JPH04360039A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a high recording speed, a high erasing rate and C/N, the maintenance of stable operations in spite of repetition of many times of recording and erasing, excellent wet heat resistance and oxidation resistance, and a long life by forming reflection layers in two-layered constitution of different thermal conductivities. CONSTITUTION:The reflection layers of the optical recording medium are constituted of two layers; the 1st reflection layer 5 and the 2nd reflection layer 6. The thermal conductivity of the 1st reflection layer 5 is set higher than the thermal conductivity of the 2nd reflection layer 6. The material of the 1st reflection layer 5 is formed by using metals, such as Al and Au, and the alloys essentially unsisting thereof, the Al added with Si, Mg, Cu, etc., or the Au added with Cr, Ag, Cu, etc., and the thickness thereof is specified to >=10nm and <=100nm. The material of the 2nd reflection layer 6 is formed by using metals, such as Ti, Zr, Hf, Cr, Mo, etc., and the thickness thereof is specified to >=20nm and <=200nm.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium on which information can be recorded, erased, and reproduced by irradiation with light.

In particular, the present invention relates to a rewritable phase-change optical recording medium such as an optical disk, an optical card, or an optical tape, which has functions for erasing and rewriting recorded information and is capable of recording information signals at high speed and high density. It is something.

0003

2. Description of the Related Art Conventional technologies for rewritable phase-change optical recording media are as follows.

These optical recording media have a recording layer containing tellurium as a main component, and during recording, a laser beam pulse focused on the crystalline recording layer is irradiated for a short period of time to partially melt the recording layer. do. The melted portion is rapidly cooled by thermal diffusion and solidified, forming an amorphous recording mark. The light reflectance of this recording mark is lower than that of the crystalline state, and it can be optically reproduced as a recorded signal.

[0005] Furthermore, during erasing, a laser beam is irradiated onto the recording mark portion and heated to a temperature below the melting point of the recording layer and above the crystallization temperature, thereby crystallizing the amorphous recording mark and removing the original unrecorded mark. Return to state.

[0006] In this optical recording medium, a heat-resistant and light-transmitting dielectric layer is usually provided on both sides of the recording layer to prevent the recording layer from deforming or opening during recording. Furthermore, a metal reflective layer such as light-reflective Al is provided on the dielectric layer on the side opposite to the light beam incident direction, and the optical interference effect improves the signal contrast during reproduction, and the cooling effect improves the Techniques are known that facilitate the formation of crystalline recording marks and improve erase characteristics and repeat characteristics. In particular, the "quenching structure" in which the dielectric layer between the recording layer and the reflective layer is made as thin as about 20 nm is superior in that there is little deterioration due to repeated rewriting of recording, and there is a wide power margin for erasing power. (T. Ohota et al.
, Japanese Journal of Appli
ed Physics, Vol 28 (1989)
Suppl. 28-3 pp123-128).

[0007]

A problem with the rewritable phase change optical recording medium having the rapid cooling structure as described above is that the recording sensitivity is low because the cooling effect of the reflective layer is large. In other words, the light irradiation power required for recording and erasing is large, and the semiconductor laser of the optical head requires a high-power semiconductor laser, which increases the equipment cost.Furthermore, in the case of disks, the light irradiation power is insufficient and recording cannot be performed at high speed rotation. There were problems such as difficulty in

In this conventional quenching structure, methods for improving recording sensitivity include (a) making the protective layer between the recording layer and the reflective layer a little thicker;
Possible methods include (b) reducing the thermal conductivity of the reflective layer to reduce thermal diffusion; and (c) reducing the thickness of the reflective layer to reduce thermal diffusion.

However, in (a) and (b), the margin of erasing power for obtaining a good erasing rate is quite narrow;
In addition, there is a problem that the erasing rate also decreases, and in (c), if the reflective layer is made thinner to a certain extent, the reflectance of the reflective layer will decrease and the irradiated light will be transmitted behind the reflective layer, resulting in a loss of optical energy. This increases the amount of light absorbed by the recording layer, making it impossible to improve sensitivity, and the mechanical strength of the reflective layer decreases, resulting in deformation and deterioration of recording characteristics when rewriting is repeated. there were.

An object of the present invention is to provide an optical recording medium which has high recording sensitivity, shows little deterioration in recording characteristics even after a large number of recording, erasing, or rewriting operations, and has excellent recording and erasing characteristics. It is to be.

Another object of the present invention is to provide a long-life optical recording medium that is excellent in oxidation resistance and heat-and-moisture resistance and is free from defects even during long-term storage.

0012

[Means for Solving the Problems] The present invention provides information recording and recording by irradiating a recording layer formed on a substrate with light.
Erasing and reproducing are possible, and information can be recorded and erased.
In an optical recording medium that undergoes a phase change between an amorphous phase and a crystalline phase, the optical recording medium has at least a recording layer, a dielectric layer, and a reflective layer, and the reflective layer has two layers having different thermal conductivities. The present invention relates to an optical recording medium that is composed of a reflective layer and characterized in that the reflective layer on the side closer to the recording layer has a higher thermal conductivity than the other reflective layer.

A typical layer structure of the optical recording medium of the present invention is as follows:
When light is incident from the substrate side, as illustrated in FIG. (Here, the direction of light incidence is shown by an arrow 9), but the structure is not limited to this. On the reflective layer, a resin layer 8 such as an ultraviolet curable resin, an adhesive layer for bonding to other substrates, and a resin layer 8 to improve adhesion and prevent diffusion between each layer, within a range that does not impair the effects of the present invention. Other layers may be provided for other purposes.

[0014] Furthermore, when light is incident from the opposite side of the substrate, a typical layer configuration is substrate/second reflective layer/first reflective layer/
This is a laminate of second dielectric layer/recording layer/first dielectric layer. However, the present invention is not limited to this, and a heat insulating layer such as a resin layer may be provided between the substrate and the second reflective layer, or a protective layer such as an ultraviolet curing resin may be provided on the first dielectric layer, as long as the effects of the present invention are not impaired. Layers may be provided.

It is preferable to have a layer structure in which light is incident from the substrate side because it is less susceptible to the influence of dust.
A structure including a laminate in the order of reflective layer/second reflective layer/ultraviolet curing resin layer as a member is preferable because the layer structure is simple and manufacturing is easy.

The material of the first reflective layer of the present invention is a metal having light reflective properties.

Metals such as Al and Au, and alloys containing these as main components are preferable because they have high light reflectivity and can have high thermal conductivity. As an example of the aforementioned alloy, Al
Si, Mg, Cu, Pd, Ti, Cr, Hf, Ta,
Addition of at least one element such as Nb, Mn, Pd, etc. in total of 5 atomic % or less, 1 atomic % or more, or A
There are materials in which at least one element such as Cr, Ag, Cu, Pd, Pt, and Ni is added to u in a total amount of 20 atomic % or less and 1 atomic % or more.

[0018] In particular, since the cost of materials can be reduced,
An alloy containing Al as a main component is preferable, and in particular, since it has good corrosion resistance, Al and at least one metal selected from Ti, Cr, and Ta are added in a total of 5 atomic % or less.
．． Alloys with 5 atomic % or more added or Al with a total of 5
% or less of Si and Mn is preferred.

The thickness of the first reflective layer is approximately 10
It is not less than nm and not more than 100 nm. The thickness is preferably 10 nm or more and 50 nm or less since recording sensitivity can be particularly high.

The first reflective layer of the present invention is made of a metal with higher thermal conductivity than the second reflective layer, cools the recording layer, increases heat diffusion in the melted portion during recording, and improves the recording marks in the amorphous state. It has a function that facilitates formation. In the present invention, by forming this first reflective layer relatively thinly,
This limits the amount of heat diffusion from the recording layer, making it easier to raise the temperature of the recording layer during recording, and increasing recording sensitivity. On the other hand, since the thermal conductivity of this layer is considerably higher than that of the dielectric layer and the recording layer, it flattens the heat distribution in the plane direction of the recording layer during erasing operation.
Since the erasing area on the track can be enlarged, a good erasing rate and a wide erasing power margin can be obtained.

In the configuration in which the reflective layer 7 of the conventional optical recording medium shown in FIG. 2 consists of a single layer, when the reflective layer is made thin in this way, the reflectance of the reflective layer decreases, and the irradiated light is reflected behind the reflective layer. Since the light passes through the light, the loss of light energy increases and the amount of light absorbed by the recording layer decreases, so the sensitivity does not improve. On the other hand, in the present invention, by providing the second reflective layer, it is possible to sufficiently increase the reflectance, so that high sensitivity can be achieved without such loss. Here, the second reflective layer mainly has the function of reflecting light and is made of a material with low thermal conductivity, so that less heat is diffused and high sensitivity can be achieved.

[0022] The material of the second reflective layer is a metal or a metal compound that has light reflectivity and has a lower thermal conductivity than that of the first reflective layer.

[0023] The main component is a metal such as Ti, Zr, Hf, Pd, Cr, Mo, or Al or Au, and the same additive elements as the first reflective layer are added in a larger amount than in the first reflective layer,
Alloys with low thermal conductivity, metal compounds with light reflective properties such as nitrides such as Ti and Zr, and Ni-Cr alloys with low thermal conductivity are preferable because they have light reflective properties and can significantly lower thermal conductivity.

[0024] In particular, it is preferable from the viewpoint of corrosion resistance that the main component is the same metal as the first reflective layer. This is preferable because the cost of materials is low.

In particular, the first reflective layer is made of Al containing a total of 0.5 atomic % or more and less than 3 atomic % of additive elements because it has good corrosion resistance and is less likely to cause hillocks.
-Ti alloy, Al-Cr alloy, Al-Ta alloy, Al-
A of either Ti-Cr alloy or Al-Si-Mn alloy
Al-Ti alloy, Al-Cr alloy, Al-Ta alloy, Al-Ti-C, which is composed of an alloy whose main component is L, and the second reflective layer contains a total of 3 atomic % or more and 50 atomic % or less of additive elements.
r alloy, Al-Zr alloy, Al-Si-Zr alloy, Al
-Si-Mn-Zr alloy is preferred.

The thickness of the second reflective layer is approximately 20
It is not less than nm and not more than 200 nm. 30 nm or more 2 because the mechanical strength of the reflective layer is high, the deterioration of recording characteristics can be minimized even after repeated rewriting, and the recording sensitivity can be particularly high.
00 nm or less is preferable.

[0027] Furthermore, the first reflective layer and the second reflective layer of the present invention are not only formed by laminating these two layers, but also by gradually applying low heat from the first reflective layer to the second reflective layer. The invention of the present application also includes variations such as replacing the reflective layer with a material whose composition has been changed, such as a metal, to make it conductive, or configuring each of the first and second reflective layers as a laminate of a plurality of layers. Needless to say, it is within the range of

Although the recording layer of the present invention is not particularly limited, Pd-Ge-Sb-Te alloy, Ni-G
e-Sb-Te alloy, Ge-Sb-Te alloy, Co-G
e-Sb-Te alloy, In-Sb-Te alloy, Ag-I
Examples include n-Sb-Te alloy and In-Se alloy.

[0029] Pd-Ge-Sb-Te alloy, Ge-Sb
-Te alloy is preferable because the erasing time is short and recording and erasing can be repeated many times, and in particular Pd
-Ge-Sb-Te alloy is preferred because it has excellent properties as described above.

The thickness of the recording layer of the present invention is not particularly limited, but is 10 to 100 nm. In particular, the thickness is preferably 10 nm or more and 30 nm or less because recording and erasing sensitivity is high and recording and erasing can be performed many times.

The dielectric layer is used to protect the substrate, recording layer, etc. from being deformed by heat during recording, thereby preventing deterioration of recording characteristics. This dielectric layer includes inorganic thin films such as ZnS, SiO2, silicon nitride, and aluminum oxide. In particular, thin films of ZnS, thin films of oxides of metals such as Si, Ge, Al, Ti, Zr, Ta, etc., thin films of nitrides such as Si, Al, etc.
, Zr, Hf, etc., and films of mixtures of these compounds are preferred because of their high heat resistance. Also,
These mixed with fluorides such as MgF2 are also available.
This is preferable because the residual stress of the film is small. In particular, a mixed film of ZnS and SiO2 is preferable because the recording sensitivity, C/N, erasing rate, etc. are unlikely to deteriorate even after repeated recording and erasing. The thickness of the first and second dielectric layers is
It is approximately 10-500 nm. The first dielectric layer preferably has a thickness of 100 to 400 nm because it is difficult to peel off from the substrate or the recording layer and is difficult to cause defects such as cracks. Also the second
The dielectric layer preferably has a thickness of 10 to 30 nm from the viewpoint of recording characteristics such as C/N and erasing rate, and stable rewriting many times. In particular, it is preferable to constitute the main part of the optical recording medium as described below because it has high recording sensitivity, enables high-speed one-beam overwriting, and has a high erasing rate and good erasing characteristics.

That is, the thickness of the first dielectric layer is 100 nm.
m ~ 400 nm, and the thickness of the second dielectric layer is 10 nm.
~30 nm, and the thickness of the recording layer is 10 nm ~30 nm.
nm, the thickness of the first reflective layer is 10 nm to 50 nm, the thickness of the second reflective layer is 30 nm to 150 nm, and the dielectric layer is Z.
It is preferable that the film is a mixture of nS and SiO2, the mixing ratio of SiO2 is 15 to 35 mol %, and the composition of the recording layer is within the range expressed by the following formula.

(Pdx Sby Te1-x-y)1-z
(Te0.5 Ge0.5)z
0.01≦x≦0.1 0.3
5≦y≦0.65 0.2≦z
≦0.4 However, x, y, z, and 0.5 represent the atomic ratio of each element.

In the present invention, a transparent material is used as the substrate because recording is performed from the substrate side using a focused light beam in order to avoid the effects of dust, scratches on the substrate, and the like. Examples of such materials include glass, polycarbonate, polymethyl methacrylate, polyolefin resin, epoxy resin, and polyimide resin.

In particular, polycarbonate resins and epoxy resins are preferred because they have low optical birefringence, low hygroscopicity, and are easy to mold. Especially when heat resistance is required, epoxy resin is preferred.

The thickness of the substrate is not particularly limited, but is practically 0.01 mm to 5 mm. 0.01mm
If it is less than 5 mm, it will be easily affected by dust even when recording with a light beam focused from the substrate side, and if it is more than 5 mm, it will be difficult to increase the numerical aperture of the objective lens, and the irradiation light beam spot size will be reduced. This makes it difficult to increase the recording density. The substrate may be flexible or rigid. The flexible substrate is used in the form of a tape, sheet, or card. Rigid substrates are card-like or digital
Use in the form of a square. Further, these substrates may be formed into an air sandwich structure, an air incident structure, or a close bonding structure by using two substrates after forming a recording layer and the like. The light source used for recording on the optical recording medium of the present invention is a high-intensity light source such as a laser beam or a strobe light. In particular, a semiconductor laser beam is suitable because the light source can be miniaturized, power consumption is low, and modulation is easy. It is preferable for certain reasons.

Recording is performed by irradiating the crystalline recording layer with a laser beam pulse or the like to form an amorphous recording mark. Alternatively, crystalline recording marks may be formed on an amorphous recording layer. Erasing can be performed by crystallizing an amorphous recording mark or by converting a crystalline recording mark into an amorphous state by laser beam irradiation.

[0038] Since the recording speed can be increased and deformation of the recording layer is less likely to occur, it is preferable to form an amorphous recording mark during recording and crystallize it during erasing.

[0039] Furthermore, when forming recording marks, the light intensity is increased;
One-beam overwrite, in which the light beam is slightly weaker during erasing and rewriting is performed by irradiating the light beam once, is preferable because the time required for rewriting is shortened.

Next, a method for manufacturing the optical recording medium of the present invention will be described. Methods for forming the reflective layer, recording layer, etc. on the substrate include known thin film forming methods in vacuum, such as vacuum evaporation, ion plating, and sputtering. In particular, the sputtering method is preferred because the composition and film thickness can be easily controlled.

The thickness of the recording layer, etc. to be formed can be easily controlled by monitoring the deposition state using a known technique such as a crystal resonator film thickness meter.

[0042] The recording layer and the like may be formed either while the substrate is fixed, or while it is being moved or rotated. Since the in-plane uniformity of the film thickness is excellent, it is preferable to rotate the substrate, and it is more preferable to rotate the substrate in combination.

In addition, after forming the reflective layer, etc., a resin protective layer such as an ultraviolet curing resin may be provided as necessary to prevent scratches and deformation, as long as the effects of the present invention are not significantly impaired. good. In addition, after forming a reflective layer or the like, or after forming the above-mentioned resin protective layer,
Two substrates may be placed facing each other and bonded together using an adhesive.

[0044]

EXAMPLES The present invention will be specifically explained below based on examples. (Analysis and measurement method) The compositions of the reflective layer and the recording layer were confirmed by ICP emission analysis (manufactured by Seiko Electronic Industries, Ltd.). Further, the carrier-to-noise ratio and erasure rate (difference in reproduced carrier signal strength after recording and after erasure) were measured using a spectrum analyzer.

The film thicknesses of the recording layer, dielectric layer, and reflective layer were monitored using a crystal resonator film thickness meter. Example 1 A polycarbonate substrate with spiral grooves with a thickness of 1.2 mm, a diameter of 13 cm, and a pitch of 1.6 μm was processed at 3/min.
A recording layer, a dielectric layer, and a reflective layer were formed by high-frequency sputtering while rotating at 0 rotations.

First, after evacuating the inside of the vacuum container to 1×10-5 Pa, S
ZnS added with 20 mol% of iO2 was sputtered,
A first dielectric layer with a thickness of 170 nm was formed on the substrate. Subsequently, an alloy target consisting of Pd, Ge, Sb, and Te is sputtered to obtain a composition of Pd1 Ge17Sb26Te5.
A recording layer with a film thickness of 20 nm was formed. Furthermore, the aforementioned second dielectric layer is formed to a thickness of 17 nm, and on top of this, M
A first reflective layer having a thickness of 15 nm was formed by sputtering n0.01Si0.04Al0.95 alloy, and Zr0.
A second reflective layer having a thickness of 70 nm was formed by sputtering a 10Mn0.01Si0.04Al0.85 alloy. Further, after taking out this disk from the vacuum container, an acrylic ultraviolet curing resin was spin-coated on the reflective layer and cured by ultraviolet irradiation to form a resin layer with a thickness of 10 μm, thereby obtaining an optical recording medium of the present invention. .

This optical recording medium was rotated at a linear velocity of 5.5 m/sec and irradiated with semiconductor laser light of a wavelength of 820 nm focused on an ellipse of 22 x 66 μm from the substrate side at a film surface intensity of 1.1 W. Then, the recording layer was crystallized and initialized. After that, at a linear velocity of 6 m/s, the numerical aperture of the objective lens was 0.5.
3. Using an optical head with a semiconductor laser wavelength of 780 nm, the frequency is 3.7 MHz, the pulse width is 50 nsec,
Peak power 11-17mW, bottom power 5-9mW
After performing overwrite recording 100 times with semiconductor laser light modulated to each condition, C/N was measured under the condition of a bandwidth of 30 kHz by irradiating semiconductor laser light with a reproduction power of 1.3 mW.

Further, this portion was irradiated with a semiconductor laser beam modulated in the same manner as before at 1.4 MHz for one-beam overwriting, and the erasure rate at 3.7 MHz at this time was measured. Peak power of 13mW or more is 50~, which is sufficient for practical use.
A C/N of 55 dB is obtained, and the bottom power is 4.5~
At 8 mW, a practically sufficient erasure rate of 20 to 27 dB was obtained.

Further, similar measurements were made after repeating one-beam overwriting 1000 times and 100,000 times under the conditions of peak power 15 mW, bottom power 6 mW, and frequency 3.7 MHz, but the C/N, The changes in erasure rate were all within 2 dB, and almost no deterioration was observed.

Further, this optical recording medium was left in an environment of 80° C. and relative humidity of 80% for 1000 hours, and then the recorded portion was reproduced, but the change in C/N was less than 2 dB, and there was almost no change. Record and erase again and C/N
When the erasure rate was measured, it was found that there was almost no change, and almost no increase in defects was observed.

Example 2 An optical recording medium having the same structure as Example 1 was produced except that the second reflective layer of Example 1 was a Ti film with a thickness of 40 nm. When the C/N and erasure rate of this optical recording medium were measured in the same manner as in Example 1, it was found that the peak power was 13 mW or more, which was sufficient for practical use.
A C/N of 0 to 54 dB can be obtained, and the bottom power is 4.
A practically sufficient erasure rate of 20 to 26 dB was obtained at 5 to 7.5 mW.

Comparative Example 1 The first reflective layer and second reflective layer of Example 1 were made of Mn0.01Si.
An optical recording medium with a conventional quenching configuration was produced in which a single reflective layer of 0.04Al0.95 alloy with a thickness of 70 nm was substituted. When this optical recording medium was measured in the same manner as in Example 1,
50 to 54 d, which is practically sufficient with a peak power of 16 mW or more.
B C/N was obtained, and a practically sufficient erasure rate of 20 to 28 dB was obtained with a bottom power of 6 to 9 mW. Compared to Examples 1 and 2, the peak power when recording with a C/N of 50 dB or more is higher by 3 mW, and Examples 1 and 2 have higher sensitivity than the optical recording medium with the conventional rapid cooling configuration of Comparative Example 1. It turned out to be.

[0053]

Effects of the Invention In the present invention, since the optical recording medium is structured to have two reflective layers having different thermal conductivities, the following effects can be obtained. (1) High sensitivity, high erasure rate, and high C/N. (2) Even after repeated recording and erasing many times, the operation is stable, with almost no deterioration of characteristics or occurrence of defects. (3) Excellent heat and humidity resistance, oxidation resistance, and long life. (4) It can be easily manufactured by sputtering.

[Brief explanation of drawings]

FIG. 1 schematically shows an example of the basic layer structure of the optical recording medium of the present invention.

FIG. 2 schematically shows an example of the basic layer structure of a conventional optical recording medium.

[Explanation of symbols]

1: Substrate 2: First dielectric layer 3: Recording layer 4: Second dielectric layer 5: First reflective layer 6: Second reflective layer 7: Reflective layer 8: Resin layer 9: Direction of light incidence

Claims (1)

[Claims] Claim 1: Information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light, and information can be recorded and erased by irradiating light onto a recording layer formed on a substrate. In an optical recording medium that performs phase change, the optical recording medium has at least a recording layer, a dielectric layer, and a reflective layer, and the reflective layer is composed of two reflective layers having different thermal conductivities, and An optical recording medium characterized in that a reflective layer closer to a recording layer has a higher thermal conductivity than another reflective layer.