JPH0296940A - Phase change optical information recording carrier and phase change optical information recording system using this carrier - Google Patents

Abstract

PURPOSE:To improve an erasing ratio by providing multiple interference films having prescribed characteristics adjacently to a recording film which is a phase change film and setting the reflectivity of the recording film so as to have the extreme value during the course of crystallization. CONSTITUTION:The recording film 7 which is changed in phase by irradiation of laser power and is thereby changed in the degree of crystallization and the reflectivity and the interference films 6', 6'' which are adjacent to the film 7 and make multiple interference of the dielectric material having a high refractive index, etc., are laminated on a substrate 5, by which the phase change optical information recording carrier is formed. The reflectivity during the course of the crystallization based on the irradiation of the laser power of the film 7 has the extreme value from the simple change if the refractive index and film thickness of the films 6', 6'' are set to prescribed values in accordance with the optical constant of the film 7. The recording near the irradiated point is uniformly erased if the laser power corresponding to the value near this extreme value is used as the laser power. The erasing ratio is thus increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a phase change type optical information carrier, and particularly to a phase change type optical information carrier suitable for improving the erasure ratio in one beam override, and a phase change type optical information carrier using the same. The present invention relates to a phase change optical information recording method for use.

[Conventional technology]

When a phase change film is heated above its melting point and then rapidly cooled, it becomes an amorphous state, and when it is heated above its crystallization temperature and maintained for a crystallization time (time required for crystallization), it becomes crystalline. If the heating method is controlled by applying the irradiation laser power, the phase change film can be brought into an amorphous state or a crystalline state simply by modulating the power of one laser beam. In other words, in recording and erasing, a pit can be brought into a recorded state or a closed state by modulating one laser beam. That is, one beam override is possible.

Regarding 1 beam override of 1 phase change model.

Institute of Electronics, Information and Communication Engineers Technical Research Report Vol. 1.87, NQ
310 CPM 87-88.89.90.

Further, provision of a phase change recording film adjacent to a dielectric material is described in Japanese Patent Laid-Open No. 62-222442.

[Problem that the invention sought to solve]

However, the above conventional technology is an idealized principle of one beam override, and in reality it has not been possible to completely control the amorphous state (recording state) and crystalline state (erasing state m) of the phase change film. not present.

Currently, a practical level signal level (difference between the reflectance of the film in the amorphous state and the crystalline state) is obtained for the rewrite reproduction signal level, but there is a problem that the signal of the previous data cannot be sufficiently erased during rewriting. .

This problem is caused by the fact that the phase change of the recording film described above cannot be completed within the erasing time (within the laser irradiation time).

To explain the phase state of a recording film, an ideal amorphous state means that no crystals exist in the organizational structure of the recording film, and an ideal crystalline state means that the entire organizational structure of the film is arranged in a crystalline state. It is that you are.

However, in reality, the amorphous state obtained by melting the recording film by laser irradiation and then rapidly cooling it is a state with a low crystallinity (degree of crystal growth), and the amorphous state obtained by rapidly cooling the recording film by irradiating it with a laser is a state with a low crystallinity (degree of crystal growth). A crystalline state is simply a state with a high degree of crystallinity.

Particularly in the crystallization process during erasing, laser irradiation - times can bring the crystallinity to a high degree, but the crystallization cannot be completed.

For this reason, when attempting to erase (crystallize) the entire data, the data erased from the amorphous state and the crystallized state may be the same in the area where data was previously written. Even if the material is different, there will be differences in the degree of crystallinity.

On the other hand, to explain the relationship between the degree of crystallinity and the reflectance of the recording film, as the degree of crystallinity increases, the reflectance increases monotonically;
As the crystallinity decreases, the reflectance decreases monotonically. Depending on the material, the increase and decrease may be reversed, but the fact remains that the reflectance changes monotonically depending on the degree of crystallinity.

Therefore, when overriding, there will be a difference in the degree of crystallinity between the area where the previous data was in an amorphous state and the area where it was in a crystalline state when crystallized (erased), and even with the same erasure, there will be a difference in reflectance The result is that This difference in reflectance becomes an unerased image and makes the erasing ratio low.

Furthermore, although JP-A-62-222442 discloses that a dielectric material is provided adjacent to the recording film, there is no mention of improving the erasure ratio by adjusting changes in reflectance. Not yet.

The above-mentioned conventional technology does not take into consideration the suppression of unerased data, and has a problem in that the erasure ratio is low.

The object of the present invention is to provide a phase change optical information recording carrier having a superior erasure ratio. Another object of the present invention is to provide a phase change optical information recording system using the above-mentioned phase change optical information recording carrier.

[Means to solve the problem]

The above purpose was to change the characteristics of the crystallinity and reflectance of records 1 from a characteristic in which the reflectance changes to 1υ1■ depending on the degree of crystallization to a characteristic in which the reflectance has an extreme value in the middle of crystallization, and to erase it. This is achieved by performing the operation near this extreme value.

In order to give the optical information recording carrier the above-mentioned characteristic in which the reflectance reaches an extreme value during crystallization, a dielectric film with a high refractive index is provided as a multiple interference film adjacent to the recording film, and the refraction of this dielectric is This is achieved by appropriately setting the ratio and sample thickness in consideration of the optical constants of the recording film.

[Effect]

The operation will be explained using drawings. FIG. 7 is a diagram showing the characteristics (relationship) between crystallinity and reflectance. The solid line indicates the present invention.
It exhibits a characteristic in which the reflectance has an extreme value of 2 during crystallization. Also,
The broken line shows the characteristic that the conventional reflectance monotonically changes according to the degree of crystallinity.

In the solid line, the reflectance (2) reaches its minimum value when the degree of crystallinity X=0.8, and shows an extreme value 2 where the slope of the tangent line becomes zero.

Here, if the erasing operation is performed near the crystallinity of X=0.8, the crystallinity becomes X=
A change around 0.8 causes almost no change in reflectance (ie, ΔR).

On the other hand, in the conventional broken line, when the degree of crystallinity changes (ΔX) around X=O,S due to the influence of the previous history during erasing, the reflectance changes gradually according to the degree of crystallinity.
A reflectance change ΔR' occurs.

As described above, in the relationship between crystallinity and reflectance, if the reflectance has an extreme value in the middle of crystallization and the erase operation is performed near this extreme value, the change in crystallinity due to the previous history at the time of override will change the reflectance. Since there are no unerased components in the reproduced signal, the erasure ratio is improved.

Further, the dielectric film functions as follows. FIG. 5 is a diagram schematically showing multiple interference caused by the dielectric film 10 to crystallized components and amorphous components.

Now, the input light is $M E = E o cosωt
When irradiated with light, the amplitude EX of the reflected light with respect to the crystallized component is
), and the amplitude of the reflected light for the amorphous component is 1.]
6 is EA=Eo RAcos (ωL + ωA).

The amplitude of the overall reflected light m E R is E if the crystallinity is
R=Ex -X0EA・(1-X)=Eo(Rx C
O8(+11 t, +ωz) ・X+RACO8((
IJ L+ωA) ・(1-X)'J, and the total amplitude reflectance R is R=lt<, CO3((11t,+ωx) ・X
+RACO9(ωt, +ωA) + (1x)l.

Here, R, and RA are the amplitude reflectances for the crystallized component and the amorphous component after multiple interference, respectively, and ω and ω6 are around the phase at the time of reflection. The ratio between R and RA and the difference between ω and O6 are determined by the optical constants (refractive index,
The extinction coefficient can be changed by appropriately setting the refractive index, film thickness, etc. of the dielectric film. FIG. 6 shows the relationship between the crystallinity X and the reflectance R using the ratio of R to RA and the difference between ω and O6 as parameters.

By appropriately setting R/RA, Δω=ω, and −O6, the reflectance can have an extreme value during crystallization (0<χ×1). Here, an example of X=088 is shown.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing the dependence of the reflectance of the optical information recording carrier of the present invention on the irradiation laser power. As the optical information recording carrier, an optical information recording carrier (optical disk) having the configuration shown in FIG. 2 was used. First, its configuration will be explained. A first interference film 6' is placed on a transparent glass substrate 5 having a diameter of 130φ with a guide groove.
The thickness of the AfiN film was 70 nm, and the thickness of the recording film 7 was 70 nm.
n S b T e appeasement change film 30 nm, second interference film 6'', ANNI pattern 70 nm, reflective film 8
The Au film was 1100n as the protective film 9, and the MN film was 1100n as the protective film 9.
The optical disc 20 has a structure in which the films are formed by sputtering in the order of 100n.

The refractive index NC of the crystalline phase change film 2 is Nc = 4.7 i 1.7 The refraction I N A of the amorphous state is N^'' 5.0-jo, 8. , AnN
The refractive index N of the films 6' and 6'' is N=2.0.
1, the amplitude reflectance ratio R/R24 of the crystalline state and the amorphous state is 0.6, and the phase difference Δω is 6
The reflectance is set to have a minimum value at crystallinity X=0.9 with 0deg.

The crystallization temperature T of the above-mentioned InSbTe-based phase change film is T = 260°C, and here, the optical disc having the configuration described above was held in an oven at 300°C for 1 hour to effect crystallization. FIG. 1 shows the results of determining the dependence of the reflectance of the optical disk 20 on the irradiation laser power while rotating the completed disk at a rotational speed of 1800 r p tn.

The operation shown in FIG. 1 will be explained. 1 is a laser power versus reflectance curve. The reflectance of the crystallized product after completion of crystallization in the oven is 14%. When this is irradiated with a laser, there is no change in the irradiation laser power up to 6 mW. When irradiated with 8rnW, the reflectance decreased.

The reflectance R=12%. The reflectance starts to increase from LOmW, and after 14 mW, the reflectance shows a tendency to saturate, reaching R222%.

Here, changing the irradiation laser power is nothing but changing the crystallinity degree of the recording film 7, and FIG. 1 shows that the crystallinity degree is lowered by increasing the irradiation laser power than in the crystallized state. become. Irradiation laser power 8mW ~ 10
Interference films 6', 6''' at crystallinity corresponding to mW
The reflectance through will have a minimum value of 2. That is, near this minimum value, even if there is a slight change in the degree of crystallinity, no change will occur in the reflectance.

Therefore, the erasing laser power is set to 4 to 8 where this reflectance reaches its extreme value.
~10mW, here it is 1゜mW),
Even if there is a slight change in the degree of crystallinity during erasure, no change in reflectance occurs, so it is possible to suppress unerasure (small change in crystallinity) during override and improve the erasure ratio. effective.

For recording laser power 3, set recording laser power 3 to 1.
It was set at 4 mW. The change in reflectance as a recording signal is R222% for the area irradiated with a recording laser power of 14rnW and R=12% for the area irradiated with an erasing laser power of 10mW.
A high C/N ratio of 50 dB is obtained.
/N was obtained.

3M from the top of the signal with frequency 2Ml1z! When the lz signal is overridden, a high cancellation ratio of 40 dB is obtained for the frequency 2 M Ih component, resulting in a high C/N and a high cancellation ratio.

Furthermore, the characteristics shown in Figure 1 can be obtained starting from the amorphous state, and when the irradiation laser power is not reduced, the crystallinity is lowered and the change in reflectance is measured, the crystallinity X = 0.9. It is clear that the reflectance becomes minimum depending on the irradiation laser power, and the reflectance has an extreme value as in FIG.

Furthermore, in order to change the degree of crystallinity, the pulse width of the irradiation laser may be changed, or in the case of a disk, the rotation speed may be changed. When the rotation speed is lowered, the laser irradiation time becomes substantially longer and crystallization is promoted.

Figure 8 shows the rotation speed at 18Q to confirm the extreme value of reflectance.
The relationship between the irradiation laser power and the reflectance was measured by lowering the laser power from Orpm to 60 Orpm. Due to the low speed rotation, the rapid cooling of Iki a Ill 7 is insufficient, so the change in reflectance at high power is small, but crystallization can be completed, so it is clear that the reflectance reaches an extreme value. I understand.

Furthermore, in the configuration of an optical disk with good cooling characteristics, extreme value 2' in the recrystallization process when heated above the melting point and extreme value 2 in the crystallization process below the melting point may appear at the same time.

FIG. 3 is a characteristic diagram of another embodiment. As shown in FIG. 3, even when the reflectance in the crystalline state is higher than that in the amorphous state, the irradiation laser power versus reflectance curve 1 can have an extreme value 2. FIG. 4 shows a phase change optical disc 20' exhibiting the characteristics shown in FIG. Jl (90 n rn , S
b S e B i-based sum change film Record 1 model 7 is 9
This is a structure in which a Q nm protective film 9 is formed by sputtering.

Jut folding index IN of crystalline state of S b S e B i flu is =5-21, and Ajl folding index N of amorphous state
A = 4-io, 5, and the refractive index of 5iaN<Ij mulberry 6 is N-2,3-/:0.05. St, N, is h
1. Sj, S on the N4 target to increase the refractive index.
An i-chip is placed and sputtered.

Based on the above, the amplitude reflectance ratio of crystal and amorphous is calculated/RA
=0.5. Crystallinity X= as phase difference Δω=8Qdeg
The reflectance is maximized at approximately 0.9.

If the irradiated laser power vs. reflectance curve 1 has an extreme value 2 as shown in Figure 3, and erasure is performed near the extreme value 2, the crystallinity will be slightly aerated due to the influence of the previous data as in Figure 1. Similarly, even if this occurs, no change in reflectance occurs, and since unerased portions can be suppressed, the erasure ratio can be improved.

The present invention is not limited to the above-mentioned embodiments, and when laser irradiation is performed, if the irradiation laser power vs. reflection polarity line has an extreme value with respect to a change in laser power, the above-mentioned unerasable It is clear that a suppressive effect occurs. Table 1 shows other examples.

Table 1 Other Examples with Extreme Values of Reflectance Figure 9 shows the relationship between crystallinity and reflectance by changing the thickness of the interference film to change the phase difference between the reflected light of the crystalline phase and the amorphous phase. FIG. 4 is a diagram showing a change in the cancellation ratio due to a change in the appearance of the extreme value when .

When the phase position is less than 60 degrees (deg), the extreme value is crystallinity X
= 1, the effect of suppressing the difference in crystallinity that remains unerased is small. The phase difference is 60 degrees (deg
) or above, the practical erasing level is 30d.
An erasure ratio of 8 or more can be obtained.

〔Effect of the invention〕

According to the present invention, it is possible to suppress the change in the crystallinity of the phase change film, which remains unerased during erasing, from being converted into a change in reflectance, thereby improving the erasing ratio during one-beam override. A phase change optical information recording carrier can be provided. In addition, phase change optical information fQ We for using this phase change optical information recording carrier
can provide a recording method.

[Brief explanation of the drawing]

FIGS. 1 and 3 are characteristic diagrams showing laser power versus reflectance curves in an embodiment of the optical disc of the present invention. FIGS. 2 and 4 are cross-sectional views showing the configuration of an embodiment of the optical disc of the present invention having the characteristics shown in FIGS. 1 and 3, respectively, and FIGS. 5 to 9 are explanatory diagrams of the operation of the present invention. . ■...Laser power vs. reflectance curve, 2...Extreme value, 5
... Substrate, 6... Interference film, 7... Phase change film. Figure 1 Challenge 2 Figure No. 0 2 4- 6 8 10
/2 /'l-16 irradiation laser par(7n
W) Collection of drawings 18 Drawings of drawings 90 /20 /sO phase envy (/eH)

Claims (1)

[Claims] 1. In a phase change optical information recording carrier having a recording film utilizing phase change on a substrate and a multiple interference film provided adjacent to the recording film, irradiation to the phase change optical information recording carrier A phase change optical information recording carrier characterized in that the reflectance has an extreme value with respect to the irradiated laser power based on the characteristics of the laser power and the reflectance of the irradiated part irradiated with the laser light. 2. In the phase change optical information recording carrier according to claim 1, the erasing operation power is set in the vicinity of the irradiation laser power that takes the extreme value of the reflectance on the irradiation laser power versus reflectance characteristic. phase change optical information recording method. 3. In an optical information recording carrier having a recording film that utilizes phase change, in terms of crystallinity vs. reflectance characteristics, when the crystallinity of the recording film is set to X (0≦X≦1), 0< A phase change optical information recording carrier characterized by having an extreme value of reflectance between X<1. 4. The phase difference between the reflected light phase of the recording film in the amorphous phase and the reflected light phase of the crystalline recording film is 60 degrees (d
eg) The phase change optical information recording carrier according to claim 1 or claim 3, wherein the refractive index and film thickness of a multiple interference film are set adjacent to the recording film as described above.