JPS61156544A - Optical recording medium - Google Patents

Abstract

PURPOSE:To record with high density only by the irradiation of a light pulse on a thin film, to erase and record when needed, and further to retain information for a long period by using an alloy consisting of bismuth, gallium, and a specified additive as an optical recording film. CONSTITUTION:The optical recording film of an optical recording medium is formed with an alloy consisting of bismuth, gallium, and an additive, and the ratio of the numbers of atoms of bismuth to gallium is regulated to 1:0.6-1.5. The additive consisting of one or >=2 kinds among aluminum, silicon, phosphorus, sulfur, germanium, arsenic, selenium, silver, cadmium, indium, tin, antimony, tellurium, thallium, and tin, and the ratio to the whole alloy is adjusted to 0-20atom%. The quantity of the light reflected from a recording film 7 is obtained as the sum signal of 4 detectors, and used for reproducing information. When information is recorded, a modulation current for modulating the intensity of a laser diode 1 is overlapped on the laser diode 1 by the signal to be recorded. When information is erased, a DC light beam is irradiated on the desired recorded part.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a medium for optically recording information, such as an optical disk, and in particular to a medium for optically recording information, such as an optical disk, and particularly for recording optical information that can be used to erase previously recorded information and record new information. Regarding recording media.

2. Description of the Related Art Optical information recording is attracting attention as a promising information recording method in the future because of its high recording speed and density. Conventionally, as an optical information recording medium, firstly, there is one in which information is recorded by irradiating a metal thin film with a laser beam and forming minute holes in the irradiated area. However, this medium has a limitation in that although it is possible to record information, it is impossible to erase and record information. Therefore,
Second, as a recording medium that can not only optically record information but also erase and re-record information,
Using an amorphous semiconductor thin film such as Ge+s Sz P z, its two structural states, namely, a stable high-resistance state (this is a so-called amorphous state in which the arrangement of atoms or molecules is disordered) It is known that information can be recorded, erased, and rerecorded by reversibly changing between the state of Kosho 47-2
(See Publication No. 6897).

Problems to be Solved by the Invention However, since the above erasable recording medium uses Li in a disordered atomic arrangement (amorphous state) on one side, it inherently suffers from instability in information retention. was. This is because the amorphous state is a metastable state that leads to the crystalline state, and because it easily transitions to the crystalline state by application of thermal energy or chemical energy, information is easily lost.

In addition, since the material is used to transition between states with large differences between amorphous and crystalline, fatigue of the material occurs during repeated recording and erasing, resulting in the number of possible repetitions of recording and erasing. The disadvantage is that there are few

Means for Solving the Problems The object of the present invention is to provide a new optical recording medium that can record information by irradiating light pulses, erase already recorded information when necessary, and stably retain information. It is about providing.

In order to achieve the above object, the present invention is directed to a thin film consisting of an aggregate of microcrystals with a regular atomic arrangement, but in which two or more stable states with different optical properties exist. By irradiating two types of light pulses with different powers and time widths, information is recorded in one of the two stable states.

We have already developed an alloy consisting of indium and antimony, as well as an alloy consisting of indium and antimony, as well as an alloy consisting of indium and antimony, as well as aluminum, silicon, and phosphorus, as an optical recording medium that performs recording and erasing between two crystalline states. , sulfur, zinc, potassium, germanium, arsenic, selenium, silver.

Disclosed a medium using an optical recording thin film made of an alloy containing one or more of cadmium, tin, tellurium, thallium, lead, bismuth, etc. information storage medium).

Upon further investigation, it was discovered that similar optical recording could be achieved in an alloy system consisting of bismuth and gallium, leading to the present invention.

That is, the optical recording film of the optical recording medium of the present invention is made of an alloy consisting of bismuth, gallium, and an additive, and the atomic ratio of bismuth and gallium is I: 0.6 to 1.5, and the additive is aluminum. (AI), silicon (Si), phosphorus (P), sulfur (S), zinc (Zn), germanium (
Ge), arsenic (As).

Selenium (Se), silver (Ag), cadmium (Cd).

Indium (In), tin (Sn), antimony (Sb)
), tellurium (Te), thallium (TI).

It is composed of one or more types of lead (Pb'') and is contained in an amount of 0 to 20 atomic % with respect to the entire alloy.

The two stable states with different optical properties for recording information in the recording thin film of the present invention are both crystalline. It utilizes the transition between two stable states that are both crystalline but have different optical properties. Here, when a thin film is called crystalline to distinguish it from amorphous, it means that the dimensions of the region where the thin film has a regular atomic arrangement (microcrystal grain size) are small (
Both refer to those with a diameter of about 5 nm or more, usually 20 to 3 Qnm or more.

The two stable states of the microcrystalline recording thin film in the present invention can be reversibly transitioned by irradiation with light pulses under appropriate conditions, so even once recorded, it cannot be erased. It can be used over and over again.

These two stable states of microcrystalline thin films generally have high electrical conductivity, but there is no essential difference between their electrical conductivities (in contrast, the amorphous state has a higher electrical conductivity than the crystalline state). conductivity is inherently low).

However, the stable states of the two crystalline states of this microcrystalline thin film have slight differences in optical properties, such as light reflectance and light transmittance. can be identified as the difference. Also,
The two stable states are accompanied by slight changes in volume and deformation of the film shape, so they have the effect of equivalently increasing the optical difference.

This recording medium does not utilize the change between amorphous and crystalline states. Since the amorphous phase is a metastable phase, it gradually transitions to a crystalline phase due to thermal action over a long period of time, so when the difference between these two phases is used to record information, information is likely to be lost. In contrast, in the present invention, information is stably retained for a long period of time because a transition is made between two states in a thermodynamically stable phase called a crystalline phase.

Such thin film materials as glass and plastic.

To form a film on a substrate made of metal or the like, raw material components may be alloyed on the substrate by co-evaporation, co-sputtering, or co-ion blating, or the alloyed raw material may be vapor-deposited or speckled.

A thin film formed in this manner generally has a disordered atomic arrangement and is amorphous, but by heating or irradiating it with light, the entire thin film or only the recording portion of the thin film can be crystallized.

An example of an optical system for recording information using the recording medium of the present invention is shown in FIG. This is exactly the same as that used in conventional write-once optical discs.

Light is emitted from the laser diode 1 (wavelength usually 780 ~
830 nm) 2 passes through a beam shaping optical system 3, a deflection beam splitter 4, and a 174 wavelength plate 5, and is focused by an objective lens 6 and irradiated onto a recording thin film 7. In the figure, 8 is the substrate, 9
is the lens actuator.

The reflected light is laterally bent by a polarizing beam splitter 4 and impinges on a photodetector 11 through a lens 10. The photodetector 11 is divided into four parts, and the difference in the signals of the diagonal components represents the degree of defocus of the irradiation beam.

Normally, the laser diode 1 emits DC light with a power of about 1 mW on the recording film surface 7, and the objective lens uses the reflected light from the recording film 7 to constantly focus the light beam on the film surface. The actuator 9 is controlled. The amount of reflected light from the recording film 7 is obtained as a sum signal of the four detectors, and is used to know the signal recording state of the recording film 7, that is, to reproduce information.

When recording information, a modulation current for intensity modulating the laser diode 1 is superimposed on the laser diode 1 according to the signal to be recorded. Furthermore, when erasing information, a direct current light beam is irradiated onto a desired recorded area. In this case as well, the optical power necessary for erasing is superimposed on the reproduction light beam.

Generally, stronger power is required when recording than when erasing.

Furthermore, erasing may not be completed with one light beam. This is because it takes a certain amount of time to change the thin film to the erased state. In that case, a complete erased state can be obtained by irradiating the same location with the eraser beam many times (multiple times).

Although not used in the example in Figure 1, two laser light sources are provided, one of which has the same configuration as in Figure 1, and the other beam is elongated in the circumferential direction on the thin film surface ( ~
It is also possible to use an optical system that irradiates the information with a shape of about 10 μm). In that case, the long beam is used exclusively for erasing, and complete erasure of information can be achieved with only -times of irradiation.

The power conditions of the light beam used during recording and erasing vary depending on the diameter of the plate and the number of revolutions, that is, the speed of the recording thin film.

Furthermore, as the reflectance changes, the transmittance also changes slightly.

Laser light, which is coherent light, is preferable as recording and reproducing light, but its wavelength is not limited to semiconductor laser light, but may also be He-Ne laser light, He-Cd laser light, Ar laser light, or others. .

We conjecture that the change in reflectance between the two states of the crystal structure is due to the following causes.

In the B1Ga alloy, Bi or Ga precipitates in the thin film depending on the light irradiation conditions, and the rate of the precipitation varies depending on the light irradiation conditions. Since the light reflectance of the B1-Ga alloy is different from that of Bi or Ga, the light reflectance of the entire thin film also changes reversibly depending on the light irradiation conditions and the amount of precipitated Ga.

Furthermore, although the thin film is in a crystalline state, two states in which the reflectance is apparently at a limit may be generated in addition to the above-mentioned possibilities. Another possibility is that the grains have different sizes and therefore different abilities to scatter light, leading to differences in reflectance.

Furthermore, a change in the shape of the thin film may cause the state of light scattering to vary. The light scattering effect clearly differs depending on whether the surface of the film is flat or deformed into a concave or convex lens shape.

Another possibility is that even though the film is crystalline, different crystal phases may be generated due to differences in the cooling process of the film. For example, when a strong and short light pulse is irradiated, the film melts but is rapidly cooled, which may result in the appearance of a metastable crystalline phase that cannot be obtained through the normal melt-cooling-solidification process.

As mentioned above, although various causes are conceivable, the result is that the reflectance or optical characteristics apparently change even though it is a crystalline body.

Example (Example 1) - Referring to FIG. 2, an alloy thin film 22 of Bi and Ga is formed by vacuum evaporation on an acrylic substrate 21 with an outer diameter of 30 cm and a thickness of 1.2 ma+. . The temperature of the vapor deposition source for each component is independently controlled, the substrate is rotated, and the rate of the component during vapor deposition is controlled to be approximately constant. The thickness of the formed thin film was 90 nm. Furthermore, a protective film 23 of organic polymer is formed thereon. The material may be any material as long as it does not have an adverse effect on the old Tj2Tl recording film; for example, it may be a thermoplastic resin such as PMMA or polystyrene, a thermosetting resin such as an epoxy resin, or an ultraviolet curing resin. As shown in FIG. 3, a very thin inorganic material (for example, 5iOz, CeO, Zn5) is used as a stabilizing layer 24 between each layer 21, 22, 23.
) may be inserted.

Tomotan ■Patients■ The medium thus prepared was evaluated in the following manner. While the disk is stationary, two types of laser light pulses with different power and pulse width are alternately irradiated with a semiconductor laser (830 nm) light focused to 1 μm using a colinate lens and an objective lens using an optical head. Measure the reflectance using a laser beam.

In this method, 15 mW, 200 ns laser light and 5 d
.

It was found that there was a difference in reflectance after irradiation with a 1 μs laser beam. The reflectance changes reversibly, increasing with high power short pulses and decreasing with low power long pulses. When the composition dependence of the alloy thin film was investigated, B
The reflectance changed reversibly within the range of i from 15 to 70 at.%. However, in areas with a large amount of Ga, patterns that appear to be due to segregation of Ga were observed under a microscope, and this was not suitable for practical use.
The appropriate range where no segregation occurs is 40 to 70 at% Bi.
It turned out to be.

The recording film was peeled off from the above-described divided disk, and the crystal structure of the film was examined using an electron microscope.

First, in the unrecorded area where no laser beam irradiation was performed after film formation, no electron diffraction due to the regular arrangement of crystals was observed, and a halo pattern characteristic of amorphous materials was observed. When we observed the part where the reflectance was lowered by multiple light pulse irradiations and the part where the reflectance increased again by strong pulse irradiation, we found that both were in a crystalline state. Observation using this electron microscope revealed that the recording film does not record information through a phase transition between crystal and amorphous (or a disordered crystal state B similar to the state after film formation), but rather through a crystallized state. It was later discovered that information is recorded through state changes between crystals.

In addition, observation using a scanning electron microscope revealed slight irregularities in the irradiated areas and the film.

Furthermore, it was confirmed that the direction of the unevenness was opposite between the recorded part and the erased part.

To investigate the durability of this medium, the medium was vapor-deposited on a slide glass, crystallized by heating at 200°C for 30 minutes, and tracks were placed on one without a protective film and one with the disk substrate formed on it. 60°rpm, 2MII
The disc recorded with Z was kept at 70°C and 85% RH, and the change in reflectance of the medium on the slide glass and the C of the disc were observed.
/N change was measured.

The results are shown in FIGS. 4 and 5, respectively.

As seen in the figure, there was little change in reflectance even after 3 months had passed, even in the medium without a protective film, and the C/N drop was less than 3 dB.

(Example 2) Additives were added to the BiGa medium and their effects were observed.

A medium in which Se was added to the total amount of 5.10.20 atomic % was evaluated by the method of Example 1. As a result, G
Even in a composition with a large amount of a, segregation of Ga no longer occurs. As shown in Figure 6, the area where segregation does not occur increases, and it is found that this is helpful for stabilization.

In FIG. 6, the ◯ mark indicates that no segregation occurs, the x mark indicates that segregation occurs, and the hatched area indicates that no segregation occurs.

Si, P, S, Ge, A instead of Se
Similar results were obtained when s was added.

(Example 3) A recording medium was created in which the atomic ratio of Ga and Bi was kept constant (40:60) and Zn was added at 5.10.20 atomic % based on the whole, and the method of Example 1 was performed. It was evaluated by The table below shows the reflectance contrast obtained by dividing the amount of change in reflectance by the reflectance in the high reflectance state.

It can be seen from the table that the contrast increases with the addition of Zn.

Al, Ag, Cd, Sn, Pb in place of Zn.

Similar results were observed when Te, Sb, and In were added.

(Example 4) A recording medium in which the atomic ratio of Bi and Ga was kept constant (40:60) and As was added to the total amount of 5.10.20 at.% was evaluated using the method of Example 1. .

At that time, only the power of the high-power, short-pulse laser light was varied to determine the contrast in reflectance. The results are shown in FIG. 7, and as seen in the figure, the addition of As improved the sensitivity of the recording medium.

Similar results were obtained when In, Pb, and Sn were added instead of As.

Effects of the Invention According to the present invention, it is possible to record at high density simply by irradiating a thin film with a light pulse, and also to be able to erase and re-record when necessary, and to retain information stably for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an optical system of an optical information storage and reproducing method according to the present invention, FIGS. 2 and 3 are sectional views of essential parts of an optical information recording medium for implementing the present invention, and FIG. The figure is a graph showing the long-term change in reflectance of the B1Ga thin film, Figure 5 is a graph showing the long-term change in the C/N ratio of the B1Ga thin film, and Figure 6 is a graph showing the long-term change in the reflectance of the B1Ga thin film. Bi −Ga indicating whether segregation of G″a occurs
-Se ternary phase diagram, FIG. 7 is a graph showing the contrast when As is added to the B1Ga thin film. 1 - Laser diode, 2 - Light, 3 - Beam shaping optical system, 4 - Polarizing beam splitter, 5 - 1/4 wavelength plate, 6 - Objective lens, 7 - Recording thin film, 8 - Substrate, 9 --Lens actuator, l〇--Lens, 11--Photodetector, 21-Acrylic substrate, 22--(nSb thin film, 23-Organic protective film, 24--Inorganic stabilizing layer.

Claims (1)

[Claims] 1. By irradiating a recording thin film made of microcrystals that can assume two stable states with different crystal structures and different optical properties with light energy under different conditions to selectively cause the above two stable states. An optical recording medium for recording and/or erasing information, wherein the optical recording film is made of an alloy of bismuth, gallium, and an additive, and the atomic ratio of bismuth and gallium is 1:0.6 to 1.5. and the additive is one of aluminum, silicon, phosphorus, sulfur, zinc, germanium, arsenic, selenium, silver, cadmium, indium, tin, antimony, tellurium, thallium, and tin.
consisting of one species or two or more species, and 0 to 0 to the entire alloy
An optical recording medium characterized in that the content is 20 atomic %.