflectance is high.
For writing information, a laser beam pulse-modulated to two kinds of laser powers is irradiated while rotating the medium M, and a recording layer is formed in a recording pit irradiated with a high-power (about 10 to 20 mW) laser beam. The temperature becomes higher than the melting points of the three materials, and the materials are melted and rapidly cooled to become amorphous. On the other hand, medium output (5
The recording pit irradiated with the laser beam (about 10 to 10 mW) is heated to a crystallizable temperature range equal to or lower than the melting point and then cooled to a crystalline state. [0004] The above-described writing operation can be performed directly after old information remains, and each recording pit changes to a state corresponding to new information. That is, overwriting by overwriting (hereinafter abbreviated as OW) is possible. Reproduction is performed by irradiating a low-output (about 1 to 2 mW) laser beam for reading to determine whether the crystalline phase has a high reflectivity or an amorphous phase having a low reflectivity, and outputs digital information of 0,1. read. The material of the recording layer 3 is Te, S
A chalcogenide of a material containing one element of e and S is suitable, and the chalcogenide has a feature that it is likely to be amorphous. Specifically, GeTe-based materials, GeSbT
There are e-based materials, InSeTlCo-based materials, InSbTe-based materials, and the like. Conventionally, in such a phase change type medium M, an interface layer made of SiO ₂ and W is formed in contact with the surface of the recording layer on the transparent substrate side or the upper and lower surfaces of the recording layer. A device having a high OW erasure rate and excellent environmental resistance has been proposed (Japanese Patent Laid-Open No. 10-106026: Conventional Example 1). As another conventional example, in a magneto-optical disk having a dielectric layer and a perpendicular magnetization film on a transparent substrate, the dielectric layer contains SiN-MX containing a hydrogen element.
(MX is a substance of at least one member of the group consisting of a transition metal element, a simple substance of a lanthanide element, and a compound other than SiN) is known (JP-A-4-139636).
Publication: Conventional Example 2). Further, as another conventional example, a phase-change type optical information recording medium, in which a lower protective layer, an optical recording layer, and an upper protective layer are provided in this order on a transparent substrate, and is provided on both sides of the optical recording layer or On one side, an adhesion layer is provided in contact with the optical recording layer,
The adhesion layer is made of at least one of the elements of Groups 4a and 6a of the periodic table and compounds thereof, and has a thickness of 1 to 4.
It is known that when the thickness is 50 nm, the adhesion between the optical recording layer and the protective layer is improved, and as a result, the repetition characteristics are improved (Japanese Patent No. 2790874: Conventional Example 3). [0009] However, in the above-mentioned prior art example 1, although the interface layer made of SiO ₂ and W is provided, the OW erasure rate is not necessarily as high as about 20 dB to 30 dB. Further, with respect to Conventional Example 2, experiments by the present inventors have revealed that the SiN-MX-based dielectric layer is inferior in adhesion and repeated recording / reproducing characteristics. Further, Conventional Example 3 has good adhesion, but has a problem that the OW erasure rate is small, the light absorption is large, and the recording sensitivity and the like are reduced. Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a high OW erasure rate, excellent adhesion, and a small light absorption coefficient, and excellent recording sensitivity. It is in. [0011] The optical recording medium of the present invention comprises:
A light having a first transparent dielectric layer, a recording layer that changes into an amorphous or crystalline phase in accordance with the output of an irradiating light beam, a second transparent dielectric layer, and a reflective layer on a transparent substrate. A recording medium, wherein the first transparent dielectric layer and the second transparent dielectric layer comprise:
It is made of the following material, and is further provided on both the upper surface side and the lower surface side of the recording layer under an environment of 85 ° C. and 95% relative humidity.
The following composition formula M
An interface layer represented by aN-Mb is provided. Material of first and second transparent dielectric layers: ZnS-Si
O ₂ , SiN-based material, SiON-based material, SiO ₂ , Si
_{O, TiO 2, Al 2 O} 3, Y 2 O 3, TaN, Al
N, ZnS, Sb ₂ S ₃ , SnSe ₂ , Sb ₂ Se ₃ ,
CeF _3, Amoruasu _{Si, TiB 2, B 4 C} , B, C [0012] MAN-Mb · · · Ma is Si or Al, Mb is B, Bi, Al, Si, P, S, Ti,
It contains at least one of each element of the element group consisting of V, Zn, Ge, Y, W, Cr, Zr, and Ta, each oxide of the element group, and each carbide of the element group. Where Ma = M
Excludes cases where b and Mb are single elements. According to the present invention, with the above-described structure, crystal nuclei of the recording layer are easily generated at the interface between the interface layer and the recording layer when the temperature rises due to light rays. As a result, the recording layer changes from an amorphous state to a crystalline state. The speed at which the OW erasure rate changes increases, and characteristics such as the OW erasure rate improve. In addition, the recording layer undergoes a phase change between a crystalline state, a liquid state, and an amorphous state during recording, but interdiffusion has occurred between the recording layer and the transparent dielectric layer adjacent thereto during conventional recording. It also has the effect of being eliminated.
Further, the interface layer is excellent in adhesion. FIG. 2 shows a basic layer structure of a medium M1 according to the present invention. In the figure, 11 is a disk-shaped transparent substrate made of polycarbonate, polyolefin, epoxy resin, acrylic resin, glass, tempered glass having a resin layer formed on the surface, translucent ceramic, etc., and 12 is ZnS
A first transparent dielectric layer 13 made of SiO ₂ or the like;
aN-Mb interfacial layer, 14 is a phase change type recording layer,
15 the interface layer, 16 is a second transparent dielectric layer made of ZnS-SiO ₂ or the like, 17 is a reflective layer made of Al or the like. In the present invention, the recording layer 14 is made of GeTe,
Materials such as GeSbTe, InSeTlCo, and InSbTe are good. Among them, GeTe and GeSbTe have a large number of rewritable times, can be crystallized for a short time when crystallizing, and have high stability in an amorphous state. preferable. [0016] In addition, in the case of a Ge _a Sb _b Te _c, 5
at (atomic)% ≦ a ≦ 70 at% is preferable, and a <5 at%
In this case, the crystallization speed is low, and when 70 at% <a, the amorphous state becomes unstable. 0 at% ≦ b ≦ 50 at% is preferred, and 5 at%
When 0 at% <b, the amorphous state becomes unstable. 40at
% ≦ c ≦ 70 at% is good. When c <40 at%, the crystallization temperature is too high, and when 70 at% <c, the crystallization temperature is too high. The recording layer 14 has a thickness of 5 to 30 nm.
If the thickness is less than 5 nm, the reflectance difference between the crystalline state and the amorphous state becomes small, and if it exceeds 30 nm, the characteristic deterioration such as BER (Bit Error Rate) due to repeated recording / reproducing increases. More preferably, it is 10 to 20 nm. The interface layers 13 and 15 of the present invention are made of the above-mentioned MaN-Mb. At this time, Ma = Mb and M
When b is a single element, for example, SiN-Si, AlN-Al
Is excluded from the category of MaN-Mb of the present invention. When Ma = Si, SiN-YAl
O is preferable, and SiN-YAlO has a large OW erasing rate and a small jitter of a reproduced signal. In addition, SiN-
In YAlO, Y may be replaced with a lanthanide element such as Ce, Pr, Nd, and Hf. In addition, SiN-
SiN and Mb nitride types such as AlN-LO type (L is a lanthanide element having an atomic number of 57 to 72), SiN-AlN type and the like; SiN and Mb carbide type such as SiN-WC and SiN-SiC; SiN-SiO It is an oxide type of SiN and Mb. The composition ratio of Mb in the SiN-Mb is preferably 3 to 50 mol%, and if it is less than 3 mol%, both the adhesion and the number of repeated recording / reproduction are inferior.
%, The light absorption coefficient exceeds 0.5, the jitter of the reproduced signal is degraded, or the number of times of repeated recording and reproduction is reduced.
In this case, if the light absorption coefficient exceeds 0.5, the interface layer 1
The laser beams 3 and 15 themselves are heated by the irradiation of the laser beam, the recording marks are distorted, and the jitter of the reproduced signal increases. The thickness of the interface layers 13 and 15 is 10 to 400 °.
If it is less than 10 °, the uniformity of the interface cannot be maintained, and if it exceeds 400 °, the recording sensitivity deteriorates. When Ma = Al, AlN—SiC—
CrO is preferred, which has a high OW erasure rate and low jitter of the reproduced signal. Mb in the AlN-Mb
Is preferably 7 to 40 mol%, and 7 mol%
If it is less than 1, the number of times of repeated recording and reproduction is small, or the OW erasing rate cannot be increased. If it exceeds 40 mol%, the light absorption coefficient exceeds 0.5 or the number of times of repeated recording / reproduction decreases. In this case, the thickness of the interface layers 13 and 15 is preferably 10 to 400 ° similarly to the above, and 10 °
If it is less than 400 ° C., the uniformity of the interface cannot be maintained, and if it exceeds 400 °, the recording sensitivity deteriorates. As a reference example, the case of Ma = Ge will be described. In this case, GeN-AlO-Cr is preferred,
The OW erasure rate increases, and the jitter of the reproduced signal decreases. Further, the composition ratio of Mb in GeN-Mb is 5-4.
5 mol% is good, and less than 5 mol% is inferior in adhesion,
If it exceeds 45 mol%, the light absorption coefficient exceeds 0.5,
Or, the adhesiveness decreases. In this case, the thickness of the interface layers 13 and 15 is preferably 10 to 400 ° similarly to the above, and if the thickness is less than 10 °, uniformity of the interface cannot be maintained, and
If it exceeds 00 °, the recording sensitivity deteriorates. The interface layers 13 and 15 of the present invention may be provided on at least one of the upper surface side and the lower surface side of the recording layer 14. However, in FIG. Preferably, in that case, the jitter of the reproduction signal for repeated recording is reduced. Furthermore, it is preferable to provide it on both the upper surface side and the lower surface side of the recording layer 14, which is effective in increasing the number of times of repeated recording and reproduction and reducing jitter. The interface layers 13 and 15 of the present invention have the following functions. Recording layer 1 by a light beam such as a laser beam
When the temperature of the recording layer 4 is increased, crystal nuclei of the recording layer 14 are easily generated at the interface between the interface layers 13 and 15 and the recording layer 14, and as a result, the recording layer 14 changes from an amorphous state to a crystalline state. The speed is increased, and characteristics such as the OW erase ratio are improved. Also,
The recording layer 14 undergoes a phase change between a crystalline state, a liquid state, and an amorphous state during recording, but inter-diffusion of component elements has occurred between the recording layer 14 and the transparent dielectric layer adjacent thereto during conventional recording. This has the effect of being eliminated. Furthermore, since the interface layers 13 and 15 are excellent in adhesion, the adhesion of the entire layer is improved. The first and second transparent dielectric layers 12 and 16
Functions as a protective layer and an intermediate layer for the recording layer 14 and the interface layers 13 and 15, and is made of ZnS-Si.
O ₂ , SiN-based material, SiON-based material, SiO ₂ , Si
_{O, TiO 2, Al 2 O} 3, Y 2 O 3, TaN, Al
N, ZnS, Sb ₂ S ₃ , SnSe ₂ , Sb ₂ Se ₃ ,
CeF ₃ , amorphous Si (hereinafter referred to as a-Si), TiB ₂ , B ₄ C, B, C, and the like are preferable. In particular, ZnS—SiO ₂ is preferable, and this material has little change in characteristics at high temperatures. (ZnS) _x (Si
O ₂ ) When _100-x , 60 at% ≦ x ≦ 95 at%
Is preferable, and when x <60 at%, heat resistance is poor, and x>
At 95 at%, the particle size of ZnS becomes large and the jitter is deteriorated. The first and second transparent dielectric layers 12, 16
The thickness is preferably from 1 nm to 200 nm, and if it is less than 1 nm, it is difficult to form a film uniformly, and if it exceeds 200 nm, characteristics such as BER for repeated recording and reproduction are greatly deteriorated. The reflection layer 17 is made of Al, A having a high reflectance.
1Cr alloy, AlCu alloy, AlTi alloy, Au, A
g, AuCu alloy, Pt, AuPt alloy and the like are preferably used. Thus, the optical recording medium of the present invention has improved properties such as the OW erasure rate, eliminates interdiffusion between the recording layer and the transparent dielectric layer, and has excellent adhesion due to the interface layer. Has an effect. In the present invention, each of the above layers is formed on the transparent substrate 11.
2 each of which is laminated on both sides of the
By attaching two transparent substrates 11, the recording capacity may be doubled. The present invention is not limited to the light intensity modulation method of pulse-modulating a laser beam, but is also applicable to a heating method using energy beams such as electron beams and electromagnetic waves. The medium M1 of the present invention is a rewritable optical disk, such as a DVD (digital video disk),
It can be applied to optical disks such as D (compact disk) and CD-ROM. It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention. Embodiments of the present invention will be described below. Example 1 The medium M1 (optical disk) shown in FIG. 2 was constructed as follows. On a main surface of a 3.5-inch-diameter disk-shaped transparent substrate 11 made of polycarbonate, a first transparent dielectric layer 12 made of ZnS-SiO ₂ , a film thickness of about 200 °, SiN-YA
interfacial layer 13 made of 10 O or the like, about 200 膜厚 in thickness, Ge ₂ S
b ₂ Te ₅ recording layer 14, thickness about 200 °, Si
An interface layer 15 made of N-YAlO or the like;
A second transparent dielectric layer 16 made of ZnS-SiO _{2, a} reflective layer 17 made of AlCr and having a thickness of about 1000 ° was formed by magnetron sputtering. As a comparative example 1, a medium M2 (optical disk) as shown in FIG. 3 was produced as follows. Medium M
Reference numeral 2 denotes a film having a thickness of about 1000 ° on a main surface of a 3.5-inch diameter disk-shaped transparent substrate 21 made of polycarbonate.
A first transparent dielectric layer 22 of ZnS—SiO ₂ , a thickness of about 200 °, a recording layer 23 of Ge ₂ Sb ₂ Te ₅ ,
A second transparent dielectric layer 24 made of ZnS-SiO ₂ and a reflective layer 25 made of AlCr and having a thickness of about 200 ° and AlCr were formed by magnetron sputtering. Next, as Comparative Examples 2 to 5, a medium M3 (optical disk) as shown in FIG. 4 was produced as follows. The medium M3 has a thickness of about 1000 on a main surface of a 3.5-inch diameter disk-shaped transparent substrate 31 made of polycarbonate.
Å, a first transparent dielectric layer 32 made of ZnS—SiO ₂ ,
Interfacial layer 33 made of SiN, SiO, AlN or Cr with a film thickness of about 200 °, Ge ₂ Sb ₂ Te _{5 with} a film thickness of about 200 °
Recording layer 34 made of SiN, Si
An interface layer 35 of O, AlN or Cr, having a thickness of about 200
Å, a second transparent dielectric layer 36 made of ZnS—SiO ₂ ,
A reflective layer 37 made of AlCr and having a thickness of about 1000 ° was formed by magnetron sputtering. Table 1 shows the results of measuring the adhesion of the entire layer, the jitter for repeated recording, the OW erasure rate, the light absorption coefficient, and the number of repeated recording / reproduction.
Table 2 shows the measurement results of the recording sensitivity of the medium M1 having the interface layers 13 and 15 made of SiN-YAlO when the thickness of the interface layers 13 and 15 was changed. [Table 1] [Table 2] In Table 1, the adhesion was evaluated by observing the peeling of the film with a microscope after leaving it for 0 hours and 1000 hours in an environment of 85 ° C. and 95% relative humidity. Those with partial peeling were marked with triangles, and those with almost the entire film peeled were marked with x. The measurement of the OW erasure rate was performed as follows. First, the linear velocity of a track on an optical disk is set to 6.1.
Irradiation with a laser beam pulse-modulated at 13 mW (corresponding to an amorphous state) and 5 mW (corresponding to a crystalline state) at a light wavelength of 830 nm and recording at 4.91 MHz and a pulse width of 30 ns at 8 m / s, Next, OW was performed at 1.84 MHz and a pulse width of 30 ns, and the difference between the carrier level at 4.91 MHz before OW and the carrier level at 4.91 MHz after OW was defined as the OW erasure rate. The jitter for repeated recording was 13 mW (corresponding to an amorphous state) at 5 nm at an optical wavelength of 830 nm, with the track linear velocity of the optical disk being 6.18 m / s.
W is irradiated with pulse-modulated laser beam (corresponding to a crystalline state), and jitter of the reproduced signal when the first recording was performed at 4.91MHz, similar records 10 ⁶ times reproduction signal after Was measured. The number of times of repetitive recording / reproduction is the number of times of repetitive recording / reproducing when the jitter exceeds 10% by repeatedly recording at the same place where the jitter was measured and measuring the jitter of the reproduced signal. As shown in Table 1, the product of the present invention exhibited superior characteristics with respect to adhesion, jitter, OW erasure rate, light absorption coefficient, and number of times of repeated recording / reproduction as compared with the comparative example. Also,
From Table 2, it was found that when the thickness of the interface layers 13 and 15 exceeded 400 °, the recording sensitivity deteriorated. (Embodiment 2) The interface layers 13 and 15 are made of AlN-
The medium M1 of Example 1 except that the medium M1 was formed of SiC—CrO or the like.
Table 3 shows the results of measuring the adhesion of these layers as a whole, the jitter with respect to repeated recording, the OW erasure rate, the light absorption coefficient, and the number of times of repeated recording / reproduction in the same manner as in Example 1. As Comparative Example 6, the interface layers 13, 1
A device having the same configuration as in Example 2 except that 5 was changed to SiO ₂ was produced. Further, for those having the interface layers 13 and 15 made of AlN—SiC—CrO,
Table 4 shows the measurement results of the recording sensitivity and the jitter when the thicknesses of the recording layers 3 and 15 were changed. [Table 3] [Table 4] As shown in Table 3, the product of the present invention exhibited superior characteristics in comparison with Comparative Example 6 with respect to adhesion, jitter, OW erasure rate, light absorption coefficient, and number of times of repeated recording / reproduction. Further, as shown in Table 4, the thickness of the interface layers 13 and 15 was 40
It was found that when the angle exceeds 0 °, the recording sensitivity deteriorated. (Embodiment 3) The interface layers 13 and 15 are made of GeN-
Except for being formed of AlO-Cr or the like, the medium was configured in the same manner as the medium M1 of Example 1, and in the same manner as Example 1, the adhesion of these layers as a whole, the jitter against repeated recording, the OW erasure rate,
Table 5 shows the measurement results of the light absorption coefficient and the number of times of repeated recording / reproduction. Further, as Comparative Example 7, a device having the same configuration as in Example 3 except that the interface layers 13 and 15 were made of GeN was produced. [Table 5] As shown in Table 5, the product of the present invention exhibited superior characteristics in comparison with Comparative Example 7 with respect to adhesion, jitter, OW erasure rate, light absorption coefficient, and number of times of repeated recording / reproduction. According to the present invention, at least one of the upper surface and the lower surface of the recording layer is provided with MaN-Mb (where Ma is Si,
Al or Ge, and Mb is B, Bi, Al, Si,
P, S, Ti, V, Zn, Ge, Y, W, Cr, Zr,
Each element of the element group composed of Ta, Mb includes at least one oxide of the element group, Mb includes each nitride of the element group, and Mb includes at least one carbide of the element group. ) Makes it easier to generate crystal nuclei of the recording layer at the interface between the interface layer and the recording layer when the temperature rises due to light irradiation, and as a result, the characteristics such as the OW erasure rate are improved. In addition, during recording, mutual diffusion between the recording layer and the transparent dielectric layer is eliminated, and the provision of the interface layer improves the adhesion of the entire layer, and further reduces the light absorption coefficient to improve recording sensitivity. It has the effect of doing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of a conventional optical recording medium M. FIG. 2 is a partial cross-sectional view of the optical recording medium M1 of the present invention. FIG. 3 is a partial cross-sectional view of an optical recording medium M2 of Comparative Example 1. FIG. 4 is a partial cross-sectional view of an optical recording medium M3 of Comparative Example 2. [Description of Signs] 1: transparent substrate 2: first transparent dielectric layer 3: recording layer 4: second transparent dielectric layer 5: reflective layer 11: transparent substrate 12: first transparent dielectric layer 13: interface layer 14 : Recording layer 15: interface layer 16: second transparent dielectric layer 17: reflective layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7/24

Claims (1)

(57) [Claim 1] A first transparent dielectric layer on a transparent substrate, a recording layer which changes into an amorphous or crystalline phase in accordance with the output of an irradiating light beam, (2) An optical recording medium having a transparent dielectric layer and a reflective layer in order, wherein the first transparent dielectric layer and the second transparent dielectric layer are made of the following materials, and further, upper and lower surfaces of the recording layer to both sides, 85 ° C., in order to be free of peeling off and left for 1,000 hours at a relative humidity of 95% RH,
An optical recording medium comprising an interface layer represented by the following composition formula: MaN-Mb. Material of first and second transparent dielectric layers: ZnS-Si
O ₂ , SiN-based material, SiON-based material, SiO ₂ , Si
_{O, TiO 2, Al 2 O} 3, Y 2 O 3, TaN, Al
N, ZnS, Sb ₂ S ₃ , SnSe ₂ , Sb ₂ Se ₃ ,
CeF ₃ , amorphous Si, TiB ₂ , B ₄ C, B, C
MaN-Mb ... Ma is Si or Al, and Mb is B, Bi, Al, Si, P, S, Ti, V, Zn, G
e, Y, W, Cr, Zr, and at least one element selected from the group consisting of elemental elements, oxides of the element group, and carbides of the element group. However, Ma = Mb and Mb
Excludes the case where is a single element.