JPS63155438A - Information recording medium - Google Patents

Abstract

PURPOSE:To permit stable recording of information by forming a recording layer of a material which can make phase transformation between >=2 kinds of crystalline materials with which activation energy is different and projecting a light beam to such recording layer to cause a phase change between the crystalline phases. CONSTITUTION:This recording medium has a substrate 1 and the recording layer 3 formed of the material which can make the phase change between two kinds of the crystalline phase varying in the activation energy for crystallization. The information is recorded and erased by projecting the light beam 8 to the recording layer 3 to cause the phase change between the crystalline phases in the irradiated part. The material for the recording layer 3 includes, for example, an InSb-Sb eutectic alloy. The recording of the information by the phase change between the crystalline phases is thereby permitted; in addition, the crystal grain sizes can be distinctly discriminated by a difference in the activation energy for the crystallization of the crystal phases constituting the respective parts in the part of recording pits and the part except the same. The stable recording of the information is thereby permitted.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) This invention records and erases information by causing a change in optical characteristics in a recording layer by irradiating a light beam, and The present invention relates to information recording media such as so-called erasable discs that reproduce information by detecting characteristics.

(Prior Art) As erasable optical discs capable of erasing information in addition to recording and reproducing information, discs that utilize phase change between crystalline and amorphous states have been developed. In this optical disc, by irradiating the recording bit part with a light beam, a phase change between crystalline and amorphous is caused in the recording bit part, and the fact that the complex refractive index of each phase is different is utilized. to read the information. For this reason, this optical disk uses a material that easily becomes amorphous when heated by irradiation with a light beam and then rapidly cooled. Conventionally, such a material is TeOx.

Chalcogenide materials such as Te-3n-8e or Ge-Te are known [Regarding TeOx, see "Rewritable high-capacity optical disks" Japan Society for the Promotion of Science 131st Committee Large 116 Study Group Materials (1983, 5)] ].

(Problems to be Solved by the Invention) However, chalcogenide-based materials have a problem in that the amorphous phase is not stable and information cannot be stably recorded.

This invention was made in view of such circumstances, and
The purpose of the present invention is to provide an information recording medium that can stably record information.

[Structure of the Invention] (Means for Solving the Problems) An information recording medium according to the present invention comprises a substrate and a material capable of phase change between two types of crystalline phases having different crystallization activation energies. The recording layer is formed by irradiating the recording layer with a light beam to cause a phase change between the crystalline phases in the irradiated portion, thereby recording and erasing information.

(Function) A recording layer is formed of a material that can undergo phase transformation between two or more types of crystalline phases with different activation energies, and a light beam is irradiated onto this recording layer to transform the irradiated portion from one of the crystalline phases. Transform to the other crystalline phase.

Then, the irradiated portion and the non-irradiated portion are formed of different crystalline phases. Since these crystalline phases have different crystallization activation energies, their crystal growth rates differ, and the crystalline phase with a lower activation energy has a higher crystal growth rate. As a result, the crystal grain size differs between the portion irradiated with the light beam and the portion not irradiated. In this case, both the irradiated part and the non-irradiated part of the light beam are crystalline and therefore stable at room temperature.
In addition, since each crystalline substance has a different grain size, it can be clearly distinguished by reflectance. Therefore, information can be recorded stably.

(Embodiments) Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a sectional view of an information recording medium (optical disk) according to an embodiment of the invention. The substrate 1 is made of a material that is transparent and has little change over time, such as glass,
It is made of materials such as quartz, PMMA resin, polycarbonate resin (PC), or epoxy resin. The substrate 1 includes a protective layer 2, a recording layer 3, a protective layer 4, and a protective layer! 11115
are formed in this order. The protective layers 2 and 4 are disposed to sandwich the recording layer 3, and prevent the recording layer 3 from scattering or forming holes due to laser beam irradiation. These protective layers 2 and 4 are made of SIO2, SiO or A
It can be formed by depositing a dielectric material such as IN using a vapor deposition method, a sputtering method, or the like. The thickness of these protective layers 2 and 4 is 1
The thickness is preferably from nm to 10 μm.

The protector 15 is provided to prevent the eaves from being damaged during handling of the optical disc, and is made of a material that has good adhesion to the protective layer 4. For example, it can be formed by applying an ultraviolet (UV) curing resin on the protective layer 4 and curing the resin layer by irradiating the resin layer with ultraviolet rays.

The recording material 13 is made of a material that can form two crystalline phases with different crystallization activation energies depending on the light beam irradiation conditions. The difference in activation energy for this crystallization is
This is because the crystal nucleation of one crystalline phase is surface nucleation, and the crystal nucleation of the other crystalline phase is volume nucleation. Examples of such materials include In5b-8
b There is a eutectic alloy. It is known that this alloy transforms into a metastable π phase by rapid solidification by splat cooling, and this π phase can exist stably at room temperature. Therefore, when this alloy is melted and then rapidly cooled, it becomes a π phase, and when it is slowly cooled, it becomes an equilibrium phase of InSb and sb. On the other hand, crystals are formed by crystal growth after crystal nucleus formation. In this crystal nucleation, the π phase is formed by surface nucleation, and the equilibrium phase is formed by volume nucleation. In this case, the activation energy for crystallization in surface nucleation is smaller than in the case of volume nucleation, and the activation energy for crystallization in the π phase is a fraction of that in the case of equilibrium phase. Therefore, the crystal growth rate of the π phase is higher than that of the equilibrium phase, and the π phase becomes single-crystal coarse grains, while the equilibrium phase becomes fine equicyclic islands. In this way, information can be recorded and erased based on the difference in reflectance due to the difference in crystal form.

Note that, in addition to the general splat cooling described above, rapid solidification can also be performed by irradiation with a pulsed light beam. This pulsed light beam irradiation method has a faster cooling rate than splat cooling, so
The range in which the non-equilibrium phase appears becomes wider, making it easier to obtain the non-equilibrium phase.

In addition, examples of materials that can take crystal forms with different activation energies for crystallization include In5b listed here.
The material is not limited to the -8b eutectic alloy, but any material that can be crystalline in a non-equilibrium phase at room temperature can be used.

The thickness of the recording layer 3 is preferably 1 nm to 5 μm. The recording layer 3 can be formed by a conventional sputtering method, vapor deposition method, or the like.

Next, the operation of the optical disc configured as described above will be explained. Here, a case will be shown in which an In5b-sb eutectic alloy is used as the recording layer 3.

In this optical disc, as shown in FIG. 1, a light beam 8 is focused by a focusing lens 7 and irradiated onto the recording layer 3 from the substrate 1 side.

LL If the recording layer 3 after film formation is amorphous or crystalline in a non-equilibrium phase, the recording layer 3 is made crystalline in an equilibrium phase before using this optical disc. Initialization of this optical disk is carried out by raising the entire disk to a temperature higher than the crystallization temperature using a heater, or by changing the phase from a non-equilibrium phase crystalline state to an equilibrium phase crystalline state.
The heating may be carried out by heating the recording layer 3 to a temperature higher than 100°C, or may be carried out by sequentially irradiating the recording layer 3 with a light beam and heating the recording layer 3 with the light beam.

When recording information on an optical disc, the recording layer 3 is irradiated with a light beam for a short time, the irradiated area 6 is once melted, and then rapidly cooled to dissolve the non-equilibrium phase crystalline π.
phase to phase change. In this case, since the π phase has a low crystallization activation energy, it becomes single-crystal coarse grains. As the light beam, it is preferable to use a fast pulsed laser beam of 10 nanoseconds to 2 microseconds. In addition, the output of this laser beam can, for example, hit the recording pit (irradiation area 6) with one pulse! If a semiconductor laser is used, it is usually 5 to 30 mW. In this way, by rapid cooling of the recording pit (area 6), this part changes to the non-equilibrium π phase, and this π phase becomes single crystal coarse grains as described above, so that information is transferred to the recording layer 3. written. In this case, the π phase exists stably at room temperature and has a clearly different particle size from the equilibrium phase, so information can be stably recorded.

(2) The information written in the recording layer 3 is read by irradiating the recording pits (irradiation area 6) with a light beam and detecting the intensity of the reflected light. In other words, the surface reflection when irradiated with a light beam is caused by an equilibrium phase that has a large crystallization activation energy and exists as fine equicyclic island crystal grains, and a π phase that has a small crystallization activation energy and exists as coarse crystal grains. By utilizing the fact that the ratios are different and detecting the intensity of the reflected light, it is determined whether the area irradiated with the light beam is in the equilibrium phase of crystalline phase or in the non-equilibrium phase of π phase.

L In5b-8b constituting the recording layer 3 is irradiated with a light beam with an output smaller than the output of the light beam during information recording for a slightly longer time than during information recording onto the recording pit (area 6) of the recording layer 3.
The co-crystal alloy is heated to a temperature higher than its bile point to once melt, and then slowly cooled. As a result, the recording pits of the recording layer 3 return to the crystalline state of the equilibrium phase of fine equicyclic islands, and the information is erased.

[Effect of the invention] According to this invention, two crystallization activation energies are different.
A recording layer is formed of a material that can form two crystal phases, and by irradiating this recording layer with a rice beam, a layer change is caused between these crystal layers, thereby recording and erasing information. In this way, information can be recorded through phase changes between crystals, and the activation energy of the crystallization of the crystal phases constituting each part can be reduced between the recording pit part and other parts. The crystal grain size can be clearly distinguished by the difference in . Therefore, information can be recorded stably.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an information recording medium according to an embodiment of the invention. 1: Substrate, 2.4, 5: Protective layer, 3: Recording layer, 8: Light beam. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (2)

[Claims] (1) It has a substrate and a recording layer formed of a material that can undergo a phase change between two types of crystalline phases with different crystallization activation energies, and the recording layer is irradiated with a light beam. An information recording medium characterized in that information is recorded and erased by causing a phase change between the crystalline phases in the irradiated portion. (2) The difference in activation energy of each phase is due to the fact that the crystal nucleation mechanism of one phase is surface nucleation, and the crystal nucleation mechanism of the other phase is volume nucleation. An information recording medium according to claim 1, characterized in that: