JP3001909B2 - Recording / erasing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention irradiates a recording layer with a light beam such as a laser beam, and induces a phase change in an irradiated portion depending on the irradiation condition to obtain information. Is recorded and erased, and the reflectance accompanying this phase change,
The present invention relates to a recording / erasing method for an information recording medium for reproducing information by detecting a change in optical characteristics such as transmittance. Such information recording media include optical disks, optical cards,
There are optical tapes and optical drums.

(Prior Art and Problems to be Solved by the Invention) Conventionally, a phase change type information recording medium such as a so-called erasable optical disk capable of erasing information is widely known. This phase-change information recording medium includes, for example, a substrate made of glass or plastic (polycarbonate resin, polymethyl methacrylate resin, etc.) and a recording layer formed on the substrate. As a material for forming the recording layer, for example, a chalcogenide alloy such as GeTe is known, and these are irradiated with a light beam (for example, a laser beam) under different conditions, so that, for example, a crystal and an amorphous are formed. The phase change reversibly occurs, so that information can be recorded and erased using this phase change, and information can be read using the change in optical characteristics such as reflectance or transmittance accompanying these phase changes. it can.

By the way, recently, overwrite technology for recording new information while erasing previous information even in a phase change type information recording medium has attracted attention.

However, when information is recorded / erased by a conventional crystal-amorphous phase change, the crystallization speed of the amorphous phase is usually low, so that high-speed erasing and single-beam overwriting are realized. There was a problem.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a recording / erasing method for an information recording medium capable of high-speed erasing and suitable for single-beam overwriting.

[Structure of the Invention] (Means for Solving the Problems) In the recording / erasing method for an information recording medium according to the present invention, a recording layer formed on a substrate is irradiated with a light beam, and the irradiated part is irradiated with a non-light A phase change mainly occurs between a crystalline phase and a non-equilibrium crystal phase which is an intermediate phase between the amorphous phase and the equilibrium crystal phase.

(Operation) In the present invention, recording / erasing is performed by causing a phase change mainly in a change between an amorphous state and a non-equilibrium crystal phase in a light beam irradiated portion of the recording layer. Since the non-equilibrium phase is a phase that appears as an intermediate phase between the amorphous phase and the equilibrium crystal phase, a phase change between the non-equilibrium phase and the amorphous phase can occur at a high speed.
Therefore, erasing of information can be speeded up, and single beam overwriting can be realized.

Hereinafter, the present invention will be specifically described with reference to the accompanying drawings. Here, an optical disk is shown as an example of the information recording medium. FIG. 1 is a sectional view showing an information recording medium (optical disk) according to an embodiment of the present invention. As shown in FIG. 1, the information recording medium according to the present invention can have a layer configuration usually used in this technical field. The substrate 1 is formed of a material commonly used in this technical field, such as a plastic such as polyolefin, epoxy, polycarbonate (PC), polymethyl methacrylate (PMMA), or glass. On this substrate 1, a protective layer 3, a recording layer 2, a protective layer 4, a reflective layer 5, and a protective layer 6 are formed in this order.

The protective layer 3 and the protective layer 4 are provided so as to sandwich the recording layer 2 and can be formed of a transparent dielectric such as Al ₂ O ₃ , SiO ₂ , ZrO ₂ , ZnS, and AlN. These protective layers 3 and 4 are used for recording / erasing by a light beam such as a laser beam during recording / erasing.
Has an effect of preventing the irradiated portion from scattering or forming a hole.

The reflective layer 5 is provided to increase the reproduction signal, and a large enhancement effect can be obtained by appropriately adjusting the thicknesses of the recording layer 2 and the protective layers 3 and 4. As the reflective layer 5, a material usually used in this field, such as gold, aluminum, or a nichrome alloy, can be used.

The protective layer 6 is for preventing scratches and the like in handling the disk, and may be made of an ultraviolet curable resin or the like.

Note that the protective layers 3, 4, 6 and the reflective layer 5 are preferably provided but are not essential.

The recording layer 2 is formed of a material having a different optical property between the amorphous phase and the non-equilibrium crystalline phase at the beam irradiated portion depending on the light beam irradiation conditions. Have been. The non-equilibrium crystal phase is obtained, for example, by quenching a high-temperature phase, and a phase that cannot exist at room temperature on the equilibrium diagram is brought to room temperature.
An InSbTe alloy is a material that can change phase between an amorphous phase and a non-equilibrium crystal phase. In addition, non-equilibrium phases can be obtained by quenching the high-temperature phase, such as Ni-Ti, Cu-Al, Cu-Z
u, Cu-Al-Zn, Cu-Al-Ni, Ti-Nb, Ti-Mn, Ti-M
o, Cu-Al-Mn, Cu-Al-Fe-Cr, Cu-Ga, Cu-Al-G
a, Cu-In, Cu-Al-In, Cu-Ge, Cu-Al-Ge, Cu-S
n, Cu-Al-Sn, Ag-Al-Cu, Ag-Al-Au-Cu, Ag-Al
-Cd, Ag-Zn, Sb-In-Se, In-Tl, Co-Mn, Au-Cd,
There are Mn-Cu, U-Mo, Fe-Mn, Fe-Cr-Ni and the like.

The recording layer 2, the protective layers 3, 4, and the reflective layer 5 can be formed by a thin film forming technique usually used in this field, such as sputtering or vacuum deposition. The thickness of each layer is set so that the optical change amount between the two layers is optimal in consideration of the optical characteristics, and is usually in the range of several nm to several μm.

The protective layer 6 is usually formed by applying an ultraviolet curable resin by a spin coating method or the like, and irradiating ultraviolet rays to cure the resin. The thickness of the protective layer 6 is usually several μm to several hundred μm.
It is.

The optical disk thus configured is initialized, recorded (overwritten), and played back information as follows.

Initialization The recording layer 2 is usually amorphous immediately after film formation. However, when an amorphous recording portion (recording mark) is formed, the recording layer 2 needs to be crystalline. By irradiating the entire surface of the recording layer 2, the recording layer 2 is non-equilibrium crystallized.

Recording (overwriting) A light beam having a high output and a short pulse width is irradiated onto the recording layer 2 while rotating the disk, and the irradiated portion is heated and quenched to change the phase to amorphous, thereby forming a recording mark. When performing single beam overwriting, as shown in FIG.
The recording layer is irradiated with a power-modulated laser beam. That is, a laser beam having a recording level power pulse superimposed thereon is applied to the erasing level power laser beam in accordance with a recording signal.

In the case of overwriting, new information can be overwritten while erasing previous information with a laser beam at an erasing level, so that information can be recorded without waiting for erasing.

In order to perform overwriting, the recording mark must be erased while the light beam passes through the recording mark, so that a high erasing speed is required. When the erased portion is crystalline and the recording mark is amorphous, information is erased by crystallization of the amorphous. Therefore, a high crystallization speed is required to enable overwriting. You. In the present invention, since the non-equilibrium phase, which is a phase that appears as an intermediate phase between the amorphous phase and the equilibrium crystal phase, and the recording layer is formed of a material that can change phase between the amorphous phase, The phase change can occur at high speed. Therefore, information can be erased at a high speed, and single beam overwriting can be performed.

The recording layer 2 on which the reproduction information is recorded is irradiated with a relatively weak light beam, and the information is read by detecting the optical characteristic, for example, the difference in the reflectance between the recording mark portion and the non-recording portion.

Next, the result of actually manufacturing an optical disk according to the present invention and testing overwriting will be described.

An optical disk having a diameter of 130 mm was manufactured in which the substrate 1 was formed of a polycarbonate resin, the protective layers 3 and 4 were formed of alumina, the recording layer 2 was formed of InSbTe, the reflective layer was formed of Au, and the protective layer 6 was formed of an ultraviolet curable resin.

This disc was rotated at 1800 rpm to produce a recording power of 160
Overwriting was performed under the conditions of mW, erasing power of 8 mW, recording frequency of 2 MHz, and recording pulse duty of 50%. afterwards,
The recorded and erased portions were subjected to an electron beam diffractometer, and their diffraction patterns were observed. As a result, dots indicating crystals appeared in the erased portion, and halos indicating amorphous appeared in the erased portion.

Next, the atomic spacing between the crystals was determined from the electron diffraction pattern of the erased portion. Table 1 shows the results. In the column of "pattern" in Table 1, ds indicates a strong dot, and d indicates a normal dot. Further, the atomic plane distance d was obtained by the following equation.

d = Lλ / R where L is the camera length (82 cm in this test), λ is the wavelength of the electron beam (0.0251 ° in this test), and R is the radius of the diffraction pattern.

From the atomic plane spacing determined in this way, it was confirmed that the crystal structure of the erased portion was very close to the crystal structure of In ₃ SbTe ₂ known as the InSbTe-based high-temperature phase. Table 2 shows the atomic plane spacing and plane index of In ₃ SbTe ₂ .

The In ₃ SbTe ₂ ternary intermetallic compound is a high temperature phase that exists in the temperature range from 420 ° C. to 568 ° C. in the equilibrium diagram. Therefore, it cannot exist at room temperature in an equilibrium state. When such a high temperature phase exists at room temperature, it is generally referred to as a non-equilibrium phase. The crystal structure of In ₃ SbTe ₂ is a cubic lattice,
It has a crystal structure that is extremely easy to crystallize from amorphous.

It is known from a thermodynamic hierarchy that the phase changes from an amorphous state to a non-equilibrium crystal phase and a stable equilibrium phase, and the recording layer is made of a material that can take a non-equilibrium crystal phase by light beam irradiation. As long as it is formed, it is considered that a non-equilibrium crystal phase appears due to moderately rapid cooling during heating and cooling by irradiation with an erasing light beam. Therefore, a crystal structure close to In ₃ SbTe ₂ , which is a non-equilibrium crystal phase, can be obtained in the erased portion.

Thus, the non-equilibrium phase is an intermediate phase between the amorphous and the stable equilibrium phase. The phase change time is shorter than the phase change between the two, and is suitable for high-speed erasing. Therefore, by forming the recording layer using a material that causes a phase change between an amorphous phase and a non-equilibrium crystalline phase, it becomes easy to realize single beam overwriting.

In order for a high-temperature phase such as In ₃ SbTe ₂ to appear at room temperature, its crystal structure must be frozen at the time of cooling.Therefore, in order to realize overwriting using the information recording medium of the present invention, Also, the erased portion (that is, the non-recorded portion) needs to be cooled to some extent. Therefore, it is more suitable for an optical disk rotating at a high speed than an optical disk rotating at a low speed.

[Effects of the Invention] According to the present invention, the crystallization of the amorphous phase can be made faster than the conventional phase change of the amorphous-equilibrium crystalline phase. An information recording medium recording / erasing method suitable for beam overwriting can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an information recording medium according to an embodiment of the present invention, and FIG. 2 is a view showing an irradiation mode of a light beam at the time of single beam overwriting. 1; substrate; 2; recording layer; 3, 4, 6; protective layer, 5; reflective layer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-244339 (JP, A) JP-A-1-162244 (JP, A) JP-A-64-72341 (JP, A) JP-A-64-72341 72340 (JP, A) JP-A-3-104019 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/26

Claims (1)

(57) [Claims] A recording layer formed on a substrate is irradiated with a light beam, and the irradiated portion is irradiated with a non-equilibrium which is an intermediate phase between the amorphous phase and the equilibrium crystal phase. A recording / erasing method for an information recording medium, characterized in that a phase change mainly comprising a change with a crystal phase is caused.