JP2002025146A - Recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record multilevel data with high density and to easily reproduce it. SOLUTION: When information is recorded in a recording part 5 of a recording medium 1 having a recording layer 3 consisting of a phase change material, information is recorded by varying a area ratio of a region whose phase state is changed in accordance with the kind of information and the multilevel data are recorded by diversely varying electrical characteristics of a recording region 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium capable of recording various types of information at a high density and reading the recorded information stably, and more particularly to an increase in the density of multilevel data.

[0002]

2. Description of the Related Art Optical recording media typified by CDs and DVDs have been progressing toward higher densities for large capacity and small size. As described above, in order to increase the density of the optical recording medium, it is necessary to miniaturize the recording bit. In order to reduce the recording bits of the optical recording medium, that is, to increase the resolution of light, it is necessary to shorten the wavelength of the incident light and increase the numerical aperture of the lens. However, there is a limit in increasing the resolution of light due to the diffraction limit of light, so that the recording bits of the optical recording medium cannot be miniaturized beyond the diffraction limit, and the miniaturized recording bits cannot be read without crosstalk.

As one of the solutions for miniaturizing the recording bit beyond the light diffraction limit, near-field light has recently been receiving attention. In the near field, light incident from one of two media having different refractive indices under the condition of total reflection or more is all reflected at the reflection boundary surface, but only the non-propagating electromagnetic field component extrudes beyond the boundary surface. A region is created and refers to this non-propagating electromagnetic field region. It is said that this near field has a lateral spread only about the same size as the aperture size. Therefore, a small mark exceeding the diffraction limit of light can be formed by reducing the size of the opening.

As a memory for a computer, information is recorded in the form of concavities and convexities such as bits, and the recorded information is reproduced by detecting a change in capacitance due to the concavity and convexity. As shown in the publication, in order to increase the density of recorded information, a ferroelectric layer is formed on a semiconductor layer, and the polarization direction of the ferroelectric is inverted by a needle-like electrode to change the capacitance. Information is recorded and the recorded information is reproduced by detecting a change in capacitance due to the polarization of the ferroelectric substance.

[0005]

When information is recorded by near-field light, recording bits exceeding the diffraction limit of light can be formed to be minute. However, when the recorded information is reproduced by detecting the reflected light, it is detected. Light intensity is low, and it is difficult to reproduce information. In addition, when information is reproduced by detecting transmitted light, a reflective layer cannot be provided on the recording layer, and there is a disadvantage that information cannot be written well.

When information is recorded in the form of concavities and convexities such as bits, or when information is recorded by a change in capacitance due to the polarization direction of a ferroelectric substance, the information is represented by binary data of "0" and "1". Although it could be recorded, multi-valued data could not be recorded and reproduced.

An object of the present invention is to provide a recording medium which can improve such disadvantages and record multi-valued data at high density and can easily reproduce it.

[0008]

According to the present invention, there is provided a recording medium in which information is recorded on a recording layer made of a phase change material by changing an area ratio of a region where a phase state changes according to the type of information. Features.

Another recording medium according to the present invention is characterized in that information is recorded on a recording layer made of a phase change material by changing the depth of a region where a phase state changes according to the type of information.

It is preferable that information is recorded by irradiating the recording layer with a light beam or an electron beam to change a crystalline phase to an amorphous phase.

Further, information may be recorded by applying a current pulse to the recording layer to change the amorphous phase into a crystalline phase.

When reading information recorded on the recording medium, the information recorded on the recording layer is read by a change in electrical characteristics of the recording layer, for example, a change in impedance or a change in resistivity, or a change in capacitance. .

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A recording medium according to the present invention has a substrate, a recording layer formed on the surface of the substrate, and a protective film formed on the surface of the recording layer. The recording layer is a chalcogenite-based material,
For example, it is formed of a phase change material such as AgInSbTe, and is gradually heated and cooled at a temperature higher than the crystallization temperature and lower than the melting point to become crystalline. When data is recorded on the recording layer of the recording medium, the crystal is changed to an amorphous phase by irradiating a laser beam, near-field light, or an electron beam, and the resistance of the recording area is increased. When recording data, the data is recorded by changing the area ratio of the recording region of the recording layer provided in a spiral shape of the recording layer, which is changed to amorphous, according to the type of data.

When reading and reproducing the data recorded on the recording layer of the recording medium, the substrate of the recording medium is dropped to the ground, and the change in impedance is measured while sliding the electrodes on the surface of the protective film. The change in the impedance to be measured differs depending on the area of the recording region in which the layer has been changed to an amorphous layer, and the multi-value data can be identified and read from the change in the impedance different depending on the area of the recording region. Further, since data is read from the change in impedance of the recording layer, unlike data reading using a laser beam, there is no restriction due to the diffraction limit of light, and high-density data can be read stably.

[0015]

FIG. 1 is a perspective view showing a recording medium according to an embodiment of the present invention. As shown in the figure, the recording medium 1 is formed in a disk shape like an optical recording medium such as a CD. As shown in the sectional view of FIG. 2, the recording medium 1 has a substrate 2, a recording layer 3 formed on the surface of the substrate 2, and a protective film 4 formed on the surface of the recording layer 3. As the substrate 2, polycarbonate, acrylic resin, polyolefin, epoxy resin,
Use a transparent substrate such as vinyl stell, ultraviolet curable resin, or glass.

The recording layer 3 is made of a phase change material containing SbTe as a main component, and is gradually heated and cooled at a temperature higher than a crystallization temperature and lower than a melting point to become crystalline. In particular, when SbxTey is used as the recording layer 3, a composition near the eutectic point with a composition ratio of x / y = 1 to 4 is preferable. In addition to SeTb as a main component, Ge, Ag, In, Ga, S
i, B, Sn, Bi, Ba group, preferably Ge, A
It is preferable to include at least one or more elements selected from the group consisting of g, In, and Ga as additive elements. The content of this additional element is 15 at% or less. In particular, when the additive element is Ag, the content is preferably 3 at% or less, when In, B, Ga, Bi is 10 at% or less, and when Ge, Si, Sn, Ba is 5 at% or less. In such a composition, the electric resistance difference between the amorphous phase and the crystalline phase becomes particularly large. And for example, AgInSbTe or GeAgInSb
A composition such as Te or GeGaSbTe is suitable for the recording layer 3. For example, AgInS having a thickness of 200 nm is formed on a glass substrate.
A single-layer film of bTe is formed, initialized to be crystalline, and a part thereof is irradiated with a laser beam to change the crystalline phase into an amorphous phase. As a result, the electric resistance of the crystalline part was 1.68 × 10 ⁻⁴ Ωcm, whereas the electric resistance of the amorphous part was 38.7 Ωcm.
cm, the electrical resistance of the crystalline part and the electrical resistance of the amorphous part have a difference of about 6 digits, and there is a large difference in the electrical characteristics. Record the data.

The protective film 4 is made of SiO ₂ , AL ₂ O ₃ , Ta
Oxides such as ₂ O ₅ , ZrO ₂ , ZnO, ZnS, Sm
Sulfide such as S, SrS, CaS, CaF ₂ , Mg
Fluoride such as F ₂ , BaF ₂ , SrF ₂ , BN, Si
A nitride material such as N or a carbide material such as SiC, DLC or i-C is used alone or as a mixture.

The recording medium 1 is for recording data and reproducing the recorded data by utilizing the fact that the electrical characteristics of the crystalline and amorphous portions are significantly different. When data is recorded on the layer 3, a crystalline phase is changed to an amorphous phase by irradiating a laser beam, near-field light, or an electron beam. When recording this data, as shown in FIG. 3, the area ratio of the recording area 6 of the recording layer 3 provided in a spiral shape of the recording layer 3 which changes to amorphous is changed according to the type of data. And record the data. When the crystallinity of the recording layer 3 is changed to an amorphous phase in this manner, the resistance value Ra of the amorphously changed recording region 6 is compared with the resistance value Rc of the crystalline portion 7 where the layer is not changed. And the electrical resistance ratio (R
a / Rc) = 1 × 10 ⁴ or more, resulting in high resistance and data recording. Also, by changing the area ratio of the recording region 6 to be changed to the amorphous phase according to the type of data, multi-valued data can be recorded in addition to the binary data at the signs “1” and “0”. . Furthermore, when data is recorded, by irradiating near-field light or an electron beam to change the crystalline phase to an amorphous phase, it is possible to form minute recording bits, thereby increasing the density of recorded information. Can be planned.

When the data recorded on the recording layer 3 of the recording medium 1 is read and reproduced, as shown in FIG. 2, the substrate 2 of the recording medium 1 is dropped to the ground, and the electrodes 8 are connected to the protective film 4.
The change in impedance is measured while sliding on the surface. The change of the impedance to be measured differs depending on the area of the recording region 6 which has changed into an amorphous layer, and the multi-value data can be identified and read from the change of the impedance which varies depending on the area of the recording region 6. Further, since data is read from a change in impedance of the recording layer 3, unlike data read using a laser beam, there is no restriction due to the diffraction limit of light, and high-density data can be read stably. . The shape of the electrode 8 for reading data from the change in impedance of the recording layer 3 may be any of a surface electrode, a needle electrode, and a spherical electrode. It may be formed as.

In the above embodiment, data is read from a change in the impedance of the recording layer 3. However, data may be read by detecting a change in the resistivity of the recording layer 3.

Further, data can be read by detecting a change in the capacitance of the recording layer 3. In this case, as shown in the cross-sectional view of FIG. 4, when data is recorded on the recording layer 3, the depth of the recording area 6 where the phase changes to amorphous changes according to the type of data. As described above, by changing the depth of the recording area 6 that changes to an amorphous phase, multi-value data can be recorded by changing the capacitance according to the depth of the recording area 6. When reading and reproducing data recorded on the recording layer 3 of the recording medium 1, the capacitance 2 is changed while the substrate 2 of the recording medium 1 is dropped to the ground and the electrode 8 is slid on the surface of the protective film 4. Is measured. The change in the capacitance to be measured differs depending on the depth of the recording region 6 where the amorphous layer has changed, and the multi-value data can be identified and read from the change in the capacitance. In addition, since data is read from a change in the electrical characteristics of the recording layer 3, high-density data can be read stably.

In the above embodiment, the case where the recording layer 3 is initialized to be in a crystalline state and the recording area 6 is changed to an amorphous layer when data is recorded, but the recording layer 3 is made of a chalcogenite-based material. When recording data, a current pulse may be applied to the recording layer 3 to change the amorphous phase into a crystalline phase. Also in this case, data can be read by detecting a change in the electrical characteristics of the recording layer 3 as in the above-described embodiment.

[0023]

As described above, according to the present invention, information is recorded on a recording layer made of a phase change material by changing the area ratio of a region where the phase state changes according to the type of information, or the phase state is changed. Since information is recorded by changing the depth of the changing area according to the type of information, the electrical characteristics of the recording area can be varied in various ways, and multi-value data can be recorded with high accuracy. it can.

When information is recorded on the recording layer, the information is recorded by irradiating a light beam or an electron beam to change the crystalline phase to an amorphous phase, or an amorphous phase is obtained by applying a current pulse to the recording layer. By recording information while changing the phase to crystalline, multi-value data can be recorded at a high density.

Further, by reading the information recorded on the recording layer by changing the electrical characteristics of the recording layer, there is no restriction due to the diffraction limit of light, unlike when reading data using a laser beam. Density data can be read stably.

Further, by reading information recorded on the recording layer by a change in impedance, a change in resistivity or a change in capacitance, high-density data can be stably read with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a recording medium according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a recording medium and a recording area where recording is performed.

FIG. 3 is an explanatory diagram showing a recording area recorded on a recording medium.

FIG. 4 is a sectional view showing another recording area recorded on a recording medium.

[Explanation of symbols]

1; recording medium, 2; substrate, 3; recording layer, 4;
5: recording unit, 6: recording area, 8: electrode.

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) // G11B 7/004 G11B 7/004 Z

Claims (8)

[Claims] 1. A recording medium for recording information on a recording layer made of a phase change material by changing an area ratio of a region where a phase state changes according to a type of information. 2. A recording medium for recording information on a recording layer made of a phase change material by changing the depth of a region where a phase state changes according to the type of information. 3. The recording medium according to claim 1, wherein information is recorded by irradiating the recording layer with a light beam or an electron beam to change a crystalline phase to an amorphous phase. 4. The information is recorded by applying a current pulse to the recording layer to change an amorphous phase into a crystalline phase.
The recording medium according to the above. 5. The recording medium according to claim 1, wherein the information recorded on the recording layer is read by a change in electrical characteristics of the recording layer. 6. The recording medium according to claim 5, wherein information recorded on the recording layer is read by a change in impedance. 7. The recording medium according to claim 5, wherein information recorded on the recording layer is read by a change in resistivity. 8. The recording medium according to claim 5, wherein information recorded on said recording layer is read by a change in capacitance.