JPH036581B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides optical and thermal information having the property that optical density decreases by rapid cooling after heating, and increases optical density by slow cooling after heating. The present invention provides a method of recording a signal by whitening the recording film using a recording member, and completely erasing the desired signal-recorded area by blackening.The recording film meets the following two conditions: The optical properties of the film can be changed by heating and heating with light using an optical/thermal information recording site whose film state changes depending on the combination of the heating temperature and secondly the cooling rate after heating.
This is a method of reversibly changing information and recording and erasing information.

The irradiation light power P _W for recording heats the film, which has been subjected to saturation blackening treatment in advance, and raises the temperature of the minute portion to be irradiated with the spot light to a temperature higher than the melting temperature. When the irradiation time of this spot light is short, less than 1 μsec, the cooling rate of the film temperature after irradiation becomes a rapid condition.
It is defined as one in which the optical density is reduced and a whitening signal can be recorded.

Next, the area containing the whitened recording bits is irradiated with light using continuous light at a constant power level _PE . This power level P _E is the same as P _W or
It is under the conditions of P _E P _W. If the value of P _E is low, the heating temperature in one irradiation is low, but by repeated irradiation, the temperature of the film and base material increases until the temperature exceeds the saturation blackening temperature or the melting temperature. As a result, the cooling rate of the film temperature after irradiation becomes a slow condition, the optical density increases, and the blackening signal can be erased.

As described above, the present invention performs blackening erasing by repeatedly irradiating the area containing the whitened recording bits with light of the power level _PE .

The method of optically recording and reproducing information allows the recording bit diameter to be as small as approximately 1 μmφ, allowing information to be recorded with high density and non-contact reproduction. Applications have recently reached the practical stage.

However, a method for recording and erasing information has not yet been established.

Examples of these are discussed below.

In terms of materials, photochromic materials, thermoplastic resins, ferroelectric materials, etc. are known to have the function of optically recording and erasing, but they require a long response time for recording or have low sensitivity. Therefore, there is a practical limit in that a high-output laser light source is required.

Meanwhile, new methods of optically and thermally recording and erasing information are emerging. It uses phase transitions of substances or changes in the bonding state between atoms to cause changes in optical properties, and a well-known method is to use chalcogenides, that is, to remove oxygen. , a thin film of a compound of elements of group 6 of the periodic table, such as S, Se, and Te, and metals and semimetals.

This is described in Dhys.Rev by SROvshinsky et al.
This method was first reported in Leffers 21 (1968) 1450, and uses a thin film of Ge ₁₅ Te ₈₁ Sb ₂ S ₂ as the material.

These methods of utilizing chalcogenides can be classified into the following two types.

The first method is to convert an amorphous film into a crystalline state and record it.This method involves irradiating a pale brown amorphous film with a minute spot light focused on 1 to μΦ.
After heating and slowly cooling, the film crystallizes and turns black, allowing information to be recorded.To erase the blackened area, the blackened area is again irradiated with a strong laser beam with a short pulse width to whiten it and erase the original information. This is a method to restore the color to a light brown color.

Similarly, a second example using a chalcogenide is a method that uses optical structure change to record an amorphous state instead of another amorphous state. As shown in No. 46464, As−
In a thin film having a composition of Se-Ge-S, irradiation with a visible laser light source, such as an Ar laser,
This is a method of blackening and recording, heating this with an infrared laser beam, etc., and whitening and erasing.

Both methods are relatively simple methods of recording and erasing information using laser light and heat.

In practical use, in the first example that uses crystallization, when an unrecorded light brown amorphous film is irradiated with a laser beam and crystallized by heating to record information, a disordered amorphous film is recorded. It consists of a rearrangement process of atoms from a state to a crystalline state.
It requires heating by light irradiation with a long pulse width of about msec, and is not suitable for high-speed recording (several 100 nsec).

Furthermore, in the erasing process, the blackened recorded area is heated and heated by irradiation with a short light pulse using a strong laser spot beam or the like, thereby whitening and erasing the area.

In this case, the light intensity distribution of the laser spot light is Gaussian, so the light intensity becomes weaker around the spot, even with strong laser power.
In this part, the light intensity is likely to reach the blackening condition,
Therefore, although the blackened portion becomes white in the center of the spot and can be erased, blackened portions are likely to be formed in the periphery, which causes problems such as unerased spots that cause noise.

In the second example, the recording, that is, the blackening process by laser light, does not utilize the temperature-raising effect, but rather the change in bonding due to absorption of photons. It has the advantage that the change occurs in proportion to the number of laser beams, and recording is possible even with a weak laser power.

Furthermore, since erasing whitens the entire surface by heating, that is, heat treatment, problems such as unerased areas are less likely to occur.
On the other hand, if it is exposed to indoor light for a long time, it may absorb even weak indoor light and cause changes, which poses some problems in handling.

In response to these, the present inventors have filed a patent application filed in S53-
100626, e.g. low oxide
A recording film containing TeOx ₁ 0 < x ₁ < 2.0 as a main component and containing Se, S, etc. has a blackening response speed of several times.
100nsec, and the response speed of whitening is similarly several
It has features such as being able to reduce the time to 100nsec or less.

All of the methods described above use different modulation conditions for recording and erasing, such as a combination of dedicated light sources such as an Ar laser and an infrared laser, or short and long pulse widths. I'm getting used to it.

In the present invention, an equivalent optical system, for example, a single optical system, or at least one recording-only optical system and an erasing-only optical system, and an equivalent light source, It provides a method for erasing and recording.

The optical recording film used in the present invention includes a vapor-deposited thin film made of a combination of chalcogenides, such as Ge-Te-Se-S, and a low-oxide recording thin film TeOx ₁ containing at least one of Se and S. GeOx, 0
<x ₁ <2.0, etc.

First, the recording member has a transparent base material, glass, acrylic resin, vinyl chloride resin, etc.
A recording thin film of 500 Å to 3000 Å is deposited on this
A protective layer consisting of SiO ₂ or a layer of transparent resin is formed. When light is irradiated from the base material side and signal reproduction is performed using reflected light, an opaque layer such as black lacquer can be used as the adhesion protective layer. Although either a tape or sheet shape is possible, FIG. 1 shows an example of a disk shape.

In the figure, a recording thin film 3 is placed on a heat-resistant base material 2.
This is then heat treated to a saturation blackening level.
Converts to black disc. This will be referred to as black disk 1 hereinafter.

The optical information recording film used in the present invention has a temperature reached by heating by light irradiation that is higher than the melting point,
If this is rapidly cooled, it will turn white, and if the temperature reached is below the melting point and below the blackening transition temperature, the film will not turn white but will be in a blackened state.

Further, even if the temperature exceeds the melting point, if it is slowly cooled, it has the property of obtaining a blackened state.

Therefore, whether to obtain a blackened state or a whitened state is determined by the combination of firstly the power level of the irradiation light and secondly the cooling (heating) conditions of rapid cooling or slow cooling. be able to.

For example, in the case of an acrylic resin base material, by changing the intensity of the irradiated laser light on the film formed on the base material,
When we determined the conditions for whitening and blackening, on a disk-shaped recording member, with a laser spot light focused on approximately 1 μφ, at a rotation speed of 1800 rpm, a blackening state was obtained up to the irradiation light power level of 5.0 mw, and 5.6 mw or more. At high power levels, he gained a bleached state.

In other words, at high power level P _W , whitening occurs,
At low power levels _PE , differences in blackening occur.

Next, the effect of the difference in cooling conditions, which is generally similar to the difference in heating conditions, will be described.

As described later, in a system that irradiates a disk rotation speed of 1800 rpm, a laser spot diameter of 1 μmφ, and a recording track position of φ100, the irradiation time of the laser beam irradiated to any one point on this track can be calculated as follows. .

Rotational linear velocity V = 9.4 m/sec at φ100 position Laser beam irradiation time at this position τ1 μm/V =
It becomes 106nsec.

In this case, time changes in temperature rise and cooling are determined. This can be found by solving the thermal diffusion equation for light irradiation with a 1 μmφ laser spot on a rotating infinite plane.

As physical constants, specific gravity of recording film (film whose main component is Te) ρ≒6.1g/cm ³ , specific heat C=0.05Kcal/Kg
℃, thermal conductivity k = 0.5Kcal/m・hr・℃, resin substrate epoxy system specific gravity ρ=1.2g/cm ³ , specific heat C=
0.3Kcal/Kg・℃Thermal conductivity k=0.192Kcal/m・
Calculated in the hr・℃ system.

The maximum temperature the film reaches is 750°C, and the film completely melts. The time required to cool this down to 300℃, which is lower than the melting point of Te (450)℃, is
It becomes 300nsec.

The cooling rate at this time is -1.5・10 ⁹ °C/sec, and with a laser beam irradiation time of 100 nsgec, the cooling rate is -10 ^{9 °C} /sec.
It becomes a rapid cooling state on the order of °C/sec, and a whitening state is obtained.
On the other hand, when the laser beam irradiation time is 1μsec, -
The cooling rate is on the order of 17 ⁸ °C/sec, which corresponds to slow cooling conditions. In order to obtain the above laser beam irradiation time of 1 μsec, the laser spot diameter may be increased or the rotation speed may be decreased. In addition, at a laser spot diameter of 1 μmφ and a rotation linear speed of 9.4 m/sec, 8 mw
When recording modulated light is irradiated, the modulation frequency is
When the speed is 5MHz or higher and the duty is 50%, the light emission pulse width (light emission time) is 100nsec or less, which leads to rapid cooling.

For example, when the recording member is rotated and irradiated with unmodulated continuous light, and when it is irradiated with modulated light, the manner in which the temperature of the recording member including the recording film increases and therefore the manner in which it is cooled differs. .

The present invention consists of a method of controlling the thermal characteristics of the heating and cooling described above using the following two factors.

The first is that the whitening signal recording light uses a modulated pulse waveform, and the irradiation light for blackening erasing is unmodulated continuous light.The second is that for blackening erasing The irradiation light is irradiated one or more times depending on the power level _PE , that is, it is irradiated once when the power level of _PE is high, and multiple times when the power level of PE is low.

The effect of the first element is that when modulated light that is turned on and off is irradiated, three-dimensional thermal diffusion occurs when the light is turned off, and the temperature rapidly decreases, approaching a rapid cooling condition. On the other hand, when continuous light is irradiated, the recording area is heated from the front due to heat conduction before the laser beam spot reaches the recording area. Furthermore, even after the laser beam spot passes through the recording area, it is heated from behind. This results in continuous heating in the direction of the recording track, which reduces thermal diffusion in this direction, lowers the cooling rate, and makes it more likely that slow cooling conditions will occur.

The effect of the second element is that even with low-power irradiation that cannot raise the temperature sufficiently by itself, repeated irradiations can raise the recording film to the blackening saturation temperature. Even in the case of high power irradiation that raises the temperature above the whitening temperature, in the case of continuous light, heating is continuous in the direction of the recording track, the slow cooling condition can be satisfied, and blackening erasure can be performed.

To summarize, when recording information, light is irradiated with a whitening signal recording power level R _W that can supply more than the energy that melts the thin film, and the irradiation time of the irradiated light to an arbitrary position on the thin film is set so that the said position is The relative movement speed of the thin film and the irradiation light and the beam diameter of the irradiation light are set so that the thin film is rapidly cooled after irradiation, and during erasing, light with a blackening erasing power level P _E lower than the energy that dissolves the thin film is used. This configuration enables complete erasure and recording with less noise.

That is, in the present invention, whitening recording is performed by rapidly increasing the temperature and cooling, and blackening is erased by gradually increasing and cooling the temperature. First, the first whitening recording will be explained.

In order to cause whitening, it is first necessary to melt the thin film, so the whitening signal recording power level P _W that can supply more than the energy to melt the thin film is required.
irradiation is required. Next, it is necessary to rapidly cool the area irradiated with the power level P _W. Therefore, when an arbitrary point on the thin film is irradiated for a long time at the power level P _W , the irradiation energy is transmitted from the thin film to the substrate, and cooling by thermal diffusion occurs immediately after the energy irradiation is completed. As a result, the whitening state cannot be obtained due to the gradual cooling. Therefore, the irradiation time at any point on the thin film should not be set for a long time, but should be set to a time during which the point is rapidly cooled after irradiation.

By the way, the irradiation time τ at any point on the thin film is
For example, if the thin film is rotated in a disk shape (rotation speed V) and the position of light irradiation is fixed, the time it takes for that point to pass through the diameter d of the beam irradiated with light is
That is, it is determined by d/V. This is a constant value regardless of the time T that the beam is on (the time T determines the size of the whitened area recorded on the thin film).

Therefore, by setting the irradiation time for any point on the thin film at the whitening signal recording power level P _W , the relative speed between the thin film and the irradiation light, and the beam diameter of the irradiation light, the arbitrary point will be rapidly cooled after irradiation. By doing this, whitening recording will be performed.

Next, for erasing blackening, gradual heating and cooling is required. For blackening, it is not necessary to melt the thin film, but only to initiate blackening transition, so a power level _PE that can bring the thin film below the melting temperature is sufficient. P _E
When the value of is low, the heating temperature in one irradiation is low, so repeated irradiation brings the thin film to the blackening saturation temperature or higher. Since the blackening erasing power level is constantly supplied, cooling by thermal diffusion is reduced and the slow cooling condition is always satisfied, so that blackening erasing is performed regardless of the irradiation time.

Whitening symbol recording and blackening erasing using this method will be explained using FIGS. 1 and 2.

For example, FIG. 1 shows an example of recording conditions for a recording member in the form of a disc. In this case, the disk shown is one that has been subjected to saturation blackening treatment (black disk).

The black disk 1 basically has a base material 2 and a recording film 3, and in recording a whitening signal, for example, a semiconductor laser light source 4 is intensity-modulated by a current waveform 6 so as to generate modulated light having a power level _PW . This beam is then combined with lens combination 7,
The black disk film is irradiated with a small spot diameter of 1 μΦ using a 8-magnetic lens. In such a configuration, the effective irradiation time during which the film is irradiated with light is determined by the diameter of the irradiation light spot on the film surface and the linear velocity of the film surface. The irradiation time corresponds to the rotation direction 5 of the disk.
100 nsec, whitening signal bit 10 is formed, and signal recording can be performed.

Reproduction of the recorded signal is performed by detecting changes in transmittance or reflectance of the recording bit portion using the same optical system.

In recording and reproducing signals, by selecting a transparent material as the base material 2, it is possible to perform recording and erasing by laser irradiation from the base material side, and also to perform reproduction by detecting reflected light.

Next, the power level of modulated light for recording
P _W and the unmodulated continuous light power level P _E for erasing blackening have a power level P _W that obtains a whitening state as shown in the modulated power waveform a shown in FIG. 2 at the disk rotation speed. Due to the modulated light, whitened recording bits q shown in FIG. 2B are formed on the film surface. The information signal is set at a frequency (FM modulation) or a duty (pulse width modulation) at a level _PW , for example.

On the other hand, the method of blackening and erasing the state of a track on which a whitened signal recording bit has already been formed similarly has an unmodulated continuous optical power level P _E as shown in Fig. 2c. By repeatedly irradiating the track shown in figure b with the laser beam once or more at the light spot r shown in figure d according to the power level P _E , the whitened recording area q' becomes black as shown in figure d. It disappears and no change occurs in other parts.

The number of repetitions of this unmodulated continuous light to eliminate blackening varies depending on the power level of _PE .
This condition will be explained in FIG.

Erasing light power level P _E is low, e.g. 3mw
In the case of , the reproduction amplitude of the recorded signal decreases as the number of repeated irradiations increases from 20 mv _PP , as shown by curve d, and erasure progresses to almost the noise level after about 100 times.

When the irradiation light power level P _E is 4 mw, erasing progresses and reaches approximately the noise level in about 10 times, as shown by curve e.

Furthermore, at a high power level P _E of 5.0 mw,
The number of repetitions is about 3, as shown by curve f, and the erasure progresses to the noise level.

Furthermore, by choosing a high P _E , blackening can be removed with one continuous light irradiation. However, in this case, the difference between the erasing power level P _E and the signal recording power level P _W becomes small, and malfunctions such as whitening and blackening are likely to occur. Therefore, it is necessary to select a high power control accuracy.

As described above, the existing signal decreases in accordance with the number of repetitions, so by constantly detecting and monitoring this signal, complete blackening removal, that is,
It becomes possible to automatically select the number of repetitions until the existing signal reaches the noise level.

In this method, as a means to completely perform blackening erasing, the following modification is made to the waveform of the irradiation light at the power level _PE for performing blackening erasing.

In other words, just before the continuous light waveform that starts blackening and erasing,
The short term standard whitening power signal waveform is connected.

By this method, standard whitening recording bits are formed in a part of the desired signal recording track before the blackening starts, and by detecting and monitoring the signal level during repeated irradiation processes, the above-mentioned monitor erasing is performed. With this method, complete blackening erasure can be performed regardless of the state of the recorded signal.

In the optical information recording system shown in FIG. 1, the recording film 3 is composed mainly of a low oxide film TeOx ₁ 0<x ₁ <2.0 and contains an additive material;
A chalcogenide containing Te as the main component and Ge and Se was used.

Using transparent epoxy resin as the base material,
It was made into a disk of 200mφ.

The saturation blackening conditions are selected from FIG. 4, which is the measurement result of the blackening transition curve with respect to heating temperature increase for these films. Depending on the material composition, the transition temperature is low,
and high. In this figure, curve k is for low oxide systems and curve l is for chalcogenides.

The blackening saturation level is obtained by heat treatment at a temperature of 110°C or higher and 150°C or higher, respectively. I got it. Optical properties of each film, that is, transmittance T% and reflectance R%
The spectroscopic measurement results are shown in FIGS. 5 and 6.

When signal reproduction using a semiconductor laser at λ=830 nm is performed using transmitted light, the curve shows the spectral characteristics of transmittance. curve, the difference between mm or curve n-
If this is done by detecting the difference between n' and using reflected light, it is a curve that shows the spectral characteristics of reflectance. curve o
This is done by detecting the difference in -o' or p-p'.

The rotation speed of these disks is 1800 rpm to 900 rpm, especially when using low oxide materials that easily blacken, and the whitening recording power is P _W = 9 to 900 rpm.
7 mw is selected, and P _E =6 to 4 mw is selected as the continuous optical power for unmodulated blackening erasure.

For calgonide thin film systems that are slightly less likely to cause blackening, it is desirable that the disk rotation speed be 900 to 300 rpm, and the whitening recording power P _W = 7 to 4 mw.
Then, P _E =5 to 3 mw can be selected as the continuous optical power for unmodulated blackening erasing.

For example, low oxide film material TeOx 0 < x ₁ < 2.0
For a film mainly composed of
By repeating the irradiation of continuous light having a power level of 5 times on the same recording track five times, the recorded signal was reduced to the noise level and complete blackening erasure could be performed.

On the other hand, for example, in the material of the chalcogenide film,
Regarding the film containing Te as the main component and Ge and Se,
After applying a 5 MHz whitening signal at a disk rotation speed of 900 rpm and a power level of 6.0 mw, continuous light having a power level of 4.3 mw is irradiated onto the recording track 10 times to achieve the above-mentioned results. I was able to perform complete blackening erasure in the same way.

The number of repeated continuous light irradiations for erasing blackening varies depending on the signal level, but can be selected from 1 to 100 times.

In particular, when selecting the continuous light power level P _E to perform blackening and erasing with one continuous light irradiation, a continuous light irradiation erasing optical head similar to the above head is provided in front of the optical head for recording. It is also possible to carry out erasing and recording at the same time by blackening and erasing the previously recorded whitened area and recording a new whitening signal in the recording head following the erasing.

Modulation signal recording using whitening power level P _W and unmodulated continuous blackening power level in the present invention
The method of erasing blackening by repeatedly irradiating _PE one or more times using _PE has the following effects.

1. Blackening and erasing of previously whitened signal recording areas can be completely performed, and information recording with less noise can be repeatedly performed.

2. Malfunctions of whitening signal recording and blackening erasing can be removed. (The difference between power P _E and power P _W can be selected according to the number of repeated irradiations, and even if P _E and P _W are close values, whitening and blackening can be reliably separated by this number of repetitions.) be able to.)

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a disk subjected to blackening saturation treatment, which is one form of a recording member used in the optical information recording and erasing method of the present invention, and a recording and erasing system to which a semiconductor laser light source is applied. Figure 2 a is
A diagram showing the modulated light power with the peak power P _W for recording a whitening signal, b is a diagram showing whitening recording bits in a film subjected to blackening treatment, and c is a diagram showing the unmodulated continuous optical power P _E , d shows the state in which blackening erasing is performed by irradiating the same unmodulated continuous light power P _E , and Figure 3 shows the case where unmodulated continuous erasing light is irradiated with the power level P _E as a parameter. Figure 4 shows the correspondence between the number of repeated irradiations and the change in the recorded signal amplitude. curve l
is a diagram showing the characteristics of chalcogenide whose main component is Te, and Figure 5 is a spectroscopic measurement curve of the transmittance and reflectance of a low oxide thin film, where m and n are the transmittance in the untreated state, m', n' is a diagram showing the transmittance and reflectance of a film subjected to blackening treatment, and Figure 6 is a spectroscopic measurement curve diagram of the transmittance and reflectance of a calgonized film whose main component is Te, with curves O and P. are the transmittance and reflectance of the untreated film, and O′ and P′ are the transmittance of the blackened film. 1... Disk, 4... Semiconductor laser light source, 7, 8
…lens.

Claims (1)

[Scope of Claims] 1. A thin film material having a property that the optical density increases when the temperature is heated and then slowly cooled, and the optical density decreases when the temperature is rapidly cooled after the heating and the temperature is raised, is formed by vapor deposition on a substrate. In an optical information recording method using a recording member, the recording thin film material is changed in advance to a blackened saturated state with high optical density, and the minute portions are selectively applied to minute portions of the film in the blackened saturated state. Information is recorded by applying light irradiation with a power that raises the temperature above the melting temperature to change it to a whitened state with low optical density, and when erasing the information, the area including the whitened part is heated to the melting temperature of the thin film material. This is a method of heating and blackening by repeatedly irradiating non-modulated continuous light with increasing power, and further, when recording the information, a pulse of recording modulated light is applied to the minute portion. The irradiation time during which the light is irradiated is selected to be such that the minute portion is rapidly cooled after irradiation by selecting the relative movement speed of the thin film material and the pulsed light and the diameter of the pulsed light beam. Optical information recording and erasing method. 2 The power of repeated non-modulated continuous light for erasing blackening compared to the irradiation power P _W for recording whitening
_2. The optical information recording and erasing method according to claim 1, characterized in that the irradiation is performed with P _E equal to or selected to be P _E P _W. 3. Optical information recording and erasing according to claim 1 or 2, characterized in that the spot diameter of the unmodulated continuous light for blackening erasing is selected to be larger than the diameter of the information bits in the whitening recording section. Method. 4 When the information recording member is a disc-shaped disc and whitening recording is performed on a film that has been brought to a blackening saturation state on the disc, the disc is rotated so that the effective pulse width is adjusted to the thin film. A modulated spot light of 1 μsec or less is irradiated to change the irradiated area to a white state. For blackening erasing, a continuous spot light of erasing light power P _E is used to erase the desired whitened recording track from the disk. 2. The optical information recording and erasing method according to claim 1, wherein the whitened area is brought into a blackened saturated state by repeated irradiation at a speed corresponding to the rotation. 5. The number of repeated light irradiations for erasing blackening is repeated until the recording level returns to the original noise level by detecting a change in the output of the whitening recording section. The optical information recording and erasing method described in item 4. 6. The number of times of repeated light irradiation for blackening erasing and the power _PE of the erasing light are selected so that the temperature of the desired whitened recording track rises above the blackening saturation temperature of the recording film. An optical information recording and erasing method according to claim 4. 7 The thin film material is a compound whose main component is TeOx ₁ 0 < x ₁ < 2.0, and the blackening saturation state is
2. The optical information recording and erasing method according to claim 1, which is obtained by heat treatment at a temperature of 110° C. or higher. 8 The thin film material is mainly composed of Te, Sn,
Claim 1: The film is a film containing at least one of In, Bi, Ge, Se, and S, and the blackening saturation state is obtained by heat-treating the film at a temperature of 150°C or higher. Optical information recording and erasing method described. 9. In erasing previously recorded signals, before irradiating the power level P _E to start erasing, irradiate a part of the desired recording track with whitening pulsed light of a constant waveform, record a whitening signal for monitoring the erase state, 5. The optical information recording and erasing method according to claim 4, wherein the blackening erasing level caused by continuous light irradiation is determined by detecting the monitor signal recording area and erasing is performed.