JPH0443330B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording medium that can record and reproduce information using laser light, and more specifically, the present invention relates to an optical recording medium that can record and reproduce information using laser light. ,
This invention relates to an optical recording medium that records by forming pits in a thin film using the heat generated therein.

(Prior Art) A write-once optical disk memory that records and reproduces information on a medium using a laser beam has an excellent feature as a large-capacity recording device because of its high recording density. Recording materials for such write-once optical disk memories include bismuth, which is a low melting point metal;
Thin films of tellurium are used for their high sensitivity (Special Publications No. 46-40479, No. 45676 No. 57, No. 41875 No. 1983, No. 15483 No. 54, No. 15483)
35356).

(Problems to be Solved by the Invention) However, these optical recording media have a problem in that the servo tends to become disconnected immediately after recording.

An object of the present invention is to provide an optical recording medium with stable servo even immediately after recording.

(Means for solving the problem) The optical recording medium of the present invention has a recording layer on one side of a substrate, removes the recording layer by irradiating a laser beam through the substrate, and records information. An optical recording medium in which a decrease in the amount of reflected light due to irradiation with a laser beam is read as information, wherein a reflective layer that is substantially transparent to the reading light is provided between the substrate and the recording layer, and the recording film The thickness of the reflective film is set so that the substrate incident reflectance when the recording layer is removed is 15% or more and less than the incident reflectance when the recording layer is present.

(Function) Optical recording media have conventionally had a configuration as shown in FIG. That is, a recording layer 2 is provided on a substrate 1. The recording laser beam 3 passes through the substrate 1 to the recording layer 2.
A pit 4 is formed by condensed light irradiation. The recording is read by scanning the pits 4 with a laser beam and detecting changes in the amount of reflected light. Therefore, in areas where there are no pits, the amount of reflected light is proportional to the reflectance when the recording layer 2 is present, and in pit areas, the amount of reflected light is proportional to the reflectance when the recording layer 2 is not present. As the transparent substrate 1, synthetic resin such as polycarbonate or acrylic resin, or glass is used. The refractive index of these materials is around 1.5 in the visible light to near-infrared light range. Therefore, the reflectance without the recording layer is 3 to 5%. On the other hand, when a recording material containing bismuth or tellurium as a main component is used as a recording layer, the reflectance (unrecorded reflectance) is as large as 25% or more.

The pits are recorded in a number of concentric or spiral tracks. In order to accurately record a large number of tracks at regular intervals, guide grooves are usually provided on the substrate. When light enters a groove approximately the diameter of the beam, the light is diffracted. Since the spatial distribution of the diffracted light intensity changes as the beam center shifts from the groove, a servo system can be configured to detect this and direct the beam to the center of the groove. Usually, the width of the groove is set to 0.3 to 1.2 μm, and the depth is set to a range of 1/12 to 1/4 of the wavelength of the recording/reproducing laser used. In addition to such tracking servo, focus servo is also performed so that the laser beam is focused on the recording layer. Further, in order to quickly identify a large number of tracks, the guide grooves may be made discontinuous or recessed portions may be formed in the guide grooves, and track addresses may be recorded on the board in advance. As described above, it is necessary to have a large unrecorded reflectance in order to improve the accuracy of reading track addresses and to operate tracking and focus servo stably. However, these optical recording media have a problem in that the servo tends to become disconnected immediately after recording. The inventors of the present invention investigated the cause of this problem in detail and found that the servo becomes unstable because the pit formation lowers the servo error sensitivity. In other words, the main reason for the decrease in servo error sensitivity is that, in addition to the large drop in reflectance after pit formation, the phase of reflected light changes by nearly 180 degrees when pits are formed due to recording by entering the substrate. We have discovered that this is the cause, and have arrived at the present invention. The present invention provides an unstable servo even after recording by providing a transparent reflective film 5 between the substrate 1 and the recording layer 2 as shown in Figure 1, and increasing the reflectance when there is no recording layer to 15% or more. It will never become. This is due to the insertion of the transparent reflective film 5, which increases the reflectance after pit formation and increases the amount of servo signal, and also because the reflection boundary surface is not a completely free end. By making the reflective film 5 transparent, this film eliminates light absorption and prevents a decrease in recording sensitivity. On the contrary, light absorption in the recording layer is increased by inserting the transparent reflective film 5.

Any material for the transparent reflective film may be used as long as it has a refractive index greater than the refractive index of the substrate. for example
_{Co3O4 , Cr2O3} , _GeO2 , _{H5O2 , MoO3 ,} NiO,
Various oxides such as SiO, SnO ₂ , Ta ₂ O ₅ , WO ₃ , ZnO, ZrO ₂ , various nitrides such as Si ₃ N ₄ , ZrN, GeS,
Various sulfides such as ZnS, cobalt phthalocyanine,
Various organic dyes such as copper phthalocyanine, magnesium phthalocyanine, nickel phthalocyanine, zinc phthalocyanine, t-butyl-substituted vanadyl phthalocyanine, and various organic substances such as dianhydride 3,4,9,10-perylenetetracarboxylic acid can be used. By depositing these materials on the substrate, the substrate incident reflectance without the recording layer can be increased to 15
% or more. Next, a recording layer is formed thereon. The reflectance at this time is desirably set to 25% or more (that is, the difference from the substrate incident reflectance is 10% or more) in order to improve the quality of the reproduced signal. Bi or Te is used as the recording layer.
Alternatively, a material containing Sn as a main component is desirable. Among them, mixtures _of Sn and _Co3O4 , Sn and NiO
mixture with Te and _Co3O4 , Te and _NiO
mixtures with Te and Se, alloys of Te and Se, plasma-polymerized organic films containing Te, Bi, In, etc., organic films in which Te, Bi, In, etc. are surrounded by alkyl groups, Te, Bi, In
Particularly desirable are organic films in which the fluorocarbons are surrounded by fluorocarbons.

Example 1 Examples of the present invention will be described below. Inner diameter
A polycarbonate resin disk substrate with a guide groove of 15 mm, outer diameter of 130 mm, and thickness of 1.2 mm was placed in a vacuum evaporation apparatus, and the atmosphere was evacuated to 2×10 ^-5 Torr or less. As an evaporation source, Sn was placed on a resistance heating boat (made of molybdenum).
3,4,9,10-perylenetetracarboxylic acid dianhydride (hereinafter abbreviated as PTCDA) was placed in another resistance heating boat, and Co ₃ O ₄ was placed in an electric beam heating crucible. First, PTCDA was deposited at 550 Å as a transparent reflective film, and then codeposited at a Sn deposition rate of 45 Å per minute and a Co ₃ O ₄ deposition rate of 17 Å per minute, resulting in a Co ₃ O ₄ volume fraction of 27%. composition of
A recording layer with a thickness of 350 Å was formed. The substrate incidence reflectance of this optical recording medium at a wavelength of 8300 Å was 28%, and the reflectance without the recording layer was 16%.
When recording at 8 mW using an AlGaAs semiconductor laser with a wavelength of 8300 Å and a medium linear velocity of 5.65 m/sec and a recording frequency of 1.25 MHz (duty 50%),
The servo did not come off, and when I played with a laser power of 0.7 mW, the servo did not come off, and when I played with a laser power of 0.7 mW, the signal-to-noise ratio (C/N) with a bandwidth of 30 kHz was 48 dB. As described above, a good quality signal with a second harmonic to signal ratio (2ndH/C) of -26 dB or less was obtained. For comparison, a disc without a PTCDA layer lost servo when recorded under the above conditions.

Example 2 650Å instead of PTCDA as transparent reflective film
An experiment similar to Example 1 was conducted using thick copper phthalocyanine. The medium reflectance was 28%, and the reflectance without the recording layer was 15%. When recording on this disk at 8mW, the servo will not come off,
Good quality signals were obtained.

Example 3 A polycarbonate resin disk substrate with a guide groove having an inner diameter of 15 mm, an outer diameter of 130 mm, and a thickness of 1.2 mm was placed in a vacuum evaporation apparatus and evacuated to 2×10 ^-5 Torr or less.
As evaporation sources, PTCDA was placed in a resistance heating boat, Te was placed in another resistance heating boat, and Se was placed in another resistance heating boat. First, PTCDA was evaporated to a thickness of 550 Å as a transparent reflective film, and then a 350 Å thick alloy film of Te and Se with a ratio of 80:20 at % was formed by controlling the deposition rate. The substrate incidence rate of this optical recording medium at a wavelength of 8300 Å was 30%, and the reflectance without the recording layer was 16%. As a result of recording and reproducing in the same manner as in Example 1, there was no servo failure and a signal of good quality was obtained. For comparison, a disk without a PTCDA layer had the problem of servo failure when recording under the above conditions.

(Effects of the Invention) As is clear from the above embodiments, the present invention provides an optical recording medium with good servo stability and good signal quality.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of the optical recording medium of the present invention, and FIG. 2 is a schematic cross-sectional view of a conventional optical recording medium. In the figure, 1 is a substrate, 2 is a recording layer, and 3 is a substrate.
4 indicates a laser beam, 4 indicates a pit, and 5 indicates a transparent reflective film.

Claims (1)

[Claims] 1 A light for recording information by providing a recording layer on one side of a substrate and removing the recording layer by irradiating a laser beam through the substrate, and reading a decrease in the amount of reflected light due to irradiation of a laser beam through the substrate as information. In the recording medium, a reflective film that is substantially transparent to the reading light is provided between the substrate and the recording layer, and the recording layer has an incident reflectance of 15% or more when the recording layer is removed. An optical recording medium characterized in that the thickness of the reflective film is set so that the incident reflectance is less than a certain value.