JPS63161545A - Information recording medium - Google Patents

Abstract

PURPOSE:To improve the stability of the recording part of a recording layer by radiating a light beam to the recording layer so as to cause the phase change of two different crystals to the radiated part, and detecting the difference of the optical characteristic between crystals so as to reduce the information. CONSTITUTION:A laser beam of a prescribed condition is radiated to a recording layer 3 via a base 1 or both the base 1 and a protection layer 2 to bring the entire crystal into a crystal of a form shown in figure (a). Then a laser beam of the different condition is radiated to cause the phase change to the crystal of a form shown in figure (b), thereby forming a recording pit of information. Moreover, the laser beam is radiated by a first condition to erase the information, a weak laser beam is radiated to the recording layer 3 to detect the reflectance thereby reproducing the information. Since the information is recorded and erased by the phase change between crystals the stability of the recorded information is improved.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an information recording system in which information is recorded by causing a phase change in a recording layer by applying heat, for example, by irradiating a laser beam. Regarding the medium.

(Prior Art) Conventionally, semiconductor materials such as Te, TeOx and TeGe are
It is known that it can exist as two stable crystalline and amorphous phases with different complex refractive indices N−n−+k (J
, 5tuke J, of, Non-cryst
alline 3olid4, 1 1970>,
Furthermore, the idea of creating an optical memory by reversibly changing these semiconductor materials between two states, crystalline and amorphous, by heat treatment using a laser beam is well known (S, R, 0).
Vshinsky et al, Metallu
aicalTransaction2.641, 19
71) Based on these, phase-change type optical discs in which information can be erased have been developed using the above-mentioned semiconductor materials in the recording layer.

Thin films of semiconductor materials such as Te, TeOx, and TeGe described above have the characteristic that they become amorphous when heated to a molten state and then slowly cooled, and become crystalline when heated to a lower temperature and slowly cooled. Since the complex refractive index expressed by n-1k is different between the amorphous state and the crystalline state, they have different optical properties. For this reason, for example, in these materials, information is recorded and erased by utilizing differences in optical properties such as differences in reflectance or transmittance between crystalline and amorphous materials.

(Problems to be Solved by the Invention) However, in the above-mentioned information recording/erasing method based on a phase change between crystalline and amorphous states, there is a problem that the stability of the amorphous state is low. be. That is, if the crystallization temperature of the material is low, the amorphous recording bits will gradually crystallize, making it impossible to distinguish between the recorded portion and the non-recorded portion. Furthermore, when using a material with a high crystallization temperature, the crystallization speed of these amorphous bits will slow down, but there is still the problem that crystallization will progress over a period of one year to several years. .

On the other hand, in order to form an amorphous bit by irradiating a crystalline part with a laser beam, the recording layer must be melted and rapidly cooled, which requires a high-power laser beam. There is a limit to the output power of semiconductor lasers.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an information recording medium in which the recording portion of the recording layer has high stability and does not require a high-output laser beam.

[Structure of the Invention] (Means for Solving the Problems) An information recording medium according to the present invention has a substrate, and microclusters and defects present therein become seeds of crystal nuclei when irradiated with a laser beam. and a recording layer formed of a material that can take two crystal forms that can be crystallized without melting, and when the recording layer is irradiated with a light beam, different two It is characterized by recording and erasing information by causing a phase change between two crystals, and reproducing the information by detecting the difference in optical properties between these crystals.

(Function) In this invention, the material forming the recording layer is irradiated with a light beam to crystallize microclusters or defects present therein as crystal nuclei, and the irradiation conditions of the light beam are changed. By doing so, two crystalline materials with different optical properties can be obtained. And in this case,
This type of crystallization does not require melting, so it is possible to erase records with a low-power laser beam, and it is possible to erase records by a phase change between two crystals, so information can be stably recorded. I can do it.

(Example) Examples of the present invention will be specifically described below.

P, pter is the process of explosively crystallizing a portion of an amorphous film by applying an energy pulse such as a short-duration laser pulse irradiation, an electrical spark, or a mechanical shock.
[Th1n-8o] reported by rard et al.
lid Files, III (1984)
141]. According to this document, amorphous, especially amorphous Ge
In this case, by irradiating laser pulses under appropriate conditions, the microclusters or defects present therein become sites for crystal nucleation, forming crystal nuclei, and these crystals crystallize explosively. do.

It has been shown that crystals typically grow into two crystalline states.

For example, - 111 of amorphous Ge created by vapor deposition
When a ruby laser and a YAG (yttrium-aluminum-garnet) laser are used for 1 and a relatively low laser power is irradiated, the tree branches start from the center of the irradiated area, as shown in Figure 2(a). Crystals 11 grow radially, and ring-shaped microcrystals 12 are formed around the dendrites 11. In addition, when a relatively large laser power is irradiated, a high-order polycrystal 13 is formed at the center of the irradiated area, and dendrites 14 grow radially from the periphery, and around this dendrite 14. Ring-shaped microcrystals 15 are formed.

In any of these forms of crystallization process, 'a
It has been demonstrated that the film does not melt, and microclusters or defects within it become seeds for crystal nuclei, undergoing an explosive, non-equilibrium crystallization process.

The inventor of the present application has found that by applying the above-mentioned non-equilibrium explosive crystallization, it is possible to obtain an information recording medium on which information can be recorded and erased without melting the recording layer.

According to the inventor's experiments, when irradiating the crystal shown in FIG. 2(a) with a high-output laser pulse, the crystal shown in FIG.
It was found that when the crystal shown in Figure 2 (b) is irradiated with a laser pulse of low output, the crystal form shown in Figure 2 (a) changes reversibly to the crystal form shown in Figure 2 (a). .

Since such a phase change between crystals does not involve melting, the output of the laser beam can be reduced.

The above-mentioned amorphous Ge has a relatively high crystallization temperature of about 500°C and a relatively high melting temperature of about 900°C. A laser such as a laser or a YAG laser is used. Furthermore, by using a material with a lower crystallization temperature and lower melting temperature, such as nSb, for the recording layer, a reversible phase change between two crystals can be caused by a similar mechanism using a laser with lower output. I can do it.

The crystal morphology shown in Figures 2(a) and (b) is permeation class mm
This can be determined by observing the crystalline state, and by irradiating these crystals with a weak laser beam that does not cause a phase change, and detecting the reflected light, (
It was found that the reflectance of a) was approximately 10% higher than that of (b).

As explained above, by forming a recording layer by applying a non-equilibrium explosive crystallization process to a material with a relatively low crystallization temperature, the recording layer can be formed into two stable crystal forms without melting. It is possible to make a reversible phase change between these two crystals, and since these crystals differ in reflectance by as much as 5 to 10%, they are fully usable as erasable optical discs. be.

The information recording medium according to this embodiment is illustrated in FIG. 1(a), for example.
It is configured as shown in . The substrate 1 is made of a material that is transparent and shows little change over time, such as glass or polycarbonate resin. A protective layer 2, a recording layer 3, and a protective layer H4 are formed on the substrate 1 in this order. The protective layer 2.4 is disposed to sandwich the recording layer 3, and prevents the recording H3 from melting. This protective layer 2.4 is made of SiO2. The recording layer 3 is formed of, for example, Ge or In-8b alloy, and by changing the laser beam irradiation conditions, it takes two crystal states that are formed through the process described above and undergo a reversible phase change. It looks like this. Note that the protective layer 2.4 may be omitted depending on the case, and in this case, the recording wI3 is formed directly on the substrate 1, as shown in FIG. 1(b).

In such an information recording medium, first, the recording layer 3
A laser beam under predetermined conditions is irradiated through the substrate 1 or the substrate 1 and the protective layer 2 to transform the entire crystal into a crystal in the form shown in FIG. 2(a). Next, a laser beam under different conditions is irradiated to change the phase of the irradiated portion to a crystalline state shown in FIG. 2(b), thereby forming a recording bit of information. Furthermore,
The information is erased by irradiating the laser beam under the first conditions.

Information is also reproduced by irradiating the recording layer 3 with a weak laser beam and detecting the reflectance.

Next, a test example will be described in which the information recording medium according to the present invention was manufactured and its recording, erasing, and reproducing characteristics were tested.

111. On top of the transparent glass substrate, 30% of amorphous Ge is deposited by vapor deposition.
00 large film, output ioomw, pulse width 5ns YA
When the recording layer was irradiated with the G laser through the substrate, the second
The crystal form shown in Figure (a) was shown. Next, this irradiated portion was irradiated with a laser beam with an output of 150 mW and a pulse width of 15 ns, resulting in a phase change to the crystal form shown in FIG. 2(b).

Furthermore, this irradiated area was again irradiated with a laser beam with an output of 100 mW and a pulse width of 5 ns, as shown in Figure 2 (a).
It returned to the crystalline form shown in . When this reversible change was repeated, it was possible to perform such a reversible phase change at least 30 times. Further, as a result of continuous irradiation of each type of crystal with a laser beam of about 2 mW, the difference in reflectance of each crystal was about 5%.

A protective layer made of SiO2 is formed on a transparent polycarbonate substrate, a recording layer made of Infost)s++ is formed on it, and a protective layer made of 5i02 is further formed on top of that to record information. A sample of the media was created. Each layer is formed by sputtering*mt, the thickness of the protective layer is 5.
00 people, and the thickness of the recording layer was 1000 people.

As a result of irradiating this sample from the substrate side with a semiconductor laser with an output of 13 mW at a pulse width of 15 μS, the irradiated area was
A crystalline form similar to that shown in Figure (b) was obtained. Also,
As a result of irradiating this irradiated area with a semiconductor laser with an output of 10 mW and a pulse width of 100 ns, the irradiated area is shown in Figure 2 (a).
The crystal form was similar to that shown in .

As in Test Example 1, as a result of reversibly changing the crystal morphology of the irradiated area under the above two irradiation conditions, at least 100
This reversible change could be repeated several times. Furthermore, as a result of continuous irradiation of each crystal form with a laser beam of approximately 0.5 mW, the difference in reflectance between each crystal was approximately 10%, and the crystal form shown in Figure 2 (a) was better than that shown in Figure 2 (b). The crystal form shown in (a) had a higher reflectance.

[Effects of the Invention] According to the present invention, since information is recorded and erased by a phase change between crystals, the stability of recorded information is high, and these changes in crystal form cannot be repeated reversibly. This allows information to be recorded and erased over a long period of time.

Furthermore, since a melting process is not included during the crystallization process, information can be recorded and erased using a semiconductor laser with a relatively low output.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are cross-sectional views showing an information recording medium according to an embodiment of the present invention, and FIGS. 2(a) and (b) are diagrams showing crystal forms formed in an embodiment of the present invention. be. 1; Substrate, 2.4=Protective layer, 3; Recording layer, 11°14;
Dendritic crystal, 12.15; microcrystal, 13; polycrystal. Applicant's agent Patent attorney Takehiko Suzue (a) (b) K151
1 (a) (b) Figure 2

Claims (3)

[Claims] (1) When the substrate is irradiated with laser light, the microclusters and defects present therein become seeds of crystal nuclei and can take two crystal forms that can be crystallized without melting. a recording layer formed of a material, and by irradiating the recording layer with a light beam, two different
records and erases information by causing a phase change between two crystals,
An information recording medium characterized in that information is reproduced by detecting differences in optical properties between these crystals. (2) The information recording medium according to claim 1, wherein the recording layer is made of germanium. (3) The information recording medium according to claim 1, wherein the recording layer is formed of an indium-antimony alloy.