JPH01100747A - Information recording medium - Google Patents

Abstract

PURPOSE:To stably maintain recorded information and to heighten a reproduction signal level by forming a recording layer of a specifically composed alloy. CONSTITUTION:The recording layer 2 is formed on a substrate 1. The recording layer 2 is formed of the alloy having the compsn. expressed by the general formula (Sb100-xTex)100-yMy, where x, y are respectively in 20<=x<=80, 0<y<=20 range by atom.%, and M is at least one kind of the element selected from Al, Mg, Zn, Cd, and Ga. The alloy having such compsn. range is changeable in phase between the crystalline state and the amorphous state and is stable in the amorphous state. The recording part of the information is thereby stably maintained and reproduction signals can be increased.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention provides optical and optical effects on the light beam irradiated portion of the recording layer by irradiating the recording layer with a light beam such as a laser beam. The present invention relates to an information recording medium such as a so-called erasable optical disk, which records and erases information by causing a change in characteristics, and reproduces information by detecting the optical characteristics.

(Prior Art) Erasable type information recording media that can record and reproduce information as well as erase information have conventionally been made of glass or plastic materials (for example, acrylic resin such as polymethyl methacrylate). It consists of a substrate and a recording layer made of the material described below, which is formed on the substrate by vapor deposition, sputtering, or the like. This recording layer is formed of a thin film of a metal or semimetal such as Te, Se, Ge, Sb, or an alloy thereof, and has a composition of, for example, Ge15Teg5. In this case, if necessary, 5
i02. A protective layer made of a transparent dielectric material such as AIN is provided to protect the recording layer from oxidation and the like.

Recording and erasing information on such optical recording media is
Conventionally, this is done as follows. First, the entire recording layer is heated and slowly cooled by irradiating the entire surface with a light beam to bring the entire recording layer into a crystalline state in which crystals are regularly arranged. Next, the recording layer is irradiated with a light beam for writing information. Pulsed light with high output and short pulse width is used as the light beam for writing, and the area irradiated with the light beam is thereby heated and rapidly cooled.

The part becomes a so-called amorphous state in which the crystal structure is disordered.

In such an amorphous state, the reflectance is lower and the transmittance is higher than in the crystalline state, so this means that information is recorded, and by detecting the difference in reflectance etc. Can read information. When erasing information, the information recording portion of the recording layer is irradiated with a light beam having a relatively low output and a long pulse width, and the portion is heated and slowly cooled to change from an amorphous state to a crystalline state.

That is, in the conventional erasable type information recording medium, information can be recorded and erased using a reversible phase change between a crystalline state and an amorphous state.

(Problems to be solved by the invention) However, the conventional information recording medium as described above,
The information recording part is in an amorphous state, but since the amorphous state is a metastable state that leads to a crystalline state, it usually changes easily to a crystalline state by adding energy and is unstable. There is a drawback. Therefore, there is a risk that the previously recorded information may be damaged. In addition, in conventional information recording media, the difference in reflectance between the recorded portion and the non-recorded portion of the recording layer, that is, the contrast, is not sufficient, and the reproduced signal level may be too low. There is a desire for an information recording medium that has a greater contrast with non-recorded portions.

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 that can stably hold recorded information and has a high reproduction signal level.

[Structure of the Invention] (Means for Solving the Problems) An information recording medium according to the present invention has a substrate and a recording layer that undergoes a phase change when irradiated with a light beam, and the light beam based on the phase change. An information recording medium in which information is recorded and erased by an optical change in an irradiated part and the information is read by detecting the optical change, the recording layer being formed of an alloy having a binding margin % formula %, X + y is 3 at % each
Within the range of 0≦X≦80, Q<y≦20, and M is AI
, Mg, Zn, Cd, and Ga.

(Function) When the recording layer is formed with the above-mentioned composition, a phase change occurs between a crystalline state and an amorphous state by irradiating the recording layer with a light beam. In this case, by setting two different light beam irradiation conditions, it is possible to enter either a crystalline state or an amorphous state, so these changes are reversible, thereby recording and erasing information. be able to. In this case, in the case of the above-mentioned composition, the structure is extremely stable even in an amorphous state.

Therefore, recorded information can be stably held. Furthermore, the element represented by M has the effect of increasing the difference in reflectance between the information recording portion and the non-recording portion of the recording layer, thereby increasing the reproduction signal level.

(Embodiments) Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a sectional view schematically showing an information recording medium according to an embodiment of the present invention. The substrate 1 is made of a transparent material that does not change much over time, such as acrylic resin such as polymethyl methacrylate or glass. A recording layer 2 is formed on this substrate 1. This recording layer 2 has the general formula (S b +oo-8T ex )
It is formed of an alloy with a composition expressed as
≦20, and M is at least one element selected from Al, Mg, Zn, Cd, and Ga.

Alloys in this composition range can undergo phase changes between crystalline and amorphous states and are stable in the amorphous state. The 5b-Te alloy, which is the main component of the recording layer 2, can change between its crystalline state and amorphous state when the Te content ranges from 100 atomic %. However, if Te exceeds 80 atomic%, the reflectance of the information recording portion (hereinafter referred to as a recording mark) changes over time, making the recording mark unstable, and if Se is less than 20 atomic%, the sb A striped pattern occurs due to segregation. Therefore, the composition of the 5b-Te alloy is defined within the above range. Further, as mentioned above, this recording layer 2 includes AI,
At least one element selected from Mg, Zn, Cd, and Ga is contained in a content of 20 atomic % or less. These elements have the effect of increasing the contrast between the recorded state and the non-recorded state of the recording layer, thereby increasing the reproduced signal. If the content of these elements is within 20 at%, the structure of the 5b-T'e alloy is not impaired and the phase can change between the crystalline state and the amorphous state, but if the content exceeds 20 at% In this case, the structure of the 5b-Te alloy will be damaged, making it impossible to obtain the desired phase change. Therefore, the content of these elements is 20 atoms, 96
The following shall apply. This recording layer 2 can be formed by a vacuum evaporation method or a sputtering method.

A protective layer 3 is formed on the recording layer 2.

The protective layer 3 is made of a thermoretroactive resin such as polymethyl methacrylate or polystyrene, or an ultraviolet curing resin (so-called 2p resin), and has the function of preventing the recording layer 2 from being damaged. ing. In addition, this protective layer 3
In some cases, oxides such as 5i02, Al2O3, etc.
Alternatively, it can also be formed from a nitride such as AIN. This protective layer 3 can be formed by a spin coding method, a vapor deposition method, a sputtering method, or the like. The thickness of this protective layer 3 is preferably about 200 μm to several tens of μm.

FIG. 2 is a sectional view schematically showing an information recording medium according to another embodiment of the present invention. This embodiment is the same as that shown in FIG. 1 except that dielectric protective layers 4 and 5 are provided to sandwich the recording layer 2.

That is, a dielectric layer 4, a recording layer 2, and a dielectric layer 5 are disposed on a substrate 1.
and the protective layer 3 are laminated in this order.

This dielectric layer 4.5 has the function of preventing the recording layer 2 from scattering or forming holes due to laser beam irradiation, and also has the function of preventing the recording layer 2 from being exposed to moisture when an acrylic substrate is used, for example. It has a function to prevent it from being affected. The dielectric layers 4 and 5 are made of SiO□ or AIN, and like the recording layer 2, they can be formed by sputtering or the like. The dielectric layers 4 and 5 preferably have a thickness of about 10 to several tens of μm.

Next, initialization, recording (writing), reproduction (reading), and erasing of such an information recording medium will be explained. The information recording medium of this embodiment is irradiated with a light beam such as a laser beam from the substrate l side to record, reproduce, and erase information.

Since the recording layer 2 immediately after initialization film formation is normally in an amorphous state, the recording layer 2 is brought into a crystalline state. In this case, for example, the recording layer 2
The entire recording layer 2 is heated and slowly cooled by sequentially irradiating the recording layer 2 with a light beam,
Change to crystalline state.

An amorphous recording mark is formed by irradiating the recording layer 2 with a pulsed light beam of high output and short width, heating and melting the irradiated area, and then rapidly cooling it.

Information is read by irradiating a light beam with a low output onto the recording layer 2 on which reproduction/recording marks have been formed and detecting the intensity of the reflected light. That is, since the intensity of the reflected light differs between the recording mark in the amorphous state and the other portion in the crystalline state, information can be read by detecting the difference in the intensity of the reflected light.

The recording mark portion of the erasing recording layer 2 is irradiated with a pulsed light beam having a smaller output and a longer width than the light beam used during recording.

As a result, the recording mark is heated and slowly cooled to change into a crystalline state, and the information is erased.

Next, a test example in which the information recording medium of this example was actually produced and tested will be specifically explained.

Test Example 1 A polymethyl methacrylate substrate having an outer diameter of 130 cm and a thickness of 1.2 nv was prepared, thoroughly cleaned, and then placed in a sputtering device. An sb target, a Se target, and a target of an element represented by M were prepared in this sputtering apparatus, and a recording layer was formed on the substrate by simultaneous sputtering of these. During this sputtering, the substrate was rotated so that these elements were uniform and the sputtering rate was constant. In this case, a plurality of samples were created in which the composition of the target was varied and the composition of the recording layer was varied. The thickness of the recording layer at this time was 1000 layers. In these samples, an ultraviolet curable resin was spin-coded on the recording layer and cured by irradiating it with ultraviolet light.
A protective layer was formed. The information recording medium samples prepared in this way were placed on the spindle, and while the samples were kept stationary, a semiconductor laser with a wavelength of 830 nm was applied.
The recording layer of each sample was irradiated with a beam shape focused to about 1 μm side using the collimator lens of the optical head and the objective lens optical head. As a result, the recording layers of all samples were in an amorphous state, but all the parts irradiated with the semiconductor laser beam changed to a crystalline state.

Next, in order to evaluate the possibility of rewriting information on these information recording medium samples, that is, the possibility of recording, erasing, and rewriting, we alternately sampled two types of pulsed laser beams with different outputs and pulse widths. 0.1 to 0.2 mW during laser beam irradiation under different conditions.
We irradiated it with a laser beam with a small output and measured the change in reflected light.

First, an output of 10 m was applied to the recording layer in the initial state of each sample.
W and a recording laser beam pulse having a pulse width of 100 nsec was irradiated. As a result, the portion irradiated with the laser beam was heated and rapidly cooled, the structure of that portion changed, and the reflectance became low. As a result of irradiating this portion with an erasing laser beam pulse having an output of 3 m W s and a pulse width of 1 μm, the structure of the irradiated portion changed and the reflectance became high. This reflectance decreased after irradiation with a laser beam with a high output and short pulse width, and increased after irradiation with a laser beam with a small output and long pulse width, and this change in reflectance was reversible. This reversible change occurred in samples with Te in the range of 1 to 100 atomic % in the 5bTe alloy that is the main component of the recording layer, but in samples with Te exceeding 80 atomic %, the reflectance of the recording mark decreased. It changed over time.

In addition, in samples containing less than 20 at% of Te, s
A striped pattern was caused by the segregation of b, which was inconvenient for recording information.

In order to compare the structural differences between the recorded portion with low reflectance and the non-recorded portion with high reflectance, the diffraction patterns of these portions were observed using a transmission electron microscope. When the protective layer was peeled off from the information recording medium sample and the diffraction pattern of the recording layer was taken, a halo pattern characteristic of amorphous materials was confirmed in the initial state without laser beam irradiation. On the other hand, regarding the recorded marks, a halo pattern peculiar to an amorphous state close to the initial state was observed. Also, in the erased part,
A ring and a spot diffracted by the crystal were obtained, and it was confirmed that the crystal was in a crystalline state.

Test Example 2 In this test example, the contrast between the recorded portion and the non-recorded portion of the recording layer was evaluated. The recording layer is Sb40
A sample was prepared in which a recording layer was formed of an alloy containing Te60 and A1 at 5, 10 and 20 atomic percent, respectively. These samples had the same layer structure as Test Example 1 and were produced in the same manner as Test Example 1.

These samples were evaluated for contrast in reflectance between recorded mark portions with low reflectance and non-recorded portions with high reflectance. As a result, the data shown in FIG. 3 was obtained.

FIG. 3 is a graph showing the relationship between the AI content on the horizontal axis and the contrast ratio on the vertical axis. Here, the contrast and ratio are values obtained by dividing the difference between the reflectance in the high reflectance state and the reflectance in the low reflectance state by the reflectance in the low reflectance state.

As shown in this figure, the contrast ratio increased as the A1 content increased, and showed the maximum value at 10 at% AI. That is, it was confirmed that the inclusion of A1 had the effect of increasing the reproduced signal.

Furthermore, similar tests were conducted on samples containing Mg, Zn, Cd, and Ga, respectively, in place of AI, and results similar to those obtained when A1 was included were obtained.

[Effects of the Invention] According to the present invention, the information recording portion can be stably held, and signal deterioration can be extremely reduced.

Therefore, the reliability of the information recording medium can be significantly improved. Furthermore, since the difference in reflectance between the recorded portion and the non-recorded portion is large, the reproduced signal can be increased.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views schematically showing an information recording medium according to an embodiment of the present invention, and FIG. 3 is a graph showing the relationship between the AI content of the recording layer and the contrast ratio. . 1: Substrate, 2: Recording layer, 3: Protective layer, 4, 5: Dielectric layer. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] A recording layer that includes a substrate and a recording layer that undergoes a phase change when irradiated with a light beam, records and erases information by an optical change in the part irradiated with the light beam based on this phase change, and the optical change is In the information recording medium for detecting and reading information, the recording layer has the general formula (Sb_1_0_0_-_xTe_x)_1_0_0_
It is formed of an alloy with a composition represented by −_yM_y,
x and y are in the range of 20≦x≦80 and 0<y≦20 in atomic %, respectively, and M is at least one element selected from Al, Mg, Zn, Cd and Ga. Information recording medium.