JPS63257932A - Information recording medium - Google Patents

Abstract

PURPOSE:To improve the contrast of the signal of a prepit by specifying the distance between the surface of an intermediate coating layer coating the bottom part of the prepit and the surface of an intermediate coating layer coating the peak part of the side wall of the prepit. CONSTITUTION:This recording medium consists of a recording layer 13 which is provided via the intermediate coating layer 12 on the prepit provided on the surface of a disk-shaped substrate 11 and permits writing and/or reading of information by laser. The distance (a) between the surface of the intermediate coating layer 12 coating the bottom part of the prepit and the surface of the intermediate coating layer 12 coating the peak part of the side wall of the prepit satisfies the conditions: lambda/5n<=a<=lambda/3n with respect to the refractive index (n) of the substrate 11 and the wavelength lambda of the laser light to be used at the time of reading the information from the recording medium. The contrast of the signal in the prepit part is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an information recording medium on which information can be written and/or read using a high energy density laser beam. More specifically, the present invention includes:
The present invention relates to an improvement of the above-mentioned information recording medium having pre-pits.

[Technical Background of the Invention] In recent years, information recording media using high energy density beams such as laser light have been developed and put into practical use.

This information recording medium is called an optical disk, and is used as a video disk, an audio disk, a large-capacity still image file, a large-capacity computer disk memory, and the like.

The basic structure of an optical disc is a disc-shaped substrate made of glass, synthetic resin, etc., and a B i, S
It has a recording layer made of metal or semimetal such as n, In, Te, etc. Note that an intermediate layer made of a polymeric substance is usually provided on the surface of the substrate on the side where the recording layer is provided, in order to improve the flatness of the substrate, improve the adhesive force with the recording layer, or improve the sensitivity of the optical disc. There are many things that happen.

Further, as a disk structure for protecting the recording layer, a recording layer is provided on at least one of the two disk-shaped substrates, and these two substrates are located inside the recording layer,
An air sandwich structure has also been proposed in which a song-shaped inner spacer and a ring-shaped outer spacer are joined together to form a space. In optical discs with such an air sandwich structure, the recording layer is not in direct contact with the outside air, and information is recorded and reproduced using laser light that passes through the substrate. It has the advantage that it will not be damaged or have dust attached to its surface, which will impede the recording and reproducing of information.

Writing and reading information to and from an optical disc is usually performed by the following method.

Information is written by irradiating this optical disk with a laser beam, and the irradiated portion of the recording layer absorbs the light, causing a local temperature rise, causing physical or chemical changes (for example, bit generation). information is recorded by changing its optical properties. Information is also read by irradiating the optical disk with a laser beam, and the information is reproduced by detecting reflected or transmitted light depending on changes in the optical characteristics of the recording layer.

As described above, writing and reading information on an optical disc is usually performed by irradiating a laser beam onto a predetermined position on the disc surface.

On the other hand, since there is a strong desire to increase the amount of information recorded on optical disks, efforts are being made to increase the density of recording parts such as bits. As the density of the recording area increases, it becomes difficult to irradiate the laser beam correctly to a predetermined position, so recently, the laser beam is guided to accurately trace the planned irradiation position (generally known as tracking). Tracking guide grooves (pre-grooves) or tracking marks (servo bits) are increasingly provided on the disk surface. The former method, in which tracking guide grooves are provided in advance on the disk, is called the continuous groove method, and the latter method, in which tracking marks are placed here and there on the track, is called the sample servo method. The sample servo method is attracting attention for reasons such as whether the focus signal is influenced by the guide groove or not. In addition to the servo bits for this sample servo system, sectors, addresses, synchronization marks, clock bits, etc. are included and are called pre-pits. Information necessary for writing and reading information to and from the optical disc is recorded in advance in this pre-pit.

Conventionally, such pre-pits have been made with a bit depth of [in/4n] taking into account the wavelength of the laser used for writing or reading (where n is the refractive index of the substrate and λ is the laser wavelength used). It has been commonly used because it has the wavelength of 100°C (°C) or because it has the best modulation degree of the reproduced signal.

[Object of the Invention] The present invention is an information recording medium comprising a recording layer attached to prepits provided on the surface of a disk-shaped substrate via an intermediate layer and capable of writing and/or reading information using a laser. The main object of the present invention is to provide an information recording medium in which the contrast of pre-pit signals is particularly improved.

[Summary of the Invention] The present invention provides an information recording medium comprising a recording layer on which information can be written and/or read by a laser, which is attached via an intermediate coating layer onto prepits provided on the surface of a disc-shaped substrate. , the distance (a) between the surface of the intermediate coating layer covering the bottom of the pre-pit and the surface of the intermediate coating layer covering the top of the side wall of the pre-pit is determined by the refractive index (n) of the substrate and the distance to the recording medium. The following conditions apply to the wavelength (on) of the laser beam used when writing information or reading information from the recording medium: λ/5 n≦a≦on/
3 n .

[Effects of the Invention] The information recording medium of the present invention has significantly improved signal contrast in the prepit portions compared to conventional information recording media with prepits of the same type.

Therefore, in the information recording medium of the present invention, compared to the conventional information recording medium with pre-pits of the same type, errors in signal reading do not occur, so that necessary information can be read faster and the hat sector ratio is reduced.

[Detailed Description of the Invention] A pre-pit consists of a groove having a cross-section of a shape such as the inverted trapezoid shown in FIG. Research is progressing in relation to this, especially the depth of the pit (h)
For, h=in/4 n [where in is the wavelength of the laser beam, and n is the refractive index of the substrate. It is already known that it is desirable to satisfy the following. Optical discs having pre-pits designed in this manner are now in use.

However, according to the research of the present inventor, even if an optical disc has pre-pits with a depth that conforms to the above regulations,
It has been found that an optical disc in which a recording layer is provided on the pre-pits via an intermediate coating layer cannot provide a sufficiently satisfactory signal contrast. Further research into the reason revealed that the thickness of the intermediate layer attached to the surface of the optical disc by the coating method differs between the bottom of the pre-pit and the top of the sidewall, and as a result, the depth of the pit is lower than the predetermined depth. I found out that this is because it becomes shallow. In other words, intermediate layers to the substrate [e.g., adhesive layer, heat insulating layer, reflective layer, sensitivity enhancement layer (gas generation layer)] are usually formed using a coating method such as a spin code method; The coating layer formed by the method is thicker at the bottom of the pre-pit, while thinner at the top of the side walls. Therefore, as a result, the depth of the pit inevitably becomes shallower than the predetermined depth.

Although it may be theoretically impossible to make the thickness of the coating layer the same at the bottom of the pre-pit and the top of the side wall, it is practically impossible.

On the other hand, the present inventor believes that the difference in the coating layer between the convex and concave parts of the substrate caused by the above coating method is due to the physical properties of the coating liquid (
It has also been found that if the coating conditions (eg, coating speed, coating amount) and coating conditions (eg, coating speed, coating amount) are kept constant, high reproducibility is exhibited for a substrate consisting of convex portions and concave portions of fixed dimensions.

Based on the above knowledge, the present inventor has determined that when an intermediate layer is provided on a prepit on a substrate surface by a coating method, the depth at of the prepit (i.e., the bottom surface of the concave part and the top of the convex part constituting the prepit) Enter the distance gl) between the surfaces/4
The contrast of the signal is improved by adjusting the pit depth in advance so that the distance between the bottom surface of the four parts of the intermediate coating layer and the top surface of the convex part matches n, rather than making it match n. The present invention has been developed based on the discovery that the present invention is effective for this purpose.

Incidentally, the pre-pits referred to in the present invention include not only pre-pits provided on a plain plane of the disk, but also pre-pits provided between pre-grooves (land surface).

When adjusting the pit depth in advance to match the above input/4n, considering the reproducibility accuracy of the coating film thickness, it is inevitable that a film thickness error of about 10% will occur during normal coating operations. On the other hand, the occurrence of such an error does not substantially reduce the effects of the present invention. However, it is preferable to keep the error in film pressure within 5% by subjecting the coating to strict control.

That is, in the information recording medium of the present invention, the distance (a) between the surface of the intermediate coating layer covering the bottom of the pre-pit and the surface of the intermediate coating layer covering the top of the side wall of the pre-pit is determined by the refractive index of the substrate ( n) and the wave center (λ) of the laser beam used when writing information to or reading information from the recording medium under the following conditions:
5 n≦a≦in/3 n Preferably, 7λ/ 30 n≦a≦4λ/ 15 n is satisfied.

In order to obtain the above information recording medium, the distance (a1) between the bottom surface of the pre-pit and the top surface of the side wall of the pre-pit before coating with the intermediate coating layer or the refractive index (n) of the substrate is determined. The wavelength (input) of the laser beam used when writing information to or reading information from the recording medium satisfies the following conditions: 5λ/16n≦a, ≦7λ/16n. That's preferable.

A typical configuration example of the information recording medium of the present invention is schematically shown in FIG. 1 of the accompanying drawings. That is, the intermediate coating layer 12 is formed on the substrate 11 by a coating method, and the recording layer 1 is formed on it.
The configuration with 3 is the most common. In the relational expression defined in the present invention, [al is the surface of the intermediate coating layer covering the bottom of the pre-pit and the intermediate coating layer covering the top of the side wall of the pre-pit as shown in FIG. This is the distance from the layer surface. [a1] means the depth of the pre-pit provided on the substrate. When using the information recording medium of the present invention, information is written and read using a laser beam that passes through the substrate. That is, in the embodiment shown in FIG. 1, the laser beam is irradiated from below.

The information recording medium of the present invention is not particularly different from conventionally known information recording media with pre-pits, except that the depth of the pre-pits on the substrate is different from the conventional size.

The information recording medium of the present invention can be manufactured, for example, by the following method.

The substrate with pre-pits (which may have pre-grooves) can be manufactured by, for example, molding a plastic material such as polycarbonate resin or polyacrylic resin, or a resin having pre-pits on a flat substrate such as a plastic plate or a glass plate. It can be manufactured by a method of laminating layers, etc., and these methods are already generally known.

In the information recording medium of the present invention, the depth of the pre-pits differs from conventional information recording media of the same type in relation to the refractive index of the substrate and the wavelength of the laser beam used. The pre-pits of the information recording medium of the present invention are as shown in (a1)' above.
The pre-pits are formed deeper within the range than the pre-pits of conventional information recording media of the same type.

The range of the depth (al) of such prepits was determined as follows.

The variation in the thickness of the coating layer between the bottom of the pre-pit and the top of the side wall that occurs during the formation of the intermediate coating layer varies depending on the predetermined average thickness of the coating layer, but is usually in the range of 200 to 400 angstroms. Therefore, in determining the depth of the pre-pit, reference can be made to known data on coating layer thickness variations in similar systems. However, for the target system, substrates with various bit depths are prepared in advance, a predetermined intermediate coating layer is formed on each, and the dimensions between predetermined portions of the coating layer are measured. a
It is preferable to determine the most suitable pre-pit depth while looking at the correspondence with the relational expression in the range of ). By this method, the pre-pit depth a1) on the substrate can be determined with high accuracy.

The formation of an intermediate coating layer on the substrate surface having pre-pits is
This can be done by a known coating method. An example of a known application method is the spin code method.

Examples include a dip coating method.

Note that examples of the intermediate layer formed by the coating method include an adhesive layer, a heat insulating layer 1 reflective layer, a sensitivity enhancement layer (gas generation layer), and the like.

When the intermediate coating layer is a heat insulating layer, for example, polymethyl methacrylate, acrylic acid/methacrylic acid copolymer,
Styrene/maleic anhydride copolymer, polyvinyl alcohol, N-methylol/acrylamide copolymer, styrene/sulfonic acid copolymer, styrene/vinyltoluene copolymer, chlorinated polyethylene, chlorosulfonated polyethylene, nitrocellulose, poly It can be formed using a coating solution in which polymeric substances such as vinyl chloride, polyester, polyimide, vinyl acetate/vinyl chloride copolymer, ethylene/vinyl acetate copolymer, polyethylene, polypropylene, polycarbonate, etc. are dissolved in a solvent. .

A coating solution using chlorinated polyethylene or nitrocellulose is preferred, and chlorinated polyethylene is particularly preferred.

With the chlorinated polyethylene layer formed as above,
It is possible to reduce the loss of thermal energy due to laser beam irradiation due to thermal conduction from the recording layer to the substrate.
In addition, since gas is generated from the irradiated portion of the chlorinated polyethylene layer, bits can be easily formed and recording sensitivity can be increased.

When forming the chlorinated polyethylene layer, it is preferable that the concentration of the coating liquid in which chlorinated polyethylene is dissolved in a solvent is within the range of 0.1 to 0.4%.
If it is less than 1%, the role of the chlorinated polyethylene layer as a sensitivity enhancing layer is reduced, which is not preferable. Also, 0.4%
If it exceeds this value, it is undesirable because uneven coating tends to occur when applying the chlorinated polyethylene coating solution, resulting in variations in sensitivity on the same disk, and as a result, jetter increases.

The layer thickness (average layer thickness) of the intermediate coating layer is determined in consideration of the characteristics required of the intermediate layer. The layer thickness of the intermediate coating layer is usually in the range 100 to 1000 angstroms.

A recording layer is provided on the intermediate coating layer.

Examples of materials used for the QR include Te, Zn, I
Metals such as n, Sn, Zr, AJI, Cu, Ge; Bi,
Examples include semimetals such as As and Sb; semiconductors such as Ge and Si; and alloys thereof or combinations thereof. Compounds such as sulfides, oxides, borides, silicon compounds, carbides, and nitrides of these metals or semimetals; and mixtures of these compounds and metals can also be used in the recording layer.

The recording layer can be formed on the intermediate coating layer using the above recording material by a method such as vapor deposition, sputtering, or ion blasting. The recording layer may be a single layer or a multilayer, but its layer thickness is generally in the range of 100 to 5500 angstroms in view of the reflectance required for optical information recording.

In addition, the back side of the substrate (the side opposite to the side where the recording layer is provided)
A thin film made of an inorganic substance such as silicon dioxide, tin oxide, or magnesium fluoride may be provided on the surface of the substrate by vacuum deposition, sputtering, etc. in order to improve scratch resistance, moisture resistance, etc.

Although the production of the information recording medium according to the present invention has been mainly explained using an example of a type consisting of a single substrate, the information recording medium of the present invention can have any configuration according to known techniques. In other words, a type of information recording medium manufactured by laminating two information recording media each made of a single substrate as described above, and a protective layer (resin layer, protective It is possible to take various configurations, such as a type of information recording medium in which a plate (such as a plate) is formed, and an air sandwich type information recording medium.

Next, Examples and Comparative Examples of the present invention will be described.

However, each of these does not limit the present invention.

[Example 1] Disc-shaped polycarbonate substrate provided with pre-pits and pre-grooves by injection molding [outer diameter = 200 mm, inner diameter: 35 mm, thickness: 1.2 mm, pre-pit depth a1 in Figure 1): 1900 angstroms, track A coating solution containing chlorinated polyethylene [methyl cellosolve/butanol/isopropanol mixed solvent (12:8:
80, volume ratio)] was coated using a spin coater, and then dried to form an intermediate coating layer.

The distance (a r in Fig. 1) between the bottom of the concave portion (corresponding to the bottom of the pre-pit) and the top surface of the convex portion (corresponding to the top of the pre-pit side wall) of the obtained intermediate coating layer was 1300 angstroms (
130nm).

Next, on the intermediate coating layer, In:GeS:Au=66
:22:12 (weight ratio) was co-deposited to form a recording layer with a thickness of 300 angstroms.

By the method described above, an optical disk having the cross-sectional configuration shown in FIG. 1 was obtained.

[Comparative Example 1] The depth of the pre-pit on the surface of the disc-shaped polycarbonate substrate was set to 1, which approximately corresponds to the optimum implantation depth of the pre-pit/4n.
An optical disc was obtained in the same manner as in Example 1 except that the thickness was 300 angstroms.

The distance between the bottom of the concave portion and the top surface of the convex portion (al in FIG. 1) of the obtained optical disk intermediate coating layer was 6010 angstroms (601 nm).

[Evaluation of Optical Disc] The signal contrast of the prepit portion of the obtained optical disc was evaluated.

The optical discs obtained in Example 1 and Comparative Example 1 were played back using a disc player (Nakamichi 0MS-1000). The reproduction conditions were as follows: rotational speed was 1800 r, pm, laser reproduction power was 0.8 mW, wavelength was 830 nm, and NA of the lens used was 0.5.

The signal strength (mV) of the signal of the pre-pit portion obtained here was measured using an oscilloscope (Tektronix Oscilloscope 2430).

Then, the signal contrast 20 (%) was determined from the following formula.

SH-5L c = x to.

SH+SL (SH: Maximum signal strength SL: Minimum signal strength) L
ll (signal contrast 20 (%)) Example 1: 33
(%) Comparative Example 1: 18 (%) As described above, it can be seen that the signal contrast of Example 1 is much better than that of Comparative Example 1, and the signal quality is improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of a prepit type information recording medium having an intermediate coating layer. 11: Substrate, 12: Intermediate coating layer, 13: Recording layer a: Distance between the surface of the intermediate coating layer covering the bottom of the pre-pit and the surface of the intermediate coating layer covering the top of the side wall of the pre-pit: al: Pre-pit depth

Claims (1)

[Claims] 1. An information recording medium comprising a recording layer on which information can be written and/or read by a laser, which is attached via an intermediate coating layer onto prepits provided on the surface of a disc-shaped substrate, The distance (a) between the surface of the intermediate coating layer covering the bottom of the pre-pit and the surface of the intermediate coating layer covering the top of the side wall of the pre-pit is the refractive index (n) of the substrate and the information on the recording medium. An information record characterized by satisfying the following condition: λ/5n≦a≦λ/3n with respect to the wavelength (λ) of a laser beam used when writing or reading information from the recording medium. Medium. 2. The distance (a) between the surface of the intermediate coating layer covering the bottom of the pre-pit and the surface of the intermediate coating layer covering the top of the side wall of the pre-pit is determined by the refractive index (n) of the substrate and the laser beam. The information recording medium according to claim 1, characterized in that the following condition for wavelength (λ) is satisfied: 7λ/30n≦a≦4λ/15n. 3. Distance (a) between the bottom surface of the pre-pit and the top surface of the side wall of the pre-pit before coating with the intermediate coating layer
_1) is based on the following conditions for the refractive index (n) of the substrate and the wavelength (λ) of the laser beam used to write information to or read information from the recording medium: The information recording medium according to claim 1, wherein the information recording medium satisfies 5λ/16n≦a_1≦7λ/16n. 4. The information recording medium according to claim 1, wherein the intermediate layer is a layer of chlorinated polyethylene resin or nitrocellulose resin. 5. The information recording medium according to claim 1, wherein the disc-shaped substrate is made of polymethacrylic acid resin or polycarbonate resin.