JP2001184744A - Recording medium and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording medium capable of heightening recording density and at the same time suppressing medium noise by isolating particles having information recording ability and at the same time reducing the defects in a film consisting of the particles and to provide a method for manufacturing the recording medium. SOLUTION: The recording medium is provided with a substrate 11 and a single particle layer 12 which is formed on the substrate 11 and in which plural particles 13 having information recording ability are isolated one another. The surfaces of the particles 13 are coated with an aromatic compound 14 having a branched chemical structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a recording medium and a method for manufacturing the recording medium.

[0002]

2. Description of the Related Art In an information-oriented society in recent years, a recording / reproducing method having a remarkably high recording / recording density, and a recording / reproducing apparatus and a recording medium based on the recording / reproducing method, corresponding to an ever-increasing amount of information. Is long-awaited. Along with this, it is required to cope with miniaturization of a recording cell which is a unit for writing information in such a recording / reproducing apparatus and a recording medium.

[0003] However, in the recording / reproducing apparatus and the recording medium described above, there are various difficulties to cope with miniaturization of recording cells at present.

For example, in the case of magnetic recording using a magnetic recording medium, a polycrystalline material having a wide particle size distribution is used for a recording layer. However, recording becomes unstable or noise occurs due to thermal fluctuation of crystals or interaction between magnetic particles. There is no problem when the recording cell is large, but when the recording cell is small, recording instability and noise increase become remarkable.

The situation is the same in optical recording using a phase change medium. At a recording density of several hundred gigabits per square inch or more where the bit size is almost the same as the crystal size of the phase change medium, medium noise is reduced. growing.

In order to avoid this problem, there has been proposed a magnetic recording medium in which the magnetic noise on the substrate is reduced by miniaturizing and isolating the magnetic particles on the substrate at the same time (SY).
Chou, et. al. J. Appl. Phys. 76
(1994), pp6673-6675).

As a method of manufacturing a magnetic recording medium having such a structure in which magnetic particles are isolated, application of a semiconductor element manufacturing technique can be considered, but its feasibility is poor in terms of processing size and processing cost.

On the other hand, for example, Japanese Patent Laid-Open No. 10-2077
No. 2 discloses a method for producing a magnetic recording medium in which magnetic fine particles are isolated on a substrate by using lithography technology, using fine particles having a diameter of several nanometers to several micrometers arranged two-dimensionally on a substrate as a mask. Is disclosed. In addition, as a method of two-dimensionally arranging the fine particles on the substrate, a fine particle coated with a long-chain alkyl group is applied on the substrate, and the self-aggregation between the fine particles during drying is applied to a relatively large area. A method for obtaining a uniform single particle layer has been reported (S. Hung, et al., Jpn. J. App.
l. Phys. , 38 (1999) pp. L473-L
476).

However, in a film forming method using only the self-assembling force of the fine particles when two-dimensionally arranging the fine particles on the substrate, the thermal fluctuation of the fine particles is large in the micro,
The fine particle spacing cannot be strictly controlled, and this has caused medium noise especially in ultra-high density memories exceeding 1 terabit per square inch.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to make the particles having information recording capability exist in isolation, and at the same time, to strictly control the distance between the particles in the film composed of the particles. Another object of the present invention is to provide a recording medium and a method of manufacturing the recording medium, which can increase the recording density and suppress medium noise.

[0011]

Means for Solving the Problems The present inventors diligently studied a method for effectively controlling the spacing between particles, and found that particles coated with a bulky aromatic compound having a branched structure were formed on the substrate surface. By doing so, it has been found that a stable particle layer in which the thermal fluctuation of the particles is suppressed and the particle interval is controlled is formed.

That is, the present invention provides a recording medium comprising at least a substrate and a recording layer formed on the substrate and having a plurality of particles having information recording ability, wherein the surface of the particle is an aromatic compound having a branched structure. A recording medium characterized by being coated with:

Further, the present invention is characterized by comprising a step of forming a particle layer comprising particles coated on a substrate with an aromatic compound having a branched structure, and a step of heat-treating the particle layer. This is a method for manufacturing a recording medium.

In the recording medium of the present invention, a plurality of particles having information recording ability are coated with an aromatic compound having a branched structure. Therefore, the particles are isolated. Further, the thermal fluctuation of the aromatic compound is smaller than that of the long-chain alkyl group, and when the aromatic compound is branched, the thermal fluctuation can be further suppressed due to crowding with the aromatic release compound. Therefore, it is possible to reduce the thermal fluctuation between particles determined by the type of the compound coated,
Not only can the particles be isolated, but also the spacing between the particles can be strictly controlled. As a result, an ultra-high-density recording medium with low medium noise can be obtained.

Further, as in the method for producing a recording medium of the present invention, a particle layer comprising particles coated with an aromatic compound having a branched structure is formed on a substrate, and the particle layer is heat-treated to form a recording medium. By obtaining the above, the control of the particle interval is performed with higher accuracy. As a result, an ultra-high-density recording medium with low medium noise can be obtained.

[0016]

FIG. 1 is a sectional view schematically showing a recording medium according to the present invention.

A recording layer 12 is laminated on the substrate 11, and information is written on the recording layer 12. The recording layer 12 is a single particle layer including a plurality of particles 13 having information recording ability. That is, the particles 13 are two-dimensionally arranged in one layer. Further, the particles 13 are covered with an aromatic compound 14 having a branched structure. Therefore, they exist apart from each other. Thus, even if the recording bits are miniaturized by miniaturizing the particles 13 on the substrate 11, a recording medium with reduced medium noise can be obtained.

In the present invention, the substrate 11 refers to a layer serving as a base of a layer in which the particles 13 coated with the aromatic compound 14 are present.

It is ideal that all the particles 13 are separated from each other in order to reduce the noise of the recording medium, but some particles 13 may inevitably be in contact with each other. .

The particles 13 having the information recording ability may be of any kind as long as they are made of a material having the information recording ability generally used for the recording layer of the recording medium. For example, if the recording medium is a magnetic recording medium, it is a magnetic substance; if it is a phase change optical recording medium, it is made of a phase change material; if it is a charge recording medium, it is made of a charge recording material; if it is a charge recording medium, it is charge recording. Examples of the material include a material made of a material, and a semiconductor material on which recording / reproduction is performed using an optical change.

The size of the particles 13 is desirably smaller as the recording density can be increased.
It is desirable to be in the range of 20 nm. In particular, in the present invention, since the space between the particles 13 is isolated and noise is reduced, the recording density can be increased by reducing the particle diameter.

FIG. 2 is a schematic view showing an example of particles coated with the aromatic compound according to the present invention.

The surface of the particles 21 is coated with an aromatic compound 22. The aromatic compound 22 is an aromatic compound having a branched structure. It is desirable that the molecules 23 of the aromatic compound bonded to the particles form a monolayer because the distance between the particles can be kept constant.

The aromatic compound 22 is preferably a dendritic molecule having a structure in which a plurality of organic groups are bonded in a dendritic manner.

The dendritic molecule is, for example, an organic group having a branched structure (for example, Y-shape), which is a basic unit bonded to the core particle 21, and a branched structure (for example, Y-shape). A plurality of organic groups having a branched structure such that a group is bonded, and an organic group having the next branched structure (for example, a Y-shape) is bonded to an organic group having a branched structure (for example, a Y-shape). It is a molecule having a structure (dendritic structure) that is sequentially and regularly connected in a dendritic manner.

The dendritic molecule is specifically Hawke
r, C.I. J. et al; Chem. Soc. , C
ommun. , 1990, p. 1010, Tomali
a, D. A. et al; Angew. Chem. In
t. Ed. Engl. 29, 138 (199
0), Hawker, C .; J. et al; Am.
Chem. Soc. 112, 7638 (199
0), Frechet, J. et al. M. J. ; Sciencec
e, 263, 1710 (1994), or Kakimoto Masaaki; Chemistry, 50, 608 (1995). If defined more strictly, the focal point (the starting point of branching) can be specified. When the molecular chain is traced from the focal point toward the molecular end, the molecular end that passes at least one branch point other than the focal point is the minimum. It is one existing molecular structure.

The fact that the particles 21 are bound to the focal point (focal position) of the dendritic molecule is as follows.
It is desirable to make the interval between them constant.

Preferably, the aromatic compound 22 is bonded to the surface of the particle 1 by a covalent bond, a coordinate bond, an ionic bond, or the like.

The aromatic compound 22 preferably has a polar group at the terminal, and the polar group is preferably located on the outermost side. The presence of such a polar group makes it easier to polar-adsorb to the substrate, and can reduce defects in which the particles 21 do not exist on the substrate. Further, the interaction between the particles 21 is large when the solvent disappears, so that it is also preferable for reducing defects and controlling the particle interval.

The polar groups include -COOH, -OH,
_{-NH 2, -SO 3 H, -SH} , -CONH 2, -PO
₃ CO and the like, and particularly preferred is -COOH because it can increase the interaction between particles.

Further, it is more preferable that the polar group is bonded to an aromatic ring since the distance between particles can be further constant.

Specific examples of the aromatic compound 22 include:
Compounds (1) to (6) Is desirable. Compound
In (1) to (6), the particles 21 in the X portion
It is desirable that they are combined. Compounds (1) to (6)
It is particularly desirable to set (2) as the distance between the particles 21.
Is better controlled.

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Embedded image (However, in chemical formulas (1) to (6), X is -S
_{H, -NH 2, -COOH, -OH} , -SO 3 H, -C
At least one selected from ONH ₂ , —PO ₃ H, and —PR ₂ (R is an alkyl group), and Y is —H, —NH ₂ , —C
OOH least one, -OH, _-SO 3 H, an alkyl group, selected from an aryl group. The recording medium of the present invention can be manufactured, for example, by the following three methods.

The first method comprises a film-forming step of forming a single particle layer composed of particles having information recording ability, which is coated on a substrate with an aromatic compound having a branched structure, and a step of heat-treating the particle layer. By doing so, a recording medium is obtained.

In the second method, first, a film forming step of forming a single particle layer composed of particles coated with an aromatic compound having a branched structure on a substrate is performed. Next, a step of heat-treating the particle layer is performed. Next, a step of attaching a mask material from the substrate surface and a step of removing particles from the substrate surface are performed. A recording medium is obtained by performing a step of perforating a position corresponding to the removed particles on the substrate by etching and filling the perforation with a material having an information recording ability.

In the third method, first, a film forming step of forming a single particle layer composed of particles coated with an aromatic compound having a branched structure on a substrate is performed. Next, a step of heat-treating the particle layer is performed. Next, a step of perforating a position where no particles are present on the substrate surface by etching to form a structure in which columns are arranged corresponding to the positions where the particles are arranged, and removing the particles from the surface of the structure Recording by performing a step, a step of forming a substrate having a perforation at a position corresponding to the cylinder using the structure from which the particles have been removed as an original plate, and a step of filling the perforation with a material having an information recording ability. Get the medium.

In the first method, the particles used in the film forming steps of the first to third methods need to be made of a material having an information recording ability in the first method.
In the second and third methods, the particles are not limited to a material having an information recording ability, and for example, silica particles, metal oxide particles, polymer particles, metal particles, and the like can be used.

The particles coated with the aromatic compound having a branched structure, which are used in the film forming step of the production method of the present invention, can be mixed with the core by various methods, for example, by adding the aromatic compound to the particle dispersion. The particles are obtained by bonding the above-mentioned aromatic compound having a branched structure to particles.

The aromatic compound used is selected according to the material of the particles.

For example, for a particle made of a noble metal, it is preferable to use a branched aromatic compound having a group containing a sulfur atom at the terminal, since a strong chemical bond between the noble metal particle and the aromatic compound is generated.

As for oxide particles such as silica, alumina and titania, since the particles are covered with the hydroxyl groups of the oxide, a branched aromatic compound having a functional group which is easily adsorbed on the particles is preferable. For example, in the case of titania, a branched aromatic compound having a terminal carboxyl group is preferable.

In magnetic medium particles such as nickel and cobalt, a branched aromatic compound having a group having a phosphorus atom at a terminal, which is easily coordinated with a transition metal, is preferred.

Organic particles such as polystyrene particles are preferably graft-polymerized with a branched aromatic compound having a vinyl group.

Various substrates can be used in the film forming step of the manufacturing method of the present invention. On the substrate-
_{OH, -COOH, -NH 2, -CONH} 2, -SO 3
H, it is desirable that the polar groups such as -PO ₃ H is formed. As the polar group, a substance based on the material of the substrate itself may be used, or another compound may be chemically bonded or physically adsorbed on the substrate. Especially Langmu
It is also effective to form a polar group using a method such as the ir-Blodgett (LB) method.

The film formation in the film formation step of the production method of the present invention may be carried out by a step of adsorbing the particles on a substrate in a solution, or by applying a solution in which the particles are dispersed to the substrate by, for example, spraying or spin coating. Can be performed. When the affinity between particles is small and a uniform monomolecular film is difficult to obtain, it is also possible to use a method similar to the LB method in which the particles are spread on the water surface, the area is reduced by a partition, and the particles are scooped. it can.

Further, extra particles on the substrate are removed by washing with a solvent to form a single particle layer. However, since a large amount of solution is required to immerse the substrate in the solution, a film can be formed by spin coating or spraying.

The heat treatment performed after the film-forming step is preferably performed at a temperature at which the bonded aromatic compound does not separate from the particles or cause a side reaction. It is desirable to carry out at a temperature of 200 ° C.

After the heat treatment step, it is desirable to perform a step of slightly shaving the particles by reactive ion etching (RIE) or the like to increase the distance between the particles.

[0048]

The present invention will be described in more detail with reference to the following examples. [Embodiment 1] FIG. 3 is a sectional view of a recording medium 30 for performing charge recording shown in this embodiment.

Optically polished diameter 120 mm, thickness 1.
An aluminum layer having a thickness of 500 nm was deposited as an electrode layer 32 on a 2 mm glass disk 31. Next, an aluminum oxide layer having a thickness of 5 nm was formed as an insulating inorganic layer (substrate) 33 by anodic oxidation. Al-OH bonds, which are polar groups, are formed on the surface of the aluminum oxide layer.

Next, the surface of gold fine particles having a particle diameter of 10 nm, which is a particle having information recording ability, is coated with a compound represented by the chemical formula (7) in ethanol, and the surface of the gold fine particles is covered with a carboxyl group. Gold fine particles 34 were obtained.

Embedded image OH groups and carboxyl groups bonded to Al have strong affinity. The coated gold fine particles 34 were dispersed in ethanol to obtain a dispersion, and the disk was immersed in the dispersion for 10 minutes, taken out, and washed with ethanol to remove extra coated gold fine particles. After drying at 80 ° C. for 1 hour, heat treatment was performed at 150 ° C. for 2 hours to obtain a fine particle layer 35.

After drying, the obtained fine particle layer 35 was observed by AFM. As a result, a single particle layer of the coated fine gold particles 34 was formed on one surface, and the distance between the fine particles was almost constant at 2 nm. . Also, almost no defects without fine particles were observed.

Next, a silicon oxide film having a thickness of 10 nm was formed as an insulating protective layer 36 by sputtering. Further, a lubricant layer was formed thereon to obtain a recording medium 30.

Using this recording medium, a recording / reproducing experiment was performed with the recording / reproducing apparatus shown in FIG. As shown in FIG. 4A, the recording medium 41 is installed so as to be rotated by a motor 42. A head 43 for recording and reading is provided near the surface of the recording medium 41. As shown in FIG. 4B, the head 43 includes a slider portion 44, a minute electrode 45 having a diameter of 50 nm for applying a voltage, and a minute FET sensor 46 for reading out electric charges.

While rotating the recording medium 41 at 4000 rpm, a high voltage is applied in a pulsed manner between the microelectrode 45 and the electrode layer of the recording medium to inject electrons into the coated gold fine particles, thereby recording by electric charge. Did.

Next, while rotating at 4000 rpm in the same manner as during recording, the presence of electric charge was read by the change in the electric field intensity by the minute FET sensor 46. A signal of 250 gigabits per square inch could be read at a CN ratio of 30 dB, and sufficient contrast was obtained.

Further, the recording could be erased by applying a reverse voltage between the microelectrode 45 and the electrode layer of the recording medium. Comparative Example 1 A recording medium was prepared in the same manner as in Example 1 except that the compound (8) was used instead of the compound (7).

Embedded image Observation of the resulting fine particle layer by AFM revealed that a single particle layer of coated gold fine particles was formed on one surface, but the spacing between the fine particles was uneven compared to Example 1.

Using this recording medium, a recording / reproducing experiment was performed with the same recording / reproducing apparatus as in the first embodiment. 400 recording media
While rotating at 0 rpm, a high voltage was applied in a pulsed manner between the microelectrode 45 and the electrode layer of the recording medium to inject electrons into the coated gold fine particles, thereby recording by electric charge.

Next, while rotating at 4000 rpm in the same manner as during recording, the presence of electric charge was read by the change in the electric field intensity by the minute FET sensor 46. A signal of 250 gigabits per square inch could be read out only at a CN ratio of 15 dB, and sufficient contrast could not be obtained. [Embodiment 2] FIG. 5 is a sectional view of a recording medium 50 shown in this embodiment.

Silicon oxide was deposited on the surface of a silicon wafer 51 as a substrate 52 for depositing magnetic particles by sputtering to a thickness of 100 nm.

Next, the surface of the gold fine particles having a particle diameter of 5 nm was coated with an aromatic compound having a branched structure represented by the compound (9) in ethanol to obtain coated gold fine particles.

Embedded image Next, the substrate 52 was immersed in water, and the ethanol dispersion of the coated fine gold particles was gently dropped on the water surface to float the fine particles on the water surface, and then gently compressed with a partition plate. Surface pressure gauge is 1
When the pressure reaches 5 dyn / cm, the compression is stopped and the substrate 5
2 was gently pulled up from below the water surface to form a single particle layer of coated fine gold particles on the surface of the substrate 52. After drying at 80 ° C for 1 hour,
Heat treatment was performed at 150 ° C. for 2 hours.

When the obtained coated gold fine particle layer was observed by AFM, a single particle layer of coated gold fine particles was formed on one surface, and the particle interval was almost constant.

Next, the substrate 52 was etched by RIE using the coated gold fine particles as a mask and subjected to ultrasonic treatment in chloroform to remove the coated gold fine particles. FIG. 6 shows a plan view of the substrate 52 at this time. Holes 54 were formed on the substrate 52 except where the coated gold particles were present.
A film of CoPtCr was formed as a magnetic material 53 by the sputtering method using the holes 54 as nuclei, and heat-treated at 300 ° C. As a result, a recording medium in which magnetic particle crystals having an average diameter of 6 nm and arranged at an average interval of 6 nm with the holes 54 as nuclei were dispersed was formed. Separation layer 5 due to impurities between magnetic crystal grains
5 are formed.

Using this recording medium, a recording / reproducing experiment was performed by writing with a magnetic head and reading with a GMR head. As a result, a signal of 400 gigabits per square inch could be read with a CN ratio of 25 dB. [Comparative Example 2] Instead of using compound (9), compound (1)
A recording medium was prepared in the same manner as in Example 1 except that 0) was used.

Embedded image When the obtained coated gold fine particle film was observed by AFM, fine particles were formed on one surface, but the distance between the coated gold fine particles was more irregular than in Example 2.

Next, the substrate was etched by RIE using the coated gold fine particles as a mask and subjected to ultrasonic treatment in chloroform to remove the coated gold fine particles. Holes were formed in the substrate except where the coated gold particles were. Using the holes as nuclei, a film of CoPtCr as a magnetic material was formed by a sputtering method, and then heat-treated at 300 ° C. As a result, a recording medium was formed in which magnetic particle crystals having an average diameter of 6 nm and having the holes as nuclei and arranged at an average interval of 6 nm were dispersed. Separation layers of impurities were formed between the magnetic crystal grains. The degree of dispersion of the crystal grains was about three times as large as that of Example 2. Example 2 using this recording medium
When a recording / reproducing experiment was carried out in the same manner as in Example 1, a 400 gigabit signal per square inch could be read only at a CN ratio of 10 dB, and a recording medium with more noise than in Example 2 was obtained.

[0065]

As described above, in the recording medium and the method of manufacturing the recording medium according to the present invention, the particles having the information recording ability are made to exist in isolation, and at the same time, the distance between the particles is made substantially constant. The density can be increased and the medium noise can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a recording medium of the present invention.

FIG. 2 is a schematic view showing an example of particles coated with the aromatic compound according to the present invention.

FIG. 3 is a cross-sectional view of the recording medium according to the first embodiment.

FIG. 4 is a schematic diagram of the recording / reproducing apparatus shown in the first embodiment.

FIG. 5 is a cross-sectional view of a recording medium according to a second embodiment.

FIG. 6 is a plan view showing one process of a recording medium shown in a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Substrate 12 ... Recording layer 13 ... Particle 14 ... Aromatic compound having a branched structure 21 ... Particle 22 ... Aromatic compound 23 ... Aromatic compound molecule 30 ... Recording medium 31 ... Glass disk 32 ... Electrode layer 33 ... Insulating property Inorganic layer (substrate) 34 ... Coated fine gold particles 35 ... Fine particle layer 36 ... Protective layer 41 ... Recording medium 42 ... Motor 43 ... Head 44 ... Slider part 45 ... Microelectrode 46 ... Micro FET sensor 50 ... Recording medium 51 ... Silicon wafer 52 ... substrate 53 ... magnetic material 54 ... hole 55 ... separation layer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G11B 7/24 516 G11B 7/24 516 7/26 531 7/26 531 // G11B 5/65 5/65 5/851 5/851

Claims (3)

[Claims] 1. A recording medium comprising at least a substrate and a recording layer formed on the substrate and having a plurality of particles having information recording ability, wherein the particle surface is coated with an aromatic compound having a branched structure. A recording medium characterized in that: 2. The recording medium according to claim 1, wherein the aromatic compound has a polar group bonded to an aromatic ring. 3. A recording medium comprising: a film forming step of forming a particle layer including particles coated on a substrate with an aromatic compound having a branched structure; and a heat treatment of the particle layer. Manufacturing method.