JP2664207B2 - Thin film for information recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a device in which an analog signal such as video or audio is FM-modulated by a recording beam such as a laser beam or an electron beam, or an electronic computer. The present invention relates to an information recording thin film capable of recording data and digital information such as a facsimile signal and a digital audio signal in real time.

[Conventional technology]

There are various recording principles of recording on a thin film by laser light, but recording by a phase transition (also called phase change) of a film material or an atomic arrangement change such as photodarkening hardly involves film deformation. It has the advantage that two-sided disks can be made by directly bonding two disks. If the composition is appropriately selected, the recording can be rewritten. Many inventions relating to this type of recording have been filed, and an example thereof is disclosed in Japanese Patent Publication No. 47-26897, for example.

Furthermore, Ge, Te, and with respect to the film on the basis of Sb, are disclosed in JP-A-61-258787, its recording film composition _{{(Sb x Te 1_x) y} Ge 1_y} 1_z M z (However, x is 0.2-0.
7, y is a number in the range of 0.4 to 0.8, z is a number in the range of 0.01 to 0.5, and M
Is an element selected from the group of 37 metal elements such as Al, Si, Ti)
It is.

[Problems to be solved by the invention]

When any of the thin films shown in the above prior art is used as a once-writable or rewritable phase-change recording film, the activation energy of crystallization at an amorphous recording point is small. It has the disadvantage that the speed is low, the stability of the amorphous state at room temperature is poor, and the reproduction signal intensity is not sufficiently high. The number of rewrites is not enough. It has drawbacks such as large loss of the previous signal when overwriting with a single beam, and is difficult to put into practical use.

Accordingly, an object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, and to provide an information recording thin film having good recording / reproducing characteristics, high sensitivity and good stability.

[Means for solving the problem]

In order to achieve the above object, in the information recording member of the present invention, the average composition of the information recording thin film in the thickness direction is represented by the general formula Ge _x Te _y Sb _z B _β . Where x, y, z,
β is each atomic percent and 20 ≦ x ≦ 60,40 ≦ y
≦ 80, 1 ≦ z ≦ 10, and 1 ≦ β ≦ 20.

B is Co, Fe, Ni, Sc, Ti, V, Cr, Mn, Cu, Zn, Y, Zr, Nb, Mo, R
It is at least one element selected from u, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, and Au.

The composition of the recording thin film of the present invention may vary in the film thickness direction as long as the average composition in the film thickness direction is within the above range. However, the change in the composition is more preferably not discontinuous. B
Is an element represented by

Transition metal elements such as Co facilitate the absorption of long-wavelength light such as semiconductor laser light, increase the recording sensitivity, and have the effect of increasing the crystallization temperature, that is, increasing the stability of the amorphous state. In addition, the compound itself has a high melting point of 600 ° C. or higher or forms a compound having a high melting point, and when crystallized by a laser beam, does not melt even at a high temperature, so that high-speed crystallization is possible.

The information recording thin film of the present invention having the above composition range has excellent recording / reproducing characteristics, and the power of the laser beam used for recording and erasing may be low. Also, the stability is excellent.

In a recording film containing only Ge, Te, and Sb as component elements, the activation energy of crystallization at an amorphous recording point is small, the minimum irradiation time (erasing time) required for erasing is long, and Poor stability. Here, by adding the element represented by B, the stability of the amorphous recording point is improved.

Among the elements represented by B, particularly preferred are Co,
Next preferred is Ti, Ni, then preferred is V, Cr
Next preferred are Pd, Zr, Nb, Mn.

It is preferable that at least one surface of the recording film of the present invention is tightly protected by another substance. More preferably, both sides are protected. These protective layers may be formed of an acrylic resin plate, a polycarbonate plate, an epoxy resin plate, or the like, which is a substrate, or an organic material such as an acrylic resin, an epoxy resin, polyimide, polyamide, polystyrene, or polyethylene. It may be made of an inorganic substance mainly containing a substance, fluoride, nitride, sulfide, carbide, boride, boron, carbon, or metal. Further, these composite materials may be used. At least one of the protective layers adjacent to the recording film is preferably made of an inorganic material. A substrate mainly composed of glass, quartz, sapphire, iron, or aluminum can also serve as one inorganic protective layer. Among organic and inorganic substances, it is preferable that the substance is in close contact with the inorganic substance in terms of heat resistance. However, increasing the thickness of the inorganic layer (except for the substrate) is likely to cause at least one of cracking, transmittance reduction, and sensitivity reduction. It is preferable that a thick organic material layer is in close contact to increase the mechanical strength. This organic material layer may be a substrate. This makes deformation less likely to occur.
As the organic material, for example, polystyrene, acrylic resin, polycarbonate, epoxy resin, polyimide, polyamide, ethylene-vinyl acetate copolymer known as hot melt adhesive, and adhesive are used. UV curable resin may be used. In the case of a protective layer made of an inorganic substance, it may be formed as it is by electron beam evaporation, spattering, etc., but after reactive spattering or forming a film made of at least one element of a metal, semimetal, or semiconductor, The production is easy if it is made to react with at least one of acetate, sulfur and nitrogen. Examples of the inorganic protective layer include Ce, La, Si, In, Al, Ge, Pb, Sn, and B.
an oxide of at least one element selected from the group consisting of i, Te, Ta, Sc, Y, Ti, Zr, V, Nb, Cr, and W; Cd, Zn, Ga, In, Sb, G
e, Sn, sulfide of at least one element selected from the group consisting of Pd, or selenide, fluoride such as Mg, Ce, Ca, Si, A
It is composed of nitrides such as l, Ta, B, etc., borides such as Ti, carbides such as boron, boron, and carbon. For example, the main components are CeO ₂ , La ₂ O ₃ , SiO, SiO ₂ , In ₂ O ₃ , Al ₂ O ₃ , GeO, GeO ₂ , P
bO, SnO, SnO ₂ , Bi ₂ O ₃ , TeO ₂ , WO ₂ , WO ₃ , Ta ₂ O ₅ , Sc ₂ O ₃ , Y ₂ O ₃ , Ti
O ₂ , ZrO ₂ , CdS, ZnS, CdSe, ZnSe, In ₂ S ₃ , In ₂ Se ₃ , Sb ₂ S ₃ , Sb ₂ Se
_{3, Ga 2 S 3, Ga} 2 Se 3, MgF 2, CeF 2, CeF 3, CaF 2, GeS, GeSe, GeSe 2,
SnS, SnSe, PbS, PbSe, Bi ₂ Se ₃ , Bi ₂ S ₂ , TaN, Si ₃ N ₄ , AlN, Si, Ti
It has a composition close to one of B ₂ , B ₄ C, B, and C.

Of these, not high surface reflectance is too a nitride, film is stable, TaN in that they are strong, Si ₃ N ₄ or A
A composition close to 1N is preferred. The preferred oxide is
Y ₂ O ₃ , Sc ₂ O ₃ , CeO ₂ , TiO ₂ , ZrO ₂ , In ₂ O ₃ , Al ₂ O ₃ , SnO ₂ or Si
It has a composition close to O ₂ . An amorphous material containing hydrogen of Si or C is also preferable. When performing recording by phase transition, it is preferable to crystallize the entire surface of the recording film in advance, but if an organic substance is used for the substrate, the substrate cannot be heated to a high temperature. It needs to be crystallized. In this case, it is preferable to perform ultraviolet irradiation and heating, irradiation of light from a flash lamp, irradiation of light from a high-output gas laser, or a combination of heating and laser light irradiation. In the case of light irradiation from a gas laser, the efficiency is good if the light spot diameter (half width) is 5 μm or more and 5 mm or less. Crystallization may occur only on the recording tracks, and may remain amorphous between tracks. Of course, it is also possible to perform recording by crystallization on a recording thin film in an amorphous state.

Generally, when light is applied to a thin film, the reflected light is superimposed on the reflected light from the front surface of the thin film and the reflected light from the back surface of the thin film, and causes interference. When a signal is read by a change in reflectance, a light reflection (absorption) layer is provided close to the recording film to increase the effect of interference and increase the read signal. In order to further increase the effect of interference, it is preferable to provide an intermediate layer between the recording film and the reflection (absorption) layer. The intermediate layer also has the effect of preventing the interdiffusion between the recording film and the reflective layer from occurring during recording rewriting. The intermediate layer is preferably made of a substance that does not absorb much light used for reading. The thickness of the intermediate layer is 3 nm or more, 400 nm or less, and,
In the recording state or the erasing state, it is preferable that the film thickness is such that the reflectance of the recording member is close to the minimum value near the wavelength of the reading light. The reflective layer may be formed between the recording film and the substrate and on any of the opposite sides. A particularly preferred thickness range of the intermediate layer is in the range of 5 nm to 150 nm. It is preferable to form a protective layer made of the above-mentioned inorganic substance on the side of the reflective layer opposite to the intermediate layer.

Further, it is preferable to form an anti-reflection layer on the light incident side of the recording layer to reduce the reflectance of at least one of the recording light, the erasing light and the reading light. The antireflection layer may also serve as a protective layer for the recording film, or a protective layer may be formed between the antireflection layer and the recording film. The anti-reflection layer and the protective layer
It is preferable that the thermal expansion coefficient changes sequentially in the order of recording layer-protective layer-antireflection layer-substrate or adhesive or gas. In the case where one of the protective layer antireflection layers is not formed or when each of the protective layers comprises two or more layers It is preferable that the thermal expansion coefficient also changes sequentially.

The recording film of the present invention may be in the form of being dispersed in an oxide, a fluoride, a nitride, an organic material or the like which can be used as a protective film by co-evaporation or co-sputtering. By doing so, there are cases where the light absorption coefficient can be adjusted and the intensity of the reproduced signal can be increased. The mixing ratio is the ratio of oxygen, fluorine, nitrogen, and carbon in the entire film.
40% or less is preferable. The formation of such a composite film usually lowers the crystallization speed and lowers the sensitivity. However, the sensitivity is improved by forming a composite film with an organic substance.

 The preferred range of the film thickness of each part is as follows.

For recording film single layer film 60 nm or more and 350 nm or less, 80 nm or more and 200
The range of nm or less is particularly preferable in view of the reproduction signal intensity and the recording sensitivity.

In the case of a structure with two or more layers with a reflective layer 15 nm or more and 100 nm or less Inorganic protective layer 5 nm or more and 200 nm or less When protecting with the inorganic substrate itself, 0.1 to 20 mm Organic protective film: 10 nm or more, 10 mm or less Intermediate layer: 3 nm or more and 400 nm Light-reflective layer: 5 nm or more, 300 nm or less Each layer is formed by vacuum deposition, gas deposition, sputtering, ion beam sputtering, ion beam deposition, ion plating, electron beam deposition, injection molding, casting, Any one of spin coating, plasma polymerization and the like is appropriately selected.

In the recording film of the present invention, it is not always necessary to use the change between the amorphous state and the collapsed state for recording, and it is sufficient to change the optical properties by any change in the atomic arrangement.

The recording member of the present invention can be used not only in a disk shape but also in other forms such as a tape shape and a card shape.

[Action]

The information recording thin film of the present invention has a high crystallization speed, a high stability of an amorphous state, a large absorption of semiconductor laser light,
High reproduction signal strength and good oxidation resistance. Therefore,
Good recording / erasing characteristics, high sensitivity, and good recording state stability.

Comparative Example 1 Hereinafter, the present invention will be described in detail with reference to Examples.

A replica of the groove for tracking, which also serves as a protective layer, is formed on the surface of a disk-shaped chemically strengthened glass plate with a diameter of 13 cm and a thickness of 1.2 mm using an ultraviolet curable resin, and one round is divided into 32 sectors, and at the beginning of each sector. A substrate in which a track address, a sector address, and the like are provided in the form of an uneven pit in the middle of a groove between grooves (this portion is called a header portion).
First, a Si ₃ N ₄ layer having a thickness of about 100 nm, which is both an anti-reflection layer and a protective layer, was formed on magnet 14 by magnetron sputtering.
Next, this substrate was placed in a vacuum deposition apparatus having an internal structure as shown in FIG. In the deposition apparatus, there are four deposition sources 1,
2,3,4 are arranged. Three of these are resistance heating evaporation ports, one of which is an electron beam evaporation source. These ports and the electron beam evaporation source are located below a portion where information is to be recorded on the substrate 14, and are located substantially on a circle having the same center as the central axis 5 of the substrate rotation. Ge-Te on two evaporation boats
Compound, Sb, and Tl were charged, and Co was charged to the electron beam evaporation source. Masks 6, 7, 8, 9 having fan slits and shutters 10, 11, 12, 13 are arranged between each boat and the substrate, respectively. The substrate 14 was rotated at 120 rpm, a current was applied to each boat, and an electron beam was applied to evaporate the deposition material.

The amount of evaporation from each evaporation source is measured using a quartz crystal film thickness monitor 1
Detected at 5, 16, 17, and 18, the current was controlled so that the evaporation rate was constant.

As shown in FIG. 1, Ge _{3 is} placed on the Si ₃ N ₄ layer 20 on the substrate 19.
A recording film 21 having a composition of ₂₈ Te ₆₂ Sb ₅ Tl ₅ was deposited to a thickness of about 100 nm. Since the refractive index of the Si ₃ N ₄ layer is higher than that of the substrate, the Si ₃ N ₄ layer also serves as an anti-reflection layer for semiconductor laser light by being appropriately formed. When the recording film is in a non-degraded state or in a state of poor crystallinity, the reflectance is almost minimized in the vicinity of the wavelength of the laser beam used for reading when the light reflected by the front surface and the back surface of the recording film interferes with each other. The film thickness is as follows. Subsequently, the thickness of the protective layer 22 having a composition close to Si ₃ N ₄ was reduced to about 100 nm by magnetron sputtering again. Another one in the same way
A protective layer 20 ′ having a composition close to Si ₃ N ₄ on a similar substrate 19 ′,
A recording film 21 ′ having a composition of Ge ₂₈ Te ₆₃ Sb ₄ Tl ₅ and a protective layer 22 ′ having a composition close to Si ₃ N ₄ were deposited. The two substrates thus obtained
UV-curable resin protective layer 2 on each deposited film of 19, 19 '
3, 23 'was applied and formed to a thickness of about 50 .mu.m, and then both were bonded together with the ultraviolet-curable resin layers 23 and 23' side inward by an effective adhesive layer 24 to produce a disk.

After heating the disk prepared as described above at 150 ° C. for about 1 hour, the disk is rotated and moved in the radial direction while converging an argon ion laser beam (wavelength) from both sides with a lens having an aperture ratio (Numerical Aperture) of 0.05. 488nm)
And the recording films 21, 21 'were sufficiently crystallized.

The recording was made as follows. 1200rpm disk
Rotate to keep the light of the semiconductor laser (wavelength 820 nm) at a level where recording is not performed, focus the light with a lens in the recording head, irradiate one recording film through the substrate, and detect reflected light. Therefore, the head was driven so that the center of the light spot always coincided with the middle of the groove for tracking. By doing so, the effect of noise generated from the groove can be avoided. In this way, while performing tracking, automatic focusing is performed so that the recording film is further focused, and recording is performed by increasing the laser power according to the information signal or returning the laser power to the original level. Was.

In addition, recording was performed by jumping to another groove as necessary.

With the above recording, a change in reflectance occurred on the recording film. In this recording film, the recording light spot with reduced power,
Alternatively, the recording can be erased by irradiating a laser beam whose length in the track direction is longer than that of the recording light spot and which spreads in the adjacent track direction at the same level as the recording light spot. If the distance between the nearest neighbors of the pit representing the address is 1/2 or more and 2 times or more the length of the erasing light spot in the track direction, the address of the track or sector can be read by the erasing light spot. . The length of the pit representing the address is preferably at least half the length of the erasing light spot in the track direction, and the same applies to other pits provided in the header. Record
Erasing could be repeated 3 × 10 ⁵ times or more. If the Si ₃ N ₄ layers formed above and below the recording film were omitted, several recordings
There was some noise increase on erasure.

Reading was performed as follows. 1200 rp disk
While rotating at m, tracking and automatic focusing were performed in the same manner as during recording, and the intensity of the reflected light was detected with a low-power semiconductor laser beam on which recording and erasing were not performed, and information was reproduced. In this embodiment, a signal output of about 100 mV was obtained. The recording film of this example has excellent oxidation resistance, and a film without a Si ₃ N ₄ protective film was treated at 60 ° C. and a relative humidity of 95%.
Hardly oxidized even under the conditions described above. The recording film of this example had excellent amorphous stability, and showed a large activation energy of 2.8 eV for crystallization of an amorphous point formed by laser light irradiation.

In the above Ge—Te—Sb—Tl-based recording film, Tl is set to 5 atomic%, and the relative ratio of the contents of Ge and Te is kept constant.
When the Sb content (z) is changed, the shortest irradiation time required for erasing (erasing time) and the activation energy (Ea) for crystallization of the amorphous recording points change as shown in Table 1 below. did.

In the above Ge—Te—Sb—Tl-based recording film, Tl is set to 5 atomic%, and the relative ratio of the contents of Ge and Sb is kept constant.
When the content (y) of Te was changed, the laser beam power (recording light power), erasing time, and crystallization temperature required for recording changed as shown in Table 2.

Example 1 In the above Ge—Te—Sb—Tl-based recording film, Ge, T
When the relative ratio of e and Sb is kept constant and Co is added instead of Tl (the content of Tl is 0 atomic%) to change the Co content (β), the recording light power and The crystallization temperature varied as shown in Table 4.

Here, in the above Ge-Te-Sb-Co system, part or all of Co is substituted, and Fe, Ni, Sc, Ti, V, Cr, Mn, Cu, Zn, Y,
Similar properties can be obtained by adding at least one of Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, and Au. Can be Of these, Ti, Ni, and Pd are preferable in terms of recording light power, V and Cr are preferable in terms of reproduction signal strength, Fe and Rh are preferable in terms of erasing time, and Zr and Zr in terms of crystallization temperature. Mn is preferable, and Nb, Pt, A
u is preferred.

Example 2 As shown in FIG. 2, a substrate 25 having grooves for tracking formed on the surface of a polycarbonate plate by an injection molding method was used as a substrate, and the thickness of the composition was close to SiO ₂ by sputtering. A 200 nm protective film 26 was formed. Next, a recording film 27 having a thickness of 60 nm was formed thereon. Subsequently, an intermediate layer 28 having a composition close to SiO _{2 and} having a thickness of 250 nm was formed, and a thickness of 80 nm was further formed.
Reflection layer 29 with a composition of Bi ₇ Sb ₃ , a thickness of 100 n with a composition close to SiO ₂
m protective layer 30 was formed. Another substrate was prepared in the same manner, and after sputtering polyimide 31 to a thickness of about 0.5 μm on the SiO ₂ layer 30 at the top of both substrates,
The two substrates were bonded together with the hot melt adhesive 32 mixed with a black pigment with the polyimide layer side inside, thereby producing a disk. If a polyimide layer is also formed on the surfaces of the polycarbonate plates 25 and 25 'by a sputtering method, a more stable disk can be obtained.

The crystallization method, recording method, erasing method, and reading method are almost the same as those in the first embodiment.

For the intermediate layer, instead of SiO, GeO ₂ , Al ₂ O ₃ , GeO ₂ , Y ₂ O ₃ , SiO, ZrO ₂ , Ta ₂ O ₅ , which can be used as a protective layer in Example 1
Other inorganic transparent materials such as AlN and TaN may be used, or an organic material layer may be used. If the intermediate layer has a thickness of 3 to 40 nm, mutual diffusion between the recording film and the reflective layer at the time of recording / rewriting is prevented, but it is almost the same as optically nonexistent. Therefore, the change in reflectance due to wavelength due to light interference is close to that of a two-layer structure of a recording film and a reflective layer.

If the reflective layer also undergoes a change in the atomic arrangement during recording, the reproduced signal becomes slightly larger.

When the thickness of the recording film is in the range of 15 nm or more and 100 nm or less, the reflectance when the recording film is in an amorphous state is reduced by interference, and a large reproduction signal is obtained. The thickness of the reflective layer is 5 nm or more and 300 nm
It is preferably in the following range, more preferably in the range of 40 nm to 200 nm. By providing the reflective layer, a large reproduction signal can be obtained in a region where the film thickness of the recording film is thinner than in the case of a single layer as described above, and therefore, even in a composition region where the absorption coefficient of the recording film is larger than in the case of a single layer. Good characteristics are obtained.

When the thicknesses of the recording film and the intermediate layer are changed, the wavelength at which the minimum occurs due to the interference of the read light reflectance changes. Minimum reflectance required for auto focus and tracking
Since it is 10 to 15%, when the minimum value of the reflectance is equal to or less than this value, it is necessary to set the minimum value on the long wavelength side or the short wavelength side with respect to the wavelength of the reading light. When the minimum value comes to the short wavelength side, the thickness of the recording film can be reduced, and energy loss due to heat conduction can be prevented. However, it is preferable that the minimum value comes to the longer wavelength side because the film thickness becomes thicker, in terms of the life of the recording film and the prevention of noise at the time of recording / rewriting.

As the material of the reflection layer, instead of Bi-Sb of the present embodiment,
Many semiconductors such as Bi, Bi ₂ Te ₃ , Te, Sn, Sb, Al, Au, Pb, Ni, and Ni—Cr, semimetals, metals, and mixtures and compounds thereof can be used.

The recording film of this embodiment is also excellent in oxidation resistance like the recording film of Embodiment 1, and even if the protective film has a pinhole, oxidation does not progress around the pinhole.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain a recording member for information with a simple manufacturing process, good reproducibility, good recording / reproducing characteristics, and stable for a long time. . Records can be rewritten many times.

[Brief description of the drawings]

FIG. 1 is a view showing the internal structure of a vacuum deposition apparatus used for producing a recording member of the present invention, and FIGS. 2 and 3 are cross-sectional views each showing the structure of a recording member in an embodiment of the present invention. . 1,2,3 …… Evaporation port, 4 …… E-beam evaporation source, 6,7,
8,9 …… a mask with fan-shaped slits, 10,11,12,13 ……
Shutter, 14 …… Substrate, 15,16,17,18 …… Quartz crystal film thickness monitor, 19,19 ′… Substrate, 20,20 ′, 22,22 ′…
... Si ₃ N ₄ layers, 21, 21 '... recording film, 23, 23' ... UV curable resin layer, 24 ... organic adhesive layer, 25, 25 '... substrate, 26,
26 ', 28,28', 30,30 '... SiO ₂ layer, 27,27' ... Recording film, 29,29 '... Bi-Sb film, 31,31' ... Polyimide resin layer, 32 ... … Hot melt adhesive layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keikichi Ando 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor Yasushi Yasushi 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Hitachi (72) Inventor Reiji Tamura 1-1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell, Inc. (56) References JP-A-64-63195 (JP, A) JP-A-61-258787 ( JP, A)

Claims (2)

(57) [Claims] 1. An information recording system which receives an irradiation of a recording energy beam formed directly on a substrate or via a protective layer made of at least one of an inorganic substance and an organic substance to cause an atomic arrangement change without deformation. In the thin film for information, the information recording thin film has a configuration in which a reflective layer is provided on the thin film for information recording via an intermediate layer made of at least one of an inorganic substance and an organic substance, Is the general formula Ge _x Te _y Sb _z B _β (where x, y, z, and β are each atomic percent, and
≦ x ≦ 60, 40 ≦ y ≦ 80, 1 ≦ z ≦ 10, 1 ≦ β ≦ 20, B is Co, Fe, Ni, Sc, Ti, V, Cr, Mn, Cu, Zn , Y, Zr, Nb, M
o, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt and at least one element selected from Au). 2. The information recording thin film according to claim 1, wherein the element represented by B is Co.