JPH0822614B2 - Optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording medium such as an optical disk and a laser COM for recording information by light. More specifically, the present invention relates to an optical recording medium that records and reproduces information by utilizing the phase transition of a recording film.

[Prior Art] Conventionally, Te- in an optical recording medium utilizing a phase transition
As the recording layer of Se system, Sn-Te-Se system (Proceedings of the 46th SPSJ Academic Lecture Proceedings 13P-E-2, E-3), Ga-Te
It is known to utilize the fact that the reflectance of the recording layer differs between an amorphous phase and a crystalline phase such as -Se series (Japanese Patent Laid-Open No. 60-251534).

[Problems to be Solved by the Invention] However, in such a recording layer, deformation of the recording portion, formation of openings or recesses, and the like are likely to occur due to irradiation light at the time of recording, so that the optical energy at recording is largely restricted. In view of this drawback, it is common practice to provide an oxide such as SiO ₂ or a nitride such as Si ₃ N ₃ as a protective layer in the Te-Se recording layer. There are problems in manufacturing such as the formation of holes, and there is also a drawback that the manufacturing cost becomes higher.

An object of the present invention is to provide an optical recording medium in which recording is performed with a stable phase transition in a wide range of irradiation energy during recording, and the manufacturing cost is relatively low.

[Means for Solving Problems] An object of the present invention is to record information by thermally irradiating a recording layer formed on a substrate with light to cause a phase transition between an amorphous substance and a crystalline substance. An optical recording medium, wherein the recording layer has a composition represented by the following general formula.

Te _(100-ab) Zn _a Se _b (where 100 is atomic% of alloy, a is Zn in alloy)
Atom% of the alloy, b represents the atom% of Se in the alloy, and 5 ≦ a ≦ 4
0 and 2.5 ≦ b ≦ 30. ) Is achieved.

The recording layer in the invention means an alloy thin film containing Te (tellurium), Zn (zinc) and Se (selenium) as main constituent elements. Its composition is represented by the following general formula.

Te _(100-ab) Zn _a Se _b (where 100 is atomic% of alloy, a is Zn in alloy)
Atom% of the alloy, b represents the atom% of Se in the alloy, and 5 ≦ a ≦ 4
0 and 2.5 ≦ b ≦ 30. ) When a is less than 5, the non-irradiated portion is likely to be deformed and an opening or a recess is easily formed due to the irradiation of recording light, which makes phase transition mode recording difficult, and when it exceeds 40, the phase transition phenomenon may occur. Hard to get up.

When b is less than 2.5, the recording layer is prone to deterioration such as oxidation over time, and when b is more than 30, the light absorption of the recording layer is small.
A large output light source is required during recording, and its use is limited.

In the phase transition type optical recording medium, it is desirable that the difference in optical characteristics between the recorded portion and the non-recorded portion of information is large, and a is approximately 10 to 30 atom%, and b is approximately 5 to 25 atom%. Is preferred, and in this range, the ratio of a to b (b /
More preferably, a) is about 0.25 to 1.5 and the sum of a and b (a + b) is about 20 to 45 atom%.

In the present invention, the TeZnSe alloy film forming the recording layer has a high light reflectance upon light irradiation, and at the same time has a low light transmittance. Since the similar change is caused by heating, it is considered that the above change is caused thermally.

FIG. 1 shows a thermal change in spectral characteristics of a TeZnSe film formed on a glass substrate. Curves (1) and (3) respectively show the reflectance and the transmittance before heating,
(2) and (4) show the reflectance and transmittance after heating at 300 ° C. for 10 minutes. It is due to interference that the reflectance has a minimum at around 900 nm on the curve (1) and around 1100 nm on the curve (2).

The transmittance decreases due to heating, and the reflectance increases after subtracting the decrease due to interference. Moreover, the valley of the interference of the reflectance is shifted to the long wavelength side by heating, and the difference of the reflectance is promoted in the vicinity of the valley of the interference before heating. The shift of the valley of this interference means the increase of the refractive index of the TeZnSe film.

Further, the resistance value of the TeZnSe film decreases from almost infinity before heating to several KΩ after heating. Considering these phenomena comprehensively, it is considered that the change of the recording layer is due to the amorphous-crystal transition.

The film thickness of the recording layer of the present invention is approximately 100 Å to 10,000 Å. In particular, in order to obtain high recording sensitivity as an optical disc, it is preferable to set it to 100Å or more and 2000Å or less. Furthermore, by utilizing the interference effect of light, it is possible to promote the difference in the reflectance between the amorphous phase and the crystalline phase of the recording layer, so the interference effect is expressed, although it depends on the composition of the alloy and the wavelength of the light source used. Because it is easy to do,
500Å to 1500Å is preferred.

The optical recording medium of the present invention can be used as a single layer structure in which the recording layers are provided adjacent to each other on the substrate. Further, it may be used as a multi-layer structure in which a dielectric layer and a reflective layer are laminated as needed. Further, it goes without saying that it can be used by being laminated with a recording layer that causes a phase transition between another amorphous phase such as TeGe and SbSe and a crystalline phase. If necessary, a protective layer or a diffusion preventing layer may be provided on the surface of these layers or between the substrate and the recording layer, or between the layers when a multilayer structure is provided.

The substrate in the present invention may be the same as a conventional recording medium such as plastic, glass and aluminum. It is preferable to use a transparent material as the substrate for the purpose of avoiding the influence of dust by recording from the substrate side by the convergent light. As the above materials, polyester resin, acrylic resin, polycarbonate resin,
Examples thereof include epoxy resin, polyolefin resin, styrene resin and the like. Preferably, because of its small birefringence and easy formation, polymethylmethacrylate,
Polycarbonate and epoxy resin. The thickness of the substrate is not particularly limited, and is 10 microns or more, 5
Millimeters or less are practical. If it is less than 10 microns, it is easily affected by dust even when recording with convergent light from the substrate side. If it is more than 5 mm, when recording with convergent light, the numerical aperture of the objective lens cannot be increased and the pit Since the size increases, it becomes difficult to increase the recording density.

The substrate may be flexible or rigid. The flexible substrate can be used in a tape shape or a sheet shape. The rigid substrate can be used in a card shape or a circular disk shape.

The recording layer can be provided on one side or both sides of the substrate as is known. Further, if necessary, two substrates may be used to form an air sandwich structure, an air incident structure, a close-bonding structure, or the like.

The light used for recording on the optical recording medium of the present invention is light such as laser light or strobe light. Especially, when a semiconductor laser is used, the light source is small, the power consumption is small, and modulation is easy. Therefore, it is preferable.

Manufacturing Method In forming the recording film of the optical recording medium of the present invention, a conventional means such as vacuum deposition using a plurality of evaporation sources, sputtering using an alloy or a plurality of targets, and ion plating can be used. An example of the method of forming the recording film of the present invention is shown below.

As shown in FIG. 2, three evaporation sources 6, 7, and 8 containing Te, Zn, and Se are heated on the disk-shaped substrate 5 to perform vapor deposition. The heating and evaporation sources are not particularly limited,
Conventional means such as resistance heating with a boat for vapor deposition, electron beam heating, and high frequency induction heating can be used. In addition, although not particularly limited, it is effective to rotate the substrate in order to make the composition ratio of Te, Zn and Se on the substrate uniform, and whether the three evaporation sources are arranged close to each other. It is effective to arrange them radially from the center of substrate rotation or on the same circumference, and it is also possible to arrange them radially from the center of substrate rotation. The composition ratio of the recording layer is determined by the evaporation amounts of Te, Zn and Se, and the evaporation amount can be controlled by the electric power supplied to the evaporation source. Specifically, electric power may be supplied to the evaporation amount calculated in advance, or the supplied electric power may be controlled while the evaporation amount is monitored by, for example, the crystal type film thickness monitors 9, 10 and 11. Further, a mask plate 18 having shutters 12, 13 and 14 and fan-shaped slits 15, 16 and 17 is arranged between the evaporation source and the substrate as necessary to make the composition on the substrate uniform and the film thickness uniform. You may. The film thickness of the recording layer is the sum of the product of evaporation amount of Te and Zn and Se per unit time, or Te and Zn.
It can be known by the sum of the monitor values of and Se.

The degree of vacuum is not particularly limited, but is, for example, 1
It is in the order of × 10 ^-6 Torr to 5 × 10 ^-3 Torr.

Applications The thus-produced optical recording medium of the present invention is effectively used for media such as optical disks, optical tapes, optical cards, optical floppy disks, microfishes, and laser combs (COM).

 A description will be given below based on examples.

Evaluation method of characteristics and evaluation of effects Evaluation sample An optical recording medium was prepared by forming a recording layer on a polycarbonate disk substrate with a groove having a diameter of 12 cm, a thickness of 1.2 mm and a pitch of 1.6 μm, and evaluated. The recording layer was formed in the vapor deposition apparatus shown in FIG. 2 by using a vapor deposition boat as an evaporation source and rotating the substrate at 300 rpm while Te and Zn.
And the evaporation amount of Se are monitored, and as the evaporation amount according to the composition ratio of the recording layer, the degree of vacuum is approximately 2 × 10 ^-5 Torr and 800Å-9
Deposition was performed to a film thickness of 00Å.

Evaluation method of recording characteristics The above optical disk was rotated so that the laser scanning speed was changed from a linear velocity of 4.0 m / sec to a linear velocity of 9.0 m / sec, and the spot diameter was 2 μm.
Semiconductor laser light with a wavelength of 830 nm focused on m is 1MHz to 2MHz
Recording was performed by irradiating the recording layer through the substrate after modulation with the pulse. After that, the output of the laser was set to 0.7 mw on the film surface to reproduce the recorded signal, and the carrier-to-noise (C / C
N) was measured.

[Example] Example 1 A film thickness of 800 Å was formed on a polycarbonate disk substrate with a composition ratio Te ₇₅ Zn ₁₃ Se ₁₂ of the recording layer. This optical recording medium is rotated at a moving speed of 4 m / sec and a frequency of 1 M
A semiconductor laser beam with a wavelength of 830 nm modulated to Hz is converged to a spot diameter of 2 μm and recorded with a power of 5 mw from the substrate side.
Playback was performed with a power of 0.7 mw. As a result, the signal voltage proportional to the reflectance of the optical recording medium was 0.2 V before recording and in the non-recording portion, but increased to 0.3 V in the recording portion. This indicates that the recording portion is a phase transition from the amorphous phase to the crystalline phase due to the laser beam, and there is no deformation, opening, or formation of a concave portion in the recording layer. The C / N under this condition was 40db. Table 1 shows C / N when the moving speed, the modulation frequency, and the recording power of this optical recording medium are changed. As is clear from this result, phase-transition recording can be performed under a wide range of conditions such as a moving speed of 4 m / sec to 9 m / sec, a recording frequency of 1 MHz to 2 MHz, and a recording power of 3 mw to 8 mw in an optical recording medium without a protective film. A good and practical C / N was obtained.

Example 2 The results of measuring the C / N of an optical recording medium formed on a polycarbonate disk substrate by changing the composition ratio of the recording layer as shown in Table 2 in the same manner as in Example 1 are shown in Table 2.

Comparative Example 1 Sn was used instead of Zn on a polycarbonate disk substrate, and the atomic number composition ratio of the recording layer was Te ₇₅ Sn ₁₃ Se ₁₂ to obtain a film thickness.
Formed to 800Å.

When this optical recording medium was evaluated in the same manner as in Example 1, the recording power was 3 mW, the recording frequency was 1 MHz, and the moving speed was 4
Phase transition occurs at m / sec, but the change in signal voltage due to recording is small, and C / N is about 35db, which is not practical. In addition, when the recording power is 4 mW to 6 mW, the recording frequency is 1 MHz, and the moving speed is 4 m / sec, the signal voltage of the recording part indicates a phase transition, and a part higher than the non-recording part indicates deformation, opening, or recess formation. A stable recording mode could not be obtained due to a mixture of lower portions.

Comparative Example 2 An optical recording medium similar to Comparative Example 1 was prepared except that the atomic composition ratio of the recording layer was changed to In ₂₀ (Te ₆₀ Zn ₃₀ Se ₁₀ ) _80, and evaluated in the same manner as in Example 1.

When recorded at a recording power of 3 mW, a recording frequency of 1 MHz, and a moving speed of 4 m / sec, the C / N of the recording could not be realized at 35 dB or more, which was not practical.

[Advantages of the Invention] Since the present invention has a recording layer of an optical recording medium made of TeZnSe, it exhibits the following excellent effects.

Since the phase transition is stable, no protective layer is required, and therefore the structure is simple, the mass productivity is excellent, and the manufacturing cost is low.

Since the phase transition is stable in a wide range of light irradiation energy, it can be applied to various uses such as recording speed and recording power.

[Brief description of drawings]

FIG. 1 is a diagram for explaining thermal changes in spectral characteristics of the recording layer of the present invention, and FIG. 2 is a schematic plan view of an apparatus showing one method of forming the recording layer. 1: reflectance before heating 2: reflectance after heating 3: transmittance before heating 4: transmittance after heating 6,7,8: evaporation source 9,10,11: monitor 12,13,14: shutter 15,16,17: Slit 18: Mask plate

Claims (1)

[Claims] 1. An optical recording medium in which information is recorded by thermally irradiating a recording layer formed on a substrate with light to cause a phase transition between an amorphous substance and a crystalline substance and recording the information. An optical recording medium, wherein the layer has a composition represented by the following general formula. Te _(100-ab) Zn _a Se _b (where 100 is atomic% of alloy, a is Zn in alloy)
Atom% of the alloy, b represents the atom% of Se in the alloy, and 5 ≦ a ≦ 4
0 and 2.5 ≦ b ≦ 30. )