JPH04271038A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To prevent a stain from sticking to a light incoming face and to prevent the face from being damaged at the time of cleaning the stuck stain when a magneto-optical recording medium is provided with a recording layer to record/reproduce information by light on the face opposite to the light incoming face of a transparent substrate. CONSTITUTION:On the light incoming face the transparent thin film of oxide is provided, whose Gibbs' oxide generating free energy per one atom of a metal element is >=860kJ/mol in an absolute value.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium on which information is recorded, reproduced, erased, etc. using light such as a laser.

More specifically, the recording layer is made of a metal thin film having an axis of easy magnetization perpendicular to the film surface, and the recording layer records information by a photothermal magnetic effect and reproduces information by a magneto-optic effect. It can be applied to a magneto-optical recording medium which is a magneto-optical recording layer.

0003

2. Description of the Related Art Various research and developments are being conducted on magneto-optical recording media as high-density, large-capacity information recording media. In particular, magneto-optical recording media from which information can be erased have a wide range of applications, and various materials and systems have been announced, and their practical use has begun.

The substrate of the magneto-optical recording medium usually has a diameter of about 130 mm or about 90 mm and a thickness of about 1.2 m.
m electrically insulating transparent organic polymer disk. One side thereof is provided with a groove-forming surface on which grooves and/or pre-pits are formed, and a laminate including a dielectric layer/magneto-optical recording layer/dielectric layer/reflective metal layer is provided thereon as an example of a laminated structure. A recording layer is provided, and a protective layer of an inorganic material and/or an organic resin is further provided on the reflective metal layer.

[0005] Recording information on the magneto-optical recording medium;
Alternatively, in a magneto-optical disk device for reproducing information, it is necessary to make the light incident surface of the magneto-optical recording medium less susceptible to dust and scratches. For this purpose, recording, reproduction, and erasing are performed on the magneto-optical recording medium by irradiating a laser beam through the transparent substrate of the magneto-optical recording medium from the side opposite to the surface on which the recording layer is formed.

[0006]

SUMMARY OF THE INVENTION The environment in which the magneto-optical disk device is used is not limited to a place where a high level of cleanliness is ensured. Therefore, if the magneto-optical disk device is used in a normal environment where high cleanliness cannot be expected, the signal error rate will increase due to static electricity, falling dust, and adhesion on the surface of the magneto-optical recording medium. Become.

[0007] For this reason, by adding a layer that has both anti-static properties and anti-friction properties to the surface of the magneto-optical recording medium, it is possible to prevent dust from adhering and to prevent scratches when cleaning dirt. It is being considered. However, this method has not yet produced satisfactory effects and also has some problems.

[0008] That is, the general method is to apply an ultraviolet curable resin containing an antistatic agent to a thickness of several micrometers to several tens of micrometers.
A coating is carried out to a thickness of m. However, this does not provide a sufficient antistatic effect at a temperature of 10 to 50° C. and a relative humidity of 10 to 80%, which is the actual use environment. Furthermore, when a coating layer of several μm or more is formed in order to improve the abrasion resistance, the error rate increases due to coating spots and foreign matter in the coating film, resulting in a decrease in production yield.

On the other hand, methods for removing dust adhering to the magneto-optical recording medium are also being studied. However, in this case, depending on the removal method, the transparent organic polymer substrate of the magneto-optical recording medium may become heavily charged, making it easier for dust to re-adhere. For example, recently, automatic cleaners (such as those used to clean glasses) that rotate a cloth made of ultra-fine fibers in contact with the magneto-optical disk have been introduced.
Auto disc cleaner PC-0 manufactured by NEC Corporation
D101-11 etc.) are on sale. However, this method has a problem in that even if it is temporarily cleaned, the transparent organic polymer substrate becomes electrically charged, making it easy for dust to re-adhere.

0010

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes the Gibbs oxide formation free energy per atom of a metal element on the light incident surface of a transparent substrate of a magneto-optical recording medium. It is characterized by providing a transparent oxide thin film whose absolute value is 860 kJ/mol or more.

[0011]

[Operation] In addition to the above-mentioned magneto-optical recording medium, the magneto-optical recording medium according to the present invention may be the well-known compact disc (
There are no particular limitations as long as information is recorded and/or reproduced by irradiating a laser onto the recording layer through the substrate, such as write-once magneto-optical disks used for storing documents such as CDs, video disks, and WORMs. . However, it is particularly suitable for magneto-optical recording media that are expected to be used as external memory for computers, which are often used continuously.

[0012] As the transparent substrate of the magneto-optical recording medium, glass, polycarbonate (PC), amorphous polyolefin (APO), acrylic resin, epoxy resin, modified products thereof, etc. are used, but in particular, organic materials that are easy to mold are used. Resins are preferred, and among them, PC is preferred from the viewpoints of cost, mechanical properties, and heat resistance.

[0013] In the present invention, when the Gibbs oxide formation free energy per atom of the metal element constituting the transparent oxide thin film becomes small, the surface hardness is insufficient and scratches occur easily during friction cleaning with a cloth. 860k in absolute value
This was done based on the discovery that unless it is at least J/mol, it is not possible to obtain a product that has both wear resistance and stain resistance. In a transparent oxide thin film with this value of less than 860 kJ/mol, for example, In2 O3 -SnO2
Although SiO has excellent stain resistance, it has poor wear resistance.
2 and Al2O3 have excellent wear resistance but poor stain resistance. Further, nitride thin films such as SiN and AlSiN are easily contaminated.

Here, the Gibbs oxide formation free energy per atom of the metal element (M) is, for example, Mx +
If the free energy change of the reaction (y/2)O2 → Mx Oy is ΔG, then ΔG/x
means.

[0015] In the case of HfO2, ΔG is -1027kJ
/mol, so the value per atom is -1027k
J/mol. Also, ΔG of Ta2O5 is -1
However, since x=2, the value per atom is -956 kJ/mol.

[0016] Although ΔG of most elements is a negative value,
The absolute value in the present invention means a value excluding this sign.

[0017] Certain elements may also take the form of several oxides. However, in this case, the value in the most stable form under standard conditions (atmosphere, 1 atm, temperature 25°C) is used for evaluation.

Oxides that satisfy such conditions include, in addition to the aforementioned HfO2 and Ta2O5, ZrO2
, Y2 O3, TiO2, Er2 O3, etc.

Among the oxides mentioned above, Ta2 O5
, HfO2, ZrO2, and Y2O3 are particularly preferred because they have excellent surface hardness, stain resistance, stability, and durability. These four types of oxides may be used as a mixture, or other oxides, nitrides, etc. may be added for the purpose of improving surface resistance, durability, etc.

The thickness of the transparent oxide thin film is appropriately selected in consideration of its hardness and the influence of the above-mentioned optical interference effect on the medium reflectance. From the viewpoint of surface hardness, the film thickness needs to be at least 10 nm or more. On the other hand, the medium reflectance changes periodically depending on the thickness of the transparent oxide thin film, and when using a laser beam with a wavelength of 830 nm, the influence becomes large around film thicknesses of 100 nm and 300 nm. When the film thickness is around 200 nm, the medium reflectance hardly changes regardless of the refractive index. If the film thickness becomes too thick, it will not only reduce productivity but also be disadvantageous in terms of film stress, so it is preferably 500 nm or less.

The method for forming these transparent oxide thin films is as follows:
Although ordinary physical and chemical deposition methods are used, sputtering methods and vapor deposition methods are preferably used. Note that an undercoat layer of a silane coupling agent, an organic silicate, or the like may be provided between the transparent substrate and the transparent oxide thin film for the purpose of improving the adhesion between both layers.

The present invention will be explained below with reference to Examples. To this end, we will first explain the sample evaluation method.

[0023] The evaluation of wear resistance is 1 per square cm.
The surface to be measured was rubbed back and forth 100 times with a gauze to which a load of 0.00 g was applied, and the condition of the surface to be measured before and after was visually observed and evaluated. At that time, those for which no scratches were found on the surface to be measured were marked as "○", and those for which scratches were found were marked as "×".
”.

[0024] In addition, the adhesion of dirt was determined by placing powder in a petri dish, bringing the surface of the sample to be measured into contact with the powder, taking it out, measuring the vertical transmittance of light at a wavelength of 500 nm before and after contact, and calculating the transmittance. Retention rate (=transmittance after contact/transmittance before contact)
The evaluation was made by determining the As a powder, SiO
2 (JIS test dust type 3), Kanto loam layer (JIS test dust type 8)
Four types of starch were used: carbon black (seed), carbon black (12 types), and potato starch. Regarding the surface to be measured,
The effect of surface charging was also investigated by rubbing with a cloth made of ultrafine fibers (Microstar manufactured by Teijin Ltd.).

[0025] The environment at the time of measurement was a temperature of 26°C and a relative humidity of 42°C.
%Met. Each measurement was performed five times, and the average value was calculated.
The results are summarized in Table 1.

Magneto-optical recording media used in Examples and Comparative Examples were manufactured as follows.

First, the diameter is 130 mm and the thickness is 1.2 mm.
A PC board with a disk shape and grooves at a pitch of 1.6 μm was placed in a vacuum chamber of a magnetron sputtering device capable of installing 3 targets, and the inside of the vacuum chamber was set to 0.
．． It was evacuated until the pressure became 4 μTorr.

Next, Ar/N2 mixed gas (Ar:N2
=70:30 vol%) was introduced into the vacuum chamber, and the pressure was adjusted to 10 mTorr. The target is AlSi with a diameter of 100 mm and a thickness of 5 mm.
Using a disk made of a sintered body of an alloy (Al:Si=30:70 atom%), the discharge power was 500 W, and the discharge frequency was 1.
High-frequency sputtering was performed at 3.56 MHz, and while rotating (rotating) the PC board, Al was sputtered as a transparent dielectric layer.
A 120 nm thick SiN film was deposited. The composition of this AlSiN film was determined using an Auger electron spectrometer (SAM manufactured by PHI).
610), the composition ratio was found to be Al:Si:N=
It was 19:39:42 atom%.

Next, a magneto-optical recording layer with a diameter of 100 m was prepared.
A TbFeCo alloy target with a thickness of 4.5 mm (Tb:Fe:Co=19:72.5:8.5 ato
m%), Ar gas pressure 4 mTorr, discharge power 1
DC sputtering was performed under the condition of 50W, and the film thickness was 22.
5 nm TbFeCo amorphous alloy film (Tb:Fe:Co
=20.5:70.9:8.6 atom%) was deposited.

The composition of the alloy film was determined by inductively coupled high frequency plasma spectroscopy (IPC). The compositions of the other alloy films listed below are all based on IPC.

[0031] Further, under the same conditions as above,
A 30 nm thick AlSiN film was deposited as a nitride transparent dielectric layer.

Furthermore, as a metal reflective layer, a diameter of 100 mm is provided.
Using a 3 mm thick Ag target, DC sputtering was performed under the conditions of Ar gas pressure of 2 mTorr and discharge power of 60 W to deposit a 30 nm thick Ag film.

[0033] During the formation of each of these layers, the PC board was rotated at 20 rpm.

Next, an ultraviolet-curable phenol borac epoxy acrylate resin was applied onto the metal reflective layer using a spin coater, and then cured by ultraviolet irradiation.
An organic protective layer of approximately 10 μm was provided.

A protective layer for a PC board as shown below was formed on the opposite surface (light incident surface) of the magneto-optical recording medium thus produced. Then, the wear resistance was evaluated. Further, regarding the adhesion of dirt, an oxide layer was provided only on the PC board, and evaluation was performed using the method described above.

[0036]

[Examples 1 to 4] Ta2O5, HfO2 on PC board
, ZrO2, and Y2O3 films were formed by high frequency sputtering. Each oxide target was used as the target, and Ar/O2 mixed gas (Ar:O2 = 8
0:20 vol%) In an atmosphere of 5 mTorr, a discharge power of 500 W and a discharge frequency of 13.56 MHz were applied. Film thickness was controlled by varying the deposition time.

[0037]

[Comparative Example 1] No protective layer was attached to the light incident surface of the PC board.

[0038]

[Comparative Example 2] AlSi target (Al:Si=30
:70atom%) and Ar/N2 mixed gas (
Ar:N2 =70:30 vol%) 5mTorr
Under the atmosphere, discharge power 500W, discharge frequency 13.5
By inputting 6MHz, A by high frequency sputtering method.
A lSiN film was deposited.

[0039]

[Comparative Example 3] An ultraviolet curable phenolvolac epoxy acrylate resin was coated on a PC board using a spin coater, and then a film with a thickness of 10 μm was formed by irradiation with ultraviolet rays.

[0040]

Comparative Example 4 A SiN film was deposited using a Si target under the same conditions as Comparative Example 2.

[0041]

[Comparative Example 5] In2 O3 - SnO2 target (In2 O3 :SnO2 =95:5 wt%)
Deposition was carried out under the same conditions as in Example 1.

[0042]

[Comparative Example 6] Using a SiO2 target, a SiO2 film was deposited under the same conditions as in Comparative Example 1.

[0043]

[Effects of the Invention] As detailed above, the present invention provides a magneto-optical recording medium in which a recording layer for recording or reproducing information using light is provided on the surface of a transparent substrate opposite to the light incident surface. Then, on the light incident surface of the transparent substrate, the Gibbs oxide free energy of formation per atom of the metal element is 8 in absolute value.
By providing a transparent oxide thin film with a density of 60 kJ/mol or more, a layer is formed to prevent the adhesion of dirt and damage during cleaning of the adhered dirt, and the magneto-optical recording medium has excellent reliability. This has the remarkable effect of being able to obtain .

[0044]

[Table 1]

Claims (2)

[Claims] 1. A magneto-optical recording medium having a recording layer for recording or reproducing information by light on the surface opposite to the light incident surface of a transparent substrate, wherein one atom of a metal element is provided on the light incident surface of the transparent substrate. 1. A magneto-optical recording medium comprising a transparent oxide thin film having a Gibbs oxide formation free energy of 860 kJ/mol or more in absolute value. 2. The magneto-optical recording medium according to claim 1, wherein the transparent oxide thin film is Ta2 O5, HfO2, ZrO2 or Y2 O3.