Metal-dielectric multilayer composite film capable of being used for optical storage and preparation method of metal-dielectric multilayer composite film

Abstract

The invention discloses a metal-dielectric multilayer composite film structure for optical storage, which is characterized by comprising two layers of composite films sequentially deposited on a substrate, and each layer of composite film is composed of a metal layer and a dielectric layer; the surface layer of the two layers of composite films is a high-absorption composite film, and the lower layer is a high-reflection composite film; and the uppermost layer of composite film can be stripped from the lower layer of composite film under the action of laser. The method is applied to the field of optical storage, lays a foundation for realizing a low-cost and high-performance optical storage technology, and has universality and application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical storage, and particularly relates to a metal-dielectric multilayer composite film for optical storage and a preparation method thereof. Background Art

[0002] As a high-density optical disc storage medium, Blu-ray Disc was first used for high-definition video storage and has gradually developed into a storage method for movies, games, archival data, etc. The data layer of Blu-ray Disc generally uses organic dyes or inorganic materials (such as metal alloys), and these materials determine the storage life of the optical disc and the ability to resist environmental factors. Dye materials are prone to degradation under long-term light exposure, temperature fluctuations or humidity changes, thus affecting the stability of data storage. Inorganic phase change materials will gradually return to the crystalline state or undergo structural deterioration at high temperatures, which limits the data storage ability in extreme environments. Although it can be maintained for decades at room temperature, the data retention stability will significantly decrease in high-temperature environments (such as above 80°C). Thermal effects may also cause physical stress accumulation such as material expansion and contraction, affecting the service life of the optical disc.

[0003] In order to improve the performance of Blu-ray Disc, some high-end materials (such as nanocomposites and holographic materials) have been considered to increase the data storage capacity and lifespan. However, the production cost of such materials is high and the process is complex, making it difficult to achieve large-scale commercialization. Therefore, finding a new type of nanostructure and material, which has better stability compared with traditional inorganic phase change materials and can be prepared on a large scale, is the key to achieving a breakthrough in Blu-ray Disc optical storage technology. Summary of the Invention

[0004] The present invention provides a laser processing optical storage technology based on a metal-dielectric multilayer composite film, which can overcome the dependence on phase change materials in traditional Blu-ray storage technology, and only uses metal film and dielectric film materials to realize the optical storage structure. Moreover, this structure is easy to process, high-temperature resistant, has stable optical properties and high optical contrast, effectively improving the performance while reducing the cost of Blu-ray storage.

[0005] The technical solution solved by the present invention is as follows:

[0006] A metal-dielectric multilayer composite film structure for optical storage, including two composite films sequentially deposited on a substrate, and each composite film is composed of a metal layer and a dielectric layer; the surface layer of the two composite films is a high-absorption composite film, and the lower layer is a high-reflection composite film; and the uppermost composite film can be peeled off from the lower composite film under the action of laser.

[0007] The composite film of the present invention produces a high reflection or high absorption (low reflectivity) effect on incident light of a specific wavelength based on the interference effect of light. By changing the number of layers of the composite film using the thermal stress of laser irradiation, the transition of the film from high reflection to high absorption can be achieved. Therefore, two types of optical storage units with high reflectivity or high absorption and areas close to the diffraction limit size can be obtained by laser processing, thereby realizing an optical storage structure with low cost and high optical contrast.

[0008] The specific principle is as follows: The laser pulse is focused on the surface of the bilayer composite film through an optical system. The metal layer in the second composite film has a large absorption coefficient, so it heats up rapidly and then peels off due to the thermal stress generated with the dielectric layer of the adjacent first composite film; the film structure in the area irradiated by the laser changes and undergoes a transition from high absorption rate to high reflectivity. The storage of information is achieved by using this regulation of the reflectivity of incident light from low to high. By controlling parameters such as the number of laser pulses, pulse time, and energy, the area and position of the optical storage unit can be precisely controlled, and different data can be stored accordingly. The reading operation is performed by irradiating the storage area with a low-power laser and detecting the change in the intensity of the reflected light. Since the reflectivities of different film structures are different, the device can read different optical reflection signals and thus extract data.

[0009] Wherein the single-layer composite film is composed of metal and dielectric, and the film system expression of the multi-layer composite film is: S / (MH)(ML), where S represents the substrate, M is the metal layer, and its thickness T M is between 30 - 80 nm, H and L are dielectric layers, and their physical thicknesses T H and T L respectively satisfy the following mathematical relationships:

[0010]

[0011] is the non-trivial phase shift generated when the incident light is reflected by the metal M, and the specific value is related to M. λ is the working wavelength for optical storage reading and writing using the laser. n1 and n2 are the refractive indices of the dielectric materials H and L respectively, and m is a positive integer greater than 0. MH is the first composite film, which has a high reflectivity for the working wavelength, and ML is the second composite film, which has a high absorption rate at the working wavelength.

[0012] Furthermore, the dielectric material is one or more of Al2O3, TiO2, Nb2O5, SiO2, Ta2O5, HfO2, ZrO2, or other metal oxides.

[0013] Furthermore, the metal material is one or more of Al, Ti, Nb, Si, Ta, Hf, Ni, Cr, etc.

[0014] Further, the substrate is silicon, quartz glass, tempered glass, plexiglass or calcium fluoride.

[0015] Further, the metal thin film and the dielectric thin film in the composite thin film are prepared by chemical vapor deposition or physical vapor deposition.

[0016] Further, the difference in reflectivity between the high-absorption composite thin film and the high-reflection composite thin film is greater than or equal to 40%.

[0017] Further, the thickness of the metal layer is 30 - 80 nm; the thickness of the dielectric layer is 50 - 150 nm.

[0018] Further, the material of the metal layer is Ti, the material of the dielectric layer is TiO2, the thickness of the metal layer is 30 nm, the thickness of the dielectric layer in the high-reflection composite thin film is 90 - 130 nm, and the thickness of the dielectric layer in the high-absorption composite thin film is 50 - 70 nm.

[0019] An optical storage disc adopts the metal-dielectric multi-layer composite thin film structure described in any one of the above technical solutions.

[0020] Further, the optical storage disc is a Blu-ray disc.

[0021] A preparation method for the metal-dielectric multi-layer composite thin film structure for optical storage described in any one of the above, comprising: preparing metal and dielectric thin films by physical vapor deposition or chemical vapor deposition.

[0022] The present invention can achieve optical storage based on laser rapid direct writing, and obtain an optical storage structure with high optical contrast and high stability. The present invention is applied to the field of optical storage, laying a foundation for realizing low-cost and high-performance optical storage technology, and has universality and application value.

[0023] Compared with the prior art, the present invention has the following technical effects:

[0024] (1) The present invention proposes a metal-dielectric multi-layer composite thin film applied to optical storage. After being irradiated by laser, this thin film structure can produce high reflection or high absorption effects on incident light of a specific wavelength (such as 405 nm blue light), thereby realizing optical storage with high optical contrast. Under laser processing, the composite thin film of the present invention changes the structure of the thin film by laser, and can achieve an optical contrast close to 1, greatly improving the accuracy of reading data in optical storage technology.

[0025] (2) Compared with the dependence on inorganic phase change materials in traditional Blu-ray storage technology, the present invention uses metal and dielectric thin film materials with a thickness of only on the order of hundreds of nanometers. Prepared by a simple thin film process, the material cost is extremely low, more environmentally friendly, and compared with inorganic phase change materials, the melting points of the metals and dielectric thin films used are higher and the hardness is stronger, and they have better physical, mechanical and chemical stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a metal-dielectric multilayer composite film that can be used for optical storage according to the present invention.

[0027] Figure 2 Reflectivity at different numbers of thin film layers.

[0028] Figure 3 Schematic diagram of changing the number of thin film layers by laser processing.

[0029] Figure 4 Actual laser processing results of a multilayer composite film prepared for 405 nm Blu-ray storage.

[0030] Figure 5 Measured reflectivity values of a multilayer composite film prepared for 405 nm Blu-ray storage. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The present invention will be further described in detail below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0032] The present invention provides a metal-dielectric multilayer composite film that can be used for optical storage, as Figure 1 shown, including a substrate 1, a high-reflection composite film 2, and a high-absorption composite film 3. The high-reflection composite film is composed of a metal layer M and a dielectric layer H, and by controlling the thickness of the two layers, a high-reflection effect for a specific wavelength can be achieved. The high-absorption composite film is composed of a metal layer M and a dielectric layer L, and by controlling its thickness, a high-absorption effect for a specific wavelength can be achieved.

[0033] The working wavelength of the high-reflection composite film and the high-absorption composite film described in the present invention is 405 nm, and they have the characteristics of high reflection and high absorption for the 405 nm wavelength respectively. Both the high-reflection composite film and the high-absorption composite film are the recording layers for optical storage. Under the irradiation of laser, the high-absorption composite film can be peeled off under the action of thermal stress to expose the high-reflection composite film, thereby realizing the transition of the working wavelength from high absorption to high reflectivity. High absorption corresponds to "0" in the stored data, and high reflection corresponds to "1" in the stored data. Therefore, by irradiating different regions of the multi-layer film with laser, a series of "pits" (data "1") and "non-pits" (data "0") regions can be obtained to complete the efficient storage of data. The multi-layer composite film structure is composed of alternating stacks of metal and dielectric materials, and the film system expression is:

[0034] S / MHML, where S represents the substrate, M is the metal layer, and its thickness T M is between 30 - 80 nm, H and L are dielectric layers. Among them, MH constitutes the high-reflection recording layer in optical storage, and ML constitutes the high-absorption recording layer in optical storage. The physical thicknesses T H and T L respectively satisfy the following mathematical relationships:

[0035]

[0036] is the non-trivial phase shift generated when the incident light is reflected by the metal M, and the specific value is related to M. λ is the working wavelength for optical storage reading and writing using laser, n1 and n2 are the refractive indices of the dielectric materials H and L respectively, and m is a positive integer greater than 0.

[0037] The substrate is silicon, quartz glass, tempered glass, plexiglass or calcium fluoride. The dielectric material is Al2O3, TiO2, Nb2O5, SiO2, Ta2O5, HfO2, ZrO2 or other metal oxides. The metal material is Al, Ti, Nb, Si, Ta, Hf, Ni, Cr, etc. The multi-layer dielectric film is prepared by chemical vapor deposition or physical vapor deposition.

[0038] In this embodiment, the substrate 1 is selected as silicon, the metal M is Ti, and the dielectric materials H and L are both TiO2. The refractive indices and absorption parameters of the metal and dielectric materials are obtained by inversion in actual coating experiments.

[0039] In the embodiment, the working wavelength is 405 nm, n1 and n2 are obtained by measuring the film, and m is selected as 1. Therefore, the thickness T M of the metal film M can be determined to be 30 nm, T H is 120 nm, T Lis 60 nm. Based on the above parameters, the theoretical reflectance values of the samples with a high-reflection composite film (S / MH) on the surface and a high-absorption composite film (MHML) on the surface are calculated respectively. The calculated reflectance curves related to the wavelength are as Figure 2 shown. Their theoretical reflectances at 405 nm are 59.41% and 2.09% respectively, showing a very large theoretical optical contrast. Therefore, this structural film can perform efficient optical storage for blue-violet light at 405 nm.

[0040] The high-reflection composite film (MH) and the high-absorption composite film (ML) after determining the parameters are successively deposited on the substrate 1. Physical vapor deposition method or chemical vapor deposition method can be used to prepare metal and dielectric films. In this embodiment, both the metal and dielectric films are prepared by physical vapor deposition method.

[0041] When the prepared multi-layer composite film is used for optical storage, the specific method is as follows: According to the absorption characteristics of different metal films in the composite film, lasers with different parameters are used to prepare optical storage units. In this implementation case, a nanosecond pulsed laser is used to perform data storage reading and writing under the objective lens of a microscopic system with a numerical aperture of 0.8. The specific parameters of the laser used are: the central wavelength of the laser is 1030 nm, the repetition frequency is 0 - 2000 kHz, and the maximum output power is 35 W. In the actual processing process, the size of the optical storage recording area is changed by changing the energy of the laser pulse. Under the action of high energy, the area of the light spot is larger. Therefore, the area of the high-absorption composite film peeled off by the laser is larger. Under the action of low energy, the area of the high-absorption composite film peeled off is smaller. As the energy decreases, the peeled-off area becomes smaller until it approaches the diffraction limit. The processing principle diagram of laser irradiation on the film to achieve storage is as Figure 3 shown. The side view of the film structure before and after laser processing is as Figure 3 (a) shown, and the top view is as Figure 3 (b) shown. In this implementation case, the parameters of the laser used are: for an input light source with a wavelength of 1030 nm, after being transmitted through the microscopic focusing system and focused at the rear focal point of the objective lens (NA = 0.8), considering M 2 = 1.3 when the laser emits light, the diameter of the light spot at the focus is 1.066 um at this time. Based on the change of laser pulse energy, while keeping other optical parameters (including laser wavelength, pulse width, repetition frequency, focal depth of focus, etc.) consistent, in the case of single-pulse output, the following three situations are given: (1). The energy of the laser pulse is 1.16 uJ, and the area of the high-reflection composite exposed after peeling off the high-absorption composite film, that is, the expected area of a unit storage cell is 42.59 um 2 , and the result is as Figure 4(as shown in (a)). (Measured area of the elliptical pattern). (2). The energy of the laser pulse is 0.038 uJ, and the area of a single storage unit is 1.86 um at this time 2 , and the results are as Figure 4 (shown in (b)). (3). The energy of the laser pulse is 0.007 uJ, and the area of a single storage unit is 0.126 um at this time 2 , and the results are as Figure 4 (shown in (c)). The morphological change of the film after laser processing is as Figure 4 (shown in (d)).

[0042] The reflectivity curve of the unirradiated surface and the change in reflectivity of the surface after irradiation and peeling are obtained by reflectivity measurement as Figure 5 shown. At a wavelength of 405 nm, the actually measured reflectivity of the unirradiated film, i.e., the high-absorption composite film (ML), is 60.09%, and the actually measured reflectivity of the film after irradiation and peeling, i.e., the high-reflectivity composite film (MH), is 2.78%. Based on this composite multi-layer film structure, a change in reflectivity from 60.09% to 2.78% can be achieved, with a difference as high as 57.31%. For the commonly used Ge2Sb2Te5 phase change material in optical storage, the difference in reflectivity under laser irradiation is usually about 20%. Therefore, the present invention has a greater optical contrast, readability, and signal-to-noise ratio in optical storage. In addition, this composite multi-layer film only uses common metal materials and dielectric materials, and the total thickness is less than 240 nm. It not only has higher high-temperature resistance characteristics than the Ge2Sb2Te5 phase change material, but also has a lower preparation cost, and is an innovative structure that takes into account both high performance and low cost.

[0043] It will be obvious to those skilled in the art that the present invention can be changed in various ways, and such changes are not considered to depart from the scope of the present invention. All such modifications that are obvious to those skilled in the art will be included within the scope of the present claims.

Claims

1. A metal-dielectric multi-layer composite film structure that can be used for optical storage, characterized in that, It includes two layers of composite films sequentially deposited on a substrate, and each layer of composite film is composed of a metal layer and a dielectric layer; among the two layers of composite films, the upper layer is a high-absorption composite thin film, and the lower layer is a high-reflection composite thin film; and the uppermost layer of composite film can be peeled off from the lower layer of composite film under the action of laser.

2. The metal-dielectric multi-layer composite thin film structure for optical storage according to claim 1, wherein The dielectric material is one or more of Al2O3, TiO2, Nb2O5, SiO2, Ta2O5, HfO2, ZrO2.

3. The metal-dielectric multi-layer composite thin film structure for optical storage according to claim 1, wherein The metal material is one or more of Al, Ti, Nb, Si, Ta, Hf, Ni, Cr.

4. The metal-dielectric multi-layer composite thin film structure for optical storage according to claim 1, characterized in that, The substrate is silicon, quartz glass, tempered glass, plexiglass or calcium fluoride.

5. The metal-dielectric multi-layer composite thin film structure for optical storage according to claim 1, characterized in that, The difference in reflectivity between the high-absorption composite thin film and the high-reflection composite thin film is greater than or equal to 40%.

6. The metal-dielectric multi-layer composite thin film structure for optical storage according to claim 1, characterized in that, The thickness T corresponding to the dielectric layer in the high-reflection composite film and the high-absorption composite film H and T L respectively satisfy the following mathematical relationships: is the non-trivial phase shift generated when the incident light is reflected by the metal layer. The specific value is related to the material of the metal layer. λ is the working wavelength for optical storage read and write using a laser. n1 and n2 are the refractive indices of the dielectric materials in the high-reflection composite film and the high-absorption composite film respectively. m is a positive integer greater than 0.

7. The metal-dielectric multi-layer composite thin film structure for optical storage according to claim 1, characterized in that The thickness of the metal layer is 30 - 80 nm; the thickness of the dielectric layer is 50 - 150 nm.

8. The metal-dielectric multi-layer composite thin film structure for optical storage according to claim 1, characterized in that, The material of the metal layer is Ti, the material of the dielectric layer is TiO2, the thickness of the metal layer is 30 nm, the thickness of the dielectric layer in the high-reflection composite thin film is 90 - 130 nm, and the thickness of the dielectric layer in the high-absorption composite thin film is 50 - 70 nm.

9. An optical storage disc, adopting the metal-dielectric multi-layer composite thin film structure according to any one of claims 1 - 8.

10. A method for preparing a metal-dielectric multi-layer composite thin film structure for optical storage according to any one of claims 1-8, comprising: The metal and dielectric thin films are prepared by physical vapor deposition method or chemical vapor deposition method.

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