JP3236374B2 - Optical record carrier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a record carrier having a laminated body having a recording layer, an interference layer and a reflection layer in this order on a substrate. It relates to an optical record carrier which can be written and read.
Here, the interference layer is a layer that causes an optical interference effect.

[0002]

2. Description of the Related Art Many known optical record carriers, such as compact discs (CD), compact disc read-only memory (CD-ROM) and laser vision (LV), are provided with information by the manufacturer in advance and the user can You can only play. There is a need in many places for writable record carriers that can be written in a special writing / reading device and that can also be read by a read-only reading device that reads the non-writable (read-only) record carrier described above. ing. For example, information in the form of audio or digital data must be distributed to a small number of customers (in which case a regular CD or CD-ROM would be too expensive). However, for this purpose, the writable record carrier must meet the same standard requirements as the read-only record carrier, and for CDs it must have an initial reflectivity of 70% or more and a contrast of 60%. . The initial reflectance is the reflectance of the non-written portion of the record carrier, and the contrast is the value obtained by dividing the difference between the reflectance of the non-written portion and the written portion by the initial reflectance. It has proven difficult to produce a writable record carrier that meets these requirements. This is especially true when a material called a phase change material is used for the recording layer. In these materials, the crystal layer changes due to the irradiation of the laser beam and the reflectance changes. The known phase change materials have too low a reflectivity to be used without any difficulty on record carriers compatible with CDs.

[0003] The record carrier of the type described in the opening letter is EP-
It is known from A0352105. The writable record carrier comprises a substrate, one side of which is the entrance surface, and comprises on the opposite side first a recording layer, then an interference layer and finally a reflective layer. The light beam entering through the substrate first strikes the recording layer,
Next, the light is incident on the interference layer and finally on the reflection layer. In other words, the recording layer of the laminate faces the incident surface. This stack increases the initial reflectance and contrast of the record carrier due to the interference action of these layers. The preferred embodiment of the record carrier described in this patent application has a recording layer of the phase change material InSb, which has a reflectivity of 72% and 38% for the non-written and written parts, respectively. Has and therefore 4
It has a contrast of 7%.

[0004]

A disadvantage of this known record carrier is that the structure of the laminate results in a corresponding increase in reflectivity and contrast for only a few recording materials. Other recording materials with good writing or erasing properties do not produce the desired high reflectivity and high contrast in this laminate structure. Increasing the contrast is desirable not only for the record carrier to meet industry standard requirements, but also for obtaining a high signal-to-noise ratio so that the record carrier can be read better.

[0005] It is an object of the present invention to provide a record carrier of the type mentioned in the opening paragraph which can use a large number of recording materials and has a sufficiently high reflectivity and a sufficiently high contrast. The present invention provides two new record carriers. Each has specific embodiments.

[0006]

A first type of record carrier according to the present invention is characterized in that the reflective layer of the laminate faces the incident surface, and the reflective layer is made of a metal or a metal alloy. If the incident light is first incident on the reflective layer and then on the recording layer via the interference layer, a record carrier with a higher reflectivity and / or contrast than known record carriers can be achieved depending on the implementation.

In one embodiment of the record carrier, the transmittance of the reflective layer is greater than 0.2, the record carrier having a higher contrast.

Another embodiment of the record carrier is characterized in that a metal reflection layer is formed on a base layer of an inorganic dielectric material. With this underlayer, an extremely thin metal reflective layer can be grown to a constant thickness.

A second type of the record carrier of the present invention is characterized in that the reflective layer of the laminate faces the incident surface, and the reflective layer comprises at least three dielectric layers. This laminate structure provides high reflectivity and high contrast simultaneously because the reflective layer does not absorb light.

A preferred embodiment of both types of record carrier is characterized in that an additional interference layer and an additional reflection layer are provided on the surface of the recording layer opposite to the interference layer. The addition of these layers further increases both reflectivity and contrast.

The additional reflective layer, as a metal layer, minimizes the amount of light passing through this reflective layer, so that the maximum amount of light can be used for reading and the record carrier has the highest reflectivity It is preferable to do so. Such a single reflection layer can be easily provided.

The laminate structure of the present invention is very suitable for realizing a record carrier having a high reflectivity and a high contrast provided with a recording layer of a phase change material.

This material is preferably a compound of Ge and Te. The advantage of this material is that it has satisfactory writing characteristics, high reflectivity and high contrast.

[0014] The use of Ta ₂ O ₅ interference layer, an interference layer at a high speed by the sputtering, can be provided at low cost, also has the advantage of having a low thermal conductivity together with the material having a high refractive index obtained . The last-mentioned property lowers the power required to write information to the recording layer.

When an antireflection film is provided on the incident surface of the record carrier, reflection loss no longer occurs on the incident surface. As a result, even if the laminate has a lower reflectivity than that of a record carrier without an antireflection film, the record carrier can have a desired reflectivity as a whole. The fact that the reflectivity of the laminate may be reduced in this manner is due to the use of a satisfactorily writable low-reflectivity phase-change material, which was considered to be unusable as a recording layer. Enable.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 shows a sectional view of a first type of optical record carrier according to the invention. The record carrier comprises a substrate 1, which may consist, for example, of a sheet of plastic or glass. A light beam generated by an optical scanning device for writing and / or reading a record carrier as described, for example, in U.S. Pat. No. 3,876,842 is incident on a substrate 1 via an entrance surface 2 of the record carrier.
This beam is schematically illustrated in FIG. A laminate 3 including a reflective layer 4, a transparent interference layer 5, and a recording layer 6 is provided on the surface of the substrate opposite to the incident surface. The surface of the laminate can be covered with a protective layer 7, which can be made of an organic material. Information is recorded on the recording layer in the form of an information area that is optically identifiable from the surrounding area. These information areas can have, for example, a different refractive index or a different reflectivity than the surroundings.

The reflection layer 4 reflects a part of the incident light. The reflectivity of the entire recording carrier is determined to a considerable extent by the reflectivity of the reflective layer. The light that has passed through the reflection layer enters the recording layer 6 via the interference layer 5. Interference layer 5, recording layer 6, and protective layer 7
Light reflected at the interface between them can be constructive or destructive depending on the thickness and refractive index of these layers. A part of the light reflected by the recording layer is reflected back to the recording layer at the interface between the interference 5 and the reflection layer 4. This light then interferes with the light that has passed through the reflective layer. This double interference determines the amplification of the optical effect caused by the information area to be read. By appropriate selection of the thickness and the refractive index of these layers in the stack 3, the reflectivity of the entire record carrier and the optical contrast of the information area can be set to desired values. It is also possible to reverse the contrast of the information areas, i.e. if the information areas of a recording layer without adjacent layers, such as layers 4 and 5, have a lower reflectivity than their surroundings, by providing these adjacent layers The reflectivity of the information area can be increased relative to its surroundings.
Such a reversal of contrast makes it possible to use materials which have not heretofore been used in the recording layer because they cannot meet the requirements of a given standard system.

The laminate according to the invention can be suitably used for a writable record carrier in which the recording layer is a phase change material. In such materials, the crystalline phase can be changed by heating with a light beam and then cooling. For example, it can be changed from a crystalline layer to an amorphous layer or vice versa. The phase-changed area can be detected by the light beam due to the different optical characteristics of both phases. The advantages of the laminate according to the invention comprising a phase-change material are described below for a record carrier using a GeTe alloy which is particularly suitable as recording material.

In the first embodiment, it is assumed that the unrecorded GeTe recording layer 6 is in an amorphous state, and when writing with a light beam, that portion becomes in a crystalline state. The thickness of the recording layer is set to an optimum thickness at which a high reflectance and a high contrast can be obtained in a crystalline state. The reflectance of the amorphous state and the crystalline state of such a recording layer provided directly on the substrate is 28%, respectively.
And 56%. The GeTe recording layer is the same as that described in EP-A035.
No. 2105, it can be embedded in a laminate comprising a Ta ₂ O ₅ interference layer and an Au reflection layer. The gold reflective layer of this laminate has a thickness of 100 nm and does not pass light.
Optimizing the thickness of these layers results in a reflectivity of 26% and 58%.
%become. When optimizing these layers, the light should be optimized to be a focused beam rather than a collimated beam. Such an optimization is known from Japanese Patent Application No. 2-158932.

In the present invention, the GeTe recording layer is buried in the reverse order of the known laminate. After the optimization, the laminate of the present invention shown in FIG. 1 has a Au reflection layer 4, 184n having a thickness of 19 nm.
It has a Ta ₂ O ₅ interference layer having a thickness of m and a recording layer 6 having a thickness of 23 nm. In this case, the reflectivity of the record carrier is 28% and 71% in the amorphous and crystalline areas, respectively. This record carrier satisfies the above-mentioned stringent requirements imposed on CD media, despite the simple structure of the laminate.

FIG. 2 shows the effect of the reflective layer on the optical characteristics of the record carrier having the laminate according to the present invention. This figure shows the reflectivity R of the record carrier as a function of the thickness d of the gold reflective layer. This record carrier has the following structure: a substrate, a gold reflective layer, a Ta ₂ O ₅ interference layer with a thickness that maximizes the reflectivity of the record carrier, and a 21 nm thick GeTe recording layer. The upper curve c in this figure shows the reflectivity of the record carrier in which the recording layer is in a crystalline state, and the lower curve a shows the reflectivity of the record carrier in which the recording layer is in an amorphous state. While the thickness of the gold reflection layer is small, the reflectance in the crystalline state increases, but the reflectance in the amorphous state remains constant. This results in an increase in contrast. When the thickness of the gold reflection layer is larger than about 25 nm, the reflectance of the amorphous state also starts to increase, the reflectance of the record carrier in both states increases, and the contrast decreases. This reduction in contrast is caused by the fact that increasing the thickness of the reflective layer reduces the transmittance of this layer. That is, a small amount of incident light is incident on the recording layer, and a small contrast occurs. If the record carrier requires a high contrast, it is preferable to maintain the transmittance of the reflective layer at about 20%. However, this transmittance is to be measured for a reflective layer provided between the substrate and the thick interference layer. The high transmittance of the reflective layer means that the reflective metal layer needs to be thin. This also has the advantage that the thermal conductivity of this layer is not too high. In the case of low heat conduction, as is known from US Pat. No. 4,984,231, the heat supplied to the recording layer is not quickly dissipated,
A low power light beam is sufficient to sufficiently heat the recording layer during writing.

By reflecting the light that has passed through the recording layer again, the contrast and reflectivity of the record carrier can be further increased. Without this additional reflection, light passing through the recording layer would be lost. FIG. 3 shows a record carrier implementing this. When viewed from the substrate 1, the laminate 3 includes a reflective layer 4, an interference layer 5, a recording layer 6, an additional interference layer 8, and an additional reflection layer 9.
Equipped. Light enters the record carrier from the entrance surface 2. Layer 8
And 9 reflect light passing through the recording layer 6. The addition of these two layers, in addition to the increase in reflectivity, leads to an increase in the degree of freedom in the design of the stack, for example to optimize the thermal properties of the stack. The effect of these two additional layers on the reflectivity of the record carrier will be described for a second embodiment of a record carrier having a GeTe recording layer that is amorphous in the unwritten state. Such a recording layer, incorporated in the stack shown in FIG. 1 and optimized for high reflectivity and high contrast in the amorphous state, is 65% and 27% in the amorphous and crystalline states, respectively. % Record carrier reflectivity. If additional interference layers 8 and reflection layers 9 are provided, the stack after optimization has the following structure: 18 nm Au reflection layer, 150 nm Ta ₂ O ₅ interference layer ₅ , 20 nm GeTe recording layer, 185 nm Ta ₂ O ₅ interference layer It has an 8 and 100 nm Au reflective layer 9. With this structure, the reflectivity of the record carrier in the amorphous state and the crystalline state is 70% and 12%, respectively.
In this example, gold having a high reflectance is used as the additional reflective layer.
If such a layer with good thermal conductivity constitutes a thermal load that is too great for the recording layer, a metal alloy or dielectric reflective layer with low thermal conductivity can be used for the additional reflective layer. Thermal load can also be reduced by providing one or more interference layers in whole or in part with organic materials to provide low thermal conductivity.

FIG. 4 shows a second type of record carrier of the present invention. In this record carrier, the metal reflection layer 4 of FIG.
It has been replaced by a dielectric reflective layer comprising three dielectric layers denoted by 0, 11 and 12. Each of these three dielectric layers has an optical thickness of about 1/4 of the wavelength of the light beam.
In this embodiment, the phase change material GeTe can also be used for the recording layer 6. In the third embodiment, the stacked body 3 is optimized so that a high reflectivity and a maximum contrast can be obtained in the amorphous state of GeTe. In this case, the laminate 3 has the following structure: 95 nm Ta ₂ O ₅ dielectric layer 10, 141 nm SiO ₂
Dielectric layer 11, 95 nm Ta ₂ O ₅ dielectric layer 12, 50 nm
SiO ₂ interference layer 5, 20 nm GeTe recording layer 6 and 190n
It has a m Ta ₂ O ₅ dielectric layer 8. In this example, the protective film 7 also functions as an additional reflective layer. The dielectric layer 8 changes the refractive index at the interface between the layers 6 and 8 as desired, and the protective film 7 protects the recording layer from overheating during writing. The reflectivity of this record carrier was determined to be 67% in the amorphous state and 28% in the crystalline state. Since the dielectric reflection layer has a lower thermal conductivity than the metal reflection layer, a small power is sufficient to write the recording layer 6. If the dielectric reflective layer comprises three layers, it is possible to achieve the same reflectivity and contrast as the record carrier comprising the metal reflective layer 4 shown in FIG.

When an injection-molded plastic substrate is used, information, for example, in the form of pits or dots, for tracking a light beam can be provided on the surface of the substrate on the laminate side. If the substrate is made of glass, this information can be more easily provided in the lacquer layer between the substrate and the laminate. Preferably, such a lacquer layer has approximately the same refractive index as the substrate, so that the laminate does not need to be changed essentially due to the presence of the lacquer layer. It is clear that the lacquer layer does not form part of the laminate, even if the laminate has a dielectric reflective layer. This is because the lacquer layer always has a low refractive index, and the first layer of the dielectric reflection layer always has a high refractive index.

When growing a thin metal layer on a substrate, many metals, especially gold, tend to be small islands at the beginning of the growth process and do not necessarily result in a layer of uniform thickness. Such non-uniform thickness is particularly large when a thin metal layer is grown on the lacquer layer. This tendency can be suppressed by growing a metal layer on an underlayer made of an inorganic dielectric material. This material may be an oxide, nitride or sulfide such as Ta ₂ O ₅ , AlN, SiO ₂ or
ZnS is preferred. FIG. 6 shows an embodiment of a record carrier having an underlayer. The substrate 1 has a lacquer layer 13 on which tracking information is embossed, and a laminate on the lacquer layer includes a base layer 14, a metal reflection layer 4, an interference layer 5, a recording layer 6, and a protective film 7. This underlayer can also be used for record carriers without a lacquer layer. This underlayer can be used to obtain a specific reflectance of the record carrier by selecting its refractive index and thickness to appropriate values, and the metal reflective layer is sealed with an inert layer, Another advantage is that it prevents degradation of the metal reflective layer caused by contaminants diffused from the substrate.

In the first to third embodiments described above, the light beam incident surface 2 is the surface of the substrate 1 on the side opposite to the laminate 3. It goes without saying that the light beam can be directly incident on the laminate without first passing through the substrate. The incident surface 2 of such a record carrier (shown in FIG. 5) is the upper surface of the reflective layer 4. The order of the layers in the stack of record carriers is the reverse of that of the stack of record carriers shown in FIGS.

The incident surface 2 reflects a part of the incident light and a part of the emitted light. Using a glass or plastic substrate, about 8% of the focused light beam is lost. When an antireflection film is coated on the incident surface, this loss is reduced to 1% or less. In this case, more light is used for writing and more light is output during reading. As a result, the laminate 3 of the record carrier having the antireflection film can have a lower reflectance than the laminate of the record carrier without the antireflection film when the same reflectance requirement is satisfied for the record carrier.
If an antireflection film is provided on the record carrier having the GeTe recording layer and having the structure shown in FIG. 4, the reflectivity of the record carrier satisfies the requirements for CD.

In the various examples described above, the various dielectric layers are made of Ta.
_{It is made of 2} O ₅ . The above-mentioned advantages of these layers can be achieved in all optical record carriers, especially those in which the writing of the recording layer requires heat.

In the illustrated embodiment, GeTe is used as the phase change material, but an alloy of GeTe and, for example, Sb or In, Se, Sn
Other phase change materials such as and / or Ga alloys can be used for the record carrier of the present invention. In principle, the invention can also be used for a record carrier with a recording material whose refractive index changes during writing. These materials can be write-once and re-writable materials such as dyes or metal alloys. The invention can also be used for a magneto-optical record carrier comprising a recording layer of a magnetic material which is written and read by a light beam.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first type of record carrier of the present invention.

FIG. 2 is a graph showing the reflectivity of the record carrier of FIG. 1 as a function of the thickness of the reflective layer.

FIG. 3 is a cross-sectional view of a record carrier having an additional reflective layer and an interference layer.

FIG. 4 is a sectional view of a second type of record carrier of the present invention.

FIG. 5 is a sectional view of another embodiment of the record carrier of the present invention.

FIG. 6 is a sectional view of a record carrier provided with an underlayer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Incident surface 3 Laminated body 4 Reflective layer 5 Interference layer 6 Recording layer 7 Protective layer 8 Additional interference layer 9 Additional reflection layer 10, 11, 12 Dielectric reflection layer 13 Lacquer layer 14 Underlayer

──────────────────────────────────────────────────の Continuation of the front page (73) Patent holder 590000248 Groenewoodseweg 1, 5621 BA Eindhoven, The Netherlands (72) Inventor Antonius Hendrikas Maria Holtslag The Netherlands 5621 Baer Eindhoven Inventor Wiener Wewma inventor 1 Van S-Speakman 5621 Beer Eindhoven Flenewwald Wech 1 Netherlands (56) References JP-A-2-166643 (JP, A) JP-A-3-248343 (JP, A) JP-A-3-183037 ( JP, A) JP-A-3-157675 (JP, A) JP-A-63-91842 (JP, A) JP-A-3-250438 (JP, A) JP-A-3-142727 (JP, A) JP 3-132942 (JP, A) JP Akira 62-205553 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) G11B 7/24

Claims (10)

(57) [Claims] 1. A record carrier comprising a laminate having a recording layer, an inorganic dielectric interference layer and a reflective layer in this order on a substrate, wherein information is written and read by a light beam incident on an incident surface thereof. An optical record carrier, wherein the reflective layer of the laminate faces the incident surface of the record carrier, and the reflective layer is made of a metal or a metal alloy. 2. The optical record carrier according to claim 1, wherein the transmission coefficient of the reflection layer is larger than 0.2. 3. The laminated body includes an underlayer in contact with the reflection layer on a side of the reflection layer facing the incident surface, and the underlayer is made of an inorganic dielectric material. The optical record carrier according to claim 1 or 2, wherein 4. A record carrier comprising a laminate having a recording layer, an inorganic dielectric interference layer and a reflective layer in this order on a substrate, wherein information is written and read by a light beam incident on an incident surface thereof. An optical record carrier, wherein the reflective layer of the laminate faces the incident surface of the record carrier, and the reflective layer comprises at least three dielectric layers. 5. The light according to claim 1, wherein an additional interference layer and an additional reflection layer are provided on a surface of the recording layer opposite to the interference layer. Record carrier. 6. The optical record carrier according to claim 5, wherein the additional reflective layer is made of a metal or a metal alloy. 7. The optical record carrier according to claim 1, wherein said recording layer is made of a phase change material. 8. The optical record carrier according to claim 7, wherein said phase change material is an alloy of germanium (Ge) and tellurium (Te). 9. The method of claim 1, wherein the at least one interference layer is tantalum oxide.
Optical record carrier according to any one of claims 1 to 8, characterized in that it consists of (Ta ₂ O _5). 10. The optical record carrier according to claim 1, wherein an antireflection film is provided on the incident surface.