JPH07262609A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To obtain an optical information recording medium ensuring a sufficiently large quantity of reflected light, enabling stable focusing and tracking, inhibiting the fluctuation of the edge and capable of selecting film thickness in a wide range. CONSTITUTION:In an optical information recording medium with a 1st protective layer 11, a recording layer 13 forming a recorded part having reflectance varied by irradiation with a light beam, a 2nd protective layer 14 and a reflecting layer 15 on the transparent substrate 10, a high refractive index layer 12 is formed between the 1st protective layer 11 and the recording layer 13 so that the reflectance of the recorded part at recording wavelength is made higher than the unreflectance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention changes the optical characteristics of a recording layer due to a change in atomic arrangement by irradiation with a laser beam, an electron beam, etc., and repeatedly records and erases information. The present invention relates to an optical information recording medium that records and reproduces information by detecting changes in optical characteristics.

[0002]

2. Description of the Related Art A recordable and erasable information recording medium has a structure in which a first protective layer, a recording layer, a second protective layer and a reflective layer are sequentially laminated on a transparent substrate. The substrate is made of glass or a plastic material (for example, polymethylmethacrylate resin or polycarbonate resin), and the first and second protective layers are made of ZnS, SiO ₂ , Al ₂ O ₃ or a mixture thereof. The recording layer 3 is made of chalcogenide such as GeSbTe, and these are formed by a deposition method such as vacuum deposition or sputtering. The reflective layer is made of Al, Au or an alloy containing these as a base material and containing Ti, Mo, Zr, Cr and the like.

Using such an information recording medium, the above recording / erasing can be performed, for example, as follows. First,
The entire surface of the information recording medium is irradiated with a light beam and heated to bring the recording layer into a state with high crystallinity (a state in which atoms are relatively correctly arranged, hereinafter referred to as a crystalline state). Then, for writing (recording) information, a short intense pulsed light is irradiated to heat and melt the recording layer, followed by rapid cooling. Then, the pulsed light irradiation portion is in a state where the crystallinity is deteriorated (a state in which the atomic arrangement is disturbed, hereinafter referred to as amorphous).

Since the structures of the atomic arrangement are different between the crystalline state and the amorphous state, the optical properties (transmittance, reflectance) change and information can be recorded. In this way, the written information can be erased by irradiating the recording portion with long weak pulsed light and heating and cooling at a temperature below the melting point. This is because the recording portion returns to the original crystalline state.

Further, by using a laser power (recording power) obtained by superimposing a strong and short pulse on a weak continuous laser power (bias power), a previously formed recording portion (amorphous state) is erased (crystal). The above state can be realized by so-called overwriting in which a new recording portion is formed at the same time.

Since the actual recording medium uses the change in reflectance between crystalline and amorphous as a signal as described above, the film thickness of each of these layers is the optical ratio of the protective layer / recording layer and the protective layer / reflection layer interfaces. It is designed considering the interference effect. Therefore, depending on the optical constants of the material used for the medium, there is an optimum film thickness that allows a large change in optical reflectance.

For example, GeSbTe is used as the recording layer material, Al is used as the reflective layer, and ZnS: S is used as the protective layer.
The reflectance of the recorded state (amorphous) and the unrecorded state (crystal) with respect to the thickness of the second protective layer when using iO ₂ was calculated, and the maximum reflectance change was obtained. Thickness is 1
Either 0 to 20 nm or 130 to 150 nm is preferable. However, when the film thickness is 10 to 20 nm, the recording is performed so that the reflectance decreases in the recording, and the film thickness is 130 nm to 1 nm.
When the thickness is 50 nm, the recording is performed so that the reflectance increases.

Optically, there is a film thickness with which a large change in reflectance can be obtained at the time of such two film thicknesses, but when the film thickness of the protective layer becomes thick, the flow of heat from the recording layer to the reflective layer is obstructed. However, it is known that the quenching cannot be controlled sufficiently by the modulation of the laser power, and the recording characteristics deteriorate (for example, T.OHTA et al. JJAP.VOL 128 (1989) SUPPL).
EMENT28-3, pp123-128). Therefore, as a conventional recording layer, G
When a recording material such as eSbTe is used, the film thickness of the second protective layer is 10 nm to 20 nm, and it is general that the recording is performed so that the reflectance decreases during recording.

FIG. 8 shows a digital data recording method using such an optical disk. (A) shows mark position recording in which recording marks 6 of the same shape are formed and information is obtained from the interval between the mark centers, and (B) is mark length recording in which information is obtained from the length 7 of the recorded marks. Indicates.

[0010]

In the conventional film thickness structure suitable for mark position recording, the recording area (amorphized region) on the disk is not larger than other unrecorded regions (crystals). On the other hand, when the mark length recording is performed, the recording area on the disc becomes larger than that of the mark position recording. For example, assuming that the diameter of the recording mark is 0.78 μm, the area ratio of the recording area to the unrecorded area on the disc in the mark position recording and the mark length recording having the same density is 26% in the case of mark position recording. In the case of mark length recording, it is 44%. When these recording methods are used for a recording medium in which the reflectance is decreased in the conventional recording, the larger the area ratio of the recording area is, the lower the average reflectance is during the reproduction than before the recording. In the case of mark position recording that has been used conventionally, a certain amount of reflected light can be obtained even when recording is performed in the direction in which the reflectance decreases during recording, and it is possible to reproduce the signal by focusing and tracking with an ordinary optical disk drive. It was

However, in order to further increase the recording density, the recording marks are packed and recorded in the mark position recording,
When a disc whose reflectance is lowered during recording is used for reproduction, the area of the recording region is larger than the entire area, and as a result, the average reflectance is 6% or less.
It will be reduced to 0% or less. In the recording medium described above, when the thickness of the second protective layer is about 20 nm,
The average reflectance is 10% or less. Generally, in order to perform stable focusing and tracking, a reflectance of at least about 10% is required. Therefore, with such a configuration, there is a problem in that the amount of reflected light required for focusing and tracking cannot be obtained. In order to increase the reflectance, the thickness of the protective layer may be increased, but this causes a problem that the amount of change in reflectance cannot be maximized.

Further, in the case of the conventional structure in which the reflectance decreases during recording, if there is no escape of light from the back surface of the reflective layer, the reflectance decreases during recording, so the absorptance of the recording portion is large and the unrecorded portion is large. The absorption rate of is small. For this reason,
Since the absorptance differs between the case where a new mark is overwritten on the recorded area and the case where a new mark is overwritten on the unrecorded area, the temperature rise during recording differs. Further, since the unrecorded portion is made of crystals, latent heat is required for melting, and when heated with the same laser power, there is a difference in how the temperature rises. Therefore, the size of the recording mark formed by the melt quenching is different. Therefore, when a recording method having information at the edge of the recording mark is used, the position of the edge fluctuates depending on the location.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical information recording medium capable of stable focusing and tracking with a sufficient amount of reflected light.

Another object of the present invention is to provide an optical information recording medium which enables recording while suppressing edge fluctuations. Furthermore, the film thickness can be selected in a wide range by reducing the change in the reflectance of the unrecorded portion with respect to the film thickness variation,
An object of the present invention is to provide an optical information recording medium whose film thickness accuracy can be easily controlled.

[0015]

In order to solve this problem, the optical information recording medium of the present invention comprises a high refractive index layer formed on a transparent substrate and a high refractive index layer formed on the high refractive index layer. A first protective layer, a recording layer formed on the first protective layer and having a reflectance of a recorded portion higher than that of an unrecorded portion at a recording wavelength; and a second protective layer formed on the recording layer. And a reflective layer formed on the second protective layer.

That is, a high refractive index layer is inserted between the substrate and the first protective layer in the layer structure including the transparent substrate / first protective layer / recording layer / second protective layer / reflection layer described above. is doing. As a result, in addition to the interference at each layer interface so far, the interference from the interface between the high refractive index layer and the first protective layer is utilized, so that the reflectivity at the time of recording is reduced instead of the conventional film thickness configuration that lowers the reflectivity at the time of recording. The film thickness is increased.

Specifically, the high refractive index layer has a refractive index higher than that of the first protective layer, and the material is an inorganic material, especially Si.
The film thickness is 20 nm to 60 nm, and the recording layer is GeS.
made of bTe and having a film thickness of 40 nm or less, and the first protective layer is Zn
S: composed of SiO ₂ , and the film thickness is 120 nm to 170 nm
Or selected from the range of 300 nm to 340 nm, the second
The protective layer is made of ZnS: SiO ₂ and has a thickness of 20 n.
m-140 nm or 70 nm-310 nm, the reflective layer is made of Al alloy, and the film thickness is 100 nm.
That is all.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an optical information recording medium according to an embodiment of the present invention. The recording medium comprises a high refractive index layer 11, a first protective layer 12, a recording layer 13, and a second protective layer 1 on a substrate 10.
4 and the reflective layer 15. The substrate 10 is made of glass or a plastic material (for example, polymethylmethacrylate resin or polycarbonate resin), and the high refractive index layer 11 is made of Si. In addition, the first and second protective layers 1
2 and 14 consist of ZnS, SiO ₂ , Al ₂ O ₃ and a mixture thereof. The recording layer 13 is made of chalcogenide such as GeSbTe, and each of these layers can be formed by a deposition method such as vacuum deposition or sputtering. The reflective layer 15 is made of Al, Au, or a base material of Al, Au, or T
It is made of an alloy containing i, Mo, Zr, Cr and the like. Since the reflective layer 15 has a role of effectively radiating the heat generated in the recording layer 13 in addition to the purpose of optical reflection, this film thickness is 10
0 nm or more is desirable.

FIG. 2 shows the reflectance and the amount of change in reflectance of the recorded portion and the unrecorded portion when the thickness of the first protective layer of the recording medium having this layer structure is changed. At this time, Si, 50 nm is used for the high refractive index layer 11, and GeSb is used for the recording layer 13.
Te, 20 nm, the thickness of the second protective layer 14 is 50 nm,
Al, 200 nm was used for the reflective layer 15. Light incident from the substrate side undergoes multiple reflection at the interface of each layer, and thus the method of changing the reflectance differs depending on the film thickness. In the case of FIG. 2, the thickness of the first protective layer 12 is 120 nm to 170 nm, 300 to
Recording in the range of 340 nm increases the reflectance. In this configuration, when the thickness of the first protective layer 12 is 150 nm, particularly 340 nm, the reflectance change amount is 18%, which is the maximum. At this time, the reflectance of the unrecorded area is 20%
After recording, the reflectance increases more than this. Therefore, stable focusing and tracking are possible, and the maximum reflectance change amount can be obtained. An appropriate film thickness for the first protective layer is a film thickness capable of taking a variation of 50% or more of the maximum reflectance variation, that is, 120 nm to 170 nm or 300 n.
m to 340 nm, particularly preferably 120 to 180 nm,
Alternatively, 320 to 340 nm is suitable.

FIG. 3 similarly shows changes in reflectance with respect to the film thickness of the high refractive index layer 11 made of Si. Due to the increase in the film thickness of the high refractive index layer 11, the reflectance is increased when recording at 14 nm or more. This is because the interference effect appears above this film thickness. As the film thickness is further increased, the reflectance decreases, and at 50 nm, the reflectance can be 20% and the maximum change in reflectance can be 18%.

If the film thickness is made thicker than this, the reflectance change amount decreases. Therefore, in terms of reflectance and the amount of change in reflectance,
The film thickness of the high refractive index layer 11 is preferably 20 nm to 60 nm. The complex refractive index of Si is 4.23− at a wavelength of 690 nm.
Although it is 0.57i, the material that can be used as the high refractive index layer is not limited to this as long as it has a complex refractive index similar to this. For example, an alloy containing Ge can obtain almost the same optical characteristics.

When a metal layer is provided instead of the high-refractive index layer, the change in reflectance of the unrecorded portion is large with respect to the change in film thickness of the metal layer. Therefore, it is necessary to accurately control the film thickness of the metal layer.

FIG. 4 shows the reflectance and the variation in reflectance of the recorded portion and the unrecorded portion when the thickness of the second protective layer is changed. It is possible to obtain a sufficient reflectance change amount in which the reflectance increases during recording in almost all regions with respect to the protective layer thickness. Two
In the range of 0 nm to 140 nm and 170 to 340 nm, the reflectance change amount of 18% and the reflectance of 20% or more can be obtained in the unrecorded area. As described above, in the case of the present invention, even if the film thickness of the second protective layer is as thin as 20 nm, a sufficient amount of change in reflectance can be obtained, so that rapid cooling can be performed, and the laser power which is a problem in the conventional configuration can be obtained. It is also possible to control the rapid cooling by modulating the.

FIG. 5 shows the reflectance and the amount of change in reflectance of the recorded portion and the unrecorded portion when the thickness of the recording layer is changed. When the film thickness of the recording layer is 50 nm or less, a change in reflectance can be obtained, but 40 n
m or less is desirable.

Here, the calculation result at a wavelength of 690 nm is shown, but this film thickness similarly changes depending on the wavelength used for recording. The optimum film thickness also changes depending on the shape of the groove provided for tracking the light beam on the substrate, but in any case, the film thickness of each layer is adjusted to increase the reflectivity at the time of recording and the reflectivity of the unrecorded part is adjusted. If it is 10% or more, it does not depart from the gist of the present invention. Further, the reflectance change amount is preferably 5% or more.

Next, a case where information recording is performed using the information recording medium having the above structure will be described. As the information recording medium used here, a polycarbonate disk with a groove of 90 mm in diameter and 1.2 mm in thickness having a groove, a Si layer having a thickness of 50 nm which is a high refractive index layer and a thickness which is a first protective layer are formed. 150 nm ZnS: SiO ₂ layer, 20 nm thick GeSbTe (composition 2: 2: 5 atomic ratio) layer that is the recording layer, and 50 nm thick Z layer that is the second protective layer.
An optical disk was used in which an nS: SiO ₂ layer and an Al layer having a thickness of 2000 Å serving as a reflective layer were sequentially formed by a vacuum sputtering method.

FIG. 6 is an explanatory view showing an apparatus for recording / reproducing information using the information recording medium of the present invention.
The optical disk 21 is rotated at a constant speed by the motor 22. The motor 22 is controlled by a motor control circuit 38. Recording of information on the optical disc 21
The reproduction is performed by the optical head 23. The optical head 23 is fixed to a drive coil 33 that constitutes a movable portion of the linear motor 51, and the drive coil 33 is connected to a linear motor control circuit 37. In addition, a permanent magnet (not shown) is provided on the fixed portion of the linear motor 51, and the drive coil 33 causes the linear motor control circuit 3 to operate.
By being excited by 7, the optical head 23 is moved in the radial direction of the optical disk 21 at a substantially constant speed.

The optical head 23 includes an objective lens 26.
Is held by a wire or a leaf spring (not shown), and the objective lens 26 is moved in the focusing direction (the optical axis direction of the lens) by the drive coil 25, and is moved by the drive coil 24 in the tracking direction (the direction orthogonal to the optical axis of the lens). ) Can be moved to.

Laser light generated by a laser diode (semiconductor laser oscillator) 29 driven by a laser control circuit 34 is irradiated onto the optical disk 21 through a collimator lens 31a, a half prism 31b, and an objective lens 26, and from this optical disk 21. The reflected light of the photodetector 28 passes through the objective lens 26, the half prism 31b, the condenser lens 30a, and the cylindrical lens 30b.
Be led to. The photodetector 28 is composed of photodetector cells 28a, 28b, 28c, 28d divided into four parts.

The output signal of the photodetector cell 28a of the photodetector 28 is supplied to one end of the adders 50a and 50c via the amplifier 32a, and the output signal of the photodetector cell 28b is supplied to the adder 50b via the amplifier 32b. , 50d, the output signal of the photodetection cell 28c is supplied to the other ends of the adders 50b and 50c via the amplifier 32c, and the output signal of the photodetection cell 28d is added to the adder via the amplifier 32d. 5
It is adapted to be supplied to the other ends of 0a and 50d. The output signal of the adder 50a is supplied to the inverting input terminal of the differential amplifier OP1, and the output signal of the adder 50b is supplied to the non-inverting input terminal of the differential amplifier OP1. As a result, the differential amplifier OP1 supplies the track difference signal to the tracking control circuit 36 according to the difference between the adders 50a and 50b. This tracking control circuit 3
Reference numeral 6 is for creating a track drive signal in accordance with the track difference signal supplied from the differential amplifier OP1.

The track drive signal output from the tracking control circuit 36 is the drive coil 2 in the tracking direction.
4 is supplied. Further, the track difference signal used in the tracking control circuit 36 is the linear motor control circuit 37.
To be supplied to. The linear motor control circuit 37 applies a voltage corresponding to the moving speed to a drive coil (conductor wire) 33 in a linear motor 51 described later according to a track difference signal from the tracking control circuit 36 and a movement control signal from the CPU 43. Is.

In the linear motor control circuit 37, the drive coil 33 in the linear motor 51 is a magnetic member (not shown).
Drive coil 33 generated at the moment of crossing the magnetic flux generated from
A speed detection circuit (not shown) is provided for detecting the relative speed between the drive coil 33 and the magnetic member, that is, the moving speed of the linear motor 51 by utilizing the electrical change inside the.

On the other hand, the output signal of the adder 50c is supplied to the inverting input terminal of the differential amplifier OP2, and the output signal of the adder 50d is supplied to the non-inverting input terminal of the differential amplifier OP2. As a result, the differential amplifier OP2 supplies a signal regarding the focus point to the focusing control circuit 35 in accordance with the difference between the outputs of the adders 50c and 50d. The output signal of the focussing control circuit 35 is supplied to the focusing drive coil 25, and the laser light is controlled so that the laser light is always in perfect focus on the optical disc 21.

Each photodetecting cell 28a of the photodetector 28 in the state where focusing and tracking are performed as described above.
28d output sum signal, that is, adders 50a, 50
The output signal from b reflects the change in reflectance from pits (recording information) formed on the track. This signal is supplied to the signal processing circuit 39, and the recording information and address information (track number, sector number, etc.) are reproduced in this signal processing circuit 39.

The laser emission output of the laser diode 29 is monitored by the photodiode 52, converted into an electric signal and fed back to the laser control circuit 34, and the laser emission output of the laser diode 29 is stabilized. A laser emission ON / OFF signal and a recording data signal are input to the laser control circuit 34 from a recording data signal control circuit 53 including a microprocessor or the like. The drive current output from the laser control circuit 34 includes
From the high frequency current generation circuit 54 to the coupling capacitor 5
A high frequency power source, which will be described later, is superposed through 5.

Further, in this apparatus, a focusing control circuit 35, a tracking control circuit 36,
A D / A converter 42 used for exchanging information between the linear motor control circuit 37 and the CPU 43 is provided. The tracking control circuit 36 includes the CPU 4
The objective lens 26 is moved in accordance with the track jump signal supplied from 3 through the D / A converter 42, and the beam light is moved by one track. The laser control circuit 34, the focusing control circuit 35, the tracking control circuit 36, the linear motor control circuit 37, the motor control circuit 38, the signal processing circuit 39, the recording data signal control circuit 53, the high frequency current generating circuit 54, etc. are connected to the bus line 40. The CPU 43 is controlled by the CPU 43 via a program stored in the memory 44.

In the apparatus having the above structure, an optical disk in which the recording layer was crystallized by irradiating an argon laser in advance was set, and a motor was rotated to record a signal. At this time, the rotation speed was 3000 rpm. The recording signal is such that the shortest mark is 1.6 μm 1,7
RLL (Run Length Limited) code random data (marks of different lengths) was used. As a result, stable focusing and tracking were possible before and after recording. The reflectance of the unrecorded portion at this time is 2
The reflectance of the recording portion was 2% and 40%.

FIG. 7 shows the reproduced signal at this time. The midpoint of the signal amplitude is the slice level of digital data,
Digital data is created while comparing with the signal. Actually reproduced digital signal and 1,7RL used for recording
When the random data of the L code were compared, they were completely in agreement, and it was confirmed that this code could be recorded and reproduced. The present invention can be applied not only to mark length recording but also to mark position recording.

[0039]

According to the present invention, by inserting the high refractive index layer between the substrate and the first protective layer, the high refractive index layer / first protective layer interface can be further added in addition to the interference at each layer interface. By utilizing the interference from the film thickness configuration that increases the reflectance during recording instead of the conventional film thickness configuration that decreases the reflectance during recording, the reflectance increases at the recording portion even when mark length recording is performed. Therefore, a sufficient amount of reflected light can be obtained, and stable focusing and tracking are possible.

Further, since the recording portion has a low absorptance and the unrecorded portion has a high absorptivity, the temperature difference between when a new mark is overwritten on the recorded portion and when a new mark is overwritten on the unrecorded portion. It is possible to correct how to go up and form recording marks of the same size. For this reason, it is possible to perform recording while suppressing edge fluctuations.

Further, since the high refractive index layer has little absorption, the change of the reflectance with respect to the change of the film thickness is gentle, the film thickness can be selected in a wide range, and the manufacturing margin can be widened. became.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an information recording medium according to the present invention.

FIG. 2 is a graph showing the reflectance and the amount of change in reflectance of the recorded portion and the unrecorded portion when the thickness of the first protective layer is changed in the information recording medium according to the present invention.

FIG. 3 is a graph showing the reflectance and the amount of change in reflectance of the recorded portion and the unrecorded portion when the thickness of the high refractive index layer is changed in the information recording medium according to the present invention.

FIG. 4 is a graph showing the reflectance and the amount of change in reflectance of the recorded portion and the unrecorded portion when the thickness of the second protective layer is changed in the information recording medium according to the present invention.

FIG. 5 is a graph showing the reflectance and the amount of change in reflectance of the recorded portion and the unrecorded portion when the thickness of the recording layer is changed in the information recording medium according to the present invention.

FIG. 6 is an explanatory diagram showing an apparatus for recording / reproducing information using the information recording medium of the present invention.

7 is an explanatory diagram showing a reproduced signal on an information recording medium recorded by using the apparatus shown in FIG.

8A and 8B show a recording method of a recording medium, FIG. 8A is a diagram for explaining mark position recording, and FIG. 8B is a diagram for explaining mark length recording.

[Explanation of symbols]

10 ... Transparent substrate, 11 ... High refractive index layer, 12 ... First protective layer, 13 ... Recording layer, 14 ... Second protective layer, 15 ... Reflective layer, 21 ... Optical disc, 22 ... Motor, 23 ... Optical head , 26 ... Objective lens, 24, 25, 33 ... Driving coil, 28 ... Photodetector, 28a, 28b, 28c, 28d
Photodetection cell, 29 ... Laser diode, 30a ... Condensing lens, 30b ... Cylindrical lens, 31a ... Collimator lens, 31b ... Half prism, 32a, 32
b, 32c, 32d ... Amplifier, 34 ... Laser control circuit,
35 ... Focusing control circuit, 36 ... Tracking control circuit, 37 ... Linear motor control circuit, 39 ... Signal processing circuit, 40 ... Bus line, 42 ... D / A converter, 43 ...
CPU, 44 ... Memory, 50a, 50b, 50c, 50
d ... Adder, 51 ... Linear motor, 52 ... Photodiode, 53 ... Recording data signal control circuit, 54 ... High frequency current generating circuit, 55 ... Coupling capacitor.

Claims (6)

[Claims] 1. A high refractive index layer formed on a transparent substrate,
A first protective layer formed on the high refractive index layer, a recording layer formed on the first protective layer and capable of forming a recording portion having optical characteristics different from that of an unrecorded portion, and the recording layer A second protective layer formed on the upper surface and a reflective layer formed on the second protective layer are provided, and in the above layer structure, the reflectance of the recording portion at the recording wavelength is higher than the reflectance of the unrecorded portion. An optical information recording medium characterized by being expensive. 2. The optical information recording medium according to claim 1, wherein the high refractive index layer has a refractive index higher than that of the first protective layer. 3. The recording layer is made of GeSbTe, the first and second protective layers are made of ZnS: SiO ₂ , the high refractive index layer is made of Si, and the reflective layer is made of Al alloy.
The optical information recording medium described in. 4. The optical information recording medium according to claim 1, wherein the recording layer has a thickness of 40 nm or less. 5. The high refractive index layer is made of Si and has a thickness of 2
0 nm to 60 nm, the recording layer is made of GeSbTe and has a film thickness of 40 nm or less, the first protective layer is made of ZnS: SiO ₂ , and the film thickness is 120 nm to 170 nm or 300 nm to 3
The thickness of the second protective layer is Zn.
The optical element according to claim 1, wherein S: SiO ₂ is formed, the film thickness is selected from the range of 20 nm to 140 nm or 70 nm to 310 nm, the reflective layer is formed of an Al alloy, and the film thickness is 100 nm or more. Information recording medium. 6. The optical information recording medium according to claim 1, wherein the recording layer is for recording recording portions having different lengths for recording and reproducing information.