JP2834150B2 - Optical information recording medium and optical information recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium, and more particularly to an optical information recording medium using a phase change, which is suitable for improving the erasing ratio in one-beam overwriting. And an optical information recording method.

[Conventional technology]

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

Regarding one-beam overwriting of phase change film, IEICE Technical Report Vol.87, No.310CPM87-88, 89, 90
It is described in.

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

[Problems to be solved by the invention]

However, the above prior art is based on the idealized principle of one-beam overwriting, and in reality, the phase change film is completely controlled in an amorphous state (recorded state) and a crystalline state (erased state). Not in.

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

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

Explaining the phase state of the recording film, the ideal amorphous state means that no crystals exist in the structure of the recording film, and the ideal crystalline state means that the structure of the film is all arranged in a crystalline state. It is that you are. However, in reality, an amorphous state obtained by irradiating a laser to melt a recording film and then rapidly cooling it is a state in which the degree of crystallinity (the degree of crystal growth) is low,
The crystal state crystallized by laser irradiation is merely a state having a high degree of crystallinity.

In particular, in the crystallization process in erasing, crystallization can be made high by one laser irradiation, but crystallization cannot be completed.

For this reason, when the whole is to be erased (crystallized), the same data is erased where the data was previously written from the amorphous state and where the data was erased from the crystalline state. Even if they are different, a difference occurs in the degree of crystallinity.

On the other hand, the relationship between the crystallinity and the reproduction laser light reflectance of the recording film will be described. When the crystallinity increases, the reproduction laser light reflectance increases monotonically, and when the crystallinity decreases, the reproduction laser light reflectance increases. Monotonically decreases. Although the increase / decrease is reversed depending on the object, the reflectance of the reproduction laser beam monotonously changes in accordance with the degree of crystallinity.

Therefore, at the time of overwriting, when the previous data is in an amorphous state and in a crystalline state, the degree of crystallinity is different when crystallized (erased). The result is a difference in reflectivity. The difference in the reflectivity of the reproduction laser light is left unerased, and the erasure ratio is set low.

Japanese Patent Application Laid-Open No. 62-222442 discloses that a dielectric is provided adjacent to a recording film. However, there is no description about improving the erasing ratio by adjusting the change in the reflectance of a reproduction laser beam. Is not described.

The prior art described above does not take into consideration suppression of unerased portions, and has a problem that the erasing ratio is low.

An object of the present invention is to provide an optical information recording medium and an optical information recording method using a phase change with an improved erase ratio.

[Means for solving the problem]

The object is to provide a recording film utilizing a phase change and a multiple interference film adjacent to the recording film on a substrate, wherein the reflected light phase of the amorphous phase recording film and the crystalline phase of the recording film By setting the refractive index and the film thickness of the multiple interference film so that the phase difference of the reflected light phase of the laser beam becomes 60 degrees (deg) or more, the laser power of the laser light applied to the recording film and the reproduction laser This is attained by providing an optical information recording medium configured so that a function representing the relationship with the reflectance of the irradiated portion irradiated with light has an extreme value.

Further, it is achieved by crystallizing the recording film by irradiating the optical information recording medium with laser light at a laser power at which the reflectance has an extreme value.

In order to provide the optical information recording medium with the characteristic that the reproduction laser light reflectance has an extreme value during the above-mentioned crystallization, a dielectric having a high refractive index is provided as a multiple interference film adjacent to the recording film. The thickness can be achieved by appropriately setting the refractive index and film thickness of the recording film in consideration of the optical constant of the recording film.

[Action]

The operation will be described with reference to the drawings. Fig. 7 shows the characteristics (relationship) of the crystallinity and the reflectance of the reproduced laser beam ("reflectance" in the figure).
FIG. The solid line indicates the characteristic of the present invention in which the reflectance of the reproduced laser beam has an extreme value of 2 during crystallization. The broken line shows the characteristic that the reflectance of the conventional reproduction laser beam monotonously changes according to the crystallinity.

In the solid line, when the crystallinity X = 0.8, the reflectance R of the reproduced laser beam becomes the minimum value and shows the extreme value 2 at which the inclination of the tangent becomes zero. Here, if the erasing operation is performed in the vicinity of the crystallinity of X = 0.8, as can be seen from the inclination of the tangent from zero, even if the crystallinity changes around X = 0.8, the reproduction laser light reflectance changes. Hardly occurs (that is, ΔR ≒ 0).

On the other hand, in the conventional broken line, when the crystallinity changes around X = 0.8 (ΔX) due to the influence of the previous history at the time of erasing, the reproduction laser light reflectance monotonously changes in accordance with the crystallinity. A laser light reflection change ΔR ′ occurs.

In the above relationship between the degree of crystallinity and the reflectance of the reproducing laser light, the extreme value of the reflectance of the reproducing laser light is given during crystallization, and the erasing operation is performed in the vicinity of the extreme value. The change in the degree can be suppressed from being converted into a change in the reflectance of the reproduction laser light, and the erasing ratio is improved because there is no remaining unerased component in the reproduction signal.

The dielectric film functions as follows. FIG. 5 is a diagram schematically showing how the dielectric component 10 causes multiple interference with the crystallized component and the amorphous component.

In this drawing, the phase change film is schematically shown in juxtaposition separately into a crystalline component and an amorphous component. The boundary between the crystal and the amorphous was schematically indicated by the crystallinity X. When the laser recording film (phase-change film), the reflected light is reflected light E _X to the crystal component
And the synthesis of the reflected light E _A for the amorphous component. Reflected light E _X
And the reflected light E _A are each crystal component, a reflected light of the result of multiple interference between the amorphous component and the dielectric film.

Here, when irradiated with light as the amplitude E = E _O cosωt as incident light, reflected light E _X against crystallization component E _X = E _O R _X
a cos (ωt + ω _X), the reflected light E _X for amorphization component is _{E X = E O R A cos} (ωt + ω A). When the whole of the reflected light E _R to the degree of crystallinity and _{X, E R = R X ·} X + E A · (1-X) = E O {R X cos (ωt + ω X) · X + R A cos (ωt + ω
_A ) · (1-X)｝. Here, R _X is the reflectivity as a result of multiple interference between the crystal component of the phase change film and the dielectric film, and ω _X is the phase displacement of the reflected light as a result of the multiple interference. R _A is the reflectance as a result of multiple interference between the amorphous component of the phase change film and the dielectric, and ω _A
Is the phase change of the reflected light resulting from the multiple interference.

Expand expressions for the reflected light E _R described above, and arranging for _{ωt, E R = E O [} {R X cosω X · X + R A cosω A · (1-X)} cosωt - {R X sinω X · X + R the _{a sinω a · (1-X} )} sinωt] = E O Rcos (ωt + α). Here, if _{C1 = R X cosω X · X} + R A cosω A · (1-X) C2 = R X sinω X · X + R A sinω A · (1-X) to, cosα = C1 / R, sinα = C2 / ^{R, R = (C1 2 +} C
2 ² ) ^1/2 , and R is nothing less than full amplitude reflectance.

Reflectance R _{^{is, R 2 = {R X cosω}} X · X + R A cosω A · (1-X)} 2 + {R X sinω X · X + R A sinω A · (1-X)} ^2, the X To summarize, R ² = R _A ² {(T ² −2Tcos (ω _X −ω _A ) +1) X ² +2 (Tcos (ω _X −ω _A ) −1) X + 1} (where T = R _X / R _A ).

Therefore, the reflectance of the reflected light with respect to the incident light has an extreme value. Note that this equation is an equation representing the relationship between the reflectance and the crystallinity, but as described later, changing the irradiation laser power is nothing but changing the crystallinity of the recording film. It can be seen from the equation that the reproduction laser light reflectance has an extreme value also in the relationship between the reproduction laser light reflectance and the irradiation laser power.

The ratio between R _X and R _A and the difference between ω _X and ω _A are determined by appropriately setting the refractive index, film thickness, etc. of the dielectric film with respect to the optical constants (refractive index, extinction coefficient) of the recording film. Can be changed by FIG. 6 shows the relationship between the crystallinity X and the reproduction laser light reflectance R (“reflectance R” in the figure) using the ratio between R _X and R _A and the difference between ω _X and ω _A as parameters. Show. The vertical axis reflectance is
This is normalized by _RA .

By appropriately setting R _X / R _A and Δω = ω _X −ω _{A, it} is possible to give the reproduction laser light reflectance an extreme value during crystallization (0 <x <1). Here, an example where X = 0.8 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 irradiation laser power dependence of the reproduction laser light reflectance (“reflectance” in the figure) of the optical information recording medium of the present invention. The optical information recording medium (optical disk) having the configuration shown in FIG. 2 was used as the optical information recording medium. First, the configuration will be described. An AlN film as a first interference film 6 'is formed on a transparent glass substrate 5 having a diameter of 130 .phi.
nm, an InSbTe phase change film as a recording film of 30 nm, an AlN film of 70 nm as the second interference film 6 ″, and an Au film of 100 n as the reflection film 8.
The optical disk 20 has an AlN film formed as a protective film by sputtering in the order of 100 nm.

The refractive index N _C of the crystalline state of the InSbTe phase change film 2 is N _C = 4.7
−i1.7, and the refractive index N _A of the amorphous state is N _A = 5.0−i 0.8
In and, _Al N film 6 ', the refractive index N of the 6 "is N = 2.0. Above refractive index and thickness of each layer, further Au layer 6',
Using a 6 ″ reflection to cause multiple interference, the amplitude reflectance ratio R _X / R _A between the crystalline state and the amorphous state is set to 0.6, the phase difference Δω is set to 60 deg, and the reproduced laser beam is reflected at the crystallinity X = 0.9. The rate is set to have a minimum value.

The crystallization temperature T _X of the above InSbTe phase change film is T _X = 260 ° C.
Here, the optical disk having the above configuration is placed in an oven for 30 minutes.
FIG. 1 shows the results obtained by measuring the irradiation laser power dependence of the reproduction laser light reflectance of the optical disk 20 while rotating the disk at 180 rpm for 1 hour at a temperature of 0 ° C. to complete the crystallization. Was.

The operation of FIG. 1 will be described. Reference numeral 1 denotes a laser power versus a reproduction laser light reflectance curve. Although the crystallization was completed in the oven, the reproduction laser light reflectance was 14%. When this is irradiated with laser, there is no change up to the irradiation laser power of 6 mW. When irradiating 8mW, the reproduction laser light reflectance decreases,
The reproduction laser light reflectance R becomes 12%. The reproduction laser light reflectance starts to increase from 10 mW, and at 14 mW or more, the reproduction laser light reflectance tends to be saturated, and R = 22%.

Here, changing the irradiation laser power is nothing but changing the crystallinity of the recording film 7, and FIG. 1 shows that the crystallinity was decreased by increasing the irradiation laser power from the state of high crystallinity. Will be. Irradiation laser power 8mW ~ 10mW
At the crystallinity corresponding to the above, the reflectance of the reproduced laser beam via the interference films 6 'and 6 "has the minimum value 2. That is, there is a slight change in the crystallinity near this minimum value. Also, no change occurs in the reproduction laser light reflectance.

Therefore, if the erasing laser power 4 is set to 8 to 10 mW at which the reflectivity of the reproducing laser beam becomes an extreme value (here, 10 mW), even if there is a slight change in the crystallinity at the time of erasing, the reproducing laser beam is reflected. Since the rate change does not occur, there is an effect that the unerased residue (a slight change in crystallinity) during overwriting can be suppressed and the erasing ratio can be improved.

For the recording laser power 3, the recording laser power 3
It was set to 14mW. The change in the reflectance of the reproduction laser light as a recording signal is R = 22% of the part irradiated with the recording laser power of 14 mW.
And a large ratio of R = 12% of the part irradiated with the erasing laser power of 14 mW, and a high C / N of C / N = 50 dB was obtained. When a 3 MHz signal is overwritten from a 2 MHz frequency signal, an erasing ratio of as high as 40 dB for a 2 MHz frequency component is obtained, and a high C / N and a high erasing ratio are obtained.

In addition, the characteristics shown in FIG. 1 may be started from an amorphous state. When the change in the reproduction laser light reflectance is measured by reducing the crystallinity while reducing the irradiation laser power, the crystallinity X =
It is clear that the reflectance of the reproduction laser beam becomes minimal at the irradiation laser power of 0.9, and has an extreme value in the reflectance of the reproduction laser beam similarly to FIG.

Further, in order to change the crystallinity, the pulse width of the irradiation laser power may be changed, or in the case of a disk, the rotation speed may be changed. Lowering the number of revolutions substantially increases the laser irradiation time and promotes crystallization.

FIG. 8 shows the relationship between the irradiation laser power and the reproduction laser light reflectance (“reflectance” in the figure) by reducing the rotation speed from 1800 rpm to 600 rpm in order to confirm the extreme value of the reproduction laser light reflectance. It is a thing. Due to the low-speed rotation, rapid cooling of the recording film 7 becomes insufficient, so that the change in the reflectivity of the reproducing laser beam at high power becomes small. However, the crystallization can be completed. You can clearly see that you are out.

Further, in the configuration of an optical disc having good cooling characteristics, an extreme value 2 'in a recrystallization process when heated to a temperature higher than the melting point and an extreme value 2 in a 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 reproduction laser light reflectance in the crystalline state is higher than that in the amorphous state, the reflection laser power versus the reproduction laser light reflectance (“reflectance” in the figure) curve 1 shows an extreme value of 2 Can be held. FIG. 4 shows a phase change type optical disk 20 'having the characteristics shown in FIG. A 90 nm Si ₃ N ₄ film as an interference film 6 on a substrate 5 and a recording film 7 as an SbSeBi-based phase change film
In this configuration, the protective film 9 is formed to a thickness of 0 nm by sputtering.

The refractive index N _{C in} the crystalline state of the SbSeBi film is N _C = 5-i1, the refractive index N _{A in the} amorphous state is N _A = 4-i0.5, and the Si ₃ N ₄ film 6
Is N = 2.3-i0.05. Si ₃ N ₄ is sputtered with a Si chip mounted on a Si ₃ N ₄ target to increase the refractive index.

As described above, the amplitude reflectance ratio of the crystal and the amorphous material R _X / R _A = 0.
5. When the phase difference Δω is 80 deg, the reflectance of the reproduced laser beam is maximized when the crystallinity X is about 0.9.

As shown in FIG. 3, when the irradiation laser power vs. the reproduction laser light reflectance curve 1 has an extreme value 2 and the erasing is performed near the extreme value 2, the crystallinity is slightly affected by the previous data as in FIG. Even if shading occurs, the reflectance of the reproduction laser beam does not change, and the unerased portion can be suppressed, so that the erasing ratio can be improved similarly.

The present invention is not limited to the above-described embodiment. When the laser irradiation is performed, if the irradiation laser power vs. the reproduction laser light reflectance curve has an extreme value with respect to the change in the laser power, the above-described eraser is used. Obviously, the remaining suppression effect occurs. Table 1 shows another embodiment.

FIG. 9 shows that when the thickness of the interference film is changed to change the phase difference between the reflected light of the crystalline phase and the amorphous phase and the relationship between the crystallinity and the reflectance of the reproduced laser beam has an extreme value, FIG. 7 is a diagram showing a change in an erasing ratio due to a change in a value appearance.

When the phase difference is 60 degrees (deg) or less, the extreme value is the crystallinity X =
Since the value is too close to 1, the effect of suppressing the difference in crystallinity that remains unerased is small. By setting the phase difference to 60 degrees (deg) or more, an erase ratio of 30 dB or more, which is a practical erase level, can be obtained.

〔The invention's effect〕

According to the present invention, it is possible to suppress conversion of the density of the phase change film remaining unerased at the time of erasing into a change in the reflectance of the reproduction laser beam. And an optical information recording medium utilizing the same.

[Brief description of the drawings]

FIG. 1 and FIG. 3 are characteristic diagrams showing a laser power versus a reproduction laser light reflectance curve in an embodiment of the optical disk of the present invention.
2 and 4 are sectional views showing the configuration of an embodiment of the optical disk of the present invention having the characteristics shown in FIGS. 1 and 3, respectively. FIGS. 5 to 9 are explanatory views of the operation of the present invention. . 1... Laser power vs. reproduction laser light reflectance curve, 2.
Extreme value, 5: substrate, 6: interference film, 7: phase change film.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Nogami 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Yukio Fukui 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi, Ltd. Home Appliance Research Laboratory (56) References JP-A-61-269247 (JP, A) JP-A-62-204449 (JP, A)

Claims (4)

(57) [Claims] 1. An optical information recording medium comprising a recording film utilizing a phase change and a multiple interference film provided adjacent to the recording film on a substrate, wherein an optical phase of the amorphous film is reflected by the recording film. The recording film is irradiated by setting the refractive index and the film thickness of the multiple interference film so that the phase difference between the reflected light phase of the recording film and the crystalline phase is 60 degrees (deg) or more. An optical information recording medium, wherein a function representing a relationship between a laser power of a laser beam and a reflectance of an irradiated portion irradiated with a reproduction laser beam has an extreme value. 2. A recording film utilizing a phase change and a multiple interference film adjacent to the recording film are provided on a substrate, and the recording film is irradiated with a laser power of a laser beam and a reproduction laser beam. Irradiating a laser beam with a laser power at which the reflectance has an extreme value to an optical information recording medium configured so that a function representing the relationship with the reflectance of the irradiating portion has an extreme value, thereby exposing the recording film. An optical information recording method characterized by crystallization. 3. A recording film utilizing a phase change and a multiple interference film are laminated on a substrate, and as the laser power of the laser light applied to the recording film increases, the reflectance of the reproduction laser light decreases. An optical information recording method comprising: irradiating a laser beam with a laser power such that the reflectivity does not change to an optical information recording medium configured to change from an increase to an increase to crystallize the recording film. 4. A recording film utilizing phase change and a multiple interference film are laminated on a substrate, and as the laser power of the laser light applied to the recording film increases, the reflectance of the reproduction laser light increases. An optical information recording method comprising: irradiating a laser beam with a laser power such that the reflectivity does not change to an optical information recording medium configured to change from a decreasing state to a decreasing state to crystallize the recording film.