JP2000268408A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a dense diamond-like carbon film and to obtain an optical recording medium excellent in durability by forming at least one dielectric layer and using a transparent electrically conductive layer for the top dielectric layer. SOLUTION: The optical recording medium contains at least one dielectric layer and a transparent electrically conductive layer is used for the top dielectric layer. Since the transparent electrically conductive layer having a prescribed refractive index is used, DC negative bias can be applied and a DLC film excellent in durability can be formed. This method is particularly effective in the case of <=80 Å film thickness of DLC. Thus, the electrification of the disk is prevented and the sticking of dust due to static electricity is suppressed. The growth of carbon atoms on the surface of a substrate is facilitated and a dense DLC film is obtained. The transparent electrically conductive film comprises In2O3, In2O3-SnO2, SnO2 or ZnO2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium on which recording and reproduction are performed by irradiating a laser beam from the recording layer side, and more particularly to improvement of durability of the optical recording medium.

[0002]

2. Description of the Related Art In recent years, an optical recording apparatus which records a large amount of data at a high density and rapidly records / reproduces the data in response to multimedia has been receiving attention. The recording size of the optical recording device is determined by the spot size formed on the recording medium by the optical system. This spot size is represented by about λ / NA, where λ is the wavelength of the laser beam and NA is the numerical aperture of the lens. In order to perform higher-density recording and reproduction, a smaller spot size of laser light is required. In order to reduce the light spot, two methods can be considered, such as reducing the laser light wavelength (λ) or increasing the numerical aperture (NA) of the lens from the above formula. Currently, the wavelength of semiconductor lasers for optical discs is mainly 680
780 nm. Furthermore, the short-wavelength 650 nm orange laser has just begun to be used as a prototype, and the green and blue lasers, which have shorter wavelengths than this orange laser, are still under development. Reducing the size involves considerable difficulty.

On the other hand, the numerical aperture (NA) of a lens is expressed as NA = sin θ, where θ is a half angle of the aperture of the lens, and is a value smaller than 1. Since the NA of the lens currently used is about 0.5, even if the NA is 0.9, which is theoretically close to the limit, the laser beam spot size is reduced to only 1 / 1.8. Actually, when the NA is increased, the depth of focus of the lens system becomes shallow due to the influence of spherical aberration, and the control system for maintaining the focus on the recording surface becomes complicated, so the NA can not be increased unnecessarily. Instead, a normal optical recording apparatus uses a lens having a maximum NA of about 0.6.

[0004]

As a method for solving the problem of the diffraction limit which restricts the recording density of a recent optical recording apparatus, there has been proposed a method of effectively increasing the NA of the lens by using an immersion lens. ing. FIG. 1 shows an example of a vision lens. When the laser beam 1 is perpendicularly incident on the surface of the objective lens 2 using the hemispherical immersion lens 3, the numerical aperture NA indicates the refractive index of the immersion lens as n.
Then, n × NA is obtained. Further, when the laser beam is focused on the bottom surface of the super-hemispherical lens using the super-hemispherical immersion lens, n2 × NA is obtained. When the immersion lens is made of glass, the refractive index of the glass is about 1.8, so the spot size can be reduced to 1 / 1.8 when using a hemispherical immersion lens and 1 / 3.2 when using a super hemispherical immersion lens. . However, in this technology, the near-field oozing from the immersion lens
Since (near field) light is used, the gap between the immersion lens and the recording film 4 needs to be set to about 1/4 of the laser wavelength. This value is 170 nm when a red laser having a wavelength of 680 nm is used, which is much smaller than the distance of several mm between the optical head and the optical recording medium of a normal optical storage device. for that reason,
When near-field light is used, recording / reproducing through a transparent substrate is impossible as in an ordinary optical storage device, and it is necessary to make laser light incident from the recording film side.

Further, an optical system such as an immersion lens
It has been proposed to incorporate and use in an aerodynamically held air suspension flying type slider 12 similar to that used in a fixed magnetic disk as shown in FIG. The medium structure in this case is as shown in FIG.
The reverse of the case where optical recording / reproduction is performed through a normal transparent substrate is performed, and the reflection layer 24, the recording layer 23, and the dielectric layer 2 are formed on the substrate 25.
2, a structure in which the protective film layer 21 is laminated in this order. Further, as described above, when recording and reproducing using an immersion lens, near-field light oozing from the immersion lens is used for recording and reproducing. Therefore, the distance between the immersion lens and the recording layer must be small. At least 170 nm or less is required.

[0006] As described above, the distance between the immersion lens and the recording layer is small, and if the immersion lens is incorporated in a floating slider to perform recording and reproduction, contact with the recording layer occurs during traveling. In addition, it is necessary to provide a protective film on the recording layer. However, if the thickness of the protective film is increased, the spacing loss increases, which is not suitable for an optical recording / reproducing method using an immersion lens.

Therefore, as a protective film layer provided on the recording layer, diamond-like carbon (hereinafter abbreviated as DLC) having high hardness, being thin and having high durability is used.

In order to form a dense DLC film, it is common to apply a DC negative bias to the substrate. However, a dielectric layer such as SiNx, SiOx, etc., which has been used in a conventional optical recording medium, is an insulator, hinders it, and it is difficult to form a DLC film having sufficient strength.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to apply a DC negative bias to a substrate so that a dense DLC film or the like can be formed, thereby improving durability. It is to provide an excellent optical recording medium.

[0010]

In order to achieve the above object, according to the present invention, a reflective layer, a recording layer, and a protective layer are sequentially provided on a substrate, and an optical recording medium for performing recording and reproduction from the recording layer side is provided. The medium includes at least one dielectric layer, and by using a transparent conductive layer as the uppermost dielectric layer, a dense DLC film or the like can be formed, and an optical recording medium with excellent durability can be provided. .

A transparent conductive film is used for the uppermost dielectric layer. Conventionally used transparent insulator films such as SiNx and S
In iOx, DC charge on the substrate is
Although the application of a negative bias was prevented, a DC negative bias can be applied by using a transparent conductive film having an equivalent refractive index, and a DLC film having excellent durability can be produced. Especially DLC
Is effective when the film thickness is 80 ° or less.

By using a transparent conductive film for the upper dielectric layer, charging of the disk can be prevented, and adhesion of dust due to static electricity can be reduced. Also, DC negative bias can be applied,
DLC facilitates the growth of carbon atoms on the substrate surface
A film can be obtained.

As the transparent conductive film, In ₂ O ₃ , In ₂ O ₃ -Sn
O ₂ , SnO ₂ , and ZnO ₂ are used. A great effect can be obtained by a structure using these transparent conductive films on the dielectric layer of the conventional SiNx or SiOx film, in addition to the form used alone as the dielectric layer. The definition of transparent conductive film is expressed by resistivity,
Its value is 1000 μΩcm or less. The light absorption coefficient is preferably 0.1 or less.

A typical example of the layer constitution in the present invention is a substrate / reflection layer / recording layer / transparent dielectric layer / DLC protective film. As the reflective layer, Al or an Al alloy (AlTi, AlCr, AlTa, AlN
d, AlNb, AlCu, AlAg, AlAu, etc.), in addition, Cu, Ag, A
u or an alloy thereof can be used. As the recording layer, TbFeCo, DyFeCo, Gd
GeSbTe, InAgSn and the like can be used in the phase change method such as a two-layer film of FeCo and TbFeCo and other magnetic super-resolution constituent films, and a dye or GeSbTe, TePbSe, and AuSn can be used in the Write Once method. Between the substrate and the reflective layer, SiOx, SiNx, Al
Ceramic layer such as Nx, TaOx or NiP, NiB, CoZr, CoM
Metallic amorphous such as o, AlTi, AlTa, AlCr may be formed to improve corrosion resistance. In addition, in order to increase the adhesion between the ceramic layer or the metal amorphous layer and the reflection layer and / or the substrate, a Ti, Ta, Cr, Mo, V, Nb, etc. A layer may be formed. In this patent, the target substrate is a resin, glass, ceramic, metal substrate, or the like. Since the laser beam does not pass through the substrate, it does not need to be a transparent material. Examples of the resin for the resin substrate include polycarbonate, polymethacrylic acid (PMMA), a norbornene-based amorphous resin, an epoxy resin, nylon, polyimide, polyamide, polyimide amide, polyethylene, and polystyrene. As the ceramic substrate, Si substrate, crystallized glass,
Including carbon.

[0015]

(Embodiment 1) An embodiment of the present invention will be described below. The configuration of the optical recording medium in this example is such that an AlTi reflective layer, a TbFeCo recording layer, an In ₂ O ₃ transparent conductive film (dielectric layer), and a DLC protective layer were sequentially laminated on a disk made of a polyolefin-based resin. . The thickness of each layer is as follows: the AlTi reflective layer (600 mm), the TbFeCo recording layer (250 mm).
Å), transparent conductive film ITO (800 Å), DLC protective layer (80
Å).

Example 2 An optical recording medium was manufactured in the same manner as in Example 1 except that the transparent conductive film In ₂ O ₃ —SnO ₂ was used.

Example 3 An optical recording medium was manufactured in the same manner as in Example 1 except that the transparent conductive film SnO ₂ was used.

Example 4 An optical recording medium was manufactured in the same manner as in Example 1 except that the transparent conductive film ZnO ₂ was used.

Example 5 An optical recording medium was manufactured in the same manner as in Example 1 except that SiN (100 °) was provided between the TbFeCo recording layer and the In ₂ O ₃ transparent conductive film. did.

Comparative Example 1 A transparent insulator film SiN was used for the dielectric layer.
An optical recording medium was manufactured in the same manner as in Example 1 except for using.

Comparative Example 2 A transparent insulator film SiOx was used for the dielectric layer.
An optical recording medium was manufactured in the same manner as in Example 1 except for using.

In the examples and comparative examples, evaluation of the surface state of the substrate using a glide head will be described below.
Generally, the air film between the head and the surface of the substrate becomes very thin immediately before the flying height of the head is reduced and sliding starts with the substrate. For this reason, the head has a small buffering effect and is affected by the fine substrate surface shape at the texture level, and vibration is induced. Then, the surface state of the substrate was evaluated by observing the signal using a glide head on which a piezo element for converting this vibration into an electric signal was mounted.

As an evaluation method, a disk was set in an apparatus as shown in FIG. 4 and measurement was performed. The signal obtained from the glide head 36 is amplified by the amplifier 35, taken into the computer 31 via the D / A converter 32, and observed as a change in the voltage value. The number of revolutions was controlled and the measurement was performed so that the flying height of the head from the substrate was about 100 nm. At this time, the case where the voltage value of the detected AE signal was equal to or higher than the slice level of 1.5 V was counted, and the number was counted.

Further, the surface of the substrate after the completion of the measurement was observed using an optical microscope to determine the level of scratches. Table 1 shows the results.

[0025]

[Table 1]

In the case of the embodiment, it is clear that the number of signals counted is small and a dense DLC film is formed on the substrate. In the comparative example, the count number was large on the entire surface of the disk, and the difference was remarkable. Also, from the observation result of the optical microscope, in the case of the comparative example, a scratch at a visual level was clearly observed.

[0027]

According to the present invention, high durability can be obtained in an optical recording medium in which recording and reproduction are performed by irradiating a laser beam from the film surface side. High-density recording becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a hemispherical immersion lens.

FIG. 2 is a schematic view of a slider.

FIG. 3 is a diagram showing a film configuration of an optical recording medium.

FIG. 4 is a schematic diagram of an evaluation machine using a glide head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser beam 2 Objective lens 3 Immersion lens 4 Recording film 11 Fixed magnetic disk 12 Slider 13 Immersion lens 14 Objective lens 15 Magnetic coil 21 Protective film layer (DLC) 22 Dielectric layer 23 Magnetic layer 24 Reflective layer 25 Substrate 31 Computer 32 D / A converter 33 Motor control 34 Filter 35 Amplifier 36 Glide head 37 Disk 38 Air spindle motor 39 Linear stage

Claims (2)

[Claims] 1. An optical recording medium in which at least a reflective layer, a recording layer, and a protective layer are sequentially provided on a substrate, and recording and reproduction are performed from the recording layer side, the optical recording medium includes at least one dielectric layer, An optical recording medium characterized in that a transparent conductive layer is used for the dielectric layer. 2. The transparent conductive layer according to claim 1, wherein In ₂ O ₃ , I ₂
An optical recording medium comprising at least one of n ₂ O ₃ -SnO ₂ , SnO ₂ and ZnO ₂ .