JP2002269742A - Phase change optical recording medium and recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording method by which a wide power margin can be secured and to provide a medium suitable for the method. SOLUTION: (1) The recording method is characterized in that when recording is performed on a phase transition type optical recording medium, the luminous waveform of a laser beam is formed in a recording pulse train consisting of a plurality of on-pulses and off-pulses succeeding thereto, recording frequencies are continuously changed from an inner periphery to an outer periphery or reversely thereto in correspondence with the recording radius position and the width of the plurality of on-pulses are controlled in accordance with the frequencies. (2) The medium is a phase transition type optical recording medium formed by laminating a first dielectric protective layer, a AInSbTeGe (A is Ag and/or Ga) phase change recording layer, a second dielectric protective layer, a SiC layer and a metal reflection layer which are laminated on a transparent substrate in this order and characterized in that the material of the first and the second dielectric protective layers consists of a mixture of ZnS and SiO2 and the metal reflection layer consists of Ag or Ag alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase-change type optical recording system capable of recording and reproducing information by irradiating a light beam with an optical change in a recording layer and performing rewritable information. The present invention relates to a medium and a recording method.

[0002]

2. Description of the Related Art Phase-change optical recording media are widely used for storing document files and image files, for backing up hard disk files, and the like. Large capacity ones are strongly desired. In particular, with the spread of DVDs and the like, large-capacity image rewritable media are required, and development of these media has been actively carried out. On the other hand, high reflectivity is required to maintain compatibility with ROM drives, but it is difficult for a phase-change optical recording medium to satisfy these conditions. In the phase-change optical recording medium, the recording layer is heated once to a high temperature and then rapidly or slowly cooled to perform recording and erasing. To perform this operation at high speed, the layer structure of the medium and recording suitable for this operation are performed. In addition to the layer composition, a light emission waveform pattern for recording / erasing, that is, a recording strategy becomes important. Further, if a single medium can support a wide range of linear velocities, it is difficult to make the same at any linear velocity only by devising materials and configurations.

On the other hand, the present inventors can apply the invention to the CAV system in which the linear velocity changes continuously from the inner circumference to the outer circumference of the medium, and the CLV system in which the linear velocity is constant regardless of the radial position. A recording method was proposed (JP-A-2000-32274).
No. 0). In this recording method, the recording frequency changes as the linear velocity changes continuously. However, the width of the light emission pulse is varied using the frequency as a parameter to simplify the recording method so as not to complicate the recording method. Moreover, a wide range of linear velocities can be handled under one medium condition. On the other hand, even in the CLV method, it is desirable that a single medium can support a wide range of linear velocities although the linear velocity is constant. Therefore, this recording method involves changing the recording layer composition and the medium configuration in one medium for each radial position. This is an excellent method in that good characteristics can be obtained even when recording is performed at a wide range of linear velocities without using a multi-layer structure. However, although it is sufficient to perform recording under one condition, for example, an optimum recording power, it cannot be said that it is still sufficient to secure a wide recording power margin including overwrite characteristics.

[0004]

The problem with recording at a higher linear velocity is that a higher linear density is also required at the same time, resulting in a higher recording frequency and a narrower pulse width for recording one bit. It is difficult to raise the temperature of the layer to near the melting point in a short time.Even if the recording power is increased and the temperature is raised as a countermeasure, a quenching time is required for forming the mark. And this time cannot be shortened. Also, if the time required for rapid cooling is sufficiently ensured, erasing by slow cooling becomes difficult this time, so that the characteristics are degraded due to unerased portions due to insufficient erasing during overwriting. These problems can be improved by the medium configuration, but if the problem cannot be solved by the recording layer material or composition, the configuration becomes complicated, such as increasing the number of layers in the medium. Accordingly, an object of the present invention is to provide a recording method capable of securing sufficient characteristics even with a recording power lower than the optimum power and securing a wide power margin, and a medium suitable for the method.

[0005]

Means for Solving the Problems The above problems are as follows:
It is solved by the invention of 3). 1) In forming a recording mark on a phase-change type optical recording medium, the emission waveform of the laser light is a recording pulse train composed of a plurality of ON pulses and an OFF pulse following the recording pulse, and each output level has a recording power Pw and a bias power Pb. Yes,
A recording method for an optical recording medium in which recording is performed by continuously changing a recording frequency ν from an inner circumference to an outer circumference or from an outer circumference to an inner circumference in accordance with a recording radius position, wherein the widths of the plurality of on-pulses are all the same. Fixed part and window width Tw
(= 1 / ν) multiplied by a constant, and the trailing end of each pulse in the recording pulse train is Tx = a from the (n + 1) × Tw reference clock (n = 1, 2, 3,... 13).
× Tw (a is an arbitrary optimal value of 1 or less) and is fixed at a time constant. Only when n = 1, the other n = 2 to 1
In the recording method in which the time constant is fixed to an earlier time constant than in the case of 3, the erasing power for erasing after the last off pulse of the recording pulse train is composed of two levels Pe1 and Pe2, and Pe1 and Pe2 satisfy Pw>Pe1>Pe2>. A recording method for a phase-change type optical recording medium, characterized in that the relationship of Pb is satisfied and the application time te1 of Pe1 is 0 <te1 <Tw. 2) A phase-change optical recording medium suitable for the recording method according to 1), wherein a first dielectric protective layer, AInS
bTeGe (A is Ag and / or Ga) phase change recording layer,
A second dielectric protection layer, a SiC layer, and a metal reflection layer are laminated in this order, and the material of the first and second dielectric protection layers is ZnS.
And a mixture of SiO ₂ and the metal reflective layer is made of Ag or Ag.
A phase change type optical recording medium characterized by being an alloy. 3) The composition of the phase change recording _layer, A _V In W _Sb X T
When e _Y Ge _Z (A is Ag and / or Ga),
V), W, X, Y, and Z are in the following ranges. 0 <V <0.10 0.03 ≦ W <0.10 0.55 <X <0.80 0.01 ≦ Z ≦ 0.07 Y = 1− (V + W + X + Z)

Hereinafter, the present invention will be described in detail. The optical recording medium of the present invention includes polycarbonate (P
C), a plastic substrate such as polymethyl methacrylate (PMMA), or a transparent substrate such as a glass substrate is used. A transparent dielectric is used for the first dielectric protection layer. Examples of the material include a sulfide such as ZnS;
₂ , oxides such as In ₂ O ₃ and ZrO ₂ ; SiN, Ge
Nitrides such as N and AlN; carbides such as SiC and ZrC;
Or a mixture thereof. As a mixture, Z
A mixture of nS and SiO ₂ is preferred, usually ZnS and Si
A molar ratio of O ₂ of 50:50 to 90:10 is used, and a molar ratio of around 80:20 is particularly preferable. These materials preferably have low absorption when the wavelength of the incident light is in the range of 400 to 780 nm, and have a refractive index of 1.5 to 2.0.
A range of 5 is preferred. The thickness of the first dielectric protection layer must be such that cracks due to heat during film formation do not occur, environmental protection for the recording layer can be maintained, and large deformation of the substrate can be prevented. There are 25
~ 250 nm is preferred. The same material as the first dielectric protection layer is used for the second dielectric protection layer. The film thickness range is 5 to 30
nm.

[0007] Al, Cu, Au, Pt, P
Metals such as d and Ag or alloys thereof are used. In particular, in high-speed recording, it is necessary to use a metal or alloy having a higher thermal conductivity, and Ag having a higher thermal conductivity than Al or an alloy in which a small amount of Cu or Ni is added to Ag to improve environmental resistance. It is desirable to use Between the second dielectric protection layer and the reflection layer, a layer such as a carbide such as SiC, an oxide such as ZnO or In ₂ O ₃ , or a nitride such as AlN is provided. This layer is provided for the main purpose of preventing the Ag reflection layer from being sulfurized in a high-temperature and high-humidity environment when the second dielectric protective layer contains a sulfide. As a material of this layer, a material having a higher thermal conductivity than the material of the second dielectric protective layer, preferably equivalent to that of the reflective layer is good. For example, if the protective layer material is Zn
In the case of a mixture of S and SiO ₂ , SiC is preferred because it has a higher thermal conductivity and a higher melting point than the mixture. The thickness of this layer is preferably thinner in consideration of heat radiation to the reflective layer.
nm. However, since SiC absorbs light, it should be noted that if the film thickness is too large, the reflectance will decrease.

[0008] The phase-change recording material has a composition of A _V In _W S
When (the A Ag and / or Ga) b _X Te _Y Ge _Z was, V, W, X, Y , Z is preferably in a range of the following. 0 <V <0.10 0.03 ≦ W <0.10 0.55 <X <0.80 0.01 ≦ Z ≦ 0.07 Y = 1− (V + W + X + Z) This material is composed of Sb and Te Binary eutectic composition (S
b: Te = 70: 30) Since the alloy is fundamental, Ga and In are added in order to further increase the crystallization speed while maintaining the composition near the eutectic composition ratio. Addition of too much Ag is undesirable because it lowers the crystallization rate. To increase the recording linear velocity, it is sufficient to use only Ga without adding Ag. Conversely, when the recording linear velocity is relatively low, only Ag without adding Ga may be used. Therefore, both Ag and Ga may be added, or only one of them may be added. 0 <V <0.10 is preferable, but 0 <Ag <0.02 and 0 <Ga <
0.07. Although the preservability is improved by increasing In, the signal degradation occurs when the reproduction power at the time of reproduction is high, so that 0.03 ≦ W <0.10, preferably 0.03 ≦ W <0.07. And Ge is an element effective for improving the storage stability. However, if Ge is excessively added, the crystallization temperature is high, so that it is difficult to initialize (change an amorphous phase into a crystalline phase before recording). Therefore, the amount of addition is 0.0
1 ≦ Z ≦ 0.07, preferably 0.01 ≦ Z ≦
0.05. Sb is set to 0.55 <X <0.80, preferably 0.65 <X <0.80. The thickness range of the recording layer is 10 to 25 nm. If it is too thin, the modulation will be small, and if it is too thick, the recording sensitivity and repetitive recording characteristics will be poor. By using this phase change recording material, good recording characteristics and storage characteristics from a low linear velocity to a high linear velocity can be obtained.

[0009] A desirable recording linear velocity range of the optical recording medium is 1 to 5 times the speed of DVD, that is, about 3.5 m / s to 16 m / s. Next, a recording method of the optical recording medium having the optimized configuration will be described. In the so-called CAV method in which the linear velocity changes continuously from the inner side to the outer side of the radial position, the recording corresponding to the linear velocity in which the pulse width of the on-pulse portion of the pulse emission waveform of the LD (laser diode) during recording changes continuously. It is determined by the sum of a time constant and a portion obtained by multiplying the window width Tw (Tw = 1 / ν) with respect to the frequency ν by a constant. FIG. 1 shows a light emission waveform pattern for recording a mark corresponding to 5 Tw in the conventional method. As shown in the figure, the pulse width of the plurality of on-pulse trains is the sum of a portion (b) in which a window width (reference clock) Tw (Tw = 1 / ν) is multiplied by a constant and a portion (a) fixed by a time constant. Is determined by Further, when the pulse start time of the leading pulse (reference clock 2Tw in the case of n = 1) of a plurality of pulse trains is started from an earlier time (part c in FIG. 1), the recording characteristics are improved. In such a case, the width may be shorter than the width (a + b) of the subsequent pulse train as shown in the portion e. Further, the off-pulse width (d in FIG. 1) after the last pulse is adjusted so as to obtain good characteristics. The waveforms of c and d in FIG. 1 are determined by Tw by determining the reference clock Tw (Tw = 1 / ν) by a constant multiplication formula.

[0010] As a specific example, when the recording frequency of the innermost part is 26.2 MHz, the head part c = Tw × 1/6, a = 4.0, b =
Tw × 1/6, (e = a + b) Other pulse portions a = 6.0, b = Tw × 1/6 Off pulse portion of the last pulse d = Tw × 0 or Tw × 1/6, a = 4.0, b =
Tw × 0, (e <a + b) • The off-pulse part d of the final pulse = Tw × １ ／. As described above, in the recording by the CAV recording method, since the waveform is determined by Tw and a constant, it can be handled without complicating the setting of the waveform.

The recording / reproducing conditions include a wavelength of 400 to 780.
Recording and reproduction are possible in the range of nm. To increase the recording density, the numerical aperture of the objective lens is set to 0.60 or more, and the beam diameter of the incident light is reduced. For example, when the wavelength is 650 nm and the numerical aperture of the objective lens is 0.60 to 0.65, the thickness of the substrate is 0.6 mm, and the track pitch of the substrate is 0.74.
μm or less, groove depth 15-60 nm, groove width 0.2-0.
3 μm. When recording is performed at a high speed and at a high density using this optical recording medium, the light emission pulse of the laser light is used for recording (P
w), erasing (Pe), and bias (Pb). The recording / erasing power is higher than the reproducing power, and the bias power is lower than the reproducing power. The bias power is the power after the irradiation of the recording power, and is necessary for forming an amorphous phase. The linear density is 0.267μ
m / bit. In the present invention, in order to obtain better characteristics at a low recording power, the erasing power is composed of two levels Pe1 and Pe2, Pe1 and Pe2 have a relationship of Pw>Pe1>Pe2> Pb, and the application time te1 of Pe1 Is set to satisfy 0 <te1 <Tw.

FIG. 2 shows waveforms. The phase change recording material used in the present invention, at the time of recording and erasing, rapidly or slowly cooled after raising the temperature to near the melting point by laser power,
Amorphous or crystalline phase. In particular, at the time of crystallization, ie, erasing, the recording layer can be erased at high speed by increasing the temperature of the recording layer as high as possible, preferably to near the melting point. In the current recording method, Pw is changed while keeping the ratio of Pe / Pw constant. Therefore, when Pw is low, Pe decreases accordingly. As a result, in the case of low Pw, the repetitive recording characteristics due to unerased data are rapidly deteriorated as compared with the case where recording is performed at a higher optimum Pw. At a low Pw, the second-time recording characteristics are further worse than the first-time recording characteristics. To improve this, Pe may be increased, but as Pw increases, Pe increases, and there is a possibility that the limit value of LD may be reached. In addition, there is an effect that the amorphous phase is recrystallized on the high Pw side and the characteristics are deteriorated. Therefore, in the present invention, the erasing power is set to two values so as to obtain better characteristics at lower Pw. Conventional Pe corresponds to Pe2, and Pe1 is newly set as a higher erasing power. The width of Pe1 is preferably as wide as possible, but it is shorter than the time corresponding to the shortest mark length. Accordingly, the width is preferably equal to or less than the window width, and is at most less than Tw × 2. By recording under these conditions,
At a power lower than the optimum recording power, the jitter characteristics, the asymmetry characteristics, and the reflectance can be improved. Further, it is desirable that Pe1 be kept constant even if Pw changes, and that Pe2 fluctuate in the ratio of Pe2 / Pw as in the past.
Under such recording conditions, even in the case of the CLV system in which the linear velocity is constant irrespective of the radial position, the recording frequency is constant with respect to the linear velocity. Is obtained.

Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Examples 1 to 9, Comparative Examples 1 to 3 Groove pitch 0.74 μm, groove width 0.3 μm, groove depth 33 n
A polycarbonate substrate having a guide groove of m and a thickness of 0.6 mm was used, and the following layers were sequentially laminated thereon by a sputtering method. First, ZnS: SiO ₂ = 80:
Using a target of 20 (mol%), high frequency power 3
Under the conditions of kW and Ar gas pressure of 0.5 Pa, a 75 nm-thick first dielectric protection layer was formed. Next, using a target having a predetermined composition, a recording layer having a composition shown in Table 1 and a film thickness of 17 nm was formed under the conditions of a direct current power of 0.3 kW and an Ar gas pressure of 0.3 Pa. Next, a second dielectric protection layer having a thickness of 10 nm was formed using the same material and conditions as those for the first dielectric protection layer. Next, a 4 nm-thick SiC film was formed. Next, a reflective layer having a thickness of 140 nm was formed using Ag at a DC power of 5.0 kW and an Ar gas pressure of 0.3 Pa. Further, an ultraviolet curable resin was applied, and another substrate without a film was bonded thereon to obtain an optical recording medium having a thickness of 1.2 mm. Thereafter, the recording layer was crystallized using a large-diameter LD at a linear velocity of 3.5 m / s and a power of 700 mW. Subsequently, the recording / reproducing wavelength is 655 nm, and the objective lens NA (numerical aperture) is 0.6.
Using the pickup head of No. 5 and the CAV method,
For each recording layer, the recording density was 0.2 at the linear velocity shown in Table 1.
Recording was performed at 67 μm / bit. The modulation method of the recording data is (8'16) modulation, the recording power is 14 mW,
The bias power is 0.2 mW, and the other parameters are the same as those shown in FIG. Table 1 shows the jitters at the first time, the second time, and after 1000 times of repetitive recording. From the results of the table, it is clear that the example is superior to the comparative example. In Table 1, “nsec.” Is “nanosecond”.
Means The width of Pe1 was Tw. (If the time length of Pe1 is about Tw, which is the length of the basic mark,
FIG. 3 shows the recording power dependence of Example 6 and Comparative Example 2. FIG. 3 shows that the recording power is 12.0 mW to 1 mW.
It can be seen that the jitter characteristic of the example is better than that of the comparative example in the range of 3.5 mW.

[0015]

[Table 1]

[0016]

According to the first aspect of the present invention, it is possible to perform recording by the CAV method in which the linear velocity changes continuously from the inner periphery to the outer periphery, and further, the signal characteristics at a lower recording power are improved. A wide recording power margin can be obtained. According to the second aspect of the present invention, good signal characteristics can be obtained from a low linear velocity to a high linear velocity by using the recording method of the first aspect. According to the third aspect of the invention, better signal characteristics can be obtained from a low linear velocity to a high linear velocity.

[Brief description of the drawings]

FIG. 1 is a diagram showing a light emission waveform pattern for recording a mark corresponding to 5 Tw in a conventional method.

FIG. 2 is a diagram illustrating a light emission waveform in the case of the present invention.

FIG. 3 is a diagram showing the recording power dependence of Example 6 and Comparative Example 2.

[Description of Signs] Tw Window Width (Reference Clock) 1 Window 2 Window 3 Window 4 Window 5 Window a Portion Fixed by Time Constant b Portion Proportional to Reference Clock Tw (Tw = 1 / ν) of Each Linear Speed c Optimum Part prepared for optimization d part prepared for optimization e indicates that only the beginning is short. Pw Recording power Pb Bias power Pe Erase power Pe1 One of two erase power levels Pe2 The other of two erase power levels te1 Pe1 application time

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) G11B 7/24 535 G11B 7/24 538E 538 B41M 5/26 X (72) Inventor Nobuaki Onagi Ota-ku, Tokyo 1-3-6, Nakamagome Ricoh F-term (reference) 2H111 EA23 FA01 FA11 FA12 FA14 FA23 FB05 FB09 FB12 FB17 FB21 5D029 JA01 LA14 LA15 LA17 5D090 AA01 BB05 BB12 CC06 DD01 EE01 KK05

Claims (3)

[Claims] In forming a recording mark on a phase-change optical recording medium, the emission waveform of a laser beam is a recording pulse train composed of a plurality of on-pulses followed by an off-pulse, and each output level has a recording power Pw and a bias. Power Pb
The recording method of the optical recording medium for recording by changing the recording frequency ν continuously corresponding to the recording radius position from the inner circumference to the outer circumference or from the outer circumference to the inner circumference, wherein the width of the plurality of on-pulses is All are fixed at the same time constant and a part that multiplies the window width Tw (= 1 / ν) by a constant. The trailing end of each pulse in the recording pulse train is (n + 1) × Tw
From the reference clock (n = 1, 2, 3,... 13)
x = a × Tw (a is an arbitrary optimal value of 1 or less) and is fixed at a time constant. When n = 1, only n = 2
, The erasing power for erasing after the last off pulse of the recording pulse train is composed of two levels Pe1 and Pe2, and Pe1 and Pe2 satisfy Pw>Pe1> Pe2. > Pb, and the application time te1 of Pe1 satisfies 0 <te1 <Tw. 2. A phase change type optical recording medium suitable for the recording method according to claim 1, wherein a first dielectric protection layer, AInSbTeGe (A is Ag and / or Ga) phase change recording on a transparent substrate. Layer, a second dielectric protection layer, a SiC layer, and a metal reflection layer are laminated in this order, the material of the first and second dielectric protection layers is a mixture of ZnS and SiO ₂ , and the metal reflection layer is made of Ag. Or a phase change type optical recording medium characterized by being an Ag alloy. 3. The composition of the phase change recording layer is represented by A_VIn_W
Sb_XTe_YGe_Z (A is Ag and / or Ga)
Sometimes, V, W, X, Y, and Z are in the following ranges.
3. The phase-change optical recording medium according to claim 2, wherein: 0 <V <0.10 0.03 ≦ W <0.10 0.55 <X <0.80 0.01 ≦ Z ≦ 0.07 Y = 1− (V + W + X + Z)