JP2528160B2 - optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical disc capable of recording / reproducing information by an irradiated light beam, and more particularly to a low-cost optical disc using a material harmless to the human body. It is a thing.

[Conventional technology]

Information is recorded on an optical disc by, for example, applying energy of a light beam such as a laser beam to a recording film of the optical disc and physically changing one structural state of the recording film to another structural state. be able to.

As a recording film for such an optical disc, a chalcogenide is known, and the chalcogenide can have two structures, for example, an amorphous state and a crystalline state. For example, when the recording film is irradiated with a light beam, heated and heated and gradually cooled, the recording film is crystallized, and when the recording film is irradiated with a light beam having a short pulse width and rapidly heated and cooled, the recording film becomes an amorphous state.

In the optical disc using the chalcogenide as a recording film as described above, a high information recording level can be obtained only by causing a physical change in the recording film and a large change in the optical constant.

However, the chalcogenide is a multi-elemental substance, and various elements are currently being studied, but it has complicated problems such as delicate control of its composition. Further, the chalcogenide contains an element harmful to the human body, and it is not desirable to use a chalcogenide recording film for a consumer optical disc. In addition, the recording film of chalcogenide,
There are various problems such as the manufacturing method, management of the film thickness, and reliability.

Examples of related optical discs of this type include those described in JP-A-61-156543.

On the other hand, there is an optical disk called MOTH.EYE disk in addition to the optical disk using such chalcogenide as a recording film.

FIG. 8 is a sectional view showing a section of a general MOTH.EYE disc.

In FIG. 8, 7 is a protrusion, 8 is a substrate, 9 is a light absorbing heat generating layer, and 10 is a flat portion.

The MOTH.EYE disc is 0.3 mm thick as shown in Fig. 8 (a).
On a substrate 8 having a plurality of projections 7 of about μm on its surface,
It is configured by forming a light absorption heat generating layer 9 made of an inert element. Then, at the time of recording, light energy is applied to the light absorption and heat generation layer 9 by the laser light, and the protrusion 7 on the surface of the substrate 8 is moved to the eighth position.
It is flattened as shown in FIG. As a result, in the initial state shown in FIG. 8A, the laser light is scattered by the projections 7 on the surface of the substrate 8 and the reflectance of the laser light from the surface of the substrate 8 is low. As shown,
By flattening the surface of the substrate 8, light scattering is eliminated and the laser light reflectance is increased. Information is recorded in these two states.

By the way, a harmless element such as Pt or Au is used for the light absorption heating layer 9 formed on the surface of the substrate 8. Therefore, MOTH.EY
The E disc is an effective recording method as compared with an optical disc using a chalcogenide as a recording film because it does not use any toxic material.

However, as described below, there is a problem in terms of low cost, which is an essential condition for consumer use.

That is, when the substrate for MOTH.EYE disk is made by the 2P method (photopolymerization) or the injection molding method,
Either method requires a stamper.

 A general stamper manufacturing process is shown in FIG.

First, a resist is applied on a glass substrate to a thickness of about 70 nm. Next, this is spirally laser-exposed and developed. Next, on the glass substrate with spiral grooves, Ni
To form a conductive film by sputtering, and then perform Ni plating. Then, Ni and the glass substrate are separated to obtain a stamper.

The laser exposure step in the stamper manufacturing process will be described in more detail with reference to FIGS. 10 and 11.

FIG. 10 is a block diagram showing a general laser exposure apparatus.

In FIG. 10, 11 is a glass substrate, 12 is a glass substrate 11
The resist applied on top, 13 is an objective lens, 14 is a light modulator, and 15 is a laser light source.

Further, FIG. 11 is a perspective view showing spiral grooves formed on the glass substrate 11 of FIG.

As shown in FIG. 10, the laser light from the laser light source 15 is
The light is modulated by the light modulator 14 and is irradiated onto the resist 12 from the objective lens 13. At this time, the glass substrate 11 is moving in the direction of arrow 16 at a constant feed rate. Thus, when forming the spiral groove as shown in FIG. 11, laser exposure was performed by moving the glass substrate 11 with one beam of laser light.

On the other hand, in the laser exposure process using the MOTH.EYE disc, minute protrusions having a width of 0.4 μm, a length of 0.55 μm and a height of 0.3 μm are formed on the glass substrate 11 as the above-mentioned protrusions. In addition to this, it is necessary to continuously form the tracking guide groove, and it is also necessary to form necessary information such as an address bit in advance.

Therefore, in the MOTH.EYE disc, the laser exposure process for forming the minute protrusions, the laser exposure process for forming the tracking guide groove, and the address pits are formed as the laser exposure process when manufacturing the stamper. Since at least three laser exposure processes are required for the laser exposure process, the number of processes is increased as compared with the case of forming the spiral groove described above, and the minute projections and the tracking guide grooves are formed. Alternatively, in order to obtain accurate position accuracy with the address pits, the accuracy of laser exposure requires several tens of times more accuracy than the case of forming the spiral groove described above, resulting in higher production cost. There was a problem that it would end up.

Items related to such MOTH.EYE discs include, for example, Denpa Shimbun or Topi dated July 18, 1985.
cal Meeting on Optical Data Storage, Presentation No.WDD4,1
The ones described in 1P to 3P, October 985 are listed.

[Problems to be Solved by the Invention]

As described above, the conventional techniques have problems such as using materials harmful to the human body and high production costs, and these problems are factors that prevent the spread of consumer optical discs. Was becoming one of.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an optical disc using a material harmless to the human body and having a low production cost.

[Means for solving the problem]

In order to achieve the above-mentioned object, in the present invention, on a substrate having a groove on its surface, a light absorbing heat generating layer that absorbs a light beam to generate heat, and a heat shrinking layer that causes volume contraction by being heated. Are sequentially formed to form an optical disc.

Further, instead of the light absorbing and heat generating layer and the heat shrinking layer, a layer which absorbs a light beam to generate heat and causes volume shrinkage due to the heat may be formed.

[Action]

FIG. 12 shows a block diagram of an optical pickup in a general optical disc device.

In FIG. 12, 18 is an optical disk having a spiral tracking guide groove, 19 is an objective lens, 20 is a semiconductor laser, 21 is a photodiode, 22 is a focus control system circuit, 23 is a tracking control system circuit, and 24 is a photo diode. A diode output voltage adder. The output of the adder 24 is proportional to the amount of reflected light from the optical disc 18, and the amount of reflected light is hereinafter referred to as I _G.

Now, when measuring the amount of reflected light I _G when irradiated with laser light tracking guide groove of the optical disc 18, the groove width, the depth, varies as shown in FIG. 13. That is, as the groove width becomes wider and the groove depth becomes shallower, the reflected light amount I _G increases.

Note that in FIG. 13, P is the pitch of the groove, W is the groove width, d is the groove depth, the I _M is the amount of reflected light, when irradiated with a laser beam to the flat portion of the optical disk 18.

Therefore, as shown in FIG. 14, a tracking guide groove 25
For example, two discs each having a light absorbing heat generating layer 2 that absorbs a laser beam 26 and generates heat are formed on a polycarbonate (hereinafter, referred to as PC) substrate 1 having a disk. Then, an air layer is provided between them with the layers inside and the substrates are bonded together to produce an optical disc having an air sandwich structure.

FIG. 15 shows the relationship between the recording laser power and the C / N (signal level to noise level ratio) of the optical disc manufactured in this way.

As shown in FIG. 15, the C / N value improves as the recording laser power increases. This sets the recording part of the optical disc to S
When observed with an EM (electron scanning microscope), as shown in FIG. 14, the tracking guide groove 25 in that portion is deformed into a flat portion 27, and the degree of deformation in that portion is It was found that it was larger than the recording laser power.

However, such an optical disc, as shown in FIG.
At 9 mW which is usually used as the laser power, the C / N value is as low as 22 dB, which is not practical.

Therefore, in the present invention, in order to induce a larger groove deformation, the heat-shrinkable layer 3 which causes volume contraction when heated is further formed on the light-absorption heat-generating layer 2.

Therefore, as shown in FIG. 16, a tracking guide groove 25
On a PC substrate 1 having a light absorbing heat generating layer 2 and a heat shrinking layer 3
Two discs formed by sequentially forming and were prepared, and the heat-shrinkable layer 3 was placed inside, and they were bonded together via an adhesive layer to produce an optical disc.

The recording laser power and C /
The relationship of N is shown in FIG.

In this optical disc, as shown in FIG. 17, the recording sensitivity (the degree to which recording can be performed with less recording laser power) becomes worse as compared with the characteristics of the optical disc in which only the light absorption heating layer 2 is formed. However, the C / N value reached a practical level of 45 dB at a recording laser power of 9 mW. This is because the deformation of the groove 25 portion melted by the heat generated by the light absorption and heat generation layer 2 worked to increase the contraction of the heat contraction layer 3.

Further, on the PC substrate 1 having the tracking guide groove 25, instead of the light absorption heat generating layer 2 and the heat shrinking layer 3, a layer having the functions of the above two layers may be formed. That is, this layer is formed of a material in which a light absorbing heat generating material is mixed in a heat shrinkable material.

In an optical disc with such a configuration, the groove of the PC substrate is melted by heat propagation from the light absorbing heat generating material that absorbs heat by laser light irradiation and heat is generated, and at the same time, the heat absorbing material is also heated to cause volume contraction, Increase the deformation of.

Now, the light absorbing and heat generating layer, the heat shrinking layer, or the layer having the functions of the two layers formed on the substrate should be sufficiently formed by using a material harmless to the human body. You can For example, the light absorption heat generating layer can be formed of an inert element such as Pt or Au. Further, since it is sufficient to form at least a groove on the surface of the substrate, the number of laser exposure steps in the stamper manufacturing process does not increase as in the conventional case, and the accuracy of laser exposure needs to be so severe. Therefore, the production cost can be kept low.

Therefore, according to the present invention, it is possible to realize an optical disc which uses a material harmless to the human body and has a low production cost. Therefore, the optical disc according to the present invention can be sufficiently spread as a consumer optical disc.

〔Example〕

 First, a first embodiment of the present invention will be described.

FIG. 1 is a sectional view showing a section of an optical disc as a first embodiment of the present invention.

In FIG. 1, 1 is a PC substrate, 2 is a light absorbing layer, 3 is a heat shrinking layer, and 4 is an adhesive layer.

First, 0.8 μm width and 70 nm depth formed by injection molding,
On a PC substrate 1 having a tracking guide groove with a pitch of 1.6 μm, a light absorbing and heat generating layer 2 made of an Au film of about 900 Å is formed by vapor deposition, and an acrylic ester composition of about 3 μm is formed thereon by spin coating. Heat shrink layer 3 (SD-17
Heat-shrinkable layer) is formed and cured by irradiating it with ultraviolet rays, and on top of that, PS45, a hot-melt black adhesive.
The adhesive layer 4 made of 0-23 (manufactured by ACI of Japan) is formed. Then, the two discs thus obtained are bonded together with the adhesive layer 4 inside, to form an optical disc.

Here, the specific composition of the acrylic ester composition is 57% by weight of hydroxyethyl methacrylate, 38% by weight of epoxy acrylate, and 5% by weight of benzoisoisopropyl ether. The chemical structures of the materials constituting the composition are as shown below.

1) Hydroxyethyl methacrylate 2) Epoxy acrylate 3) Benzoisoisopropyl ether Next, the state change of this optical disc during recording will be described.

First of all, a semiconductor laser is placed on this optical disk from the PC substrate 1 side.
Irradiate 830 nm laser light. In the irradiated portion, the laser light is absorbed by the light absorbing heat generating layer 2 and the light absorbing heat generating layer 2
Heats up. Due to this heat, the tracking guide groove on the PC substrate 1 is melted and deformed. At the same time, the heat of the light absorption and heat generation layer 2 is propagated to the heat contraction layer 3 to cause volume contraction.
Due to the volume shrinkage of the heat shrinkable layer 3, the tracking guide groove becomes shallow and the deformation increases in the direction in which the groove width widens.

Figure 2 shows the recording laser power and C / N of this optical disc.
The relationship of (signal level to noise level ratio) is shown. As is clear from FIG. 2, the C / N value sharply increases from 7 mW of the recording laser power to reach 45 dB at 9 mW.

When this optical disc was left at 60 ° C and 95% RH, the C / N value did not decrease even after 5000 hours.

According to this embodiment, a pollution-free and highly reliable optical disk can be supplied.

 Next, a second embodiment of the present invention will be described.

FIG. 3 is a sectional view showing a section of an optical disc as a second embodiment of the present invention.

In FIG. 3, 1 is a PC substrate, 4 is an adhesive layer, and 5 is a light absorbing and heat generating / heat shrinking layer.

First, on a PC substrate 1 having a tracking guide groove formed by injection molding, an acrylic peroxide type resin that is hardened by ultraviolet rays and heat and ultrafine particles of Mo are mixed at a ratio of 3: 1.
Spin-coated the mixture of about 1 μm and heat-treat it at 80 ° C for 30 minutes while irradiating it with ultraviolet light to form a light-absorbing heat-generating / heat-shrinking layer 5, on which PS450-23 An adhesive layer 4 made of (made by ACI Japan, Inc.) is formed. Then, the two discs thus obtained are bonded together with the adhesive layer 4 inside, to form an optical disc. Here, the acrylic peroxide type resin is obtained by adding trimethylolpropane triacrylate and t-butyl hydroperoxide to the acrylic acid ester composition, and the composition ratio of each is 27% by weight of hydroxyethyl methacrylate. Epoxy acrylate 36% by weight, benzoisoisopropyl ether 5% by weight, trimethylolpropane triacrylate 27% by weight, and t-butyl hydroperoxide 5% by weight. The chemical structures of trimethylolpropane triacrylate and t-butyl hydroperoxide are as shown below.

1) Trimethylolpropane triacrylate 2) t-butyl hydroperoxide Hereinafter, the above composition is referred to as an acrylic peroxide type resin.

Next, the state change of this optical disc during recording will be described.

First, the optical disc is irradiated with laser light from the PC substrate 1 side. In the irradiated portion, the laser light is absorbed by the light absorption and heat generation / heat shrinkage layer 5, and the light absorption heat generation / heat shrinkage layer 5 generates heat. Due to this heat, the tracking guide groove on the PC substrate 1 is melted and deformed. At the same time, the light absorption and heat generation / heat shrinkage layer 5 causes heat shrinkage, which increases the deformation of the tracking guide groove.

Fig. 4 shows the recording laser power and C / N of this optical disc.
Shows the relationship. As is clear from FIG. 4, the C / N value increases at a recording laser power of 7 mW and becomes 45 dB at 9 mW.

Therefore, also in this embodiment, the same effect as that of the first embodiment described above can be obtained. Moreover, in this embodiment, the light absorption and heat generation layer 2 and the heat contraction layer 3 shown in FIG. 1 are unified into a light absorption and heat generation and heat contraction layer 5, and the light absorption and heat generation and heat contraction layer 5 is spun. First because it can be formed by a coat
This embodiment is superior to the first embodiment in that it does not require a vacuum device for vapor deposition as in the second embodiment, and the manufacturing process can be simplified.

By the way, in the present embodiment, by changing the mixing ratio of the acrylic peroxide type resin and the ultrafine particles of Mo in the light absorbing and heat generating / heat shrinking layer 5, the refractive index of the light absorbing heat generating / heat shrinkable layer 5 is changed. The extinction coefficient (attenuation rate of incident light) can be controlled. Incidentally, as a limiting condition at this time, the reflectance of the light absorbing and heat generating and heat shrinking layer 5 needs to be 10% or more.

FIG. 5 shows the relationship between the recording laser power and the C / N when the refractive index and extinction coefficient of the light absorption / heat generation / heat contraction layer 5 are changed.

In FIG. 5, a is a mixture of acrylic peroxide-type resin and ultrafine particles of Mo at a ratio of 5: 1, the extinction coefficient of the light-absorbing heat-generating / heat-shrinking layer 5 is 0.5, and the refractive index is 1.2. It is a characteristic when doing. Further, b is a characteristic when the extinction coefficient is 0.8 and the refractive index is 2.9, similarly mixed at a ratio of 10: 3. Also, c is also mixed at a ratio of 1: 1 and the extinction coefficient is
These are the characteristics when the refractive index is 2.6 and the refractive index is 3.2.

As is clear from FIG. 5, as the extinction coefficient becomes smaller, the penetration depth of the laser light becomes deeper, and the recording sensitivity gradually decreases. However, on the contrary, if the extinction coefficient is too large, the penetration depth of the laser light becomes too shallow, and the temperature of the surface of the PC substrate 1 rises efficiently, but the heat shrinkage function does not work sufficiently, so C / N Sufficient value cannot be obtained.

Therefore, when Mo is used as an element to be mixed with the acrylic peroxide resin, it is desirable that the mixing ratio of the acrylic peroxide resin and the ultrafine particles of Mo is 10: 3.

In addition, the thermal shrinkage of acrylic peroxide resin is 10
%, So in order to deform the 70 nm tracking guide groove by 10% in the depth direction,
A penetration depth of about 400 nm is required, and an extinction coefficient of 0.2 to 0.4 is required for this purpose. Further, at this time, in order to make the reflectance 10% or more, it is necessary to set the refractive index to 2.9 to 3.4.

 Next, a third embodiment of the present invention will be described.

FIG. 6 is a sectional view showing a section of an optical disc as a third embodiment of the present invention.

In FIG. 6, 1 is a PC substrate, and 5 is a light absorption and heat generation / heat absorption layer.

On the PC substrate 1 having a tracking guide groove formed by injection molding, acrylic peroxide type resin and Mo
A mixture of 3: 1 and the ultrafine particles of 3 is spin-coated to form a light absorption / heat generation / heat absorption layer 5. Then, the two discs thus obtained are bonded together with the light absorption and heat generation / heat absorption layer 5 inside, and then annealed and cured at 100 ° C. to form an optical disc.

The state change at the time of recording on this optical disk is the same as the second one described above.
The second embodiment is similar to the second embodiment, and the relationship between the recording laser power and the C / N is similar to that of the second embodiment.

According to this embodiment, a double-sided contact type optical disc can be manufactured only by forming the light absorbing and heat-generating / heat-shrinking layer 5 on the PC substrate 1. Therefore, the manufacturing process is further improved compared to the second embodiment. It can be simplified and the optical disc can be manufactured at low cost.

In each of the above embodiments, the present invention has been described as applied to the optical disc of the type in which tracking is performed using the tracking guide groove. However, in addition to the optical discs, there are also optical discs of the type in which tracking is performed by two wobbled pits.

Therefore, as a fourth embodiment of the present invention, a case where the present invention is applied to an optical disc of a system in which tracking is performed by wobble pits for tracking will be described.

FIG. 7 shows an optical disk according to a fourth embodiment of the present invention.
It is a top view showing the surface of a PC board.

In FIG. 7, 28 is a wobble pit for tracking, 29 is a clock pit, 30 is a groove, and 31 is a recording area. The alternate long and short dash line indicates the center line of the virtual track.

The recording area 31 shown in FIG. 7 is originally a flat surface, but in the present embodiment, the depth 70 is previously formed on this flat surface.
A groove 30 having a width of nm and a width of 0.6 μm is formed in advance. And like this
An optical disk having the same configuration as that of the second embodiment described above is manufactured using the PC substrate.

Also in this embodiment, the same effect as that of the second embodiment described above can be obtained.

〔The invention's effect〕

In the present invention, the light absorption and heat generation layer, the heat shrinkage layer, or the layer having the functions of the two layers formed on the substrate can be sufficiently formed by using a material harmless to the human body. . Further, in the present invention, since it is sufficient to form at least a groove on the surface of the substrate, the number of laser exposure steps in the stamper manufacturing process does not increase unlike the conventional case, and the accuracy of laser exposure is not so high. Since there is no need to be strict, production costs can be kept low.

As described above, according to the present invention, it is possible to realize an optical disc which uses a material harmless to the human body and has a low production cost. Therefore, the optical disc according to the present invention can be sufficiently spread as a consumer optical disc. You can

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a cross section of an optical disc as a first embodiment of the present invention, FIG. 2 is a characteristic diagram showing a relationship between recording laser power and C / N of the optical disc in FIG. 1, and FIG. FIG. 4 is a cross-sectional view showing a cross section of an optical disc as a second embodiment of the present invention, FIG. 4 is a characteristic diagram showing the relationship between the recording laser power and C / N of the optical disc in FIG. 3, and FIG. A characteristic diagram showing the relationship between the recording laser power and the C / N when the refractive index and extinction coefficient of the light absorption / heat generation / heat absorption layer are changed,
FIG. 6 is a sectional view showing a section of an optical disc as a third embodiment of the present invention, FIG. 7 is a plan view showing a PC substrate surface of an optical disc as a fourth embodiment of the present invention, and FIG. Is a cross-sectional view showing a cross section of a general MOTH.EYE disc, FIG. 9 is an explanatory view for explaining a general stamper manufacturing process, FIG. 10 is a configuration diagram showing a general laser exposure apparatus,
11 is a perspective view showing a spiral groove formed on the glass substrate of FIG. 10, FIG. 12 is a block diagram showing an optical pickup in a general optical disk device, and FIG.
FIG. 14 is a characteristic diagram showing the relationship between the groove depth and the reflected light amount ratio when the groove of the optical disk is irradiated with laser light, using the groove width as a parameter. FIG. 14 is a sectional view showing the cross section of a conventional optical disk, FIG. FIG. 14 is a characteristic diagram showing the relationship between recording laser power and C / N of the optical disc in FIG. 14, FIG. 16 is a sectional view showing a cross section of the optical disc according to the present invention, and FIG. 17 is a recording laser power of the optical disc in FIG. It is a characteristic view showing the relationship of C / N. Explanation of reference numerals 1 ... PC substrate, 2 ... light absorbing heat generating layer, 3 ... heat shrinking layer,
4 ... Adhesive layer, 5 ... Light absorbing and heat generating / heat shrinking layer.

Front page continuation (72) Inventor Yasuhiro Ota, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Home Appliances Laboratory, Hitachi, Ltd. (72) Inventor Hiroaki Ikeda 292, Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Inside the laboratory (72) Akane Kiko, Akane Kiko, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Home Appliance Laboratory, Hitachi, Ltd.

Claims (4)

(57) [Claims] 1. An optical disc capable of recording / reproducing information by an irradiating light beam, wherein a light absorbing heat generating layer which absorbs the light beam to generate heat is formed on the surface of a substrate having a groove on the surface thereof. And a heat shrink layer that causes volumetric shrinkage to thereby form information, and information can be recorded / reproduced by deformation of the groove that occurs when the substrate is irradiated with a light beam. 2. An optical disk capable of recording / reproducing information by an irradiating light beam, the surface of which has a groove on the surface thereof absorbs the light beam to generate heat, and the heat causes volume contraction. An optical disk characterized in that a layer is formed and information can be recorded / reproduced by the deformation of the groove that occurs when the substrate is irradiated with a light beam. 3. In an optical disc capable of recording / reproducing information by an irradiated light beam, two substrates each having a groove on the surface absorb the light beam to generate heat, and the heat causes volume contraction. An optical disk, which is made by bonding materials so that the grooves of the respective substrates are on the inner side, and enables the recording and reproduction of information by the deformation of the grooves that occurs when the substrate is irradiated with a light beam. 4. An optical disc, wherein the layer according to claim 2 or the material according to claim 3 has an extinction coefficient of 0.2 to 0.4 and a refractive index of 2.9 to 3.4. .