JPH04113529A - Optical recording medium - Google Patents

Abstract

PURPOSE:To enable rewriting by about one million times without causing deterioration of the substrate on rewriting of record by forming a heat-resistant protective film between the substrate and a dielectric protective film of the optical recording medium. CONSTITUTION:On the substrate 1, a dielectric protective film 2, phase transition-type recording film 3, second dielectric protective film 4, reflecting and cooling film 6, and surface protective film 5 are successively formed in the order listed. Information is recorded, reproduced or erased by irradiating the medium with laser light entering from the substrate side to cause reversible phase transition in the phase transition type recording film 3. A heat-resistant protective film 8 is provided between the substrate 1 and the first dielectric protective film 2 of the medium. By providing the heat-resistant protective film 8 between the substrate 1 and the first dielectric protective film 2 to constitute the medium, transfer of heat of laser light to the tracking grooves in the substrate 1 is suppressed. This heat is required for the phase transition-type recording film 3 and is given by the laser light entering from the substrate side. Thus, the defectless state of the medium is maintained for about one million times of rewriting of record.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overwritable rewritable optical storage medium (original disk).

[Conventional technology]

In recent years, there has been an increasing demand for higher density and larger capacity information recording, and research and development has been actively conducted both domestically and internationally, but optical recording media that use lasers as a light source have fallen short of conventional magnetic recording media. It has a recording density that is approximately 10 to 100 times higher than that of the previous one, and information is recorded in a non-contact state between the recording/reproducing head and the recording medium.

Because it can be played back, there is little damage to the recording medium and it has a long lifespan, so it can record a huge amount of information.
It is promising as a means of regeneration.

These recordable media can be roughly divided into three types depending on the purpose: reproduction-only, write-once, and rewritable. The read-only type is a read-only recording medium that can only read information, and the write-once type is a must! Although it is possible to record and reproduce information according to the information, it is impossible to erase the recorded information.

On the other hand, the rewritable type allows information to be recorded, raised, and even recorded information to be erased and rewritten.
It is desired to be used as a data file for computers and has the highest expectations.

Two recording methods are being developed for rewritable optical recording media: an optical lull method and a phase change method. Of these two recording methods, the phase change method will be described here.

The phase change method generally focuses a laser beam on the recording surface of an optical recording medium and heats it, and then controls the pulse output and pulse width of the laser beam to change the phase of the recording material, that is, from a crystalline state to an amorphous state. It causes a state transition or phase transition, and records and erases information based on the difference in reflectance in each state.

An example of the structure of an optical recording medium using this phase change method is shown in the second section.
This is shown in the schematic cross-sectional view of the figure. In fig.

This optical recording medium has many tracking grooves on a transparent substrate such as polycarbonate.

First dielectric protective film made of ceramic lx such as ZnS2. This first dielectric protective film 2 is coated with a recording material, ie, a phase change recording film 3 such as Ge5bTe. Furthermore, a second dielectric protective film 4 made of the same ceramic material as the first dielectric protective film 2 and a surface protection @5 of an organic material are applied on top of the first dielectric protective film 2.
It has a structure in which nine layers are stacked.

In addition, FIG. 3 (FIG. 3) shows a schematic cross-sectional view of an example in which cooling @ 6 such as h13 is also provided between the second g-heavy protection film 4 and the interface protection film 5. The cooling film 6 is for increasing the cooling rate from a molten state when the phase change recording film 3 changes from a crystalline state to an amorphous state.
At this time, the two dielectric protective films 2.4 also serve as a heat insulating layer. Even more cooling! [6] In addition to having a cooling effect, it also functions as a reflective film for incident light;
Regarding its effect, see Alan, E. Beil et al.
e8 for 0ptlcal recording''
by IEEE, J., Quant, Ele.
ct, , QE-14, No. 7, 487Jj (19
78). The laser beam is normally incident on the side of the substrate opposite to the side with the laminated layer, and the laser beam is applied to the transparent substrate in the form of a spot of about 1 pfrL.
The light comes into the tracking groove.

In a normal phase-change optical recording medium, the phase-change recording film 3 is initially in a crystalline state, and when recording information, it is irradiated with laser light to melt the film and then rapidly cooled to form an amorphous state. Form a spot. During erasing, the amorphous C spot is annealed with a laser beam to return it to a crystalline state.

In porous mft recording media, overriding can be performed using a single laser light source. In other words, by modulating the power of the light source over time, the data is erased rather than being rewritten with new data through a two-step process of erasing and rewriting over previously written data. You can rewrite the data with new data in one go without having to worry about it. Figure 3 shows how the power of a light source is modulated over time and is recorded.
It is a relationship diagram showing a pair with slight reduction data. In FIG. 3, data 1 is the recording power, data 0 is the erasing power, and the source adjusted to f is irradiated onto the rotating optical recording medium in the form of a spot for a time series and overriding is performed. 7 represents the window width.

[Problem to be solved by the invention]

In a device using an optical recording medium, rewriting of the digital recording for recording code data takes only one time.
Approximately 1,000,000 times are required. However, at present, data on a phase change optical recording medium can only be rewritten approximately 100,000 times. The reason for this is that the heat applied to the phase change recording film 3, which causes a reversible phase change, is transmitted to the surface of the tracking groove of the transparent substrate 1 of this medium, and this heat deteriorates the transparent substrate 1, which is made of polycarbonate or the like, which has low heat resistance. In particular, the shape of the tracking groove may be damaged.

The present invention has been made in view of the above points.

The purpose of this is to create a structure with a heat-resistant protective film, so that the substrate will not deteriorate when replacing the recording.
The purpose of the present invention is to provide an optical recording medium that can be rewritten approximately one million times.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides a heat-resistant protective film interposed between the substrate of the one-source recording medium and the first dielectric support 1i.

[Effect]

As described above, since the optical recording medium of the present invention is configured to provide a heat-resistant protective film between the substrate and the first dielectric protective film, phase change recording of laser light irradiated from the substrate side is possible. The heat required for the film is suppressed from being transmitted to the tracking grooves of the substrate, and the integrity of the substrate can be maintained for about 1 million times when recording is rewritten.

〔Example〕

The present invention will be explained below based on examples.

FIG. 1 is a schematic cross-sectional view showing the structure of an optical recording medium according to the present invention, and the same reference numerals are used for common parts with FIGS. 2 and 3. The optical recording medium of the present invention is provided with a heat-resistant protection @ 8 between the transparent substrate 1 and the first electrolyte protection film 2, and other basic features are shown in FIGS. 2 and 3. An improved version of the optical recording medium of FIG. 3 is shown having the same structure as shown, but now with cooling@6. Heat resistant usage! I
Of course, the film 8 can also be applied to an optical recording medium having the structure shown in FIG.

The optical recording medium shown in FIG. 1 can be manufactured more easily than the usual RF or DC magnetron sputtering method, and the manufacturing procedure is as follows. First, 1 (on a polycarbonate transparent substrate 1 by F magnetron sputtering method,
A film of 5 tOa, s with a film thickness of 207 am is formed as a heat-resistant protective film 8, and a ZnS film with a film thickness of 120 nm is formed thereon as a dielectric protective film 2, and then a G film is formed as a phase change recording film 3.
ezSbzTes+ZnS with a thickness of 180 nm is sequentially formed as the second dielectric protective film 4. Next, using υ as a target, DC sputtering is performed in argon gas,
An AJ cooling film 6 with a film thickness of Zoo nm is formed, and a U241I resin is further applied by a spin code method, followed by UV curing to provide a surface protection layer 1[15] with a thickness of 1 OPfF1. The diameter of the optical recording medium is 130 mm.

At this time, the refractive index of the polycarbonate of the substrate 1 is 1.58.
Since the refractive index of the first dielectric material @gj2 is 2.33, the heat-resistant protective film 8 is made of 5iOo,s with a refractive index of 2.0 so that it has a refractive index between these two. The film thickness is determined by the refractive index (λ), which is twice the wavelength of the laser light used (λ).
The value divided by n) was set as λ/2n.

Next, the optical recording medium obtained in this way has a circumferential speed of g 2c
Wavelength 830 nm r while rotating at n/sec
Initialization was performed by irradiating a laser beam with an output of 10 mW.

The diameter of the laser spot on the surface of the optical recording medium is about 1 μm. The phase change recording film 3 after sputtering was in an amorphous state and had a light reflectance of about 6%, but the light reflectance increased to about 18% after laser light irradiation. When the same location on the optical recording medium was irradiated with laser light again under the same conditions, no change was observed in the 1st reflection force from 18%. The reason why the reflectance changes is because the phase change recording film 3 changes from an amorphous state to a crystalline state, and the reason why the reflectance does not change after the second laser beam irradiation is because it was crystallized by the first laser beam irradiation. It shows that this has been done sufficiently.

After performing the above initialization, the rotation speed of the optical recording medium is increased to 3.
60 Orpm and the recording level shown in Figure 4 is 11
mW and a power of 6 mW as the erasing level.The window width 7 shown in FIG. 4 was set to 67n'sf, and recording was performed using the (2,7) RLI code.

After writing the information, writing was performed under the same conditions as above, and the reproduction output of the optical recording medium was 48 in CN ratio.
A value in dB was obtained. When the previous information was erased using the same power as above, the remaining signal level dropped to 13 dB, making it possible to erase it almost completely.

In addition, from the results of overriding with a random pattern of (2,7) RLL codes, it was found that a conventional optical recording medium without a heat-resistant protective film 8 would have no write or read errors after 10,000 overrides. However, it was also confirmed that the optical recording medium of the present invention does not cause write or read errors even after overwriting one million times.

Furthermore, after overwriting both the optical recording medium of the present invention and the conventional optical recording medium 100,000 times for comparison, they were immersed in hydrofluoric acid, leaving only the transparent substrate 1 and other parts. As a result of exploding and observing a sample from which the substrate 1 had been completely removed, it was found that the tracking groove shape of the substrate 1 of the conventional optical recording medium was dimpled, whereas the shape of the tracking groove of the substrate 1 of the optical recording medium of the present invention was diluted. In No. 1, the shape of the tracking groove was not changed at all from the initial state. This also shows that the optical recording medium of the present invention has a significantly longer rewriting life.

〔Effect of the invention〕

In phase-change optical recording media, the heat applied to the phase-change recording film deteriorates the substrate such as polycarbonate, causing deformation of the tracking groove, which makes it impossible to rewrite digitally recorded data. However, in the optical recording medium of the present invention, as described in the second embodiment, there is a heat-resistant insulation layer between the substrate and the first I-electric protection film. ! !
Because the film is interposed, heat is suppressed from being transmitted to the tracking groove of the substrate when the recording film undergoes a crystalline/amorphous phase change, and recording can be rewritten over 1 million times without deforming the tracking groove. Now you can go around.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing the S configuration of the optical recording medium according to the present invention, FIGS. 2 and 3 are schematic sectional views showing the structure of a conventional optical recording medium, and FIG. It is a perspective view of power modulation shown in relation. 1: Transparent substrate, 2: First current feeding body retention film, 3: Phase change recording film, 4: Second energy retention body 1i film. 5: Surface protection@, 6: Cooling film, 7: Window width, Ne1
figure

Claims (1)

[Claims] 1) A first dielectric protective film, a phase change recording film, and a second dielectric protective film on a substrate.
A dielectric protective film, a reflective cooling film, and a surface protective film are laminated in this order, and a laser beam is incident from the substrate side to cause a reversible phase change in the phase change recording film, thereby recording and reproducing information. . An optical recording medium, characterized in that a heat-resistant protective film is formed between the substrate of the optical recording medium to be erased and the first dielectric protective film. 2) The optical recording medium according to claim 1, wherein the refractive index of the heat-resistant protective film has a value between the refractive index of the substrate and the refractive index of the first dielectric protective film. . 3) The optical recording medium according to claim 1 or 2, characterized in that the thickness of the heat-resistant protective film is λ/2n (λ is the wavelength of the laser beam used, and n is the refractive index of the heat-resistant protective film). optical recording medium. 4) In the optical recording medium according to claims 1 to 3, the substrate is polycarbonate, and the heat-resistant protective film is SiO_0_. ＿
An optical recording medium characterized by comprising 6.