JP2011094240A - Titanium oxide based thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film which has a high refractive index to a laser beam of short wavelength than a ZrS based thin film, has excellent thermal impact resistance, also has high stability to heat and can be deposited by a deposition process with high efficiency such as d.c. sputtering. <P>SOLUTION: The titanium oxide based thin film essentially consists of titanium oxide and comprises niobium oxide as an auxiliary component, whose refractive index to light of 400 nm wavelength is ≥2.5, and also has an amorphous structure. The titanium oxide based thin film is, e.g., used for an optical recording medium. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a titanium oxide thin film having titanium oxide as a main component and niobium oxide as a subcomponent and having a high refractive index with respect to short wavelength light.

  Conventionally, a thin film having a high refractive index with respect to light such as visible light and excellent stability against heat has been used in applications such as a laser condensing lens and an optical recording medium.

  For example, an optical recording medium having a phase change type recording layer that records a laser beam irradiation signal as a phase change of the recording layer is called a phase change type optical recording medium, and is called CD-RW, DVD-RAM, DVD + RW. It is used as an optical disc.

  As shown in a schematic diagram of a general phase change type optical recording medium in FIG. 4, the phase change type optical recording medium 20 has a first protective layer 12a, A phase change recording layer (hereinafter simply referred to as a recording layer) 13 made of Te alloy or Sb alloy 13 and a second protective layer 12b are laminated in this order. Finally, aluminum, gold, silver, or these as a main component When the laser beam is irradiated from the substrate 11 side, the laser beam is transmitted through the second protective layer 12b and irradiated to the recording layer 13, and the recording layer 13 is recorded. The laser light that has passed through the layer 13 passes through the first protective film 12a and is reflected by the reflective layer 14, and the reflected laser light is again the first protective film 12a, the recording layer 13, and the second protective layer. 12b and return to the irradiation side, At the time of recording, a laser beam modulated in accordance with the signal intensity is irradiated, and the recording layer 13 is phase-shifted by the thermal energy (for example, the alloy thin film of the recording layer 13 is changed). The signal information is recorded as this phase change, and at the time of reproduction, the laser beam is irradiated to reproduce the change in the reflection intensity of the laser beam accompanying the phase change in the recording layer 13. Was detected as a signal.

  The protective layers 12a and 12b used in the phase change type optical recording medium 20 are provided for the purpose of transmitting laser light and contacting the recording layer 13 to protect both surfaces. At the time of recording / erasing by laser light irradiation, heat of 400 ° C. to 700 ° C. is instantaneously applied and a large temperature change is caused. Therefore, a zinc sulfide thin film excellent in thermal shock resistance is used. It was.

However, when heat is repeatedly applied by laser light irradiation, the ZnS crystal in the zinc sulfide thin film undergoes grain growth and the properties of the thin film deteriorate. Therefore, in order to prevent this grain growth, the protective layers 12a and 12b are made of SiO. ₂ containing zinc sulfide thin film, for example, in molar ratio,
It has been proposed to use a zinc sulfide-based thin film having a composition of 80 mol% ZnS-20 mol% SiO ₂ (see Patent Document 1).

Further, in order to manufacture a phase change type optical recording medium having protective films 12a and 12b made of a zinc sulfide-based thin film, a substrate 11 and a ZnS-SiO ₂ -based sintered material are placed in an RF sputtering apparatus. A protective film 12a made of a zinc sulfide-based thin film containing SiO ₂ is deposited on the substrate 11 by arranging a sputtering target material made of a body and generating high-frequency plasma in a high vacuum and dilute Ar. After the recording layer 13 made of Te alloy or Sb alloy is formed on the protective layer 12a, the protective layer 1 made of a ZnS—SiO ₂ thin film is further formed on the recording layer 13.
After 2b was deposited by an RF sputtering apparatus, it was formed by depositing a reflective layer 14 and a resin layer 15 made of aluminum, gold, silver, an alloy mainly containing these, or the like.

JP 11-278936 A

  By the way, in recent years, in order to increase the density of the phase change optical recording medium, the rotation speed has been increased and the laser light has been shortened. Conventionally, laser light having a wavelength of 830 nm or 780 nm has been used. On the other hand, it has been proposed to use a laser beam having a wavelength of 400 nm. By shortening the wavelength of this laser beam, the rate of change of the recording layer 13 due to the phase change of the refractive index decreases (signal). The S / N ratio of the protective layer 12a, 12b is required to be increased.

However, in the case where the protective films 12a and 12b are formed of a zinc sulfide thin film, the refractive index (n) for 400 nm wavelength light has a relatively high refractive index of about 2.35. There is a disadvantage that the ZnS crystal in the thin film causes grain growth due to laser light irradiation and the characteristic of the thin film is deteriorated. On the other hand, the protective films 12a and 12b are formed of a zinc sulfide-based thin film containing SiO ₂ . The refractive index with respect to the laser beam is deteriorated as a whole due to the inclusion of SiO ₂ , and particularly the refractive index (n) with respect to the laser beam having a wavelength of 400 nm is further lower than 2.35, thereby increasing the recording density of the optical recording medium. There was a problem that it was not possible.

Therefore, in order to increase the refractive index (n) for laser light having a wavelength of 400 nm, it is conceivable to increase the thickness of the protective layers 12a and 12b made of a zinc sulfide-based thin film containing SiO _2. Since the thin film has a low thermal conductivity, the heat stored in the protective layers 12a and 12b due to the irradiation of the laser beam at the time of recording / erasing cannot be immediately dissipated, and the thermal expansion between the recording layer 13 and the substrate 11 occurs. There was a risk of peeling due to thermal stress generated with the difference. In addition, when the optical recording medium has a CD specification, the thickness of the base 11 made of a polymer can be maintained with a certain thickness of about 1.2 mm. Becomes as thin as 0.6 mm. In this case, there is a fear that the base 11 made of the polymer is deformed by thermal stress.

  Further, when the protective layers 12a and 12b made of a zinc sulfide-based thin film are heated to a temperature range of 400 ° C. to 700 ° C. by laser light irradiated at the time of recording / erasing, sulfur in the zinc sulfide-based thin film There has also been a problem that the reliability of the optical recording medium is remarkably impaired by reacting with the alloy and being corroded.

In addition, the ZnS—SiO ₂ sintered body as a sputtering target material used to form the protective layers 12a and 12b made of a zinc sulfide-based thin film has a high volume resistivity, and therefore, an RF sputtering method is used. However, the RF sputtering method has a disadvantage that the film forming speed is slow and the productivity of the optical recording medium cannot be increased.

  Therefore, the inventor of the present invention has a higher refractive index for short-wavelength light than a zinc sulfide thin film, excellent thermal shock resistance, high stability against heat, and efficient film formation such as DC sputtering. As a result of extensive research on thin films that can be formed by means, it was found that a titanium oxide-based thin film containing titanium oxide as a main component and niobium oxide as a subcomponent may be used, and the present invention was achieved. .

  That is, the titanium oxide-based thin film of the present invention contains titanium oxide as a main component and niobium oxide as a subcomponent, has a refractive index of 2.5 or more with respect to light having a wavelength of 400 nm, and has an amorphous structure. It is characterized by having.

The titanium oxide thin film of the present invention is preferably characterized in that the content of the niobium oxide is in the range of 2.5% by weight to 11% by weight in terms of Nb ₂ O ₅ .

In the titanium oxide thin film of the present invention, preferably, the content of niobium oxide is in the range of 5% by weight to 10% by weight in terms of Nb ₂ O ₅ and the refractive index with respect to light having a wavelength of 400 nm is greater than 2.8. It is characterized by that.

  The titanium oxide thin film of the present invention is preferably characterized in that the refractive index of the titanium oxide thin film with respect to light having a wavelength of 400 nm to 800 nm is 2.4 or more.

  The titanium oxide thin film of the present invention is preferably characterized in that the titanium oxide thin film forming the protective layer has a refractive index of 2.4 or more with respect to light having a wavelength of 400 nm to 1500 nm.

As described above, according to the present invention, since the titanium oxide thin film containing titanium oxide as a main component and niobium oxide as a subcomponent is used, the refractive index for wavelength light of 400 nm is 2.5 or more. In addition, since a higher refractive index than that of the zinc sulfide-based thin film can be obtained, and thus the thickness of the protective film can be reduced, heat dissipation can be improved.
In particular, a titanium oxide thin film containing niobium oxide in the range of 2.5% by weight to 11% by weight in terms of Nb ₂ O ₅ can obtain a high refractive index of 2.6 or more with respect to light having a wavelength of 400 nm. it can.

It is a schematic sectional drawing which shows the optical recording medium which used the titanium oxide type thin film which concerns on this invention as a protective layer of a phase change type recording layer. It is a graph which shows the relationship between content of niobium oxide, and the refractive index of a titanium oxide type thin film. (A) is a graph which shows the refractive index with respect to the 300 nm-1500 nm wavelength light of the titanium oxide type thin film whose content of niobium oxide is 2.5 weight%, (b) is content of niobium oxide being 5.0. It is a graph which shows the refractive index with respect to the wavelength light of 300 nm-1500 nm of the titanium oxide type thin film which is weight%. It is a schematic sectional drawing which shows the conventional optical recording medium.

  Hereinafter, embodiments of the present invention will be described.

  The titanium oxide-based thin film of the present invention contains titanium oxide as a main component and niobium oxide as a subcomponent, and has a refractive index of 2.5 or more for light having a wavelength of 400 nm.

That is, the present inventor conducted extensive research on a material having a refractive index with respect to short wavelength light higher than that of the zinc sulfide thin film, and found that titanium oxide has a refractive index comparable to that of zinc sulfide. It has been found that by containing niobium oxide as a main component and a subcomponent, the refractive index can be increased as compared with titanium oxide (TiO ₂ ) or zinc sulfide (ZnS) alone.

Then, it was repeated experiments about the content of niobium oxide, by containing in the range of 0.5 wt% to 14 wt% calculated as Nb ₂ O _5, the refractive index with respect to wavelength of 400 nm 2.5 or more and Preferably, the refractive index for light having a wavelength of 400 nm is 2.6 or more by containing the niobium oxide content in the range of 1 wt% to 13 wt% in terms of Nb ₂ O _5. More preferably, by containing the niobium oxide content in the range of 2.5% by weight to 11% by weight in terms of Nb ₂ O ₅ , the refractive index for light having a wavelength of 400 nm is 2.8 or more. Desirably, the refractive index with respect to light having a wavelength of 400 nm is set to 2.85 or more by containing the niobium oxide content in the range of 5 wt% to 10 wt% in terms of Nb ₂ O _5. Can .

  Therefore, if the titanium oxide thin film of the present invention is used, it can be suitably used for applications such as a laser condensing lens and an optical recording medium that require a high refractive index for short wavelength light.

  In addition, since this titanium oxide thin film has an amorphous structure and is excellent in heat stability, even if heat as high as 700 ° C. is applied, titanium oxide crystals are generated or grain growth occurs. In addition, since the titanium oxide thin film does not react with other materials, it can be used even in an environment where heat is applied. Moreover, since it has an amorphous structure, the internal stress remaining in the film during film formation is small, so there are few restrictions on compatibility with the substrate to be deposited, and it can be deposited on various substrates with relatively good adhesion. .

  By the way, in order to manufacture the titanium oxide-based thin film of the present invention, a vapor deposition method such as a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method, an electron beam deposition method, or the like is used. However, among these vapor deposition methods, a titanium oxide thin film can be formed relatively easily and inexpensively by using a sputtering method.

As a sputtering target material, a titanium oxide-based sintered body containing niobium oxide having a composition substantially equivalent to that of a titanium oxide-based thin film may be used. Specifically, titanium oxide is a main component and niobium oxide is used as a subcomponent. It is preferable to use a titanium oxide-based sintered body that contains Nb ₂ O _{5 in} a range of more than 0.5 wt% and not more than 15 wt%.

That is, when the content of niobium oxide is 0.5% by weight or less in terms of Nb ₂ O ₅ , the content of niobium oxide in the formed titanium oxide thin film is 0.5% by weight in terms of Nb ₂ O _5. This is because the bending rate with respect to light having a wavelength of 400 nm cannot be made 2.5 or more. Conversely, when the content of niobium oxide exceeds 15% by weight in terms of Nb ₂ O ₅ , the formed titanium oxide This is because the content of niobium oxide in the system thin film exceeds 14% by weight in terms of Nb ₂ O ₅ and the bending rate with respect to light having a wavelength of 400 nm cannot be 2.5 or more.

Titanium oxide, which is the main component, is an insulating material. By containing niobium oxide in a range of more than 0.5% by weight and 15% by weight or less in terms of Nb ₂ O ₅ , titanium oxide-based firing is achieved. The sheet resistance value of the bonded body can be set to 100Ω / □ or less, and not only the RF sputtering method but also the DC sputtering method having a high film formation rate can be used, so that the film formation time of the titanium oxide thin film is greatly increased. It can be shortened. The niobium oxide content of the titanium oxide-based sintered body is preferably 1% to 10% by weight in terms of Nb ₂ O ₅ , so that the sheet resistance value of the titanium oxide-based sintered body is reduced. It can be set to 30Ω / □ or less, and the film formation rate by the DC sputtering method can be further increased.

  Next, application examples using the titanium oxide thin film according to the present invention will be described.

  FIG. 2 is a schematic sectional view showing an optical recording medium using the titanium oxide thin film according to the present invention as a protective layer of the phase change recording layer.

  This phase change optical recording medium 10 contains titanium oxide as a main component and niobium oxide as a subcomponent on a disc-shaped substrate 1 made of a polymer or the like by a vapor deposition method including a DC sputtering method. After coating the first protective layer 2a made of a titanium oxide thin film having a refractive index of 2.5 or more with respect to laser light having a wavelength of 400 nm, a phase change made of Te alloy or Sb alloy is formed on the protective layer 2a. A laser having a wavelength of 400 nm, which covers the mold recording layer 3 and further contains titanium oxide as a main component and niobium oxide as a subcomponent on the recording layer 3 by a vapor phase film forming method including a DC sputtering method. A second protective layer 2b made of a titanium oxide-based thin film having a refractive index with respect to light of 2.5 or more is coated, and aluminum, gold, silver, or these as main components are formed on the protective layer 2b The laser beam irradiated from the substrate 1 side is transmitted to the recording layer 3 through the second protective layer 2b, and the recording layer 3 is irradiated to the recording layer 3. The transmitted laser light passes through the first protective film 2a and is reflected by the reflective layer 4, and the reflected laser light passes through the first protective film 2a, the recording layer 3, and the second protective layer 2b again. Then, it returns to the irradiation side and is extracted as an electrical signal. During recording, a laser beam modulated in accordance with the signal intensity is irradiated, and the recording layer 3 is phase-shifted by the thermal energy ( For example, the alloy thin film of the recording layer 3 is mutually changed into a crystalline phase and an amorphous phase), signal information is recorded as this phase change, and the phase change in the recording layer 3 is performed by irradiating a laser beam during reproduction. Of reflection intensity of laser light And it detects a signal.

  The optical recording medium 10 of the present invention has an amorphous structure in which the titanium oxide thin film forming the protective layers 2a and 2b contains titanium oxide as a main component and niobium oxide as a subcomponent and is stable against heat. Therefore, even when heated to 400 ° C. to 700 ° C. by laser light repeatedly irradiated at the time of recording / erasing, crystallization and grain growth of titanium oxide are prevented, and the S / N ratio accompanying crystallization and grain growth is reduced. Reduction can be prevented.

  Moreover, since the titanium oxide thin film of the present invention is chemically stable, it does not react with the Te alloy or Sb alloy used as the recording layer 3 even when heated to a high temperature by laser light, and the recording is performed. Corrosion of the layer 3 can be prevented.

  In addition, since the titanium oxide thin film has an amorphous structure, the internal stress remaining in the titanium oxide thin film is small, and the protective layers 2a and 2b can be prevented from being peeled off or damaged. When 10 is a DVD specification, the occurrence of warpage can be prevented and the reliability of the optical recording medium 10 can be improved.

In addition, since a titanium oxide thin film containing niobium oxide in a range of 2.5 wt% to 11 wt% in terms of Nb ₂ O ₅ is stable to heat, it is irradiated during erasing / recording of an optical recording medium. Even when heated to a high temperature of 400 ° C. to 700 ° C. by a laser beam generated, titanium oxide crystals are hardly generated and grain growth hardly occurs, and an amorphous structure can be stably maintained. It can be suitably used as a protective layer for protecting the recording layer of the recording medium.

  Furthermore, the titanium oxide thin film of the present invention is not limited to the conventional RF sputtering method as a method for obtaining the thin film, but includes a vacuum vapor deposition method, a plasma CVD method, a photo CVD method, an ion plating method, an electron beam vapor deposition method and the like. A film forming method can be used, and since the thin film has stable thermal characteristics and has a low electric resistance value compared to the zinc sulfide-based thin film, the titanium oxide-based sintered body Direct current sputtering can be used for forming a thin film, and by increasing the grain strength of electric power, the sputtering rate can be increased to increase the productivity of the thin film when formed as a protective layer of an optical recording medium.

  In addition, since the titanium oxide thin film of the present invention is chemically stable, it is possible to prevent corrosion of the recording layer in a phase change optical recording medium using a Te alloy or Sb alloy for the recording layer. The reliability of the recording medium can be increased.

  In addition, since the titanium oxide thin film of the present invention has a refractive index larger than that of a conventionally used zinc sulfide thin film, the thickness of the protective films 2a and 2b can be reduced to 10 nm to 500 nm. Thereby, the heat dissipation of the protective layers 2a and 2b can be improved, and thermal failure such as peeling of the protective layers 2a and 2b can be prevented.

Furthermore, in the conventional protective layer composed of a zinc sulfide-based thin film containing SiO ₂ , the DC sputtering method capable of increasing the film formation rate could not be applied. However, the titanium oxide-based thin film of the present invention is not subjected to the DC sputtering method. Since the optical recording medium 10 can be used, productivity of the optical recording medium 10 can be increased. Thus, according to the present invention, a highly reliable optical recording medium can be provided.

  As mentioned above, although embodiment of this invention was shown, this invention is not limited only to the said embodiment, It cannot be overemphasized that it can improve and change in the range which does not deviate from the summary of this invention.

(Example 1) Here, titanium oxide thin films having different niobium oxide contents were prepared, and experiments were conducted to measure the refractive index with respect to laser light having a wavelength of 400 nm.

  In this experiment, a sputtering target material was first manufactured to form a titanium oxide thin film.

Specifically, as a starting material, an average particle size of 1 with respect to a TiO ₂ powder having an average particle size of 2.0 μm.
. A slurry was obtained by adding 0 μm of Nb ₂ O ₅ powder in the range of 0.05 wt% to 15 wt%, and further adding water and an organic binder and mixing. Next, the obtained slurry is spray-dried at 200 ° C. to produce granulated powder. After the granulated powder is filled in a mold and formed into a disk-like body by press molding, a degreasing step is performed. After that, by sintering for about 3 hours at a temperature of 1400 ° C., a titanium oxide-based sintered body containing niobium oxide is manufactured, and a sputtering target material is manufactured by cutting to a diameter of 76 mm × thickness of 5 mm. did.

  And using the sputtering target material which consists of the obtained titanium oxide type sintered compact, the titanium oxide type thin film which varied the content of niobium oxide on the glass substrate by DC sputtering method was deposited with a thickness of 100 nm, The refractive index of the titanium oxide thin film with respect to laser light having a wavelength of 400 nm was measured with a spectroscopic ellipsometer. The conditions of the DC sputtering method were an input power of 1000 W and a mixed gas pressure of Ar and oxygen of 1 Pa.

As shown in FIG. 1, the refractive index of the titanium oxide thin film increases rapidly until the niobium oxide content exceeds 0.5 wt% in terms of Nb ₂ O _{5 and} reaches 2.5 wt%. From 2.5% by weight to 10% by weight, it increases relatively slowly, and when it exceeds 10% by weight, the refractive index decreases. When the content of niobium oxide is in the range of 0.5% to 14% by weight in terms of Nb ₂ O ₅ , the refractive index with respect to light having a wavelength of 400 nm can be 2.5 or more. When the content is in the range of 2.5% by weight to 11% by weight in terms of Nb ₂ O ₅ , the refractive index for light having a wavelength of 400 nm can be 2.8 or more, and the content of niobium oxide is Nb _2. It can be seen that the refractive index with respect to light having a wavelength of 400 nm can be 2.85 or more in the range of 5 to 10% by weight in terms of O ₅ .

Moreover, in order to see the refractive index with respect to light of other wavelengths, the titanium oxide thin film whose niobium oxide content is 2.5% by weight in terms of Nb ₂ O ₅ and the niobium oxide content in terms of Nb ₂ O ₅ The refractive index with respect to the laser beam which has a wavelength of 300 nm-15 nm was measured using the titanium oxide type thin film which is 5.0 weight%.

The refractive index of the titanium oxide thin film having a niobium oxide content of 2.5% by weight is shown in FIG. 2 (a). The refractive index of the titanium oxide thin film having a Nb ₂ O ₅ content of 5.0% by weight is shown in FIG. Are as shown in FIG.

  As a result, the same tendency is observed in any of the titanium oxide thin films, and the refractive index for laser light having a wavelength of 300 nm to 600 nm can be made 2.5 or more, and a laser having a wavelength of 600 nm to 1500 nm. The refractive index with respect to light did not decrease so much and had 2.4 or more.

  As a result, if a titanium oxide thin film having a niobium oxide content of 2.5% by weight or more is used, a high refractive index of 2.4 or more is obtained even for laser light having a wavelength of 800 nm or less. As a result, it can be suitably used as a protective layer for protecting a phase change recording layer made of Te alloy or Sb alloy, and can be used for laser light having a wide wavelength range. In addition to providing a medium, the protective layer can be thinned using a high refractive index, and thermal stability can be ensured. Therefore, a reliable optical recording medium without peeling of the protective layer is provided. Can be provided.

  (Example 2) Next, the titanium oxide thin film of Example 1 and the conventional zinc sulfide-based thin film containing silicon oxide were subjected to a DC sputtering method with a high film formation rate and an RF sputtering method with a low film formation rate. An experiment was conducted to examine the time required for film formation.

As a sputtering target material for forming a conventional zinc sulfide-based thin film containing silicon oxide, a ZnS (80 wt%)-SiO ₂ (20 wt%) sintered body was used.

  Further, the surface resistance value of the sputtering target material comprising the titanium oxide-based sintered body and the zinc sulfide-based sintered body used for forming the titanium oxide-based thin film of Example 1 and the conventional zinc sulfide-based thin film was investigated. The results measured by the needle method are as shown in Table 1.

Also, the RF sputtering method conditions include an input power of 800 W, a mixed gas pressure of 1 Pa for Ar and oxygen, and a film thickness of 100 nm is formed on a glass substrate. 1000 W, a mixed gas pressure of 1 Pa was selected from Ar and oxygen, and a film was formed on a glass substrate so as to have a film thickness of 100 nm.

  The results are as shown in Table 2.

  As a result, as can be seen from Table 2, according to the DC sputtering method, it is found that the sputtering rate is improved by about 40% as compared with the RF sputtering method. Thus, in terms of efficiency of thin film production, the conventional zinc sulfide-based thin film can be formed only by the RF sputtering method, and its sputter rate is small, but the titanium oxide-based thin film can increase the sputter rate. I understand.

  In addition, the conventional zinc sulfide-based thin film may change the optical characteristics of the thin film immediately after the start of use of the sputtering target in the sputtering method and when the target consumption in the latter half of the use is severe, but in the titanium oxide-based thin film, It has been confirmed that the optical characteristics do not change.

In addition, since a titanium oxide thin film containing niobium oxide in a range of 2.5 wt% to 11 wt% in terms of Nb ₂ O ₅ is stable to heat, it is irradiated during erasing / recording of an optical recording medium. Even when heated to a high temperature of 400 ° C. to 700 ° C. by a laser beam generated, titanium oxide crystals are hardly generated and grain growth hardly occurs, and an amorphous structure can be stably maintained. It can be suitably used as a protective layer for protecting the recording layer of the recording medium.

  Furthermore, the titanium oxide thin film of the present invention is not limited to the conventional RF sputtering method as a method for obtaining the thin film, but includes a vacuum vapor deposition method, a plasma CVD method, a photo CVD method, an ion plating method, an electron beam vapor deposition method and the like. A film forming method can be used, and since the thin film has stable thermal characteristics and has a low electric resistance value compared to the zinc sulfide-based thin film, the titanium oxide-based sintered body Direct current sputtering can be used for forming a thin film, and by increasing the grain strength of electric power, the sputtering rate can be increased to increase the productivity of the thin film when formed as a protective layer of an optical recording medium.

  In addition, since the titanium oxide thin film of the present invention is chemically stable, it is possible to prevent corrosion of the recording layer in a phase change optical recording medium using a Te alloy or Sb alloy for the recording layer. The reliability of the recording medium can be increased.

1: substrate 2a: first protective layer 2b: second protective layer 3: recording layer 4: reflective layer 5: resin layer 10: optical recording medium 11: substrate 12a: first protective layer 12b: second protection Layer 13: Recording layer 14: Reflective layer 15: Resin layer 20: Optical recording medium

Claims (5)

  A titanium oxide thin film comprising titanium oxide as a main component and niobium oxide as a subcomponent, having a refractive index of 2.5 or more with respect to light having a wavelength of 400 nm and an amorphous structure. 2. The titanium oxide thin film according to claim 1, wherein the content of niobium oxide is in the range of 2.5 wt% to 11 wt% in terms of Nb ₂ O ₅ . In the range content of 5 wt% to 10 wt% calculated as _Nb 2 _{O 5} of the above niobium oxide, according to claim 1 or 2 refractive index for wavelength light 400nm is equal to or greater than 2.8 Titanium oxide thin film.   The titanium oxide thin film according to any one of claims 1 to 3, wherein the titanium oxide thin film has a refractive index of 2.4 or more with respect to light having a wavelength of 400 nm to 800 nm.   The titanium oxide thin film according to claim 4, wherein the titanium oxide thin film forming the protective layer has a refractive index of 2.4 or more with respect to light having a wavelength of 400 nm to 1500 nm.

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