JPH0251391B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an optical recording system in which information can be recorded and reproduced using a laser beam, and more particularly to an optical recording system in which recording is performed by utilizing changes in the state of matter using optical energy at the oscillation wavelength of a semiconductor laser. Conventionally, Te alloys, Te oxides, bulb-forming media, organic dyes, and the like have been used as optical recording media for the above-mentioned recording methods. Te alloy is used as a solid solution alloy of Te and semiconductors such as As and Se. This medium has relatively high writing sensitivity and is compatible with semiconductor lasers, which can make the optical system for recording and reproduction compact, but it is chemically unstable and easily deteriorates when left in the air. There is a problem that (Te, As, Se, etc.) exhibit toxicity. Although Te oxide is more stable than Te alloy, its optical properties, such as absorption and reflectance, depend sensitively on the oxidation state. Therefore, this medium has the disadvantage that the oxidation state must be tightly controlled during the formation of the medium. The bulb-forming medium has a layered structure consisting of a reflective layer, a transmitting layer, and an absorbing layer, and increases light absorption through repeated reflection and interference to achieve high sensitivity. Therefore, this medium is currently one of the most sensitive media, but due to its multilayer structure, it requires a large number of film formations, and the repeated reflection interference greatly depends on the thickness of each layer, making it difficult to form a film. The drawback is that the film thickness must be strictly controlled. On the other hand, organic dye media have been developed in various forms. They can be roughly divided into single dye types and compatible types in which the dye is dissolved in a polymer resin using a solvent. For example, as disclosed in Japanese Patent Application Laid-Open No. 161690/1983, a compatible medium is a method in which polyvinyl acetate, which is a polymer resin, is mixed with polyester yellow as a pigment using a solvent, and then formed on a substrate using a spin coating method. be done. This medium has a relatively short wavelength range (400
It exhibits absorption in the wavelength range of ~500 nm), but has almost no absorption in the wavelength range of semiconductor lasers (~800 nm), so it cannot be used as a medium for recording devices that use semiconductor lasers. Furthermore, in general, the method for forming a compatible medium is limited to solvent coating, and when a resin is used for the substrate, there is a restriction that a solvent that does not dissolve the resin must be selected. On the other hand, as a single dye medium, for example, a medium in which squarylium dye is formed by vapor deposition method is published in Japanese Patent Application Laid-Open No.
Disclosed in No. 46221. This dye has relatively large absorption in the near-infrared wavelength region, which is the oscillation wavelength of semiconductor lasers, but its recording sensitivity is worse than Te alloy. An object of the present invention is to improve the above-mentioned drawbacks of the prior art and to provide a highly sensitive and chemically stable optical recording system in the wavelength region of semiconductor lasers. That is, in the present invention, on one side of the substrate, the general formula (In the formula, R represents OH, NH ₂ , NHX or NX ₂ ,
R′ is OH, NH ₃ , NHX, NX ₂ or

Represents [formula]. (Here, X represents an alkyl group, and X' represents a hydrogen atom, an alkyl group, an allyl group, an amino group, or a substituted amino group.) The recording/reproduction is performed from the substrate side. The naphthoquinone dyes represented by the above general formula are collectively called 2,3-dicyano-1,4-naphthoquinone, and the absorption peak wavelength varies from the visible region to the red depending on the types of sub-groups R and R' at the 5th and 8th positions. Move to the outer realm. All of the auxiliary groups R and R' listed above have absorption peak wavelengths in the infrared region, but as R in the general formula above, NH ₂ and R'

A compound to which [Formula] is added is most compatible with the oscillation wavelength of a semiconductor laser, and a compound in which X' is an alkyl group is most preferable considering other conditions. for example 5-amino-2,3-dicyano-8 represented by
When measuring -(4'-butylanilino)-1,4-naphthoquinone in an acetone solvent, the absorption maximum wavelength λmax of the spectrum of this dye is 759 nm,
It can be seen that the wavelength matches well with the oscillation wavelength of the semiconductor laser. The naphthoquinone dye compound is stable even under relatively high temperature and high humidity environmental conditions, and does not show deterioration due to air oxidation unlike Te alloys. This means that it can withstand long-term use without a protective film. In addition, this compound has a low thermal conductivity similar to general organic dyes, and its value is 1/10 to 1/100 of that of metals. Therefore, the diffusion of heat in the medium during laser beam recording is reduced, and the temperature of the medium at the light irradiation part can be efficiently raised. The recording medium is formed by depositing the above naphthoquinone dye on one side of a substrate by vapor deposition or solvent coating. Among the naphthoquinone dyes mentioned above, R is NH ₂
R′ is

In the case of [Formula] (X' is an alkyl group), vapor deposition is possible at about 210°C to 250°C.
Although various materials can be used as the substrate material, glass and synthetic resin are generally preferred. Examples of synthetic resins include polymethyl methacrylate (PMMA), polysulfone, and polycarbonate. The substrate shape can be a disk shape, a tape shape, or a sheet shape. When a naphthoquinone dye film formed on a substrate is irradiated with semiconductor laser light focused by a lens, the dye film in the irradiated area is removed and holes are formed. Although the mechanism of this pore formation is not clear, it is thought to be due to melting and aggregation accompanied by evaporation (sublimation). The size of the hole formed depends on the focused diameter of the laser beam, laser power, and irradiation time, but it is preferably about 0.2 to 33 μm. The laser energy required to form such a hole is small, and therefore the hole can be formed in a short time. in particular,
Beam diameter of AlGaAs semiconductor laser light with wavelength 830nm
When the light is focused to 1.4 μm, holes can be formed with a power on the dye film surface of 2 to 10 mW and an irradiation time of 50 to 300 nsec. Naturally, holes can be formed under conditions that exceed the upper limits of the above power or irradiation time, but the above conditions are desirable usage conditions. Information is recorded by correlating the presence or absence of holes in binary information. Usually, a disk-shaped medium is rotated at a constant speed, holes are formed in accordance with the recorded information, and information is recorded. In the above case, the thickness of the pigment film is 0.01 to 0.5 μm, preferably 0.02 to 0.2 μm. The information (holes) recorded in this manner is read out by detecting changes in the amount of light reflected or transmitted from the medium. Generally, a method of detecting reflected light is adopted. This is because the optical system for reflected light detection is simpler. That is, this is because one optical system can project and collect light. For reading, laser light is continuously irradiated. The light intensity at that time is set to a weak energy that does not cause any shape change to the medium, and is 1/5 to 1/5 of the light intensity during normal recording.
It is 1/10. There are two directions of incidence of light during recording and reproduction: toward the medium surface and toward the substrate surface. When incident on the substrate side,
This is a more desirable form because it allows recording and reproduction without being affected by dust attached to the surface of the medium. Note that if the substrate thickness is 1 mm or more, the beam diameter on that surface is sufficiently large to prevent dust adhering to the surface of the substrate opposite to the surface on which the medium is formed, as well as defects such as scratches on that surface. Does not adversely affect recording or playback. Information is recorded as a series of holes. The rows of holes generally form a number of concentric or spiral tracks. When reproducing, the light beam needs to accurately track the hole rows of a specific track. One way to achieve this is to increase the precision of the rotating mechanism by using air bearings or the like. However, in this case, the rotation system becomes complicated and expensive, which is impractical. A more desirable method is to provide a light guide groove on the substrate. When light enters a groove about the diameter of a beam, it is diffracted. As the beam center shifts from the groove, the spatial distribution of the diffracted light intensity changes, and by detecting this, a servo system can be formed so that the beam is incident on the center of the groove. Usually, the width of the groove is set in the range of 0.6 to 1.2 μm, and the depth is set in the range of 1/8 to 1/4 of the recording/reproducing wavelength used. The recording layer is therefore formed on the grooved substrate surface. A thin film of 2,3-dicyano-1,4-naphthoquinone dye can be easily formed by a conventional resistance heating vapor deposition method. When a thin film is formed on a substrate kept at room temperature, its crystallinity becomes amorphous, that is, it becomes amorphous. Since the reflected light from the amorphous film does not include grain boundary noise seen in polycrystalline films, the reproduction S/N is good when using the amorphous film. Embodiments of the present invention will be described below with reference to the drawings. Figure 1 shows the 5-
This figure shows the absorption spectrum of a thin film of amino-2,3-dicyano-8(4'-butylanilino)-1,4-naphthoquinone dye. Than this,
The oscillation wavelength of AlGaAs semiconductor laser is ~800nm
There was an absorption maximum in the vicinity, and it was confirmed that this dye is suitable as an optical recording medium using a semiconductor laser. Next, 5-amino-2,3-dicyano-8-(4'-butylanilino)-1,4-naphthoquinone dye was vapor-deposited onto a 1.2 mm thick disc-shaped PMMA substrate using a resistance heating method to a film thickness of 550 Å. A film was obtained. The resistance heating boat material was Mo, and the degree of vacuum before and during vapor deposition was 6 x 10 ^-6 Torr and 9 x 10 ^-6 Torr, respectively.
The substrate was left to stand at room temperature, and almost no rise in substrate temperature due to vapor deposition was observed. As the port temperature was gradually raised, the dye melted at 220°C, and was then fixed at this temperature for vapor deposition. Deposition rate is 5Å/sec
It is. FIG. 2 shows the medium 1 thus formed. A dye film 20 is formed on a PMMA substrate 10. This medium 1 was irradiated with a semiconductor laser beam having a wavelength of 830 nm through the substrate 10 from the direction of the arrow 50 after being focused by an optical system (not shown). In this case, the laser beam has a power of 2 to 12 m on the medium surface.
The test was carried out under the conditions of W and irradiation time of 50 to 300 nsec. The recording sensitivity at this recording wavelength was 16 mJ/cm ² .
As a result of this recording, holes 40 with a diameter of about 0.9 μm were formed in the pigment film 20. Similar to the previous example, R′ is

[Formula] is 5-amino-2,3-dicyano-8-anilino-1,4-naphthoquinone and R' is

[Formula] is 5-amino-2, 3-dicyano-8-(4'-methylanilino)-1,
Each thin film was obtained by vapor depositing 4-naphthoquinone dye using a resistance heating method. The former has a port temperature of 240℃
Sublimation begins at 250°C, and the latter melts at 250°C and becomes ready for vapor deposition. When each film (thickness: 250 Å) was written with a semiconductor laser and the writing sensitivity was determined, the same results as in the previous example were obtained. As is clear from the above examples, the optical recording system obtained by the present invention has excellent characteristics such as higher sensitivity than Te alloy media, chemical stability, durability for long-term storage, and good reproduction S/N. It turns out that it has advantages.

[Brief explanation of the drawing]

Figure 1 shows 5-amino-2,3-dicyano-8-
Graph showing the absorption spectrum of (4'-butylanilino)-1,4-naphthoquinone dye deposited film, 2nd
The figure is a cross-sectional view of an optical recording medium according to an embodiment of the present invention, in which 10 is a substrate, 20 is a dye film,
Reference numeral 50 indicates the direction of incidence of light, and reference numeral 40 indicates a hole.

Claims (1)

[Claims] 1. On one side of the substrate, a general formula (In the formula, R represents OH, NH ₃ , NHX or NX ₂ ,
R′ represents OH, NH ₂ , NHX, NX ₂ or [Formula]. (Here, X represents an alkyl group, and X' represents a hydrogen atom, an alkyl group, an allyl group, an amino group, or a substituted amino group.) An optical recording method characterized by recording and reproducing information from the substrate side.