JPS63300441A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To enable reading out of information of a rewritable recording medium with a reproduction-only device by laminating a thin film having a specific refractive index on the light bean incident side of the recording film of the recording medium which is recorded with the information by the phase transfer of the recording film. CONSTITUTION:The rewritable recording medium is constituted by providing the recording film 13 on a substrate 11 and providing a thin film adjusting layer 12 having >=2.5 refractive index therebetween. The substrate 11 in the figure consists of glass; the recording film 13 is a thin GeTe film having 100nm thickness, and the adjusting layer 12 is a thin GeSe film having 3.2 refractive index, 0.13 attenuation coefft. and 65nm thickness. A recording and reproducing beam 14 is projected through the substrate 11 to the recording film 13. The reflectivity in the part irradiated with the laser beam 14 is lower than the reflectivity in the unirradiated part and, therefore, the reproduction signal has the same polarity as the polarity of the reproduction signal of the reproduction- only device. The interchangeability with the reproduction-only type recording medium is thereby provided to this medium.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical information recording medium on which information is recorded and reproduced using a light beam.

(Prior art) In an optical information recording medium, a recording thin film is irradiated with a light beam, and the reflectance is measured by changing the optical constant due to the amorphous-crystalline or crystalline-crystalline phase transition of the material constituting the recording thin film. Methods of causing changes and recording information are known. Known examples of such recording materials include germanium-tellurium compounds, low tellurium oxides, and antimony triheptadonide, all of which have a reflectance n' of the light-irradiated portion of the recording film that is not irradiated with a light beam. Information is recorded by increasing the reflectance of the area n.

For example, a GeTe thin film used as a recording film has an amorphous structure at room temperature, has a reflectance n=4°2, and an optical constant of an extinction coefficient=0.7. This thin film is heated to 180℃
When heated above, it transforms into a crystalline structure and n'=5,4
, k=2, and changes to have new optical constants of 4. The optical constants of this crystalline thin film remain unchanged even when cooled to room temperature. Therefore, a recording laser beam is irradiated onto a conventional optical information recording medium in which a GeTe thin film with a thickness of l Q Q nm is deposited on a glass substrate, and the recording film in the laser beam irradiated area is transformed from amorphous to crystalline. As is well known, the reflectance at the wavelength λ = 830 nm changes from 15% to 48% due to the change in optical constants as described above, and the interference effect of light changes, and the reflectance of the information recording area is high. It has the following properties.

Moreover, the Te-0 thin film also used as a recording film is
At room temperature, it has a microcrystalline structure; n=3゜5, n=0
．． It has an optical constant of 5, but when irradiated with laser light, the particles of Te crystal become large, n=3.8. to = 0.8
It changes to a new optical constant called . The optical constants of this crystalline film remain unchanged even when cooled to room temperature. Therefore, in an optical information recording medium having a structure in which a Te-0 thin film with a thickness of 120 nrn is deposited on a PMMA substrate, the optical interference effect changes as is well known due to the change in the optical constants as described above due to laser beam irradiation. The reflectance at a wavelength of 830 nm changes from 15% to 27%, indicating that the reflectance of the information recording area is high. Furthermore, the Sb2Se3 thin film used as the recording film has an amorphous structure at room temperature, n=3.95. When this thin film 63 is heated to 180° C. or higher, it transforms into a crystalline structure, and has an optical constant of n=4.75. k=0.54
It has a new optical constant: The optical constants of this crystalline thin film remain unchanged even when cooled to room temperature. Therefore, on a glass substrate, a thickness of 40 nm (F) 8b2
8e3 recording film and 40nm Bi2Te.

When a recording laser beam is irradiated onto an optical information recording medium having a thin film structure, the recording film in the laser beam irradiated area transitions from amorphous to crystalline, so the reflection at wavelength λ = 830 nm in this area The rate is 10% as above
The reflectance of the information recording area increases.

(Problem to be solved by the invention) However, in read-only optical information media such as laser discs and compact discs, information is recorded as unevenness called bits, and pits are affected by diffraction and interference effects of light beams. The reflectance of the reproduction light beam becomes low.

As described above, the polarity of the reproduction signal obtained when information is read by the reflected light beam of the recording thin film light beam irradiation section is opposite to the polarity of the reproduction signal of the read-only optical information medium. Therefore, in order to read information from such an additional recording device i-information recording medium using a read-only optical information medium reproducing apparatus, it is necessary to add a function to invert the polarity of the reproduced signal to the read-only optical information medium reproducing apparatus. Playback equipment becomes expensive. Furthermore, a reproducing apparatus that does not have a function of reversing the polarity of a reproduced signal has the disadvantage that information recorded on the above-mentioned additional recording type optical information recording medium cannot be reproduced.

(Means for Solving the Problems) The present invention solves the above-mentioned drawbacks and makes it a read-only type optical recording medium.The present invention is characterized by a light beam recording medium having a thin recording film on the light beam incident side of the recording film. The reason is that thin films having optical constants with a refractive index n of 2.5 or more and an extinction coefficient k of less than 1.3 are laminated (Example) FIG. 1 shows an optical information recording system according to the present invention. An example of the medium is shown. That is, 11 is a glass substrate, and recording film 13 is
germanium telluride (GeT) with a thickness of 1100 nm as
e) Germanium selenide (GeSe) with a thickness of 65 nm having a refractive index n=3.2 and an extinction coefficient=0.13 between the glass substrate 11 and the recording film 13.
) It is an optical information recording medium with a structure in which thin & is laminated. The recording/reproducing light beam 14 is irradiated onto the recording film through the glass substrate.

In FIG. 2, Ge is deposited on the light beam incident side of the GeTe recording film 13.
3 shows the relationship between the reflectance and the thickness of the Gene thin film of the optical information recording medium according to the present example in which the Gene thin film is laminated. 21
22 represents the reflectance of the area not irradiated with the laser beam, that is, the area where information is not recorded, and 22 represents the reflectance of the area irradiated with the laser beam, ie, the information recording area.

Here, in the conventional example where the film thickness is 01, that is, there is no Gene thin film, the reflectance 22 of the information recording area is higher than the reflectance 21 of the information unrecorded area as shown in FIG.
In the optical information recording medium according to this embodiment in which the Te recording film 13 is laminated on the light beam incident side, the thickness of the QeSe thin film is 40 to 9
If the wavelength is selected to be 0 nm or 180 to 230 nm, the reflectance 22 of the information recording area can be made lower than the reflectance 21 of the information unrecorded area, as shown in FIG. G of this example
When the thickness of the ene thin film 12 is 65% m, the reflectance of the information recording area is 4%, and the reflectance of the information unrecorded area is 21%. That is, similar to the above-mentioned normal read-only optical information recording medium, a result is obtained in which the reflectance of the information recording portion is lower than that of the non-information recording portion. Therefore, the optical information recording medium according to this practical example on which information has been recorded by irradiating the laser beam 14 can be used without adding a function of reversing the polarity of the reproduction signal to the reproduction-only optical information recording medium reproducing apparatus. Information can be reproduced by a recording medium reproduction device.

In the embodiment shown in FIG. 1, G is used as the recording film 13.
eTe thin film is used, but Ge8nTe, Ge in which part of the Ge of GeTe is replaced with Sn or Pb is used.
Even in pbTe, Ge5nPbTe films, and other thin films containing GeTe as the main component and adding a third element, GeTe
The present invention can be applied similarly to thin films.

Further, in this embodiment, since the recording/reproducing light beam 14 is irradiated from the glass substrate 11 side, the glass substrate 11
A GeSe thin film is laminated between the GeTe recording film 13 and the recording/reproducing light beam 14.
When irradiating from the side, GeSe thin film-G e T
The same effect as this embodiment can be obtained by forming a structure in which the e-recording film and the glass substrate are laminated in this order.

FIG. 4 shows another embodiment of the optical information recording medium according to the present invention, in which a polymethyl methacrylate (PMMA) substrate is used for the glass substrate 11 in FIG.
3, a tellurium oxide (Te-0) thin film with a thickness of 120 nm is used, and a refractive index n=3 is used between the substrate 41 and the recording film 43.
．． This optical information recording medium has a structure in which a germanium (Ge) thin film 42 having an extinction coefficient of 8 and an optical constant of 0 and 17 and a thickness of 5 Q nm is laminated. Recording/reproducing light beam 44
1t, the recording film is irradiated through the PMMA substrate.

FIG. 5 shows the relationship between the reflectance and the thickness of the Ge thin film 42 of the optical information recording medium according to this embodiment in which the Ge thin film 42 is laminated on the light beam incident side of the TeO recording film 43. 51
52 indicates the reflectance of the area not irradiated with the laser beam, that is, the area where no information is recorded, and 52 indicates the reflectance of the area irradiated with the laser beam, ie, the information recording area.

Here, in the conventional example where the film thickness is O1, that is, there is no Ge thin film, the reflectance of the information recording area is higher than that of the non-information recording area, but the Ge thin film 42 is placed on the light beam incident side of the TeO recording film 43. In the laminated optical/information recording medium according to this example, G
e The thickness of the thin film 42 is 20 to 90 nm or 125 to 1
If 95 nm is selected, as can be seen from FIG. 5, the reflectance 52 of the information recording area can be made lower than the reflectance 51 of the information unrecorded area. The thickness of the Ge thin film 42 in this example is 5Qnm.
In this case, the reflectance of the information recording area is 23%, and the reflectance of the information unrecorded area is 40%. That is, similar to the aforementioned ordinary read-only optical information recording medium, the reflectance of the information recording area is lower than that of the non-information recording area.

Therefore, the optical information recording medium according to the present embodiment on which information is recorded by irradiating the laser beam 44 can be used as a read-only optical information recording medium without adding a function of reversing the polarity of the read signal to the read-only optical information recording medium reproducing apparatus. The information can be played back on a media playback device.

FIG. 6 shows another embodiment of the optical information recording medium according to the present invention. That is, 61 is a glass substrate and a recording film 63 is
Antimony triselenide (8b, S
es), bismuth tritellide (Bi2Te3) with a thickness of 4 Qnm is used as the light absorption film 64, and the substrate 6
1 and the recording film 63, the refractive index n=3.1. This optical information recording medium has a structure in which antimony trisulfide (Sb, S,) thin films 62 having a thickness of 60% m and having an optical constant of extinction coefficient = 0.13 are laminated. The recording/reproducing light beam 65 is irradiated onto the recording film 63 through the glass substrate 61 .

Figure 7 shows an Sb2Se3 recording film with 5b2s on the beam incidence side.
, shows the relationship between the reflectance of the optical information recording medium according to this example in which thin films are laminated and the Sb2S3 thin film layer. Reference numeral 71 indicates the reflectance of the area not irradiated with the laser beam, that is, the area where information is not recorded, and 72 indicates the reflectance of the area irradiated with the laser beam, ie, the information recording area.

5b2s, in the conventional example where the film thickness is O without the presence of a thin film, the reflectance of the information recording area is higher than that of the non-information recording area, but in 5b2s, the thin film is laminated on the light beam incident side of the GeTe recording film. In the optical information recording medium according to this example, 5b2
S. If the thin film thickness is selected to be 26 to 110 nm, the reflectance of the information recording area can be made lower than that of the information-unrecorded area. When the sb, s, and thin film thicknesses of this example are 5 Q nm, the reflectance of the information recording area is 17%, and the reflectance of the information unrecorded area is 46%. That is, similar to the read-only optical information recording medium described above, a result is obtained in which the reflectance of the information recording portion is lower than that of the non-information recording portion. Therefore, the optical information recording medium according to this embodiment in which information is recorded by irradiating a laser beam can be used in a reproduction-only optical information recording medium reproducing apparatus without adding a function of reversing the reproduction signal polarity. Information can be reproduced by a recording medium reproduction device.

The reason why the reflectance reversal phenomenon as described above occurs will be explained in more detail. .

If a recording film with a refractive index n and a film thickness d is deposited on a transparent substrate, and the wavelength of the recording light is λ, the reflectance will be nd=λ/2・m due to the optical interference effect.・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・(υ(However, m=1, 2, 3...) It shows the minimum value under the condition that nφd=λ/4・(2m+1) ・・・・・・・・・
・・・・・・・・・・・・・・・・・・(2) (however, m=0.1, 2...) It shows the maximum value under the following conditions.

Here, in the secondary optical information recording medium, information is recorded in such a manner that the reflectance of the light-irradiated portion of the recording film is higher than that of the light-beam-unirradiated portion, as described above.

On the other hand, in the above-mentioned example, the refractive index n and the optical thicknesses u, d, +n of the area not irradiated with the light beam are
n, d, +n2d, = (1+172)n4 d
B=3/4λ ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・(4)(
-〇・7! ;l) The reflectance is maximum in the area not irradiated with the light beam.

/ On the other hand, the refractive index n of the light beam irradiated part, / is 1.1 n, ≦n, /≦ in the recording film shown in the embodiment of the present invention.
1.35n, Therefore, the optical thickness ratio of the light beam irradiation part is '10π, dzt is 1.5n, d, ≦n, '-d, + n, d2≦1.
85 n1ct.

It is. Therefore, if 1 O18λ:n, @d, +n2d2≦0.93λ, the reflectance approaches the minimum value, which is smaller than the maximum value. Therefore, the reflectance of the light irradiation part and the light irradiation part are reversed.

In each of the above Wbd examples, n=2.5 or more and n=1.
When a thin film of 3 or less is laminated on the light beam incident side of the recording film,
(Reflection overlap of information recording area) A reversal phenomenon occurs in which the reflectance becomes lower than that of the information non-recording area, so this point will be explained in more detail below.

That is, the refractive index and extinction coefficient of the recording film and the thin film laminated on the light beam incident side of the recording film are as follows: The refractive index n1 of the recording film light irradiation part shown in each of the above-mentioned examples is 3.5 to 4.2, and the extinction coefficient is 0.1 to 0.7. Refractive index of thin film n2
must be greater than or equal to 2.5. Note that in consideration of practicality, the extinction coefficient needs to be 1.3 or less.

Figure 3 shows a glass substrate 11°GeTe as shown in Figure 1.
In an optical information recording medium having a recording film 13 and a thin film 12 laminated on the light beam incident side of the GeTe recording film, the thin film 12 is variously changed and the refractive index n2 of the thin film 12 is opposite to that of the obtained optical information recording medium. Shows the relationship with the car. 31 indicates the reflectance of the information-unrecorded area, and 32 indicates the reflectance of the information-recorded area.

This figure shows that the reversal phenomenon in which the reflectance of the information recording area is lower than that of the non-information recording area, similar to read-only optical information recording media, occurs because the refractive index n2 of the thin film is 2.5 or more. It can be seen that it is.

4 and 6 also show Ge and Sb2, respectively.
It can be seen that by using various thin films for S3, the above-mentioned reverse development occurs when the refractive index n2 of these thin films is 2.5 or more.

Furthermore, in the above embodiments, since the recording/reproducing light beam is irradiated from the substrate side of glass or PMMA resin, etc., a thin film of GeSe, Sb2S8, etc. is laminated as an adjustment layer between the substrate and the recording film. However, when the recording/reproducing light beam is irradiated from the side opposite to the substrate, a thin adjustment layer →
The same effect as this embodiment can be obtained by forming a structure in which the recording film→absorbing film→substrate are laminated in this order.

In the above embodiments, glass or polymethyl methacrylate (PMMA) is used for the substrate 11, but the present invention is not limited to this, and for example, epoxy, polycarbonate, or polyester may be used.

Light-transmitting resins such as polyolefins can also be used.

In the above embodiments, GeSe, 5b2S8. Although a thin film of Ge or the like is used, the present invention is not limited to these, and other materials can be used as long as the refractive index n=2.5 or more. It is desirable that the extinction coefficient is less than 1.3. Therefore, for example, 5b2Ses.

Ge8. Si, 5nSe, 0dTe, 0dSe.

CdS can be used.

(Effects) As described in detail above, there is a substrate and a recording film formed on the substrate, and the recording film is irradiated with a light beam to cause a phase transition of the recording film. The optical information recording medium of the present invention is characterized in that a thin film having a refractive index n of 2.5 or more is laminated on the light beam incident side of the recording film in an optical information recording medium that records information by increasing the optical reflectance. Due to the optical interference effect caused by the thin film, the reflectance of the information recording area irradiated with light is lower than the reflectance of the non-information recording area irradiated with light. The reproducing apparatus can reproduce information without adding a reproduction signal polarity reversal function, and is compatible with reproduction-only optical information recording media.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIGS. 2 and 3 are line diagrams for explaining its operation, FIG. 4 is a cross-sectional view showing another embodiment of the present invention, and FIG. 6 is a sectional view showing still another embodiment of the present invention, and FIG. 7 is a diagram explaining the operation. 11.41.61...Substrate 12,42,62・
...Adjustment 113.43,63...Recording film' so +00 15
0 ADDtest all fL4 Amamae Kanrin λ Tanen Yutaka＼

Claims (1)

[Claims] It has a base and a recording film formed on the base, and information is transmitted by irradiating the recording film with a light beam to cause a phase transition in the recording film and changing the optical reflectance of the light irradiated part of the recording film. 1. An optical information recording medium for recording, characterized in that a thin film having a refractive index n of 2.5 or more is laminated on the light beam incident side of the recording film.