Ultra-thin data storage device

Abstract

A data carrier comprising a ceramic substrate having a first and an opposite second surface and a thickness of at most 500 µm, wherein the first surface of the substrate has a plurality of laser-ablated depressions encoding information, each depression having a depth of at most 1 µm.

Description

[0001] The present invention relates to an ultra-thin.

[0002] On average, humans generate an estimated 2.5 quintillion bytes per day. While a large portion of this data may be generated only for short-term use, the demand for long-term data storage is increasing daily. Clearly, current storage media, such as flash memory, hard disk drives (HDDs), and magnetic tapes, are far from ideal for long-term storage. Therefore, companies like Microsoft are currently researching alternative storage technologies (see, for example, the so-called "Project Silica" and US 10,719,239 B2).

[0003] Another technique for long-term information storage was described in WO 2021 / 028035 A1. This technique is based on the use of a ceramic substrate coated with a layer of another material and the encoding of information on the coated substrate, e.g., using a laser to manipulate localized areas of the coated substrate. This technique has been proven to enable information storage that is highly resistant to moisture, electromagnetic fields, acidic and corrosive substances, etc., thus providing the encoded writable ceramic disk with a durability not found in other commonly used information storage media. However, a potential disadvantage of this technique is the use of rather bulky ceramic disks with a thickness of approximately 1 mm.Accordingly, the data storage density per volume may not reach the data storage densities of the disks currently in use.

[0004] Accordingly, there is a need for further improvement of data storage devices suitable for long-term use and storage.

[0005] The inventors of the present invention have now surprisingly recognized that the techniques described in WO 2021 / 028035 A1 can be applied analogously to thin layers of glass ceramic, ceramic or glass material.

[0006] Accordingly, according to a first aspect, the present invention relates to a data carrier comprising a ceramic (glass-ceramic or glass) substrate with a first and an opposite second surface and a thickness of at most 500 µm, preferably of at most 200 µm, more preferably of at most 150 µm, wherein the first surface of the substrate has a plurality of laser-ablated depressions that encode information, each depression preferably having a depth of at most 1 µm. Although these ceramic films are mechanically less stable due to their thickness, as they can break, for example, under excessive bending, their resistance to moisture, electromagnetic fields, and acidic or corrosive substances is just as high as that of the ceramic substrates described in WO 2021 / 028035 A1.At the same time, by reducing the thickness of the data carrier by at least a factor of 2 (preferably 5, more preferably 6), the data storage density per volume automatically increases by the same factor.

[0007] The information encoded by the plurality of recesses may be analog and / or digital information. Thus, the plurality of recesses, in conjunction with one another, may form an analog image, text, numbers, or the like. Alternatively, the plurality of recesses may encode digital information, similar to, for example, digital information encoded on a CD, DVD, Blu-ray Disc, or a data matrix code. In any case, the encoded information may preferably be optically decoded, either visually with the naked eye or with the aid of suitable optics such as a microscope or the like, or with the aid of an optical decoder.

[0008] Unlike the information storage medium according to WO 2021 / 028035 A1, the data carrier according to the first aspect of the present invention does not require any additional coating. Since the ceramic foils used for the data carrier of the present invention are sufficiently flexible to be wound onto a roll, it can be challenging under certain conditions to coat the ceramic foil and retain this coating after data encoding and bending of the substrate. Accordingly, it is the substrate of the data carrier according to the first aspect that has the plurality of recesses in which the information is encoded.These depressions are created using a laser beam and can have different shapes and / or depths, as described in detail in WO 2022 / 002418 A1, which is incorporated herein by reference in its entirety, particularly with regard to all information contained therein explaining in detail how information is encoded using the depth of the depressions. In the simplest form of this first aspect, each depression has approximately the same depth, and the optical decoder detects the difference between a substrate area without a depression and a depression, for example, by measuring a phase difference or detecting changes in reflectivity (e.g., if the substrate surface is polished and the bottom of the depression is curved or roughened). In order to distort the thin ceramic film material as little as possible, the depressions should have the smallest possible depth, e.g.at most 100 nm, preferably at most 50 nm and even more preferably at most 30 nm. It is also preferred that the depth of each recess is less than 1%, preferably less than 0.1%, more preferably less than 0.05% of the thickness of the substrate.

[0009] To create well-defined, easily visible depressions, the depressions are preferably created by laser ablation with a picosecond or femtosecond laser. The use of such pulsed lasers results in cylindrical depressions without edges of molten material at the upper perimeter of each depression.

[0010] To further increase data storage density, it is preferred that the second surface of the substrate also comprise a plurality of laser-ablated pits encoding information, each pit having a depth of at most 1 µm and similar properties to those described above. Since the thickness of the substrate is at least two orders of magnitude greater than the depth of each pit, known techniques can be used to distinguish whether the light was reflected from the first surface, from the bottom of a pit on the first surface, or from the opposite second surface.

[0011] According to a second aspect, the present invention relates to a data carrier comprising a ceramic substrate with a first and an opposite second surface and a thickness of at most 500 µm, preferably of at most 200 µm, even more preferably of at most 150 µm, wherein the first surface of the substrate is coated with a first coating, wherein the material of the first coating differs from the material of the ceramic substrate, wherein the first coating has a plurality of laser-ablated depressions that encode information. Compared to the first aspect of the present invention described above, the additional coating offers the advantage of enabling more complex optical effects, which are described in detail in WO 2021 / 028035 A1, the entire content of which is incorporated herein by reference.For example, the material of the first coating may have different optical properties than the ceramic substrate. For example, if the material of the ceramic substrate is light or white in color, while the material of the first coating is dark or black in color, ablating the material of the first coating to create depressions that extend to or even into the ceramic substrate creates a strong optical contrast between the overall surface of the first coating on the one hand and the individual depressions on the other. This contrast may be visible (e.g., to the naked eye) and give the impression of an image, text, or the like, or it may provide a digital encoding (depression versus no depression) that can be easily and reliably decoded by an optical decoder.

[0012] However, with regard to the intended long-term use of the data carrier according to the invention, care must be taken to ensure that the first coating adheres reliably to the ceramic substrate, preferably even when the substrate is bent or wound onto a roll. Therefore, it is preferable to apply a rather thin coating with a thickness of at most 10 µm, preferably at most 1 µm, more preferably at most 200 nm, even more preferably at most 150 nm, even more preferably at most 100 nm, even more preferably at most 50 nm, even more preferably at most 30 nm, and most preferably at most 20 nm. With regard to the optical effect to be achieved, e.g., through optical contrast, it is sufficient to provide a thickness that allows for significant absorption, multiple scattering, reflection, or the like.

[0013] To facilitate the coating process, and especially the decoding process, it is preferable that the average roughness Ra of both the substrate surface and the coating surface be less than 10 nm, preferably less than 5 nm, and more preferably less than 3 nm. Ra is the arithmetic mean of a filtered roughness profile determined from the deviations around the centerline along the evaluation length.

[0014] Since the first coating on the ceramic substrate can lead to stress on the data carrier, it can be advantageous to coat both surfaces of the ceramic substrate to achieve symmetrical stress. It is therefore preferable for the second surface of the substrate to be provided with a second coating, the material of the second coating being different from the material of the ceramic substrate (and preferably identical to the material of the first coating). If a second coating is provided, it can of course also be used to encode additional information, thereby doubling the amount of data to be stored on the data carrier. Accordingly, it is preferred that the second coating also has a plurality of laser-ablated depressions that encode information.

[0015] To ensure a strong bond between the first and second coatings and the ceramic substrate, the data carrier can be annealed during and / or after the coating process. Such annealing can create a sintered interface between the substrate and the first coating and / or between the substrate and the second coating, with the sintered interface improving the bond between the substrate and the coating(s). Preferably, the sintered interface consists of at least one element from the substrate and at least one element from the respective coating.

[0016] As already mentioned, the data carrier according to the second aspect enables an optical contrast or other difference in an optical property between areas with an undisturbed coating and areas with a depression. To this end, it is preferred that each depression in the first and / or second coating has a depth equal to or greater than the thickness of the respective coating. In other words, it is preferred that the coating material at each depression is substantially completely ablated (or evaporated or otherwise removed) to make the ceramic substrate material accessible for optical decoding (e.g., with the naked eye, a microscope, a camera, or a more sophisticated optical decoder). In this context, it would be ideal to precisely remove all of the coating material at a depression location without affecting the ceramic substrate.However, it can be difficult to control this reliably and reproducibly. Accordingly, it may be advantageous to control the laser system used for ablation such that each depression in a first and / or second coating has a depth slightly greater than the thickness of the respective coating. For example, the ratio between the depth of each depression and the thickness of the respective coating may be in a range between 1.01 and 1.2, preferably between 1.01 and 1.1, more preferably between 1.02 and 1.05. Preferably, each depression extends into the ceramic substrate to a depth of at most 1 µm, preferably of at most 100 nm, more preferably of at most 50 nm, even more preferably of at most 30 nm, even more preferably of at most 20 nm, and most preferably of at most 10 nm.

[0017] It may also be advantageous for each depression in the first and / or second coating to have a depth that is smaller than the thickness of the respective coating. For example, the depth of each depression can be optimized so that the depression never touches the ceramic substrate, while at the same time the bottom material beneath the depression of the respective coating is thin enough for laser light of a specific wavelength to at least partially penetrate the coating material and reach the material of the ceramic substrate to achieve the optical contrast described above. For this purpose, it is preferred that the ratio between the depth of each depression and the thickness of the respective coating is in a range between 0.9 and 0.99, preferably between 0.95 and 0.99, more preferably in a range between 0.97 and 0.99.Alternatively, each recess in the first and / or second coating may have a depth that is significantly less than the thickness of the respective coating. In this case, the recesses may be used in a manner similar to the first aspect of the present invention. In other words, the ceramic substrate in this case serves merely as a carrier substrate, with encoding and decoding taking place exclusively on the coating material.

[0018] Preferably, the first and / or second coating consists of one or a combination of the following materials: Cr, Co, Ni, Fe, Al, Ti, Si, W, Zr, Ta, Th, Nb, Mn, Mg, Hf, Mo, V; a metal nitride such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; a metal carbide such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; a metal oxide such as Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; a metal boride such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4 or a metal silicide such as TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi2Mg2Si.

[0019] Of course, all features discussed above with respect to the first aspect that can also be used in connection with the second aspect should also be considered as disclosed for the second aspect. Furthermore, all features discussed below apply equally to both aspects of the present invention.

[0020] Preferably, the ceramic substrate consists of one or a combination of the following materials: silicon oxide, aluminum oxide, boron oxide, sodium oxide, potassium oxide, lithium oxide, zinc oxide, magnesium oxide.

[0021] Preferably, the substrate is transparent for at least one wavelength range in the visible spectrum, preferably across the entire visible spectrum, i.e., between 400 nm and 700 nm, and / or in the UV spectrum, preferably across the entire UV spectrum, i.e., between 100 nm and 400 nm. Preferably, the substrate has a transmittance of at least 80%, preferably of at least 90%, and more preferably of at least 95%, for at least one wavelength range in the visible spectrum, preferably across the entire visible spectrum, i.e., between 400 nm and 700 nm, and / or in the UV spectrum, preferably across the entire UV spectrum, i.e., between 100 nm and 400 nm.

[0022] The data carriers of the present invention can be supplied in thin plates that can be stacked on top of one another. Each data carrier can be, for example, a circular, disc-shaped, rectangular, or square plate, for example, a plate measuring 10 cm x 10 cm. Such plates are easy to handle during encoding and decoding and can be stacked on top of one another, for example, 50 or even 500 plates forming a stack.

[0023] Alternatively, the data carrier can also be an elongated film that can be wound onto a roll. For this purpose, it is particularly advantageous if the substrate (and preferably the entire data carrier) has a modulus of elasticity of at most 80 GPa, preferably at most 75 GPa. It is further preferred that the data carrier does not break at a radius of curvature of 100 mm, preferably 50 mm, more preferably 25 mm, more preferably 10 mm, more preferably 5 mm, and more preferably 2.5 mm. To achieve these mechanical properties, it is preferred to design the data carrier as thin as possible. The thickness of the data carrier is preferably at most 130 µm, more preferably at most 110 µm, even more preferably at most 100 µm, even more preferably at most 90 µm, and most preferably at most 80 µm.

[0024] As already mentioned, the depressions can have any shape and be elliptical, round, rectangular, square, or the like. Various depressions with different shapes can also be used to encode information. However, the simplest and most straightforward method is to create several essentially identical, essentially round depressions using a laser beam, preferably with picosecond or femtosecond laser pulses. These depressions can be arranged in a regular pattern such as a rectangular, square, or hexagonal pattern to encode digital information. Preferably, the diameter of these depressions is as small as possible, but still large enough to allow correct decoding.Preferably, each depression has a maximum extent perpendicular to its depth of at most 1 µm, preferably of at most 500 nm, more preferably of at most 300 nm, even more preferably of at most 200 nm and most preferably of at most 150 nm.

[0025] Preferably, the data carrier has at least 10 megabytes of coded information per cm 2 (per substrate surface), more preferably at least 100 megabytes of coded information per cm 2 and even more preferably at least 1 gigabyte of information per cm 2 .

[0026] Also described is a (non-proprietary) method for producing a data carrier as described above. To produce the data carrier according to the first aspect, a ceramic substrate is provided, and a plurality of depressions are created in one or both surfaces of the substrate by means of laser ablation, preferably with picosecond or femtosecond laser pulses. To produce a data carrier according to the second aspect, a ceramic substrate is provided, one or both surfaces of the substrate are coated with first and / or second coatings, and a plurality of depressions are created in the first and / or second coatings by means of laser ablation, preferably with picosecond or femtosecond laser pulses.

[0027] Laser ablation can be performed, for example, with a pulsed laser, preferably a femtosecond laser. To obtain predominantly cylindrical depressions, a laser beam with a Gaussian or Bessel shape is preferably used.

[0028] Coating one or both surfaces of the substrate with a first and / or second coating can be achieved using various known techniques. Particularly preferred techniques are physical or chemical vapor deposition.

[0029] As already mentioned, annealing can improve the bond between the substrate and the coating. Therefore, the method preferably comprises annealing the coated substrate at a temperature of at least 200°C, preferably at least 500°C, and more preferably at least 1,000°C.

[0030] Alternatively, the ceramic substrate can be treated on one or both surfaces using one or more of the following techniques: heating, sputtering, HiPIMS (High Power Impulse Magnetron Sputtering), and exposure to forming gas such as nitrogen and / or hydrogen. These techniques can improve the surface quality of the substrate and / or result in a stronger bond between the substrate and the coating(s).

[0031] The ceramic substrate is preferably transparent to the wavelength of the laser light used for laser ablation, with laser ablation preferably being performed with laser light transmitted through the ceramic substrate. This prevents debris generated during ablation from interfering with the optics used for ablation, as the data carrier forms a barrier between the ablated material and the optics.

[0032] Also described is a (non-proprietary) method for reading a data carrier as described above. According to the method, the data carrier of the first or second aspect is illuminated with light of a first wavelength. The light transmitted through the data carrier and / or reflected by the data carrier is detected and analyzed to decode the information encoded in the recesses of the data carrier. For example, light passing through the recesses (in the substrate in the case of the first aspect or in the coating in the case of the second aspect) and light blocked on the data carrier where no recess is present (e.g., by the impermeable substrate or the impermeable coating) can, in combination, produce a pattern (light / dark) such as a QR code, which can then be decoded using known techniques.

[0033] The data carrier preferably consists of a ceramic substrate and a coating with laser-ablated depressions on a surface of the ceramic substrate, wherein the ceramic substrate is transparent to the first wavelength and light transmitted through the ceramic substrate is detected. This can be done in both transmission and reflection mode. In particular, the data carrier can preferably be illuminated through the ceramic substrate from the side opposite the coating. Furthermore, the light emanating from the depressions can also be detected through the ceramic substrate from the side opposite the coating. This technique improves the signal-to-noise ratio because the side opposite the coating with the depressions is generally cleaner and / or has a smoother surface, which facilitates imaging.If dust particles are present on the side with the recesses, it is particularly advantageous to illuminate and detect from the opposite side, with the illumination and / or detection focus located at the bottom of the recesses to achieve minimal influence of the dust (or other contaminants) on the optical beam.

[0034] An example of the present invention will now be described in more detail with reference to the figures, which show: ◯ Fig. 1: Transmission micrograph of an exemplary data carrier at 5x magnification; ◯ Fig. 2: Transmission microscopic image of the data carrier from Fig. 1 at 10x magnification; ◯ Fig. 3: Transmission microscopic image of the data carrier from Fig. 1 at 20x magnification; ◯ Fig. 4: Transmission microscopic image of the data carrier from Fig. 1 at 50x magnification; ◯ Fig. 5: Transmission microscopic image of the data carrier from Fig. 1 at 100x magnification; ◯ Fig. 6: Transmission micrograph of another exemplary data carrier labelled with digitally encoded information; and ◯ Fig. 7: Transmission microscopy image of another exemplary data carrier labeled with single-line font of 2-8 µm height.

[0035] For the examples, a 10 mm x 10 mm ceramic substrate consisting of a 100 µm thick sapphire substrate (Al2O3) was coated with a 100 nm thick CrN layer by physical vapor deposition (PVD). Circular pits with a diameter of approximately 1 µm (Example 1) and approximately 500 nm (Examples 2 and 3) were ablated from the coating using a 200 femtosecond laser at a wavelength of 515 nm.

[0036] The resulting data carrier from Example 1 was imaged with an Olympus BX-51 at various magnifications. The corresponding transmission micrographs at 5x, 10x, 20x, 50x, and 100x magnification are shown in the Fig. 1-5 shown.

[0037] As can be seen from the figures, it is possible to reliably and irreversibly create depressions in the coating, thus achieving an excellent optical contrast between the material of the ceramic substrate (which is transparent) and the material of the coating layer (which absorbs light). While the depressions of this example 1 encode analog information, namely the photo of the zebra, it is equally possible to use the various depressions to encode digital information (depression present versus depression absent), as in Fig. 6 (Example 2), or alphanumeric characters, as in Fig. 7 (Example 3). In Example 2, the individual "pixels" are less than 500 nm wide. In Example 3, the line width of the characters is approximately 500 nm.

[0038] The coating and ablation techniques illustrated in the examples above can be applied analogously to a ceramic substrate with a maximum thickness of 200 µm. The same coating can be applied, for example, to the so-called glass ribbon (reference number 2010-03E), available from Nippon Electric Glass. The glass ribbon is available in thicknesses between 4 µm and 50 µm and in lengths up to 100 m. Alumina ribbon ceramic or zirconia ribbon ceramic (both with a thickness of only 20 µm), available from Corning, can also be used. Other suitable and particularly preferred materials are: AGC Spool, AGC Dragontrail, Corning® Willow® Glass, Corning standard glass supports SGC 3.4, SGC 7.8 and SGC 9.0, Nippon Electric Glass - G-Leaf (ultra-thin glass), SCHOTT AS 87 eco, SCHOTT AF 32 Eco and SCHOTT Xensation® Flex. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 10,719,239 B2

[0002] WO 2021 / 028035 A1 [0003, 0005, 0006, 0008, 0011] WO 2022 / 002418 A1

[0008]

Claims

[1] A data carrier comprising a ceramic substrate having a first and an opposite second surface and a thickness of at most 500 µm, the first surface of the substrate having a plurality of laser-ablated depressions encoding information, each depression having a depth of at most 1 µm. [2] The data carrier according to claim 1, wherein the thickness of the data carrier is at most 200 µm, preferably at most 150 µm. [3] The data carrier according to claim 1 or 2, wherein the second surface of the substrate has a plurality of laser-ablated depressions encoding information, each depression having a depth of at most 1 µm. [4] The data carrier according to claim 1, 2 or 3, wherein each depression has a depth of at most 100 nm, preferably of at most 50 nm and / or wherein the depth of each depression is less than 1%, preferably less than 0.1%, more preferably less than 0.05% of the thickness of the substrate. [5] A data carrier comprising a ceramic substrate having a first and an opposite second surface and a thickness of at most 500 µm, wherein the first surface of the substrate is coated with a first coating, the material of the first coating being different from the material of the ceramic substrate, the first coating comprising a plurality of laser-ablated pits encoding information. [6] The data carrier according to claim 5, wherein the thickness of the ceramic substrate is at most 200 µm, preferably at most 150 µm. [7] The data carrier according to claim 5 or 6, wherein the second surface of the substrate is coated with a second coating, the material of the second coating being different from the material of the ceramic substrate, the second coating comprising a plurality of laser-ablated pits encoding information. [8] The data carrier according to claim 5, 6 or 7, wherein the thickness of the first and / or second coating is at most 10 µm, preferably at most 1 µm, more preferably at most 100 nm, even more preferably at most 50 nm. [9] The data carrier according to any one of claims 5 to 8, wherein each depression in the first and / or second coating has a depth of at most 10 µm, preferably at most 1 µm, more preferably at most 100 nm, even more preferably at most 50 nm. [10] The data carrier according to any one of claims 5 to 9, wherein each depression in the first and / or second coating has a depth that is less than the thickness of the respective coating; or wherein each depression in the first and / or second coating has a depth that is substantially equal to the thickness of the respective coating; or wherein each depression in the first and / or second coating has a depth that is greater than the thickness of the respective coating. [11] The data carrier according to claim 10, wherein each recess extends into the substrate with a depth of at most 1 µm, preferably of at most 100 nm, more preferably of at most 50 nm. [12] The data carrier according to any one of claims 5 to 11, wherein a sintered interface is present between the substrate and the first coating and / or between the substrate and the second coating, wherein the sintered interface preferably comprises at least one element from the substrate and at least one element from the respective coating. [13] The data carrier according to one of claims 5 to 12, wherein the first and / or the second coating comprises one or a combination of the following materials: a metal such as Cr, Co, Ni, Fe, Al, Ti, Si, W, Zr, Ta, Th, Nb, Mn, Mg, Hf, Mo, V; a metal nitride such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; a metal carbide such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; a metal oxide such as Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; a metal boride such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; or a metal silicide such as TiSi2, ZrSi2, MoSi2, MoSi, WSi2, PtSi2, Mg2Si. [14] The data carrier according to any one of the preceding claims, wherein the ceramic substrate comprises one or a combination of the following materials: silicon oxide, aluminum oxide, boron oxide, sodium oxide, potassium oxide, lithium oxide, zinc oxide, magnesium oxide. [15] The data carrier according to any one of the preceding claims, wherein the data carrier is wound on a roll.

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