JPS60219647A - Multi-layer recording medium - Google Patents

Abstract

PURPOSE:To attain multiple recording with high density by forming an optical guide track on each recording layer in a multi-layer optical recording medium where plural recording layers are overlapped via a transparent medium separating layer. CONSTITUTION:A recording layer 16a comprising a guide track forming thin film 12a and an optical recording material thin film 13a is formed on a substrate 11 on which a recording medium is formed and a medium separating layer 14 is formed on the layer 16a. Moreover, a recording layer 16b comprising a guide track forming thin film 12a and an optical recording material thin film 13b is formed on the medium separating layer 14, and a protection layer 15 is formed on the layer 16b. A recessed groove 17 as an optical guide track is formed respectively to the guide track forming thin films 12a, 12b respectively and the recessed groove is formed also on the optical recording medium thin films 13a, 13b. Since the optical guide track is formed on each recording layer, the limit of the recording density of a conventional optical recording medium is improved remarkably and a specific position of the desired recording layer is accessed easily.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multilayer optical recording medium in which a plurality of recording layers are stacked with a transparent medium separation layer interposed therebetween, and optical recording and reproduction are performed.

"Prior Art" Optical recording systems using laser beams have the advantage of being able to perform high-density real-time recording and reproduction, so optical recording media using various materials and substances have been researched or put into practical use. In such optical recording media, methods to further improve the recording density include (1) miniaturization of recording pits and (2) multiplexing of recording. Regarding (1), the diameter of the recording pits currently reaches 1 μm, which is on the wavelength order, and it is difficult to miniaturize the recording pits further. Therefore, (2) multiplexing of recording is the only method for increasing the density of optical recording media, and several types of multilayer optical recording media have recently been proposed as one of these multiplexing methods. Problems with these multilayer optical recording media are the determination of the layer in which pits are recorded and reproduced and the method of determining the recording position.

In a normal single-layer optical recording medium, in order to determine the recording position, a light guide groove called an optical guide track is provided on the substrate on which the medium is made, and the recording/reproducing optical head is detected to detect any deviation from this optical guide track. The optical head is driven to perform recording and reproduction along the optical guide track, and by increasing the density of the optical guide track, υ high-density recording and reproduction is performed.

Such an optical guide trunk is usually manufactured through the following steps.

(1) Coat a photoresist on a glass substrate and draw an optical diagonal track using a laser beam.

(2) Dry the first resist drawn in (1),
It is developed using an appropriate method such as wet development to create irregularities.

(3) Is there Cr, Ni, etc. in the uneven pattern? : Thinly sputtered or vapor deposited to provide conductivity.

(4) The master disc obtained in (3) is electrolytically plated to produce a stand back with the pattern of the optical guide track reversed.

(5) Using this stamper as a mold, injection molding is performed using acrylic resin or polycarbonate resin as a material to produce a resin substrate having optical guide tracks.

Although the above method allows mass production of the same type of substrate by injection molding, it cannot be applied to multilayer optical recording media. The reason for this is that since the resin material is press-fitted into the mold, the recording layer that has already been formed is adversely affected by pressure and heat.

In the above item (5), injection molding may be replaced by a 2P method (photopolymer) in which a stamper is transferred using a photopolymerizable resin. Since this method is performed one by one, the productivity is lower than that of the injection molding method, but high quality optical guide tracks can be produced. However, the solvent used in the photopolymer coating process has an adverse effect on the recording layer that has already been formed, and baking before exposure (pre-bake) and baking after development (post-bake)
Since the heat treatment would adversely affect the already formed recording layer, it could not be applied to the optical guide track of a multilayer optical recording medium.

``Object of the Invention'' An object of the present invention is to provide a multilayer optical recording medium that allows higher density multiple recording than conventional optical recording media.

"Structure of the invention" FIG. 1 shows an example of a multilayer optical recording medium according to the present invention.

A substrate 11, which is a glass plate or a plastic plate made of acrylic resin, polycarbonate resin, etc., and supports a recording medium.
A guide track forming thin film 12a is formed thereon, an optical recording material thin film 13a is formed on the guiding track forming thin film 12a, and a medium separation layer 14 is formed thereon. Furthermore, a thin layer of 8'J t 2 for forming a guide track is formed on the medium separation layer 14.
A b% optical recording material thin film 13b' is sequentially formed, and a protective layer 15 is formed thereon. The guide track forming thin film 12a and the optical recording material thin film 13a1 The guide track forming thin film 12b and the optical recording material thin film 13b constitute recording layers 16a and 16b, respectively. Such a recording layer may be further configured into multiple layers with the medium separation layer 14 interposed therebetween. In this example, grooves 17 are formed as optical guide tracks in each of the guide track forming thin films 12a and 12b, and within the grooves 17 there are also ≠band guide track forming thin films 12a,
12b is transparent to the light of the pit recording light source and the optical recording material thin films 13a and 13b, respectively, and optical recording material thin films 13a and 13b are formed thereon, and these optical recording material thin films 13a and 13b also have concave grooves. It is formed.

and! This material has a large absorption coefficient for the light from the recording light source for forming guide tracks. Specifically, when a semiconductor laser that is easy to electrically modulate is used as a light source for pit recording, its wavelength is above 7800 m12, so steel phthalocyanine, fluorescein, acrylic, tisperse, etc., which are transparent to these wavelengths, are used. An organic dye thin film such as Yellow 51 can be used as the guide track forming thin films 12a and 12b.

Te is used as the optical recording material thin films 13a and 13b.

Bi l A5 Te + As Se S * Te
Dispersed C82 plasma polymerized films, metals such as Pb, Sλ, semimetals, or kavacogenite thin films are used. When using organic materials, use Squaric dyes N1 and HyP such as vanadyl phthalocyanine and dimethylaminophenol squarylium.
The t-dithiolate complex, titanyl phthalocyanine, can be used as the perforated recording material thin film. Also T
When materials such as e-lower oxides are used in thin films, they can be used as rewritable optical recording material thin films 13a and 13b that utilize reversible changes due to phase transformation of substances.

The medium separation layer 14 is made of phenolphthalein, crystal violet lactone, malachite leucogreen, thymol phthalein, 36 dibenzylamino-7-diethylaminofluoran, RED-DCKIi (trade name of Tsuchiya Chemical), Paris "Kanken Polymer Film CVCC Co., Ltd." A glassy inorganic thin film such as 5i02* WOs 1 'rio2 can be used. Optical recording material thin film 13a
, 13b is changed, D RA W (direct
Since deformation of the optical recording medium occurs when a read-after-write type material is used, the medium separation layer 14 sandwiching the medium is preferably made of an organic material having a relatively low melting point. The optical recording material thin film 13a is a rewritable material that utilizes phase changes such as amorphous and crystallization.

When used as the medium separation layer 13b, it is preferable to use a material that is not easily deformed by heat, that is, an inorganic material, a polymer film such as Paris, etc. As the protective layer 15, the same layer as the medium separation layer 14 is used.

The groove 17, which is an optical guide track, is constructed by the following method.

The above-mentioned guide track forming thin films 12a and 12b are made of fluorescein or the like and have a strong resistance to the oscillation wavelengths of argon lasers and HeNe lasers. For example, fluorescein is vapor-deposited before forming the optical recording material thin films 13°a and 13b'l, and the shape of the desired optical guide track is drawn on the guide track forming thin film using an Ar laser to form the thin film 12a.

12b absorbs the Ar laser, and that part becomes the jump groove 17.
is formed. The depth of the groove 17 is determined by the thickness of the thin films 12a, 12b and the intensity of the Ar laser, and may be a cut groove. Next is the optical recording material thin film 13a.

13b to 11. The above operations are repeated depending on the number of layers. As a result, it is possible to form optical guide tracks that can be used in each recording layer of a multilayer optical recording medium, which was not possible using conventional optical guide track forming methods such as the stamper method. Although the optical guide tracks in this method are individually produced by direct writing, the number of steps required to obtain the optical guide tracks is significantly reduced compared to the number of steps in the conventional standby method. Therefore, the optical guide track has the advantage of having fewer defects. In terms of productivity, high-output Ar laser equipment currently exists, and the recording sensitivity of fluorescein to Ar laser is sufficiently high. Can be formed at the same time. For example, 50,000 optical guide tracks (track part width 1°C111 track pitch 2 /
''' ) k 1000 rpm.

When formed in a rotating state, it takes approximately 50 minutes/surface to form grooves with a single beam, but by simultaneously scanning with 10 beams, it is possible to fabricate grooves in 5 minutes/surface.

When copper phthalocyanine or the like is used as the guide track forming thin films 12a and 12b, it is better to use a (.-Ne laser) rather than an Ar laser to form the grooves 17 as optical guide tracks.

When it is determined that the optical guide track of the straight groove 17 shown in FIG. 1 is not suitable when producing the optical recording material thin films 13a and 13b, the optical recording medium shown in FIG. 2 is used. Second
In the figure, parts corresponding to those in FIG. 1 are given the same numbers. The guide track forming thin films 12a and 12b cause a change in refractive index or photochromism (change in absorption rate) when exposed to specific transparent light to the optical recording material thin films 13a and 13b, and when recording and reproduction light is applied to the optical recording material thin films 13a and 13b. has no change in refractive index.

For example, AS405e25 Ge1OS25' is subjected to high frequency sputtering to form the guide trunk forming thin films 12a and 12b.

Co+lD wails 12a and 12b are A with a wavelength of 455 nm
Irradiation with the r laser causes a change in refractive index or photochromism for light in the wavelength region of 830 nm.

However, the volume of this thin film does not change when irradiated with the Ar laser. Therefore, during this Ar laser irradiation, a refractive index changing portion (absorption rate changing portion) 8 is formed as an optical guide track. This method of forming the optical guide trough also has the advantage of not changing the local thickness of the medium.

The present invention will be explained in more detail with reference to examples below.
The invention is not limited to these examples.

"Example 1" Fluorescein f 700 A 71 on acrylic substrate
This was applied to form a thin film for forming a guide track, and the portion where an optical guide track was to be formed was irradiated with an Ar laser.

As a result, the fluorescein in the irradiated area was removed and the depth was 7
A concave optical guide track of 00'A was formed. Next, Te was evaporated at 100X to form an optical recording material thin film. Crystal violet lactone (
CVL) was deposited to a thickness of 10 μm, and fluorescein e 700X was further deposited thereon. The second laser beam was focused by focusing the Ar laser only on the top fluorescein film.
A concave groove was formed as an optical guide track. Next, Te1
After a second optical recording material thin film was formed by t5oX vapor deposition, a protective layer of 2 μm thick was formed using Varile/ to produce a multilayer optical recording medium.

When this multilayer optical recording medium is scanned from the acrylic substrate side with a semiconductor laser (LD) focused on the first optical recording material thin film, a tracking signal is generated by the reflected light of the semiconductor laser from the groove of the first optical guide track. appears, and by guiding it to the tracking servo of the recording head, the first
Tracking of the optical guide track of the recording layer became possible.

If pit recording is performed using a semiconductor laser in this state, the first
A pit row could be recorded along the concave groove of the optical guide track.

Next, the focus of the semiconductor laser was moved by the thickness of the medium separation layer to align it with the second recording layer. Similarly to the above, a tracking signal of the concave groove of the second optical guide track appeared, and it became possible to track the optical guide track of the second recording layer. Here, we were able to draw recording pits using a semiconductor laser. It was possible to independently reproduce the pits in the recording layer in each layer.

"Example 2" AS40 se2. on a glass substrate. Ge10825 7
A thin film for forming a guide track was prepared by sputtering on 00', then a thin film of vanadyl phthalocyanine of 50 OA as an optical recording material thin film, 5 μm of leucomalachite green lactone as a medium separation layer, and AS40 as a medium separation layer.
5e25'Gel. 8.25 was prepared by 7000X sequential sputtering and 1 vanadyl phthalocyanine'e 10
00A thickness, and finally a 2μm C layer as a protective layer.
VL was deposited. Tsume 9 Glass // AS40
5ez5Ge1o S2'5/VI'C/MG
L/ AS40 Se2+, Ge, o S25/V-
A multilayer optical recording medium having Po//CVL layers was produced.

The A3-8e7Ge-3 thin film for forming the first guide track was irradiated with an Ar laser from the glass substrate side to cause a change in refractive index, thereby producing a refractive index changing portion as a first optical guide track. Next, an Ar laser was irradiated from the protective layer side to cause a refractive index change in the second As-8e-Ge-8 layer, thereby providing a refractive index changing portion as a second optical guide track. Since the vanadyl phthalocyanine, leucomalachite green layer is transparent to the Ar laser, writing of the optical guide track by the Ar laser was not disturbed. Recording and reproducing experiments were conducted on the thus obtained optical recording medium in the same manner as in Example 1, and it was found that tracking along the first and second optical guide tracks was possible, and recording and reproducing of independent pits in each layer using a semiconductor laser was possible. It was possible.

"Example 3" Alarin i800 A was vapor-deposited on an acrylic substrate to form a first guide track forming thin film, and concave grooves were formed thereon as optical guide tracks using an Ar laser. next'
reot, t Ge0.1 was laminated at 500A, and Parylene was further coated to a thickness of 5 μm. On top of that, Aralin 1sooX
After forming a concave groove as an optical guide track using an Ar laser on this second guide track forming thin film, 're01. PMMA//A(1/
TB O+ , lG(, d, x/P A L /
A multilayer optical recording medium of Au/TeOGe//PAL was obtained.

When recording and reproducing experiments were conducted on the thus obtained multilayer optical recording medium in the same manner as in Example (1), it was possible to track the recording head along the concave grooves serving as the first and second optical guide tracks, and it was found that the recording head had a high energy density. Pit writing due to crystal-amorphous transition in a thin film of optical recording material by a laser pulse of It was possible to perform and reproduce each layer independently without any difference.

"Effects" As explained above, since the multilayer optical recording medium according to the present invention has optical guide tracks formed in each recording layer, it is possible to significantly improve the recording density limit of conventional optical recording media. Moreover, it has the advantage that a desired specific position of the recording layer can be easily accessed. Moreover, the optical guide tracks of each layer can easily be used without major changes to the optical tracking technology that is being established for ordinary optical recording disks.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a multilayer optical recording medium according to the present invention, and the second factor is a sectional view showing an example of a multilayer optical recording medium according to the invention. 1: substrate; 12a, 12b: thin film for forming guide track;
13a, 13b: optical recording material thin film, 14: medium separation layer,
15: protective layer, 17: concave groove as optical guide track,
18: Refractive index changing part as an optical guide track. Patent applicant Taku Kusano, representative of Nippon Telegraph and Telephone Public Corporation

Claims (3)

[Claims] (1) In a multilayer optical recording medium in which a plurality of recording layers are stacked with a transparent medium separation layer interposed therebetween, each of the recording layers includes an optical recording material thin film made of a substance that optically changes when irradiated with light; A multilayer optical recording medium comprising a guide track forming thin film on which optical guide tracks are formed. (2) The thin film for forming a guide track is not made of an organic dye and is transparent to the recording and reproducing light on the thin film of optical recording material, and the thin film of optical recording material absorbs specific transparent light, and the optical guide track has a concave groove. The multilayer optical recording medium according to claim 1, characterized in that: (3) The thin film for forming a guide track is transparent to the recording and reproducing light for the thin film of optical recording material, and is not made of a substance that causes photochromism or a change in refractive index due to specific light that is transparent to the thin film of optical recording material, and the optical guide 2. The multilayer optical recording medium according to claim 1, wherein the track is made up of regions having different refractive indexes.