JP2629746B2 - Optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rewritable optical recording medium such as an optical disk and an optical card capable of recording, reproducing and erasing information by light.

[Conventional technology]

2. Description of the Related Art Conventionally, there are the following optical recording media for recording and erasing information by utilizing an optical change between an amorphous state and a crystalline state or a plurality of crystalline states.

Recording and erasing by reversible transition between the amorphous state and the crystalline state include a recording layer of a Te81Ge15Sb2S2 thin film containing Te as a main component (Japanese Patent Publication No.
26897), a recording layer made of a TeGeSn alloy thin film (JP-A-6
1-3324), a recording layer of a Te80Sb10Se10 film containing Te as a main component (JP-A-61-145737, etc.), and a recording layer of an Sb-Se alloy having a composition such as Sb2Se (JP-A-60 -155495), InSb compound semiconductor with a small amount of Te added to make a recording layer (SPIE Vol.529 P51), Te-Sb binary alloy as a recording layer (1986 Applied Physics Scientific Lectures 1986 29a- ZE-3,
4), a recording layer made of a thin film mainly composed of low oxide of Te (Japanese Patent Laid-Open No. 185048/1984), and a thin film mainly composed of a Te-Ge alloy
Te-O-Sn-Ge-Au (JP-A-61-2595), Te-O-In-Ge-Au (JP-A-61-2592), Te-O-Bi-Ge-Au (JP-A-61-2592) -2593), Te-
Some have a recording layer of O-Sb-Ge-Au (JP-A-61-2595).

Further, recording and erasing by optical change between different crystal states capable of reversible transition are performed by using a thin film containing a binary alloy such as In-Sb as a main component as a recording layer (Japanese Patent Application Laid-Open No. 61-227238).

[Problems to be Solved by the Invention] However, in the case of the above-described conventional technology, there are the following problems.

That is, a recording layer of a thin film of Te81Ge15Sb2S2,
In the case where the recording layer is made of Te-Ge-Sn or Te-Ge-Sn, the high-speed erasing function of recording and the practical recording sensitivity that can be recorded by a semiconductor laser cannot be achieved at the same time. Also Te80Sb
10Se10 film as recording layer, and S of composition such as Sb2Se
b-Se alloy as recording layer, In-Sb compound semiconductor 10
%, A recording layer made of a small amount of Te added, or a recording layer made of a Te-Sb binary alloy, in terms of oxidation resistance,
Although relatively excellent, there were the following problems.

That is, in the case of a Te-Sb-Se alloy film such as a Te80Sb10Se10 film, recording and erasing with a laser beam required a time of about 20 μsec, and the erasing speed was slow and lacked in practicality. on the other hand,
When the recording layer is made of an Sb-Se alloy having a composition such as Sb2Se, there is a problem that when recording and erasing are repeated, noise is sharply increased and the quality of a recording signal is reduced. Further, when a recording layer was formed by adding a small amount of Te to an In-Sb compound semiconductor, the recording laser power required for amorphization was large, and the change in reflectance during recording was small, which was not practical. Further, the recording layer having this composition has a disadvantage that it is extremely difficult to amorphize once it is crystallized. Further, when the Sb2Te3 alloy was used as the recording layer, the crystallization temperature was low, the reliability was poor, and the time required for erasure was long, which was not practical.

A recording layer composed of a thin film mainly composed of a low oxide of Te (Japanese Patent Laid-Open No. 59-185048), a Te-OS composed mainly of a Te-Ge alloy
n-Ge-Au (JP-A-61-2595), Te-O-In-Ge-Au (JP-A-61-9561)
2592), Te-O-Bi-Ge-Au (JP-A-61-2593), Te-O-Sb-Ge
-Au (Japanese Patent Application Laid-Open No. 61-2595) has a disadvantage that the time required for erasing the recording is long. In addition, in the case of a recording layer containing a binary alloy such as In-Sb as a main component for performing recording by utilizing a difference in optical properties accompanying a transition between different crystal states, the recording layer is preliminarily heated by an oven. However, there are practical disadvantages such as the necessity of initializing to a crystalline state for example, and the fact that the recording state is deteriorated when the light beam scanning speed during recording is high.

An object of the present invention is to solve the above problems and to provide a highly reliable optical recording medium which has low toxicity of a recording layer, low power required for recording, and enables high-speed erasure of recording.

[Means for solving the problem]

The object of the present invention is to provide a recording layer on a substrate, by irradiating the recording layer with light, information recording, reproduction and erasure is possible in the optical recording medium, the composition of the recording layer, the following: The optical recording medium is characterized by being in the range represented by the general formula:

(SbxTe100-X) 100-Y (Te50Ge50) Y where X is 75>X> 70, Y is 25 ≧ Y ≧ 1, X and 100-X in parentheses are components in parentheses, respectively. The atomic ratio of antimony (Sb) to tellurium (Te) is shown.
Also, 50 and 50 in parentheses indicate the atomic ratio of tellurium (Te) and germanium (Ge), which are the components in parentheses, respectively. Further, 100-Y and Y outside the parentheses are Te and Sb, respectively.
And the atomic ratio of the total of Te and Ge.

Atomic% is the percentage of the total number of atoms of each element in parentheses when the number of atoms in the total composition shown in the formula is 100 atomic%.
It is shown by.

In the above composition range, approximately 500 nsec ~ 40 nsec
With the light pulse, an amorphous mark can be formed on the crystalline recording layer to record information. Further, the amorphous mark once formed is approximately 1000 nsec to 200 nse.
The crystal can be returned to the crystalline state by the light irradiation of c, and the record can be erased.

The main components of the recording layer of the present invention are shown in parentheses in the general formula,
Sb-Te alloy mainly composed of Sb. This Sb-Te alloy is composed of Sb,
The melting point is lower than that of the Sb2Te3 compound, and recording by amorphization is easy.

Regarding Sb contained in the recording layer of the present invention, it is preferable that X (atomic%) representing Sb in the general formula indicating the composition of the recording layer is in the range of 75>X> 70. When X is 75 atomic% or more, irreversible phase separation easily occurs in the recording layer, noise at the time of recording / reproduction becomes extremely large, and repetition of recording / erasing becomes difficult. In addition, the contrast of the recording signal is reduced, which is not practical. On the other hand, when X is 70 atomic% or less, the irradiation time of light required for erasing the record becomes longer,
There are drawbacks such as low thermal stability of the recording mark.

Further, the composition of Te50Ge50 added to the recording layer is preferably added to the above-mentioned Sb-Te alloy in a range of 25 ≧ Y ≧ 1, whereby the time required for erasure by crystallization is reduced, and In addition to the effect of enabling high-speed erasing of a recorded mark, the effect of reducing the unerased residue after erasing the recorded mark is obtained. Further raise the crystallization temperature of the recording layer,
It has the effect of improving thermal stability. When Te50Ge50 component is not included, the erasability of the amorphous recording mark is poor,
In addition, since the contrast of the reproduced signal is low, it is not practical. If the total Y of the atomic percentages of Te50Ge50 is more than 25 atomic%, the irradiation time of light required for erasing the recording becomes longer, the recording sensitivity decreases, and an inexpensive semiconductor laser with relatively low output is used. It is not practical because it cannot be done. Also,
When Y is less than 1 atomic%, the effects of improving the erasing speed and reducing the unerased portion are not recognized.

A good composition that enables high-speed erasure of recording, has a large signal intensity during recording and reproduction, and provides a good carrier-to-noise ratio is obtained when X is 75 to 70 atomic% and Y is 10 to 25 atomic%. %.

The recording layer of the present invention is formed on a substrate with a thickness of 10 to 1000 nm. In particular, in order to obtain high sensitivity as an optical disk, the thickness is preferably 10 nm or more and 50 nm or less, and in order to obtain a more favorable carrier-to-noise ratio of a recording / reproducing signal, it is preferably 60 nm to 150 nm.

Further, a protective layer may be laminated adjacent to the recording layer of the present invention. In this case, deformation of the recording layer during recording hardly occurs, and the number of times of erasing and rewriting of the recording can be improved. The protective layer of the inorganic thin film such as SiO _2,
A heat-resistant polymer thin film such as a polyimide resin is preferable. In particular, a metal oxide thin film of Si, Ge, Ti, Zr, Te or the like is preferable because it has high heat resistance and can prevent oxidation of the recording layer.

The substrate used in the present invention may be the same as a conventional recording medium such as plastic, glass, and aluminum. For the purpose of avoiding the influence of dust by recording from the substrate side with convergent light, it is preferable to use a transparent material for the substrate. Materials such as the above, polyethylene terephthalate, polymethyl methacrylate,
Polycarbonate, epoxy resin, polyolefin resin, and glass are preferred. More preferably, polymethyl methacrylate, polycarbonate, and epoxy resin are preferable because of low birefringence and easy formation.
Although the thickness of the substrate is not particularly limited, it is practically 10 μm or more and 5 mm or less. If it is less than 10 microns, it is easily affected by dust even when recording with convergent light from the substrate side, and if it exceeds 5 mm, it is not possible to increase the numerical aperture of the objective lens when recording with convergent light, Since the bit size becomes large, 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 the form of a card or a circular disk. In addition, if necessary, an air sandwich structure, an air incident structure using two substrates,
It is also possible to use a close bonding structure.

The light used for recording on the optical recording medium of the present invention is light such as laser light or strobe light. In particular, the use of a semiconductor laser means that the light source is small, the power consumption is small, and the modulation is easy. Is preferred.

The recording layer and the protective layer can be formed by a thin film forming method in a vacuum such as a sputtering method, a resistance heating evaporation method, an electron beam heating evaporation method, and an ion plating method. In particular, a sputtering method is preferable because a recording layer and a protective layer with few defects can be formed.

Recording can be performed by forming an amorphous mark on the crystalline recording layer by irradiating a laser beam. Further, although the recording speed may be slow, the amorphous mark can be crystallized or the crystallized mark can be made amorphous by irradiating the amorphous recording layer with laser light. .

A method of irradiating a recording layer in a crystalline state with laser light to form an amorphous mark to perform recording, and in the case of erasing, performing crystallization of the amorphous mark by laser light irradiation to increase the recording speed. This is preferable because it is possible and the recording layer hardly deforms.

When an amorphous mark is formed on a crystalline recording layer to perform storage, the recording layer is previously irradiated with light such as a laser beam,
Alternatively, it is preferable to crystallize by heating with warm air or the like.

[Examples] Hereinafter, the present invention will be described based on examples.

The characteristics in the examples were evaluated by the following methods.

Composition of Recording Layer The composition of the formed recording layer was confirmed by ICP emission analysis (FTS-1100, manufactured by Seiko Instruments Inc.).

The carrier-to-noise ratio of the recording / reproducing signal was measured using a spectrum analyzer.

Example 1 A protective layer and a recording layer were formed by a sputtering method while a spiral-shaped group-made polycarbonate substrate having a thickness of 1.2 mm, a diameter of 13 cm and a pitch of 1.6 μm was rotated at 30 rpm.

First, a 100 nm SiO ₂ protective layer is formed on a substrate, and Te, Sb and Te 50 Ge 50 are further formed under a condition of a vacuum degree of 5 × 10 ⁻³ torr.
The alloy was simultaneously sputtered while being monitored by a quartz crystal film thickness meter to form a 90 nm thick recording layer having an elemental composition ratio of (Sb73Te27) 77 (Te50Ge50) 23. Further, a protective layer was formed on the recording layer with a thickness of 100 nm of SiO ₂ to constitute an optical recording medium of the present invention.

The optical recording medium is rotated at a linear velocity of 1.5 m / sec, and scanning on a track is performed while irradiating a semiconductor laser light having a wavelength of 830 nm condensed from the substrate side with an objective lens having a numerical aperture of 0.5 at a film surface intensity of 3.0 mW. The recording layer was crystallized. At this time, the reflectance of the recording layer increased due to crystallization. Then, using the same optical system, at a linear velocity of 4 m / sec, at a frequency of 1.75 MHz
Recording was performed with a semiconductor laser beam of 10 mW modulated at z and a duty ratio of 50%.

After recording, the recording portion was scanned with the intensity of the semiconductor laser set to 0.9 mW, and the recording was reproduced. As a result, it was confirmed that the reflectance of the recording mark portion was reduced and recording was performed. The C / N ratio of this playback signal is set at a bandwidth of 30 kHz.
As a result of measurement, a value of 42 dB that can be digitally recorded was obtained. Further, when the recording portion was scanned once with a 5.5 mW semiconductor laser beam, the recording was erased. The erasure rate at this time was -35 dB. In addition, recorded on this erased part
It was possible to repeat erasure.

Further, the amorphous mark in the recording portion was stably present even after the optical recording medium was heated to 70 ° C. for 30 minutes in a ventilation oven.

Example 2 An optical recording medium was manufactured in the same manner as in Example 1 except that the recording layer of Example 1 was a recording layer having a composition of (Sb73Te27) 80 (Te50Ge50) 20. When recording and reproduction of this optical recording medium were performed by the same apparatus as in the first embodiment, the C / N
The ratio was 40dB. In addition, this recording part is linear velocity 3m / se
c) It was possible to erase by one irradiation per track under the condition of laser light power of 4.0 mW. C / N after erasure
Was 10 dB.

Comparative Example 1 In Example 1, the composition of the recording layer was changed from (A) to
Optical recording media were produced in the same manner as in Example 1 except that (d) was changed.

(B) (Sb50Te50) 98 (Te50Ge50) 2 (b) (Sb80Te20) 98 (Te50Ge50) 2 (c) Sb66Te34 (d) (Sb65Te35) 20 (Te50Ge50) 80 In the case of an optical recording medium of composition (a), It took a long time to erase the amorphous mark after recording, and it was difficult to erase by a single irradiation of the semiconductor laser light in a state where the mark was rotated at a linear velocity of 1.5 / sec.

In the case of the composition (b), since the contrast of the recording signal was reduced, the recording power required for forming the amorphous mark was large, and recording was difficult with a semiconductor laser beam of 10 mW.

In the case of the composition (c), recording and erasing are possible, but when tested under the same recording conditions as in Example 1, the crystallization time becomes longer and the C / N ratio is as low as 36 dB, which is practical. Did not reach the standard. Further, when erasing was performed in the same manner as in Example 1, the erasing rate was as low as -23 dB because there were many unerased parts. Further, the crystallization temperature of the amorphous portion was about 10 ° C. lower than that of Example 1, and the thermal stability was poor.

In the case of the composition (d), the recording sensitivity was low and recording was difficult with a semiconductor laser beam of 10 mW or less.

Example 3 After the optical recording medium of Example 1 was left in a normal indoor environment for 6 months, recording, reproduction and erasing were performed in the same manner as in Example 1, but no particular deterioration was observed.

In addition, no abnormalities were observed after standing at 60 ° C. and 80% relative humidity for 20 days.

[Effects of the Invention] In the present invention, since the recording layer of the optical recording medium is constituted by a specific composition comprising Sb, Te and Ge, the following excellent effects can be obtained.

(1) An optical recording medium which requires low power for recording, enables high-speed erasure of recording, and has high thermal stability of recording marks.

(2) An optical recording medium having excellent wet heat resistance was obtained.

Claims (1)

(57) [Claims] 1. An optical recording medium having a recording layer on a substrate and capable of recording, reproducing and erasing information by irradiating the recording layer with light, wherein the composition of the recording layer is as follows: An optical recording medium characterized by being within the range represented by the formula. (SbXTe100-X) 100-Y (Te50Ge50) Y where X is 75>X> 70, Y is 25 ≧ Y ≧ 1, and X and 100-X in parentheses are components in parentheses, respectively. The atomic ratio of antimony (Sb) to tellurium (Te) is shown. Also, 50 and 50 in parentheses indicate the atomic ratio of tellurium (Te) and germanium (Ge), which are the components in parentheses, respectively.
Further, 100-Y and Y outside the parentheses indicate the atomic ratio of the total of Te and Sb and the total of Te and Ge, respectively.