JPS613324A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To permit ternary recording by selecting suitably the compsn. ratio of a thin film and concn. of additive as well as the radiation intensity and radiation time of a laser beam and using a recording medium which can be varied optionally among the three signal levels: high, middle and low. CONSTITUTION:The laser beam is circularly stopped down and is irradiated instantaneously at relatively strong light power P1 and time T1 on a recording film in a black state. The temp. of the irradiated part is then sharply increased and the irradiated part is melted, then solidified relatively randomly to a white state 4, by which the recording of the level L1 is executed. The power is in succession decreased to P2 and the beam is irradiated during the time T2, then the irradiated part is melted, then solidifed but is made into an ash state 5 on account of a difference in the ultimate temp., by which the recording of L2 is executed. No changes arises even if the beam is further irradiated thereto by decreasing the light power. There is the relations P1>P2, T1=T2 in this stage. Namely, the recording of 0, 1, 2 is made possible simply by controlling the laser power when the laser beam is irradiated on the medium. The three states: the state of high reflectivity, the state of the low reflectivity and the intermediate state thereof are thus respectively independently obtd. by controlling the ultimate temp. and cooling rate.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides high-density and high-quality recording using a recording medium that reversibly changes between three independent stable states by irradiating it with a laser beam or the like. The present invention relates to a method for recording rewritable information.

Conventional structure and problems Generally speaking, as a recording medium that records in a heat mode by irradiating a laser beam and erases in a heat mode, the optical constants (refractive index n, extinction coefficient k)
There are known methods based on the principle that the optical constant increases, and then the optical constant decreases upon rapid cooling. For example, Tokuko Sho 47-2689
In No. 7, a chalcogenide glass thin film excluding oxygen, G e 1s T e s 1S b 2 S 2
, A 82 S 3. A S 20 S e
There is a proposal for eoG e2°. Regarding oxide systems, for example, Tea
x-Se.

TeOx-8 has been proposed, and a patent application was filed in 1982-5.
As described in No. 8158, for example, S is added to the Te-TeO2 system.
This property has also been found in systems with additions of n, Ge, Pb, Sb, etc., and rewritable optical discs using this system have been prototyped. (1983LAPAN
DISPLAY Proceedings P46-P48) The recording/erasing mechanism of these recording films is, for example, in the case of the former, the order of atoms changes before and after recording, and a phase transformation occurs between crystalline and amorphous. In the latter case, for example, Te in the film
In addition to changes in the orderliness of small particles, increases and decreases in crystal grain size are thought to be dominant, but in either case there are only two stable states, and binary recording of 0.1 is performed. It's been coming.

A proposal has already been made to record a large amount of information at the same bit density on a disk of the same size by giving each recording bit three or more meanings (Japanese Patent Laid-Open No. 58
-137148). For example, as a recording thin film, Sb
2Se3. Materials such as Sb2Te3, which are recorded in heat mode by laser irradiation and whose optical properties change, are used singly or in a stacked structure.

In other words, when used as a single layer, the power of the irradiated light is controlled to irradiate with relatively weak power, locally change the optical characteristics of the irradiated area, and irradiate with relatively strong backlight. Based on the principle of locally melting the irradiated area and forming a hole, two different levels of recording are performed and an unrecorded level is added to obtain three different levels of 0 and 1.2.

In addition, when using a laminated structure, the power of the irradiation light is controlled by utilizing the difference in the temperature change of each layer, and the light is irradiated with a relatively weak power, so that only the layers with a relatively low temperature change are used. Based on the principle of changing the temperature and irradiating light with relatively strong power to change even the layers with relatively high temperature changes, it is possible to perform recording at multiple levels, and using this recording medium The same trunk pitch on the same size optical disk as before,
With the same recording bit interval, it is possible to record 1.5 times the amount of information compared to the conventional method.

However, this proposed system involves irreversible changes in the shape of the film during recording, and it is difficult to selectively raise the temperature of each stacked film individually. cannot be used to construct a rewritable recording medium.

That is, no proposal has yet been made regarding a rewritable recording medium having three or more levels, or a recording and erasing method thereof.

Purpose of the Invention The purpose of the present invention is to change the recording signal level from the conventional binary level to three levels.
As a value, it improves the recording information density and at the same time allows for free rewriting between them, that is, 3.
An object of the present invention is to provide a method for sweeping recording and erasing using a recording medium that can change signal levels arbitrarily.

Structure of the Invention The present invention uses, for example, a Te-Te0-based thin film or a Te-based chalcogenide thin film, appropriately selects its composition ratio and additive concentration, and further appropriately selects the irradiation intensity and irradiation time of a laser beam. By controlling the temperature reached and the cooling rate, three states of high reflectance, low reflectance, and an intermediate state can be independently and stably obtained.

DESCRIPTION OF EMBODIMENTS The present invention is disclosed in, for example, Japanese Patent Application No. 58-58158 and Japanese Patent Application Laid-open No. 58-581.
In the rewritable optical information recording thin film based on a mixture of To and TeO2 described in No. 6-146630 and added with additives such as Ge + Sn + Au, or in the chalcogenide thin film based on Te. It can be constructed by appropriately selecting the additive concentration and the irradiation intensity and irradiation time of the laser beam during recording and erasing.

As mentioned above, these systems based on Te-based chalcogenide glass thin films or To-TaO2 have a so-called black state (a state where the refractive index n and extinction coefficient are large) and a white state (a state where the refractive index n and extinction coefficient are large). (state with small damping coefficient) 2
Reversible structural changes between two states are used to record a rewritable binary value of 0.1, but in the past, the intermediate state was not stable enough, and even if that state appeared, It immediately changed and moved into a different state.

Therefore, conventionally, compositions and laser irradiation conditions have been selected so that intermediate states are unlikely to occur.

In the present invention, in order to actively utilize this intermediate state, which can be called a gray state, we set a material composition in which the intermediate state tends to exist stably and laser light irradiation conditions suitable for revealing and erasing the intermediate state. By finding this, a 0, 1.2 rewritable recording method can be obtained.

As the recording film applied to the present invention, for example, Te-Ge
-3n ternary system + T e -G e -S n-〇 quaternary system, Te-Ge-8n-Au-0, Te-Ge-
8e-Au-0 six-element system, Te-Ge-3n-Au-8
There are six-element systems such as e-0. These Te-based recording thin films can be produced by changing the laser beam irradiation conditions. For example, by irradiating relatively strong and short laser pulses, the temperature of the irradiated area is locally raised, and then the optical constant is rapidly cooled. By irradiating a relatively weak and long laser pulse light, the temperature of the irradiated area is raised over a rather wide range, and then it is gradually cooled, and the optical constant increases.
Erasing is performed repeatedly. This phenomenon is caused by T in the film.
It is thought that the main cause is a change in the state of the e-atom, such as a change in grain size or crystallinity, and other elements can be said to modify the thermal conditions, amount of change, etc. required for the change. For example, in the To-Ge-3n-Au-8e-0 system, Ge combines with To to change the state (progress of crystallinity).
increase the temperature required for Ss has the effect of lowering the melting point of the entire system and can form a solid solution with Te in any ratio, so it is effective in making Te amorphous.

Au is useful as a nucleating material when Te crystallinity progresses. 0Il-i Increases the heat capacity of the entire system and lowers the heat transfer coefficient, etc. Further, Sn has the effect of increasing the light absorption effect and, in some cases, has the functions of both Se and Au. As described above, the thermal change characteristics of the entire system are controlled by each additive concentration, and characteristics suitable for the purpose of use are obtained.

In the present invention, while considering the concentration of various additives,
We created a thin film composition suitable for ternary recording in which a clear intermediate state exists in the composition range, with a slightly increased amount of crystal nucleating material and a commensurate amount of amorphous material compared to the composition conventionally used for binary recording. I was able to get it.

For example, T870G810""201 "50"10""
20020+"50G810"'6"15o20+"
Examples are f50G01o"5"""10"5020, etc.These thin films have large optical constants (thermal state) depending on the laser beam irradiation conditions.

The state where the optical constant is small (pre-white) and its intermediate state (
You can freely transform between the three states (ash state). Here, the ash state refers to the possibility that, for example, a very small thermal region and a non-white region are mixed together in a recording thin film, or a second thermal state. Alternatively, there are two possibilities: it is a completely homogeneous different phase state, which can be called a second state of affairs.
At present, the mechanism is not clear, but the fact is that both the refractive index and the consumption coefficient are located between the black and white states.

FIG. 1 shows a sectional view of an embodiment of the optical information recording member of the present invention. As the base material 1, a general resin base material or glass base material, such as acrylic resin, vinyl chloride, polycarbonate, etc., which is normally used in the production of optical discs is used. The recording film 2 is formed by the method described in Japanese Patent Application No. 58-58158, for example, by vapor deposition, sputtering, or the like.

Next, an embodiment in which rewritable three-value recording is performed using these recording thin films will be described.

FIG. 2 schematically shows how a ternary signal is recorded on one trunk of the recording member and its reproduced signal. The freshly deposited film is in a white state with low optical constants, but as will be explained later, the laser irradiation conditions necessary for transformation between each state are suitable for recording changes from black to white or black to gray. Therefore, the state a before recording is set to the thermal state 3 in advance. At this time, by selecting the film thickness to block light, it is possible to generally maximize the reflectance and minimize the transmittance.
The case in FIG. 2 is an embodiment in which reflected light is used as a signal, and in this case, the signal level before recording is L(3).

FIG. 2 shows a signal train and its reproduced signal after ternary values have been recorded on a heated track. A relatively strong optical power P is focused on the recording film in a heated state by focusing the laser beam into a circle.
When irradiated for an instant of time T1 at 1, the temperature of the irradiated area rises rapidly, goes through a molten state, and then solidifies in a relatively random state, becoming a white state 4, and recording at level L(1) is performed. If the optical power is subsequently lowered to P2 and irradiated for a period of T2, the irradiated area will still undergo a rapid temperature rise and will solidify after passing through a molten state, but due to the difference in the reached temperature, it will remain in a somewhat ordered state. It solidifies and becomes ash state 5, and level L (2) is recorded. Even if the light power is further reduced and irradiation is performed, no change occurs in the irradiated area. At this time, the relationship between the irradiation time and the irradiation bar is P1>P2, T1-12. In other words, it is possible to record 0, 1, and 2 simply by controlling the irradiating laser power. However, what contributes to the change is the total amount of energy that determines the temperature reached.
It is also possible to record at two levels, L(1) and L(2), by changing the irradiation time as Pl-P2 so that T1>T2.

FIG. 2C shows that the signal train b is transmitted with a relatively weak power p2,
This is the state after irradiation for a time t2, which is slightly longer than that during recording. In this case, the white state changes to the gray state, but no change occurs in other parts. Similarly b
It was confirmed that when the signal train is irradiated with the same power p1 for a longer time t3 than before, this signal train is completely erased and the original state a is restored.

In addition, as a third experiment, the irradiation power p3 was kept as it was,
When the irradiation time was selected to be t3, which is between tl and t2, and similar irradiation was performed on the signal train shown in Figure 2, the gray bits were blackened, but only transformed into white bits. Between the irradiation power and the irradiation time, p, -p2=p3. tl〉t
3> t2 holds, and from these results, it is possible to convert only the white bits to gray bits or convert only white bits to gray bits by simply changing the irradiation time of the irradiation light for the white bits and gray bits on the black track. It can be seen that it is possible to leave the original ash bits as , and erase them to the thermal state, or to completely erase all the pits to the thermal state. In this case, as well as when recording
1-12-t3 and change the power of the irradiated laser beam,
For example, each of the above metamorphoses can be supported by setting pl>p3>p2.

Next, an embodiment in which binary recording is performed on a gray track will be described. FIG. 3a shows a track in an unrecorded state, and the signal level in this case is L(2). b is
Mizuko looks at the situation after recording. When the recording film is in a gray state, the laser beam is focused circularly onto the recording film and irradiated instantaneously at T3 with a relatively strong optical power P3, the temperature of the irradiated area rises rapidly and, as in the case of Fig. 2, a molten state is obtained, resulting in a relatively random state. The white state level L(1) is recorded. At this time, blackening recording can also be performed by lowering the laser power to p3 and irradiating for a relatively long time t3, but there will be a large difference in recording speed between whitening recording and, for example, when rotating It is not practical to record both white and black on tracks within the same circumference on a disc with a 3D image. When this signal train is irradiated with an optical power p2 that is relatively weaker than that during recording and for a slightly longer period t2, the white bit is erased and the original state a is restored. It was also confirmed that in both cases a and b, if irradiation was carried out for a longer period of time, it would transform into a blackened state as shown in C.

For this reason, when using the gray track as the starting point, binary recording is practical, but since generally t2<t3, there is an advantage that the erasing speed is higher than when using the black track as the starting point.

As explained above, it can be seen that it is possible to arbitrarily transform between the three states of black, gray, and white by selecting the irradiation power and irradiation time.

The table below summarizes the irradiation conditions required for each transformation of A-)B, and in each column, the upper side represents the laser power and the lower side represents the relative relationship between the laser irradiation time. Strength, weakness, and length are not absolute levels.

Note that the signal reproduction method can be either a reflection type or a transmission type, and in the case of a transmission type, it can be considered in the same way as in the reflection type, only that the signal level is reversed.

Effects of the Invention The present invention provides a rewritable three-value recording method, which enables higher density recording on information optical discs and more compact systems than ever before, making it suitable for image processing, computer data processing, etc. became possible to apply.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment of the optical information recording member used in the present invention, FIG. 2 is a diagram showing the state of a ternary recording signal train and a reproduced signal in an embodiment of the present invention, and FIG. FIG. 7 is a diagram showing a signal train and a reproduced signal in another embodiment. 1... Base material, 2... Recording film. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 figure

Claims (5)

[Claims] (1) An optical information recording method characterized by performing rewritable three-value recording using an optical information recording medium that can be arbitrarily transformed between three independently stable states by light irradiation. (2) A patent claim characterized by using a recording medium that utilizes the fact that the orderliness of atomic arrangement or crystal grain size changes discontinuously and reversibly depending on the light irradiation conditions, and the optical constants thereof change. The optical information recording method according to scope 1. (3) The optical information recording method according to claim 2, which uses a transformation direction in which an optical constant decreases when recording an information signal, and uses a transformation direction in which an optical constant increases during erasing. (4) Recording power density to obtain a large signal change level L(1) when recording an information signal is P_1mW/μm^2
, the irradiation time is T_1nsec, and the recording power density to obtain a small signal change level L(2) is P_2mW/μm^
2. When the irradiation time is T_2nsec, P_1>P_2
, and T_1=T_2, or P_1≧P_2 and T_
Claim 1 characterized in that 1>T_2.
Optical information recording method described in section. (5) When erasing the information signal, the erasing power density when changing from the large signal change level L (1) to the pre-recording level L (3) is p_1 mW/μm^2, and the irradiation time is t.
_1nsec, and the erase power density when changing from the small signal change level L(2) to L(3) is p.
When _3mW/μm^2 and irradiation time is t_3nsec, p_1=p_3 and t_1>t_3, or t_1
The optical information recording method according to claim 1, characterized in that =t_3 and p_1<p_3.