Method for long-term information storage and increased storage capacity of an information storage medium

Abstract

The present invention relates to an information storage medium and a method for long-term storage of information.

Description

Technical Field

[0001] The present invention relates to a method for long - term storage of information and to an information storage medium for long - term storage. Background Art

[0002] Currently, there is a wide variety of information storage options available for selection. With the advent of the digital age, the need for inexpensive and efficient information storage systems has become increasingly urgent, and a large number of new technologies have emerged. However, the proliferation of information storage mechanisms has brought about some unforeseen consequences. Today's information storage systems are highly vulnerable and prone to damage. Storage media such as hard disk drives and optical discs have a service life of only a few years only when they are properly stored and maintained. Even old technologies such as paper and microfilm have a service life of only a few centuries at best. All these information storage technologies are sensitive to heat, humidity, acids, etc., and may thus be prone to deterioration, resulting in information loss.

[0003] As the demand for data storage has grown exponentially, the methods for storing data have become increasingly vulnerable to damage and susceptible to the passage of time. However, many types of information should be preserved from natural degradation to ensure information continuity for future generations. In the case of natural disasters such as, for example, strong electromagnetic radiation emitted by the sun, a large amount of data may be damaged or destroyed. Therefore, there is a need for information storage devices that are resistant to environmental degradation and can thus store information over long time periods. Summary of the Invention

[0004] The object of the present invention is to provide a method and a medium for long - term information storage.

[0005] This object is achieved by the features of the independent claims. The dependent claims refer to preferred embodiments.

[0006] According to a first aspect, the present invention relates to a method for storing information. The method comprises the steps of: providing a ceramic substrate; and forming a plurality of recesses in the surface of the ceramic substrate by using a laser and / or a focused particle beam so as to encode information on the ceramic substrate. The plurality of recesses have different depths and each depth corresponds to a predefined information bit.

[0007] According to a second aspect, the present invention relates to a method for storing information. The method comprises the steps of: providing a ceramic substrate; coating the ceramic substrate with a layer of a second material different from the ceramic substrate; optionally tempering the coated ceramic substrate to form a writable plate; and forming a plurality of depressions in the surface of the second material by using a laser and / or a focused particle beam in order to encode information in the second material. The plurality of depressions have different depths and each depth corresponds to a predefined information bit.

[0008] The coated ceramic substrate may optionally be tempered before and / or after information encoding to improve the durability of the coated ceramic substrate including the encoded information. This tempering is particularly desirable in the case of ultra-long-term information storage (e.g., more than 1,000 years) and / or in the case of storage under particularly harsh conditions such as high humidity or in an acidic environment. Generally, it is preferred to temper the coated substrate before information encoding, as this allows the final coated substrate to be provided to the customer or end user in the form of a writable plate, who can then simply write the information on the plate. However, depending on the material combination used and / or the writing technique, it may also be preferred to first form the plurality of depressions and then temper only the coated ceramic substrate including the encoded information. This final tempering will allow the depressions to be more easily generated, for example, with a lower-power laser source, since the untempered second material is less durable than the tempered second material.

[0009] In another alternative applicable to all aspects and embodiments discussed further below, the tempering may not be carried out as a separate method step before and / or after information encoding. Instead, certain coating techniques such as high-temperature PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), PECVD (Plasma-Enhanced Chemical Vapor Deposition) or ALD (Atomic Layer Deposition) may be carried out at a high enough temperature to achieve in-situ tempering during coating.

[0010] According to a third aspect, the present invention relates to a method for storing information. The method comprises the steps of: providing a ceramic substrate; coating the ceramic substrate with two or more layers of different second materials different from the ceramic substrate; and forming a plurality of depressions in the layers of the second material by using a laser and / or a focused particle beam in order to encode information in the layers of the second material. The plurality of depressions have different depths and extend into different ones of the two or more layers, and each depth corresponds to a predefined information bit.

[0011] The coated ceramic substrate can optionally be tempered before and / or after information encoding to improve the durability of the coated ceramic substrate including the encoded information. Such tempering is particularly desirable in the case of ultra-long-term information storage (e.g., over 1,000 years) and / or in the case of storage under particularly harsh conditions such as high humidity or in an acidic environment. Generally, it is preferred to temper the coated substrate before information encoding, as this allows the final coated substrate to be provided to the customer or end user in the form of a writable plate, and the customer or end user can then simply write the information on the plate. However, depending on the material combination and / or writing technique used, it may also be preferred to first form a plurality of recesses and then temper only the coated ceramic substrate including the encoded information. This final tempering will allow recesses to be more easily formed, for example, using a lower-power laser source, since the untempered second material is less durable than the tempered second material.

[0012] In the case where there are two or more layers, it may also be preferred to, for example, temper the partially coated substrate after coating the ceramic substrate with a first layer of a different material and then apply one or more additional layers of a different material.

[0013] In other words, the present invention, which is the basis of aspects 1 to 3, is based on the concept of using depth encoding in combination with an extremely durable and stable substrate and / or layered structure. In various experiments, it has been demonstrated that different predetermined depths of recesses can be repeatedly formed in these materials using a laser and / or a focused particle beam. Since these depths can also be measured during a subsequent decoding process, various bits can be easily encoded at specific points on the surface of the coated substrate, the points having an area corresponding to the cross-sectional area (parallel to the substrate surface) of the recess. For example, a first depth d1 can encode the bit 00, a second depth equal to 2×d1 can encode the bit 01, a third depth equal to 3×d1 can encode the bit 10, and a fourth depth equal to 4×d1 can encode the bit 11. Of course, more than four depths can be used to encode even more bits at the same point. To achieve stable encoding and decoding, it is preferred that the minimum difference between subsequent predetermined depths (equal to d1 in this example) is much greater than the standard deviation of the depth d1 obtained during the formation of the recesses, preferably 5 times, and more preferably 10 times.

[0014] When using very small depths and depth differences, it may be difficult to rely on, for example, the absolute positioning of the bottom of each recess, which may also depend on thickness variations in either the substrate and / or one of the other layers. Thus, it may be preferable to encode the bit information in relative depth rather than absolute depth. For example, each recess may include a step having two different depths (a reference depth and an encoded depth), or for each recess, a double recess having a reference depth may be provided. Then the difference between, for example, the encoded depth and the reference depth may be used to encode the bits. This allows the substrate and optionally additional layers to be produced with lower precision and reduces the manufacturing cost. Of course, this principle can be extended to two or more encoded depths measured relative to the same reference depth. For example, a matrix of 3×3 or 5×5 recesses may all rely on a central reference depth.

[0015] The substrate can have any shape and size suitable for storing information. For example, the substrate can be rectangular, square, circular, or can have a polygonal or other shape. The size can vary between 1 cm 2 and 1 m 2 preferably between 10 cm 2 and 1.000 cm 2 more preferably between 50 cm 2 and 250 cm 2 and vary.

[0016] A layer of a second material or two or more layers of different second materials is preferably directly coated onto the ceramic substrate, i.e., there is no intermediate layer, in order to achieve a strong bond between the ceramic substrate and the layer of the second material during tempering. However, tempering may produce a sintered interface between the ceramic substrate and the layer of the second material or the bottom layer of two or more layers of different second materials. The sintered interface may contain at least one element of both the substrate material and the bottom layer of the second material or two or more layers of different second materials, since one or more elements from one of the two adjacent layers may diffuse into the other of the two adjacent layers. The presence of the sintered interface may further strengthen the bond between the ceramic substrate and the layer of the second material or the bottom layer of two or more layers of different second materials. There may be additional sintered layers between the respective layers of different second materials, where each sintered layer may contain at least one element from two adjacent layers.

[0017] The layer of the second material or two or more layers of different second materials is preferably continuous and preferably extends over most (e.g., at least 80% or at least 90%) and more preferably the entire ceramic substrate. Preferably, the second material or two or more layers of different second materials are different from the material of the ceramic substrate, i.e., the second material may have an elemental composition different from that of the ceramic substrate or the second material, and the ceramic substrate differs in their microstructure (e.g., their crystalline state, etc.).

[0018] Annealing is a process that can be performed on certain materials such as ceramics and metals to enhance their durability by altering the basic physical or chemical properties of the materials. The annealing process can help to permanently fix the material of the bottommost layer of a second material or two or more layers of different second materials to a ceramic substrate. In some cases, a portion of the second material layer or the bottommost layer of two or more layers of different second materials can form a chemical bond with the underlying ceramic substrate, such as an intermetallic bond or an interceramic bond for example. Annealing can increase the adhesion between the substrate and the material of the second material or the bottommost layer of two or more layers of different second materials and the hardness of the layer of the second material or the bottommost layer of two or more layers of different second materials by at least 5%, preferably at least 10%. Additionally, annealing can form a sintering interface as discussed above. A similar effect can be achieved between two or more layers of different second materials: the adhesion between adjacent layers can be increased and the hardness of each of these layers can be increased. Annealing can occur in the presence or absence of oxygen.

[0019] If annealing is carried out in an oxygen-containing atmosphere, the surface or the topmost sublayer of one or more layers of the second material exposed to oxygen can be at least partially oxidized. Thus, a metal oxide layer can be formed on top of one or more layers of the second material. This can further increase the hardness and / or the melting point and / or the resistance to a corrosive environment.

[0020] Providing a writable board with a ceramic substrate having a layer coated with a second material as described herein allows information to be stored thereon, which is highly resistant to moisture, electric / magnetic fields, acids, corrosive substances, etc., such that the encoded writable board provides durability unattainable from other commonly used information storage media.

[0021] Preferably, each of the two or more layers according to the third aspect has a thickness of less than 1 μm, preferably less than 100 nm, more preferably less than 10 nm.

[0022] Preferably, the two or more layers include a metal layer and a metal oxide layer adjacent to each other, wherein the metal element of the metal layer is preferably the same as the metal element of the metal oxide layer. It has been proven that the depth difference between the surface of the metal layer and the surface of the metal oxide layer can be particularly easily measured by interference, because selective reflection of a wide electromagnetic wave spectrum occurs upon exposure to broadband white light, or the reflection coefficient increases upon exposure to a narrowband laser beam (compare Figure 6)。In addition, it is particularly advantageous to use the interface between the metal layer and the metal oxide layer, as such a system does not tend to further oxidize, which enhances the stability of the layer. For this particular embodiment, it is therefore preferred that one of the different depths is the depth exposing the surface of the metal layer and the other of the different depths is the depth exposing the surface of the metal oxide layer, so as to benefit from the optical difference between these surfaces during decoding.

[0023] In addition, these material combinations also achieve color effects. Since different parts of the visible spectrum are typically reflected and / or absorbed by the metal and its corresponding oxide, the apparent color of the surface of the coated substrate depends on the depth of the respective recesses. By using different metal / metal oxide combinations, a plurality of different colors can thus be encoded by different recess depths. Thus, a multicolor ceramic microfilm can be manufactured. Decoding is also particularly simple in this case, as the plate can simply be irradiated with white light and the color response measured. Of course, it is also possible to combine different ways of encoding some information by color and additional information by depth within the same material layer (corresponding to the same color response, such as black, grey and white shades).

[0024] Of course, in the case of other material combinations, the optical properties of the different materials of the individual layers can also be utilized during decoding. For example, n layers of n different materials can be used, and each of the n different depths can be assigned to a single one of these n layers for encoding log2(n) information bits. During decoding, the optical material response can then be measured in order to determine the depth instead of performing an actual depth measurement.

[0025] Preferably, the plurality of recesses have at least two, preferably at least three, more preferably at least four, even more preferably at least five, even more preferably at least six, even more preferably at least seven, even more preferably at least eight, even more preferably at least sixteen and most preferably at least thirty-two different depths, where each depth corresponds to a predefined information bit.

[0026] Preferably, each recess is formed by one or more pulses of the laser and / or the focused particle beam, where the depth of each recess is controlled by one or a combination of the following parameters: the energy of the pulse, the duration of the pulse, the number of pulses of the laser and / or the focused particle beam.

[0027] Preferably, the minimum depth difference between the plurality of recesses is at least 1 nm, more preferably at least 10 nm, more preferably at least 30 nm, more preferably at least 50 nm, even more preferably at least 70 nm and most preferably at least 100 nm. Preferably, the minimum depth difference between the plurality of recesses is at most 5 μm, more preferably at most 1 μm, more preferably at most 500 nm, more preferably at most 300 nm, even more preferably at most 200 nm and most preferably at most 100 nm.

[0028] Preferably, the cross-sectional area of each recess is less than 100 μm 2 , preferably less than 1 μm 2 , more preferably less than 100 nm 2 , even more preferably less than 10 nm 2 .

[0029] According to a fourth aspect, the present invention relates to a method for storing information. The method comprises the steps of: providing a ceramic substrate; coating the ceramic substrate with a layer of a second material different from the material of the ceramic substrate; and forming a plurality of nanostructures in the surface of the second material by using a laser and / or a focused particle beam in order to encode information in the second material. The plurality of nanostructures have different optical properties, wherein each optical property corresponds to a predefined information bit.

[0030] Also, the coated ceramic substrate may optionally be tempered before and / or after information encoding to improve the durability of the coated ceramic substrate including the encoded information.

[0031] In other words, the present invention underlying this fourth aspect is based on the concept of using surface modification encoding in combination with an extremely durable and stable substrate and / or layered structure. In various experiments, it has been demonstrated that nanostructures such as nanoripples with different optical properties can be repeatedly formed using a laser and / or a focused particle beam. Since these optical properties can also be measured during a subsequent decoding process, various bits can be easily encoded at specific points on the surface of the coated substrate. For example, a first orientation of the nanoripples may encode bit 00, a second orientation of the nanoripples may encode bit 01, a third orientation of the nanoripples may encode bit 10, and a fourth orientation of the nanoripples may encode bit 11. Of course, more than four orientations of the nanoripples can be used to encode even more bits at the same point.

[0032] Preferably, the different optical properties of the plurality of nanostructures include one or more of the following: the orientation or polarization of the nanoripples, the frequency or wavelength of the nanoripples, the amplitude of the nanoripples. Preferably, the plurality of nanoripples have at least two, preferably at least three, more preferably at least four, even more preferably at least five, even more preferably at least six, even more preferably at least seven, even more preferably at least eight, even more preferably at least 16, and most preferably at least 32 different orientations, polarizations, frequencies, wavelengths, or amplitudes, and each orientation, polarization, frequency, wavelength, or amplitude corresponds to a predefined information bit.

[0033] Unless otherwise specified, each of the following preferred features applies to each of the above four aspects.

[0034] Preferably, the ceramic substrate for the method of information storage comprises an oxide ceramic, more preferably the ceramic substrate comprises at least 90 wt%, most preferably at least 95 wt% of one or a combination of the following: Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3, or any other oxide ceramic material. These materials are known to be particularly durable and / or resistant to environmental degradation in various situations. Therefore, these materials are particularly suitable for long-term storage under different conditions. Particularly preferably, the ceramic substrate comprises one or a combination of Al2O3, ZrO2, ThO2, SiO2, and / or MgO. According to the present invention, the term "ceramic material" preferably includes glass ceramics having an amorphous phase and one or more crystalline phases. In addition, the above-mentioned ceramic materials may also exist in the form of polycrystalline materials or single-crystalline materials. For example, single-crystalline alumina (i.e., sapphire) is particularly suitable as a substrate material in terms of durability because it has a very high melting point and a very high Mohs hardness.

[0035] Preferably, the ceramic substrate comprises a non-oxide ceramic, more preferably the ceramic substrate comprises at least 90 wt%, most preferably at least 95 wt% of one or a combination of the following: metal nitrides such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; metal carbides such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; metal borides such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; and metal silicides such as TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si; or any other non-oxide ceramic material. These materials are known to be particularly durable and / or resistant to environmental degradation in various situations. Therefore, these materials are particularly suitable for long-term storage under different conditions. Particularly preferably, the ceramic substrate comprises one or a combination of BN, CrSi2, SiC, and / or SiB6.

[0036] Preferably, the ceramic substrate comprises one or a combination of Ni, Cr, Co, Fe, W, Mo, or other metals with a melting point higher than 1,400 °C. Preferably, the ceramic material and the metal form a metal matrix composite material, wherein the ceramic material is dispersed in the metal or metal alloy. Preferably, the metal accounts for 5 wt% - 30 wt%, preferably 10 wt% - 20 wt% of the ceramic substrate, i.e., the metal matrix composite material. Particularly preferred metal matrix composite materials are: WC / Co-Ni-Mo, BN / Co-Ni-Mo, TiN / Co-Ni-Mo, and / or SiC / Co-Ni-Mo.

[0037] Preferably, the second material comprises at least one of the following: metals such as Cr, Co, Ni, Fe, Al, Ti, Si, W, Zr, Ta, Th, Nb, Mn, Mg, Hf, Mo, V; or ceramic materials such as metal nitrides such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; metal carbides such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; metal oxides such as Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; metal borides such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; metal silicides such as TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si; or any other ceramic material; preferably, wherein the second material comprises CrN, Cr2O3 and / or CrAlN. These materials provide sufficient hardness and resistance to environmental degradation. In addition, the materials can provide sufficient visual contrast with the underlying ceramic substrate. Further, experiments have shown that these materials, once coated, for example, by PVD (Physical Vapor Deposition), sputtering, CVD (Chemical Vapor Deposition), PECVD (Plasma Enhanced Chemical Vapor Deposition) or ALD (Atomic Layer Deposition), adhere firmly to the substrates mentioned above. Additional tempering, in the presence or absence of oxygen, can further increase the strength of these joints. Thus, a durable, permanent connection between one or more coating layers and the substrate can be achieved. Particularly preferably, the second material comprises one or a combination of Co, Ni, B4C, HfC, Cr2O3, ZrB2, CrB2, SiB6, Si3N4, ThN, CrN, Cr2O3 and / or CrAlN.

[0038] In the context of the present invention, various material properties can play an important role. On the one hand, the materials of both the substrate and the coating need to be sufficiently durable, stable and resistant. In addition, a strong bond or connection is required between the coating and the substrate material. Taking into account all these constraints, the following material combinations are particularly preferred: Al2O3 / CrN, SiO2 / Cr, SiO2 / CrN, Al2O3 / Co, ZrO2 / ZrB2, Al2O3 / SiC, SiB6 / Cr2O3, SiC / HfC, BN / ZrB2, BN / ZrB2, BN / B4C, BN / ThN and CrSi2 / Si3N4.

[0039] Generally, a ceramic substrate can be coated with a layer of a second material or two or more layers of different second materials using any technique suitable for achieving a thin coating (such as physical vapor deposition, sputtering, chemical vapor deposition, or any other thin film coating method). Preferably, physical vapor deposition is used to coat the ceramic substrate with a layer of a second material or two or more layers of different second materials. This particularly allows for reliably providing an extremely thin coating that continuously covers the substrate without any defects that could be misinterpreted as the encoded information. Since it may be difficult to use PVD for some of the materials mentioned above, it is preferred that during physical vapor deposition, the ceramic substrate is positioned intermediate the source of the material of the second material or two or more layers of different second materials and the conductive plate and / or wire grid. The plate or grid positioned behind the ceramic substrate helps to direct the vapor of the second material to adhere to the (non-conductive) ceramic substrate.

[0040] Preferably, the layer of the second material or two or more layers of different second materials have a thickness of no greater than 10 μm, more preferably no greater than 5 μm, even more preferably no greater than 1 μm, even more preferably no greater than 100 nm, and even more preferably no greater than 10 nm.

[0041] By providing one or more thin layers of one or more second materials, the laser or particle beam removal of local regions of the second material can be performed more quickly and effectively. In addition, if one or more layers of one or more second materials are thin, much smaller local regions can be changed more precisely. Thus, the information content of each region can be improved.

[0042] Preferably, tempering the coated ceramic substrate involves heating the coated ceramic substrate to a temperature in the range of 200 °C to 4,000 °C, more preferably in the range of 1,000 °C to 2,000 °C. The tempering process can include a heating stage with a temperature increase of at least 10 K per hour, a plateau stage lasting at least 1 minute at the peak temperature, and finally a cooling stage with a temperature decrease of at least 10 K per hour. The tempering process can help to harden the ceramic substrate and / or permanently bond the second material to the ceramic substrate.

[0043] Preferably, for the writing / encoding process, a local area of the coated substrate is heated to at least the melting temperature and / or decomposition temperature of the second material, such that the local area of the second material is heated to a temperature of at least 3,000 °C, even more preferably at least 3,200 °C, most preferably at least 3,500 °C, most preferably at least 4,000 °C. For example, CrN decomposes into Cr (solid) and N (gaseous) at a temperature of about 1,500 °C, while the melting temperature of Cr is only reached at about 1,900 °C. However, Cr (silver) is significantly different from CrN (light gray). Alternatively, treating the surface of the coated substrate with, for example, a femtosecond laser can cause a so-called Coulomb explosion, resulting in material ablation.

[0044] Preferably, the laser is configured to generate a laser having a wavelength in the range of 10 nm to 30 μm, preferably in the range of 100 nm to 2,000 nm, more preferably in the range of 200 nm to 1,500 nm.

[0045] Preferably, the laser emitted by the laser has a minimum focal diameter of no more than 50 μm, more preferably no more than 15 μm, more preferably no more than 10 μm, more preferably no more than 5 μm, more preferably no more than 1 μm, more preferably no more than 500 nm, more preferably no more than 100 nm, more preferably no more than 50 nm, more preferably no more than 10 nm. The small focal diameter allows information to be encoded on the writable board at a higher density.

[0046] Preferably, an ultrashort pulse laser (picosecond, femtosecond or attosecond pulse) is used to encode information. This allows for a minimum focal diameter of no more than 10 μm and a structure with a width of no more than 5 μm, more preferably no more than 1 μm, more preferably no more than 500 nm, more preferably no more than 100 nm, more preferably no more than 50 nm, more preferably no more than 10 nm.

[0047] The laser beam is preferably guided to a predetermined point on the surface of the coated substrate by a suitable scanning technique (such as a galvanometer scanner, a polygon scanner, a digital micromirror device, a spatial light modulator, etc.) for encoding bits at these predetermined points. In addition, appropriate optical devices may be involved. For example, the laser beam can be guided through a microscope objective for precise positioning. Oils, water, and other fluids with a high refractive index can be used for immersion of the optical devices in this context.

[0048] Preferably, the particle beam emitted by the focused particle beam equipment has a minimum focal diameter of no more than 5 μm, more preferably no more than 1 μm, more preferably no more than 100 nm, more preferably no more than 10 nm. The extremely small focal diameter allows information to be encoded on the writable board at an ultra-high density.

[0049] Preferably, the method further includes the step of reading information encoded on the writable board, more preferably using a digital scanner, a digital microscope, a laser scanning microscope, optical coherence tomography, or a scanning electron microscope.

[0050] Preferably, the area of the coated substrate includes at least 1 MB of information per cm 2 more preferably at least 10 MB of information per cm 2 even more preferably at least 100 MB of information per cm 2 even more preferably at least 1 GB of information per cm 2 even more preferably at least 10 GB of information per cm. 2 A greater information storage density allows for the storage of a large amount of information.

[0051] According to a fifth aspect, the present invention relates to an information storage medium. The information storage medium includes: a ceramic substrate, wherein the surface of the ceramic substrate includes a plurality of recesses encoding information on the information storage medium, wherein the plurality of recesses have different depths, and wherein each depth corresponds to a predefined information bit.

[0052] According to a sixth aspect, the present invention relates to an information storage medium. The information storage medium includes: a ceramic substrate, the ceramic substrate coated with a layer of a second material; and a sintering interface located between the ceramic substrate and the layer of the second material, wherein the second material is different from the material of the ceramic substrate, wherein the sintering interface contains at least one element from both the substrate material and the second material, wherein the layer of the second material includes a plurality of recesses encoding information on the information storage medium, wherein the plurality of recesses have different depths, and wherein each depth corresponds to a predefined information bit.

[0053] According to a seventh aspect, the present invention relates to an information storage medium. The information storage medium includes: a ceramic substrate, the ceramic substrate coated with two or more layers of different second materials; and a sintering interface located at least between the ceramic substrate and the lowermost layer of the two or more layers, wherein the second material is different from the material of the ceramic substrate, wherein the sintering interface contains at least one element from both the substrate material and the material of the lowermost layer, wherein the information storage medium includes a plurality of recesses encoding information on the information storage medium, wherein the plurality of recesses have different depths, and wherein each depth corresponds to a predefined information bit.

[0054] Preferably, each of the two or more layers has a thickness of less than 1 μm, preferably less than 100 nm, more preferably less than 10 nm.

[0055] Preferably, the two or more layers include a metal layer and a metal oxide layer, wherein the metal element of the metal layer is preferably the same as the metal element of the metal oxide layer.

[0056] Preferably, the plurality of recesses have at least two, preferably at least three, more preferably at least four, more preferably at least five, even more preferably at least six, more preferably at least seven, even more preferably at least eight, even more preferably at least 16, and most preferably at least 32 different depths, and wherein each depth corresponds to a predefined information bit.

[0057] Preferably, the minimum depth difference between the plurality of recesses is at least 1 nm, more preferably at least 10 nm, more preferably at least 30 nm, more preferably at least 50 nm, even more preferably at least 70 nm, and most preferably at least 100 nm. Preferably, the minimum depth difference between the plurality of recesses is at most 5 μm, more preferably at most 1 μm, more preferably at most 500 nm, more preferably at most 300 nm, even more preferably at most 200 nm, and most preferably at most 100 nm.

[0058] According to an eighth aspect, the present invention relates to an information storage medium. The information storage medium includes: a ceramic substrate coated with a layer of a second material; and a sintering interface between the ceramic substrate and the layer of the second material, wherein the second material is different from the material of the ceramic substrate, wherein the sintering interface contains at least one element from both the substrate material and the second material, wherein the surface of the layer of the second material includes a plurality of nanostructures, wherein the plurality of nanostructures have different optical properties, and wherein each optical property corresponds to a predefined information bit.

[0059] Preferably, the different optical properties of the plurality of nanostructures include one or more of the following: the orientation or polarization of the nanoripples, the frequency or wavelength of the nanoripples, the amplitude of the nanoripples. Preferably, the plurality of nanoripples have at least two, preferably at least three, more preferably at least four, more preferably at least five, more preferably at least six, more preferably at least seven, even more preferably at least eight, more preferably at least sixteen, and most preferably at least 32 different orientations, polarizations, frequencies, wavelengths, or amplitudes, and wherein each orientation, polarization, frequency, wavelength, or amplitude corresponds to a predefined information bit.

[0060] Unless otherwise specified, each of the following preferred features applies to each of the fifth to eighth aspects described above.

[0061] Preferably, the ceramic substrate of the information storage medium comprises an oxide ceramic, more preferably wherein the ceramic substrate comprises at least 90% by weight, even more preferably at least 95% by weight of one or a combination of the following: Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3 or any other oxide ceramic material.

[0062] Preferably, the ceramic substrate of the information storage medium comprises a non-oxide ceramic, more preferably wherein the ceramic substrate comprises at least 90% by weight, even more preferably at least 95% by weight of one or a combination of the following: metal nitrides such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; metal carbides such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; metal borides such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; and metal silicides such as TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si; or any other non-oxide ceramic material.

[0063] Particularly preferably, the ceramic substrate comprises one or a combination of BN, CrSi2, SiC and / or SiB6.

[0064] Preferably, the ceramic substrate comprises one or a combination of Ni, Cr, Co, Fe, W, Mo or other metals with a melting point higher than 1,400 °C. Preferably, the ceramic material and the metal form a metal matrix composite material, wherein the ceramic material is dispersed in the metal or metal alloy. Preferably, the metal accounts for 5% to 30% by weight, preferably 10% to 20% by weight of the ceramic substrate, i.e., the metal matrix composite material. Particularly preferred metal matrix composite materials are: WC / Co-Ni-Mo, BN / Co-Ni-Mo, TiN / Co-Ni-Mo and / or SiC / Co-Ni-Mo.

[0065] Preferably, the second material of the information storage medium comprises at least one of the following: metals such as Cr, Co, Ni, Fe, Al, Ti, Si, W, Zr, Ta, Th, Nb, Mn, Mg, Hf, Mo, V; metal nitrides such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; metal carbides such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; metal Oxides, such as Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; metal borides, such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; metal silicides, such as TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si; or any other ceramic material; preferably, wherein the second material comprises CrN, Cr2O3 and / or CrAlN.

[0066] Preferably, the layer of the second material has a thickness of not more than 10 μm, more preferably not more than 5 μm, even more preferably not more than 1 μm, even more preferably not more than 100 nm, even more preferably not more than 10 nm.

[0067] Preferably, the area of ​​the coated substrate comprises 2 At least 1KB of information, more preferably per cm 2 At least 10KB of information, more preferably per cm 2 At least 100KB of information, even more preferably per cm 2 At least 1MB of information, even more preferably per cm 2 At least 10MB of information, even more preferably per cm 2 At least 100MB of information, even more preferably per cm 2 At least 1 GB of information, even more preferably per cm 2 At least 10GB of information. Providing high information density on the coated substrate allows more information to be stored per board and can reduce production costs.

[0068] Preferably, the ceramic substrate has a flat plate or computer readable disk shape. The flat plate or computer readable disk shape can allow a computer or digital scanner to easily read the encoded information and is compatible with existing scanning systems.

[0069] The invention also relates to the use of an information storage medium for long-term information storage.

[0070] Preferably, in use, the information storage medium is stored for a period of at least 10 years, more preferably at least 100 years, more preferably at least 1,000 years, more preferably at least 10,000 years, and even more preferably at least 100,000 years.

[0071] The present invention also relates to a method for decoding information encoded on the above information storage medium. The method includes the following steps: providing the above information storage medium; measuring the depth of at least one subset of the plurality of recesses or the optical properties of at least one subset of the plurality of nanostructures; and decoding the information bits corresponding to the measured depth or the measured optical properties.

[0072] Preferably, the measuring of the depth or the optical properties is performed using a laser beam and / or a focused particle beam such as an electron beam.

[0073] Preferably, the measuring of the depth is based on one or a combination of the following: interference, reflection, absorption, ellipsometry, frequency comb technology, fluorescence microscopy such as STED or STORM, optical coherence tomography, scanning electron microscopy, digital (immersion) microscopy (using reflected light or transmitted light).

[0074] Preferably, the measuring of the optical properties is based on one or a combination of the following: absorption, transmission, reflection, polarization, interference of incoherent light and / or laser light.

[0075] Although the above method mainly relies on directly ablating materials using a laser or a particle beam, it should be noted that alternative methods for forming recesses of different depths in a coating are known and can be used in place of the direct ablation techniques discussed above. For example, the coated substrate can be coated with an additional layer of photoresist, and the additional layer can be exposed to light or other radiation to produce a specific pattern. After the exposed photoresist is developed, the coated substrate together with the photoresist can be etched so as to ablate the material of a layer of a second material, for example, from the substrate wherever there is no developed photoresist. Thus, a pattern of recesses will be formed. In order to form recesses of different depths, the process must be repeated several times, where the number of etching times occurring at a specific location corresponds to the depth of the recess at that location. Suitable techniques for such etching processes are known in the art and are described, for example, in the second edition of the Handbook of Semiconductor Manufacturing Technology edited by Robert Doering and Yoshio Nishi of CRC Press. For example, chromium can be wet-etched using ammonium cerium nitrate and certain acids including perchloric acid, acetic acid, nitric acid, and hydrochloric acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The subject matter of the present invention will be explained in more detail hereinafter with reference to the preferred exemplary embodiments shown in the drawings, in which:

[0077] Figure 1 Schematically depicts a cross-section through an information storage medium according to a preferred embodiment of the present invention;

[0078] Figure 2 Schematically depicts an example of the process of physical vapor deposition coating of a ceramic substrate;

[0079] Figure 3 Schematically shows a perspective view of an example of encoding information onto a writable plate using a laser;

[0080] Figure 4 Schematically depicts a cross-section through an information storage medium according to a preferred embodiment of the present invention;

[0081] Figure 5 Schematically depicts the interference principle in the case of a metal / metal oxide layer system;

[0082] Figure 6 Depicts a graph of reflectance versus wavelength in the case of a metal / metal oxide layer system;

[0083] Figure 7 Schematically depicts a cross-section through an information storage medium according to a preferred embodiment of the present invention;

[0084] Figure 8a and Figure 8b Depicts micrographs showing exemplary encoding at two different magnifications;

[0085] Figure 8c Shows Figure 8b A 3D visualization of a portion of the micrograph;

[0086] Figure 8d Shows a cross-sectional height profile through Figure 8a The micrograph;

[0087] Figure 9a and Figure 9b Depicts micrographs showing exemplary encoding at two different magnifications; and

[0088] Figure 10 Depicts a SEM image obtained from the exemplary encoding.

[0089] In principle, the same parts in the drawings are provided with the same reference numerals. Detailed Description

[0090] Figure 1A cross section through an information storage medium suitable for long-term storage of information according to a preferred embodiment of the present invention is schematically depicted. The information storage medium comprises a ceramic substrate 150 coated with a layer of a second material 170, the second material 170 being different from the material of the ceramic substrate 150. As mentioned above, due to an optional tempering process, a sintering interface (not shown) may exist between the ceramic substrate 150 and the layer of the second material 170. The layer of the second material 170 comprises a plurality of recesses 10 (four of which are shown exemplarily) having different depths, wherein each depth corresponds to a predefined information bit. Figure 1 In the embodiment shown, four bits of information can be encoded. For example, the minimum depth of the depressions 10 (or, alternatively, a surface without any depressions at all) can correspond to the code "0000". For example, the maximum depth of the depressions 10 extending all the way through the second layer 170 to the substrate 150 can correspond to the code "1111". Similarly, each of the intermediate depths also corresponds to a specific predefined information bit. Although the depth difference between subsequent codes is Figure 1 is shown as being constant, but this is not necessarily the case.

[0091] certainly, Figure 1 The 4-bit code shown in is just one specific example. More or fewer bits may be encoded, depending on the thickness of the second layer 170 and the depth differences of the various recesses 10 that can both be reliably manufactured for encoding and reliably measured for decoding.

[0092] In order to produce such an information storage medium, a method for storing information is described herein. Initially, a ceramic substrate 150 is provided. Figure 2 As schematically shown, the ceramic substrate 150 is then coated with a layer of a second material 170. The layer of the second material 170 is preferably no more than 50 μm thick. The writable plate 110 comprising the ceramic substrate 150 and the layer of the second material 170 may be stored until ready for use or may be subsequently encoded with information 120 using, for example, a laser or focused particle beam 190. The laser or focused particle beam 190 is directed towards the layer of the second material 170 and then, for example, local areas of the second material 170 that fall within the focus of the laser or focused particle beam are heated so that depressions are formed at these local areas. This method will now be described in more detail.

[0093] The initially provided ceramic substrate 150 can account for the majority of the materials by weight of the writable board 110. A variety of different materials can be used for the ceramic substrate 150. In certain configurations, the ceramic substrate 150 comprises an oxide ceramic that includes at least one of Al2O3, TiO2, SiO2, ZrO2, ThCO2, MgO, Cr2O3, Zr2O3, V2O3, or any other oxide ceramic material. Alternatively, the ceramic substrate can comprise a non-oxide ceramic that includes at least one of the following: metal nitrides such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; metal carbides such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; metal borides such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; and metal silicides such as TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si; or any other non-oxide ceramic material. The amount of the oxide or non-oxide ceramic present can vary. Preferably, the amount of the oxide or non-oxide ceramic constitutes at least 90 wt% of the ceramic substrate 150. More preferably, the amount of the oxide or non-oxide ceramic substrate constitutes at least 95 wt% of the ceramic substrate 150. One preferred configuration is the ceramic substrate 150 that includes at least 90 wt% of Al2O3 or SiO2 by weight measurement.

[0094] The second material 170 is formed as a layer on the ceramic substrate 150. As compared to the thickness of the ceramic substrate 150 ( Figure 1Compared with (not drawn to scale), the layer of the second material 170 is a thin layer, and the second layer 170 is preferably at most 50 μm thick. The second material 170 may mainly comprise at least one of the following: metals such as Cr, Co, Ni, Fe, Al, Ti, Si, W, Zr, Ta, Th, Nb, Mn, Mg, Hf, Mo, V; metal nitrides such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; metal carbides such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; metal oxides such as Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; metal borides such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; metal silicides such as TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si; or any other ceramic material; preferably, wherein the second material comprises CrN, Cr2O3 and / or CrAlN.

[0095] A preferred configuration is a layer of the second material 170 that mainly comprises CrN, Cr2O3 and / or CrAlN.

[0096] Figure 2 An exemplary method for coating the second material 170 onto the ceramic substrate 150 using physical vapor deposition (PVD) is shown. During the PVD process, the ceramic substrate 150 together with the source 160 of the second material 162 is placed into a physical vapor deposition chamber. A vacuum is pumped on the physical vapor deposition chamber and the source 160 of the second material is heated until a significant portion of the second material 162 contained within the physical vapor deposition chamber is evaporated or sublimated. The airborne particles 164 of the second material are then dispersed throughout the physical vapor deposition chamber until they contact the surface 152 of the ceramic substrate 150 and adhere to the surface.

[0097] Although physical vapor deposition is a commonly used method for coating metal substrates, coating ceramic substrates can prove challenging for particle attachment. Thus, to improve the attachment of second material particles 164 to the surface 152 of the ceramic substrate, a conductive wire mesh or conductive metal plate 180 can be placed on the far side of the ceramic substrate 150 such that the ceramic substrate 150 is positioned between the wire mesh 180 and the source 160 of the second material 162. Such a conductive mesh / plate 180 can attract ionized particles of the second material 164 when conducting an electric current, and the ionized particles then collide with the surface 152 of the ceramic substrate 150 and are held against it such that they then attach to the surface 152 of the ceramic substrate. This coating process can also be repeated to coat multiple different surfaces of the ceramic substrate, as discussed further below.

[0098] Depositing a layer of the second material 170 on the ceramic substrate 150 can be performed using other coating methods such as sputtering or sublimation sandwich coating. Basically, any method capable of producing a layer of the second material 170 can be used. The second material 170 may not necessarily cover the entire ceramic substrate 150. Instead, only a portion of the ceramic substrate 150 or a single side 152 of the ceramic substrate 150 can be coated with the second material 170.

[0099] Once the ceramic substrate 150 is coated with the second material 170, the coated ceramic substrate then preferably undergoes an optional tempering process. Tempering is generally understood as a process that improves the strength and / or other properties of a material. In the case of ceramics, tempering can involve heating the ceramic article such that its chemical composition undergoes chemical and / or physical changes, thereby causing the article to become fixed or hardened. Tempering the coated ceramic substrate can involve heating the coated ceramic substrate 150 to a temperature in the range of 200 °C to 4,000 °C, preferably in the range of 1,000 °C to 2,000 °C. The tempering process can include a heating phase with a temperature increase of at least 10 K per hour, a plateau phase lasting at least 1 minute at the peak temperature, and finally a cooling phase with a temperature decrease of at least 10 K per hour. The tempering process can help to permanently fix the second material 170 to the ceramic substrate 150. In some cases, a portion of the layer of the second material 170 can form a chemical bond with the underlying ceramic substrate 150. After tempering the ceramic substrate 150 with the second material 170, a writable plate 110 is formed. The characteristics of the writable plate 110 are determined by the exact materials used within the writable plate 110. The writable plate 110 can now store or be directly encoded with information 120. As mentioned above, additionally or alternatively, the coated substrate can be tempered before and / or after information encoding.

[0100] Figure 3Depiction of encoding information onto the writable board 110. During encoding, a laser or focused particle beam 190 directs a collimated laser or focused particle beam onto a layer of a second material 170 of the writable board 110. The laser or focused particle beam alters a portion of the second material 170 within a local region 175 such that the portion is distinguishable (e.g., optically) from the surrounding second material 170. Although Figure 3 a laser or focused particle beam imprint of text is schematically shown, it should be noted that multi-bit encoding according to the present invention is most suitable for digital encoding of information. However, alternatively, different depths can also be used to achieve color effects that can be used to provide colored text or colored images on the writable board 110.

[0101] Preferably, the laser or focused particle beam heats the local region 175 of the second material 170 to at least the melting temperature and / or decomposition temperature of the second material 170. The melting point of the second material 170 depends on its chemical composition. Preferably, heating the local region 175 above the melting point can involve heating the local region to a temperature of at least 3,000 °C, more preferably at least 3,200 °C, even more preferably at least 3,500 °C, and most preferably at least 4,000 °C. Applying such high temperatures to these local regions can cause rapid expansion of the second material 170 within the local region 175. This rapid expansion can cause ablation and / or vaporization of the second material 170 within the local region 175.

[0102] Suitable laser wavelengths for the laser encoding method can include wavelengths in the range of 10 nm to 30 μm, preferably in the range of 100 nm to 2,000 nm, more preferably in the range of 150 nm to 1,500 nm. More importantly, the minimum focal diameter of the laser or focused particle beam, which determines the minimum size of each recess. Preferably, the laser or focused particle source 190 is capable of focusing the laser or focused particle beam to have a minimum focal diameter of no greater than 50 μm, preferably no greater than 15 μm, preferably no greater than 5 μm, preferably no greater than 1 μm, preferably no greater than 100 nm, and more preferably no greater than 10 nm.

[0103] The form of the writable board 110 can be determined according to the needs of the user and the type of information 120 to be encoded. In some cases, the writable board 110 can be formed in a flat plate shape for storage, preferably no greater than 200 mm × 200 mm, more preferably no greater than 100 mm × 100 mm, and more preferably no greater than 10 mm × 10 mm. In other cases, a computer-readable disk shape can preferably have a diameter of no greater than 30 cm, more preferably no greater than 12 cm, and more preferably no greater than 8 cm.

[0104] The information storage medium 110 according to the present invention is resistant to environmental degradation and preferably capable of withstanding temperatures between -273 °C (0 °K) and 1,200 °C without suffering information loss. The information storage medium 100 may also be resistant to electromagnetic pulses, water damage, corrosion, acids, and / or other chemicals. It is envisioned that the information storage medium 100 as described herein may store the information 120 for a period of at least 10 years, preferably at least 100 years, preferably at least 1,000 years, more preferably at least 10,000 years, more preferably at least 100,000 years. Under certain storage conditions including storing the information storage medium 100 within an underground salt dome, the information storage medium may be capable of storing the information for at least one million years.

[0105] Figure 4 Schematically depicts a cross-section through an information storage medium suitable for long-term storage of information according to another preferred embodiment of the present invention. The information storage medium includes a ceramic substrate 150 of four layers 171 to 174 coated with a different second material different from the material of the ceramic substrate 150. Also, a sintering interface (not shown) may exist at least between the ceramic substrate 150 and the lowermost layer 171 of the four layers. The sintering interface may contain at least one element from both the substrate material and the material of the lowermost layer 171. Similar to Figure 1 the embodiment shown, Figure 4 the information storage medium of the embodiment shown includes a plurality of depressions 10 encoding information on the information storage medium, where the plurality of depressions 10 have different depths and where each depth corresponds to a predefined information bit. Also, Figure 4 16 different depths corresponding to a 4-bit code are shown in

[0106] However, different from Figure 1 the embodiment shown, in Figure 4 the case of the embodiment shown, four different bits (by different depths) are encoded in each of the four layers 171 to 174. If the four layers 171 to 174 are made of different materials, the optical response of each layer may be different. This allows for high precision during decoding since the achieved depth information may be correlated with, for example, the optical response.

[0107] Of course, depending on the number of bits to be encoded, there may be more or fewer than four layers of different second materials.

[0108] Figure 4 A particularly preferred example of the multilayer coating shown is a bilayer coating where a metal layer 171 is coated on the substrate 150 and a metal oxide layer 172 (of the same metal) is coated on the metal layer 171. If as Figure 5Schematically showing such a double-layer coating irradiated with incident white light, a part of the incident light 1 is reflected (2) at the oxide layer, while another part of the incident light 1 is refracted (3) into the oxide layer and reflected (4) at the oxide / metal interface. The light beam reflected at the oxide layer and the light beam reflected at the metal layer can be in phase, resulting in a visible color, or out of phase, so that the color is not visible. Therefore, a specific color is visible wherever there is an oxide layer (which depends on the refractive indices of both the oxide layer and the metal layer and the thickness of the oxide layer), but is not visible if the depth of a certain recess causes destructive interference at this specific point.

[0109] Figure 6 An exemplary graph depicting that the reflectivity of a laser depends on the wavelength for Ti / TiO2 double-layers with different TiO2 layer thicknesses (17 nm, 24 nm, 28 nm, 31 nm, 40 nm, and 46 nm). As Figure 6 can be seen, the minimum reflectivity depends to a large extent on the layer thickness and shifts from approximately 400 nm (for a thickness of 17 nm) to approximately 700 nm (for a thickness of 46 nm), thus changing the color impression from yellow to blue. Therefore, the entire chromatogram can be encoded with multiple recesses of different depths corresponding to the respective minimum reflectivities.

[0110] Therefore, in principle, a metal / metal oxide layer system can be utilized and different colors can be encoded by different depths of recesses to form a multicolor microfilm.

[0111] Figure 7 Schematically depicting a cross-section through an information storage medium suitable for long-term information storage according to another preferred embodiment of the present invention. The information storage medium includes a ceramic substrate 150 with a layer of a second material 170 coated thereon. Similarly, a sintering interface (not shown) can be present between the ceramic substrate 150 and the layer of the second material 170, where the sintering interface contains at least one element from both the substrate material and the second material. The surface of the layer of the second material 170 includes a plurality of nanostructures 20, where the plurality of nanostructures 20 have different optical properties and each optical property corresponds to a predefined information bit. In Figure 7 the specific example shown, the different optical properties of the plurality of nanostructures 20 correspond to different orientations of so-called nanoripples. In the depicted example, four different orientations of such nanoripples corresponding to a 2-bit code are shown. Such nanoripples with different orientations can be manufactured as follows: Wave-shaped nanostructures called nanoripples can be formed on the surface of a ceramic (e.g., CrN) or a metal (Cr) using a femtosecond laser. Dozens to hundreds of linearly polarized femtosecond laser pulses and an energy flux far below the ablation threshold produce the above-mentioned nanoripples parallel to the polarization direction.

[0112] Several examples will be described below.

[0113] As a first example, a ceramic substrate made of Rubalit 708s containing at least 96% Al2O3 with a size of 20 cm × 20 cm and available from CeramTec GmbH (Germany) is used as the raw material.

[0114] A CrN layer is coated on a plate of the ceramic substrate having a size of 10 cm × 10 cm and a thickness of 1 mm using physical vapor deposition. For this purpose, the ceramic plate is mounted on a steel conductive plate having a size of 10 cm × 10 cm. The ceramic plate together with the conductive plate is placed in a physical vapor deposition machine available from Oerlikon Balzers AG (Liechtenstein).

[0115] Then, an enhanced sputtering process from Oerlikon Balzers AG is used CNI performs physical vapor deposition at a process temperature below 250 °C.

[0116] After deposition, a CrN layer with a constant thickness of 5 μm is provided on one side of the ceramic substrate (opposite to the side facing the conductive plate).

[0117] Subsequently, the coated ceramic substrate is tempered in a batch furnace model "N 150 / H" available from Nabertherm GmbH. For tempering, the temperature is ramped from room temperature (20 °C) to 1,000 °C in 2 hours. Then, the temperature is increased from 1,000 °C to 1,200 °C at a rate of 100 K / h and the maximum temperature of 1,200 °C is maintained for 5 minutes. Subsequently, the substrate is cooled at a rate of -200 K / h in 6 hours.

[0118] After tempering, the material stack includes a ceramic substrate made of Rubalit 708s containing at least 96% Al2O3, a CrN coating with a thickness of about 5 μm, and another Cr2O3 metal oxide layer with a thickness of about 1 μm. Z.B. Qi et al. (Thin Solid Films 544 (2013), 515 - 520) have described a similar metal oxide layer.

[0119] The metal oxide surface has a dark green, almost black appearance.

[0120] The surface of the material stack is scribed with thin lines having a width of 10 μm - 20 μm at different depths using a femtosecond laser "CARBIDE" available from the company Light Conversion. The laser parameters for scribing are a pulse width of 230 fs, a wavelength of 515 nm, and repetition rates of 60 kHz and 100 kHz.

[0121] Depending on the number of pulses used, the laser-formed depressions reach several depth levels between 4 μm and 10 μm. Figure 8a and Figure 8b Micrographs showing the surface of the probe taken with a Keyence VHX-7000 high-resolution 4K microscope at different magnifications (the horizontal bars at the lower right of the two micrographs correspond to 1,000.00 μm and 100.00 μm respectively), where the depth (and width) decreases from left to right.

[0122] Figure 8c Shows a 3D visualization of a cross-section through the Figure 8b micrograph. As can be seen from the figure, each depression has a substantially constant width and depth along its length. Figure 8d Shows a cross-sectional height profile of a portion of the Figure 8a micrograph. Again, the depth decreases significantly from left to right. As can be clearly seen, the depth of each depression can be controlled by the number of pulses used for writing, where each pulse forms a depth of 500 nm - 1,000 nm.

[0123] Interestingly, due to the cold ablation effect (Coulomb explosion) of the ultrashort pulses, the edges of the writing do not show signs of molten coating materials (CrN and Cr2O3).

[0124] As a second example, a material stack identical to the material stack described in the first example is produced.

[0125] The surface of the material stack is inscribed with thin lines of 1.92 μm width at different depths using a Spectra Physics Femtosecond-Laser Spirit-1040HE30 (1040 nm, <400 fs, up to 120 μJ) with a focal length of 56 mm. Each laser pulse engraves a linear depression with a depth of 1 μm. Each subsequent pulse at the same point increases the depth by approximately 1 μm. Thus, five different linear depressions with widths of 1.92 μm and depths of 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm can be achieved. Figure 9a and Figure 9b Micrographs showing the surface of the probe taken with a Keyence VHX-7000 high-resolution 4K microscope at different magnifications (the horizontal bar at the upper left of the two micrographs corresponds to 20 μm), where the depth increases from left to right.

[0126] As a third example, a ceramic substrate with dimensions of 22 mm × 7 mm made of Rubalit 708s containing at least 96% Al2O3 and available from CeramTec GmbH has been coated with 500 nm CrN in a Leybold Z400 deposition system, where the process parameters are as follows:

[0127] · 3-inch Cr target (Plansee Composite Materials GmbH)

[0128] · Base pressure below 5 × 10-6 mbar

[0129] · Working gas pressure: 0.36 Pa, where the N2 / Ar flow ratio is 16 / 16 sccm / sccm

[0130] · DC target power: approximately 200 W (current controlled at 0.5 A)

[0131] · No substrate heating

[0132] · No substrate bias (therefore, floating potential)

[0133] The surface of the probe is inscribed with fine lines of 30 nm width at different depths using an FEI Quanta 200 3D DFIB (Focused Ion Beam - FIB - workstation equipped with a Ga ion source) at 0.1 nA and 30 kV (which corresponds to 2 * 1014 J / m3 or 0.2 mJ / μm3) with a charge density of 6.667 nC / μm3. The ion beam is focused to a spot size of 11.5 nm. The focused ion beam engraves a depth of 50 nm in the initial pass. In the case of another ion beam pass, each subsequent inscription increases the depth by approximately 50 nm. Thus, ten different linear depressions with a width of 30 nm and depths of 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, etc. can be achieved. Figure 10 An SEM image of the surface of the probe taken with an FEI Quanta 250 FEG (Field Emission Gun Scanning Electron Microscope - FEGSEM) is shown, where the depth increases from left to right. The spacing identified by two arrows in the SEM image corresponds to 30.0 nm.

[0134] Although the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description should be considered illustrative or exemplary and not restrictive; thus, the invention is not limited to the disclosed embodiments. By studying the drawings, the disclosure, and the appended claims, those skilled in the art and those practicing the claimed invention can understand and implement variations of the disclosed embodiments. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality and can mean "at least one".

Claims

1. A method for storing information, comprising the steps of: Providing a ceramic substrate; And Forming a plurality of recesses in the surface of the ceramic substrate by using a laser and / or a focused particle beam to encode information on the ceramic substrate; Wherein the plurality of recesses have different depths and each depth corresponds to a predefined information bit.

2. A method for storing information, comprising the steps of: Providing a ceramic substrate; Coating the ceramic substrate with a layer of a second material different from the material of the ceramic substrate; And Forming a plurality of recesses in the surface of the layer of the second material by using a laser and / or a focused particle beam to encode information in the layer of the second material; Wherein the plurality of recesses have different depths and each depth corresponds to a predefined information bit, Wherein the second material comprises at least one of the following: a metal; or a ceramic material comprising a metal nitride, a metal carbide, a metal oxide, a metal boride, or a metal silicide.

3. A method for storing information, comprising the steps of: Providing a ceramic substrate; Coating the ceramic substrate with two or more layers of different second materials different from the material of the ceramic substrate; And Forming a plurality of recesses in the layers of the second material by using a laser and / or a focused particle beam to encode information in the layers of the second material; Wherein the plurality of recesses have different depths and extend into different ones of the two or more layers, and each depth corresponds to a predefined information bit, Wherein the second material comprises at least one of the following: a metal; or a ceramic material comprising a metal nitride, a metal carbide, a metal oxide, a metal boride, or a metal silicide.

4. The method according to claim 2 or 3, wherein the coated ceramic substrate is tempered before and / or after information encoding to improve the durability of the coated ceramic substrate.

5. The method according to any one of claims 1-3, wherein the minimum depth difference between the plurality of recesses is at least 10 nm.

6. The method according to any one of claims 1-3, wherein the ceramic substrate comprises at least 90 wt% of one or a combination of the following: Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3.

7. The method according to any one of claims 1-3, wherein the ceramic substrate comprises at least 90 wt% of one or a combination of the following: metal nitrides, metal carbides, metal borides, and metal silicides.

8. The method according to claim 7, wherein the metal nitride comprises CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; the metal carbide comprises TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; the metal boride comprises TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; and the metal silicide comprises TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si.

9. The method according to claim 2 or 3, wherein the metal comprises Cr, Co, Ni, Fe, Al, Ti, Si, W, Zr, Ta, Th, Nb, Mn, Mg, Hf, Mo, V; the metal nitride comprises CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; the metal carbide comprises TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; the metal oxide comprises Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; the metal boride comprises TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; and the metal silicide comprises TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si.

10. The method according to any one of claims 1-3, wherein the one or more second materials comprise CrN, Cr2O3 and / or CrAlN.

11. The method according to claim 1, wherein forming the recessed portion comprises: The surface of the substrate is treated with a femtosecond laser to cause Coulomb explosion, thereby resulting in material ablation.

12. The method according to any one of claims 2-3, wherein forming the recessed portion comprises: The surface of the coated substrate is treated with a femtosecond laser to cause Coulomb explosion, thereby resulting in material ablation.

13. An information storage medium, comprising: A ceramic substrate, wherein the surface of the ceramic substrate includes a plurality of depressions encoding information on the information storage medium, wherein the plurality of depressions have different depths, and wherein each depth corresponds to a predefined information bit.

14. An information storage medium, comprising: A ceramic substrate coated with a layer of a second material; and a sintering interface located between the ceramic substrate and the layer of the second material, wherein the second material is different from the material of the ceramic substrate, wherein the sintering interface comprises at least one element from both the substrate material and the second material, wherein the layer of the second material comprises a plurality of depressions encoding information on the information storage medium, wherein the plurality of depressions have different depths, and wherein each depth corresponds to a predefined information bit, wherein the second material comprises at least one of the following: a metal; or a ceramic material comprising a metal nitride, a metal carbide, a metal oxide, a metal boride, or a metal silicide.

15. An information storage medium, comprising: A ceramic substrate coated with two or more layers of different second materials; and a sintering interface located at least between the ceramic substrate and the lowermost layer of the two or more layers, wherein the second material is different from the material of the ceramic substrate, wherein the sintering interface comprises at least one element from both the substrate material and the material of the lowermost layer, wherein the information storage medium comprises a plurality of depressions encoding information on the information storage medium, wherein the plurality of depressions have different depths, and wherein each depth corresponds to a predefined information bit, wherein the second material comprises at least one of the following: a metal; or a ceramic material comprising a metal nitride, a metal carbide, a metal oxide, a metal boride, or a metal silicide.

16. The information storage medium according to any one of claims 13-15, wherein a minimum depth difference between the plurality of depressions is at least 10 nm.

17. The information storage medium according to any one of claims 13-15, wherein the ceramic substrate comprises at least 90 wt% of one or a combination of the following: Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3.

18. The information storage medium according to claim 14 or 15, wherein the metal nitride comprises CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; the metal carbide comprises TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; the metal boride comprises TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; and the metal silicide comprises TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si.

19. The information storage medium according to any one of claims 13-15, wherein the one or more second materials comprise at least one of the following: a metal; or a ceramic material comprising a metal nitride, a metal carbide, a metal oxide, a metal boride, or a metal silicide.

20. The information storage medium according to claim 19, wherein the metal comprises Cr, Co, Ni, Fe, Al, Ti, Si, W, Zr, Ta, Th, Nb, Mn, Mg, Hf, Mo, V; the metal nitride comprises CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; the metal carbide comprises TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; the metal oxide comprises Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; the metal boride comprises TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; and the metal silicide comprises TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi, Mg2Si.

21. The information storage medium according to any one of claims 13 - 15, wherein the one or more second materials comprise CrN, Cr2O3, and / or CrAlN.

22. The information storage medium according to claim 14, further comprising: An oxide layer, the oxide layer being on top of the layer of the second material.

23. The information storage medium according to claim 15, further comprising: An oxide layer, the oxide layer being on top of the topmost layer of the two or more layers of different second materials.

24. The information storage medium according to claim 14, wherein the melting temperature of the ceramic substrate is equal to or greater than the melting temperature of the layer of the second material.

25. The information storage medium according to claim 15, wherein the melting temperature of the ceramic substrate is equal to or greater than the melting temperature of the two or more layers of different second materials.

26. A method for decoding information encoded on an information storage medium according to any one of claims 13 - 25, comprising the steps of: Providing an information storage medium according to any one of claims 13 - 25; Measuring the depth of at least one subset of the plurality of recesses or the optical properties of at least one subset of the plurality of nanostructures; And Decoding the information bits corresponding to the measured depth or the measured optical properties.

27. The method according to claim 26, wherein measuring the depth or the optical properties is performed using a laser beam and / or a focused particle beam.

28. The method according to claim 26 or 27, wherein measuring the depth is based on one or a combination of the following: interference, reflection, absorption, ellipsometry, frequency comb technology, fluorescence microscopy, optical coherence tomography, scanning electron microscopy, digital microscopy.

29. The method according to claim 26 or 27, wherein measuring the optical properties is based on one or a combination of the following: absorption, transmission, reflection, polarization, interference of incoherent light and / or laser light.

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