Data recording on ceramic materials

Abstract

The invention relates to a method for recording data in a layer of ceramic material and to a device for recording data in a layer of ceramic material.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for recording data in a layer of a ceramic material and to an apparatus for recording data in a layer of a ceramic material. BACKGROUND

[0002] The applicant of the present invention has developed a method for long-term storage of information and a storage medium thereof (see PCT / EP2019 / 071805 and PCT / EP2020 / 068892). According to one aspect of the method for long-term storage of information, information is encoded on a writable board comprising a ceramic material by manipulating local areas of the writable board using a laser beam. While this method can in principle be performed with a laser beam having a fixed focus by mounting the writable board on an XY positioning system and moving those local areas of the writable board to the laser focus point to be encoded, the method is tedious and time consuming.

[0003] US 4,069,487 and US 4,556,893 also disclose laser recordable recording media utilizing recording layer materials such as metal oxides and metal carbides. However, the recording in both cases is based on a rotating disc technology which is disadvantageous due to the slow recording process resulting from the fact that pits have to be produced one after the other along a recording spiral. SUMMARY

[0004] It is therefore an object of the present invention to provide an improved method for recording data in a layer of a ceramic material which is suitable for recording large amounts of data in a relatively short time.

[0005] This object is achieved by the method as claimed in claim 1 and the apparatus as claimed in claim 23. Preferred embodiments of the invention are described in the dependent claims.

[0006] The present invention therefore relates to a method for recording data in a layer of a ceramic material. According to the method, a layer of a ceramic material is provided and a digital micromirror device (DMD) is used to selectively irradiate a plurality of regions of the layer of the ceramic material with a laser beam. The parameters of the laser beam and the irradiation time for each of the selected regions are such that each of the selected regions is ablated in order to record data in the layer of the ceramic material by creating recesses in the layer of the ceramic material.

[0007] The laser beam is preferably derived from a picosecond laser or a femtosecond laser. The use of a picosecond laser or a femtosecond laser is very advantageous for producing well-defined recesses. The ablation technique disclosed in US 4,556,893 uses a focused modulated laser diode beam which, depending on the laser power, produces pits or bubbles. Since the recording layer material is light-absorbing, this layer is locally heated and thus melts and / or evaporates. However, these processes are rather uncontrolled and often lead to disadvantageous hole shapes. For example, as also indicated in US 4,556,893, a ring of melted and subsequently solidified material can be formed around the edges of the hole. This is unacceptable when producing very small recesses in order to increase the data density, since it is necessary to reproducibly produce these recesses and to allow reproducible readout techniques. Figure 4

[0008] The inventors of the present invention have performed numerous experiments with different ablation techniques for ceramic materials. It turned out that the use of a picosecond laser or a femtosecond laser allows to produce very well-defined holes with a circular cross-section and very sharp edges. It is believed that this is due to the ablation process induced by a picosecond laser or a femtosecond laser. The picosecond or femtosecond laser pulse does not heat the ceramic material but interacts with the electrons of the material. It is assumed that the picosecond or femtosecond laser pulse interacts with the valence electrons responsible for the chemical bonding, which are thus stripped from the atom, leaving the latter positively charged. Given the mutual repulsion between the atoms whose chemical bonds are broken, the material "explodes" into a small cloud of high-energy ion plasma with a speed higher than the speed seen in thermal emission. This phenomenon is called Coulomb explosion and is clearly different from regular laser ablation with e.g. nanosecond lasers, which heat the material on the surface to melt and evaporate, leaving melted material at the edges of the impact area. The Coulomb explosion is a physical process which is clearly limited to the laser impact area only, whereas heat-induced ablation is affected by an undefined heat flow within the material. Therefore, in terms of producing a large number of small recesses, this Coulomb explosion is ideal, allowing a drastic increase in data density compared to known techniques. While good results can be obtained with a picosecond laser, the use of a femtosecond laser is advantageous in this respect. Therefore, the laser preferably has a pulse duration of less than 10 ps, more preferably less than 1 ps.

[0009] Preferably, the fluence of each of the plurality of laser beams emitted by the DMD is greater than 100 mJ / cm 2 , preferably greater than 400 mJ / cm 2 , more preferably greater than 800 mJ / cm 2 , most preferably greater than 1 J / cm 2 .

[0010] ​In the context of the present invention, the term "recess" relates to a hole, groove or indentation in the ceramic material. In other words, a recess forms a volume, without any ceramic material being present. This volume is in fluid communication with the atmosphere. In other words, each recess is open to the atmosphere, without being covered or closed.

[0011] This open recess is advantageous with respect to the technique described in US 4,069,487 of using a protective layer that covers the information recording portion, because the open recess allows a clean and complete ablation of the material that is already present in the recess before ablation. In particular, this is important when very small recesses are created in order to increase the data density, since these recesses need to be reproducibly created and allow a reproducible read-out technique.

[0012] The DMD comprises an array or matrix of micromirrors that allow a predetermined pixel on the ceramic material to be selectively illuminated by adjusting the corresponding micromirror of the array or matrix. Thus, a large number of pixels on the ceramic material can be illuminated simultaneously and in a well-controlled manner, which can easily be automated. Depending on the number of micromirrors present in the DMD, millions of selected areas (i.e. pixels) of the layer of ceramic material can be simultaneously manipulated during the time span sufficient to ablate one selected area in order to record data. These digital micromirror devices are readily available and can be easily implemented into the recording device.

[0013] Preferably, the pixels on the ceramic material (i.e. predetermined positions at which a subset of recesses can be formed) are configured in a regular matrix or array, i.e. in a repeating two-dimensional pattern having a lattice structure or lattice-like structure. Particularly preferred matrices or arrays include, for example, a square pattern or a hexagonal pattern. These matrices or arrays allow an optimal data density that is substantially greater than the data density of, for example, a CD, DVD or Blu-ray disc, since the individual pixels or bits are not separated by a track pitch (e.g. 320 nm for a Blu-ray disc) that is more than twice the size of a single pixel of the bit size (e.g. 150 nm for a Blu-ray disc). The known disc-shaped recording media are also limited in terms of the maximum rotational speed that can be safely achieved during recording or reading. Thus, the writing / reading speed that can be achieved with these matrices or arrays is much greater than the writing / reading speed that is possible in the case of pits configured in a spiral shape.

[0014] Preferably, the recesses have a circular cross-section. The recesses can extend only partially into the layer of ceramic material or can form a through-hole in the layer of ceramic material. In the former case, recesses or holes of different depths can be produced, wherein each depth corresponds to a predefined bit of information as described in PCT / EP2020 / 068892. To this end, the layer of ceramic material can be irradiated with two or more laser pulses, wherein the micromirrors of the DMD are adjusted between subsequent pulses in order to achieve regions of the layer of ceramic material which are (i) never irradiated, (ii) irradiated once with a single laser pulse, (iii) irradiated twice with two laser pulses, etc.

[0015] The applicants have previously shown in experiments that a CrN layer with a thickness of 5 pm can be manipulated significantly and reliably by a single femtosecond laser pulse (see PCT / EP2020 / 068892). Thus, the method of the present invention allows to encode at least several thousand and up to several million pixels within a few hundred femtoseconds. Thus, the recording speed of the method of the present invention is limited only by the number of micromirrors of the DMD and the time required to adjust the micromirrors.

[0016] Preferably, the layer of ceramic material is moved or translated laterally during recording, e.g. by an XY positioning system such as a scanning stage, wherein the z-axis is perpendicular to the surface of the layer. Thus, once a pixel array or matrix has been recorded, an adjacent pixel array or matrix can be recorded by simply moving the layer of ceramic material to an adjacent region.

[0017] Thus, the method of the present invention preferably comprises the steps of selectively irradiating a plurality of regions within a first region of the layer of ceramic material with the laser beam using the DMD, wherein the first region can be covered by the DMD; translating the layer of ceramic material such that a second region different from the first region can be covered by the DMD; and selectively irradiating a plurality of regions within the second region of the layer of ceramic material with the laser beam using the DMD.

[0018] If the DMD and the XY positioning system are suitably controlled, data recording speeds of at least 10 MB / s, preferably at least 100 MB / s, preferably at least 1 GB / s and more preferably at least 10 GB / s can be achieved.

[0019] Preferably, the laser beam (i.e. the plurality of laser beams emitted from the DMD) is focused onto the layer of ceramic material by a lens (or a more complex optical device) having a high numerical aperture, preferably a numerical aperture of at least 0.5, more preferably at least 0.8. Preferably, immersion optics are used in order to further increase the numerical aperture. If immersion optics are used, the numerical aperture can be at least 1.0, preferably at least 1.2.

[0020] It is further preferred to make use of beam shaping devices to generate certain beam shapes that are advantageous for data recording. For example, a matrix of laser zone plates can be transmitted by the multi-beam laser beam originating from the DMD. These laser zone plates can be adapted to generate needle Bessel beams for each of the multi-beam laser beams, for example.

[0021] Bessel beams have the advantage of substantially increasing the depth of focus. The focal length of a regular Gaussian beam is about the wavelength of the focused light, whereas with Bessel beams a focal length can be achieved that is at least 4 times the wavelength of the focused light. At the same time, the width of the focal point is about half the width of the focal point that can be achieved with Gaussian beams.

[0022] In general, the size of the features that can be achieved by the method of the present application (e.g. the diameter of the recesses in the ceramic material) varies between 2 / 3 λ (air) and 1 / 2 λ (immersion) for Gaussian beams and between 1 / 3 λ (air) and 1 / 4 λ (immersion) for Bessel beams (where λ is the wavelength of the laser light). Thus, the advantage of the Bessel beam shape is that smaller process features can be achieved and, thus, a larger recording data density can be achieved. Furthermore, the increased focal length of the Bessel beam has the advantage that, for example, deeper recesses can be generated. This is particularly relevant if features of different depths are to be generated in order to encode information by, for example, the depth of the recesses. Since the focal point of a Gaussian beam is conical, increasing the depth of the recesses means increasing the diameter of the recesses at the surface. In contrast, the more cylindrical focal point of the Bessel beam allows for the generation of deeper recesses with almost constant diameter.

[0023] These Bessel beams can also be generated by other beam shaping devices. One particularly preferred example of a beam shaping device is a spatial light modulator, which is particularly versatile in use, since it can be used to generate Bessel beams to allow for optical proximity control and to provide a phase shift mask.

[0024] Preferably, the layer of ceramic material comprises: metal nitrides such as CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si3N4, ThN, HfN, BN; and / or metal carbides such as TiC, CrC, Al4C3, VC, ZrC, HfC, ThC, B4C, SiC; and / or metal oxides such as Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; and / or metal borides such as TiB2, ZrB2, CrB2, VB2, SiB6, ThB2, HfB2, WB2, WB4; and / or metal silicides such as TiSi2, ZrSi2, MoSi2, WSi2, PtSi, Mg2Si. Particularly preferred materials are B4C, HfC, Cr2O3, ZrB2, CrB2, SiB6, Si3N4, ThN, CrN and CrAlN. These materials provide sufficient hardness and resistance to environmental degradation for long-term storage of recorded data.

[0025] Preferably, the step of providing a layer of ceramic material comprises providing a substrate and coating the substrate with a layer of ceramic material that is different from the material of the ceramic substrate. Thus, only a small amount of possibly expensive coating material is required, while structural integrity is achieved with a robust and possibly inexpensive substrate. The layer of ceramic material preferably has a thickness of no more than 10 μιη, more preferably no more than 5 μιη, more preferably no more than 2 μιη, more preferably no more than 1 μιη, even more preferably no more than 100 nm and most preferably no more than 10 nm.

[0026] Preferably, the substrate has a thickness of less than 1 mm, preferably less than 250 μιη, more preferably less than 200 μιη and most preferably less than 150 μιη.

[0027] Furthermore, the use of a substrate can allow for creating an optical contrast between the substrate (where the holes are created in the coating) and the surrounding coating material. Thus, using a digital micromirror device to selectively irradiate a plurality of regions of the layer of ceramic material with a laser beam preferably comprises fusing away sufficient material at each of the regions where the recesses extend towards the substrate. Preferably, the manipulation of the selected regions makes these regions distinguishable from the surrounding material. For some applications, this can include obtaining optical distinguishability. However, in other cases (in particular, if the encoded structures are too small), these regions can only be distinguishable from the surrounding material by, for example, scanning electron microscopy or other measurements of physical parameters such as magnetic, dielectric or conductive properties.

[0028] Preferably, the ceramic substrate comprises an oxidic ceramic, more preferably the ceramic substrate comprises at least 90%, best at least 95% by weight of one or a combination of: AI2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3. These materials are known to be particularly durable and / or resistant to environmental degradation in various cases. Thus, these materials are particularly suitable for long-term storage under different conditions. It is particularly preferred that the ceramic substrate comprises one or a combination of: sapphire (AI2O3), silicon dioxide (SiO2), zirconium silicate (Zr(SiO4)), zirconium oxide (ZrO2), boron monoxide (B2O), boron trioxide (B2O3), sodium oxide (Na2O), potassium oxide (K2O), lithium oxide (Li2O), zinc oxide (ZnO), magnesium oxide (MgO).

[0029] Preferably, the ceramic substrate comprises a non-oxidic ceramic, more preferably the ceramic substrate comprises at least 90%, best at least 95% by weight of one or a combination of: metal nitrides such as CrN, CrAIN, TiN, TiCN, TiAIN, ZrN, AIN, VN, Si3N4, ThN, HfN, BN; metal carbides such as TiC, CrC, AI4C3, 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, WSi2, PtSi, Mg2Si. These materials are known to be particularly durable and / or resistant to environmental degradation in various cases. Thus, these materials are particularly suitable for long-term storage under different conditions. It is particularly preferred that the ceramic substrate comprises one or a combination of: BN, CrSi2, SiC and SiB6.

[0030] 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 1400 °C. Preferably, the ceramic material forms a metal matrix composite with the metal, wherein the ceramic material is dispersed in the metal or metal alloy. Preferably, the metal constitutes 5 to 30%, preferably 10 to 20% by weight of the ceramic substrate (i.e. the metal matrix composite). Particularly preferred metal matrix composites are: WC / Co-Ni-Mo, BN / Co-Ni-Mo, TiN / Co-Ni-Mo and / or SiC / Co-Ni-Mo.

[0031] The layer of ceramic material is preferably coated directly onto the ceramic substrate, i.e. without any intermediate layer, in order to achieve a strong bond between the ceramic substrate and the layer of ceramic material. The coated ceramic substrate is preferably tempered before and / or after recording in order to achieve this strong bond. The tempering can create a sintered interface between the ceramic substrate and the layer of ceramic material. The sintered interface can comprise at least one element from both the substrate material and the ceramic material, since one or more elements from one of the two adjacent layers can diffuse into the other of the two adjacent layers. The presence of a sintered interface can further strengthen the bond between the ceramic substrate and the layer of ceramic material.

[0032] 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 comprise a heating phase with a temperature increase of at least 10 K per hour, a plateau phase at the peak temperature for at least 1 minute and a cooling phase with a temperature decrease of at least 10 K per hour. The tempering process can help to harden the ceramic substrate and / or to permanently bond the ceramic material to the ceramic substrate.

[0033] Laser ablation of selected areas of the layer of ceramic material can reveal the underlying ceramic substrate, resulting in a (optical) distinguishable contrast of the manipulated areas relative to the rest of the layer of ceramic material.

[0034] According to a particularly preferred embodiment of the present application, the substrate is transparent for the wavelength of the laser beam. Preferably, the substrate has a transmittance of at least 95%, more preferably at least 97% and best at least 99% for light having the wavelength of the laser beam. For example, the substrate can comprise a glass-like transparent ceramic material or a crystalline ceramic material, such as sapphire (AI2O3), silicon dioxide (SiO2), zirconium silicate (Zr(SiO4)), zirconium oxide (ZrO2), boron monoxide (B2O), boron trioxide (B2O3), sodium oxide (Na2O), potassium oxide (K2O), lithium oxide (Li2O), zinc oxide (ZnO), magnesium oxide (MgO).

[0035] Particularly suitable crystalline ceramic materials are sapphire (AI2O3), silicon dioxide (SiO2), zirconium silicate (Zr(SiO4)), zirconium oxide (ZrO2), magnesium oxide (MgO).

[0036] This transparent material is particularly advantageous since it allows to selectively irradiate areas of the layer of ceramic material (coated onto the substrate) through the transparent substrate. Thus, any debris generated during recording is generated on the surface of the coated substrate opposite the recording optics. This surface can thus be easily cleaned and / or cooled without affecting the recording optics.

[0037] Due to the high transmission factor of the transparent substrate material, the laser light does not interact with the substrate but simply passes through the substrate in order to, for example, only melt the coating. In particular, the substrate material is not substantially heated by the laser beam.

[0038] Preferably, the laser beam, i.e. each of the multiple laser beams emitted from the DMD, has a minimum focal spot diameter of no more than 400 nm, more preferably no more than 300 nm, even more preferably no more than 200 nm and most preferably no more than 100 nm.

[0039] Preferably, the wavelength of the laser beam is less than 700 nm, preferably less than 650 nm, more preferably less than 600 nm, even more preferably less than 500 nm and most preferably less than 400 nm. Smaller wavelengths allow for the creation of smaller structures and thus a larger data density. Furthermore, the energy per photon (action quantum) increases for smaller wavelengths.

[0040] The present invention further relates to a device for recording data in a layer of a ceramic material. The device comprises a laser source, a digital micromirror device (DMD) adapted to emit a plurality of laser beams, collimating optics for collimating the laser light emitted by the laser source onto the DMD, a substrate holder for mounting a substrate and focusing optics adapted to focus each of the plurality of laser beams emitted by the DMD onto the substrate mounted on the substrate holder. The fluence of each of the plurality of laser beams emitted by the DMD is greater than 100 mJ / cm 2 , preferably greater than 400 mJ / cm 2 , more preferably greater than 800 mJ / cm 2 , most preferably greater than 1 J / cm 2 . The laser source preferably comprises a picosecond laser or a femtosecond laser. The laser source preferably has a pulse duration of less than 10 ps, more preferably less than 1 ps.

[0041] All preferred features discussed above in the context of the inventive method can likewise be used in the inventive device and vice versa.

[0042] The power density of the laser beam is preferably adapted to sufficiently manipulate the layer of ceramic material in order to record data on or in the layer of ceramic material. Preferably, the power density of the laser beam allows for melting the above-mentioned ceramic material.

[0043] The focusing optics preferably comprise a lens (or a more complex optical device) with a high numerical aperture, preferably a numerical aperture of at least 0.5, more preferably at least 0.8. If immersion optics are used, the numerical aperture can be at least 1.0, more preferably at least 1.2.

[0044] The apparatus preferably further comprises a beam shaping device, preferably comprising a matrix of laser wave plates or a spatial light modulator, in order to generate e.g. a plurality of Bessel beams as discussed above. This beam shaping device is preferably located before the focusing optics. In this case, preferably a plurality of lenses, preferably Fresnel lenses, are located directly behind the beam shaping device in order to focus e.g. the Bessel beams.

[0045] At the substrate, each of the plurality of laser beams is preferably a Bessel beam. At the substrate, each of the plurality of laser beams preferably has a minimum focal spot diameter of no more than 400 nm, more preferably no more than 300 nm, even more preferably no more than 200 nm and most preferably no more than 100 nm.

[0046] The substrate holder is preferably mounted on an XY positioning system, such as a scanning stage. The apparatus preferably comprises a processor to control the DMD and the XY positioning system in order to sequentially irradiate adjacent areas or pixel arrays of a substrate mounted on the substrate holder.

[0047] The processor (or additional processing unit) is preferably adapted and to receive a set of data to be recorded (i.e. analog or digital data, such as text, numbers, pixel arrays, QR codes or the like) and to control the components of the apparatus, in particular the DMD and the XY positioning system and optionally the beam shaping device, to perform the inventive method in order to record the received data set on or in the layer of ceramic material.

[0048] Preferably, the wavelength of the laser source is less than 700 nm, preferably less than 650 nm, more preferably less than 600 nm, even more preferably less than 500 nm and most preferably less than 400 nm. BRIEF DESCRIPTION OF DRAWINGS

[0049] The preferred embodiments of the present invention will be further clarified by a consideration of the following detailed description taken in connection with the accompanying drawings, in which:

[0050] Figure 1 Schematic view of an apparatus for recording data according to a preferred embodiment;

[0051] Figure 2a Schematically a first recording alternative;

[0052] Figure 2b Schematically a second recording alternative;

[0053] Figure 3 Schematically an apparatus for recording data according to another preferred embodiment; and

[0054] Figure 4Schematic diagram of a combination of a polarizer, a wave plate and a lens and a resulting beam shape and a graph of the focal length along the axis of the laser beam. DETAILED DESCRIPTION

[0055] Figure 1 A schematic diagram of an apparatus for recording data in a layer of a ceramic material according to a preferred embodiment of the present application is shown. The apparatus comprises a laser source 2 emitting laser light onto a DMD 3 comprising a plurality of micromirrors 3a configured in an array. For each micromirror in the "off state, the DMD 3 is adapted to emit a plurality of laser beams 4 along a first direction, i.e. for recording, or along a second direction, indicated with reference numeral 9, thereby diverting those laser beams 9 into a beam dump stack (not shown). Typically, the apparatus will further comprise collimating optics (not shown in Figure 1

[0056] In the example shown in Figure 1 , the substrate 7 comprises a ceramic coating or layer of ceramic material 1 which is locally ablated by the focused laser beams 4. In Figure 1 , the ceramic coating 1 is provided on top of the substrate 7 (see also Figure 2a ). Alternatively, as shown in Figure 2b , the ceramic coating can be provided on the bottom or backside of the substrate 7. Since in this case the laser beams 4 have to pass through the substrate 7, in this case the material of the substrate 7 needs to be transparent for the wavelength of the laser light. Furthermore, in this case it is preferred that the substrate holder 6 comprises a frame 6a supporting only the outer edges of the substrate 7 (whereas in the case of top ablation as shown in Figure 2a , the substrate can be fully supported). Thus, the part of the ceramic coating 1 which is exposed to ablation is not supported due to the free space 6b underneath (see Figure 2b ).

[0057] This is a particularly preferred embodiment, since any debris generated during ablation will be separated from the focused optics 8 by the substrate 7. In contrast, any material ablated from the ceramic layer 1 will be emitted into the free space 6b of the sample holder 6 and can be extracted or sucked from there. Thus, the focused optics 8 are not negatively affected by this debris and it is easier to clean the surface of the ceramic coating 1 after recording or even during recording.​

[0058] Preferably, the thickness of the substrate is suitable for the focusing optics of the device used. For example, the thickness of the substrate should be less than the focal length of the focusing optics in order to reach the ceramic coating.

[0059] also, Figure 2b The configuration shown also allows the ceramic coating 1 to be cooled during melting, for example, by allowing a cooling fluid to flow along the ceramic coating 1. This improves the accuracy of the melting process because heat transfer from the laser focus to the surrounding area can be eliminated. For example, this can be achieved by cross-spraying air (e.g., air blades) or liquids such as water or other immersion liquids. Additionally, this cross-spraying can remove debris generated during melting.

[0060] exist Figure 2a This cross-jet can also be provided in the configuration shown. However, the cross-jet in this embodiment must be designed not to interfere with the optics. For example, if immersion optics are used, the immersion liquid can be provided in a cross-flow, which is preferably laminar to avoid any optical effects attributable to turbulence within the immersion liquid.

[0061] Because this cross-jet of air or liquid can generate vibrations, these vibrations may compromise the accuracy of the recording, and because... Figure 2a The implementation shown would be complicated by using cross-spraying, therefore a method is provided as follows: Figure 2a and Figure 2b The negatively charged mesh or sheet 15 shown is preferred. As explained above, a picosecond or femtosecond laser will generate plasma in the ceramic material to be melted. Simply put, portions of the atomic shell of the ceramic material will be removed due to interaction with the laser pulse. Subsequently, the remaining positively charged atomic nuclei are ejected during a so-called Coulomb explosion. These positively charged nuclei can then be attracted by the negatively charged mesh or sheet 15. This process is... Figure 2a The embodiment shown is particularly advantageous in which the laser beam 4 can pass through an opening in the mesh or plate. All debris is then collected by the charged mesh or plate, and therefore does not negatively affect, for example, the focusing optics 8.

[0062] Figure 3 Further details of another preferred embodiment of the device of the present invention are shown below. For example, Figure 3 This diagram illustrates collimating optics 5 for collimating the laser emitted from laser source 2 onto DMD 3, as well as additional optical components such as spatial filters 10 and 11. Figure 3In this case, the substrate holder 6 is an XY positioning system for translating the substrate 7 along the x-y plane (where z is perpendicular to the surface of the substrate 7). Both the DMD 3 and the XY positioning system 6 are controlled by a computer 13 which is used to control the DMD 3 and the XY positioning system 6 in order to perform the following steps: selectively irradiate a plurality of zones within a first region of the layer 1 of ceramic material using the laser beam of the DMD 3, wherein the first region can be covered by the DMD 3; translate the layer 1 of ceramic material (i.e. the entire substrate 7 in the present case) such that a second region different from the first region can be covered by the DMD 3; and selectively irradiate a plurality of zones within the second region of the layer 1 of ceramic material using the laser beam of the DMD 3.

[0063] As discussed previously, the apparatus preferably comprises a beam shaping apparatus to obtain e.g. Bessel beams. For example, a matrix of laser zone plates 12 can be provided between the DMD 3 and the focusing optics 8 in order to shape each of the laser beams 4 (see Fig. 1) into a Bessel beam shape. Each Bessel beam is then focused onto the substrate 7 by the respective lens (e.g. Fresnel lens) 8. In order to properly irradiate the matrix of laser zone plates 12, additional collimating optics 14a and 14b can be provided. This principle is further illustrated in Figure 1 Figure 4 Figure 4 It is shown (for a single beamlet) how a Bessel beam is generated from a combination of an optical element 12a which generates circularly polarized light and a binary phase element 12b for generating a Bessel beam, which is then focused onto the substrate 7 by the respective high-NA lens 8 (or Fresnel lens 8). Also as shown in Figure 4 By using this Bessel beam, a focal length of at least 4 times the wavelength of the laser can be achieved. Furthermore, the focal spot has a more cylindrical shape than a Gaussian beam.​​

Claims

1. A method for recording data in a layer of ceramic material, the method comprising the steps of: providing a layer of ceramic material; and selectively irradiating, using a digital micromirror device, a plurality of regions of the layer of ceramic material with a laser beam; wherein a plurality of parameters of the laser beam and an irradiation time for each of the selectively irradiated zones are used to fuse each of the selectively irradiated zones in order to record data in the layer of ceramic material by creating a plurality of recesses in the layer of ceramic material, wherein the laser beam originates from a picosecond laser or a femtosecond laser, and wherein a fluence of the laser beam emitted by the digital micromirror device is greater than 100 mJ / cm 2 .

2. The method of claim 1, wherein the laser beam is a Bessel beam.

3. The method of claim 2, wherein the Bessel beam is generated by a laser wave plate or a spatial light modulator.

4. The method of claim 1, wherein the recess is open to the atmosphere.

5. The method of claim 1, wherein the layer of ceramic material is moved laterally during recording, and wherein the method further comprises the steps of: selectively irradiating, using the digital micromirror device, a plurality of regions within a first area of the layer of ceramic material with the laser beam, wherein the first area can be covered by the digital micromirror device; translating the layer of ceramic material so that a second area, different from the first area, can be covered by the digital micromirror device; and selectively irradiating, using the digital micromirror device, a plurality of regions within the second area of the layer of ceramic material with the laser beam.

6. The method of claim 1, wherein the layer of ceramic material comprises at least one of: a metal nitride; a metal carbide; a metal oxide; a metal boride; or a metal silicide.

7. The method of claim 1, wherein providing a layer of ceramic material comprises: providing a substrate and coating the substrate with the layer of ceramic material, the material of the layer of ceramic material being different from the material of the substrate, wherein the layer of ceramic material has a thickness of no more than 10 pm.

8. The method of claim 7, wherein the substrate comprises at least 90% by weight of one or a combination of: AI2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, V2O3; and / or wherein the substrate comprises at least 90% by weight of one or a combination of: a metal nitride; a metal carbide; a metal boride; and a metal silicide.

9. The method of claim 7, wherein the substrate has a thickness of less than 1 mm.

10. The method of claim 7, wherein the substrate is transparent to the wavelength of the laser beam.

11. The method of claim 10, wherein the substrate comprises a glassy transparent ceramic material or a crystalline ceramic material and / or wherein the substrate comprises one or a combination of: sapphire (AI2O3), silicon dioxide (SiO2), zirconium silicate (Zr(SiO4)), zirconium oxide (ZrO2), boron monoxide (B2O), boron trioxide (B2O3), sodium oxide (Na2O), potassium oxide (K2O), lithium oxide (Li2O), zinc oxide (ZnO), magnesium oxide (MgO).

12. The method of claim 10, wherein selectively irradiating the plurality of regions of the layer of ceramic material with a laser beam using a digital micromirror device comprises: irradiating the layer of ceramic material through the transparent substrate.

13. The method of claim 7, wherein selectively irradiating the plurality of regions of the layer of ceramic material with a laser beam using a digital micromirror device comprises: melting sufficient material at each of the regions where the recess extends towards the substrate.

14. The method of claim 7, wherein the coated substrate is tempered before and / or after recording.

15. The method of claim 1, wherein the laser beam has a minimum focal spot diameter no greater than 1000 nm.

16. The method of claim 1, wherein the laser beam has a wavelength less than 700 nm.

17. The method of claim 1, wherein the recesses are created at one or more of a plurality of predetermined locations, and wherein the predetermined locations are configured in a regular matrix or array.

18. The method of claim 17, wherein the regular matrix or array is a square pattern or a hexagonal pattern.

19. The method of claim 1, wherein the recesses have a circular cross-section.

20. The method of claim 1, further comprising: Collecting positively charged debris using a negatively charged mesh or sheet.

21. The method of claim 20, wherein the layer of ceramic material is positioned between the digital micromirror device and the negatively charged mesh or sheet.

22. The method of claim 20, wherein the negatively charged mesh or sheet is positioned between the digital micromirror device and the layer of ceramic material.

23. The method of claim 22, wherein the negatively charged mesh or sheet includes openings that allow the laser beam to pass through.

24. An apparatus for recording data in a layer of ceramic material (1), the apparatus comprising: a laser source (2) comprising a picosecond laser or a femtosecond laser; a digital micromirror device (3) adapted to emit a plurality of laser beams (4); collimating optics for collimating the laser emitted by the laser source onto the digital micromirror device (3); a substrate holder (6) for mounting a substrate (7); and focusing optics (8) adapted to focus each of the plurality of laser beams (4) emitted by the digital micromirror device (3) onto a substrate (7) mounted on the substrate holder (6), the substrate comprising the layer of ceramic material. wherein the fluence of each of the plurality of laser beams (4) emitted by the digital micromirror device (3) is greater than 100 mJ / cm 2 .

25. The apparatus of claim 24, wherein the focusing optics (8) comprise a lens having a numerical aperture of at least 0.

5.

26. The apparatus of claim 24, wherein the apparatus further comprises a beam shaping device.

27. The apparatus of claim 26, wherein the beam shaping device is a matrix of laser zone plates or a spatial light modulator.

28. The apparatus of claim 24, wherein each of the plurality of laser beams at the substrate has a minimum focal spot diameter no greater than 1000 nm.

29. The apparatus of claim 24, further comprising a processor to control the digital micromirror device.

30. The apparatus of claim 24, further comprising a processor to control the digital micromirror device and an XY positioning system, the substrate holder being mounted on the XY positioning system.

31. The apparatus of claim 24, wherein the laser source has a wavelength less than 700 nm.

32. The apparatus of claim 24, further comprising a negatively charged mesh or sheet (15) for collecting positively charged debris.

33. The apparatus of claim 32, wherein the substrate holder (6) is positioned between the focusing optics (8) and the negatively charged mesh or sheet (15).

34. The apparatus of claim 32, wherein the negatively charged mesh or sheet (15) is positioned between the focusing optics (8) and the substrate holder (6).

35. The apparatus of claim 34, wherein the negatively charged mesh or sheet (15) comprises openings that allow the plurality of laser beams (4) to pass through.

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