Method for long-term storage of information and storage medium therefor

Abstract

The present invention relates to an information storage medium and a method for long-term storage of 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, the layer having a thickness no greater than 10 μm; tempering the coated ceramic substrate to form a writable plate or disc; encoding information on the writable plate or disc by using a laser and/or a focused particle beam to manipulate localized areas of the writable plate or disc.

Claims

1. A method for storage of information comprising: providing a ceramic substrate comprising a first material; coating the ceramic substrate with a layer of a second material different from the first material of the ceramic substrate, the layer having a thickness no greater than 10 μm, wherein the second material comprises a metal carbide, a metal oxide, a metal nitride, a metal silicide, or a metal boride; tempering the coated ceramic substrate to form a writable plate; and encoding information on the writable plate by using a laser and/or a focused particle beam to manipulate localized areas of the writable plate.

2. The method of claim 1, wherein the ceramic substrate first material comprises an oxidic ceramic.

3. The method of claim 1, wherein the first material comprises a non-oxidic ceramic.

4. The method of claim 1, wherein the first material comprises one or a combination of Ni, Cr, Co, Fe, W, Mo.

5. The method of claim 1, wherein the first material comprises a ceramic material and a metal that form a metal matrix composite.

6. The method of claim 1, wherein physical vapor deposition, sputtering, or chemical vapor deposition is used to coat the ceramic substrate with the layer of the second material.

7. The method of claim 1, wherein manipulating the localized areas of the writable plate comprises heating, decomposing, oxidizing, ablating or vaporizing the localized areas.

8. The method of claim 1, wherein manipulating the localized areas of the writable plate causes the layer of the second material to be at least partly removed from the localized areas of the writable plate.

9. The method of claim 1, wherein tempering the coated ceramic substrate generates a sintered interface between the ceramic substrate and the layer of the second material.

10. The method of claim 1, wherein tempering the coated ceramic substrate causes oxidation of at least a topmost sub-layer of the layer of the second material.

11. The method of claim 10, wherein manipulating the localized areas of the writable plate causes the oxidized sub-layer to be at least partly removed from the localized areas of the writable plate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the attached drawings, in which:

(2) FIG. 1 schematically depicts an information storage medium for long-term storage of information;

(3) FIG. 2 schematically depicts an example of the process of physical vapor deposition coating of the ceramic substrate;

(4) FIG. 3 schematically shows a perspective view of an example of encoding the writable plate with information using a laser; and

(5) FIG. 4 shows a photograph of an inscribed product according to an example.

(6) In principle, identical parts are provided with the same reference signs in the figures.

DETAILED DESCRIPTION

(7) FIG. 1 illustrates a schematic version of the information storage medium 100 according to the present invention. The information storage medium 100 includes a writable plate 110. In this example the writable plate 110 has been encoded with information 120.

(8) In order to produce such an information storage medium 100, a method for long-term storage of information is described herein. Initially, a ceramic substrate 150 (see FIG. 3) is provided, then the ceramic substrate 150 is coated with a layer of a second material 170. The layer of second material 170 is no greater than 50 μm thick. After coating the ceramic substrate 150 and the second material 170 are subjected to a tempering process to form a writable plate 110. The writable plate may either be stored until ready for use or may subsequently be encoded with information 120 using, e.g., a laser 190. The laser 190 is directed toward the layer of second material 170 and then, e.g., heats localized areas of the second material 170 which fall within the beam of the laser beam such that these localized areas then become, e.g., optically distinguishable from the surrounding second material 170. This method will now be described in more detail.

(9) The ceramic substrate 150 which is initially provided may comprise the majority of the material by weight of the writable plate 110. A number of different materials may be used for the ceramic substrate 150. In certain configurations the ceramic substrate 150 comprises an oxidic ceramic comprising at least one of Al.sub.2O.sub.3, TiO.sub.2, SiO.sub.2, ZrO.sub.2, ThO.sub.2, MgO, Cr.sub.2O.sub.3, Zr.sub.2O.sub.3, V.sub.2O.sub.3 or any other oxidic ceramic material. Alternatively, the ceramic substrate may comprise a non-oxidic ceramic comprising at least one of a metal nitride such as CrN, CrAlN, TiN, TiCN, ZrN, AlN, VN, Si.sub.3N.sub.4, ThN, HfN, BN; metal carbide such as TiC, CrC, Al.sub.4C.sub.3, VC, ZrC, HfC, ThC, B.sub.4C, SiC; a metal boride such as TiB.sub.2, ZrB.sub.2, CrB.sub.2, VB.sub.2, SiB.sub.6, ThB.sub.2, HfB.sub.2, WB.sub.2, WB.sub.4 and a metal silicide such as TiSi.sub.2, ZrSi.sub.2, MoSi.sub.2, WSi.sub.2, PtSi, Mg.sub.2Si, or any other non-oxidic ceramic material. The amount of the oxidic or non-oxidic ceramic present may vary. Preferably the amount of oxidic or non-oxidic ceramic makes up at least 90% by weight of the ceramic substrate 150. More preferably the amount of the oxidic or non-oxidic ceramic substrate makes up at least 95% by weight of the ceramic substrate 150. One preferred configuration is a ceramic substrate 150 comprising at least 90% Al.sub.2O.sub.3 measured by weight.

(10) The second material 170 is formed as a layer on the ceramic substrate 150. The layer of second material 170 is a thin layer in comparison with the thickness of the ceramic substrate 150, the second layer 170 being at most 50 μm thick. The second material 170 may principally comprise at least one of 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, Si.sub.3N.sub.4, ThN, HfN, BN; a metal carbide such as TiC, CrC, Al.sub.4C.sub.3, VC, ZrC, HfC, ThC, B.sub.4C, SiC; a metal oxide such as Al.sub.2O.sub.3, TiO.sub.2, SiO.sub.2, ZrO.sub.2, ThO.sub.2, MgO, Cr.sub.2O.sub.3, Zr.sub.2O.sub.3, V.sub.2O.sub.3; a metal boride such as TiB.sub.2, ZrB.sub.2, CrB.sub.2, VB.sub.2, SiB.sub.6, ThB.sub.2, HfB.sub.2, WB.sub.2, WB.sub.4; a metal silicide such as TiSi.sub.2, ZrSi.sub.2, MoSi.sub.2, WSi.sub.2, PtSi, Mg.sub.2Si or any other ceramic material; preferably wherein the second material comprises CrN and/or CrAlN.

(11) One preferred configuration is a layer of second material 170 comprising principally CrN and/or CrAlN. Importantly, the material used for the second layer 170 provides a sufficient degree of, e.g., optical contrast with the material of the ceramic substrate 150 after tempering.

(12) The degree of optical contrast may be visible to a human observer in terms of color and/or brightness. Alternatively, the optical contrast may be detected by an automated system in non-visible wavelengths. The localized areas may then be optically distinguishable by means of an optical reader or scanner being sensitive in the respective portion of the spectrum. The optical contrast may be measured using Weber contrast, wherein the Weber contrast fraction of the information encoded on the writable plate is preferably at least 1%, more preferably at least 3%, more preferably at least 5%. However, in other instances (in particular, if the encoded structures are too small) the localized areas may only be distinguished from the surrounding material by means of, e.g., a scanning electron microscope or measurement of another physical parameter change.

(13) FIG. 2 illustrates an exemplary method for coating the second material 170 onto the ceramic substrate 150 using physical vapor deposition (PVD). In the PVD process the ceramic substrate 150 is placed into a physical vapor deposition chamber together with a source of second material 160. A vacuum is drawn on the physical vapor deposition chamber and the source of second material 160 is heated until a significant portion of the second material 162 contained therein is evaporated or sublimated. The airborne particles 164 of second material then disperse throughout the physical vapor deposition chamber until they contact a surface 152 of the ceramic substrate 150 and adhere thereto.

(14) Although physical vapor deposition is a method commonly used for coating metal substrates, coating ceramic substrates can prove challenging for particles to adhere to. Thus, in order to improve adherence of second material particles 164 to the ceramic substrate surface 152, a conductive wire mesh or conductive metal plate 180 may be placed on the far side of the ceramic substrate 150, such that the ceramic substrate 150 is positioned in between the wire mesh 180 and the source of second material 160. Such a conductive mesh/plate 180 when conducting current may attract ionized particles of second material 164 which then encounter the surface 152 of the ceramic substrate 150 and are held there against such that they then adhere to the surface 152 of the ceramic substrate. This coating process may also be repeated in order to coat multiple different surfaces of the ceramic substrate.

(15) Depositing a layer of second material 170 on the ceramic substrate 150 may be performed using other coating methods, such as sputtering or sublimation sandwich coating. Essentially, any method capable of producing a layer of second material 170 maximally 50 μm thick may be used. Preferably the layer of second material may have a thickness of maximally 10 μm. More preferably the second material 170 may have a maximal thickness of 5 μm. Even more preferably, the second material 170 may have a maximal thickness of 1 μm, even more preferably no greater than 100 nm, even more preferably no greater than 10 nm. A thin layer of second material 170 may be advantageous in that laser or particle beam ablation of the writable plate 110 may then be easier, resulting in a faster, less energy-intensive encoding process. The second material 170 may not necessarily cover the entire ceramic substrate 150. Instead only portions of the ceramic substrate 150 or a singular side 152 of the ceramic substrate 150 may be coated with the second material 170.

(16) Once the ceramic substrate 150 is coated with a second material 170, the coated ceramic substrate then undergoes a tempering process. Tempering is generally understood to be a process which improves the strength and/or other qualities of a material. In the case of ceramics, tempering can involve heating a ceramic item such that the chemical components thereof undergo chemical and/or physical changes such that the item becomes fixed or hardened. Tempering of the coated ceramic substrate may involve heating the coated ceramic substrate 150 to a temperature within a range of 200° C. to 4000° C., preferably within a range of 1000° C. to 2000° C. The tempering process may comprise a heating phase with a temperature increase of at least 10 K per hour, a plateau phase at a peak temperature for at least 1 minute and finally a cooling phase with a temperature decrease of at least 10 K per hour. The tempering process may assist in fixing the second material 170 permanently to the ceramic substrate 150. In some cases, a portion of the second material layer 170 may form a chemical bond to the underlying ceramic substrate 150. After tempering the ceramic substrate 150 with the second material 170, the writable plate 110 is formed. The properties of the writable plate 110 are determined by the exact materials used within the writable plate 110. The writable plate 110 may now be stored or directly encoded with information 120.

(17) FIG. 3 depicts the encoding of information onto the writable plate 110. During encoding, a laser 190 directs collimated laser light onto a layer of second material 170 of the writable plate 110. The laser beam alters the portion of second material 170 within the localized area 175 such that it is (optically) distinguishable from the surrounding second material 170. Preferably the laser or focused particle beam heats the localized area 175 of the second material 170 to at least the melting temperature of the second material 170. The melting point of the second material 170 is dependent on the chemical composition thereof. Preferably, heating the localized areas 175 past the melting point may involve heating the localized areas to a temperature of at least 3,000° C., more preferably at least 3,200° C., and even more preferably at least 3,500° C., most preferably at least 4,000° C. Imparting these localized areas with such high temperatures may cause a rapid expansion of the second material 170 within the localized areas 175. This rapid expansion can cause the second material 170 within the localized areas 175 to be ablated and/or vaporized. As the second material 170 provides an optical contrast to the underlying ceramic substrate 150, the localized areas 175 can be formed by the laser or focused particle beam into symbols, letters, lines, photographs, pictures, images, graphics or other forms, thereby encoding information into the writable plate 110. Preferably, the encoded information 120 relative to the rest of the second material 170 exhibits a Weber contrast fraction of at least 1%, more preferably at least 3%, more preferably at least 5%. In a preferred configuration the second material 170 after tempering exhibits an opaque gray/black color and the ceramic substrate 150 exhibits a yellow/white color. Thus, following laser or focused particle beam encoding, the information storage medium 100 exhibits white lettering/symbols relative to a dark background.

(18) Suitable laser wavelengths for the laser encoding methods may include a wavelength within a range of 10 nm to 30 μm, preferably within a range of 100 nm to 2000 nm, more preferably within a range of 200 nm to 1500 nm. Of further importance is the minimum focal diameter of the laser light or focused particle beam which dictates the minimum size of symbols, letters, photographs, pictures, images, graphics and/or other forms which can be encoded on the writable plate 110. Preferably the laser or focused particle beam 190 is capable of focusing the laser light or focused particle beam to have a minimum focal diameter no greater than 50 μm, preferably no greater than 15 μm, more preferably no greater than 10 μm. Under such conditions a resolution of 2,500 dpi is possible, enabling the encoding of 5,000 symbols/letters within a space of 1 cm.sup.2. This can also result in being able to print 1000 pages of a book (˜2 million symbols/letters) with 2,000 letters per page within a single 20 cm×20 cm writable plate.

(19) Reading out the encoded text can be performed by eye if the letters/symbols are large enough. Preferably the encoded information could be read out through using a digital scanner using methods such as optical character recognition (OCR) among other methods. Such a digital scanner can quickly and accurately reproduce the encoded information in a size more accessible for human reading. As previously mentioned, the information 120 may be encoded on the writable plate 110 using a number of different formats. The information 120 may be encoded in a human-readable format using letters, symbols, photographs, pictures, images, graphics and/or other forms. The information 120 may also be encoded in a computer-readable format using, for instance, a QR code or an iQR code and or any other digital coding and encryption method. The use of such computer-readable encoding methods may serve to further increase the information density of the information storage medium 100. For example, the iQR code can enable 40,000 characters to be stored within 1 cm.sup.2, or equivalently 8-16 megabytes on a 20 cm×20 cm writable plate. Preferably the writable plate can store a minimum of 1 kilobyte of information per cm.sup.2, more preferably at least 10 kilobytes of information per cm.sup.2, and even more preferably at least 100 kilobytes of information per cm.sup.2, even more preferably at least 1 Megabytes of information per cm.sup.2, even more preferably at least 10 Megabytes of information per cm.sup.2, even more preferably at least 100 Megabytes of information per cm.sup.2, even more preferably at least 1 Gigabytes of information per cm.sup.2, even more preferably at least 10 Gigabytes of information per cm.sup.2.

(20) For ease of reading and/or scanning, information may be encoded onto the writable plate within distinct blocks. These blocks of information, indicated as B in FIG. 1, are preferably no larger than 100 mm by 100 mm, more preferably no larger than 24 mm by 36 mm, more preferably no larger than 10 mm by 10 mm, more preferably no larger than 1 mm by 1 mm, more preferably no larger than 0.1 mm by 0.1 mm.

(21) The form of the writable plate 110 can be determined by the needs of the user and the types of information 120 to be encoded. In some instances, the writable plate 110 can be formed in a tablet shape for storage, preferably no larger than 200 mm by 200 mm, more preferably no larger than 100 mm by 100 mm, more preferably no larger than 10 mm by 10 mm. In other instances a computer readable disk-shape may be preferable with a diameter no larger than 30 cm, more preferably no larger than 12 cm, more preferably no larger than 8 cm.

(22) The information storage medium 100 according to the present invention is resistant to environmental degradation and is preferably able to withstand temperatures between −273° C. (0° K) and 1200° C. without suffering information loss. The information storage medium 100 may also resist electro-magnetic pulses, water damage, corrosion, acids and/or other chemicals. It is envisioned that the information storage medium 100 as herein described could preserve information 120 for a time period of at least 1000 years, preferably at least 10,000 years, more preferably at least 100,000 years. Under certain conditions of storage, including storage of the information storage medium 100 within an underground salt dome, the information storage medium may be able to preserve information for at least 1 million years.

(23) One particularly preferred example will be described in the following.

(24) A ceramic substrate made of Rubalit 708s containing at least 96% Al.sub.2O.sub.3 having the dimensions of 20 cm×20 cm available at CeramTec GmbH (Germany) was used as the raw material.

(25) A plate of said ceramic substrate having the size of 10 cm×10 cm and a thickness of 1 mm was coated with a layer of CrN using physical vapor deposition. For this purpose, the ceramic plate was mounted on an electrically conductive plate made from steel with a size of 10 cm×10 cm. The ceramic plate together with the electrically conductive plate was brought into a physical vapor deposition machine available from Oerlikon Balzers AG (Lichtenstein).

(26) Physical vapor deposition was then performed using the enhanced sputtering process BALI-NIT® CNI from Oerlikon Balzers AG at a process temperature below 250° C.

(27) After the deposition, a layer of CrN with a constant thickness of 3 μm was present on one side of the ceramic substrate (opposite to the side facing the electrically conductive plate).

(28) Subsequently, the coated ceramic substrate was tempered in a batch furnace model “N 150/H” available from Nabertherm GmbH. For tempering, the temperature was ramped up from room temperature (20° C.) to 1,000° C. within 2 h. The temperature was then increased with a rate of 100 K/h from 1,000° C. to 1,200° C. and the maximum temperature of 1,200° C. was maintained for 5 min. Subsequently, the substrate was cooled down with a rate of −200 K/h over 6 h.

(29) After tempering, the stack of material comprised the ceramic substrate, a coating layer of CrN having a thickness of about 2-2.5 μm and a further metal oxide layer of Cr.sub.2O.sub.3 having a thickness of about 0.5-1 μm. Similar metal oxide layers have been described in Z. B. Qi et al. (Thin Solid Films 544 (2013), 515-520).

(30) The metal oxide surface had a darkish, almost black appearance.

(31) Using a ProMarker 100 laser available from Trotec Laser GmbH (Austria) a text with single line font and a QR code was written into the two upper coatings. For this purpose, pulses of 100 ns at a wavelength of 1064 nm with a power of maximal 5W were applied at a frequency of 20 kHz.

(32) The laser light was focused by a lens with a focal length of 100 mm. The focus of the laser light had a width of about 25 μm yielding encoded structured of a width of about 15 μm or 1,750 dpi micro inscription.

(33) The encoded lines/surfaces had a light, almost white appearance and were clearly visible vis-à-vis the dark metal oxide surrounding surface. A photograph showing a detail of the inscribed product is shown in FIG. 4.

(34) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and non-restrictive; the invention is thus not limited to the disclosed embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. 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 may mean “at least one”.