Compact write and read head for data recording in ceramic materials.

Abstract

The present 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 and for reading said data.

Description

[Technical field]

[0001] The present 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. [Background technology]

[0002] The applicant of the present invention has developed a method for long-term storage of information and a storage medium therefor (see WO 2021 / 028035 and WO 2022 / 002418). According to one aspect of said method for long-term storage of information, information is encoded on a writable plate comprising a ceramic material by using a laser beam to manipulate local areas of the writable plate. This method can in principle be carried out with a laser beam having a fixed focus by mounting the writable plate on an XY positioning system and moving these local areas of the writable plate to the laser focus where the encoding should take place, but said method is laborious and time-consuming.

[0003] Also, U.S. Patent No. 4,069,487 and U.S. Patent No. 4,556,893 disclose laser recordable recording media utilizing recording layer materials such as metal oxides and metal carbides. However, recording in both cases is based on rotating disk technology, which is disadvantageous due to the slow recording process caused by the fact that pits must be formed one after the other along the recording spiral. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 028035 [Patent Document 2] International Publication No. 2022 / 002418 [Patent Document 3] U.S. Pat. No. 4,069,487 [Patent Document 4] U.S. Pat. No. 4,556,893 Summary of the Invention

[0005] It is therefore an object of the present invention to provide an improved method for recording data in a layer of ceramic material which is suitable for recording large amounts of data in a relatively short amount of time.It is a further object of the present invention to provide an improved device for recording data in a layer of ceramic material which has a compact write head.

[0006] This object is achieved by a method according to claim 1 and a device according to claim 23. Preferred embodiments of the invention are set out in the dependent claims.

[0007] The present invention therefore relates to a method for recording data in a layer of ceramic material, according to which a layer of ceramic material is provided and a plurality of regions of the layer of ceramic material are selectively irradiated with a laser beam using a digital micromirror device (DMD), parameters of the laser beam and irradiation time for each of the selected regions are configured to ablate each of the selected regions to record data in the layer of ceramic material by forming recesses in the layer of ceramic material.

[0008] The laser beam preferably originates from a picosecond or femtosecond laser. Utilizing a picosecond or femtosecond laser is highly advantageous for generating well-defined recesses. The ablation technique disclosed in US Pat. No. 4,556,893 utilizes a focused, modulated laser diode beam that forms pits or bubbles depending on the laser power. Since the recording layer material is light absorbing, said layer is locally heated and thus melts and / or vaporizes. However, these processes are rather uncontrolled and typically result in unfavorable hole shapes. For example, as also shown in FIG. 4 of US Pat. No. 4,556,893, a ring of melted and then solidified material may form around the edge of the hole. This is not acceptable when forming extremely small recesses to increase data density, since it is required to form these recesses reproducibly and to enable reproducible readout techniques.

[0009] The inventors of the present invention have carried out several experiments using different ablation techniques for ceramic materials. It has been found that utilizing picosecond or femtosecond lasers allows for the creation of very well-defined holes with circular cross-sections and very sharp edges. This is believed to be due to the ablation process initiated by the picosecond or femtosecond laser. The picosecond or femtosecond laser pulse does not heat the ceramic material, but rather interacts with the electrons of said material. It is hypothesized that the picosecond or femtosecond laser pulse interacts with the outer valence electrons that are responsible for the chemical bonds, thus moving them away from the atoms, leaving them positively charged. Given the mutual repulsion between atoms whose chemical bonds have been broken, the material "explodes" into a small plasma cloud of energetic ions at a faster rate than would be seen with thermal release. This phenomenon is known as Coulomb explosion and is clearly different from regular laser ablation, for example with nanosecond lasers, which heats and melts and vaporizes the material on the surface, leaving molten material at the edge of the impact area. Coulomb explosion is a physical process, which is obviously limited to the area of ​​the laser shock, whereas thermally induced ablation suffers from an undefined heat flow in the material. Said Coulomb explosion is therefore ideal in that it generates a huge number of small recesses, which allows a dramatic increase in data density compared to known techniques. Although good results can be achieved with picosecond lasers, the use of femtosecond lasers is advantageous in this respect. The laser therefore preferably has a pulse duration smaller than 10ps, more preferably smaller than 1ps.

[0010] The fluence of each of the multiple laser beams emitted by the DMD is 100 mJ / cm 2 greater than 400 mJ / cm 2 More preferably, 800 mJ / cm 2 greater than 1 J / cm 2 It is preferable that it is greater than .

[0011] Preferably, the laser beam passes, in turn, through a prism or semi-transparent mirror, strikes the digital micromirror device, and passes through the prism or semi-transparent mirror again before selectively irradiating a plurality of areas of the layer of ceramic material. Utilizing such a prism or semi-transparent mirror is particularly advantageous in that it allows for a compact arrangement of the various components of the device used for recording. The laser beam preferably passes two more times through a λ / 4 plate disposed between the prism or semi-transparent mirror and the digital micromirror device. Changing the polarization of the laser beam by such a λ / 4 plate allows the laser beam from the laser to be directed through the prism or semi-transparent mirror to the digital micromirror device, and again through the prism or semi-transparent mirror to selectively irradiate a plurality of areas of the layer of ceramic material.

[0012] In the context of the present invention, the term "recess" relates to a hole, a groove or a depression in a ceramic material. In other words, a recess forms a volume without the presence of any ceramic material. Said volume is in fluid communication with the atmosphere. In other words, each recess is open to the atmosphere and is not covered or closed.

[0013] Open recesses are advantageous over the technique described in U.S. Patent No. 4,069,487, which utilizes a protective layer covering the information recording portion, because such open recesses allow for clean and complete ablation of the material that was in the recess prior to ablation. This is particularly important when forming very small recesses to increase data density, as these recesses need to be formed reproducibly to allow for reproducible readout techniques.

[0014] The DMD includes an array or matrix of micromirrors that allows selective illumination of a given pixel on the ceramic material by adjusting each micromirror in the array or matrix. Thus, a huge number of pixels on the ceramic material can be illuminated simultaneously in a well-controlled manner that can be easily automated. Depending on the number of micromirrors present in the DMD, millions of selected areas (i.e., pixels) of a layer of ceramic material can be manipulated simultaneously during a time sufficient to ablate one selected area to record data. Such digital micromirror devices are readily available and can be easily implemented in a recording device.

[0015] Preferably, the pixels on the ceramic material, i.e. the predetermined locations in the portions where recesses can be formed, are arranged in a regular matrix or array, i.e. in a repeating two-dimensional pattern with a lattice structure or lattice-like structure. Particularly preferred matrices or arrays include, for example, square patterns or hexagonal patterns. Such matrices or arrays allow for optimized data densities, which are substantially greater than those of, for example, CDs, DVDs or Blu-Ray discs, since the individual pixels or bits are not separated by a track pitch (e.g., 320 nm for Blu-Ray discs) that is more than twice the size of the individual pixels in the bit dimension (e.g., 150 nm for Blu-Ray discs). Conventional disc-shaped recording media are also limited in terms of maximum rotational speed than can be safely achieved during recording or reading. The writing / reading speed achievable by such matrices or arrays is therefore much greater than the writing / reading speed possible by pits arranged in a spiral shape.

[0016] Preferably, the recesses have a circular cross section. The recesses may only partially extend into the ceramic layer or may form through holes in the ceramic layer. In the former case, recesses or holes of different depths may be formed, each depth corresponding to a predetermined bit of information as described in WO2022 / 002418. To this end, the layer of ceramic material may be irradiated with two or more laser pulses, and the micromirrors of the DMD are adjusted between subsequent pulses to achieve multiple regions of the layer of ceramic material that are (i) not irradiated at all, (ii) irradiated once with a single laser pulse, (iii) irradiated twice with two laser pulses, etc.

[0017] Previous experiments by the applicant have shown that a layer of CrN with a thickness of 5 μm can be visually and reliably manipulated by a single femtosecond laser pulse (see WO 2022 / 002418). Thus, the method of the invention makes it possible to encode at least thousands and even millions of pixels within a few hundred femtoseconds. The recording speed of the method of the invention is therefore only limited by the number of micromirrors of the DMD and the time required to adjust the micromirrors.

[0018] Preferably, the layer of ceramic material is laterally moved or translated during recording, for example by an XY positioning system (with the z-axis perpendicular to the surface of the layer) such as a scanning stage. Thus, once an array or matrix of pixels has been recorded, an adjacent array or matrix of pixels can be recorded by simply moving the layer of ceramic material to an adjacent area.

[0019] Thus, the method of the present invention preferably includes the steps of selectively irradiating a laser beam using a DMD to a plurality of regions within a first area of ​​a layer of ceramic material that can be covered by the DMD, translating the layer of ceramic material so that a second area different from the first area can be covered by the DMD, and selectively irradiating a laser beam to a plurality of regions within the second area of ​​the layer of ceramic material using the DMD.

[0020] If both the DMD and the XY positioning system are properly controlled, data recording rates 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.

[0021] Preferably, the laser beam (i.e., multiple laser beams emitted from the DMD) is focused onto the layer of ceramic material by a lens (or more complex optics) having a high numerical aperture, preferably at least 0.5, more preferably at least 0.8. Preferably, immersion optics are used to further increase the numerical aperture. If immersion optics are used, the numerical aperture may be at least 1.0, preferably at least 1.2.

[0022] It is further preferred to utilize a beam shaping device to form a particular beam shape advantageous for data recording. For example, a matrix of laser zone plates may be transmitted by the multiple laser beams generated from the DMD. These laser zone plates may be adapted to form, for example, a needle-shaped Bessel beam for each of the multiple laser beams.

[0023] Bessel beams have the advantage that the depth of focus is substantially increased: while the focal length of a regular Gaussian beam is on the order of the wavelength of the focused light, the focal length that can be achieved with a Bessel beam is at least four times the wavelength of the focused light. At the same time, the width of the focal spot is about half that which can be achieved by a Gaussian beam.

[0024] In general, the feature sizes that can be achieved by the method of the invention (e.g., the diameter of the recess in the ceramic material) vary between 2 / 3λ (air) and 1 / 2λ (immersion) for Gaussian beams and between 1 / 3λ (air) and 1 / 4λ (immersion) for Bessel beams (λ is the wavelength of the laser light). The Bessel beam geometry is therefore advantageous in that smaller process features and thus a greater recorded data density can be achieved. Moreover, an increase in the focal length of the Bessel beam is advantageous in that, for example, deeper recesses can be produced. This is particularly relevant if features of different depths are to be produced, for example to encode information by the depth of the recess. Since the focus of the Gaussian beam is conical, increasing the depth of the recess means increasing the diameter of the recess at the surface. In contrast, the more cylindrical focus of the Bessel beam allows for the formation of much deeper recesses with an almost constant diameter.

[0025] Such Bessel beams can also be generated by other beam shaping devices, one particularly preferred example of which is a spatial light modulator, which is particularly versatile as it can be utilized to shape Bessel beams, enable optical proximity control and provide phase shifting masks.

[0026] 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, which provide sufficient hardness and resistance to environmental degradation for long-term preservation of recorded data.

[0027] Preferably, the step of providing a layer of ceramic material includes providing a substrate and coating the substrate with a layer of ceramic material different from the material of the ceramic substrate. Thus, structural integrity is achieved with a robust and potentially less expensive substrate while less of the potentially more expensive coating material is required. The layer of ceramic material preferably has a thickness of 10 μm or less, more preferably 5 μm or less, more preferably 2 μm or less, more preferably 1 μm or less, even more preferably 100 nm or less, and most preferably 10 nm or less.

[0028] Preferably, the substrate has a thickness of less than 1 mm, preferably less than 250 μm, more preferably less than 200 μm, and most preferably less than 150 μm.

[0029] Furthermore, the use of a substrate may allow for the creation of optical contrast between the substrate (where holes are created in the coating) and the surrounding coating material. Thus, selectively irradiating a laser beam onto a plurality of regions of a layer of ceramic material using a digital micromirror device preferably includes ablating enough material in each of the regions that recesses extend towards the substrate. Preferably, the manipulation of the selected areas makes these areas distinguishable from the surrounding material. In some applications, this may include achieving optical distinguishability. However, in other instances (especially when the encoded structures are too small), these areas can only be distinguished from the surrounding material by, for example, scanning electron microscopy, or by measuring changes in another physical parameter, for example magnetic, dielectric or conductive properties.

[0030] Preferably, the ceramic substrate comprises an oxide ceramic, more preferably, the ceramic substrate comprises at least 90% by weight, most preferably at least 95% by weight, of one or a combination of Al2O3, TiO2, SiO2, ZrO2, ThO2, MgO, Cr2O3, Zr2O3, and V2O3. These materials are known to be particularly durable under various circumstances and / or resistant to environmental degradation. 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 (Al2O3), silica (SiO2), zirconium silicate (Zr(SiO4)), zirconium oxide (ZrO2), boron monoxide (BO), boron trioxide (BO3), sodium oxide (Na2O), potassium oxide (KO), lithium oxide (Li2O), zinc oxide (ZnO), and magnesium oxide (MgO).

[0031] Preferably, the ceramic substrate comprises a non-oxide ceramic, more preferably, the ceramic substrate comprises at least 90% by weight, most preferably at least 95% by weight, of one or a combination of 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, WSi2, PtSi, Mg2Si. These materials are known to be particularly durable under various circumstances and / or resistant to environmental degradation. 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.

[0032] Preferably, the ceramic substrate comprises one or a combination of Ni, Cr, Co, Fe, W, Mo or other metals with a melting point above 1,400°C. Preferably, the ceramic material and the metal form a metal matrix composite in which the ceramic material is dispersed in the metal or metal alloy. Preferably, the metal represents 5-30% by weight, preferably 10-20% 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.

[0033] The layer of ceramic material is preferably coated directly on the ceramic substrate, i.e., without any intermediate layer, so as 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 to achieve such a strong bond. The tempering may generate a sintered interface between the ceramic substrate and the layer of ceramic material. The sintered interface may include 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 may diffuse into the other layer of the two adjacent layers. The presence of a sintered interface may further strengthen the bond between the ceramic substrate and the layer of ceramic material.

[0034] Preferably, tempering the coated ceramic substrate comprises 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 may comprise a heating stage with a temperature increase of at least 10 K / hr, a plateau stage at the peak temperature for at least 1 minute, and finally a cooling stage with a temperature decrease of at least 10 K / hr. The tempering process may help harden the ceramic substrate and / or permanently bond the ceramic material to the ceramic substrate.

[0035] Laser ablation of selected areas of the layer of ceramic material exposes the underlying ceramic substrate, which can result in an (optically) distinguishable contrast of the engineered areas relative to the remainder of the layer of ceramic material.

[0036] According to a particularly preferred embodiment of the invention, the substrate is transparent to the wavelength of the laser beam. Preferably, the substrate has a transmittance of at least 95%, more preferably at least 97%, and most preferably at least 99% for light having the wavelength of the laser beam. The substrate may comprise, for example, a glassy transparent ceramic material or a crystalline ceramic material, such as sapphire (Al2O3), silica (SiO2), zirconium silicate (Zr(SiO4)), zirconium oxide (ZrO2), boron monoxide (BO), boron trioxide (BO3), sodium oxide (Na2O), potassium oxide (KO), lithium oxide (Li2O), zinc oxide (ZnO), magnesium oxide (MgO).

[0037] Particularly suitable crystalline ceramic materials are sapphire (Al2O3), silica (SiO2), zirconium silicate (Zr(SiO4)), zirconium oxide (ZrO2), and magnesium oxide (MgO).

[0038] Such transparent materials are particularly advantageous because they allow selective illumination of multiple areas of the layer of ceramic material (coated on the substrate) through the transparent substrate. Thus, debris generated during recording occurs on the surface of the coated substrate opposite the recording optics. Said surface can therefore be easily cleaned and / or cooled without affecting the recording optics.

[0039] Due to the high transmittance of the transparent substrate material, the laser light does not interact with the substrate but simply passes through it, e.g. to ablate only the coating, and in particular the substrate material is not substantially heated by the laser beam.

[0040] Preferably, the laser beam (ie, each of the multiple laser beams emitted from the DMD) has a minimum focal diameter of 400 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and most preferably 100 nm or less.

[0041] Preferably, the wavelength of the laser beam is smaller than 700 nm, preferably smaller than 650 nm, more preferably smaller than 600 nm, even more preferably smaller than 500 nm, and most preferably smaller than 400 nm. Smaller wavelengths allow smaller structures to be formed, thus allowing greater data density. Moreover, the energy per photon (action quantum) increases with smaller wavelengths.

[0042] The invention further relates to a device for recording data in a layer of ceramic material, the device comprising a laser source, a digital micromirror device (DMD) adapted to emit a plurality of laser beams, a prism or semi-transparent mirror arranged between the laser source and 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 a substrate mounted on the substrate holder.

[0043] The device preferably further comprises collimating optics for collimating the laser light emitted by the laser source onto the DMD.

[0044] Preferably, the device further comprises a λ / 4 plate disposed between the prism or semi-transparent mirror and the DMD.

[0045] The prism or semi-transparent mirror is preferably positioned between the laser source and the DMD such that light emitted from the laser source passes, in order, through the prism or semi-transparent mirror, optionally the λ / 4 plate, and passes again, optionally through the prism or semi-transparent mirror, before hitting the DMD and selectively irradiating multiple regions of the substrate.

[0046] The fluence of each of the multiple laser beams emitted by the DMD is preferably 100 mJ / cm 2 greater than 400 mJ / cm 2 More preferably, 800 mJ / cm 2greater than 1 J / cm 2 Greater than.

[0047] The laser source preferably comprises a picosecond or femtosecond laser. The laser source preferably has a pulse duration of less than 10 ps, ​​more preferably less than 1 ps.

[0048] All preferred features mentioned above in the context of the method of the invention may be used in the device of the invention as well, and vice versa.

[0049] The fluence of the laser beam is preferably adapted to sufficiently manipulate the layer of ceramic material to record data on or in the layer of ceramic material. Preferably, the fluence of the laser beam makes it possible to ablate said ceramic material.

[0050] The focusing optics preferably includes a lens (or more complex optics) with a high numerical aperture, preferably at least 0.5, more preferably at least 0.8. If immersion optics are used, the numerical aperture may be at least 1.0, more preferably at least 1.2.

[0051] The device further comprises a beam shaping device, preferably a matrix of laser zone plates or a spatial light modulator, for example to form a plurality of Bessel beams as described above. Such a beam shaping device is preferably arranged before the focusing optics. In this case, preferably a plurality of lenses, preferably Fresnel lenses, are located directly behind the beam shaping device, for example to focus the Bessel beams. The device preferably further comprises a flat-top beam shaper, preferably located in the optical path before a prism or a semi-transparent mirror.

[0052] 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 diameter of 400 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and most preferably 100 nm or less.

[0053] The substrate holder is preferably mounted on an XY positioning system, such as a scanning stage. The device preferably includes a processor configured to control the DMD and the XY positioning system to sequentially illuminate adjacent areas or pixel arrays of a substrate mounted on the substrate holder.

[0054] This processor (or additional processing unit) is preferably adapted and configured to receive a set of data to be recorded (i.e. analog or digital data such as text, numbers, an array of pixels, a QR code, etc.) and to control the components of the device (in particular the DMD and the XY positioning system, and optionally the beam shaping device) to perform the method of the invention so as to record the received set of data on or within the layer of ceramic material.

[0055] 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.

[0056] The device preferably further comprises a reading device configured to image the recorded data. Thus, a single write and read head can be utilized both for encoding (writing) data in the layer of ceramic material and for decoding (reading) data encoded in such a data carrier. Utilizing the above-mentioned prisms or semi-transparent mirrors allows such a combined write and read head to be designed in a particularly compact form.

[0057] The device preferably further comprises a beam splitter between the prism or semitransparent mirror and the focusing optics to allow the light emitted from the substrate to pass through the reading device. The device preferably further comprises a further light source (e.g., an LED) adapted to illuminate the substrate through the prism or semitransparent mirror and the DMD during reading / decoding. Preferably, the light source emits linearly polarized light.

[0058] The reading device may comprise a digital camera or other optical detector. Preferably, the reading device comprises a single optical sensor, where each "pixel" on the data carrier is addressed by a DMD, which allows each "pixel" to be illuminated at once. In an alternative reading mode utilizing SIM or SSIM, a specific illumination pattern ("structured illumination") may be generated by the DMD. In that case, the reading device should comprise a digital camera or other multi-pixel detector. In a further reading mode, planar illumination may be achieved by simply setting all micromirrors of the DMD to "on". In that case, the reading device should also comprise a digital camera or other multi-pixel detector.

[0059] The device preferably further comprises a processor configured to decode the imaged recorded data, the processor may be adapted, for example, to perform SIM and / or SSIM analysis and control the DMD accordingly.

[0060] Preferred embodiments of the present invention will now be further described with reference to the following drawings. [Brief description of the drawings]

[0061] [Figure 1] FIG. 2 is a schematic diagram of a device for recording data according to a preferred embodiment. [Figure 2a] FIG. 2 is a schematic diagram of a first recording alternative; [Figure 2b]FIG. 2 is a schematic diagram of a second recording alternative; [Diagram 3] FIG. 4 illustrates a schematic representation of a device for recording data according to another preferred embodiment. [Figure 4] 1 is a schematic diagram of a combination of a polarizer, a zone plate and a lens, and a graph of the resulting beam shape and focal length along the axis of the laser beam. [Diagram 5] FIG. 4 illustrates a schematic representation of a device for recording data according to another preferred embodiment. [Figure 6] FIG. 4 illustrates a schematic representation of a device for recording data according to another preferred embodiment. [Figure 7] FIG. 4 illustrates a schematic representation of a device for recording data according to another preferred embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] FIG. 1 shows a schematic diagram of a device for recording data in a layer of ceramic material according to a preferred embodiment of the invention. The device comprises a laser source 2 emitting laser light onto a DMD 3 comprising a plurality of micromirrors 3a arranged in an array. The DMD 3 is adapted to emit, for each micromirror in the "off" state, a plurality of laser beams 4 along either a first direction (i.e. for recording) or a second direction (indicated by reference number 9) and to deflect the laser beams 9 to a beam dump (not shown). Typically, the device further comprises collimation optics (not shown in FIG. 1) for collimating the laser light emitted by the laser source 2 onto the DMD 3. The device further comprises 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 DMD onto the substrate 7 mounted on the substrate holder. The focusing optics 8 may, for example, comprise standard microscopy optics with a high numerical aperture. The substrate holder 6 is adapted to support, and preferably mount, the substrate 7 and may be mounted on or part of an XY stage.

[0063] In the example shown in FIG. 1, the substrate 7 comprises a ceramic coating or layer 1 of a ceramic material that is locally ablated by the focused laser beam 4. In FIG. 1, the ceramic coating 1 is provided on top of the substrate 7 (see also FIG. 2a). Alternatively, the ceramic coating can be provided on the bottom or back side of the substrate 7, as shown in FIG. 2b. Since the laser beam 4 in this case must pass through the substrate 7, the material of the substrate 7 must be transparent to the wavelength of the laser light in this case. Moreover, in this case the substrate holder 6 preferably comprises a frame 6a that supports only the outer edge of the substrate 7 (the substrate can be fully supported in the case of top ablation as shown in FIG. 2a). The part of the ceramic coating 1 that is exposed to ablation is therefore unsupported by the free space 6b below it (see FIG. 2b).

[0064] This is a particularly preferred embodiment, since the debris generated during ablation is separated from the focusing optics 8 by the substrate 7. Rather, the material being ablated from the ceramic layer 1 is released into the free space 6b of the sample holder 6, from where it can be extracted or aspired. The focusing optics 8 is therefore not adversely affected by said debris, and it is much easier to clean the surface of the ceramic coating 1 immediately after or even during recording.

[0065] Preferably, the thickness of the substrate is adapted to the focusing optics of the device in which it is being used, for example, the thickness of the substrate should be smaller than the focal length of the focusing optics in order to reach the ceramic coating.

[0066] Moreover, the arrangement shown in Fig. 2b also makes it possible to cool the ceramic coating 1 during ablation, for example by flowing a cooling fluid along said coating. This improves the accuracy of the ablation process, since heat transfer from the laser focus to the surrounding area can be eliminated. For example, for this purpose, a cross-jet of air (for example an air blade) or a liquid such as water or another immersion liquid can be performed. Furthermore, said cross-jet can expel debris generated during ablation.

[0067] Such a cross-jet may also be implemented in the case of the arrangement shown in Figure 2a. However, said cross-jet in this embodiment must be designed so as not to interfere with the optics. For example, if immersion optics are used, the immersion liquid may be provided in a cross-flow that is preferably laminar in order to avoid optical effects due to turbulence in the immersion liquid.

[0068] Since such cross jets of air or liquid can generate vibrations that can jeopardize the recording accuracy and since the use of cross jets for the embodiment shown in FIG. 2a is complicated, it is preferable to provide a negatively charged mesh or sheet 15 as shown in FIG. 2a and FIG. 2b. As explained above, the use of a picosecond or femtosecond laser creates a plasma in the ceramic material to be ablated. In simple terms, parts of the atomic shell of the ceramic material are removed by interaction with the laser pulse. The remaining positively charged atomic cores are then released during a so-called Coulomb explosion. These positively charged atomic cores can then be attracted by the negatively charged mesh or sheet 15. This is particularly advantageous in the case of the embodiment shown in FIG. 2a, where 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, so that it does not adversely affect, for example, the focusing optics 8.

[0069] Further details of another preferred embodiment of the device of the present invention are shown in Fig. 3. For example, Fig. 3 shows collimating optics 5 for collimating the laser light emitted by the laser source 2 onto the DMD 3, as well as further optical components such as spatial filters 10, 11. The substrate holder 6 is, in Fig. 3, an XY positioning system for translating the substrate 7 along the xy plane (z being perpendicular to the surface of the substrate 7). Both the DMD 3 and the XY positioning system 6 are controlled by a computer 13 configured to control the DMD 3 and the XY positioning system 6 to perform the following steps: selectively irradiating a plurality of regions in a first area of ​​the layer 1 of ceramic material with a laser beam using the DMD 3, where the first area can be covered by the DMD 3; translating the layer 1 of ceramic material (i.e., the entire substrate 7 in this case) so that a second area different from the first area can be covered by the DMD 3; and selectively irradiating a plurality of regions in a second area of ​​the layer 1 of ceramic material with a laser beam using the DMD 3.

[0070] As mentioned above, the device preferably comprises a beam shaping device, for example to achieve a Bessel beam. For example, a matrix of laser zone plates 12 may be provided between the DMD 3 and the focusing optics 8 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 an associated lens (e.g., Fresnel lens) 8. Additional collimating optics 14a and 14b may be provided to properly illuminate the matrix of laser zone plates 12. This principle is further explained in FIG. 4, which shows how a Bessel beam is generated (for a single beamlet) by a combination of an optical element 12a forming a circular polarization and a binary phase element 12b for forming a Bessel beam, which is then focused onto the substrate 7 by an associated high NA lens 8 (or Fresnel lens 8). As also shown in FIG. 4, by using such a Bessel beam, a focal length of at least four times the wavelength of the laser light may be achieved. Moreover, the focal point has a more cylindrical shape than a Gaussian beam.

[0071] Further details of another preferred embodiment of the device of the present invention are shown in FIG. 5. For example, FIG. 5 further shows an optional flat-top beam shaper 21 disposed between the collimating optics 5 and the DMD 3. More importantly, the preferred embodiment shown in FIG. 5 includes a prism 16. The prism 16 (which can also be replaced by a semi-transparent mirror) is disposed between the laser source 2 and the DMD 3 such that the light emitted from the laser source 2 passes through the prism 16, the λ / 4 plate 17a, hits the DMD 3, and passes through the λ / 4 plate 17a and the prism 16 again before selectively irradiating a plurality of regions of the substrate 7.

[0072] The linearly polarized light impinging on the prism 16 from the upper optical path is reflected to the right, i.e., towards the DMD 3. By passing through the λ / 4 plate 17a twice, the polarization axis of the laser light is rotated by a total of 90°. Thus, the again linearly polarized light impinging on the prism 16 from the right optical path passes through the prism 16.

[0073] An additional λ / 4 plate 17b can be provided to convert the linearly polarized light into a circularly polarized light, which is particularly advantageous for forming a Bessel beam in the laser zone plate 12. As mentioned above, the Bessel beam makes it possible to form a well-defined cylindrical recess.

[0074] The preferred embodiment shown in FIG. 5 further comprises a reading device 18 configured to image the recorded data. Thus, a single writing and reading head can be utilized both for encoding (writing) data in the layer of ceramic material and for decoding (reading) data encoded in such a data carrier. A beam splitter 19 between the prism 16 and the focusing optics 8 allows the light emitted from the substrate to pass through the reading device 18. A further light source 20 (e.g., an LED) is adapted to illuminate the substrate via the prism 16 and the DMD 3 during reading / decoding. For this purpose, a further beam splitter 23 is provided. By passing twice through the λ / 4 plate 17b, the polarization axis of the laser light originating from the light source 20 is again rotated by 90°. Thus, the again linearly polarized light impinging on the beam splitter 19 passes through said beam splitter 19.

[0075] Of course, other arrangements of the optical components of the device shown in Fig. 5 are also conceivable. For example, the reading device 18 can also be arranged on the optical axis of the focusing optics 8 as shown in Fig. 5, but on the fourth face of the prism 16 as shown in Fig. 6. In this case, the beam splitter 19 is no longer required. The λ / 4 plate 17b again ensures that the laser light originating from the light source 20 is rotated by a total of 90°. The again linearly polarized light impinging on the prism 16 is thus reflected towards the reading device 18.

[0076] In the read mode, the DMD 3 can be utilized in a different way to illuminate the data carrier with light emitted by the further light source 20. As mentioned above, the data carrier can be illuminated pixel-by-pixel using the DMD 3. In this case, only a single detector is needed in the read device and the scanning of the image is performed by the DMD 3.

[0077] In an alternative reading mode utilizing SIM or SSIM, a specific illumination pattern ("structured illumination") is generated by the DMD 3. In that case, the reading device 18 should comprise a digital camera or other multi-pixel detector.

[0078] In a further readout mode, planar illumination can be achieved by simply setting all micromirrors of the DMD 3 "on." The readout device 18 should still comprise a digital camera or other multi-pixel detector.

[0079] Of course, if the functionality of the DMD 3 is not used (planar illumination), the reading light path does not need to incorporate the DMD 3. Rather, the data carrier can be illuminated with a further light source, arranged, for example, as shown in FIG. 7. Here, the linearly polarized light emitted by the light source 20 is reflected by the beam splitter 24 towards the data carrier 7. Since the light is circularly polarized after passing through the λ / 4 plate 17b, said light passes through the beam splitter 19 and impinges on the data carrier 7. The light reflected or otherwise emitted from the data carrier 7 has passed again through the beam splitter 19 and the λ / 4 plate 17b. The light is then again linearly polarized (rotated by 90°) and thus passes through the beam splitter 24 to reach the reading device 18.

Claims

1. 1. A method for recording data in a layer of ceramic material, comprising the steps of: Providing a layer of ceramic material; selectively applying a laser beam to a plurality of regions of the layer of the ceramic material using a digital micromirror device; Including, parameters of the laser beam and exposure time for each selected region are configured to ablate each of the selected regions to record data in the layer of ceramic material by forming recesses in the layer of ceramic material; the laser beam originates from a picosecond laser or from a femtosecond laser, passes sequentially through a prism or semi-transparent mirror, impinges on the digital micromirror device, and passes through the prism or semi-transparent mirror again before selectively irradiating a plurality of regions of the layer of the ceramic material; method.

2. The laser beam is preferably a Bessel beam formed by a laser zone plate or a spatial light modulator. The method of claim 1.

3. The recess is open to the atmosphere. The method according to claim 1 or 2.

4. the laser beam passes through a λ / 4 plate disposed between the prism or the semitransparent mirror and the digital micromirror device two more times; The method according to any one of claims 1 to 3.

5. The layer of ceramic material may be CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si ３ N ４ , metal nitrides such as ThN, HfN, and BN, TiC, CrC, and Al ４ C ３ , VC, ZrC, HfC, ThC, B ４ Metal carbides such as C and SiC, Al ２ O ３ , TiO ２ , SiO ２ , ZrO ２ , ThO ２ , MgO, Cr ２ O ３ , Zr ２ O ３ , V ２ O ３ Metal oxides such as TiB ２ , ZrB ２ , CrB ２ , V.B. ２ , SiB ６ , ThB ２ , HfB ２ , W.B. ２ , W.B. ４ or a metal boride such as TiSi ２ , ZrSi ２ , MoSi ２ , WSi ２ , PtSi, Mg ２ at least one of a metal silicide such as Si; The method according to any one of claims 1 to 4.

6. wherein the step of providing a layer of ceramic material comprises providing a ceramic substrate and coating the substrate with the layer of ceramic material different from a material of the ceramic substrate, the layer of ceramic material preferably having a thickness of 10 μm or less, more preferably 5 μm or less, more preferably 2 μm or less, more preferably 1 μm or less, even more preferably 100 nm or less, and most preferably 10 nm or less. The method according to any one of claims 1 to 5.

7. The ceramic substrate is made of at least 90% by weight, preferably at least 95% by weight, of Al. ２ O ３ , TiO ２ , SiO ２ , ZrO ２ , ThO ２ , MgO, Cr ２ O ３ , Zr ２ O ３ , V ２ O ３ and / or the ceramic substrate comprises at least 90% by weight, preferably at least 95% by weight, of CrN, CrAlN, TiN, TiCN, TiAlN, ZrN, AlN, VN, Si ３ N ４ , metal nitrides such as ThN, HfN, and BN, TiC, CrC, and Al ４ C ３ , VC, ZrC, HfC, ThC, B ４ C, metal carbides such as SiC, TiB ２ , ZrB ２ , CrB ２ , V.B. ２ , SiB ６ , ThB ２ , HfB ２ , W.B. ２ , W.B. ４ Metal borides such as TiSi ２ , ZrSi ２ , MoSi ２ , WSi ２ , PtSi, Mg ２ Si or a combination of metal silicides, The method according to claim 6.

8. The ceramic substrate has a thickness of less than 1 mm, preferably less than 500 μm, more preferably less than 200 μm and most preferably less than 100 μm, more preferably less than 50 μm and most preferably less than 10 μm; The method according to claim 6 or 7.

9. the ceramic substrate is transparent to the wavelength of the laser beam; The method according to any one of claims 6 to 8.

10. The ceramic substrate comprises a glassy transparent ceramic material or a crystalline ceramic material, and / or the ceramic substrate is made of sapphire (Al ２ O ３ ), silica (SiO ２ ), zirconium silicate (Zr(SiO ４ )), zirconium oxide (ZrO ２ ), boron monoxide (B ２ O), boron trioxide (B ２ O ３ ), sodium oxide (Na ２ O, potassium oxide (K ２ O), lithium oxide (Li ２ Oxide (ZnO), zinc oxide (ZnO), magnesium oxide (MgO), or a combination thereof; 10. The method of claim 9.

11. selectively irradiating a plurality of regions of the layer of the ceramic material with a laser beam using a digital micromirror device includes irradiating the layer of the ceramic material through the transparent substrate.

11. The method according to claim 9 or 10.

12. selectively irradiating a laser beam onto a plurality of regions of the layer of ceramic material using a digital micromirror device includes ablating sufficient material in each of the regions such that the recess extends toward the substrate. The method according to any one of claims 6 to 11.

13. The coated substrate is tempered before and / or after recording. The method according to any one of claims 6 to 12.

14. The laser beam is further passed through a flat-top beam shaper before hitting the digital micromirror device. The method according to any one of claims 1 to 13.

15. the wavelength of the laser beam is less than 700 nm, preferably less than 650 nm; The method according to any one of claims 1 to 14.

16. the recesses are formed at a portion of the predetermined locations, the predetermined locations being arranged in a regular matrix or array; The method according to any one of claims 1 to 15.

17. The regular matrix or array is a square pattern or a hexagonal pattern; 17. The method of claim 16.

18. The recess has a circular cross section. The method according to any one of claims 1 to 17.

19. further comprising the step of collecting the positively charged debris using a negatively charged mesh or sheet; 19. The method according to any one of claims 1 to 18.

20. the layer of ceramic material is disposed between the digital micromirror device and the negatively charged mesh or sheet; 20. The method of claim 19.

21. the negatively charged mesh or sheet is disposed between the digital micromirror device and the layer of ceramic material; 20. The method of claim 19.

22. the negatively charged mesh or sheet includes openings that allow the laser beam to pass therethrough; 22. The method of claim 21.

23. A device for recording data in a layer of ceramic material (1), comprising: A laser source (2) including a picosecond or femtosecond laser; a digital micromirror device (3) adapted to emit a plurality of laser beams (4); a prism (16) or semi-transparent mirror disposed between the laser source (2) and the digital micromirror device (3); A substrate holder (6) for mounting a substrate (7); a focusing optical system (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); Equipped with device.

24. the focusing optics (8) comprises a lens having a numerical aperture of at least 0.5, more preferably at least 0.8; 24. The device of claim 23.

25. the device further comprises a beam shaping device, preferably a flat-top beam shaper (21), a matrix of laser zone plates (12) or a spatial light modulator, 25. A device according to claim 23 or 24.

26. the device further comprises a λ / 4 plate (17a) arranged between the prism (16) or the semitransparent mirror and the digital micromirror device (3); A device according to any one of claims 23 to 25.

27. a processor configured to control the digital micromirror device, and optionally an XY positioning system to which the substrate holder is mounted. A device according to any one of claims 23 to 26.

28. Further comprising a collimating optical system (5) for collimating the laser light emitted by the laser source (2) onto the digital micromirror device (3). A device according to any one of claims 23 to 27.

29. further comprising a negatively charged mesh or sheet (15) for collecting positively charged debris; A device according to any one of claims 23 to 28.

30. The substrate holder (6) is disposed between the focusing optics (8) and the negatively charged mesh or sheet (15).

30. The device of claim 29.

31. the negatively charged mesh or sheet (15) is disposed between the focusing optics (8) and the substrate holder (6); 30. The device of claim 29.

32. The fluence of each of the plurality of laser beams (4) emitted by the digital micromirror device (3) is 100 mJ / cm ２ Greater than A device according to any one of claims 23 to 31.

33. the prism (16) or the semi-transparent mirror is disposed between the laser source (2) and the digital micromirror device (3) such that light emitted from the laser source (2) passes, in turn, through the prism (16) or the semi-transparent mirror, strikes the digital micromirror device (3), and passes through the prism (16) or the semi-transparent mirror again before selectively irradiating multiple regions of the substrate; A device according to any one of claims 23 to 32.

34. a reading device (18) configured to image the recorded data; A device according to any one of claims 23 to 33.

35. a beam splitter (19) between the prism (16) or the semi-transparent mirror and the focusing optics (8) for allowing the light emitted from the substrate to pass to the reading device (18); 35. The device of claim 34.

36. a further light source (20) adapted to illuminate the substrate via the prism (16) or the semi-transparent mirror and the digital micromirror device (3) and / or via the beam splitter (19), 36. A device according to claim 34 or 35.

37. the reading device (18) comprises a single optical sensor; 37. The device of claim 36.

38. the further light source (20) is arranged to illuminate the substrate through a further λ / 4 plate (17b) and through the beam splitter (19), 37. The device of claim 36.

39. the further λ / 4 plate (17b) and the beam splitter (19) are arranged between the reading device (18) and the focusing optics (8), 39. The device of claim 38.

40. and a processor configured to decode the captured and recorded data. A device according to any one of claims 34 to 37.

41. the processor is adapted to perform SIM and / or SSIM analysis; 41. The device of claim 40.

42. Utilizing a device according to any one of claims 23 to 41 23. The method according to any one of claims 1 to 22.

43. 1. A method for decoding data encoded in a layer of ceramic material by recesses in the layer, comprising: Providing a layer of ceramic material having a recess and preferably coded according to any one of claims 1 to 22; selectively applying a laser beam to a plurality of regions of the layer of the ceramic material using a digital micromirror device; detecting light reflected from each of the plurality of regions; Including, method.

44. Utilizing a device according to any one of claims 34 to 41 44. The method of claim 43.

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