KR20020002431A - An optical recording medium and method for using same - Google Patents

Abstract

Recording and reproducing by irradiating a beam to the recording medium from an optical head positioned on a surface of the upper inorganic layer, the recording layer including a substrate and at least a recording layer and an upper inorganic layer sequentially formed on the substrate. The upper inorganic layer is formed so that foreign materials existing on the upper surface of the optical recording medium are not vaporized when the recording beam is irradiated. Preferably, A) the upper inorganic layer is configured to cause the recording beam to A first dielectric layer having a thickness such that when irradiated to a recording medium, the temperature of the upper surface of the recording medium does not increase to a level at which foreign material present on the upper surface of the optical recording medium vaporizes, or B) the upper portion In the inorganic layer, when irradiating a recording light beam onto the recording medium, an upper surface temperature of the recording medium is present on the surface of the optical recording medium. Includes a laminate having a layered structure sequentially formed of a second dielectric layer, a metal layer, and a third dielectric layer that do not increase to the level at which the foreign material vaporizes.

Description

Optical recording medium and method of using the same {AN OPTICAL RECORDING MEDIUM AND METHOD FOR USING SAME}

Most of the recording media generally used today are of a type in which a laser beam is irradiated onto the recording layer through the substrate.

In contrast, recently, the type of laser beam irradiation using an optical head located at a very small distance from the surface of the medium has attracted attention, which has a flying slider similar to the head of a hard disk, and an objective lens is mounted. Using a flying optical head, the laser is irradiated onto the medium from the surface of the recording layer without passing through the substrate (Japanese magazine 'Electronics' pages 87-91 published in May 1996 by publisher Ohm Co.). This type of medium is called a layer side incident type medium.

In such a layer plane incidence type medium, the focus of the beam is focused on the recording layer by allowing the optical head to fly at a constant height from the surface of the medium without using the focus control actuator used for the ordinary optical head. As described in the above document, bringing the optical head closer to the surface of the recording medium is preferable, since the diameter of the beam at the focus can be made smaller to further increase the recording density. The interval between the surfaces of the recording medium is 1 탆 or less.

Another layer plane incidence type has been proposed. That is, unlike the small gap system described above, a focal point similar to that of an optical head used in conventional substrate-side incident type mediums for recording and reproducing information on the optical recording medium is described. Although an optical head with a control actuator is used, the beam is incident on the medium from the recording layer side without passing through the substrate (the magazine "O plus E" Vol. 20, published in February 1998 by the publisher Shin-Gijutsu Communications, No. 2, pages 183-186, and presentation WA2, pages 131-133 of the OSA Technical Digest Series Volume 8, "Optical Data Storage Conference Edition", May 10-13, 1998).

The above two documents describe an optical system with a high numerical aperture (NA) obtained with a combination of two specific lenses and an organic coating layer that can increase the recording density to a significant degree compared to the media currently used (e.g., It is intended to increase the recording density by combining the optical properties of a transparent layer or a photocurable resin layer formed to a thickness of 100 mu m on the surface on which the beam is incident. In this technique, however, the distance between the optical head and the recording layer increases at least by the thickness of the organic coating layer, and due to the use of an optical system such as a substrate-side incident type, the surface of the optical head and the medium Since the distance between them increases, the recording density is limited.

On the contrary, the layer spacing type medium of the micro-gap type has attracted attention because it can theoretically obtain a higher recording density. Although research has already begun as layer side incident type media can have higher recording densities than conventional media, various problems to be solved in the future as practical recording and reproduction have not yet been achieved. There is.

The present invention is directed to the improvement of a layer side incident type medium of a small spacing method, and is intended to solve the following problems found by the present inventors.

That is, the present inventors have conducted research on a layer side incident type medium composed of a reflective layer, a lower dielectric layer, a recording layer, and an upper dielectric layer on a polycarbonate substrate, and mounted on a flying optical head. We found that the objective lens is blurred or dusty. During playback, there was no problem with tracking control. However, irradiating a relatively high power laser beam for recording or erasing not only makes the tracking control difficult immediately because of dust in the objective lens, but even reproduction is impossible.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, and to provide a layer side incident type medium in a small gap manner that can prevent dust from getting into the lens and can be used for a long time. will be.

The present invention relates to an optical recording medium and a method for recording and reproducing the recording medium. More specifically, the optical recording medium of the present invention is a type in which a laser beam is irradiated onto the surface of the medium from the surface of the recording layer of the medium facing the substrate by the optical head located at a very small distance from the surface of the recording medium.

1 is a diagram showing a system for optically recording onto a recording medium or an optical disc by irradiating a beam using a flying optical head without passing through the substrate from the layer surface of the medium.

2 shows the relationship between the reflectance of the medium and the thickness of the upper dielectric layer.

3 to 5 are sectional views of the optical recording medium according to the present invention.

According to the present invention, the above and other objects include a substrate and at least a recording layer and an upper inorganic layer sequentially on the substrate, and irradiating a beam to the medium from an optical head located on the upper inorganic layer surface. Recording and reproducing, and wherein the upper inorganic layer is configured so that foreign materials existing on the surface of the optical recording medium are not vaporized when the recording beam is irradiated to the recording medium. By providing a recording medium, this can be achieved. In particular, the upper inorganic layer is configured to have one of the following two characteristics.

A) The upper inorganic layer is a dielectric layer having a thickness such that the upper surface temperature of the recording medium does not increase to the level at which foreign materials present on the surface of the optical recording medium vaporize when the recording beam is irradiated onto the recording medium (the present invention) A first aspect of); or

B) said upper inorganic layer comprises a laminate formed on said recording layer in the order of a second dielectric layer, a metal layer and a third dielectric layer, thereby being present on the surface of said optical medium when a recording beam is irradiated on said recording medium. The temperature of the upper surface of the recording medium does not increase to the level where the foreign substance vaporizes (second aspect of the present invention).

In this specification, the term recording is used in a broad sense and includes writing (also called writing in a narrow sense) and erasing. In a phase change-type optical recording medium, a pulse beam having a high energy for writing and a medium energy for erasing is usually used for recording, but a beam having low energy for reproduction. Use to overwrite directly. In a magneto-optical recording medium, recording is usually performed by first scanning with a medium energy erasing beam and then scanning with a high energy writing beam. In the present invention, it is necessary to suppress the temperature rise of the surface of the medium during writing in a broad sense, i.e., writing and erasing.

The study by the inventors revealed that the clouding and dust of the objective lens are attached to foreign substances, in particular water and organic substances contained in the water. The present inventors have repeated experiments and considerations to identify the cause of dust and the mechanism by which dust adheres to the lens, and the cause is caused by foreign substances, especially those attached to the surface of the recording medium, that is, the layered incident type optical recording medium. It has been concluded that it is an organic component such as oil mist in air contained or adsorbed in water and / or its attached water.

The lens dimming mechanism was thought to cause the surface of the medium to reach a high temperature due to the irradiation of a laser with a relatively high power, condensing on the objective lens of the flying optical head by vaporizing moisture and organic substances attached to the surface of the medium. . Nevertheless, since the optical recording medium is a removable medium unlike a hard disk, since it is used in air, it is impossible to prevent the optical recording medium from coming into contact with moisture or organic substances in the air, and therefore, on the surface of the medium, The presence or adhesion of moisture or organic matter in the water is usually unavoidable.

The inventors have come up with the idea that the above problem can be solved by lowering the temperature of the surface of the medium than the temperature at which the substances attached to the surface of the medium vaporize, and have studied the idea in various ways.

First, the inventors have simulated the temperature during recording and reproduction of an optical recording medium having a conventional structure, and found that it is impossible to lower the temperature of the medium surface in such a structure.

Here, according to the first aspect of the present invention, the inventors have conceived that the thickness of the upper dielectric layer can be increased in order to lower the temperature of the surface of the medium, and when the thickness of the upper dielectric layer is increased, the medium is desired as an optical recording medium. The determination was made to determine if it could have the desired lower surface temperature of the medium. Figure 2 shows the relationship between the reflectance of the medium and the thickness of the upper dielectric layer as a result of the computer simulation.

As shown in FIG. 2, it can be seen that even if the thickness of the upper dielectric layer is increased, the same reflectance, that is, the reflectance required for the optical recording medium, can be obtained. Therefore, the insulation of the upper dielectric layer with the increased thickness while the laser beam is irradiated is shown. It was estimated that the temperature of the surface of the medium can be suppressed by the method.

Based on the results of the above computer simulations and considerations, an optical recording medium having an increased thickness of the upper dielectric layer was produced, recording and reproducing experiments were performed using a flying optical head, and as a result, by confirming the significant improvement as expected. The present invention, particularly the first aspect of the present invention, has been completed.

Similarly, in accordance with a second aspect of the present invention, the inventors have separated the top dielectric layer into two dielectric layers, as in conventional media, and inserted a metal layer with high thermal conductivity between the two dielectric layers so that the temperature of the surface of the media It was conceived that can be lowered. Hereinafter, the two dielectric layers and the metal layer therebetween are collectively referred to as an inorganic protecting layer or an upper inorganic layer. The inventors have determined whether the optical recording medium can have the desired surface temperature of the optical recording medium while maintaining the properties required as the optical recording medium when changing and adjusting the structure of the upper inorganic layer using the upper inorganic layer as described above. Investigate.

As described above, an optical recording medium having an upper inorganic layer composed of three layers was manufactured and recording and reproduction were tested using a flying optical head, and as a result, it was confirmed that the improvement was considerably improved. Completed the second aspect.

As can be seen from the above, in the present invention, the foreign material is a foreign material attached to the upper surface of the optical recording medium, and the surface temperature of the medium is kept lower than the temperature at which the foreign material is vaporized while the recording beam is irradiated. It is necessary to make it possible. The main foreign substance is moisture. Therefore, it is preferable to keep the surface temperature of the medium not higher than 150 ° C, and even more preferably not higher than 100 ° C.

In addition, according to the present invention, the following method is provided.

Providing a recording medium comprising a substrate and a layer sequentially formed on said substrate with at least a recording layer and an upper inorganic layer, and

Irradiating a beam to the recording medium from an optical head located on the surface of the inorganic layer to perform recording and reproduction;

And the upper inorganic layer is formed so that foreign materials existing on the upper surface of the optical recording medium are not vaporized when the recording beam is irradiated to the recording medium. To provide.

Preferably, the upper inorganic layer has one of the two features A) and B) described above.

The optical recording medium of the present invention comprises at least a recording layer and an upper inorganic layer in sequence on a substrate, and irradiates a beam from the surface of the upper inorganic layer for recording and reproduction. Preferably, the medium includes a reflective layer, a lower dielectric layer, a recording layer, and an upper dielectric layer sequentially formed on a substrate.

As an example, a brief description will be given of the layer plane incident type optical recording medium which irradiates a beam from the upper inorganic layer to the medium using a flying optical head for recording and reproduction.

Referring to FIG. 1, a flying slider 2 suspended in a suspension 3, on or above an optical recording medium or disk 1 comprising a layered structure 1b comprising a substrate 1a and a recording layer. ) Is shown. While the optical disk 1 is rotating, the flying slider 2 is flying on the optical disk 1, and the flying altitude H is the rotational speed of the optical disk 1 and the shape, weight, etc. of the flying slider 2, and the like. Determined by way of example, and may have about 100 nm, for example. In this example, an objective lens including a combination of two lenses 4 and 5 is mounted on the flying slider 2. The laser beam 6 is irradiated through the optical system. In the case of a magneto-optical recording medium, an additional magnetic field (not shown) is applied.

Recording and reproduction are performed as in the case of the conventional optical recording system, except that the optical system uses a flying optical head and the laser beam is irradiated to the medium from the side of the layer without passing through the substrate.

(1st aspect of this invention)

EMBODIMENT OF THE INVENTION Hereinafter, the 1st aspect of this invention is demonstrated.

3 is an example of an optical recording medium which is the first aspect of the present invention. In Fig. 3, reference numeral 11 is a substrate, numeral 16 is a heat insulating layer, numeral 12 is a reflective layer, numeral 13 is an optical recording layer such as a recording layer of a phase change type, numeral 15 is an upper dielectric layer. This reflective layer structure comprising a reflective layer 12 and a lower dielectric layer 13 is currently most commonly used in recording media of magneto-optical and phase change types, and provides a high S / N (noise to reproduction signal output ratio) value, It is preferable to use the edge recording system in which the reflective layer makes use of the edge of the recording spot for information recording by preventing unnecessary heat diffusion called rapid cooling construction. Further, in the present invention, it is preferable to use the structure having such a reflective layer for high recording density.

Next, the thickness of the upper dielectric layer 15 will be described with reference to Table 1 and FIG. Table 1 shows the structure and optical properties of the layers of the phase change type recording medium used in the experiment. In Table 1, the materials and optical properties of the substrate are not shown because they are independent of reflectance.

Table 1

Configuration matter Thickness (nm) Refractive index Extinction coefficient Board - Reflective layer AlCr 150 1.226 5.417 Lower dielectric layer ZnS, SiO ₂ 18 2.18 0.02 Recording layer GeSbTe 22 4.099 3.788 Upper dielectric layer ZnS, SiO ₂ 0-600 2.18 0.02

2 shows the simulation results of the reflectance of the optical recording medium having the above structure when the thickness of the upper dielectric layer 15 is changed, as shown in Table 1, and the abscissa is the thickness of the upper dielectric layer 15, and is vertical. The coordinate is the reflectance. In FIG. 2, due to the interference of light, the primary peak of the media reflectance appears at approximately 150 nm, the secondary peak is approximately 300 nm, and the tertiary peak is approximately 450 nm. In addition, the characteristics of these reflectances were confirmed in experiments on the optical recording medium actually produced.

Since there is no need to use a thickness that is as large as the thickness of the second or more peaks, and as the layer becomes thicker in this way, productivity decreases, the thickness of the upper dielectric layer used in conventional optical recording media has a primary peak. Was in range.

Here, the peak area is defined as an area including a peak having a reflectance equal to or greater than the reflectance required for recording and / or reproducing, as previously defined by the specification or the like. In particular, in the example of FIG. 2, when the lower limit of the reflectance is 20%, the primary peak range is approximately 90 nm to 195 nm of the upper dielectric layer thickness.

The reflectance of the optical recording medium required in the magneto-optical recording medium or the phase change type optical recording medium depends on the design or standard of the drive, but is usually in the range of 20 to 50%.

An example of a standard for optical recording media is ISO / IEC 13963 with a reflectance of 12 to 25% for a 3.5 inch magneto-optical recording medium with a capacity of 230 MB, a groove of 120 mm DVD-RAM with a capacity of 2.6 MB. ISO / IEC 16824 with 15-25% reflectivity in the groove land region, and 120-mm DVD-RAM with 4.7 GB or 9 GB double layer capacity for 45-85% single layer reflectivity There is ISO / IEC 16448 which is 18-30%.

In a first aspect of the invention, the thickness of the upper dielectric layer is equal to a value at which the temperature of the surface of the medium on the side where light is incident is lower than the temperature at which the foreign material attached to the surface of the medium vaporizes and the reflectance of the medium is required. Choose to have a larger value. The thickness of the upper dielectric layer is preferably equal to or greater than the secondary peak region. By using the upper dielectric layer of such a thickness, even if the temperature of the recording layer rises to a high temperature, the temperature of the surface of the medium can be suppressed. If a thickness equal to or greater than the third peak area is used, a more significant effect can be obtained. Incidentally, suppressing the temperature rise of the medium surface can significantly reduce the requirement for the heat resistance of the lubricating layer that can be formed on the upper dielectric layer as an additional effect.

In the above considerations and experiments, a phase change type optical recording medium is used in which the reflectance decreases at the time of recording as compared with erasing, but the reversed-type medium, i.e., the reflectance at the time of erasing is used. Obviously, the same effect can be obtained with an increasing phase change type optical recording medium. It is obvious that the same effect can be obtained also in the case of a magneto-optical recording medium.

The thickness of the upper dielectric layer 15 is preferably thicker for lowering the temperature of the medium surface, and thinner for productivity. Therefore, it is preferable that the thickness of the upper dielectric layer 15 does not exceed 1 micrometer. In addition, when the thickness exceeds 1 mu m, the stress of the upper dielectric layer becomes too high, and the layer is peeled off or warped.

The distance between the upper surface of the medium and the objective lens of the optical head is preferably as small as possible to increase the recording density. Therefore, the present invention is particularly preferably applied when the distance between the upper surface of the medium and the objective lens of the optical head is approximately 1 탆 or less. Here, the objective lens means the output end of the beam of the optical system, and includes the solid immersion lens described in the above-mentioned document "Electronics".

The refractive index of the upper dielectric layer is preferably at least 1.70. Injecting oil with high refractive index between the objective lens and the sample or object under microscope is known to increase the resolution of the microscope. In the present invention, the use of an upper dielectric layer having a high refractive index can further suppress beam waist spreading. When the upper dielectric layer is composed of a plurality of dielectric layers, the refractive index of the upper dielectric layer is a calculated complex regulation. This complex refractive index can be obtained from the entire transmission matrix obtained from the product of each transmission matrix of the multilayer film (Metal-dielectric multilayer, J. Macdonald, Adam Hilger (London), page 8, 1971).

The upper dielectric layer is composed of calcogenides, nitrides, such as ZnS.SiO ₂ , ZnS, SiN, GeN, AlSiN, Al ₂ O ₃ , SiO ₂ , Ta ₂ O ₅ , TiO ₂ and Y ₂ O ₃ , Oxide and combinations thereof. The composition of these layers can be stoichiometric or nearly stoichiometric. Among them, the layer of ZnS.SiO ₂ is preferable because it is a stable amorphous state having low thermal conductivity and cannot be easily crystallized by heat. The upper dielectric layer may be formed by physical vapor deposition, such as sputtering. The ZnS.SiO ₂ layer may be formed by sputtering a mixture of about 80 mol% to about 20 mol% ZnS and SiO ₂ .

4 shows a preferred embodiment of the first aspect of the invention divided into two layers, first upper dielectric layer 15a and second upper dielectric layer 15b. The first dielectric layer 15a has a low thermal conductivity and the second dielectric layer 15b has a high hardness.

If the upper dielectric layer is made up of a plurality of layers, the overall thickness is set to maintain the media surface temperature lower than the temperature at which the foreign material on the media surface is vaporized. For example, in FIG. 2, the thickness of the secondary peak region or more may be used. The rigid second top dielectric layer can be formed of silicon nitride or hydrogenated diamond-like carbon (DLC). In this case, the thickness of the solid top dielectric layer typically ranges from 10 to 150 nm, and the remaining portion of the top dielectric layer consists of the top dielectric layer with low thermal conductivity.

The upper dielectric layer having low thermal conductivity preferably has a thermal conductivity of 5 Watt / (m × K) or less, and since it is difficult to directly measure the thermal conductivity of the dielectric layer, the thermal conductivity is indirectly measured by simulation. Where m is the meter and K is the absolute temperature.

In FIG. 4, an upper barrier or crystallization acceleration layer 17 and a lower barrier or crystallization acceleration layer 18 are shown, but these layers are optional.

(2nd aspect of this invention)

Next, a second aspect of the present invention will be described.

5 shows an example of an optical recording medium according to the second aspect of the present invention. In Fig. 5, reference numeral 21 denotes a substrate, reference numeral 26 denotes a heat insulating layer, reference numeral 22 denotes a lower dielectric layer, reference numeral 24 denotes an optical recording layer such as a phase change type recording medium, and reference numeral 25 denotes an inorganic protective layer. The inorganic protective layer 25 includes a first top dielectric layer 25a (topmost dielectric layer), a second top dielectric layer 25b (bottom top dielectric layer), and a metal layer 25c. This reflective layer structure comprising reflective layer 22 and lower dielectric layer 23 is most commonly used in current magneto-optical and phase change type recording media, and as described in connection with the first aspect of the present invention, a high C / It provides N (carrier to noise ratio). In addition, in FIG. 5, although optional, together with the thermal insulation layer 26, an upper barrier or crystallization acceleration layer 27 and a lower barrier or crystallization acceleration layer 28 are shown.

Next, an inorganic protective layer is demonstrated. The metal layer 25c functions as a heat diffusion layer that prevents the surface temperature rise of the medium, which is the most important role of the present invention. That is, during recording or erasing, the beam is mainly absorbed by the recording layer and converted into heat. As the heat of such a recording layer moves to the surface of the medium, the temperature of the surface of the medium rises. However, in the second aspect of the present invention, since there is a metal layer having high thermal conductivity in the path from the recording layer to the surface of the medium, heat diffuses laterally along the metal layer, whereby the rise of the medium surface temperature is prevented. Suppressed. This was confirmed through experiments.

In order for the metal layer to function as a heat diffusion layer, it is desirable to have high thermal conductivity. Therefore, the metal layer preferably contains gold, silver, copper, aluminum and alloys thereof. In particular, alloys containing silver containing at least 0.5 at% (atomic%) of Cu have high thermal conductivity, are inexpensive compared to Au, have higher thermal conductivity than Al, and are superior in corrosion resistance to single Ag. In the present invention, Ag alloy is preferable. Silver alloys with Cu of 20 at% or less are preferred because of their lower dependence on performance and the use of one optical head for various wavelengths. In addition, up to about 3 at% of Ti, Ta, Pd, Nb, Ni, or the like may be added to the alloy of Ag and Cu.

Since the measurement of the thermal conductivity is difficult, it is difficult to find the thermal conductivity of the metal layer. However, it is considered from simulations or the like that the thermal conductivity of the metal layer is approximately 50 W / (m × K) or more (m is a meter and K represents an absolute temperature).

The thickness of the metal layer is preferably in the range of 5 to 50 nm. If the thickness is less than 5 nm, the effect of thermal diffusion is insufficient and the effect of suppressing the increase in the surface temperature of the medium is reduced. If the thickness is larger than 50 nm, the reflectance of the medium becomes too large to deviate from the range of about 20% to about 50%, which is the standard reflectivity in current magneto-optical recording media or phase change type recording media. The reflectivity of the required media can be adjusted by the design including the amplification gain of the drive, but too high reflectance should be avoided since the new version must be compatible with the older version. Further, the present invention is preferably applied to a phase change type optical recording medium in which a reproduction signal is obtained by using the difference in reflectance between the crystalline state and the amorphous state of the recording layer. However, in the phase change type optical recording medium, when the metal layer is thicker than 50 nm, the difference in reflectance when the recording layer is crystalline and when it is amorphous becomes small, so that an excellent C / N ratio cannot be obtained, which is not preferable. .

Further, in a phase change type optical recording medium having a metal layer having a thickness of 20 to 50 nm, the reflectance of the medium when the recording layer is amorphous (recorded portion) is made larger than the reflectance when crystalline (erased portion). Can be. Such medium is referred to as "low to high polarity" because the reflectance of the medium increases when recording, which is known to reduce jitter in high density recording. In particular, in a phase change type optical recording medium characterized by easy direct overwriting, if the temperature increase of the recording layer differs between the recorded mark portion (amorphous portion) and the erased portion (crystal portion), the previously recorded The recorded mark portion newly written in the mark portion and the recorded mark portion newly written in the previous erased portion have different sizes and shapes, resulting in deterioration of the signal quality (increasing jitter). Therefore, writing a new recording mark portion in the erased portion (crystal portion) requires a higher heat capacity by heat of melting crystalline than writing a new recording mark portion in the amorphous portion. Therefore, it is desirable for the medium to absorb the beam by an increased amount of energy corresponding to the heat capacity to melt the crystalline, i.e., to reduce the reflectance of the medium by a level corresponding to the above heat capacity. This is because a medium in which the reflectance of the medium is smaller in the erased portion (crystalline portion) than in the amorphous portion is preferable.

In addition, the inorganic protective layer 25 includes a first upper dielectric layer 25a between the recording layer 24 and the metal layer 25c and a second upper dielectric layer 25b on the metal layer 25c.

The refractive index of the first and second upper dielectric layers is preferably 1.70 or more. In the present invention, spreading of the beam focus can be further suppressed by using an upper dielectric layer having a high refractive index.

The first upper dielectric layer 25a provides an appropriate recording sensitivity and serves to protect the recording layer 24 and the metal layer 25c. Without the first upper dielectric layer 25a, the temperature rise of the recording layer is very small and the recording sensitivity is very small while the beam is being irradiated, so that melting of the recording layer and mixing of the recording layer components cannot be suppressed. In view of the recording sensitivity, the first upper dielectric layer is preferably an amorphous material which has a low thermal conductivity and is thermally stable, i.e., does not deteriorate at high temperatures and is stable.

The first upper dielectric layer is a chalcogenide such as ZnS.SiO ₂ , ZnS, SiN, GeN, AlSiN, Al ₂ O ₃ , SiO ₂ , Ta ₂ O ₅ , TiO ₂ and Y ₂ O ₃ , nitrides, oxides, and their It may be a combination layer. The composition of these layers can be stoichiometric or nearly stoichiometric. Among them, the layer of ZnS.SiO ₂ is preferable because it is a stable amorphous that has low thermal conductivity and is not easily crystallized by heat. The first upper dielectric layer can be formed by physical vapor deposition, such as sputtering. The ZnS.SiO ₂ layer may be formed by sputtering a mixture of ZnS and SiO ₂ having a ratio of about 80 mol% to about 20 mol%. Preferably, the first upper dielectric layer has a thermal conductivity of 5 Watt / (m × K) or less, and it is indirectly measured by simulation or the like because it is difficult to directly measure the thermal conductivity of the dielectric layer, where m is a meter. K represents absolute temperature.

The thickness of the first upper dielectric layer is preferably at least 10 nm or more from the viewpoint of the recording sensitivity and the protection of the recording layer, and preferably not more than 1 µm from the viewpoint of productivity. Some dielectric materials, if the thickness of the layer exceeds 1 μm, exert too high stress on the first upper dielectric layer to cause it to delaminate or bend the layer.

The second upper dielectric layer 25b serves to prevent corrosion of the metal layer 25c, to prevent damage to the surface of the media by contact of the optical head, and to prevent the rise of the media surface temperature. In view of this, the thickness of the second upper dielectric layer 25b is preferably at least 10 nm or more, and even more preferably 40 nm or more in order to obtain a better effect of preventing damage to the surface of the medium and suppressing the temperature rise of the surface of the medium. Do. In addition, the effect of suppressing the temperature rise of the medium surface is preferable because it can significantly alleviate the requirement for the heat resistance of the lubrication layer that can be formed on the second upper dielectric layer 25b. However, it is preferable that the thickness of the second dielectric layer 25b does not exceed 1 μm from the viewpoint of productivity. If the thickness of the layer exceeds 1 μm, some dielectrics cause too high stress on the second upper dielectric layer, causing the layer to peel off or warp.

Further, even when a dielectric layer having a refractive index of 1.70 or more is used, it is preferable that the distance between the recording layer 24 and the objective lens of the optical head is as small as possible in order to obtain higher recording density. Therefore, the total thickness of the inorganic protective layer 25, that is, the total thicknesses of the first and second upper dielectric layers 25a and 25b and the metal layer 25c preferably does not exceed 1 μm.

The material of the second upper dielectric layer 25b may be the same as the material of the first upper dielectric layer 25a. In addition, the second upper dielectric layer directly faces the flying light head, so that the head slider can contact or damage the second upper dielectric layer 25b. Therefore, a solid dielectric layer that can withstand such contact and damage is desirable. This rigid second top dielectric layer may be made of silicon nitride or hydrogenated diamond-like carbon (DLC).

(Other components of the medium)

It is desirable to insert a barrier layer 17 or 27 between the upper inorganic layer and the recording layer to prevent the components of the upper inorganic layer from diffusing into the recording layer in order to stabilize the quality. In addition, in order to manufacture a phase change type optical recording medium that can be used when rotating at high speed, the crystallization acceleration layer may be inserted adjacent to or in contact with the recording layer. Further, for the same reason, a barrier layer or a crystallization acceleration layer 18 or 28 may be inserted between the lower dielectric layer 13 or 23 and the recording layer 14 or 24.

Typical examples of barrier layers include GeN layers and SiN layers, which are not easy to analyze, but the ratio between Ge / N and Si / N is assumed to be 3/4 or close to stoichiometric ratio. In addition, a GeN layer to which Cr is added, that is, a layer made of GeCrN and a SiAlN layer is used. The GeCrN layer is formed by sputtering a Ge alloy target containing 10-30 at% Cr in a mixed gas atmosphere of Ar and N ₂ (about 10-50% N ₂ ). The SiAlN layer can be formed by sputtering a SiAl target in a mixed gas atmosphere of Ar and N ₂ . Since nitride is generally high in density and excellent in heat resistance, the nitride layer has an excellent effect in preventing the diffusion of sulfur elements of ZnS.SiO ₂ commonly used in phase change type optical recording media into the recording layer. When such a nitride layer is provided facing the GeSbTe layer, which is a typical phase change type optical recording layer, it is believed that the sensitivity is improved upon erasing of the medium, and the nitride layer has an excellent effect of accelerating crystallization. While the theoretical reason for accelerating crystallization is not clear, it is believed that the nitride layer has the effect of accelerating or increasing nucleation for crystallization when the GeSbTe layer is heated to the crystallization temperature.

The lubricating layer may be formed on the second upper dielectric layer, if necessary, to mitigate the impact caused by contact and collision of the optical head, as long as it does not damage the optical properties.

In the magneto-optical recording layer of the magneto-optical recording medium, the coercive force of the recording layer is reduced by irradiating a light beam, typically a laser beam, to raise the temperature of the recording layer, and the magnetic moment of the heated portion of the recording layer is controlled by an external magnetic field. Reverse and recording and / or erasing is performed. The temperature of the recording layer increases to about 200 ° C.

In a phase change type optical recording layer of a phase change type optical recording medium, a light beam, usually a laser beam, is irradiated for a change between amorphous and crystalline material, that is, a phase change, and the phase change is used for recording and / or erasing. . The temperature of the recording layer rises to about 600 ° C. during recording and rises to about 170 ° C. during erasing. A phase change type optical recording medium is advantageous in that it has a lower material cost than that of a magneto-optical recording medium, and a drive can be inexpensive because the recording and erasing mechanism is as simple as using phase change in comparison with the optical-magnetic recording medium. It is easy to be compatible with the CD-ROM).

Magneto-optical recording layers of magneto-optical recording media are known and may be made of, for example, rare earth or transition metal alloys such as TbFeCo. A phase change type optical recording layer of a phase change type optical recording medium is known, and may be made of a chalcogenide alloy such as GeSbTe and InSbTe, for example. The thickness of the recording layer is not particularly limited, but is generally in the range of 12 to 30 nm.

In the case of a phase change type optical recording medium compared to a magneto-optical recording medium (for example, 200 ° C.), the temperature of the recording layer is increased to a higher temperature (for example, 600 ° C.), and is blurred when the surface temperature of the medium is high. Since the dust problem becomes more serious, it is more preferable to apply it to a phase change type optical recording medium. In the case of a phase change type optical recording medium, the effects of the present invention can be obtained more clearly and advantageously.

The reflective layer is generally made of an aluminum alloy containing 2 to 5% of Ti, Ta, Cr, Au and the like. Alternatively, Ag alloys or Au alloys may also be used. In the present invention, the material and the thickness of the reflective layer are not particularly limited.

In general, the thickness of the reflective layer is in the range from 40 to 200 nm.

The lower dielectric layer may be similar to the upper dielectric layer.

In general, the thickness of the lower dielectric layer is in the range of 15 to 50 nm.

In the present invention, since the substrate is independent of the optical properties of the medium, the substrate is not particularly limited in the present invention, and may be any known material such as glass or plastic. Among these materials, a polycarbonate resin having excellent cost and mechanical properties desirable. In cases where low hygroscopicity is required, amorphous aliphatic polyolefin resins are preferred.

When the heat resistance of the substrate is low, a heat insulating layer may be formed between the substrate and the reflective layer. Such a heat insulating layer has an effect of preventing deformation of the substrate due to the heat effect generated in the recording layer. In particular, the substrate may be more easily deformed in an initial heat treatment step for crystallization or in an initialization step of heating a large area of media at one time, in which the effect of the thermal insulation layer is important. This insulating layer should have low thermal conductivity and have a thickness of at least 2 nm.

The heat transfer method from the recording layer to be heated is considered as follows. The heat of the recording layer usually dissipates through the lower dielectric layer along the reflective layer of aluminum alloy with high thermal conductivity, while the heat of part of the reflective layer is transferred to the substrate. If the heat of the reflecting layer only diverges along the reflecting layer, there is no problem that the temperature of the substrate rises.

Therefore, the thermal conductivity of the thermal insulation layer is determined in relation to the thermal conductivity of the reflective layer. If the heat conductivity of the reflective layer is high, heat hardly reaches the substrate and heat insulation of the heat insulating layer is unnecessary. If the thermal conductivity of the reflective layer is low, the thermal conductivity of the thermal insulation layer should be sufficiently low. The thermal conductivity of the insulating layer should be approximately 1/10 of that of the reflective layer. If the heat insulation layer thickness is too thin, the heat insulation layer effect cannot be obtained, so the thickness must be at least 2 nm.

The heat insulating layer material may be selected from the group consisting of chalcogenides such as ZnS SiO ₂ , ZnS, SiN, GeN, AlSiN, Al ₂ O ₃ , SiO ₂ , Ta ₂ O ₅ , TiO ₂ and Y ₂ O ₃ , nitrides, oxides and combinations thereof. Any one of the materials described for the upper dielectric layer, including the material.

The thermal conductivity of the thermal insulation layer is preferably as similar as the thermal conductivity of the upper dielectric layer, or the first upper dielectric layer. This thermal conductivity is considered to be approximately 5 Watt / (m × K).

In particular, the optical recording medium of the present invention is preferable when the medium is used in an optical head system in which the distance between the medium and the objective lens of the optical head system is approximately 1.0 mu m or less. A general example of such an optical head system is a flying optical head. In flying optical heads, the distance between the medium and the objective lens of the optical head system is very small, and it is very serious that the objective lens is blurred by vaporized material. The flying optical head is as shown in FIG. The flying head travels at a distance from the surface of the medium in an air flow due to the rotation of the medium. In particular, a slider supported by a leaf spring structure called gimbals fixes the objective lens and flies a certain distance from the surface of the medium by air flow caused by the rotation of the medium.

Example

(Examples 1 to 4 and Comparative Examples 1 to 3)

A phase change type recording medium (no barrier layer or crystallization acceleration layers 17 and 18 were formed) having a structure similar to that of FIG. In particular, the medium includes a substrate 11, an insulating layer 16, a reflective layer 12, a lower dielectric layer 13, a recording layer 14, a first upper dielectric layer 15a and a second upper dielectric layer 15b. The thickness of the first upper dielectric layer 15a was varied. The phase change type optical recording medium thus produced was evaluated.

The substrate 11 used was a polycarbonate plastic substrate having a thickness of 1.2 mm and a diameter of 120 mm as well as a hole having an internal diameter of 15 mm, and was of the following form. The substrate 11 had a V-shaped helical groove having a radius of 25 mm to 58 mm formed by injection molding for continuous servo. The grooves were 90 nm deep, 0.12 μm bottom width, and 0.7 μm trek pitch. A record was made on the land.

In order to obtain a phase change type optical recording medium, the following layers were formed on the substrate, and a beam was irradiated from the layer side of the medium. The heat insulating layer 16, the lower dielectric layer 13 and the first upper dielectric layer 15a were ZnS-SiO ₂ layers obtained by sputtering a ZnS-SiO ₂ target having a molar% ratio of 80:20. The thickness of the heat insulating layer 16 was 80 nm, the thickness of the lower dielectric layer 13 was 18 nm, and the thickness of the first upper dielectric layer 15a was as shown in Table 2. The refractive index of the ZnS-SiO ₂ layer was approximately 2.18.

The recording layer 14 was a GeSbTe layer deposited by sputtering a GeSbTe alloy target having an atomic ratio of Ge: Sb: Te of 2: 2: 5 and having a thickness of 22 nm. The reflective layer 12 was an AlCr alloy layer deposited by sputtering an AlCr alloy having an atomic ratio of Al: Cr of 97: 3, and the thickness was 150 nm.

The second upper dielectric layer 15b was a SiN layer obtained by sputtering a Si target in a mixed gas atmosphere of Ar and N ₂ . The atomic ratio of the SiN layer was thought to be close to the stoichiometric ratio of 3: 4, but precise analysis was difficult. The second upper dielectric layer 15b had a refractive index of 2.08 and a thickness of 120 nm.

The inorganic layer was formed on the substrate 11 by magnetron sputtering. The equipment used was an in-line sputtering equipment (type ILC3102-manufactured by Anelva Corp.) with a target of 8 inches in diameter, rotating and revolving around the axis with a predetermined radius. The thickness of the deposited layer was controlled by the deposition time.

Table 2 shows the thicknesses of the upper dielectric layers in the first to fourth examples and the first to third comparative examples in which the thickness of the first upper dielectric layer was changed. In addition, Table 2 shows the reflectance of the medium after the initial heat treatment for crystallization, and the order of the corresponding peak area to which the entire upper dielectric layer belongs. Peak areas were defined previously in terms of interference peaks.

TABLE 2

Number of samples Layer thickness Order of peak area Reflectance of the medium (wavelength is 685 nm) First upper dielectric layer (nm) Second upper dielectric layer (nm) Total dielectric layer (nm) Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 155205325485154575 120 120 120 120 120 120 120 275325445605135165195 2nd 2nd 3rd 4th 1st 1st 1st 32383637384225

The above-described phase change type optical recording medium was analyzed in a device with a flying optical head having a laser diode having a wavelength of 685 nm. Since it was difficult to directly measure dust or blur, the disorder of the tracking error signal when the laser beam was irradiated was observed to evaluate the blur and contamination of the objective lens. The flying optical head was controlled as described above and shown in FIG. 1, in a slider manner, in which an objective lens was mounted on the slider and the objective lens was flying at a distance of 0.38 μm from the surface of the medium. Tracking control detects the light coming back by a dual photodetector and is called a push-pull signal or so-called tracking error signal (hereinafter referred to as "TES"). This was done using the difference between the lights that were split into two and returned. The rotational speed of the medium was constant at 8 m / sec. This analysis procedure was as follows.

After the initial heat treatment for crystallization, a sample of the recording medium was placed in the analysis equipment. In order to measure the jump signal as a reference amplitude for evaluating the disorder of TES, a reproducing beam of 1.2 mW output was repeatedly irradiated on the same track. The reproduction by the repeated irradiation of this beam was the reproduction of the stop mode for the erased portion. Since the track is spiral, the beam must move or jump a distance of one track pitch per revolution in order to play the same track repeatedly, which is called "track jump". If repetitive playback is normal in still mode, the beam is directed towards the center of the track except that a large output (called jump amplitude) in sinusoidal form is observed when a track jump occurs once per revolution. During one revolution, TES approaches zero.

In general, TES disorder is assessed by the percent amplitude of the maximum amplitude at one revolution to the jump amplitude, excluding the amplitude at track jump. If the allowable off-track width is 0.05 [mu] m in media with a 0.7 [mu] m track pitch, this disorder should not exceed 43%. The permissible off-track width is chosen to be 43%, taking into account the general requirements of conventional optical recording media that do not have a fixed value but irradiate a beam from the surface of the substrate since it depends on the S / N of the system. If the disorder is greater than 43% of this criterion, it means that the beam passes over a point or line outside the permissible area from the center of the track. If the disorder is greater, the beam cannot stay on the track, i.e. tracking control becomes impossible.

In all the samples of Examples 1-4 and Comparative Examples 1-3, normal tracking control was possible when only the regeneration was performed, and the disorder of TES per revolution was at most 20%, indicating that the medium was normal. It did not exceed. Thus the jump amplitude of the sample was measured.

Next, dust and cloudiness were evaluated by the following experiment on the samples. A strong beam (hereinafter referred to as an "evaluation laser output") corresponding to the recording beam is irradiated to the sample for approximately one rotation period along the path where the reproduction beam having an output of 1.2 mW was irradiated in the stop mode as described above in the evaluation. The disorder of TES was measured for performance evaluation.

Here, in general, a strong laser power is used for recording and erasing because the recording layer requires a high temperature. In the samples tested, a laser power of about 4 mW was needed to erase the recording marks and about 7.8 mW laser peak power for recording.

In this experiment, while irradiating a regeneration beam of 1.2 mW in the stationary mode, a strong evaluation laser power was irradiated to the sample for a period of about one rotation, and then TES disorder was evaluated for performance evaluation. In this evaluation, the sample must, of course, meet the criterion that the disorder of the TES should not exceed 43% of the reference value after the laser has been irradiated at least about 4 mW corresponding to the erase power. However, in actual use, after irradiating a laser output of about 6 mW or less than about 7.8 mW of the peak power of the recording beam, if the TES disorder does not exceed the reference value of 43%, no problem arises. This is because the temperature of the medium is higher than when irradiating a continuous beam (a DC laser beam having a constant intensity), thereby irradiating the pulse beam actually used with the evaluation output. This latter fact or threshold was confirmed by separate regeneration experiments on 1-7 modified random data. Therefore, when the disorder of TES reached an allowable limit of 43%, the evaluation laser power of each sample was determined. Samples that meet this criterion can be satisfactory, and as mentioned above, there are no problems in actual use. The results are shown in Table 3.

TABLE 3

Total thickness of upper dielectric layer (nm) Order of peak area Assess laser power at the limits of TES disorder Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 275375445605135165195 1st peak 1st peak 3rd peak 4th peak 1st peak 1st peak 1st peak 6.06.47.17.83.84.35.2

As shown in Table 3, in Comparative Example 1, the evaluation laser power was low as 3.8 mW, and tracking control was not possible when the 6 mW evaluation criteria were applied. That is, the disorder of the TES exceeded the evaluation limit, and the flying optical head could not stay on the predetermined track.

In order to know the cause of the above problem, observation of the recording medium and the optical head was repeated before and after the experiment. As a result, no problem was found in the inside of the medium or on the surface of the medium, but it was found that droplets adhered to the surface of the objective lens facing the medium. Raman analysis and infrared absorption analysis were performed to find mainly water containing small amounts of hydrocarbons. Hydrocarbons were present in very small amounts and their identification was not possible, but they were thought to be oil components normally present in air. In Comparative Example 1, TES disorder was observed even with an evaluation power of 2.5 mW. As the evaluation power gradually increased, the limit of 43% was exceeded at the evaluation output of 3.8 mW.

As shown in Table 3, in Examples 1 to 4, even at an evaluation reference power of 6 mW, the TES disorder was within the limit of 43%, indicating that the medium was a practically useful medium. In contrast, in Comparative Examples 1 to 3, the TES disorder exceeded the 43% limit at an evaluation output lower than the 6 mW reference output, indicating that the medium does not allow stable recording.

(Examples 5 to 9 and Comparative Examples 4 to 7)

A phase change type optical recording medium (barrier layers or crystallization acceleration layers 27 and 28 are not formed) having a structure similar to that of FIG. In particular, the medium includes a substrate 21, a heat insulating layer 26, a reflective layer 22, a lower dielectric layer 23, a recording layer 24, a first upper dielectric layer 25a, a metal layer 25c and a second upper dielectric layer 25b. ). The thicknesses of the first upper dielectric layer 25a, the metal layer 25c and the second upper dielectric layer 25 were varied. The metal layer used in Examples 5-19 was an AgCu layer containing 5 wt% Cu. In Comparative Examples 4 to 7, a medium having no metal layer (Comparative Examples 4 to 5) and a medium having a thick AgCu metal layer having a thickness of 55 nm (Comparative Examples 6 and 7) were prepared.

The used substrate 21 was the same polycarbonate plastic substrate as in Example 1.

Each layer was formed on the substrate in order to obtain a phase change type optical recording medium in which a beam is irradiated from the layer plane. The heat insulating layer 26, the lower dielectric layer 23 and the first upper dielectric layer 25a were ZnS-SiO ₂ layers obtained by sputtering targets of ZnS and SiO _{2 having} a molar% ratio of 80:20. The thickness of the thermal insulation layer 26 was 80 nm and the thickness of the lower dielectric layer 23 was 18 nm. The thickness of the first upper dielectric layer 25a is one of three types, namely 40 nm (Examples 5 and 6 and Comparative Example 4), 80 nm (Examples 7 to 10 and Comparative Example, as shown in Table 3). 5 and 6) and 120 nm (Examples 11 to 19 and Comparative Example 7). The refractive index of the ZnS-SiO ₂ layer was about 2.18.

The recording layer 24 and the reflective layer 22 were the same as in the first embodiment. That is, the recording layer 24 was a GeSbTe layer deposited by sputtering a GeSbTe alloy target having an atomic ratio of Ge: Sb: Te of 2: 2: 5, and the thickness was 22 nm. The reflective layer 22 was an AlCr alloy layer deposited by sputtering an AlCr alloy having an atomic ratio of Al: Cr of 97: 3, and the thickness was 150 nm.

The second upper dielectric layer 25b was a SiN layer obtained by sputtering a Si target in a mixed gas atmosphere of Ar and N ₂ . The atomic ratio of the SiN layer is estimated to be close to the stoichiometric ratio of 3: 4, but the exact analysis was difficult. The second upper dielectric layer 25b has a refractive index of 2.08 and the thickness was varied over the range of 42 nm to 225 nm as shown in Table 4.

The metal layer 25c was an AgCu layer obtained by sputtering an AgCu target having a mass ratio of Ag and Cu of 95: 5. The thickness of the metal layer 25c was varied over a range of 5 nm to 50 nm (Examples 5 to 19) and 55 nm (Comparative Example 6 and Comparative Example 7).

The inorganic layer was deposited on the substrate 21 by the same magnetron sputtering as in Example 1. Eight substrates were placed side by side in a sputtering equipment (type ILC3102- made by ANELVA Corp.) and the same layer was simultaneously deposited on the eight substrates. The thickness of the deposited film was controlled by the sputtering time.

Table 4 shows the thicknesses of the first dielectric layer 25a, the metal layer 25c and the second dielectric layer 25b in Examples 5 to 19 and Comparative Examples 4 to 7. Table 4 also shows the difference between the reflectance of the medium with the amorphous recording layer immediately after sputtering, the reflectance of the medium with the crystalline recording layer after initial heat treatment for crystallization, and the above reflectance. In addition, the results of this measurement are shown in Table 4. As a medium in which the difference in positive reflectance is negative in Table 4, a medium in which the reflectance of the medium having an amorphous recording layer is larger than the reflectance of the medium having a crystalline recording layer is called a "low to high structure" (or low to high polarity). It is called a medium. This type of medium is a preferred medium structure since jitter, i.e., the degree of dispersion of the signal that senses the position at the time of edge writing is small.

Performance evaluation was performed on samples of optical media in the same manner as in Examples 1-4 and Comparative Examples 1-3.

In Comparative Examples 6 and 7, the reflectance was too large and the focus control and tracking control were difficult in the performance evaluation equipment, and sufficient evaluation was not possible. In Comparative Examples 8 and 9, it was evident that the carrier to noise ratio (C / N) ratio would be very small in practical use, even if the refractive index was too small to improve the performance evaluation equipment to control the optical head position.

In Examples 5 to 19 and Comparative Examples 4 and 5, normal tracking control was possible when only playback was performed and the jump signal of the medium was measured. TES disorder indicated that the media was normal with peaks below 20%. That is, the laser power for regeneration was 1.2 mW, and there was no problem at this low power.

In Comparative Example 4, the evaluation laser power was as small as 3.5 mW, and tracking control was impossible after 6 mW, which is the evaluation reference output. That is, the TES signal became disordered beyond the limits for performance evaluation, making it impossible to keep the optical head on a given track.

In order to find the cause of the problem, observation of the recording medium and the optical head was repeated before and after the experiment. As a result, no problem was found in the inside of the medium or on the surface of the medium, and it was found that droplets were attached on the surface of the sieve objective lens in contact with the medium. Raman analysis and infrared absorption analysis were conducted mainly to find droplets containing traces of hydrocarbons. Hydrocarbons are so small that their identification is impossible, but they were thought to be oil components normally present in air. In Comparative Example 4, the TES disorder was also observed by the evaluation output of 2.5 mW. Gradually increasing the evaluation output, the TES disorder also gradually increased, exceeding 43% of the evaluation output at 3.5 mW.

As shown in Table 4, in Comparative Example 5, it was expected to have a good C / N ratio because the reflectance difference is 20.3%, but the TES disorder exceeded the allowable limit of 43% at 4.3 mW of the evaluation laser. In contrast, in Comparative Examples 5 to 19, the evaluation laser output was satisfactory. That is, unlike Comparative Examples 4 and 5, by providing only the AgCr alloy metal layer, an evaluation output of 6 mW or more was obtained.

In Examples 11-17 and 19, the medium was a low to high polarity medium, as can be seen from the fact that the reflectance difference is negative. Since the absolute value of the reflectance difference in each sample was 17% or more, the medium provided a sufficient C / N ratio, and because the medium had low to high polarity, the instability, i.e., the reproduction signal by the edge mark recording required for high density recording The variance of was expected to be small.

In the samples of each example, the evaluation laser power was satisfactory at 6 mW or more.

As described above, in Comparative Examples 6 and 7 in which the thickness of the metal layer was 55 nm, sample analysis by the performance evaluation equipment was impossible because of the too high reflectance. Improving the gain of the amplification can perform the above performance evaluation, but even if the evaluation equipment is modified and evaluated, the absolute value of the reflectance difference is so small that a sufficient C / N ratio cannot be obtained.

Therefore, no such evaluation was performed.

From the above examples, it can be seen that dust and clouding of the optical head can be prevented by forming a metal layer having a thickness of 5 nm to 50 nm. A metal layer having a thickness of 20 nm to 50 nm is preferred for increasing the recording density, since it can easily provide a polar medium of low to high structure.

Table 4

reflectivity Evaluation at Limits of TES Disorder Laser Power (mW) Second upper dielectric layer Metal layer First upper dielectric layer Crystalline Amorphous Difference Example 5 42 10 40 30.3 9.7 20.7 6 Example 6 42 15 40 50.7 28.5 22.2 6.2 Example 7 60 5 80 40.8 20.6 20.2 6.3 Example 8 60 10 80 33.4 12.1 21.3 6.5 Example 9 60 15 80 33.8 11.0 22.1 6.8 Example 10 60 25 80 49.7 28.8 20.8 7.5 Example 11 60 20 120 5.6 23.7 -18.1 7.6 Example 12 60 30 120 14.8 37.1 -22.2 8 Example 13 60 40 120 27.3 49.9 -22.6 8.3 Example 14 60 45 120 40.7 61.1 -20.4 8.7 Example 15 60 50 120 53.1 70.1 -17.0 9.3 Example 16 120 10 120 16.1 34.7 -18.5 7.7 Example 17 120 15 120 26.0 47.7 -21.7 8 Example 18 225 5 120 25.2 5.6 19.6 8.2 Example 19 225 35 120 14.9 37.1 -22.3 9.2 Comparative Example 4 42 0 40 18 5 15 3.5 Comparative Example 5 60 0 80 52.1 31.8 20.3 4.3 Comparative Example 6 60 55 80 76.5 65.1 11.4 N.D Comparative Example 7 60 55 120 63.7 77.1 -13.4 N.D.

Note) N.D. : Not measurable

Claims (28)

An optical recording medium comprising a substrate and at least a recording layer and an upper inorganic layer sequentially formed on the substrate, wherein recording and reproduction are performed by irradiating a beam to the recording medium from an optical head located on the upper inorganic layer plane, And the upper inorganic layer is formed so that foreign materials existing on the upper surface of the optical recording medium do not vaporize when the recording light beam is irradiated onto the recording medium. The method of claim 1, wherein the upper inorganic layer has the following two characteristics, A) The upper inorganic layer has a thickness such that, when irradiating the medium with the recording light beam, the temperature of the upper surface of the recording medium does not increase to the level at which foreign material present on the upper surface of the optical medium vaporizes. Or a first dielectric layer having, or B) The upper inorganic layer, when irradiating a recording light beam onto the recording medium, does not increase the temperature of the upper surface of the recording medium to the level where the foreign material present on the upper surface of the optical medium vaporizes. A laminate having a layered structure sequentially formed of a second dielectric layer, a metal layer, and a third dielectric layer, Is an optical recording medium having any one of features 3. The optical record carrier as claimed in claim 2, wherein the foreign material is mainly water. The optical recording medium according to claim 2, wherein the temperature of the upper surface of the recording layer does not increase to 150 ° C or more when the recording or reproducing light beam is irradiated on the recording medium. 3. The optical recording medium of claim 2, further comprising a reflective layer between the recording layer and the substrate. 6. The optical recording medium according to claim 5, wherein the substrate is made of plastic, and the optical recording medium further comprises a heat insulating layer between the substrate and the reflective layer. 7. The optical recording medium of claim 6, further comprising a fourth dielectric layer between the recording layer and the reflective layer. 8. The optical recording medium of claim 7, further comprising a barrier layer or a crystallization acceleration layer between the recording layer and the fourth dielectric layer. 3. The optical recording medium of claim 2, further comprising a barrier layer or a crystallization acceleration layer between the recording layer and the upper inorganic layer. 3. The optical recording medium of claim 2, wherein the recording layer is a phase change type recording layer. The optical recording medium according to claim 2, wherein a distance between the optical head and the recording medium for use with the recording medium is 1 µm or less. An optical recording medium according to claim 2, wherein said optical head used with said recording medium is a flying optical head. The optical recording medium according to claim 2, wherein the upper inorganic layer satisfies the feature A). 15. The method of claim 13, wherein the first dielectric layer has a thickness in which the minimum thickness of the second peak region of the reflectance of the optical recording medium as the thickness of the first dielectric layer increases is greater than the thickness generated by optical interference. An optical recording medium. 14. The optical recording medium of claim 13, wherein the first dielectric layer has a thickness of less than 1 mu m. The optical recording medium of claim 13, wherein the first dielectric layer is an inorganic material layer having a refractive index of at least 1.70 at a wavelength of the recording or reproducing beam. 14. The optical recording medium of claim 13, wherein the first dielectric layer includes fifth and sixth dielectric layers sequentially on the recording layer, and the sixth dielectric layer has a greater hardness than the fifth dielectric layer. . The optical recording medium according to claim 2, wherein the upper inorganic layer satisfies the feature B). 19. The optical recording medium according to claim 18, wherein the metal layer comprises at least one of Au, Ag, Cu, and Al as main components, and has a thickness of 5 to 50 nm. 19. The optical recording medium of claim 18, wherein the second and third dielectric layers are inorganic materials having a refractive index of at least 1.70 at a wavelength of the recording or reproducing beam. 19. The optical recording medium of claim 18, wherein the third dielectric layer has a greater hardness than the second dielectric layer. The optical recording medium of claim 2, wherein the recording medium has a reflectance required by a standard standard of the recording medium. 23. The optical recording medium of claim 22, wherein the standard is an ISO standard. 23. The optical recording medium according to claim 22, wherein the recording medium has a reflectance within a range of 20 to 50% as a larger reflectance between the recorded and erased state of the information. Providing a recording medium comprising a substrate and a layer sequentially formed on said substrate with at least a recording layer and an upper inorganic layer; And Irradiating a beam to the recording medium from an optical head located on a surface of the inorganic layer to record and reproduce the same; And the upper inorganic layer is formed so that foreign materials existing on the upper surface of the optical recording medium are not vaporized when the recording beam is irradiated to the recording medium. . 27. The method of claim 25, wherein the inorganic layer has two characteristics, A) The upper inorganic layer has a thickness such that, when irradiating the medium with the recording light beam, the temperature of the upper surface of the recording medium does not increase to the level at which foreign substances present on the upper surface of the optical medium vaporize. Or a first dielectric layer having, or B) The upper inorganic layer, when irradiating a recording light beam onto the recording medium, does not increase the temperature of the upper surface of the recording medium to the level where the foreign material present on the upper surface of the optical medium vaporizes. A laminate having a layered structure sequentially formed of a second dielectric layer, a metal layer, and a third dielectric layer, Has a characteristic of any one of the features. 27. The method of claim 26, wherein the foreign material is primarily water. 27. The method of claim 26, wherein the temperature of the upper surface of the recording medium does not increase to 150 ° C or more when the recording beam is irradiated onto the recording medium.