JPH0572018B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an information storage medium that records information optically.

(Prior art) Optical disks as information storage media have high density,
It has attracted attention as a large-capacity recording medium and is widely used as image information files and external memory for electronic computers.

These optical discs are available in read-only type and write-once type (DRAW; Direct Read).
There are two types: an after-write type and an erasable type.In recent years, the erasable type, which allows information to be repeatedly recorded and erased, has become widely popular due to its convenience.

As an erasable type optical disc, it is possible to record and
Depending on the erasing method, magneto-optical type, phase change type, etc. are known. For example, in the magneto-optical type, information is recorded by changing the perpendicular magnetization direction of an amorphous rare earth-transition metal alloy thin film between recorded and unrecorded areas, and the difference in Kerr rotation angle of reflected light between these areas is recorded. is detected and the information is reproduced.

In addition, in the phase change type, recording is performed by transferring the phase of the recording layer from an equilibrium phase to a non-equilibrium phase, for example from a crystalline phase as an equilibrium phase to an amorphous phase as a non-equilibrium phase, and the recorded non-equilibrium phase portion The difference in reflectance from the unrecorded equilibrium phase portion is read and reproduced.

By the way, when using the above-mentioned erasable optical disc, the optical disc is There is also information that would be problematic if erased, such as the registration of a code unique to the disk user or address information inside the disk.

Conventionally, as an attempt to make information recorded on an erasable optical disk non-erasable, there has been a method of irradiating a powerful laser beam to form a hole in the recording portion of the recording layer. However, optical discs are generally provided with protective layers made of SiO or the like on both the top and bottom surfaces to prevent oxidation, deterioration, etc. of the recording layer, making it difficult to form holes. In addition, increasing the output of the laser beam to form the hole has the problem of exceeding the output of a typical semiconductor laser, which is 30 to 50 mW.

(Problems to be Solved by the Invention) As described above, it has been difficult for conventional erasable type optical discs to have a function that makes it impossible to erase recorded information.

The present invention is based on the above-mentioned circumstances, and its purpose is to provide an information storage medium of this type that can easily make it impossible to erase information.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention comprises a substrate, a recording layer capable of repeatedly recording and erasing information by irradiating it with a light beam. The information storage medium has a base layer that is provided between the substrate and the recording layer and is made of a material that forms bubbles in a portion heated by light beam irradiation, and the base layer has bubbles formed in the base layer. It is characterized by making it impossible to erase the information recorded on the recording layer in the portion where it is formed.

(Function) When the recording layer is a magneto-optical type, the perpendicular magnetization direction of the recorded portion is reversibly reversed with respect to the unrecorded portion.
Information is recorded and erased in the same direction.

Further, when the recording layer is of a phase change type, information is recorded and erased by reversibly changing the phase of the recording portion between a non-equilibrium phase and an equilibrium phase.

On the other hand, in order to make it impossible to erase the recorded information recorded on the recording layer, if a light beam is irradiated and heated on the underlayer part corresponding to the recorded part of the recording layer, bubbles will be formed in the underlayer at this heated part. Ru. This bubble remains in its shape even after cooling.

Information can be easily reproduced due to the difference in reflectance between the bubble-formed portion and the non-bubble-formed portion.

(Embodiment) An embodiment of the information storage medium according to the present invention will be described below.

FIG. 1 shows a cross-sectional structure of a first embodiment (Example-1) of an information storage medium according to the present invention. A protective layer 4a, a recording layer 3, a second protective layer 4b, and a reflective layer 5 are laminated in this order to form a disk shape.

The substrate 1 is a transparent substrate made of an organic resin material such as acrylic, epoxy, polycarbonate (PC), polyimide, polyamide, glass, A ₂ O ₃ , ZrO ₂ or the like.

The base layer 2 is a plasma polymerized film, and contains CH ₄ (methane), C ₂ H ₆ (ethane), C ₃ H ₈ (propane), and C ₂ H ₄
(ethylene), SiH ₄ (monosilane), etc. alone or in a mixture, or in these gases alone or in a mixture, O ₂ , O ₃ , NH ₃ ,
It is formed by mixing gases that form hydrophilic functional groups such as CO ₂ and SO ₂ (CN) ₂ . The reason for mixing the gas that forms these hydrophilic functional groups is to increase the affinity with the protective layer 4a and the recording layer 3 formed of inorganic materials and to prevent peeling.

The first protective layer 4a and the second protective layer 4b are
It is made of an inorganic dielectric material such as SiO or SiO ₂ to a thickness of 50 to 5000 Å by sputtering or vapor deposition. These protective layers 4a and 4b prevent the formation of holes due to oxidation of the recording layer 3 and evaporation of the recording layer 3 during irradiation with a light beam.

The recording layer 3 of this example is a thin film having magnetic anisotropy perpendicular to the surface of the substrate.
It is selected from various materials such as amorphous rare earth-transition metals such as GdTbFe and GdFeCo. The film thickness is several 10
Å to several thousand Å.

The reflective layer 5 is made of metal such as Cu, Al, Au, etc.
Laminated at about 1000A. Of the laser beams irradiated from the substrate 3 side by this reflective layer 3,
All the light that has passed through the recording layer 3 without being reflected can be reflected back to the substrate 1 side, so that the reflected light from the recording layer 3 and the reflected light from the reflective layer 5 are weighted together, and due to the multiple interference effect. Recording sensitivity is greatly improved.

In the optical disk having the above configuration, information is recorded by first focusing a laser beam modulated according to a recording information signal on the recording layer 3, which has been magnetized in a certain direction in advance, as shown in FIG. , the temperature of the irradiation bit section 6 is raised, and then an external magnetic field H opposite to the magnetization direction of the optical disk is applied.
When the temperature of the irradiated bit portion 6 reaches the Curie point or higher, the magnetization direction of the irradiated bit portion 6 of the recording layer 3 is reversed, and recording is performed by maintaining this reversed state even at room temperature.

To reproduce stored information, a reproduction laser beam is irradiated from the substrate 1 side, and among the reflected light from the recording layer 3,
This is done by detecting the difference in car rotation angle between the recorded bit area and the unrecorded area and measuring the light intensity.

In order to erase the recorded information, a magnetic field is applied to the initial magnetization direction of the recording layer 3 (the magnetization direction of the unrecorded part), and the recorded bit part to be erased is heated above the Curie point to change the magnetization direction. All you have to do is restore it.

On the other hand, to make it impossible to erase recorded information, the third
As shown in the figure, a laser beam L2 having a higher power than the recording laser beam is irradiated onto the recording bit portion where information is recorded, thereby forming a bubble 7 in the underlayer 2. Once this bubble 7 is formed, it becomes possible to read the information with high accuracy using a reading device similar to that used in conventional read-only type optical discs.

FIG. 6 shows a cross-sectional structure of another embodiment (Example 2) of the information storage medium according to the present invention, and this optical disk as an information storage medium includes a substrate 1, an underlayer 2, a recording layer 3, and a protective layer 4 are sequentially laminated to form a disk.

The substrate 1, the base layer 2 and the protective layer 4 are the first
It has the same configuration as the embodiment.

The recording layer 3 is formed of a metal or a semiconductor material that undergoes a reversible phase transition between an equilibrium phase and a non-equilibrium phase, for example, between a crystalline state and an amorphous state, when heated by, for example, laser beam irradiation. This material is
Selected from various materials such as Te, TeGe, and InSb.

In the above configuration, information is recorded by, for example, irradiating the recording layer with a laser beam modulated by recorded information and rapidly heating and cooling the recording layer, so that the recording layer in the laser beam irradiated area changes from crystal to amorphous, for example. This is done by undergoing a phase transition. Further, erasing of a record is performed by irradiating the recorded amorphous portion with an erasing laser beam to heat it, and then slowly cooling it to transform it back into a crystal. Furthermore, information is reproduced by irradiating a reproduction laser beam and reading the difference in reflectance between the amorphous portion where information is recorded and the crystalline portion where information is not recorded.

On the other hand, in order to make it impossible to erase the recorded information, the output and pulse width of the laser beam is increased to form a bubble 7 in the underlayer 2 by irradiating it onto the storage bit area, as in the previous embodiment. good. This makes it impossible to erase the recording, and the recorded state can be stably maintained for a long period of time. Furthermore, information can be easily reproduced.

Specific examples will be described below.

(Example 1) A substrate 1 made of PC resin was used, and after attaching it to a rotating table (not shown) and evacuating the reaction container to vacuum,
Introducing SiH ₄ gas containing 1% CO ₂ in terms of partial pressure ratio,
A predetermined high frequency power was applied to the substrate 1 to deposit a plasma polymerized film (underlying layer 2) using SiH ₄ gas.
The film thickness was 10,000 Å. Next, the first protective layer 4a made of SiO is deposited to a thickness using a sputtering method.
Laminated at 500 Å.

Further, a photomagnetic film made of TbFeCO was formed to a thickness of 500 Å on the first protective layer 4a to form the recording layer 3.

Next, a second protective layer 4b made of SiO is laminated to a thickness of 500 Å on this recording layer 3, and a reflective layer 5 made of Al is further laminated to a thickness of 1000 Å on this protective layer 4b.
The optical disk shown in FIG. 1 was produced by laminating the optical discs with a thickness of 100 nm.

The optical disk formed as described above was irradiated with a laser beam of varying output (mW) and pulse width to examine its characteristics. In this case, the externally applied magnetic field was kept constant at 2000e.

As a result, as shown in FIG. 4, in area A,
No change occurred in the recording layer 3, and no information could be recorded.

Further, in the B region, the magnetization of the recording layer 3 was reversed and information could be recorded, and the recording could be erased by irradiation with an erasing laser beam with varying laser output and pulse width. In this area B, the base layer 2
There was no bubble.

Furthermore, in the C region, the magnetization of the recording layer 3 was reversed and information could be recorded, and bubbles were formed in the underlayer 2, and these bubbles remained as they were even after cooling.

The reproduction characteristics in region B are: reflectance 30%, Kerr rotation angle 0.6deg, C/N ratio 50dB.
(1.25MHz), we were able to obtain extremely excellent characteristics.

On the other hand, the base layer (SiH ₄ + CO ₂ plasma polymerized film)
Both the sample with layer 2 formed and the sample with no base layer 2 formed at a temperature of 65℃ and relative humidity.
An environmental test was conducted under 90%RH, and the reflectance change (R/
R ₀ ) was investigated.

As a result, as shown in FIG. 5, in the sample having the underlayer 2 as shown by the solid line in the figure, no change in appearance was observed in the recording layer 3 even after 15 days. On the other hand, in the sample without the base layer 2, peeling occurred between the PC resin substrate 1 and the base layer 2, and the reflectance decreased, and after 15 days, the reflectance decreased to about 40% of the initial reflectance R ₀ . It turned out that

(Example 2) A base layer 2 was formed by laminating a plasma polymerized film using CH ₄ gas to a thickness of 3000 Å on a substrate 1 made of PC resin.

Next, a recording layer 3 consisting of In ₅₀ Sb ₅₀ was formed on the underlayer 2 by a dual simultaneous sputtering method by adjusting the high frequency power applied to the In target and the Sb target.
It was formed with a thickness of 500 Å.

Next, a protective layer 4 made of SiO was laminated to a thickness of 500 Å on the recording layer 3 by sputtering to obtain the optical disk shown in FIG. 4.

The optical disc thus formed was irradiated with a laser beam, and its characteristics were investigated by varying the laser output and pulse width.

As a result, as shown in FIG. 7, in area A,
It was found that the cooling rate after irradiation was relatively slow, and the InSb entered an equilibrium phase, reducing its reflectance.

It was also found that in region B, the cooling rate of the recording layer was relatively fast, and InSb was turned into a non-equilibrium phase, resulting in an increase in reflectance.

Furthermore, it was found that in region C, the CH ₄ plasma polymerized film (base layer) was gasified and bubbles 7 were formed.

Therefore, in the optical disc of this embodiment, erasable information can be recorded in area B and erased in area A, and in order to make erasure impossible, it is sufficient to irradiate the laser beam in area C. found. Note that no change occurred in the recording layer 3 in the D area.

Next, the characteristics of this optical disk after repeated recording and erasing were determined by adjusting the output and pulse width of the recording and erasing laser beams to 10 mW, 50 ns, and 10 ns, respectively.
Tested at 3mW and 1μsec.

As a result, as shown in Figure 8, the first 5 to 10
It was found that although the reflectance increased with each repetition, it remained constant after that, and the reflectance remained stable even after 10 ⁴ repetitions.

[Effects of the Invention] As explained above, according to the information storage medium of the present invention, since the base layer is laminated on the substrate to form bubbles by irradiation and heating with a light beam,
Information can be easily made unerasable. Therefore, the range of applications of the information storage medium is expanded and its convenience is improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an embodiment of the information storage medium according to the present invention, FIG. 2 is a diagram explaining the information recording principle of the information storage medium of FIG. 1, and FIG.
4 is a diagram showing the irradiation pulse width-output characteristics of the information storage medium of the embodiment in FIG. 1, and FIG. 5 is an environmental test of the embodiment in FIG. 1. FIG. 6 is a sectional view showing the configuration of another embodiment of the information storage medium according to the present invention, and FIG. 7 shows the irradiation pulse width-output characteristics of the information storage medium of the embodiment shown in FIG. The figure shown in FIG. 8 is a diagram showing the recording and erasing repetition characteristics of the embodiment shown in FIG. 1...Substrate, 2...Underlayer, 3...Recording layer,
4, 4a, 4b...protective layer, 5...reflection layer, 7...
…bubble.

Claims (1)

[Scope of Claims] 1. An information storage medium having a substrate and a recording layer on which information can be repeatedly recorded and erased by irradiation with a light beam, provided between the substrate and the recording layer, It has an underlayer made of a material that forms bubbles in areas heated by beam irradiation, making it impossible to erase information recorded on the recording layer in areas where bubbles are formed in this underlayer. An information storage medium characterized by: 2 The base layer contains CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₂ H ₄ ,
2. The information storage medium according to claim 1, which is a plasma polymerized film using SiH ₄ alone or a mixture thereof. 3 The base layer contains CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₂ H ₄ ,
O ₂ to SiH ₄ alone or a mixture thereof,
Claim 1, which is a plasma polymerized membrane using a gas mixed with a gas that forms a hydrophilic functional group such as O ₃ , NH ₃ , CO 2 , SO ₂ (CN) _{2 ,} etc. Information storage medium.