JPH03169682A - Method for recording and erasing information - Google Patents

Abstract

PURPOSE:To obtain an information recording and erasing method performing stable recording at high speed by laser beam of lower power by performing the recording and erasure of information by the phase change between a multi- phase of a non-equilibrium phase and an amorphous phase and the non- equilibrium phase generated at a beam irradiated part when a recording layer is irradiated with laser beam. CONSTITUTION:A substrate 1 is formed from a material such as plastic, for example, polyolefin or glass and a protective layer 3, a recording layer 2, a protective layer 4 and a protective layer 5 are formed thereon in this order. The recording layer 2 is formed from a material capable of generating a phase change between a multi-phase of a non-equilibrium phase and an amorphous phase and the non-equilibrium phase by the irradiation with laser beam. The phase change is rapid and can be generated by laser beam of relatively low power and there is In-Sb-Fe as a material having high recording stability. By controlling the composition of In-Sb-Te, a phase change can be generated between a multi-phase of an In3SbTe ternary compound and an amorphous phase and the In3SbTe2 ternary compound phase.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention records and erases information by irradiating a light beam such as a laser beam to induce a phase change in the irradiated area. The present invention relates to a method for recording and erasing information on an information recording medium, which reproduces information by detecting encapsulation of optical properties such as reflectance and transmittance due to this phase change. Information recording media used in this method include optical discs,
There are optical cards, optical tapes, optical drums, etc.

(Prior Art and Problems to be Solved by the Invention) Phase change type media have been widely known as information recording media from which information can be erased, such as so-called erasable optical discs. This phase change type 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. Chalcogenide alloys such as GeTe are known as materials for forming this recording layer, and these alloys can be used for light beams under different conditions (
By irradiating it with a laser beam (for example, a laser beam), the phase changes reversibly between crystal and amorphous, so this phase change is used to record and erase information, and the reflection accompanying these phase changes is Information can be read using changes in optical properties such as rate or transmittance.

As such a recording layer, a material having a eutectic structure or a material forming an intermetallic compound that easily undergoes a phase change depending on the irradiation conditions of the light beam is suitable.

However, it cannot be said that the recording and erasing of information using the phase change between crystal and amorphous interrogation, which has been conventionally performed on phase change type information recording media, maintains sufficiently satisfactory characteristics. In particular, it is desired to further speed up recording and erasing to enable single beam overwriting.

It is also desirable to be able to record and erase information using a light beam with even lower power, and to further increase the stability of recording.

This invention was made in view of such circumstances, and
It is an object of the present invention to provide a method for recording and erasing information that can perform recording and extinguishing at high speed, can perform recording and erasing with a lower power light beam, and has high recording stability.

[Structure of the Invention] (Means for Solving the Problem) The information recording and erasing method according to the present invention comprises a substrate and a recording layer whose phase changes between two phases whose irradiated portions are redundant when irradiated with a light beam. A method for recording and erasing information on an information recording medium, wherein the recording and erasing of information eliminates non-equilibrium crystal phases and amorphous phases that occur in the beam irradiated area when the recording layer is irradiated with a light beam. It is characterized by being formed by phase encapsulation between a mixed phase and a non-equilibrium crystalline phase.

(Function) In the present invention, information is recorded and erased by causing a phase change between a mixed phase of a non-equilibrium crystalline phase and an amorphous phase and a non-equilibrium crystalline phase by irradiation with a light beam. Such a phase change is faster than the phase change between an equilibrated crystalline phase and an amorphous phase that occurs in conventional phase change recording media. Therefore, information can be captured and deleted at high speed. Furthermore, recording and erasing can be performed with a light beam of moderate power, and recording stability is high.

(Example) The following describes this invention with reference to the attached drawings. Explain physically. FIG. 1 is a sectional view showing an example of an information recording medium used in the present invention.

The substrate 1 is made 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, and a protective layer 5 are formed in this order.

The protective layer 3 and the protective layer 4 are disposed to sandwich the recording layer 2, and are made of an organic polymer material, such as a thermoplastic resin such as PMMA or boristyrene, or an ultraviolet curing resin (so-called 2
P resin) or SiO■, A12 0q, AIN, Zn
S, or ZrO. It is formed of a dielectric material such as These protective layers 3.4 have the function of preventing the recording layer 2 from being affected by moisture in the air, and prevent the irradiated portion of the recording layer 2 from being scattered by a light beam such as a laser beam during recording or erasing. It has a function of preventing the formation of holes or a function of controlling the temperature of the recording layer. These protective layers 3 and 4 can be suitably formed by a coating method, a vapor deposition method, a sputtering method, or the like. In addition,
The thickness of these protective layers 3.4 is preferably 10 μm to several tens of μm.

The protective layer 5 is provided to prevent scratches, dust, etc. on the surface when handling the information recording medium, and is made by applying an ultraviolet curable resin using a subin coating method or the like and curing it by irradiating it with ultraviolet rays. It is formed by etc. This protective layer 5
The layer thickness is preferably from 100 μm to several tens of μm.

Although it is preferable to provide the protective layers 3, 4.5, they do not necessarily have to be provided.

Further, as shown in FIG. 2, a reflective layer 6 may be provided between the protective layer 4 and the protective layer 5. This reflective layer 6 has the function of reflecting the reproduction light beam to increase the reproduction signal through multiple interference, and the function of rapidly cooling the recording layer 2 when recording/erasing information to facilitate overwriting, which will be described later. have. The reflective layer 6 includes Au, A, Q, Cu, Cr,
Metals or alloys such as Ni-C' can be used.

In order to achieve the above function, the thickness of the reflective layer 6 is preferably from several tens of layers to 3,000 layers.

The recording layer 2 is formed of a material that undergoes a phase change between a mixed phase of a non-equilibrium crystal phase and an amorphous phase and a non-equilibrium viscous crystal phase when irradiated with a light beam. Here, the non-equilibrium phase refers to a phase that does not exist in an equilibrium state, such as a metastable phase. Such a phase change is fast and therefore can speed up recording and erasing. Furthermore, such a phase change can be caused with a relatively low power light beam, making it easy to record. Furthermore, recording stability is high. In-Sb-TeSGe-Sb-TeSAu is a material that can undergo such a phase change.
-Sb-Te, Ag-Sb-Te, etc.

When the recording layer 2 is formed of, for example, In-Sb-Te, when it is melted and rapidly cooled by irradiation with a pre-beam, it may become amorphous depending on the quenching conditions, or it may become 1 nM, which is the Hatate temperature phase.
There are cases where the S b T e 2 ternary compound appears as a non-equilibrium phase. In-Sb-Te alloy inherently has a high crystallization rate, and this amorphous and In3SbTe2
Since the phase change between the ternary compound (non-equilibrium crystal phase) and the ternary compound (non-equilibrium crystal phase) is extremely fast, the composition of the recording layer is set to In. By using SbTe2, initialization, recording, and erasing can be made faster. The composition of the recording layer is In. In the case of SbTe2,
Since the crystal phase of this composition is extremely stable, extremely high power light beam irradiation is required to form an amorphous phase. Moreover, strictly adjusting the In3 SbTe2 ternary compound composition is disadvantageous from the viewpoint of reproducibility. On the other hand, by adjusting the composition of In-Sb-Te,
Roughing can be carried out between the mixed phase of the In3 SbTe2 binary compound and the amorphous phase and the In3 SbTe2 ternary compound phase. This phase change is caused by the above-mentioned amorphous and In3
It is possible to eliminate the disadvantages of phase change between SbTe2 and the ternary compound, and moreover, it is extremely fast. Therefore, initialization, recording, and erasing can be speeded up. Additionally, this alloy has high stability in the mixed state. By utilizing such a phase change, recording and erasing can be performed over a relatively wide range of groups in the In-Sb-Te alloy.
(2) Recording and erasing is possible by irradiating a low-power light beam. That is, it is extremely easy to record and erase information.

This recording layer 2 can be suitably formed by a vapor deposition method, a sputtering method, or the like. Note that when performing vapor deposition or sputtering using an alloy target, it is necessary to take into account that there is a difference between the target composition and the composition of the film actually formed.

Further, a film can also be formed by simultaneous multi-dimensional vapor deposition or simultaneous multi-dimensional sputtering. The thickness of the recording layer 2 is preferably 100 to 3000 μm.

Next, an example of a method for forming a recording layer of an information recording medium according to this length embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a vertical cross-sectional view showing a schematic configuration of a sputtering apparatus used to form the recording layer of this example, and FIG. 4 is a cross-sectional view thereof. In the figure, 10 indicates a vacuum vessel, and this vacuum vessel 10 has a gas introduction boat 1 on its bottom surface.
1 and a gas discharge boat 12. Gas exhaust port
The exhaust system t12 is connected to an exhaust system 13, and this exhaust system t
The inside of the vacuum container 10 is evacuated via the exhaust port 12 by the xtl3. Further, the gas introduction port 11 is connected to an argon gas cylinder 14, and argon gas as a sputtering gas is introduced from the cylinder 14 into the vacuum vessel lo via the gas introduction boat 11. At the top of the vacuum container 1o, there is a batten-shaped quadrilateral base 15 for supporting the substrate.
is arranged with its surface horizontal, and the substrate 1 is supported on the lower surface thereof and is rotated by a motor (not shown). Further, in the vicinity of the bottom of the vacuum chamber 1o, sputtering sources (targets) 2 each formed of the elements constituting the recording layer are placed so as to face the base 15.
1, 22, and 23 are arranged, and a high frequency power source (not shown) is connected to each sputtering source. Recording layer 2
When the sputtering sources 21, 22, and 23 are formed of InSb-Te ternary alloy, the sputtering sources 21, 22, and 23 are formed of In and SbTe, respectively.

Above these sputtering sources 21, 22, 23,
Monitor devices 24, 25, and 26 are provided respectively, and these monitor devices monitor the amount of sputtering from each sputtering source and adjust the amount of power input to each sputtering source so that the recording layer has a predetermined composition. It looks like this.

In such a sputtering apparatus, first, the inside of the vacuum chamber 10 is evacuated to, for example, 10-' Torr using an exhaust device. Next, while introducing argon gas into the container 10 via the gas introduction boat 11, the exhaust amount of the exhaust device 13 is adjusted to maintain the inside of the vacuum container 10 in an argon gas atmosphere at a predetermined pressure. In this state, while rotating the substrate 1, a predetermined power is applied to the sputtering sources 21 and 22 for a predetermined running time. As a result, a recording layer having a predetermined composition is formed on the substrate 1. Note that when forming the protective layer, prior to forming the recording layer 2, the protective layer 3 is formed on the substrate 1 by sputtering as described above using a sputtering source adjusted to the composition of the protective layer. In the case where the recording layer 2 is then formed and the protective layer 3 is formed, the protective layer 4 can be formed on the recording layer 2 under the same conditions as l and i1.

Further, when forming the reflective layer 6, sputtering is performed in the same manner using a sputtering source made of the material of the reflective layer 6.

Next, initialization, recording, erasing, and reproduction of information in the information recording medium of the present invention will be explained.

The initialized recording layer 2 is usually amorphous immediately after forming a film, but in order to record information, it needs to be crystalline, so the entire surface of the recording layer 2 is irradiated with a light beam such as a laser beam to gradually heat it. Cool and crystallize the recording layer 2. The light beam irradiation at this time is carried out at a power level such that the recording layer 2 becomes a non-hybrid crystalline phase.

A light beam with high recording power and short pulse width is irradiated onto the recording layer 2,
The irradiated area is heated and rapidly cooled to change the phase from a nonequilibrium condensed phase to a mixed phase of a nonequilibrium crystalline phase and an amorphous phase, thereby forming a recording mark.

A light beam having a lower output and a longer pulse width than that used during recording is irradiated onto the recording mark portion formed on the erasing recording layer 2 to change the phase of the recording mark portion into a crystal, thereby erasing information. The light beam irradiation at this time is performed at a power level such that the recording mark portion becomes a non-plain crystal phase.

A relatively weak light beam is irradiated onto the recording layer 2 on which reproduced information has been recorded, and the information is read by detecting the difference in optical characteristics, such as reflectance, between the recorded mark portion and the non-recorded portion.

The information recording and erasing method according to this invention is +1
It is possible to apply it to T-beam overwriting. llj-beam overwriting is to power-modulate the laser beam emitted from the tit- light source between the erase level PFL and the recording level PW, as shown in FIG. 5, to create a light beam at the erase power level. This involves superimposing pulses at the recording power level to erase previously recorded information while overwriting new information.

The reason why this invention can be applied to single beam overwriting is that the transformation in this method is performed at high speed. That is, in the case of single beam overwriting, recording and erasing are performed only by modulating the power of the beam, so high recording and erasing speeds are required.

Therefore, a high phase change rate is required.

Incidentally, single beam overwriting can be further facilitated by forming the medium into the layered structure shown in FIG. 2, providing the protective layers 4 and 5 with a heat insulating function, and providing the reflective layer 6 with a rapid cooling function. can. In other words, the heat insulating function of the protective layer facilitates erasing, and the rapid cooling function of the reflective layer ensures amorphization, thereby facilitating lli-beam overwriting.

Furthermore, it is also possible to perform multi-level recording in which the power or pulse width of the light beam during recording is varied in several stages, and the reflection speed of the recording mark is set in multiple stages.

Next, test examples of the present invention will be explained.

Test Example 1 An optical disk sample having the layer structure shown in FIG. 1 and having a recording layer made of an In-Sb-Te ternary alloy was produced. In the equilibrium phase diagram of the In-Sb-Te ternary system, 435℃
At higher temperatures, an In3 SbTe2 ternary compound appears. The range in which this high temperature phase appears is I n q T
e 7, InSb, Sb, Ini Tea is reported to be a certain range (Z. Mcta
l l kdcBd. 71 (1.980)H. 9)
. In this test example, the recording layer set was IniSbT.
I n tb. which is the neighborhood composition of the e2 ternary compound. ,S
A sample was prepared at b 34 and T e 30.

Regarding this sample, a semiconductor laser beam with a wavelength of 830 tv with various pulse widths was irradiated from the substrate side at a constant intensity onto the recording layer using an objective lens, and the structure of the irradiated area was examined using a transmission electron microscope ( TEM). The results are shown in FIG. FIG. 6 is a diagram showing the state of the irradiated portion, with the horizontal axis representing the pulse width of the irradiated laser beam and the vertical axis representing the laser beam intensity. In this diagram,
Region A is a region in which the irradiated portion has become amorphous, and region C is a region in which the irradiated portion has become a crystalline phase in an equilibrium phase.

Further, region D is a region where the crystalline phase of the equilibrium phase is formed after melting, and region B is a region where film destruction has occurred.

In addition, region ■ is a region where a high-temperature phase of In3SbTe2 ternary compound (non-equilibrium phase) has appeared, and region M is a region where In3SbTe2 ternary compound (non-equilibrium phase) has appeared.
This region is a mixed phase of a Te2 ternary compound (non-equilibrium phase) and an amorphous phase.

Conventionally, between A2 and C2 or between A3 and . Information has been recorded by utilizing the phase change between I3, that is, the phase change between an amorphous state and an equilibrium phase crystal, or between an amorphous state and a nonequilibrium phase crystal. On the other hand, in this invention, Ml-11 in the figure
Utilizing the phase change between That is, the present invention utilizes a phase change between a mixed phase of a non-equilibrium I n3 SbTe2 crystal and an amorphous phase and a non-equilibrium I n3 SbTe2 crystal phase. As is clear from FIG. 6, the recording and erasing method of the present invention has a wider operating range than the conventional method. It is possible to operate with wider and shorter pulses, and it is possible to record with lower power than the A3 and I3 variations. In other words, it has been confirmed that recording and erasing can be performed at higher speed and with lower power than before.

Test Example 2 The dynamic recording characteristics of the sample used in Test Example 1 were evaluated. In this test example, overwriting was performed between power levels A2 and C2 in FIG. 6, and overwriting was performed between power levels M1 and I1.

The sample overwritten in this way was heated to 8
The sample was placed in a constant temperature and humidity chamber at 5°C and relative humidity of 85%, and an accelerated deterioration test was conducted. FIG. 7 shows the change in C/N of the reproduced signal at that time. In FIG. 7, ×−× indicates the C/N change of the sample overwritten between A2 and C2,
〇1〇C shows the C/N change of the sample overwritten between M1 and I1. As shown in this figure, A2 and C
The sample overwritten between M1 and M1 had a large deterioration in C/N, and the sample overwritten between M1 and M11 had a small deterioration in C/H. In other words, In3 S
Compared to the recorded state when changing between the Ilj phase of the bTe2 nonequilibrium phase and the amorphous phase, the difference between the In3 SbTe2 nonequilibrium phase and the mixed phase of the amorphous phase and the In,SbTe2 nonequilibrium phase It was confirmed that the recording state when the phase was changed was more stable.

[Effects of the Invention] According to the present invention, information is recorded and erased by causing phase envelopment between a mixed phase of a non-equilibrium phase and an equilibrium phase and a non-equilibrium phase by irradiation with a light beam. Recording and erasing can be performed at high speed, and information can be recorded and erased using a relatively low power beam. Furthermore, the operating range for recording and erasing is wide, and recording stability is high.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing an information recording medium according to an embodiment of the present invention, FIG. 3 is a vertical cross-sectional view showing a schematic configuration of an apparatus for forming a recording layer, and FIG. 4 is a cross-sectional view thereof. Figure 5 is a diagram showing the laser power during overwriting, Figure 6 is a diagram showing the state of the irradiated area when the laser beam irradiation conditions on the recording layer are changed, and Figure 7 is the diagram in the acceleration test. It is a graph diagram showing deterioration of C/H. 1; Substrate, 2; Recording layer, 3, 4.5. Protective layer, 6: Reflective layer

Claims (1)

[Claims] The irradiated area differs depending on the substrate and the light beam 2.
A method for recording and erasing information on an information recording medium having a recording layer that changes phase between two phases, wherein the recording and erasing of information is performed by non-conforming that occurs in the beam irradiated area when the recording layer is irradiated with a light beam. A method for recording and erasing information, characterized in that the method is performed by a phase change between a mixed phase of an equilibrium crystalline phase and an amorphous phase and a non-equilibrium crystalline phase.