KR100796228B1 - Write-once-read-many optical recording medieum - Google Patents

Abstract

It is an object of the present invention to provide a WORM type optical recording medium having very high recording and reproducing characteristics at short wavelengths of blue laser wavelength or less, that is, below 500 nm, especially at wavelengths near 405 nm and having high density recording. do. In order to realize this object, the WORM type optical recording medium of the present invention includes a recording layer using a material represented by BiO _x (O <x <1.5), and the marks recorded in the recording layer are the crystals of Bi and / or Or crystals of Bi oxides. In addition, the present invention is Bi, O and M (M is Mg, Al, Cr, Mn, Co, Fe, Cu, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Mo, V, Nb, Y And a recording layer comprising one or more elements selected from the group consisting of Ta), wherein the marks recorded in the recording layer are formed of crystals and element oxides of the elements contained in the recording layer. Include a decision.

Description

VOR-type optical recording medium {WRITE-ONCE-READ-MANY OPTICAL RECORDING MEDIEUM}

The present invention relates to a WORM type (Write-Once-Read-Many: write once and read multiple times) optical recording medium. More specifically, the present invention relates to a WORM type optical recording medium which enables particularly high density recording at a blue laser wavelength. Further, the present invention relates to a sputtering target that can be used to form an oxide layer, which is a layer constituting a WORM type optical recording medium.

Regarding the WORM type optical recording medium capable of recording and reproducing at a short wavelength of blue laser wavelength or shorter, the development of the blue wavelength enabling ultra high density recording is rapidly progressing, and the WORM type optical recording medium sensitive to the blue laser wavelength. Development is being promoted.

In a conventional WORM type optical recording medium, a recording pit is formed by irradiating a laser beam onto a recording layer containing an organic material, mainly causing a change in refractive index due to decomposition and alteration of the organic material. The optical constants and resolution behavior of the organic materials used in the recording layer play an important role in forming good recording pits.

For use in recording layers of WORM type optical recording media sensitive to blue laser wavelengths, the organic material must have suitable optical properties and resolution behavior with respect to light at blue laser wavelengths. More specifically, the wavelength at which recording is performed results in higher higer modulated amplitude by increasing the reflectance of the unrecorded portion and substantially increasing the difference in refractive index caused by decomposition of the organic material upon laser irradiation. In order to be located at the long wavelength side tail of the main absorption band. This is because the wavelength located at the long wavelength side tail of the main absorption band of such organic materials yields an appropriate absorption coefficient and high refractive index.

However, no organic material has yet been found to have optical properties for light at blue laser wavelengths comparable to those of conventional materials. In order to produce such an organic material having an absorption band in the vicinity of the blue laser wavelength, the molecular skeleton must be made small or the conjugate system must be made short. However, this results in a lower absorption coefficient and a lower refractive index. More specifically, there are many organic materials with absorption bands near the blue laser wavelength, although it is possible to control the absorption coefficients of the organic materials, but such organic materials do not have sufficiently high refractive indices and have a higher modulated value. It does not calculate the magnitude of the amplitude.

Therefore, the use of inorganic materials and organic materials and materials using only inorganic materials for materials having optical properties sensitive to light at the blue laser wavelength are currently under consideration. As using an oxide, Patent Document 1 discloses a recording layer containing Bi, rare earth, Ga, Fe, and O, and the present invention describes a composition capable of forming a garnet. Patent document 2 discloses an optical recording medium using an organic oxide.

However, these prior arts do not examine what kind of form it is effective to form a recording mark in order to form a very good recording mark and to yield a very good characteristic. Of course, these techniques do not take into account the shape of the recording mark, which yields a higher modulated amplitude when using blue wavelength light, which is a problem in the present invention.

In addition, in the case of a WORM type optical recording medium using a metal or semimetal oxide as the recording layer, Patent Documents 3 and 4 propose TeOx-Pd recording layers having high-reliabilities. In Patent Documents 3 and 4, the composition ratio of the TeOx-Pd recording layer is varied in the thickness direction of the layer in order to enhance reliability such as storage stability. Moreover, although recording layers containing TeOx-Pd are also disclosed in Non-Patent Documents 1 and 2, these documents have only a description of controlling the degree of oxidation in the content as a method of improving the reliability.

Regarding materials containing bismuth oxides similar to the present invention, such materials are also disclosed in the following patent documents, respectively: Patent Document 5 discloses the formula A _x (M _m O _n ) _y (Fe ₂ O ₃ ) _z ( Wherein amorphous ferromagnetic oxides are represented by various oxides of A, various elements of M, and individual ratios of x, y, and z as defined); Patent Document 6 discloses the formula (Bi ₂ O ₃ ) _x (M _m O _n ) (Fe ₂ O ₃ ) _z (wherein the individual ratios of m and n of M _m O _n , and the individual ratios of x, y and z are Metal oxides comprising 50% or more amorphous phases, as defined); Document 7 discloses an amorphous compound having a composition represented by the formula (B ₂ O ₃ ) _x (Bi ₂ O ₃ ) _1-x , wherein x is a range of composition and a quenching method; Patent document 8 discloses a bismuth-iron amorphous composite material having a composition of the formula (Bi ₂ O ₃ ) _1-x (Fe ₂ O ₃ ) _x , wherein x is represented by 0.90 ≥ x ≥ 0.

However, these techniques relate to amorphous oxide materials that are optically transmissive and ferromagnetic, respectively, which are typically optoelectronic optical recording media, functional devices that control light by means of magnetic action, optoelectronic sensors, transparency and electrical conductivity. Film, piezo-electric film and the like. In addition, these techniques provided by other companies are basically for the purpose of patenting a material and / or a method of manufacturing the material, and have no description of the application to the WORM type optical recording medium.

On the other hand, as one of methods for manufacturing a recording layer for an optical recording medium, a sputtering method has existed. Sputtering methods are widely known in the art as one of methods for forming a thin layer in the vapor phase, and have been used to prepare thin layers for industrial purposes. In the sputtering method, a target material having a component identical to that of the layer to be formed is prepared, and argon gas ions generated by glow-discaharge are typically collided with the target material to thereby form constituent atoms of the target material. The layer is formed by implanting and depositing atoms on the substrate. Since the oxides typically have a high melting point, it is not suitable to form them by an evaporation method or the like, and a high frequency sputtering method for applying a high frequency is usually used.

There are a number of implementations of the sputtering method in the manufacturing method, which is also advantageous in terms of throughput. However, when forming a layer containing a mixed material of two or more elements, there may be cases where the composition of the target is not the same as the composition of the layer, and therefore the composition of the target must be considered. In addition, there are many cases in which the structure and characteristics of the layer will depend on the form of the compound constituting the target, and this should also be considered.

As a technique known in the art, for example, Patent Document 9 discloses a target containing Bi oxide as a sputtering target for forming a dielectric film. However, Patent Document 9 does not mention a target containing Fe. Because of the variety of constituent elements, not only the relationship between the target composition and the constituent compounds, but also the relationship between the structure and the composition of the layer. Therefore, the structure of the target must be changed, and the findings disclosed in Patent Document 9 do not serve as a reference for the sputtering target proposed in the present invention.

Furthermore, Patent Document 10 discloses a target for producing a thin layer made of Bi ₃ Fe ₅ O ₁₂ . However, the present invention is for producing a thin layer having a garnet structure, wherein a high degree of magnetic optical effect is obtained, and the invention uses a Bi: Fe ratio of 3: 5 to 3.5: 4.5. Therefore, the target is different from the sputtering target proposed in the present invention.

Patent Document 1: Japanese Patent Application Laid-Open No. 10-92027

Patent Document 2: Japanese Patent Application Publication (JP-A) No. 2003-48375

Patent Document 3: Japanese Patent Application Laid-Open Publication (JP-A) No. 06-150366

Patent Document 4: Japanese Patent Application Laid-Open No. 06-93300

Patent Document 5 Japanese Patent Application Laid-Open (JP-A) No. 61-101450

Patent Document 6: Japanese Patent Application Laid-Open (JP-A) No. 61-101448

Patent Document 7: Japanese Patent Application Laid-Open (JP-A) No. 59-8618

Patent Document 8: Japanese Patent Application Laid-Open (JP-A) No. 59-73438

Patent Document 9: Japanese Patent Application Laid-Open No. 11-92922

Patent Document 10: Japanese Patent Application Laid-Open (JP-A) No. 02-42899

[Non-Patent Document 1] [pp. 23-28, Proceedings of The 14th Symposium on PC0S2002]

Non Patent Literature 2: Literature [pp. 5-8, Vol. 28, Eijogaku Giho]

Summary of the Invention

Therefore, it is an object of the present invention to enable recording and reproducing and high density recording at WORM type optical recording media, especially at wavelengths near 405 nm, which can exhibit very good recording and reproducing characteristics and high density recording at wavelengths of 500 nm or less. To provide a WORM type optical recording medium.

In addition, another object of the present invention is to provide a sputtering target which can be used to prepare an oxide layer, which is a layer constituting an optical recording medium, and which is suitable for arbitrarily forming a layer having a stable composition and stable structure, and a method for producing the same. To provide.

A first aspect of the invention is a WORM type optical recording medium comprising a substrate, a recording layer and a reflection layer, wherein the recording layer comprises a material represented by BiO _x (0 <x <1.5), and a recording mark on which information is recorded. Is a WORM type optical recording medium containing crystals of Bi and / or crystals of Bi oxide.

A second aspect of the present invention is a WORM type optical recording medium in which the recording mark in the first aspect includes tetravalent Bi.

A third aspect of the invention is a WORM type optical recording medium comprising a substrate, a recording layer and a reflection layer, wherein the recording layer contains Bi, O and M as constituent elements, and M is Mg, Al, Cr, Mn, Co , Fe, Cu, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Mo, V, Nb, Y and Ta, at least one element selected from the group consisting of: A WORM type optical recording medium comprising at least one crystal derived from a crystal of at least one element and a crystal of an oxide of at least one element contained in the.

A fourth aspect of the present invention is a WORM type optical recording medium wherein, in the third aspect, the recording mark includes tetravalent Bi.

A fifth aspect of the present invention is a WORM type optical recording medium wherein, in the third aspect, the ratio of the total amount of elements M to the number of atoms of bismuth is 1.25 or less.

According to a sixth aspect of the present invention, in the third aspect, the WORM type optical recording medium has a layer structure in which at least a recording layer, an upper coating layer, and a reflective layer are disposed on the substrate in this order, and at least a reflective layer, an upper coating layer, a recording layer, and A WORM type optical recording medium in which any cover layer retains any one of the layered structures including the layered structure in which the cover layer is disposed on the substrate in this order.

According to a seventh aspect of the present invention, in the third aspect, the WORM type optical recording medium is produced by using a sputtering target including at least one selected from BiFeO ₃ , Bi ₂₅ FeO _40, and Bi ₃₆ Fe ₂ O ₅₇ . It is a WORM type optical recording medium.

An eighth aspect of the present invention is a WORM type optical recording medium comprising a substrate, a recording layer and a reflective layer, wherein the recording layer contains Bi, O and L as constituent elements, the recording layer comprises Bi oxide, and L is At least one element selected from the group consisting of B, P, Ga, As, Se, Tc, Pd, Ag, Sb, Te, W, Re, Os, Ir, Pt, Au, Hg, Tl, Po, At and Cd It is a WORM type optical recording medium shown.

In a ninth aspect of the present invention, in the eighth aspect, the element L represents one or more elements selected from the group consisting of B, P, Ga, Se, Pd, Ag, Sb, Te, W, Pt, and Au. Type optical recording medium.

A tenth aspect of the present invention is a WORM type optical recording medium wherein, in the eighth aspect, the ratio of the total amount of elements L to the number of atoms of bismuth is 1.25 or less.

In an eleventh aspect of the present invention, in the eighth aspect, the WORM type optical recording medium further includes a top coating layer, and has a layered structure in which the recording layer, the top coating layer, and the reflective layer are disposed on the substrate in this order. WORM type optical recording medium.

According to a twelfth aspect of the present invention, in the eleventh aspect, the WORM type optical recording medium further includes a bottom coating layer, wherein the bottom coating layer, the recording layer, the top coating layer, and the reflective layer are disposed on the substrate in this order. It is a WORM type optical recording medium having a structure.

In a thirteenth aspect of the present invention, in the eighth aspect, the WORM type optical recording medium further includes a top coating layer and a cover layer, and the reflective layer, the top coating layer, the recording layer, and the cover layer are disposed on the substrate in this order. It is a WORM type optical recording medium having a layered structure.

In a fourteenth aspect of the present invention, in the thirteenth aspect, the WORM type optical recording medium further includes a bottom coating layer, and the reflective layer, the top coating layer, the recording layer, the bottom coating layer, and the cover layer are disposed on the substrate in this order. It is a WORM type optical recording medium having a layered structure.

In a fifteenth aspect of the present invention, in the eighth aspect, the WORM type optical recording medium further includes at least any one of a lower coating layer and an upper coating layer, and at least any one of the lower coating layer and the upper coating layer is ZnS and / or Or a WORM type optical recording medium comprising SiO ₂ .

According to a sixteenth aspect of the present invention, in the eighth aspect, the WORM type optical recording medium further includes a bottom coating layer and a top coating layer, and at least any one of the bottom coating layer and the top coating layer comprises an organic material. It is an optical recording medium.

A seventeenth aspect of the present invention is a WORM type optical recording medium in which recording and reproduction in the eighth aspect are possible by a laser beam having a wavelength of 680 nm or less.

An eighteenth aspect of the present invention is a sputtering target containing Bi, Fe, and O.

A nineteenth aspect of the present invention is the sputtering target according to the eighteenth aspect, wherein the sputtering target is made of Bi, Fe, and oxygen.

In a twentieth aspect of the present invention, in any one of the aspects comprising the eighteenth and nineteenth aspects, the sputtering target is a recording for an optical recording medium in which recording and reproduction are performed by a laser beam having a wavelength of 550 nm or less. It is a sputtering target that is used to form a layer.

In a twenty-first aspect of the present invention, the sputtering target according to any one of the aspects including the eighteenth to twentieth aspects, wherein the sputtering target comprises Bi oxide and Fe oxide, or comprises a complex oxide of Bi and Fe. Target.

A twenty-second aspect of the present invention is the sputtering target according to the twenty-first aspect, wherein the sputtering target comprises a complex oxide of Bi and Fe, and further includes at least one selected from Bi oxide and Fe oxide.

In a twenty-third aspect of the present invention, in the eighteenth aspect, the sputtering target comprises at least one selected from Bi oxide, Fe oxide, and a composite oxide of Bi and Fe, wherein the oxide has a lower amount compared to the stoichiometric composition. It is a sputtering target which is an oxide which carries oxygen.

In a twenty-fourth aspect of the invention, in any one of the aspects comprising the eighteenth to twenty-third aspects, the sputtering target comprises at least one selected from BiFeO ₃ , Bi ₂₅ FeO _40, and Bi ₃₆ Fe ₂ O ₅₇ . In sputtering target.

A twenty-fifth aspect of the present invention is the sputtering target according to any one of the aspects including the eighteenth to twenty-fourth aspects, wherein the sputtering target comprises Bi ₂ O ₃ and / or Fe ₂ O ₃ .

A twenty sixth aspect of the present invention is the sputtering target according to any one of the aspects including the eighteenth to twenty fifth aspects, wherein the sputtering target does not contain Bi ₂ Fe ₄ O ₉ .

 A twenty seventh aspect of the present invention is the sputtering target of any one of the aspects including the eighteenth to twenty-sixth aspects, wherein the content of Co, Ca, and Cr is below the detection limit of inductively coupled plasma emission spectroscopy.

A twenty eighth aspect of the present invention is the sputtering target of any one of the aspects comprising the eighteenth to twenty-seventh aspects, wherein the sputtering target has a packing density of 65% to 96%.

A twenty-ninth aspect of the present invention is a sputtering target, wherein in any one of the aspects including the eighteenth to twenty-eighth aspects, the atomic ratio of Bi and Fe satisfies the requirement of Bi / Fe ≧ 0.8.

A thirtieth aspect of the present invention is a sputtering comprising calcinating powders of Bi ₂ O ₃ and Fe ₂ O ₃ to produce a sputtering target according to any one of the embodiments comprising the eighteenth to twenty-ninth embodiments. It is a target manufacturing method.

A thirty first aspect of the invention is an optical recording medium comprising a substrate, a recording layer, and a reflective layer, wherein the recording layer comprises a sputtering target comprising one or more selected from BiFeO ₃ , Bi ₂₅ FeO ₄₀ , and Bi ₃₆ Fe ₂ O ₅₇ . It is an optical recording medium which is formed using.

Brief description of the drawings

FIG. 1 is a diagram showing a radial distribution function around the unrecorded and O (oxygen) atoms in the recording.

Fig. 2 is a diagram showing the distribution distribution of a radius around the O (oxygen) atoms of Bi oxides measured according to the FEFF calculation.

3 is a diagram showing the measurement result of Example B-26.

4 is a diagram showing the X-ray diffraction pattern of the sputtering target 1.

FIG. 5 is a diagram showing recording characteristics of an optical recording medium manufactured using sputtering target 1. FIG.

FIG. 6 is a diagram illustrating an X-ray diffraction pattern of sputtering target 2. FIG.

FIG. 7 is a diagram showing recording characteristics of an optical recording medium manufactured using sputtering target 2. FIG.

8 is a diagram showing the X-ray diffraction pattern of the sputtering target 3.

9 is a diagram illustrating an X-ray diffraction pattern of sputtering target 4. FIG.

FIG. 10 is a diagram showing recording characteristics of an optical recording medium manufactured using a sputtering target having a different ratio of Bi / Fe.

FIG. 11 is a diagram showing the X-ray diffraction pattern of the sputtering target 5. FIG.

12 is a diagram illustrating the X-ray diffraction pattern of the sputtering target 6.

example Implement the invention  Most preferred aspect for

Hereinafter, the present invention will be described in detail.

In order to realize a WORM type optical recording medium capable of performing very good recording at a short wavelength of blue laser wavelength or shorter, the following items (1) to (3) are treated as important tasks:

(1) Possibility of forming small recording marks.

(2) Less interference between recording marks.

(3) High stability of recording marks.

In the case of using a blue laser, unlike the case of using the lasers in the near infrared wavelength and the red wavelength used for CD and DVD, it is necessary to select a material that can perform recording very well at the blue wavelength.

Since Bi oxide absorbs light at the blue wavelength, very good recording can be expected.

A first aspect of the WORM type optical recording medium according to the present invention includes a substrate, a recording layer, and a reflective layer, wherein a recording material using BiO _x (0 <x <1.5) is used for the recording layer, and information is recorded. The mark includes crystals of Bi and / or crystals of Bi oxide. In order to calculate a higher modulated amplitude, the difference in refractive index between the recorded mark and the unrecorded portion needs to be large. In the case of using a material represented by BiO _x (0 <x <1.5) in the recording layer to form the crystals of Bi and / or the crystals of Bi oxide in the recording mark, the change in refractive index becomes larger and the higher modulated Amplitude can be realized. For example, when the unrecorded portion is amorphous and the record mark includes a crystallized portion, a higher modulated amplitude can be calculated. When the unrecorded portion contains Bi oxide, by forming a precipitate of a simple substance of Bi-metal other than the oxide in the recording mark, the difference in refractive index is much larger, and a much higher modulated amplitude can be calculated. Although a method of forming a recording mark by crystallizing an amorphous portion has been conventionally used, in the present invention, when recording with an oxide, by using the phenomenon that the recording portion is changed to a substance except oxide and the recording portion is crystallized, You can expect more effect. Since mixed crystals each holding a different crystal structure can inhibit the growth of crystals, recording marks containing crystals having two or more different crystal structures can suppress crystal growth and leading to small recording marks. It is possible to form.

Regarding the change of the recording layer induced by the recording, the following is further explained.

Although the material represented by BiO _x (0 <x <1.5) is in a metastable state in which it is difficult to exist in normal conditions, such a state can be realized by forming a recording layer by sputtering in an optical recording medium. When the temperature is increased by irradiating a laser beam to the recording layer of BiO _x (0 <x <1.5) in a metastable state, BiO _x is more likely to return to a more stable state, which makes it easier to separate Bi and Bi oxides. At this point, it is believed that some Bi oxides will be present in the state of Bi, which is no longer an oxide by isolating oxygen. Since the more stable state is the crystalline state, Bi crystals and Bi oxides are formed, and thus the recording mark is in a state in which the crystals of Bi and / or the crystals of Bi oxide are contained.

Embodiments of the WORM type optical recording medium of the present invention include a substrate, a recording layer and a reflective layer, wherein the recording layer includes Bi, O and M as constituent elements, and M is Mg, Al, Cr, Mn, Co, Fe , At least one element selected from the group consisting of Cu, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Mo, V, Nb, Y and Ta, and a recording mark on which information is recorded is contained in a recording layer One or more crystals derived from crystals of at least one element and oxides of at least one element. Another aspect of the WORM type optical recording medium includes a substrate, a recording layer and a reflective layer, wherein the recording layer comprises Bi, O and L as constituent elements, the recording layer comprises Bi oxide, and L is B, P At least one element selected from the group consisting of Ga, As, Se, Tc, Pd, Ag, Sb, Te, W, Re, Os, Ir, Pt, Au, Hg, Tl, Po, At and Cd.

Bismuth may be contained in any of states such as metal bismuth, bismuth alloy, bismuth oxide, bismuth sulfide, bismuth nitride, bismuth fluoride and the like, but the recording layer preferably includes one bismuth oxide. The recording layer containing bismuth oxide makes it possible to lower the thermal conductivity of the recording layer, to realize high-sensitivity and lower jitter value, and to achieve a complex index of refraction. Since it is possible to make the virtual portion lower, the recording layer retains very excellent transparency and easily forms a multi-layered recording layer.

Bismuth, Mg, Al, Cr, Mn, Co, Fe, Cu, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Mo, V, Nb, Y, Ta, B, P, Ga, As At least one element selected from the group consisting of Se, Te, Pd, Ag, Sb, Te, W, Re, Os, Ir, Pt, Au, Hg, Tl, Po, At and Cd may be used to improve stability and thermal conductivity. It is preferable to exist in an oxidation state in the recording layer from the viewpoint, but it does not necessarily need to be completely oxidized. In other words, when the recording layer of the present invention contains three elements of bismuth, oxygen and one element such as Mg, the recording layer is formed of bismuth, bismuth oxide, element (eg Mg), and element (eg Mg). Oxides.

A method for producing bismuth or metal bismuth and Bi oxides mixed in a recording layer, that is, a method for forming a recording layer in which bismuth elements exist in different states includes the following methods (A) to (C):

(A) a method of sputtering a recording layer using a bismuth oxide target;

(B) a method of sputtering a recording layer using a bismuth target and a bismuth oxide target; And

(C) A method of sputtering a recording layer using a bismuth target while introducing oxygen into the recording layer, or a co-sputtering method.

When using method (A), bismuth in the target is completely oxidized, and this method utilizes a phenomenon in which oxygen tends to be insufficient depending on sputtering conditions such as the degree of vacuum and sputtering power.

The following describes a first aspect of a WORM type recording medium in which the recording layer contains Bi, M and oxygen as constituent elements. Element M is at least one element selected from the group consisting of Mg, Al, Cr, Mn, Co, Fe, Cu, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Mo, V, Nb, Y and Ta It should be noted that it is indicated.

Recording can be performed very well with respect to light at a blue wavelength by using a material containing Bi, M and oxygen in the recording layer. In the aspect of the WORM type optical recording medium of the present invention, wherein the recording layer contains M, by forming the recording mark in a state in which crystals of two or more kinds of oxides are mixed, the refractive index between the recording mark and the unrecorded portion is increased. The difference is greater and can yield a higher modulated amplitude. In addition, a larger effect can be obtained by allowing not only the crystals of the oxides but also the crystals of the elements alone to be present in the recording layer. Since the growth of crystals can be suppressed by mixing crystals of different elements or crystals having different crystal structures, respectively, recording marks containing crystals and / or crystal structures of two or more different elements suppress the growth and inversion of crystals. And the crystal makes it possible to form small recording marks.

The recording mark preferably contains tetravalent Bi. Typically, as the valence of Bi, trivalent Bi is the most stable, but to produce a much higher modulated amplitude, tetravalent Bi is used. It is possible to make the valence of Bi tetravalent, depending on the condition of the oxygen surrounding the Bi atom. By changing the valence of Bi alters the physical properties, higher modulated amplitudes can be calculated.

BiO ₂ is mentioned as an example of a tetravalent Bi compound. Typically, Bi-oxides having a structure of Bi ₂ O ₃ are present in a stable state. However, the Bi-oxide may take the same structure as BiO ₂ depending on the conditions. By having the recording layer retain crystalline structures that are not typically used, higher modulated amplitudes can be produced.

Hereinafter, another aspect of the WORM type optical recording medium of the present invention will be described. In the WORM type optical recording medium, the recording layer contains Bi, L, oxygen and Bi oxide as constituent elements. Element L is selected from the group consisting of B, P, Ga, As, Se, Tc, Pd, Ag, Sb, Te, W, Re, Os, Ir, Pt, Au, Hg, Tl, Po, At and Cd Note that it represents more than one element. The recording layer contains bismuth as a main component. The element M can be named as an element to be added to the recording layer containing Bi and O as a constituent element. However, according to the examination of the basic properties of the constituent elements that can be added to the constituent elements, the element L can also be named. One of the reasons why element L can be added as a constituent element to a recording layer containing bismuth as a main component and a Bi oxide is that it reduces the thermal conductivity and facilitates the formation of fine recording marks. Since thermal conductivity is a value that can be attributed to the presence of photon scattering, thermal conductivity is due to a decrease in particle size and crystal size, when there are a large number of atoms constituting the material, when the difference in atomic weight of the constituent atoms is large, When there is a reason, it may decrease. Thus, by adding L as a constituent element to the recording layer containing bismuth as the main constituent and containing the Bi oxide, it is possible to control the thermal conductivity and improve the high density recording characteristics.

In addition, in the recording layer containing bismuth as a main constituent and additionally containing bismuth oxide, the size of crystals and crystallized particles can be controlled by element L, although bismuth oxide and bismuth are crystallized by recording information. have. Thus, the element L makes it possible to control the size of the crystallized and crystallized particles in the recording section, and to further improve recording and reproduction characteristics such as jitter. This is another reason for adding L to the recording layer as a constituent element.

In terms of thermal conductivity, there are some requirements that are assumed by element L that can be added as a constituent element to the recording layer except for simple requirements, such as the stability of the raw materials and the difficulty of manufacture. However, the inventors of the present invention have found that the reliability of the recording layer, that is, the reproduction stability and the storage stability, is substantially dependent on the selected element L, and there is a limited requirement assumed by the element L regarding reliability.

That is, as a result of earnestly examining the requirement of the element L to be added as a constituent element to the recording layer, the inventors of the present invention found that the following requirements (I) and (II) were effective:

(I) an element having a fouling electronegativity value of at least 1.80.

(II) Electron negative value of 1.65 or higher and the standard formation enthalpy ΔH _f ^{o of} oxides, except transition metal Element having at least -1,000 (kJ / mol).

By using the element L satisfying (I) or (II), it is possible to realize a WORM type optical recording medium having very good recording and reproducing characteristics such as jitter and high reliability.

Hereinafter, requirements (I) and (II) will be described in detail.

The degradation of the reliability of the recording layer containing bismuth as a main constituent of the constituent elements and containing bismuth oxide is mainly caused by the progress of oxidation, or a change in oxidation state, such as a change in valence, and other causes. The fouling electronegative value and the standard formation enthalpy “ΔH _f ^o ” of the oxide are actually important as the physical property values of the element L, since the progress of oxidation and the change in oxidation state are likely to lead to reduced reliability. In order to sufficiently enhance the reliability of the optical recording medium, it is preferable to first select an element having a fouling electronegativity value of 1.80 or more as the element L. This is because it is difficult to proceed by an element having a high fouling electronegative value and it is difficult to guarantee satisfactory reliability, and an element having a fouling electronegative value of 1.80 or more is effective. Standard Formation Enthalpy of Oxide "ΔH _f ^o May take any value, provided that the fouling electronegativity value is greater than or equal to 1.80.

Examples of the element L having an electronegativity value of 1.80 or more include B, Si, Fe, Co, Ni, Cu, Ga, Ge, As, Se, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Sb, Te , W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Po and At.

Hereinafter, the electronegativity will be briefly described.

Electronegativeness is a measure of how strongly atoms in a molecule can pull electrons. Methods for determining the value of electronegativity include Pauling's electronegativity, Mulliken's electronegativity, and Allred-Rochow's electronegativity. The validity of is determined by using fouling electronegativity.

The fouling electronegativity is that the binding energy E (AB) of molecules A and B is greater than the average binding energy of molecules AA and BB (E (AA) and E (BB), respectively), and the difference between the energies is It is defined as the square of the difference between the electronegativity (X _A , X _B ) of. That is, it is represented by the following equation (1).

E (AB)-[E (AA) + E (BB)] / 2 = 96.48 (X _A -X _B ) ² ..... (1)

In fouling electronegativity, the equation includes a conversion factor of 96.48 (1 eV = 96.48 kJmol ⁻¹ ) because the electronegativity value is determined by using electron volts.

Since electronegativity depends on which valence a given element takes in the molecule, the following definition applies in the case of determining electronegativity in the present invention.

That is, as shown below, where the elements of each of the following groups each take on the following valency, the value is defined as the fouling electronegativity value of the element:

The elements of group 1 are monovalent; The elements of group 2 are divalent; An element of Group 3 is trivalent; The elements of Groups 4 to 10 are divalent; The elements of Group 11 are monovalent; The elements of group 12 are divalent; An element of Group 13 is trivalent; An element of Group 14 has a tetravalent value; The elements of group 15 are trivalent; The elements of Group 16 are divalent; An element of Group 17 is monovalent; Elements of Group 18 have zero valences.

For those elements each having an electronegativity of at least 1.80, each fouling electronegative value defined in the present invention is B (2.04), Si (1.90), P (2.19), Fe (1.83), Co (1.88) , Ni (1.91), Cu (1.90), Ga (1.81), Ge (2.01), As (2.18), Se (2.55), Mo (2.16), Tc (1.90), Ru (2.20), Rh (2.28) , Pd (2.20), Ag (1.93), Sn (1.96), Sb (2.05), Te (2.10), W (2.36), Re (1.90), Os (2.20), Ir (2.20), Pt (2.28) , Au (2.54), Hg (2.00), Tl (2.04), Pb (2.33), Po (2.00) and At (2.20).

These elements can be added as constituent elements to the recording layer in a combination of two or more.

In addition, the inventors of the present invention found that even if the fouling electronegativity value is less than 1.80, the fouling electronegativity value is 1.65 or more and the standard formation enthalpy ΔH _f ^o of elemental oxide. It has been found that elements with more than -1,000 (kJ / mol) make it possible to ensure satisfactory reliability. The reason why the requirement is effective is that, if the element has a larger value of the standard formation enthalpy ΔH _f ^o of the oxide, the element is less likely to form an oxide, even if the fouling electronegativity is somewhat small. Because.

In the present invention, when determining the fouling electronegativity value, the value is determined by each valence fixed to each group of elements, and the same definition applies when determining the standard formation enthalpy ΔH _f ^o .

That is, the value when the oxide is composed of the following valences in the elements of each group is defined as the standard formation enthalpy ΔH _f ^o of the element.

That is, the elements of group 1 are monovalent; The elements of group 2 are divalent; An element of Group 3 is trivalent; The elements of Groups 4 to 10 are divalent; The elements of Group 11 are monovalent; The elements of group 12 are divalent; An element of Group 13 is trivalent; An element of Group 14 has a tetravalent value; The elements of group 15 are trivalent; The elements of Group 16 are divalent; An element of Group 17 is monovalent; Elements of Group 18 have zero valences. However, in the case of transition metals, it is impossible to easily determine the standard formation enthalpy ΔH _f ^o of the oxide, since the transition metal forms oxides at various valences. Typically, the higher the valence of the element forming the oxide of the element, the higher the enthalpy of formation of the oxide ΔH _f ^o Becomes even lower.

In other words, in the case of transition metals, the oxide (s) are easily formed such that oxides having various valences are formed, so it is preferable in the present invention not to use transition metals as element L.

For example, since V (vanadium), a second take Add, V (vanadium) standard of oxide formation enthalpy ΔH _f ^o assuming a value = -431 (kJmol ^-1) of the standard enthalpy of formation ΔH _f ^o of the VO, which It belongs to requirement (II) for element L in the present invention. However, V (vanadium) also easily forms oxides such as V ₂ O ₃ (trivalent), V ₂ O ₄ (tetravalent), V ₂ O ₅ (pentavalent). The ΔH _f ^o values of these oxides are V ₂ O ₃ (-1,218 kJmol ^-1 ), V ₂ O ₄ (-1,424 kJmol ^-1 ) and V ₂ O ₅ (-1,550 kJmol ^-1 ), respectively. It does not belong to the requirement (II) for element L in the invention. In other words, assuming that V forms an oxide with almost divalent, V (vanadium) belongs to the requirements (I) and (II) of the present invention, while V (vanadium) is an oxide other than divalent oxide. Easily formed, the oxide is easily oxidized, that is, oxidized to a more stable state. Thus, these oxides are excluded from the preferred element L of the present invention.

The description of the exclusion is clearly described as "exclusion transition metal" in requirement (II) for element L of the present invention.

Hereinafter, the standard formation enthalpy ΔH _f ^o will be briefly described.

Typically, the chemical reaction is represented by the following chemical equation (2).

H ₂ (gas) + (1/2) O ₂ (gas) = H ₂ O (liquid) ...... (2)

Here, the left side of the chemical equation is called the original system and the right side of the equation is called the product. The coefficient given to the molecule is called the stoichiometric coefficient.

The heat coming in and out associated with the chemical reaction of the system at a constant temperature is called the heat of reaction, and the heat of reaction at a constant pressure is called the heat of reaction at a constant pressure.

In most cases, under typical laboratory conditions, the heat of reaction is measured at a constant pressure, so it is common to use the heat of reaction at a constant pressure. The heat of reaction at constant pressure is equivalent to the enthalpy difference “ΔH” between the product and the original system.

 The reaction represented by ΔH> 0 is called an endothermic reaction, and the reaction represented by ΔH <0 is called an exothermic reaction.

The heat of reaction generated from the reaction to form the compound from the chemical element of the compound is called the heat of formation or formation enthalpy. The heat of reaction generated from the reaction to form 1 mole compound under standard conditions from chemical elements of the compound is referred to as standard formation enthalpy. In standard conditions, the standard forming enthalpy is indicated using a specified temperature, typically 298K, at a pressure of 0.1 MPa or nearly equal to 1 atmosphere, and the standard forming enthalpy is indicated by the symbol of ΔH _f ⁰ . Under standard conditions, the enthalpy of each chemical element is determined to be zero.

Thus, it can be said that the smaller the standard formation enthalpy value of the oxide of the element or the larger the negative value of the standard formation enthalpy, the more stable the oxide and the element are easily oxidized.

Specific values of the standard forming enthalpy are described, for example, in "Electrochemistry Handbook Vol. 5" (Denki-kagaku Binran) edited by The Electrochemistry Society of Japan, Maruzen.

Since the standard formation enthalpy ΔH _f ⁰ depends on which valence a given element takes in the molecule to form its oxide, the above-mentioned requirement applies when the standard formation enthalpy of the oxide of each element is determined in the present invention. .

Examples of elements having a fouling electronegativity value of at least 1.65 and an oxide having a standard formation enthalpy ΔH _f ⁰ -1,000 (kJ / mol) or more include Zn, Cd and In. For fouling electronegativity values according to the definition of the present invention, these elements are determined as follows: Zn (1.65), Cd (1.69) and In (1.78), respectively. For the standard forming enthalpy ΔH _f ⁰ according to the definition of the present invention, these elements are determined as follows: Zn (-348 kJmol ^-1 ), Cd (-258 kJmol ^-1 ) and In (-925 kJmol ^-1) ).

The ratio of the total amount of elements L to the number of atoms of bismuth is preferably 1.25 or less.

The recording layer of the present invention is based on the assumption that it contains bismuth as the main constituent of the recording layer and also contains Bi oxides, so that when the ratio of the total amount of element L to the number of atoms of bismuth is larger than 1.25, the unique recording And reproduction characteristics cannot be obtained.

In addition, adding B, P, Ga, Se, Pd, Ag, Sb, Te, W, Pt, and Au as the element L to the recording layer is preferable in terms of improving the storage stability of the recording layer. Improvements in storage stability may be due to the fact that it is difficult to break the crystalline structure once formed once by strengthening the bonding force between atoms, or in the lattice of atoms of size lower than the valence of size when particles of different sizes are present side by side. This is very likely to occur due to the fact that the crystalline structure is stabilized. In particular, elements such as B and Pd, when bonded to oxygen and bringing Bi and O together, are effective in stabilizing the amorphous structure. As a result, the structure of the crystal can be stabilized, which leads to an improvement in the storage stability of the WORM type recording medium.

In the WORM type optical recording medium of the present invention, recording and reproducing of information are preferably performed through the use of a laser beam at a wavelength of 680 nm or less. Unlike dyes, the recording layer of the present invention has a moderate absorption coefficient and a high refractive index over a wide range of wavelengths, so that not only is it possible to perform recording and reproduction with a laser beam at a red laser wavelength of 680 nm or less, but also very excellent recording and It is possible to realize reproduction characteristics and high reliability. Particularly the most preferred of these is the performing of recording and reproduction with a laser beam at a wavelength of 450 nm or less. This is because the recording layer containing bismuth as the main component and the Bi oxide has a complex refractive index which is particularly suitable for WORM type optical recording media used by laser beams at wavelengths of 450 nm or less.

The WORM type optical recording medium according to the present invention preferably has the following forms, but is not particularly limited to those forms:

(A) a substrate, a recording layer, an upper coating layer, a cover layer, and a reflective layer.

(B) a substrate, lower coating layer, recording layer, upper coating layer, and reflective layer.

(C) Substrate, reflective layer, top coating layer, recording layer and reflective layer.

(D) substrate, reflective layer, top coating layer, recording layer, bottom coating layer and cover layer.

In addition, based on the above form, the structure of the layers may be formed into a multi-layered structure. For example, when formed into two layers based on the form of (A), it may have the following form: substrate, recording layer, top coating layer, reflective or translucent layer, binder layer, recording layer, top Coating layer, reflecting layer and substrate.

In the case of the lower coating layer and the upper coating layer, the following oxides and nonoxides are available. Examples of oxides are simple oxides such as B ₂ O ₅ , Sm ₂ O ₃ , Ce ₂ O ₃ , Al ₂ O ₃ . MgO, BeO, ZrO ₂ . UO ₂ , and ThO ₂ ; Silicates such as SiO _2, 2MgO and SiO _2, MgO and SiO _2, CaO and SiO _3, ZrO ₂ and SiO _2, 3Al ₂ O ₃ and 2SiO _2, 2MgO and 2Al ₂ O ₃ and 5SiO _2, Li ₂ O and Al ₂ O ₃ ㆍ 4SiO ₂ ; Double oxides such as Al ₂ TiO ₅ , MgAl ₂ O ₄ , Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ , BaTiO ₃ , LiNbO ₃ , PZT [Pb (Zr, Ti) O ₃ ], PLZT [(Pb, La ) (Zr, Ti) O ₃ ], and ferrite. Examples of nonoxides include nitrides such as Si ₃ N ₄ , AlN, BN and TiN; Carbides such as SiC, B ₄ C, TiC and WC; Borides such as LaB ₆ , TiB ₂ and ZrB ₂ ; Sulfides such as ZnS, CdS and MoS ₂ ; Silicides such as MoSi ₂ ; And carbon such as amorphous carbon, graphite and diamond.

Organic materials such as dyes and resins may also be used in the bottom and top coating layers.

Examples of the dyes include polymethine dyes, naphthalocyanine dyes, phthalocyanine dyes, squarylium dyes, croconium dyes, pyryllium dyes, naphthoquinone dyes, anthraquinone dyes, xanthene dyes and triphenylmethane dyes. , Azulene dyes, tetrahydrocholine dyes, phenanthrene dyes, triphenothiazine dyes, azo dyes, formazan dyes, and metal complexes of these compounds.

Examples of the resins include polyvinyl alcohol, polyvinyl pyrrolidone, cellulose nitrate, cellulose acetate, ketone resins, acrylic resins, polystyrene resins, urethane resins, polyvinyl butyral, polycarbonates and polyolefins. Each of these resins may be used alone or in combination of two or more thereof.

The layer containing the organic material can be formed by means of deposition, sputtering, CVD, that is, chemical vapor deposition, solvent coating, etc. which are commonly used. When using the coating method, the above-mentioned organic materials and the like are dissolved in an organic solvent, and the solvent is coated by commonly used coating methods such as spraying, roller-coating, dipping, and spin-coating.

Examples of typical organic solvents that can be used include alcohols such as methanol, ethanol, and isopropanol; Ketones such as acetone, methyl ethyl ketone, and cyclohexanone; Amides such as N, N-dimethylacetoamide and N, N-dimethylformamide; Sulfoxides such as dimethyl sulfoxide; Ethers such as tetrahydrofuran, dioxane, diethyl ether and ethylene glycol monomethyl ether; Esters such as methyl acetate and ethyl acetate; Aliphatic halocarbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride, and trichloroethane; Aromatic series such as benzene, xylene, monochlorobenzene, and dichlorobenzene; Cellosolves such as methoxyethanol and ethoxyethanol; And hydrocarbons such as hexane, pentane, cyclohexane, and methylcyclohexane.

In the case of the reflective layer, a light reflective material having a high reflectance for the laser beam is used.

Examples of light reflecting materials include metals such as Al, Al-Ti, Al-In, Al-Nb, Au, Ag and Cu, semimetals, and alloys thereof. Each of these materials may be used alone or in combination of two or more.

When the reflective layer is formed of an alloy, it is possible to produce the reflective layer by using the alloy as the target material and using sputtering. In addition, it is also possible to form the reflective layer by cosputtering (eg using an Ar target and a Cu target) and by a tip-on-target method ( For example, a Cu tip is placed on an Ar target material to form a reflective layer).

It is also possible to use a low refractive index layer and a high refractive index layer by alternately stacking them to form a multi-layered structure and use this as a reflective layer.

The reflective layer can be formed by, for example, sputtering, ion-plating, chemical vapor deposition, and vacuum deposition. This reflective layer preferably has a thickness of 5 nm to 300 nm.

The material for the substrate is not particularly limited as long as the material has very good thermal and mechanical properties, and also when recording and reproducing is performed from the side of the substrate and throughout the substrate, it also has very good light transmission properties. Done.

In particular, examples of the material include polycarbonate, polymethyl methacrylate, amorphous polyolefin, cellulose acetate, polyethylene terephthalate, of which polycarbonate and amorphous polyolefin are preferable.

The thickness of the substrate depends on the application, and is not particularly limited.

The material for the protective layer, the optical transparent layer, or the like to be formed on the reflective layer is not particularly limited, provided that the material is capable of protecting the reflective layer, the optical transparent layer, etc. from external forces. Examples of the organic material include thermoplastic resins, thermosetting resins, electron beam curable resins, and ultraviolet curable resins. Examples of the inorganic material include SiO ₂ , Si ₃ N ₄ , MgF ₂ and SnO ₂ .

On a reflective layer, an optical transparent layer, etc., a protective layer can be formed using a thermoplastic resin and / or a thermosetting resin. First, the coating solution is prepared by dissolving the thermoplastic resin and / or thermosetting resin in a suitable solvent. The coating solution is then coated on a reflective layer and / or an optical clear layer and dried to form a protective layer.

The protective layer using the ultraviolet curable resin may be coated directly with the ultraviolet curable resin on the reflective layer and / or the optical transparent layer, or by dissolving the ultraviolet curable resin in a suitable solvent to prepare a coating solution and the coating solution is the reflective layer and / or the optical transparent layer. After coating on, it can form by irradiating an ultraviolet-ray to a coating solution and hardening the coating solution.

In the case of ultraviolet curable resins, for example, acrylate resins such as urethane acrylate, epoxy acrylate and polyester acrylate can be used.

Each of these materials may be used alone or in combination of two or more, and may be formed not only in a single layer but also in a multi-layered structure.

In the case of the method of forming the protective layer, a coating method such as spin-coating and casting, sputtering, chemical vapor deposition, or the like is used, among which spin-coating is preferable.

Although the thickness of the protective layer is typically 0.1 μm to 100 μm, in the present invention, it is preferred that it is 3 μm to 30 μm.

In addition, the substrate may be disposed on the surface of the reflective layer or the optical transparent layer. The reflective layer and the optical transparent layer can be aligned to face each other. The two sheets of the optical recording medium can be laminated after aligning the reflective layer and the optical transparent layer to face each other.

In addition, an ultraviolet curable resin layer, an inorganic resin layer, or the like may be formed on the mirror surface side of the substrate to protect its surface, and / or may protect the surface from dust or the like attacking the surface.

For higher recording density, the optical transparent layer or cover layer should form an optical transparent layer or cover layer when using a lens with a high numerical aperture. If the numerical aperture is increased, the portion through which the regenerated light passes should have a reduced thickness. This is because a tolerance in aberration occurs when the direction perpendicular to the surface of the medium deviates from the optical axis of the optical pickup, and the deviation angle called the inclination angle decreases with increasing numerical aperture. to be. The inclination angle is proportional to the inverse of the wavelength of the light source and the square of the object lens multiplied by the numerical aperture, and is easily affected by the aberration due to the thickness of the substrate. In order to reduce the aberration due to the thickness of the substrate, the thickness of the substrate is reduced.

For this purpose, some optical recording media such as substrates, recording layers with concave or convex irregularities, reflective layers, and optical transparent layers or cover layers that transmit light are arranged in this order in a layered structure, and the reproduction light is optical An optical recording medium is provided which is irradiated from a transparent layer to reproduce information in a recording layer. Another example is an optical recording medium in which a reflective layer, a recording layer, and an optical transparent layer or cover layer having optical transparency are disposed on the substrate in this order, and reproduced light is irradiated from the optical transparent layer to reproduce information in the recording layer. have. These optical recording media can allow the use of objective lenses with high numerical aperture by reducing the thickness of the optical transparent layer. That is, high density recording can be performed by recording and / or reproducing information on a medium having a thin optical transparent layer, where the reproduction light is irradiated from the optical transparent layer.

The cover layer may typically comprise a polycarbonate sheet or an ultraviolet curable resin. As used herein, a cover layer can include a binder layer that couples the cover layer to adjacent layers.

Hereinafter, a sputtering target suitable for use in the optical recording medium of the present invention having a recording layer containing Bi, Fe and oxygen, and a manufacturing method thereof will be described in detail.

Sputtering targets according to the invention include Bi, Fe and O. The sputtering target is suitably used for forming a recording layer of an optical recording medium which performs recording and reproduction with a laser beam at a wavelength of 550 nm or less.

The relationship between the extinction coefficient k which is one of the optical constants and the coefficient which shows the degree of light absorption, and the wavelength of light is examined. If the value of k is zero, the value indicates no absorption of light at all, and as the value of k increases, the light absorption increases. The recording layer formed using the sputtering target of the present invention containing Bi, Fe, and O has almost zero light absorption at wavelengths of 600 nm or more, and has a value of approximately zero, thus making it difficult to record information. . However, the k value is suddenly larger than at wavelengths smaller than 550 nm and very good recording is possible. In particular, in the vicinity of the wavelength of 400 nm, the light absorption becomes substantially larger, and extremely very excellent characteristics appear as the recording layer of the optical recording medium.

The sputtering target of the present invention preferably comprises Bi oxide and Fe oxide or a composite oxide of Bi and Fe. The sputtering target may comprise a composite oxide of Bi and Fe, and further includes one or more selected from Bi oxide and Fe oxide. Depending on the composition, there may be cases where Bi oxides and Fe oxides remain in the sputtering target without forming a complex of Bi and Fe under very well controlled conditions. An embodiment of the sputtering target comprises Bi oxide and Fe oxide, or another embodiment of the sputtering target comprises a composite oxide of Bi and Fe, or another embodiment of the sputtering target comprises a composite oxide of Bi and Fe and further And at least one selected from Bi oxide and Fe oxide. In any of the above-mentioned aspects, the optical recording medium produced using such a sputtering target as described above exhibits very excellent characteristics. In particular, by including Bi oxide as a constituent of the recording layer, the manufactured recording layer can contain Bi oxide. Since the recorded mark can be recorded very well by precipitating Bi metal, it is remarkably very effective to use a sputtering target containing Bi oxide.

The sputtering target of the present invention preferably comprises at least one selected from Bi oxide, Fe oxide, and a composite oxide of Bi and Fe, wherein the oxide is an oxide having a smaller amount of oxygen as compared to the stoichiometric composition. desirable. Examples of Bi oxides, Fe oxides, or complex oxides of Bi and Fe, which have less oxygen in comparison with the stoichiometric composition, include BiO _x (x <1.5), FeO _x (x <1.5), BiFeO _x (x <3), Bi ₂₅ FeO _x (x <40), and Bi ₃₆ Fe ₂ O _x (x <57) are mentioned. By reducing the amount of oxygen to enhance the metal properties, sputtering is made possible through the use of direct current power (DC power). DC sputtering has the advantage that the devices used in manufacturing are less expensive than those used in RF sputtering, and that the devices used in DC sputtering are smaller in size than those used in RF sputtering. When the layer is formed by DC sputtering, the amount of oxygen in the layer can be controlled by introducing oxygen externally. By using DC sputtering, the recording characteristics are easily controlled.

Sputtering targets having a smaller amount of oxygen compared to the stoichiometric composition are calcined after mixing the Bi metal and Fe ₂ O ₃ . It is also possible to produce a target with a small amount of oxygen by a method such as controlling the temperature to reduce the amount of oxygen remaining in the target.

The sputtering target of the present invention preferably comprises at least one selected from BiFeO ₃ , Bi ₂₅ FeO ₄₀ , and Bi ₃₆ Fe ₂ O ₅₇ as main constituents. As mentioned above, the optical recording medium using the recording layer containing Bi, Fe and oxygen exhibits very good recording characteristics. Although sputtering targets containing Bi, Fe and oxygen for magnetic optical recording and having a garnet structure exist, such sputtering targets are used in the present invention as main components in terms of the composition for forming the garnet structure. It does not contain a compound. Sputtering targets containing three elements of Bi, Fe, and oxygen have not been used until now, because it is impossible to form a garnet structure with only these three elements. In addition, the present invention does not relate to a magnetic optical recording medium, and the present invention mainly includes Bi, Fe and oxygen in the case of an optical recording medium which does not use magnetic, in particular in the case of a WORM type optical recording medium which enables high density recording. A sputtering target used to form a layer (hereinafter referred to as a BiFeO layer).

It is preferable that a sputtering target consists of three elements, Bi, Fe, and oxygen.

In this case, although the sputtering target may include impurity elements other than three elements, it is not preferable to include microelements which impair the properties of the layer.

The sputtering target of this invention is manufactured by mixing and baking the powder of the oxide which is a raw material. It is possible to produce the spotting target using the firing treatment of the powder of Bi oxide and the powder of Fe oxide. It is also possible to produce a sputtering target by preparing a powder of a compound mainly containing Bi, Fe and oxygen, followed by calcining the powder. As the firing treatment method, a press-heat firing process such as hot-pressing, hot isothermal pressing or HIP can be used. In the case of the firing temperature, higher temperatures are preferred for enhancing the strength of the sputtering target, but for compounds containing Bi, Fe and oxygen, the phase separation and / or melting at temperatures of approximately 800 ° C. or higher Occurs, and it is difficult to uniformly bake the compound. Therefore, the firing treatment temperature should be controlled not to be greater than about 750 ° C.

In particular, an optical recording medium having a BiFeO layer formed using a sputtering target containing at least one selected from BiFeO ₃ , Bi ₂₅ FeO ₄₀ , and Bi ₃₆ Fe ₂ O ₅₇ as the main constituent for the recording layer has very excellent characteristics. Indicates. The presence of BiFeO ₃ , Bi ₂₅ FeO ₄₀ , and Bi ₃₆ Fe ₂ O ₅₇ can be confirmed by X-ray diffraction means. For radiation sources, Cu is used to measure its presence at 2θ ° angles of an X-ray diffractometer at 5 ° to 60 °. The term major constituent means that the highest content or highest mass% is contained in the compound. Typically, the material showing the highest diffraction peak as a result of X-ray diffraction analysis can be determined as the major constituent, but the content may not be present in proportion to the measure of the diffraction peak. For sputtering targets containing two or more elements selected from BiFeO ₃ , Bi ₂₅ FeO ₄₀ , and Bi ₃₆ Fe ₂ O ₅₇ as main constituents, the contents of these two or more compounds are the same and the contents of these two or more compounds are different. It means higher than the ingredients.

The sputtering target preferably comprises Bi ₂ O ₃ and / or Fe ₂ O ₃ . The optical recording medium in which the BiFeO layer is formed using a sputtering target containing such a compound for the recording layer exhibits very excellent characteristics. The presence of Bi ₂ O ₃ and / or Fe ₂ O ₃ can be confirmed by X-ray diffraction means. For radiation sources, Cu is used to measure its presence at 2θ ° angles of an X-ray diffractometer at 5 ° to 60 °.

BiFeO ₃ , Bi ₂₅ FeO ₄₀ , Bi ₃₆ Fe ₂ O ₅₇ , Bi ₂ O ₃ And in X-ray diffraction analysis to identify the constituents of Fe ₂ O ₃ , when the angle of 2θ where the diffraction peak is expected to be detected is defined as θ1, it actually has diffraction peaks falling within the range of θ1 ± 1 °. It is determined that the substance is included in the above-mentioned compound.

 In X-ray diffraction analysis, the lattice constant changes, and misalignment depends on the cause, such as the measurement temperature, the internal stress of the layer, the measured X-ray wavelength error, and the compositional shift at the angle at which the diffraction peak appears. Occurs. In the case of well-known materials, whether or not diffraction peaks are detected at any angle can be determined by using American Society for Testing and Material (ASTM) cards and JCPDS searches. When the sample is analyzed to identify the components, ASTM cards and JCPDS card charts are widely used. The term JCPDS stands for Joint Committee on Powder Diffraction Standards (JCPDS), which is a chart of X-ray diffraction patterns distributed by an organization called the International Center for Diffraction Data (ICDD) and for the search of diffraction patterns of standards. Stores multiple charts. The X-ray diffraction pattern chart of the sample having the unknown component is compared with the chart of the standard material to determine which chart of the standard material corresponds or is closely related. Through this comparison, the material of the sample is identified. The verification method using the JCPDS card chart is not only described in the X-ray diffraction analysis standard, but also in the Japanese Industrial Standard (JIS) description of the X-ray diffraction analysis standard, as well as in Ceramics Basic Structures 3 edited by Tokyo Institute of Technology, as described in the description of X-ray diffraction analysis, is a method widely used in the world. In the measurement, the material is identified after examining whether the X-ray diffraction pattern of the material having the unknown component corresponds or closely related to the pattern of the standard material.

nλ = 2d sinθ

In the above equation, n represents a positive integer, λ represents a wavelength, d represents a distance in the grating plane, and θ represents a glancing angle or a supplementary angle of incident angle.

Since the Bragg principle is accepted, the diffraction peak also appears at a position where n represents an integer multiple on the highest angle side of 2θ. The identification of the substance is made possible by analyzing the peak at the position expressed by an integer multiple at the same time as the analysis of the diffraction peak based on 2θ. As described above, in the X-ray diffraction analysis, the lattice constant changes, and the misalignment occurs at an angle at which the diffraction peak appears due to the measurement temperature, the internal stress of the layer, the X-ray wavelength error to be measured, the composition shift, etc. If the material of has a diffraction peak near the angle at which the diffraction peak appears in the known material, the material can be determined to correspond to the known material having the diffraction peak.

In the case of misregulation of the diffraction peak, the peak having 2θ = 22.491 ° obtained from, for example, a standard chart of BiFeO ₃ (reference code 20-0169) is examined. The measurement results for the four sputtering targets produced in the same manner and under the same conditions are respectively observed. 2θ of the standard data of BiFeO ₃ is 22.491 °. On the other hand, these targets exhibit very slight misalignment of 22.380 °, 22.500 °, 22.420 ° and 22.420 °, respectively. In this review, a misalignment of approximately ± 1 ° falls within the error of measurement during repeated measurements. Therefore, even if a mismatch of ± 1 ° of such diffraction peaks is observed, it can be identified as a known peak. For example, if any material has a peak of uncontrolled ± 1 ° from 22.491 °, the BiFeO ₃ described herein may be determined to be included in that material. Sputtering targets containing Bi, Fe and O and having diffraction peaks at 22.380 ° ≦ 2θ ≦ 22.500 ° are particularly effective for recording characteristics.

Similarly, according to the standard data of _{Bi 36 Fe 2 O 57, Bi} 36 Fe 2 O 57 shall have a peak at 2θ = 27.681 °. When measuring the four targets mentioned above, they appear to have peaks at 27.65 °, 27.64 °, 27.76 ° and 27.67 °, respectively.

According to standard data of Bi ₂₅ FeO ₄₀ , it has a peak at 2θ = 27.683 °. When measuring the four targets mentioned above, they appear to have peaks at 27.66 °, 27.64 °, 27.76 ° and 27.68 °, respectively.

Since misregulation of about ± 1 ° occurs in repeated experiments, any of these materials is considered to fall within the measurement error range of ± 1 ° in 2θ.

The sputtering target is more preferably that do not further comprise a Bi ₂ Fe ₄ O ₉ as. As the content of Bi increases, the content of Bi ₂ Fe ₄ O ₉ tends to be lowered. The presence of Bi ₂ Fe ₄ O ₉ can be confirmed by X-ray diffraction means. For radiation sources, Cu is used to measure its presence at 2θ ° angles of an X-ray diffractometer at 5 ° to 60 °. An optical recording medium in which a BiFeO layer for a recording layer is formed using a sputtering target whose presence of Bi ₂ Fe ₄ O ₉ is confirmed by X-ray diffraction means does not exhibit satisfactory recording characteristics and is suitable for high density recording. Not.

The sputtering target preferably retains the contents of Co, Ca and Cr below the detection limit. When using a sputtering target containing an impurity, the layer formed also likewise contains an impurity element. In optical recording, recording is performed by irradiating and absorbing a laser beam onto the recording layer to induce physical or chemical changes. The term physical or chemical change means a change such as crystallization. The layer containing the impurity is preferably not used for the recording layer because the crystallization temperature changes and the crystal size varies during crystallization.

For the detection of impurities, the composition is analyzed quantitatively by means of inductively coupled plasma emission spectroscopy. Such an assay is suitable for analyzing minute amounts of atoms, and even when using such an assay, sputtering targets preferably retain the Co, Ca and Cr content below the detection limit.

The sputtering target preferably has a packing density of 65% to 96%.

The higher the packing density of the sputtering target, the higher the strength of the target, and the time for forming the layer tends to be shortened due to its high density element, and at the same time the compositional difference between the target and the formed layer tends to increase.

Although there may be cases where the composition of the target can approach the composition of the layer by reducing the density of the target, the reduced density target not only causes the problem of delayed layer formation rate but also the target itself breaks during layer formation. It causes a breakdown problem. The term filling density here refers to a value obtained as a density by comparing the weight of the target actually produced with the weight of the target calculated when the weight of the target is filled to 100% with the desired material.

1 illustrates the use of a Bi ₁₀ Fe ₅ O _X target having a diameter of 76.2 mm and a thickness of 4 mm, the packing density of the target, the state of the target during or after the layer formation, and the layer being formed. The recording characteristics of the recording medium are shown. When the filling density is 50% or less, the target cannot be formed as a sputtering target even after the firing treatment. If the packing density is 61%, the target can be formed, but is easily destroyed immediately after applying 100 W of electrical force. When the filling density is 98%, the density becomes very high and the target becomes very hard and is easily broken. When the packing density is 65% to 96%, the target can be formed without any problem, and exhibits very good recording characteristics. Even in the case where the packing densities are 61% and 98%, very good recording characteristics are obtained by forming the layer under conditions that ensure no splitting of the target during layer formation. As can be seen from the above results, the filling density of the sputtering target is preferably 65% to 96%.

Fill density (%) The state of the target Recording characteristics 50% less than Sputtering target formation is impossible. - 61% When the high frequency power 100W is applied, the sputtering target is easily damaged, and is damaged at 50W. Very good 65% Sputtering target can be formed when high frequency power is applied 100W Very good 83% Sputtering target can be formed when high frequency power is applied 100W Very good 96% Sputtering target can be formed when high frequency power is applied 100W Very good 98% Sputtering ticket easily damaged when applying high frequency power 100W, damaged at 50W Very good

The sputtering target preferably has an atomic ratio of Bi to Fe which satisfies the relationship Bi / Fe ≧ 0.8. An optical recording medium having a BiFeO layer formed using a target exhibits very good characteristics and is particularly suitable for high density recording.

Theoretically, the upper limit of the ratio Bi / Fe is substantially about 15 although it is 25 based on the assumption of using a sputtering target containing Bi ₂₅ FeO ₄₀ as the main component. The sputtering target production method of the present invention relates to a method of producing the BiFeO target of the present invention by calcining powders of Bi ₂ O ₃ and Fe ₂ O ₃ . Bi ₂ O ₃ naturally exists as an oxide of Bi and Fe ₂ O ₃ exists as an oxide of Fe. These powders are ground in a dry or wet process and then classified into uniform size particle diameters. Next, the powder is mixed, heated, pressed to form a shape, and then calcined at a maintained temperature of 750 ° C. in the air. The strength of the sputtering target can be improved by repeating the process of regrinding the calcined target, heating and pressing to form a shape. The sputtering target can be obtained by bonding the calcined target as described above with a metal bond or a resin bond to a backing plate made from oxygen-free copper.

The present invention also provides an optical recording medium comprising a BiFeO layer formed using the sputtering target of the present invention. The optical recording medium forms a necessary layer on a resin substrate containing polycarbonate or the like. Grooves and pits can be formed on the resin substrate to control tracking and the like. The BiFeO layer is formed by applying a high frequency while introducing argon gas under vacuum. In addition, the metal layer and the protective layer can be disposed as the reflective layer in order to improve the characteristics.

The above paragraphs focus on the optical recording medium to describe the sputtering target of the present invention, and the application of the sputtering target of the present invention is not limited to the optical recording medium and can be used for other purposes as long as the performance of the layer meets the requirements. It explains. For example, a sputtering target can be used to form a thin layer made from a magnetic material, to form a thin layer for manufacturing an optical control insulator, and to form a thin layer for an optical switch.

In the case of an approximate manufacturing line for forming a sputtering target, it is possible to take and use a procedure comprising a step of weighing raw materials, mixing by a ball mill in a dry process, hot-pressing step, forming step in form, and bonding step. It is possible. It is also possible to take procedures which include washing the raw materials, mixing with a ball mill in a dry process, spray-drying step, hot-pressing step, forming step in form, and bonding step.

According to the present invention, it is possible to provide a WORM type recording medium capable of recording small recording marks at a higher degree of modulated amplitude with stability. Because of the use of additional elements not found so far, it is possible to provide a WORM type optical recording medium having very good recording and reproducing characteristics, and reliability.

In addition, the present invention can provide a sputtering target suitable for arbitrarily forming a layer having a stable composition and structure, and a manufacturing method thereof, and can also provide a high density optical recording medium using the target.

The present invention is then specifically described with respect to an optical recording medium using the material of the present invention represented by BiO _x (0 <x <1.5) and a WORM type optical recording medium containing Bi, M and oxygen as constituent elements of the recording layer. Although described in detail with reference to the embodiments, the invention is not limited to the disclosed embodiments.

Example  A-1

A layer having a composition of BiO _x (0 <x <1.5) and a thickness of 10 nm was formed by sputtering on a polycarbonate-substrate having a guide groove having a groove depth of 21 nm. The WORM type optical recording medium was calculated. This layer was formed at a high frequency power of 100 W and an Ar gas flow rate of 40 sccm using a sputtering target having a composition Bi ₂ O ₃ and a diameter of 76.2 mm.

Recording was performed on the optical recording medium under the following conditions using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a lens numerical aperture of 0.65 at a wavelength of 405 nm.

Modulation method: 1-7 modulation

-Writing linear density: shortest mark length (2T) = 0.231 mu m

Record linear velocity: 6.0 m / s

Waveform equalization: normal equalizer

As a result, a very good jitter value of 99% was obtained in the recording section continuously at a recording power of 5.2 mW, and a very good binary recording characteristic with a modulated amplitude of 55% was realized.

Example  A-2

The WORM type recording medium of the present invention was produced by sputtering a layer containing Fe and O and having a thickness of 10 nm on a polycarbonate having a guide groove having a depth of 21 nm. This layer was formed at a high frequency power of 100 W and an Ar gas flow rate of 40 sccm using a sputtering target having a composition Bi ₁₀ Fe ₅ O _x and a diameter of 76.2 mm. The target was prepared by calcining a mixture of Bi ₂ O ₃ and Fe ₂ O ₃ (a ratio of 2: 1). Theoretically, the target had Bi ₁₀ Fe ₅ O _22.5 . However, since the amount of oxygen cannot be measured precisely because of the oxygen leaked in the firing process, oxygen is expressed as O _x .

The optical recording medium was performed on the optical recording medium under the following conditions using an optical disk evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a lens numerical aperture of 0.65 at a wavelength of 405 nm.

Modulation method: 1-7 modulation

-Writing linear density: shortest mark length (2T) = 0.231 mu m

Record linear velocity: 6.0 m / s

Waveform Equalization: Normal Equalizer

As a result, a very good jitter value of 8.9% was obtained in the recording section continuously at a recording power of 5.8 mW, and a very good binary recording characteristic with a modulated amplitude of 52% was realized.

Example  A-3

Reflective EELS measurements were performed using a WORM type optical recording medium prepared and used for recording in Example A-1. For this measurement, a scanning Auger electron spectrometer PHI4300 (manufactured by Perkin-Elmer) was modified. EELS stands for Electron Energy Loss Spectroscopy and is a spectroscopic system in which electrons are irradiated onto a sample to determine the scattered electron energy distribution by interaction with the outer surface of the sample. When the primary electrons of a particular energy excite the inner shell of an atom to be measured, electrons of a particular energy are discharged, resulting in scattering of the primary electrons. During this process, some energy is lost by interaction with adjacent atoms. Therefore, by examining the manner in which the electrons are scattered, information such as the radial distribution function of neighboring atoms can be obtained.

The radius distribution function in the vicinity of the oxygen atom was measured based on the EELS spectrum obtained by EELS measurement. The longitude distribution function indicates the probability of electron presence around the atom and allows the calculation and inference of the valence and structure of the atom. Among the analysis software packages based on the photoelectron multiple scattering theory, in particular FEFF software (Washington University) is widely used. The valence and structure of the atoms can be estimated by using such analysis software and by referring to the calculated values for the actually measured values.

Figure 1 illustrates the value of the Tokyo distribution function measured by the method as described above.

FIG. 2 illustrates the Tokyo distribution function calculated using FEFF. This diagram is in the case of Bi-3valent which can be taken by Bi; In case Bi-3 is but takes the structure of β-Bi ₂ O ₃ ; And a longitude distribution function, respectively, in the case of BiO ₂ of Bi-4.

When comparing these longitude distribution functions, the peaks 1011 and 1012 around 6 Hz in the recording were clearly distinguished. When comparing two diagrams, the peaks 1011 and 1012 coincide with each other. This proves that BiO ₂ , that is, tetravalent BiO ₂ , exists in the recording section.

WORM type optical recording media having such recording marks enable recording with higher modulated amplitude and high density recording.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples with respect to the WORM type optical recording medium using the element L used in the present invention as an additional element, but the present invention is not limited to the disclosed embodiments.

( Example  B-1 to B-18)

WORM type optical recording media include polyolefin-substrate (manufactured by ZEONOR, NIPPON ZEON CO., LTD.); A recording layer containing bismuth and Bi oxide as a main constituent of the elements constituting the recording layer; Insulating layer; And a structure in which the reflective layer was formed into a layered structure, and produced by using the following materials for each of these layers.

The sputtering target was prepared using a raw material in which Bi ₂ O ₃ and oxides of the elements shown in Table 2 were mixed in a ratio of 2: 1 to 5: 1, and the recording layer was then such that the sputtering target had a thickness of about 7 nm. It was formed using.

Table 2 shows each fouling electronegativity value of each element L added to each resulting recording layer, and the standard shape enthalpy ΔH _f ° of the oxide of element L, but these values are based on the definition of the present invention. do. If the fouling electronegativity value is greater than or equal to 1.80, the standard formation enthalpy ΔH _f ° of the oxide of element L is not important, so some elements of Table 2 do not have their ΔH _f ° values.

As described above, in the present invention, the fouling electronegativity value and the standard formation enthalpy value of the oxide of the element L were obtained by each valence fixed to each element group. In addition, the individual valences of the individual atoms based on the definition of the present invention are also listed in Table 2.

In Table 2, the term type A represents an element L belonging to definition (I) of the present invention, and the term type B represents an element L belonging to definition (II) of the present invention.

In the case of the insulating layer, ZnS-SiO ₂ was formed to have a thickness of 15 nm using a ratio of 85:15 (mol%).

In the case of the reflective layer, Ag alloy was formed to have a thickness of 100 nm.

The track pitch of the polyolefin substrate was 0.437 mu m and the thickness was 0.6 mm.

Recording was performed on the optical recording medium under the following conditions using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a lens numerical aperture of 0.65 at a wavelength of 405 nm.

As a result, extremely excellent recording and reproducing characteristics, i.e., jitter values, shown in Table 2 were realized.

<Recording and playback conditions>

Modulation method: 1-7 modulation

-Writing linear density: shortest mark length (2T) = 0.204 mu m

Record linear velocity: 6.6 m / s

Waveform Equalization: Limit Equalizer

Renewable power: 0.5 mW

Next, such a WORM type optical recording medium was left under the conditions for 100 hours at a temperature of 80 ° C. and a relative humidity of 85% to measure the amount of change in the jitter value. The change in jitter value is calculated as follows:

(Jitter value after storage test)-(initial jitter value)

Table 2 shows the results.

As can be clearly seen from Table 2, the elements satisfying the definition (I) for the element L of the present invention have a very good jitter value and a small decrease in the jitter value during the storage test, respectively. Prove it.

In addition, the standard formation enthalpy “ΔH _f °” of the oxide also demonstrates that it can take any value as long as definition (I) is met.

In addition, the elements satisfying the definition (II) for the element L of the present invention are also shown to have a very good initial jitter value and a small decrease in the jitter value during the storage test.

In this embodiment, although the wavelength for recording and reproducing was set to 405 nm, recording was also very good with jitter values of 9% or less for the laser beam at wavelength 660 nm by adjusting the thickness of the insulating layer from 15 nm to 120 nm. Performed well. In this test, the track pitch of the substrate was 0.74 mu m, and the recording and reproducing conditions were based on the conditions of DVD + R. The amount of increased jitter value obtained in the same storage test as the above example provided results substantially similar to those shown in Table 2.

( Comparative example  B-1)

A WORM type optical recording medium was produced in the same manner as in Example B-1, except that the main component was bismuth, and instead of the recording layer containing Bi oxide, a recording layer formed by sputtering through the use of a metal bismuth target was used. . Next, the optical recording medium was evaluated.

As a result of analysis by X-ray photoelectron spectroscopy, no bismuth oxide was detected in the recording layer except at the interface between the substrate and the recording layer and at the interface between the recording layer and ZnS-SiO ₂ . Thus, this proved that the recording layer prepared in Comparative Example B-1 did not contain Bi oxide.

As a result of measuring the recording and reproducing characteristics, the initial jitter value exceeded 15%, and it was impossible to measure the jitter value after the storage test.

From the results, the importance of the recording layer containing not only bismuth but also Bi oxide as a main component was confirmed.

( Example  B-19)

On a polycarbonate substrate having a guide groove having a groove depth of 50 nm and a track pitch of 0.40 µm, a ZnS-SiO ₂ layer, that is, a lower coating layer having a thickness of 65 nm and a BiPdO layer, that is, a recording layer having a thickness of 15 nm Was arranged in a layered structure by sputtering in this order. The atomic number ratio of Bi to Pd, ie Bi: Pd, was approximately 3: 1.

Next, on the recording layer, an organic material layer, that is, an upper coating layer containing a pigment or dye represented by the following formula (1) was formed by spin-coating to have an average thickness of about 30 nm. On the organic material layer, after placing a reflective layer containing Ag and having a thickness of 150 nm by sputtering, the reflective layer prepared from an ultraviolet curable resin having a thickness of 5 탆 by spin coating is disposed on the reflective layer, thereby providing the WORM of the present invention. The type recording medium was calculated.

Pigments or dyes represented by Formula 1 are typically used in materials of conventional DVD ± R, each of which has little absorption at the blue laser wavelength.

Formula 1

Recording and playback were performed on the optical recording medium under recording and playback conditions according to HD and DVD-R, so that the optical disc evaluation system DDU-10 (PULSTEC INDUSTRIAL CO., LTD.) Had a numerical aperture of 0.65 at a wavelength of 405 nm. Product) to evaluate the medium.

As a measurement result of the optical recording medium, a very good value of PRSNR 22 was produced at a recording power of 5.8 mW, and very good recording and reproduction characteristics were realized.

( Example  B-20)

On a polycarbonate substrate having a groove groove having a groove depth of 20 nm and a track pitch of 0.32 μm, a reflective layer made from Ag having a thickness of 100 nm, a ZnS-SiO ₂ layer, that is, a top coating layer having a thickness of 16 nm, and BiPdO layers or recording layers having a thickness of 7 nm were arranged in a layered structure by sputtering in this order. The atomic number ratio of Bi to Pd, ie Bi: Pd, was approximately 3: 1.

Next, a cover layer made of a resin having a thickness of 0.1 mm was laminated on the recording layer to produce the WORM type recording medium of the present invention.

Recording and playback were performed on the optical recording medium under recording and playback conditions according to BD-R, using an optical disc evaluation system (product of PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.85 at a wavelength of 405 nm. The medium was evaluated.

As a measurement result of the optical recording medium, a very good jitter value of 6.0% was produced at a recording power of 7.0 mW, and very good recording and reproducing characteristics were realized.

( Example  B-21)

The WORM type optical recording medium of the present invention was produced in the same manner as in Example B-19, except that a BiBO layer was used for the recording layer. Next, the WORM type optical recording medium was evaluated. The atomic number ratio of Bi to B, ie Bi: B, was approximately 2: 1.

As a result of the measurement of the optical recording medium, a very good value of PRSNR 23 was produced at a recording power of 5.6 mW, which showed by way of example that a very good recording and reproducing characteristic could be realized by the optical recording medium.

( Example  B-22)

The WORM type optical recording medium of the present invention was produced in the same manner as in Example B-20, except that a BiBO layer was used for the recording layer. Next, the WORM type optical recording medium was evaluated. The atomic number ratio of Bi to B, ie Bi: B, was approximately 2: 1.

As a measurement result of the optical recording medium, a very good jitter value of 5.9% was produced at a recording power of 6.7 mW, and very good recording and reproduction characteristics were realized.

( Example B-23)

On a polycarbonate substrate having a groove groove having a groove depth of 50 nm and a track pitch of 0.32 μm, a reflective layer made of Ag having a thickness of 100 nm was formed by sputtering, and represented by an organic material layer, that is, represented by Chemical Formula 1 After the top coating layer containing the pigment or dye to be formed by spin coating to have an average thickness of about 30 nm, the BiBO layer, that is, the recording layer and the ZnS-SiO ₂ layer, i. It was arranged in a layered structure by sputtering in order. The atomic number ratio of Bi to B, ie Bi: B, was approximately 2: 1.

Next, on the recording layer, a cover layer made of a transparent resin having a thickness of 100 nm was laminated to yield a WORM type recording medium of the present invention.

Recording and reproduction were performed on the optical recording medium under recording and reproduction conditions according to BD-R, using an optical disc evaluation system (product of PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.85 at a wavelength of 405 nm. The medium was evaluated.

As a measurement result of the optical recording medium, a very good value of 6.5% was produced at a recording power of 4.8 mW, and very good recording and reproducing characteristics were realized.

 ( Example  B-24)

On a polycarbonate substrate having a guide groove having a groove depth of 40 nm and a track pitch of 0.74 µm, a BiBO layer, that is, a recording layer having a thickness of 15 nm and a ZnS-SiO ₂ layer, that is, a top coating layer having a thickness of 40 nm Was arranged in a layered structure by sputtering in this order. The atomic number ratio of Bi to B, ie Bi: B, was approximately 2: 1.

Next, the WORM type recording medium of the present invention was calculated by arranging a reflective layer made of Ag having a thickness of 100 nm and a protective layer made of an ultraviolet curable resin having a thickness of about 5 μm on the recording layer.

Recording and reproduction were performed on the optical recording medium under the recording and reproduction conditions according to DVD + R, and the optical disc evaluation system DDD-1000 (product of PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.65 at a wavelength of 660 nm. ) To evaluate the medium.

As a measurement result of the optical recording medium, a jitter value of 7.2% was generated at a recording power of 12.0 mW, and very good recording and reproduction characteristics were realized.

( Example  B-25)

The WORM type optical recording medium of the present invention was produced in the same manner as in Example B-24, except that Sb was added to the material of the recording layer. Next, the WORM type optical recording medium was evaluated. The atomic number ratio of Bi to Sb, ie Bi: Sb, was approximately 4: 1.

As a measurement result of the optical recording medium, a very good jitter value of 7.6% was produced at a recording power of 10.0 mW, and very good recording and reproduction characteristics were realized.

( Example  B-26)

On a polycarbonate substrate having a guide groove having a groove depth of 20 nm and a track pitch of 0.437 μm, a BiPdO layer, that is, a recording layer having a thickness of 5 nm and a ZnS-SiO ₂ layer, that is, a top coating layer having a thickness of 15 nm Was arranged in a layered structure by sputtering in this order. The WORM type of the present invention is formed by sputtering a reflective layer having a thickness of 100 nm and comprising Ag on a ZnS-SiO ₂ layer and further disposing a protective layer containing an ultraviolet curable resin having a thickness of about 5 μm by spin coating. The recording medium was calculated.

In Example B-26, the jitter value was evaluated by changing the ratio of the total amount of Pd to the number of bismuth atoms in the recording layer. Recording and reproduction conditions were the same as those described in Examples B-1 to B-18.

As shown in Fig. 3, the measurement of the optical recording medium showed by way of example that excellent jitter values can be obtained in the range where the atomic number ratio of the total amount of Pd to bismuth is 1.25 or more. The value 1.25 is indicated by the dotted line in FIG. 3. Further, as illustrated, the elements defined in the present invention except for Pd each showed a similar tendency as above.

Next, the present invention will be described in detail with reference to Examples and Comparative Examples with respect to the sputtering target, but the present invention is not limited to the disclosed examples.

Example  C-1

The Bi ₂ O ₃ powder and the Fe ₂ O ₃ powder were mixed so that the atomic ratio of Bi: Fe was 6: 5, and then mixed in a ball mill for 1 hour by a dry process. The mixed powder was pressed and molded at 100 MPa to 200 MPa, and then calcined at 750 ° C. for 5 hours in air to yield a sputtering target. The target had a diameter of 152.4 φ and a thickness of 4 mm. The target was bound to a backing plate made from oxygen free copper by metal bonding to yield sputtering target 1. The sputtering target had a fill density of 75%.

The X-ray diffraction pattern of the sputtering target was measured. Measurement conditions are as described in Table 3 below. 4 shows the result of the measurement.

In order to confirm the diffraction peak position obtained by the measurement, the diffraction peak position was examined and confirmed as that of a known substance. At the top of FIG. 4, the diagram marked with (a) shows the diffraction pattern of target 1. FIG. Diagrams marked with (b) show the diffraction peak positions of BiFeO ₃ based on known data. In X-ray diffraction analysis, data relating to diffraction lines and data on material intensity were compiled into a database derived from a source of data relating to X-ray diffraction measured in the past. Therefore, the measured material can be confirmed by comparing the measured diffraction data with the previous data. After comparing the BiFeO ₃ data marked with (b) with the measurement data marked with (a), as a result of irradiation, the diffraction peak with mark ^"o" was confirmed to be the diffraction peak of BiFeO ₃ . Similarly, the diagrams marked (c) were known data of Fe ₂ O ₃ and the diagrams marked (d) were known data of Bi ₂ O ₃ . Similarly, diffraction peaks of Bi ₂ O ₃ and Fe ₂ O ₃ were confirmed. The largest peak corresponds to BiFe ₂ O ₃ , demonstrating that the compound is a major component. In addition, sputtering targets were subjected to ICP analysis, ie inductively coupled plasma emission spectroscopy. A portion of the sputtering target was dissolved in aqua regia to sample and then diluted with ultrapure water for analysis. About this solution, the elements of Co, Ca, and Cr were analyzed, respectively. As a result of analysis, the content of each element was below the detection limit.

Light source Cu wavelength 1.54056 Å Monochromator use Tube current 100 mA X-ray tube voltage 40 kV Data range 5-60 ° Scan axis 2θ / θ Sampling interval 0.020 ° Scanning speed 8.000 ° / min Diverging slit 1.00 ° Scattering slit 1.00 ° Photon detection slit 0.15 mm

Example C-2

An optical recording medium was produced using the sputtering target prepared in Example C-1.

 On a polycarbonate substrate having a groove groove having a groove depth of 50 nm and a track pitch of 0.44 μm, a BiFeO layer having a thickness of 15 nm was formed by sputtering, and a pigment or dye represented by the following formula (1) was formed on the BiFeO layer: The containing organic material layer was formed by spin-coating to have an average thickness of about 30 nm, and a reflective layer made of Ag having a thickness of 150 nm was disposed on the organic material layer by sputtering, and then on the reflective layer, a thickness of about 5 μm was further applied. The WORM type recording medium of the present invention was calculated by disposing the protective layer made from the ultraviolet curable resin having by spin coating. Typically, the pigment or dye represented by the formula (1) was used as a material of the conventional DVD + R, each of which absorbed little at the blue laser wavelength.

Formula 1

Binary recording was performed on the optical recording medium using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.65 at a wavelength of 405 nm under the following conditions.

<Recording condition>

Modulation method: 8-16 modulation

Recording linear density: 1T = 0.0917 μm

                Shortest mark length (3T) = 0.275 μm

Record linear velocity: 6.0 m / s

Waveform Equalization: Normal Equalizer

As shown in Fig. 5, as a result, a very good jitter value of 10.2% was obtained at a recording power of 6.1 mW, and a very good recording characteristic was realized.

Example C-3

Sputtering target 2 was prepared in the same manner as in Example C-1, except that Bi ₂ O ₃ powder and Fe ₂ O ₃ powder were mixed so that an atomic ratio of Bi to Fe was 35: 5. This sputtering target had a fill density of 67%.

The X-ray diffraction pattern of the sputtering target was measured. The measurement conditions are shown in Table 3. 6 shows the measurement results.

In order to confirm the diffraction peak position obtained in the measurement, the diffraction peak position was referred to that of a known material. As shown in FIG. 6, the peak of most, but not all, diffraction patterns was consistent with that of Bi ₂₅ FeO ₄₀ . Of course, the highest peak was that of Bi ₂₅ FeO ₄₀ , demonstrating that the compound is the main constituent.

Example C-4

An optical recording medium was produced using the sputtering target prepared in Example C-3.

On the polycarbonate substrate having a groove groove having a groove depth of 50 nm and a track pitch of 0.44 μm, a ZnS-SiO ₂ layer having a thickness of 50 nm and a BiFeO layer having a thickness of 15 nm were layered by sputtering in this order. Disposed in a structure, and formed on the BiFeO layer by spin-coating an organic material layer containing the pigment or dye represented by Formula 1 to have an average thickness of about 30 nm, and on the organic material layer having a thickness of 150 nm and comprising Ag After arranging the reflective layer by sputtering, a WORM-type recording medium of the present invention was calculated by further arranging a protective layer made of an ultraviolet curable resin having a thickness of about 5 μm by spin coating on the reflective layer. Typically, the pigment or dye represented by the formula (1) was used as a material of the conventional DVD + R, each of which absorbed little at the blue laser wavelength.

Binary recording was performed on an optical recording medium using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.65 at a wavelength of 405 nm under the following conditions.

<Recording condition>

Modulation method: 8-16 modulation

Recording linear density: 1T = 0.0917 μm

                Shortest mark length (3T) = 0.275 μm

Record linear velocity: 6.0 m / s

Waveform Equalization: Normal Equalizer

As a result, as a result, a very good jitter value of 8.6% was obtained at a recording power of 7.0 mW, and a very good recording characteristic was realized.

Even if the recording power exceeded the optimum recording power, WORM type optical recording media having a high modulated amplitude and a wide recording power boundary became possible without a very large change in the reproduction signal level or the RF level of the recording unit.

Example C-5

Sputtering target 3 was obtained in a similar manner to Example C-1, except that Bi ₂ O ₃ powder and Fe ₂ O ₃ powder were mixed so that an atomic ratio of Bi to Fe was 1: 5. This target had a fill density of 67%.

The X-ray diffraction pattern of the sputtering target was measured. The measurement conditions are shown in Table 3. 8 shows the result of the measurement.

In order to confirm the diffraction peak position obtained by a measurement, the diffraction peak position was investigated and confirmed about the thing of a well-known substance. As a result, although the sputtering target had diffraction peaks corresponding to those of Bi ₂ Fe ₄ O ₉ , Bi ₂ O ₃ and Fe ₂ O ₃ , it was found that the other diffraction peaks of the sputtering target did not coincide with that of the known material. lost. The largest peak was the peak corresponding to Fe ₂ O ₃ , demonstrating that the compound is the main component.

Example C-6

An optical recording medium was produced using the sputtering target prepared in Example C-5.

On the polycarbonate substrate having a groove groove having a groove depth of 50 nm and a track pitch of 0.44 μm, a ZnS-SiO ₂ layer having a thickness of 50 nm and a BiFeO layer having a thickness of 10 nm were layered by sputtering in this order. Disposed in a structure, an organic material layer containing the pigment or dye represented by the formula (1) on the BiFeO layer was formed by spigot coating to have an average thickness of about 30 nm, and a reflective layer made from Ag having a thickness of 150 nm on the organic material layer After sputtering, the WORM type recording medium of the present invention was calculated by further disposing a protective layer having a thickness of about 5 μm and containing an ultraviolet curable resin by spin coating on the reflective layer. Typically, the pigment or dye represented by the formula (1) was used as a material of the conventional DVD + R, each of which absorbed little at the blue laser wavelength.

Binary recording was performed on the optical recording medium using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.65 at a wavelength of 405 nm under the following conditions.

<Recording condition>

Modulation method: 8-16 modulation

Recording linear density: 1T = 0.0917 μm

                Shortest mark length (3T) = 0.275 μm

Record linear velocity: 6.0 m / s

Waveform Equalization: Normal Equalizer

The recordings resulted in a jitter value of 22.6% that was reduced at 8.1 mW of recording power.

In addition, although the thickness of the BiFeO layer was changed to 15 nm and 20 nm, respectively, the resulting jitter values became even worse and measurement was impossible.

Example C-7

Sputtering target 4 was obtained in a similar manner to Example C-1, except that Bi ₂ O ₃ powder and Fe ₂ O ₃ powder were mixed so that an atomic ratio of Bi to Fe was 4: 5. Sputtering Target 4 had a fill density of 77%.

The X-ray diffraction pattern of the sputtering target was measured. The measurement conditions are shown in Table 3. 9 shows the result of the measurement.

The diffraction pattern obtained by the measurement is shown to (a) in FIG. The diffraction peak positions of the sputtering targets were referred to those of known materials of (b) BiFeO ₃ and (c) Bi ₂ Fe ₄ O ₉ . The results showed that the sputtering target only had diffraction peaks corresponding to those of BiFeO ₃ and Bi ₂ Fe ₄ O ₉ . The largest peak was corresponding to BiFeO ₃ , demonstrating that the compound is a major component.

Example C-8

The optical recording medium was produced using the sputtering target prepared in Example C-7.

On the polycarbonate substrate having a groove groove having a groove depth of 50 nm and a track pitch of 0.44 μm, a ZnS-SiO ₂ layer having a thickness of 50 nm and a BiFeO layer having a thickness of 10 nm were layered by sputtering in this order. Placed in a structure, an organic material layer containing a pigment or dye represented by Formula 1 on the BiFeO layer was formed by spin coating to have an average thickness of about 30 nm, and a reflective layer made from Ag having a thickness of 150 nm on the organic material layer. After the sputtering was carried out, the WORM type recording medium of the present invention was calculated by further disposing a protective layer made of an ultraviolet curable resin having a thickness of about 5 m on the reflective layer by spin coating. Typically, pigments or dyes represented by Formula 1 were used as materials of conventional DVD ± R, each of which absorbs little at the blue laser wavelength.

Binary recording was performed on the optical recording medium using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.65 at a wavelength of 405 nm under the following conditions. The performance of high density recording was examined by setting the shortest mark length to 0.205 mu m.

<Recording condition>

Modulation method: 1-7 modulation

-Writing linear density: shortest mark length (2T) = 0.205 mu m

Record linear velocity: 6.0 m / s

Waveform Equalization: Normal Equalizer

10 shows the results.

Example C-9

The optical recording medium was prepared in the same manner as in Example C-8 using the sputtering target prepared in the same manner as in Example C-7, except that the sputtering target was prepared by changing the atomic ratio of Bi to Fe. The optical recording medium was measured under the same conditions as in the examples. 10 shows the measurement results. As shown in FIG. 10, a sputtering target having an atomic ratio of Bi / Fe ≧ 0.8, that is, a sputtering target having an atomic ratio of Bi / (Bi + Fe) ≧ 4/9 in FIG. 10. The optical recording medium obtained was proved to be about 14% jitter value, demonstrating that very good jitter values can be obtained even in high density recordings. The jitter value is substantially improved, even when using an optical recording medium obtained using a sputtering target having an atomic ratio represented by Bi (Bi + Fe) ≥ 3/8, which indicates that the optical recording medium is effective. Proved.

Example C-10

Sputtering target 5 was prepared in a similar manner to Example C-1, except that Bi ₂ O ₃ powder and Fe ₂ O ₃ powder were mixed so that an atomic ratio of Bi to Fe was 10: 5. This target had a fill density of 85%.

The X-ray diffraction pattern of the sputtering target was measured. The measurement conditions are shown in Table 3. 11 shows the measurement results.

In order to confirm the diffraction peak position of the diffraction pattern (a) obtained in the measurement, the diffraction peak position referred to those of known materials (b) to (e). As a result, although diffraction peaks corresponding to those of Bi ₂₅ FeO ₄₀ , BiFeO ₃ , Bi ₂ O ₃ and Fe ₂ O ₃ were present, the other diffraction peaks of the sputtering target did not coincide with those of the other materials. The largest peak was corresponding to Bi ₂₅ FeO ₄₀ , demonstrating that the compound is a major component.

Sputtering targets were subjected to ICP analysis, ie inductively coupled plasma atomic emission spectroscopy. A portion of the sputtering target was dissolved in aqua regia to sample and then diluted with ultrapure water for analysis. In the case of the solution, the elements of Co, Ca and Cr were analyzed respectively. As a result of analysis, the content of each element was below the detection limit.

In addition, a sputtering target 6 in which 0.003 mass% Al and 0.001 mass% Co was detected as an impurity was also prepared in the same manner as above.

Example C-11

The optical recording medium was produced using the sputtering targets 5 and 6 produced in Example C-10, respectively.

On the polycarbonate substrate having a groove groove having a groove depth of 50 nm and a track pitch of 0.44 μm, a ZnS-SiO ₂ layer having a thickness of 50 nm and a BiFeO layer having a thickness of 15 nm were layered by sputtering in this order. Placed in a structure, an organic material layer containing a pigment or dye represented by Formula 1 on the BiFeO layer was formed by spin coating to have an average thickness of about 30 nm, and a reflective layer made from Ag having a thickness of 150 nm on the organic material layer. After sputtering, the WORM-type recording medium of the present invention was produced by further spin-coating a protective layer made from an ultraviolet curable resin having a thickness of about 5 m on the reflective layer. Typically, pigments or dyes represented by Formula 1 were used as materials of conventional DVD ± R, each of which absorbs little at the blue laser wavelength.

Binary recording was performed on the optical recording medium using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.65 at a wavelength of 405 nm under the following conditions.

<Recording condition>

Modulation method: 8-16 modulation

Recording linear density: 1T = 0.0917 μm

               Shortest mark length (3T) = 0.275 μm

Record linear velocity: 6.0 m / s

Waveform Equalization: Normal Equalizer

As a result, very good jitter values were obtained. Specifically, the optical recording medium using the target 5 had a jitter value of 8.4% at 5.0 mW of recording power, and the optical recording medium using the target 5 had a jitter value of 8.2% at 5.0 mW of the recording power. Very good recording characteristics have been realized.

Even if the recording power exceeded the optimum recording power, WORM type optical recording media having a high modulated amplitude and a wide recording power boundary became possible without a large change in the reproduction signal level or the RF level of the recording unit.

Example C-12

Sputtering target 7 was obtained in a similar manner to Example C-1, except that Bi ₂ O ₃ powder and Fe ₂ O ₃ powder were mixed so that an atomic ratio of Bi to Fe was 10: 5. This target had a fill density of 71%.

The X-ray diffraction pattern of the sputtering target was measured. The measurement conditions are shown in Table 3. 12 shows the result of the measurement.

In order to confirm the diffraction peak position obtained in the measurement, the diffraction peak position was referred to that of a known material. The diagram marked with (a) shows the diffraction pattern of target 7 and the diagram marked with (b) shows the diffraction pattern with known data of Bi ₃₆ Fe ₂ O ₅₇ . Diagrams marked with (c) represent known data of BiFeO ₃ , and diagrams marked with (d) represent known data of Fe ₂ O ₃ . The largest peak was corresponding to Bi ₃₆ Fe ₂ O ₅₇ , demonstrating that the compound is a major component.

Example C-13

The optical recording medium was produced using the sputtering targets 5 and 6 prepared in Example C-12, respectively.

On a polycarbonate substrate having a guide groove having a groove depth of 21 nm and a track pitch of 0.44 μm, a BiFeO layer having a thickness of 5 nm, a ZnS-SiO ₂ layer having a thickness of 14 nm and Ag having a thickness of 150 nm were formed. The prepared reflective layer was arranged in a layered structure by sputtering in this order. On the reflective layer, a WORM-type recording medium was produced by disposing a protective layer made from an ultraviolet curable resin having a thickness of about 5 mu m by spin coating.

Binary recording was performed on the optical recording medium using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.65 at a wavelength of 405 nm under the following conditions.

<Recording condition>

Modulation method: 8-16 modulation

Recording linear density: 1T = 0.0917 μm

               Shortest mark length (3T) = 0.275 μm

Record linear velocity: 6.0 m / s

Waveform Equalization: Normal Equalizer

As a result, with the WORM type optical recording medium, a very good jitter value 6.2% was obtained at a recording power of 10.1 mW, which enabled very good recording characteristics.

Example C-14

Sputtering target 8 was obtained in a similar manner to Example C-1, except that Bi ₂ O ₃ powder and Fe ₂ O ₃ powder were mixed so that an atomic ratio of Bi to Fe was 35: 5. This target had a fill density of 69%.

X-ray diffraction patterns of the sputtering targets showed that very weak peaks of Bi and Fe were observed, clearly indicating that the compounds corresponding to Bi ₂₅ FeO ₄₀ or the compounds corresponding to Bi ₃₆ Fe ₂ O ₅₇ were the main constituents. Showed.

Example C-15

The optical recording medium was produced using the sputtering targets 5 and 6 prepared in Example C-14, respectively.

On a polycarbonate substrate having a groove groove having a groove depth of 50 nm and a track pitch of 0.44 μm, a ZnS-SiO ₂ layer having a thickness of 20 nm and a BiFeO layer having a thickness of 13 nm were layered in this order by sputtering. Placed into structure. The BiFeO layer was formed at the same time by introducing oxygen into the layer at a flow rate of 2% relative to Ar. A ZnS-SiO ₂ layer having a thickness of 20 nm was formed on the BiFeO layer, an Al-alloy reflective layer having a thickness of 100 nm was formed by sputtering on the ZnS-SiO ₂ layer, and further, about 5 μm in thickness on the Al-alloy reflective layer. The WORM type optical recording medium was calculated by disposing a protective layer made from an ultraviolet curable resin having spin coating by spin coating.

Binary recording was performed on a WORM type optical recording medium using an optical disc evaluation system DDU-1000 (manufactured by PULSTEC INDUSTRIAL CO., LTD.) Having a numerical aperture of 0.65 at a wavelength of 405 nm under the following conditions.

<Recording condition>

Modulation method: 8-16 modulation

Recording linear density: 1T = 0.0917 μm

               Shortest mark length (3T) = 0.275 μm

Record linear velocity: 6.0 m / s

Waveform Equalization: Normal Equalizer

As a result, with the WORM type optical recording medium, a very good jitter value of 7.6% was obtained at a recording power of 9.0 mW, which enabled very good recording characteristics.

Even if the recording power exceeded the optimum recording power, it has become possible to realize a WORM type optical recording medium having a high modulated amplitude and a wide recording power boundary without a large change in the reproduction signal level or the RF level of the recording unit.

Example C-16

For the sputtering target of BiFe ₅ O _x , four targets were prepared in the same manner. X-ray diffraction patterns of these sputtering targets were measured. Table 4 below shows the 2θ values of diffraction peaks of the targets of these BiFe ₅ O _x detected as the measurement results. A target having such a peak at the 2θ angle shown in Table 4 can be presented as an example of the sputtering target of the present invention.

Claims (31)

A wite-onece-read-many optical recording medium comprising a substrate, a recording layer, and a reflective layer, The recording layer comprises a material represented by BiO _x (0 <x <1.5), and the recording mark on which the information is recorded comprises a crystal of Bi and / or a crystal of Bi oxide. The WORM type optical recording medium according to claim 1, wherein the recording mark comprises tetravalent Bi. A WORM type optical recording medium comprising a substrate, a recording layer, and a reflective layer, The recording layer contains Bi, O and M as constituent elements, and M is Mg, Al, Cr, Mn, Co, Fe, Cu, Zn, Li, Si, Ge, Zr, Ti, Hf, Sn, Mo, V , At least one element selected from the group consisting of Nb, Y and Ta, wherein the recording mark in which the information is recorded includes at least one crystal derived from crystals of at least one element contained in the recording layer and crystals of at least one element of oxide WORM type optical recording medium. 4. The WORM type optical recording medium according to claim 3, wherein the recording mark comprises tetravalent Bi. The WORM type optical recording medium according to claim 3, wherein the ratio of the total amount of elements M to the number of atoms of bismuth is 1.25 or less. 4. The WORM type optical recording medium according to claim 3, wherein the WORM type optical recording medium has a layered structure in which at least a recording layer, an upper coating layer and a reflective layer are disposed on the substrate in this order, and at least a reflective layer, an upper coating layer, a recording layer and a cover layer are substrates in this order. A WORM type optical recording medium having any one of a layered structure including a layered structure disposed on the layer. The WORM type optical recording medium according to claim 3, wherein the WORM type optical recording medium is produced using a sputtering target comprising at least one selected from BiFeO ₃ , Bi ₂₅ FeO _40, and Bi ₃₆ Fe ₂ O ₅₇ . A WORM type optical recording medium comprising a substrate, a recording layer, and a reflective layer, The recording layer contains Bi, O and L as constituent elements, the recording layer contains Bi oxide, L is B, P, Ga, As, Se, Tc, Pd, Ag, Sb, Te, W, Re, A WORM type optical recording medium representing at least one element selected from the group consisting of Os, Ir, Pt, Au, Hg, Tl, Po, At and Cd. The WORM type optical recording medium according to claim 8, wherein the element L represents at least one element selected from the group consisting of B, P, Ga, Se, Pd, Ag, Sb, Te, W, Pt, and Au. The WORM type optical recording medium according to claim 8, wherein the ratio of the total amount of elements L to the number of atoms of bismuth is 1.25 or less. 9. The WORM type optical recording medium according to claim 8, wherein the WORM type optical recording medium further includes a top coating layer, and has a layered structure in which the recording layer, the top coating layer, and the reflective layer are disposed on the substrate in this order. . 12. The WORM type optical recording medium according to claim 11, wherein the WORM type optical recording medium further includes a bottom coating layer and has a layered structure in which the bottom coating layer, the recording layer, the top coating layer, and the reflective layer are disposed on the substrate in this order. Type optical recording medium. 9. The WORM type optical recording medium further comprises a top coating layer and a cover layer, wherein the reflective layer, the top coating layer, the recording layer and the cover layer have a layered structure arranged on the substrate in this order. WORM type optical recording medium. The optical recording medium according to claim 13, further comprising a lower coating layer, wherein the reflective layer, the upper coating layer, the recording layer, the lower coating layer, and the cover layer have a layered structure disposed on the substrate in this order. WORM type optical recording medium. The WORM type optical recording medium of claim 8, further comprising at least one of a bottom coating layer and a top coating layer, wherein at least any one of the bottom coating layer and the top coating layer comprises ZnS and / or SiO ₂ . Type optical recording medium. The WORM type optical recording medium according to claim 8, wherein the WORM type optical recording medium further comprises at least one of a bottom coating layer and a top coating layer, and at least any one of the bottom coating layer and the top coating layer comprises an organic material. . The WORM type optical recording medium according to claim 8, wherein recording and reproducing are possible by a laser beam having a wavelength of 680 nm or less. delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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