Microstructured device with particles having sorbing and / or catalytic properties, and manufacturing process

Abstract

Embodiments according to the present invention comprise a method for producing a microstructured device (100, 200b,c, 300a,b, 400a,b,c), wherein the method comprises the following steps: providing a substrate (110) with at least one cavity (120), wherein the cavity (120) is partially filled with first particles (130) in the form of loose, dry powder and wherein the first particles (130) have sorbing and / or catalytic properties. Furthermore, the process comprises filling the at least partially filled cavity (120) with second particles (140) in the form of loose, dry powder and coating the second particles (140) resting on the loose first particles (130) by means of a coating process, such that the coated second particles (142) combine to form a porous body (150) and such that the first particles (130) are arranged between the porous body (150) and the substrate (110).Furthermore, a corresponding microstructured device is disclosed.

Description

Technical area

[0001] Embodiments of the present invention relate to microstructured devices comprising particles with sorbing and / or catalytic properties, as well as associated manufacturing methods.

[0002] Furthermore, embodiments relate to the integration of reactive powders into miniaturized components. Background of the invention

[0003] A wide variety of sensors and devices are based on the interaction of sorbent, chemically or catalytically active materials with gases or liquids. During sorption, ions, atoms, or molecules of other substances are enriched in the volume of the sorbent (absorption) or on its surface (adsorption). Absorbent materials are used, for example, in exhaust gas purification and water treatment plants or air filters to remove toxic substances. Adsorbents are widely used, for example, in chromatographic columns for substance separation or in gas detection systems for the enrichment of substances that must be detected in extremely low concentrations. Getter materials, which are used to maintain a vacuum in a closed volume, can be based either on sorption or on a chemical reaction with the gas to be bound. Catalysts accelerate chemical reactions on a surface on which they are located.

[0004] All of these materials are also of great interest for microsystems (MEMS), e.g., in miniaturized gas sensors and microreactors or pre-concentrators for gas chromatographs. In conventional devices, these materials are used in powder form, as the largest possible surface area is important or even essential. The powder particles are often comparatively large (e.g., up to 400 µm in diameter) and highly porous, meaning they have a large internal surface area. The integration of such large particles into relatively small MEMS components without altering their surface area and properties remains an unsolved problem.

[0005] Conventional approaches in this field of technology are known, for example, from DE 10 2015 206 377 A1. DE 10 2015 206 377 A1 deals with a device comprising a substrate having a recess and a plurality of particles arranged in the recess. A first portion of the particles is bonded to a porous structure by means of a coating. A second portion of the particles is not bonded by means of the coating. The first portion of particles is arranged closer to an opening of the recess than the second portion of particles, thus preventing the second portion of particles from escaping from the recess through the opening.

[0006] DE 10 2016 215 617 A1 discloses a method for producing a device, wherein a substrate is provided having a recess. A plurality of loose particles is introduced into the recess. A first portion of the particles is coated using a coating process, such that the first portion is bonded to form a solidified porous structure. The penetration depth of the coating process into the recess is adjusted such that a second portion of the particles is not bonded by means of the coating, and such that the solidified first portion of the particles is arranged between the second portion of the particles and an area surrounding the recess. The second portion of the particles is at least partially removed from the recess.

[0007] DE 10 2020 209 525 A1 discloses a method for filling microcavities, in which microcavities are filled with a powdered material containing particles having an average particle size d50 in the range of 1 µm to 20 µm. For this purpose, the powdered material is conveyed into the microcavities and compacted therein by means of vibrations in the frequency range of 25 Hz to 150 Hz and superimposed vibrations in the frequency range of 10 kHz to 100 kHz. Excess powdered material is then removed so that the surfaces of the fills in the microcavities are flush with the planar surface of the carrier.

[0008] Therefore, one object of the invention is, inter alia, to provide a concept for microstructured devices and associated manufacturing methods for integrating reactive powders in the form of sorbing and / or catalytically active materials, which enables an improved compromise between a complexity and thus a manufacturing effort of such a device and an effectiveness of the device with regard to the use of the sorbing and / or catalytically active materials.

[0009] This object is achieved by the subject matter of the independent claims. Further developments of the invention are defined in the subclaims. All embodiments and examples of the description that do not fall within the scope of the claims are not part of the invention and serve only for illustrative purposes. Summary of the invention

[0010] Embodiments according to the present invention comprise a method for producing a microstructured device, the method comprising the following steps: providing a substrate having at least one cavity, the cavity being partially filled with a plurality of first particles in the form of loose, dry powder, the first particles having sorbing and / or catalytic properties. Furthermore, the method comprises filling the partially filled cavity with a plurality of second particles in the form of loose, dry powder and coating the second particles resting on the loose first particles by means of a coating process, such that the coated second particles combine to form a porous body, and such that the first particles are arranged between the porous body and the substrate. The first particles can be significantly larger than the second particles, i.e.the first particles have a larger average diameter compared to the second particles.

[0011] In many applications, such as pre-concentrators for air analysis systems, it is desirable to integrate the first particles with sorbing or catalytic properties into devices with the smallest possible dimensions. However, due to their size, integrating the first particles at the microstructural level (MEMS) is problematic. This means that the miniaturization of such systems has so far failed, among other things, due to the lack of suitable MEMS-based pre-concentrators.

[0012] However, within the scope of the present disclosure, a method is presented by which the first particles, which have sorbing and / or catalytic properties (and can therefore also be referred to as sorption particles below), can be integrated into a microstructured device with the aid of the relatively smaller second particles.

[0013] For this purpose, a substrate with a cavity is first provided, whereby the first particles in the form of loose, dry powder partially fill the substrate cavity, e.g., down to below the substrate surface or below the upper edge of the cavity. The cavity is therefore not completely filled with the first particles to the brim, but only partially, e.g., so that no further first particles can be added without them protruding over the edge of the cavity. For example, doctoring off the first, large particles can ensure that the cavity is not filled to the brim with the first particles.

[0014] Since the first particles do not completely fill the cavity volume, a gap remains between the substrate surface and the upper surface of the first particles in the cavity. This remaining gap can then be filled with the relatively smaller second particles.

[0015] The aforementioned gap between the first particles and the upper edge of the cavity can be large enough that one or more layers of the second particles can be filled and / or poured on without them protruding above the upper edge of the cavity. Any protruding second particles can be removed, e.g., by doctoring. The height of the gap can, for example, roughly correspond to the diameter of the larger first particles. This results, for example, from the above-mentioned doctoring of the larger first particles. In this case, several layers of the smaller second particles preferably find space in the gap above the larger first particles.

[0016] It is conceivable that the fill level of the first particles in the cavity is so far below the upper edge that, on average, at least five layers of the second particles still fit into the gap between the first particles and the upper edge of the cavity. In other words, the unused "fill level" of the cavity may be such that, on average, more than five layers of the smaller second particles can be filled or piled up. "On average" means that there may be fewer layers in some places and more layers in others.

[0017] The smaller second particles can then be poured into the cavity. These are, for example, piled onto the larger first particles. The smaller second particles can fall or trickle through the first particles, at least partially, until they reach a base structure of the cavity. However, the smaller second particles can also essentially fill an area between the larger first particles and a cavity opening, so that the first and second particles are essentially present in separate layers.

[0018] The smaller second particles resting on top of the first particles are then coated using a coating process, which solidifies them. The coated second particles lying on top can form a rigid porous body. The extent (e.g., vertical extent or thickness) of the porous body can be controlled by the penetration depth of the coating process. The porous body thus comprises the portion of the second particles agglomerated by the coating. Uncoated second particles can remain in the cavity below the porous body.

[0019] In addition, the porous body can optionally be connected to a wall area of ​​the cavity by means of the coating and thus form, for example, a kind of lid or plug for the cavity.

[0020] The inventors have recognized that this porous body can be used to enclose the larger first particles, which have sorbing and / or catalytic properties, in the cavity. Furthermore, the inventors have recognized that such powder-based processes are suitable for manufacturing microstructures, so that devices according to the invention can be provided in the form of MMS (micromechanical) or MEMS (microelectromechanical) components.

[0021] The inventors have further recognized that the coating according to the invention of the deposited second particles makes it possible to prevent or at least inhibit an undesirable change in the properties (specifically the sorbing and / or catalytic properties) of the first particles. In other words, the smaller second particles resting on the larger first particles can form a type of protective layer against undesirable processing influences. For example, the penetration depth of the coating process can be controlled such that a mechanically stable, solidified layer in the form of the rigid porous body is provided without deactivating the properties of the first particles, for example, in particular their surface properties (e.g., properties due to a nanoporous surface).

[0022] In particular, processing based on coating processes enables a reduction of undesirable thermal influences on the first particles, which could also impair desired properties.

[0023] As mentioned at the beginning, both the first particles and the second particles can be in the form of a dry powder. A powder, in turn, can be in the form of a granular material or in the form of a powder, for example. Such powders can therefore comprise a large number of small particles or be formed from such a number. The particles can, for example, have average or maximum particle sizes of less than 1000 µm or less than 500 µm, or less than 300 µm, or less than 100 µm, or less than 50 µm. A mean particle size can, for example, be specified using the factor D50. The particle size distribution D50 can, for example, be referred to as the median value or mean value of the particle size distribution. This is, for example, the value of the particle diameter at 50% in the cumulative distribution.

[0024] According to embodiments, the rigid porous body can be arranged within the cavity. Thus, for example, a planar, i.e., flat, surface can be formed by means of the porous body and the parts of the substrate surrounding the cavity. Thus, for example, further MEMS elements, such as heating elements, can be arranged on the porous body and the surrounding surface.

[0025] Alternatively, the rigid porous body can also extend beyond the cavity opening, for example, if the second particles are not applied flush with the substrate surface after being poured on and subsequently coated. Optionally, such a porous body can extend across multiple cavities and, optionally, also form a planar layer on the substrate surface as a whole. Thus, further elements, such as heating elements, can be applied to such a porous, planar layer.

[0026] According to embodiments, the coating process may include atomic layer deposition (ALD). The use of atomic layer deposition enables precisely adjustable layer thicknesses and penetration depths, so that the second particles can be coated to a predefined depth. The porous body produced by the coating can thus have a predefined mechanical strength. At the same time, underlying first and / or second particles can remain substantially uncoated.

[0027] According to embodiments, a layer thickness of a layer produced by means of the coating process can be less than 100 nm. The inventors have recognized that this allows a good compromise to be achieved between the stability and robustness of the device, in particular of the porous body, and the time required for production. In order to carry out the coating process within an acceptable timeframe, it can be advantageous to limit the layer thickness to a maximum of 100 nm. The height of the rigid, porous body or its vertical extension (perpendicular to the substrate plane) between the substrate and a surface of the device opposite the substrate is determined, among other things, by the penetration depth of the ALD layer, i.e., by the number of layers of particles that are solidified by means of the ALD layer. Depending on the type and size of the particles, an ALD layer as small as 30 nm can be sufficient for solidification.

[0028] In other words, the height, or vertical extension, or the dimension in the vertical direction of the rigid, porous body can be determined by the penetration depth of the ALD layer, i.e., for example, a penetration depth in this vertical direction. Vertical describes a direction (perpendicular to the substrate plane or to the main extension direction of the substrate) corresponding to a stacking sequence of substrate and particle beds, i.e., for example, the direction perpendicular to a bottom surface of the substrate, which forms a lower end of the device.

[0029] Such a vertical extension of the porous body can be referred to as thickness, for example, but should not be confused with the layer thickness or a corresponding definition of the thickness of the ALD layer. The ALD layer deposits on particles of the particle mixture and has a defined layer thickness perpendicular to the surface of the particle to which it is deposited. Particles of the particle mixture that have agglomerated, i.e., grown together, by means of the coating can form the porous body, whose vertical extension (i.e., height or thickness perpendicular to the substrate plane) is measured based on the penetration depth of the ALD layer.

[0030] Penetration depth and ALD layer thickness can therefore be two different, independent parameters. The penetration depth can be determined, for example, by the amount and residence time of the precursors in the reactor. The layer thickness, in turn, can be a function of the number of cycles, i.e., how often the ALD cycle is repeated.

[0031] For example, a 30 nm ALD layer thickness may be sufficient for small particles to solidify into a rigid, porous structure (e.g., for 5 µm NdFeB particles in a 400 µm deep cavity). However, the penetration depth should preferably be several particle layers, otherwise solidification might not be achieved even with an ALD layer thickness of 200 nm.

[0032] According to embodiments, the coating process can be carried out such that at least some first particles and / or at least some intermediate second particles (i.e., arranged between the first particles, for example) remain uncoated. Thus, for example, sorbing and / or catalytic properties of the first particles can be preserved and / or ensured. Accordingly, desired properties of the second particles, which would be altered, for example, by the coating, can also be preserved, for example, likewise sorbing and / or catalytic properties and / or properties with respect to thermal conductivity. Furthermore, an uncoated particle mixture of the first and second particles embedded in the cavity can thus be provided.

[0033] Under certain circumstances, at least partial coating of the first particles cannot be avoided when carrying out the coating process. However, according to embodiments, for example, at least 50% of the first particles can remain uncoated, or at least 70%, or at least 90%. Complete coating of the first particles in the cavity is not advisable according to some embodiments.

[0034] According to embodiments, the first particles and the second particles can each comprise a different material. Thus, the first particles can be selected, for example, based on their sorbing and / or catalytic properties, and the second particles can be selected based on their coatability and suitability for providing a robust and mechanically stable body, essentially independently of one another.

[0035] The geometric shape of the second particles can also be an important factor. Gravel-like powder, for example, with a D50 of 10 µm, and a relatively broad size distribution can result in a significantly stronger porous structure than unidisperse, round particles, e.g., with a diameter of 10 µm (or D50). In other words, according to embodiments, the second particles can be configured in the form of a gravel-like powder. The second particles can thus, for example, be in the form of angular, broken particles.

[0036] According to embodiments, the first particles and the second particles can each comprise the same material. This allows manufacturing and material costs to be kept low, for example. Furthermore, the amount of sorbing and / or catalytic material in the device can be increased, for example, if the second particles also have sorbing and / or catalytic properties. In such a case, the second particles can, for example, comprise, in particular, smaller particles of the same material, e.g., to form more robust porous bodies. Size separation can be achieved, for example, by means of sieving.

[0037] According to embodiments, the coating of the second particles can have processing temperatures of at least 20°C and at most 300°C, or of at least 75°C and at most 200°C. The inventors have recognized that processing according to the invention within these temperature ranges makes it possible to ensure good functionality of the sorbing and / or catalytic properties of the device. This means that within these temperature ranges, the sorbing and / or catalytic properties of the first particles are not destroyed. Temperatures exceeding these ranges can lead to irreversible damage to the sorbing and / or catalytic properties. The processing temperatures can be, for example, average or maximum ambient temperatures achieved during coating, or temperatures to which the first particles are specifically heated during production.

[0038] According to embodiments, the first particles may have an average particle size of at least 50 µm and at most 400 µm, or of at least 150 µm and at most 400 µm.

[0039] According to embodiments, the second particles can have an average particle size of at most 15 µm, or of at most 10 µm, or of at most 5 µm. The smaller the second particles, the stronger the porous structure that can be created by coating the second particles. Furthermore, the inventors have recognized that the shape of the particles can also influence the strength of the porous structure.

[0040] According to embodiments, the first particles can be larger than the second particles on average by at least a factor of 5, or at least a factor of 10, or at least a factor of 20, or at least a factor of 30, or at least a factor of 50. The inventors have recognized that relatively large first particles can be particularly robustly secured in the cavity with relatively smaller second particles.

[0041] Since the ALD layer can be limited to 100 nm in some embodiments, the second particles to be coated should preferably be as small and irregularly shaped as possible (e.g. gravel-like) in order to achieve a particularly robust or solid porous structure.

[0042] At the same time, the porous structure should have a defined extent (e.g., vertical extent or thickness), meaning the ALD layer should not penetrate to any desired depth, so that the first particles remain essentially uncoated. For this purpose, the second particles should also be as small as possible, as this also minimizes the cavities through which the ALD precursors penetrate the powder bed, while simultaneously providing a large surface area.

[0043] According to embodiments, the second particles can have a thermal conductivity of at least 30 W / (m·K), or of at least 80 W / (m·K), or of at least 130 W / (m·K). The second particles can thus be used as a thermal bridge to the first particles in order to enable rapid heating, e.g. to fulfill a gas sensor functionality. This can be particularly advantageous, for example, if the second particles form a particle mixture with the first particles below the porous body in the cavity, so that good heat conduction can be provided, e.g. starting from the porous body (e.g. heated by means of heating elements which are optionally applied to the porous body), i.e. the solidified second particles, via underlying, loose second particles to the first, loose particles.

[0044] The thermal conductivity can be, for example, at least 30 W / (m·K), such as Al2O3, or at least 80 W / (m·K) (e.g. using Si3N4 with, for example, 90 W / (m·K)), or at least 130 W / (m·K) (e.g. silicon with 148 W / (m·K), AlN with 320 W / (m·K), diamond with 2200 W / (m·K)). According to embodiments, all of these materials can be used individually or together. Furthermore, these materials can be easily processed in powder form. The above materials are also available at low cost with a D50 in the range of a few µm.

[0045] According to embodiments, the method can further comprise the following steps: providing spherical elements, wherein the spherical elements have a diameter that is greater than a maximum width or a maximum diameter of the cavity, generating vibrations, e.g. in the frequency range 25 Hz to 150 Hz, and superimposed vibrations, e.g. in the frequency range 10 kHz to 100 kHz, in order to compact the first particles in the cavity by means of the spherical elements, removing the spherical elements and doctoring off the excess first particles from the substrate surface. Subsequently, filling the partially filled cavity with the second particles in the form of the loose, dry powder and doctoring off excess second particles. The first particles can thus be compacted in the cavity in order, for example, to achieve the highest possible sorbing and / or catalytic effect of the device.By means of doctoring, a flat surface can be created on which, after coating, further MEMS elements, such as heating elements, can be arranged.

[0046] If the large particles are introduced using the described vibration-based process, the substrate surface should subsequently be freed of excess large particles, e.g., using a doctor blade, before the small particles are applied. Otherwise, it may not be possible to achieve a fill level below the top edge of the cavity or below the substrate surface, allowing the small particles to fill this residual gap. The thickness or depth of the residual gap should preferably be significantly greater than the thickness of a layer of small particles to enable the creation of a mechanically strong porous structure.

[0047] According to embodiments, the substrate may have a plurality of cavities, and the method may further comprise the following steps: Partially filling the cavities with the first particles in the form of the loose, dry powder, wherein the at least partial filling comprises a metered injection of a predetermined amount of the first particles into the respective cavity, Pouring the second particles in the form of the loose, dry powder into the at least partially filled cavities, doctoring off excess second particles, and at least partially solidifying the second particles to produce a plurality of porous bodies arranged in the cavities, such that the loose, first particles are arranged between respective porous bodies and the substrate.

[0048] The sorbing and / or catalytic first particles can, for example, be particles with limited availability, the production and / or extraction of which can be associated with high effort and thus expense. Dosed injection can be carried out, for example, using syringes or syringe arrays, so that as few first particles as possible miss the respective cavity and the first particles are thus utilized as completely as possible in the process. In order to still achieve a high processing speed and thus a high production throughput, the second, e.g. cheaper and / or readily available, particles can be applied over a large area of ​​the substrate, e.g. a wafer, in order to create the fill in the respective cavity. Excess second particles are then appropriately doctored off, e.g.

[0049] Furthermore, embodiments according to the present invention comprise a microstructured device comprising a substrate with at least one cavity, first and second particles, and a porous body, wherein the porous body is formed from coated second particles. First particles, e.g., in the form of loose first particles, are arranged between the porous body and the substrate, wherein the first particles have sorbing and / or catalytic properties.

[0050] Devices according to the invention can be based on the same or corresponding findings and / or considerations as corresponding methods according to the invention. Therefore, corresponding devices can have the same or corresponding features, as well as the same or corresponding advantages, as an associated manufacturing method. The same applies accordingly to features disclosed in the context of a microstructured device for manufacturing methods according to the invention.

[0051] According to embodiments, the porous body can form a planar surface together with a substrate surface. As previously explained, additional MEMS elements, such as heating elements, can thus be arranged on the shared planar surface.

[0052] According to embodiments, loose second particles may be arranged between the loose first particles between the porous body and the substrate.

[0053] According to embodiments, the device can be configured in the form of a miniaturized sorption column, a pre-concentrator, e.g., for gas sensors or mobile chromatographic systems, a sorbing and / or catalytically active protective cap, e.g., for MEMS components that communicate with the environment, a getter, e.g., for vacuum packages, a gas sensor, e.g., a catalytic gas sensor, and / or a catalyst. Thus, embodiments enable the addressing of a wide variety of applications. Short character description

[0054] Examples according to the present disclosure are explained in more detail below with reference to the accompanying figures. With regard to the schematic figures shown, it should be noted that the illustrated functional blocks are to be understood both as elements or features of the device according to the disclosure and as corresponding method steps of the method according to the disclosure, and corresponding method steps of the method according to the disclosure can also be derived therefrom. They show: Fig. 1 is a schematic view of a microstructured device according to embodiments of the present invention; Fig. 2a-c schematic views of devices with integrated heater, according to embodiments; and Fig. 3a-c schematic views of devices with particles of different particle sizes, according to embodiments. Detailed description of the examples according to the figures

[0055] Before exemplary embodiments of the present invention are explained in more detail below with reference to the drawings, it is pointed out that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same or similar reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0056] The following examples refer to particles with sorbing and / or catalytic properties. Adsorption includes, among other things, physical adsorption, also referred to as physisorption, and chemical adsorption, also referred to as chemisorption. Chemisorption is a fundamental process in catalysis with solid catalysts, which is why, in the context of the present disclosure, catalysis, and in particular heterogeneous catalysis, also falls under the term adsorption. Accordingly, the terms "sorbing property" and "catalytic property" used herein can be used synonymously. Therefore, if, for example, sorption particles are mentioned in the context of this disclosure, these sorption particles can have sorbing and / or catalytic properties.

[0057] Fig. Figure 1 shows a schematic view of a microstructured device 100 according to embodiments of the present invention. The microstructured device 100 comprises a substrate 110 with a cavity 120, as well as first and second particles 130, 140 located therein. According to the invention, the first particles 130 have sorbing and / or catalytic properties.

[0058] Furthermore, the device 100 comprises a rigid porous body 150. This body can be formed from coated second particles 142. In other words, the second particles 140 can be coated by means of a coating, so that they become coated second particles 142. These coated second particles 142, in turn, form the rigid porous body 150. The solidification of the second particles 140 can also be referred to as agglomeration.

[0059] Optionally, the second particles 140 may also comprise loose particles 144 in addition to the previously mentioned solidified particles 142. These may, for example, be uncoated second particles 140. That is, uncoated loose second particles are identified herein by reference numeral 144, while second particles solidified by the coating are identified by reference numeral 142.

[0060] The loose second particles 144 can, for example, be arranged below the porous structure 150 in the cavity 120 or enclosed therein. The extent (e.g., vertical extent or thickness) of the porous structure 150 can be controlled by the process duration, and thus by the penetration depth of the coating material used during the coating process.

[0061] The first particles 130, which are also arranged in the cavity 120 or enclosed beneath the porous structure 150, can be in the form of loose particles. Depending on the penetration depth of the coating material, it can also happen that at least a portion of the first particles 130 is coated, intentionally or inadvertently. Alternatively or additionally, a portion of the first particles 130 can be at least partially solidified by the coating. Thus, for example, a particle mixture of loose and / or partially solidified first and second particles 130, 144 can be present beneath the porous body 150 in the cavity 120.

[0062] It would also be conceivable that the coating may penetrate into the cavity 120 to below the porous body 150, so that some particles (first and / or second particles) may be coated, but only to the extent that coating material is deposited on a respective particle surface, but the coating has not grown so extensively that neighboring particles would be connected to one another.

[0063] The rigid porous body 150 can be designed to be permeable to a fluid to be sorbed and / or catalyzed, so that the fluid can flow (or, for example, flow through) the rigid porous body 150 to reach the cavity 120. There, the fluid can then encounter the first particles 130, which have sorbing and / or catalytic properties. The fluid can then react accordingly with the first particles 130.

[0064] For example, pores can occupy or make up approximately 50% of the volume of the porous body. They are not much smaller than the particles and are also interconnected (e.g., all interconnected), meaning they can form a three-dimensional network with low flow resistance, allowing the fluid to be sorbed and / or catalyzed to flow through the network, specifically the pores of the porous body.

[0065] As in Fig. 1, the porous body 150 can optionally form an at least substantially planar surface together with a substrate surface. Alternatively, however, the porous body 150 can also protrude beyond the cavity 120 and extend laterally onto the substrate material.

[0066] It should be noted that the illustrated size ratios of the first and second particles 130, 140 are only to be understood as an example.

[0067] Based on Fig. 1, a manufacturing method for a microstructured device 100 is explained below. First, a substrate 110 having a cavity 120 is provided. Subsequently, the cavity 120 is at least partially filled with the first particles 130 in the form of loose, dry powder. The cavity 120 can, for example, be filled with first particles 130 to the extent that they just do not protrude beyond the edge or upper edge of the cavity 120. This can be ensured, for example, by doctoring off the excess particles. In this way, all particles that protrude beyond the upper edge of the cavity can be removed. Alternatively, a substrate with an already partially filled cavity can be provided.

[0068] The second particles 140, in the form of loose, dry powder, can then be poured onto the first particles 130. The first particles 130 can have a significantly larger diameter than the second particles 140. Some of the smaller second particles 140 can, for example, trickle through the relatively larger first particles 130 or arrange themselves between the larger first particles 130. However, the second particles 140 can also, as shown in Fig. 1 as an optional feature, remain essentially on the particles 130.

[0069] At least a portion (particles 142) of the second particles 140 is then coated, whereby this coated portion 142 of the second particles 140 is solidified into a rigid porous body 150. Thus, the first particles 130, and any loose second particles 144, can be enclosed between the porous body 150 and the substrate 110.

[0070] The coating can, for example, bond the solidified particles 142 not only to each other but also to the wall regions of the cavity 120, so that the porous body 150 acts, for example, like a fixed plug for the cavity 120. Due to the porosity of the body 150, a fluid can interact with the first particles 130 (and optionally second particles 144) through the porous body 150. It should be noted again that a portion of the first particles 130 can also be coated.

[0071] As in Fig. 1, the porous body 150 can be arranged within the cavity 120. Optionally, as previously explained, the porous body 150 can also extend to the substrate surface, for example, if the second particles 140 are not removed flush with the cavity 120 and subsequently solidified.

[0072] In particular, the use of atomic layer deposition enables precise and reliable adjustment of the coating penetration depth to produce robust porous bodies with short processing times. Corresponding layer thicknesses can be less than 100 nm, for example.

[0073] Substrates 110 can, for example, have PowderMEMS structures and have the advantage that they are compatible with standard MEMS and semiconductor manufacturing processes and can therefore be further processed in a clean room.

[0074] The production of PowderMEMS structures can be carried out as described in EP 2670880 B1 or US 9221217 B2. Automated filling of loose powder into microcavities in a planar substrate can be carried out as disclosed in DE 10 2020 209525 A1.

[0075] Furthermore, the PowderMEMS process according to the invention can be used for introducing and fixing powder materials for miniaturized getter pumps or pre-concentrators. In this case, the particle bed in the cavity is not completely agglomerated, but only to a certain depth. The particles below the agglomerated area (e.g., below the porous body) remain essentially uncoated or in their original state, allowing a gas or liquid to interact with them through the agglomerated porous body.

[0076] Fig. Figure 2 shows schematic views of possible designs of a getter pump or a pre-concentrator with integrated heater by partial agglomeration of the particles, according to embodiments. In the structure 300a according to Fig. 2a, the substrate 110 is heated directly (see heater 310). In the structure 300b according to Fig. 2b, a planar heater 320 is created on the porous structure 150. It should be noted that the additional heating and passivation structures of devices 300a and 300b are optional features.

[0077] Optional features are shown in the examples of Fig. 2a and Fig. 2b, the first particles 130 are completely uncoated and the second particles 140 are completely coated. As explained above, a particle mixture of first and second particles can also be uncoated, i.e., loosely arranged beneath the porous body 150. Likewise, a portion of the first particles 130 can also be coated and thus, for example, be part of the porous body 150 (or simply with a coated particle surface without cohesion to neighboring particles).

[0078] Furthermore, the device has an optional passivation 330. Fig. Figure 2c shows an SEM image 300c of a partially agglomerated structure after sawing. The porous body 150 (which can be configured, for example, in the form of a porous membrane) is, for example, 130 µm thick. The particles used here in this non-limiting example have a D50 of 6 µm, i.e., corresponding to the extent (e.g., vertical extent or thickness) of 130 µm, approximately twenty layers (130 µm / 6 µm) of the second particles are arranged on the first particles. The loose particles 130 originally located underneath were flushed out of the cavity 120 during sawing. The total depth of the cavity 120 is, for example, 530 µm.

[0079] In other words, show Fig. 2a and Fig. 2b schematic views of two possible designs according to exemplary embodiments. If one saws through such a structure, the uncoated particles 130 fall out, while the rigid porous body 150 remains, see Fig. 2c.

[0080] The mechanical strength of PowderMEMS structures can vary depending on the size and shape of the particles used, as well as the thickness of the ALD layer and the materials involved. The layer thickness of conventional ALD processes, for example, ranges from a few nanometers to several hundred nm. For the PowderMEMS process, layer thicknesses below 100 nm are used to avoid very long processing times.

[0081] With increasing particle size, the strength of the porous body can decrease. The maximum particle size that allows sufficient strength of the porous body for further processing or use can, for example, or typically, be in the range below 25 µm (D50). As mentioned above, however, many sorbent or chemically or catalytically active powders consist of much larger particles (e.g., 150-400 µm). Therefore, it is difficult to integrate such large sorbent / catalytic particles into small, microstructured MEMS devices.

[0082] Regarding the use of such large particles for corresponding MEMS components according to Fig. 2, the optional embodiments according to Fig. 3, which enable efficient implementation, particularly for large first particles. Thus, implementation problems of MEMS components with such large particles can be solved using exemplary embodiments according to conventional solutions.

[0083] In general, for example, the first particles 130 can have an average particle size (D50) of at least 50 µm and at most 400 µm, or an average particle size (D50) of at least 150 µm and at most 400 µm. The second particles 140 can have an average particle size (D50) of at most 15 µm, of at most 10 µm, or of at most 5 µm. In particular, the first particles 130 can be larger on average than the second particles 140 by at least a factor of 5, at least a factor of 10, at least a factor of 20, at least a factor of 30, or at least a factor of 50.

[0084] Examples of embodiments, in particular those described below in the context of Fig. 3 explained embodiments, enable that • the uncoated first particles 130 are securely held in the cavity 120 due to the high mechanical strength of the porous membrane 150 (which is formed, for example, by means of smaller, coated second particles 140), e.g. even when using particularly large first particles 130; • the further processing is not restricted, for example, by a high roughness of the porous structure 150 (e.g. due to the use of smaller second particles 140 instead of large, sorbing and / or catalyzing particles 130 for the formation of the porous body 150), so that, for example, a heating element 320 according to Fig. 2b can be produced efficiently; • the extent (e.g. vertical extent or thickness) of the porous body 150 can be well controlled, ie that a limitation of the penetration depth of the ALD layer can be efficiently possible due to the appropriately selected, e.g. small, particle gaps.

[0085] Fig. 3 illustrates a solution approach according to embodiments, which in particular enables an efficient integration of particularly large first particles 130. Fig. Figure 3 shows schematic illustrations of the partial agglomeration according to Fig. 2 using a second powder B, i.e. second particles 140, with a substantially smaller particle size compared to the first particles 130, according to embodiments.

[0086] The powder with the large first particles 130 (e.g. sorption, getter, catalyst material) is referred to below as powder A, the powder with the correspondingly smaller second particles 140 of any material, powder B. First, the powder A 130 is introduced into the cavities 120 in the substrate 110, see Fig. 3a. This can be done, for example, using the process described in DE 10 2020209525 A1. In a special device, the dry powder A 130 can be dosed onto the substrate surface together with rubber balls, and the particles of powder A 130 can then be transported into the cavities 120 and compacted by superimposing a low-frequency vibration with ultrasound (see also [3]).

[0087] In an optional second step, the surface of the substrate 110 can be freed of excess powder A 130, for example by doctoring. As shown by the structure 400a, the "protruding" particles A 130 can thereby be removed from the cavities 120, so that the filling level of the cavity 120 is below the substrate surface.

[0088] According to some embodiments, the doctoring off of the first, large particles may even be necessary at this point because otherwise there would be no space in the cavity for the small, second particles.

[0089] In a second filling process, the cavities 120 are filled or poured with powder B 140, see structure 400b in Fig. 3b. This can be achieved by applying powder B 140 to the substrate surface, then spreading it over the substrate surface and then doctoring it off. This can also at least partially fill the gaps between the large particles 130.

[0090] The subsequent coating process, e.g., an ALD process, can optionally be adjusted so that only powder B 140 is agglomerated to a certain depth (particle 142), and the large particles 130 of powder A (e.g., at least 50%) as well as a portion of the small particles of powder B (particle 144) remain uncoated. In this way, a porous membrane 150 with high strength and a comparatively flat surface can be formed independently of powder A 130, see device 400c in Fig. 3c.

[0091] In general, methods according to embodiments optionally comprise providing spherical elements, wherein the spherical elements have a diameter that is greater than a maximum width or a maximum diameter of the cavity 120, generating vibrations, e.g. in the frequency range 25 Hz to 150 Hz, and superimposed vibrations, e.g. in the frequency range 10 kHz to 100 kHz, in order to compact the first particles 130 in the cavity 120 by means of the spherical elements, removing the spherical elements, scraping off the excess first particles from the substrate surface, filling the partially filled cavity 120 with the second particles 140 in the form of loose, dry powder, and scraping off excess second particles 140.

[0092] A decisive advantage of the approach according to Fig. 2 and Fig. 3 is the low temperature of the coating processes optionally used for agglomeration, such as ALD processes, which is typically between room temperature and 300°C and preferably between 75°C and 200°C. Sorbent or chemically and / or catalytically active powders 130 can be temperature-sensitive, i.e., at temperatures above 300-400°C, these powders 130 can undergo detrimental changes to their function or be completely deactivated.

[0093] Thus, embodiments include coating the second particles 140 in which processing temperatures of at least 20°C and at most 300°C or of at least 75°C and at most 200°C arise or prevail.

[0094] For this reason, conventional approaches make it difficult to integrate such powders into many components in parallel at the wafer level and subsequently seal them using standard wafer-level packaging processes, such as glass frit bonding or metal solder bonding. However, embodiments may enable such approaches. In particular, the rigid porous body 150 can act as a protective layer for the particles 130 against the processing influences of subsequent processing steps.

[0095] Protection against processing influences can be provided by preventing particles from falling out or being washed out. Protection against gases, chemicals, and temperature can be provided for the initial particles, for example, by an additional layer that closes the pores of the rigid porous body.

[0096] In Fig. 3, the aspect ratio of powder A to powder B is approximately 4:1, only for illustrative purposes. However, much higher aspect ratios may be more realistic for some applications. For example, the adsorbent material used in [1] is Carboxen 1000 with particle sizes of 60-80 mesh, i.e., 177-250 µm in diameter.

[0097] Powder B 140 can or should preferably consist of particles with a D50 of less than 10 µm, and particularly preferably with a D50 of less than 5 µm, or comprise particles of the same size in order to obtain a mechanically strong porous membrane 150 with the lowest possible roughness (or roughness). However, powder B 140 can also have a D50 of up to 25 µm, e.g., if the size distribution of powder 140 includes many small particles.

[0098] The type of material of powder B 140 can, for example, for the solution according to Fig. 3, can be freely selected. In principle, it can also be the same sorbing or chemically or catalytically active material from which the particles A 130 are made. In other words, the first particles 130 and the second particles 140 can therefore comprise a different material or the same material.

[0099] Under certain circumstances, it may be advantageous if powder B 140 is made of a material with good thermal conductivity. After, for example, in a pre-concentrator according to Fig. 2, a substance to be detected has been enriched, it should then be released as quickly as possible. This is done, for example, by heating the adsorbing particles of powder A 130. The heating process is faster if the rigid porous body 150 consists of thermally highly conductive particles B 140 or is formed by them (see in particular Fig. 2b), or when the spaces between the large particles A 130 are at least partially or even completely filled with small particles B 140.

[0100] In other words, the second particles 140 can have, for example, a good thermal conductivity, for example a thermal conductivity of at least 30 W / (m·K), of at least 80 W / (m·K) or of at least 130 W / (m·K).

[0101] Based on Fig. 3, further optional features of exemplary embodiments will be discussed below. For example, to provide the structure 400a, e.g., at the wafer level, the filling or filling of the first particles 130 can be carried out by means of a metered injection, e.g., using a syringe or a syringe array. Thus, efficient filling of the cavities 120 with minimal material waste can be achieved, particularly for expensive or difficult-to-obtain first particles 130.

[0102] To ensure a high production throughput, e.g., in the course of mass production, cheaper and / or more readily available second particles 140 can be applied by depositing the second particles 140 onto the substrate surface at the wafer level and then doctoring them into the cavities 120 across the plurality of cavities 120. The agglomeration of the applied second particles 142 into porous bodies 150 can thus also be carried out at the wafer level. This allows a good compromise between material consumption and production speed to be achieved.

[0103] With regard to the effects and advantages of exemplary embodiments, it should be noted in general that for many applications, there are already established and commercially available powders with surface or material properties precisely tailored to the application. The exemplary embodiments and procedures described above allow the integration of any powder, e.g., with a D50 of up to several hundred µm, into microstructures without the powder material being modified or requiring modification.

[0104] Embodiments thus enable and create miniaturized systems, e.g., in the form of pre-concentrators, for the detection of organic contaminants (VOCs - volatile organic compounds) in the ambient air. For the analysis, for example, air is pumped through the pre-concentrator for several minutes to enrich the substances to be detected. The enrichment occurs using the first particles 130 in the cavity 120.

[0105] The pre-concentrator is then connected to a gas chromatograph. By heating, the adsorbed substances can be released abruptly. This can increase the sensitivity of gas analysis by orders of magnitude.

[0106] Embodiments enable miniaturization of such systems, e.g., due to the attachment of relatively large first particles 130 by means of the coated, smaller second particles 142, so that corresponding MEMS-based pre-concentrators can be provided. Manufacturing methods according to the invention are particularly suitable for mass production.

[0107] In general, technical application areas of exemplary embodiments include the integration of, for example, existing powders optimized for the respective application with defined surface properties into microstructures (MEMS), such as: miniaturized sorption columns, pre-concentrators for gas sensors or mobile chromatographic systems, sorbing or catalytically active protective caps for MEMS components that must communicate with the environment, getters for vacuum packages, catalytic gas sensors.

[0108] All lists of materials, environmental influences, electrical properties and optical properties listed herein are to be considered exemplary and not exhaustive.

[0109] Although some aspects have been described in the context of a device, it should be understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Analogously, aspects described in the context of or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware apparatus, such as a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, some or more of the key method steps may be performed by such an apparatus.

[0110] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein. References [1] H.-Y. Kuo, W.-R. Cheng, T.-H. Wu, H.-J. Sheen, C.-C. Wang, and C.-J. Lu, “A MEMSµ- Preconcentrator Employing a Carbon Molecular Sieve Membrane for Highly Volatile Organic Compound Sampling,” Chemosensors, vol. 9, no. 5, p. 104, 2021, doi: 10.3390 / chemosensors9050104. [2] T. Lisec, 0. Behrmann, and B. Gojdka, „PowderMEMS-A Generic Microfabrication Technology for Integrated Three-Dimensional Functional Microstructures,“ Micromachines, vol. 13, no. 3, p. 398, 2022, doi: 10.3390 / mi 13030398. [3] C. Kostmann, T. Lisec, M. T. Bodduluri, and 0. Andersen, „Automated Filling of Dry Micron-Sized Particles into Micro Mold Pattern within Planar Substrates for the Fabrication of Powder-Based 3D Microstructures,“ Micromachines, vol. 12, no. 10, p. 1176, 2021, doi: 10.3390 / mi 12101176.

Claims

[1] A method for producing a microstructured device (100, 300a,b, 400a,b,c), the method comprising the following steps: Providing a substrate (110) having a cavity (120) which is at least partially filled with first particles (130) in the form of loose, dry powder, wherein the first particles (130) have sorbing and / or catalytic properties; Filling the at least partially filled cavity (120) with second particles (140) in the form of loose, dry powder; and Coating second particles (140) resting on the loose first particles (130) by means of a coating process such that coated second particles (142) combine to form a porous body (150), and such that the first particles (130) are arranged between the porous body (150) and the substrate (110); wherein the first particles (130) have an average particle size of at least 50 µm and at most 400 µm; and wherein the first particles (130) are on average at least a factor of 5, or at least a factor of 10, or at least a factor of 20, or at least a factor of 30, or at least a factor of 50 larger than the second particles (140). [2] The method according to claim 1, wherein the porous body (150) is disposed within the cavity (120). [3] A method according to any one of claims 1 or 2, wherein the coating process comprises atomic layer deposition. [4] Method according to one of the preceding claims, wherein a layer thickness of a layer produced by means of the coating process is less than 100 nm. [5] Method according to one of the preceding claims, wherein the coating process is carried out such that at least some first particles (130) and / or at least some intermediate second particles (144) remain uncoated. [6] Method according to one of the preceding claims, wherein the first particles (130) and the second particles (140) comprise different material. [7] Method according to one of claims 1 to 5, wherein the first particles (130) and the second particles (140) comprise the same material. [8] Method according to one of the preceding claims, wherein the coating of the second particles (140) has processing temperatures of at least 20°C and at most 300°C or of at least 75°C and at most 200°C. [9] Method according to one of the preceding claims, wherein the first particles (130) have an average particle size of at least 150 µm and at most 400 µm. [10] Method according to one of the preceding claims, wherein the second particles (140) have an average particle size of at most 25 µm, of at most 10 µm or of at most 5 µm. [11] Method according to one of the preceding claims, wherein the second particles (140) have a thermal conductivity of at least 30 W / (m·K), or of at least 80 W / (m·K), or of at least 130 W / (m·K). [12] Method according to one of the preceding claims, wherein providing the substrate (110) comprises filling the cavity with the first particles (130) in the form of loose, dry powder; and the method further comprising the following steps: Providing spherical elements, wherein the spherical elements have a diameter greater than a maximum width or a maximum diameter of the cavity (120); Generating vibrations, e.g. in the frequency range 25 Hz to 150 Hz, and superimposed vibrations, e.g. in the frequency range 10 kHz to 100 kHz, in order to compress the first particles (130) by means of the spherical elements in the cavity (120); Removing the spherical elements; and scraping off excess first particles (130) from the substrate surface; Pouring the second particles (140) in the form of the loose, dry powder into the at least partially filled cavity (120) and scraping off excess second particles (140). [13] Method according to one of the preceding claims, wherein the substrate (110) has a plurality of cavities (120) and wherein the method further comprises the following steps: partially filling the cavities (120) with the first particles (130) in the form of loose, dry powder, wherein the at least partial filling comprises a metered injection of a predetermined amount of the first particles (130) into the respective cavity (120); Filling the at least partially filled cavities (120) with the second particles (140) in the form of loose, dry powder, and scraping off excess second particles (140); and at least partially solidifying the second particles (140) to produce a plurality of porous bodies (150) arranged in the cavities (120), such that the loose first particles (130) are arranged between respective porous bodies (150) and the substrate (110). [14] Method according to one of the preceding claims, wherein the porous body (150) is arranged in the cavity (120); and wherein the porous body (150) has on average at least five layers of second particles (140) piled up one above the other. [15] Microstructured device (100, 300a,b, 400a,b,c) having the following features: a substrate (110) having at least one cavity (120); first and second particles (130, 140); a porous body (150), wherein the porous body (150) is formed by means of coated second particles (142); wherein first particles (130) are arranged between the porous body (150) and the substrate (110), and wherein the first particles (130) have sorbing and / or catalytic properties; wherein the first particles (130) have an average particle size of at least 50 µm and at most 400 µm; and wherein the first particles (130) are on average at least a factor of 5, or at least a factor of 10, or at least a factor of 20, or at least a factor of 30, or at least a factor of 50 larger than the second particles (140). [16] Device (100, 300a,b, 400a,b,c) according to claim 15, wherein the porous body (150) forms a planar surface together with a substrate surface. [17] Device (100, 300a,b, 400a,b,c) according to one of claims 15 or 16, wherein loose second particles (144) are arranged between loose first particles (130) between the porous body (150) and the substrate (110). [18] Device (100, 300a,b, 400a,b,c) according to one of claims 15 to 17, wherein the device (100, 300a,b, 400a,b,c) is designed in the form of a miniaturized sorption column, a pre-concentrator, e.g. for gas sensors or mobile chromatographic systems, a sorbing or catalytically active protective cap, e.g. for MEMS components that communicate with the environment, a getter, e.g. for vacuum packages, a gas sensor, e.g. a catalytic gas sensor and / or a catalyst.

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