Micromechanical system with particles having first and second mass densities, and method for producing corresponding micromechanical systems

Abstract

Micromechanical system (100, 200, 300, 400, 600 1-3 ) with: a substrate (110, 210, 310, 410, 610, 710); a mass element suspended from the substrate in an oscillating manner (120, 220, 320, 420 1-2 , 620 1-3 ), wherein the mass element is a particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770); and wherein first particles (130a, 230a, 330a, 430a, 630a) of the particle mixture have a first mass density and wherein second particles (130b, 230b, 330b, 430b, 630b) of the particle mixture have a second mass density.

Description

Technical area

[0001] Embodiments according to the present invention relate to micromechanical systems with particle mixtures with particles having first and second mass densities, as well as methods for producing such systems.

[0002] Furthermore, embodiments relate to methods for design-independent adjustment of the resonance frequency of micromechanical oscillators. Background of the invention

[0003] Micromechanical oscillators are used in a variety of technical applications. Examples of MEMS oscillator applications include sensors for various gas and liquid measurements, measuring probes in atomic force microscopes, frequency generators, and vibration energy harvesters. In all of these applications, the resonant frequency of the oscillator is important or even crucial for the function of the component. Sensor applications, for example, utilize a variable-dependent shift in the resonant frequency to measure the target variable. Frequency generators, for example, generate a defined frequency from the resonant frequency of the mechanical oscillator. Vibration energy harvesters, referred to below as vibration harvesters, generate electrical energy when the oscillator is set into vibration by an external mechanical excitation.

[0004] Miniaturized vibration harvesters that can harvest energy from ambient vibration sources are of great interest for the battery-free power supply of wireless sensor nodes. The frequencies of ambient vibration sources can, for example, range from a few Hz to a few kHz. Since the natural frequency of a vibration harvester must match that of the excitation signal for high energy yield, or should ideally match that frequency, a component with an application-specific, well-defined resonance frequency is required or at least advantageous for every application (e.g., every vibration source). "Macroscopic" vibration harvesters manufactured using precision engineering methods or assembled from individual parts can be customized, but are not cost-effective to manufacture.Using semiconductor and MEMS manufacturing techniques, much smaller vibration harvesters could be manufactured very cost-effectively, but not with a freely adjustable resonance frequency for each individual component. With the current state of the art, any modification to a MEMS component involves costly interventions in the design and manufacturing process. The production of vibration harvesters with individually adjusted, arbitrary resonance frequencies using semiconductor and MEMS manufacturing techniques is therefore not economically attractive and is seen as a key technological challenge and a major obstacle to their widespread use [1]. State of the art

[0005] Previous conventional solutions are discussed below.

[0006] The resonance frequency of a vibration harvester can be defined by a suitable design of the vibrating structure (e.g. oscillator) contained in the component, in a simple, or in the simplest case a bending beam with a seismic mass at the free end, see Fig. 9 (a).

[0007] Fig. Figure 9 shows in (a) a schematic cross-section through a piezoelectric vibration harvester according to the state of the art, (b) a representation of an implementation by Microgen [2], where the large silicon mass at the end of the bending beam is clearly visible and (c) a representation of piezoelectric vibration harvesters from Fraunhofer ISIT with different resonance frequencies on one and the same substrate.

[0008] In MEMS-based vibration harvesters, the seismic mass is typically made of the substrate material, usually silicon. The cantilever is created by patterning a thick Si layer deposited on the substrate surface. State-of-the-art technology involves the use of a so-called monocrystalline silicon layer (SOI wafer) or a thick polysilicon layer (epi-poly). Due to their higher energy density compared to inductive and capacitive vibration harvesters and their easier integration at the substrate level, piezoelectric transducers are primarily used in MEMS components. Typically, two metal electrodes and aluminum nitride, aluminum scandium nitride, or lead zirconate titanate (PZT) layers are deposited on the vibrating structure. Fig. Figure 9 (b) shows an example of a piezoelectric vibration harvester BOLT-R0120 from Microgen with a resonance frequency of 120 Hz [2]. It is striking that in the case of silicon with a density of only 2.33 g / cm 3 a large seismic mass is necessary to achieve such low resonance frequencies.

[0009] To adjust the resonance frequency of a MEMS-based vibration harvester, the lateral dimensions of the seismic mass are typically changed, as their depth is or can be predetermined by the substrate thickness. For example, the dynamics of the oscillator must first be recalculated, e.g., in FEM simulations, to determine the correct dimensions. For example, new photomasks are then manufactured. In addition to the design development time, such a mask set generates costs of several thousand euros. However, much higher costs can arise from subsequent optimization of the manufacturing process. Key processes such as Deep Reactive Ion Etching (DRIE), also known as the Bosch process, must, or should, for example, be adapted to each mask design. Aside from the costs, a substantial amount of time is to be expected.

[0010] Alternatively, a limited number of design variants can be fabricated on a wafer to create vibration harvesters with different resonant frequencies, see Fig. 9 (c). In this case, however, only components with the desired resonance frequency can be used for specific customer requirements. A significant portion of the substrate area is thus lost to unwanted components. The more variations are kept on a wafer to offer customers prefabricated components with a suitable resonance frequency, the higher the proportion of unused components. Accordingly, this approach also does not offer a cost-effective solution for the production of customized vibration harvesters.

[0011] There are a variety of approaches to adjusting the resonance frequency of a vibration harvester by introducing a mechanical preload into the moving structure. For macroscopic components, passive devices based on screws and springs are used in EP 2 677 656 B1 and US 8,188,622 B1, see Fig. 10 (a).

[0012] Fig. Figure 10 (a) shows a schematic view of a macroscopic vibration harvester from EP 2 677 656 B1 (with reference numerals associated with the document) with purely mechanical preloading of the bending beam, and (b) a schematic view of a hybrid-mounted vibration harvester, based on a Si chip, with contactless magnetic preloading of the movable structure [3]. Both systems are passive and require manual adjustment.

[0013] In addition to passive adjustments, actively controlled systems are also described. US 2021 / 159816 A1 describes a component whose resonant frequency can be slightly altered by an electrically controllable spring made of an ionic polymer metal composite resting on the cantilever. US 8,471,439 B2 describes how a dielectric layer integrated into the cantilever acts as a variable capacitor. Applying a DC voltage changes the impedance and consequently the Young's modulus and stiffness of the cantilever. US 9,344,014 B2 achieves an analogous effect using an inductor. This also allows slight changes in the resonant frequency. In all three cases, the active control loop consumes energy.

[0014] In US 10,644,579 B2, the movable structure of the harvester is prestressed contactlessly using magnetic forces. This can be done passively using permanent magnets or actively using electromagnets and with corresponding energy consumption. Contactless prestressing of the mechanical structure is also known for MEMS components. In [3], for example, the movable silicon structure, manufactured using MEMS techniques, is provided with a permanent magnet at the chip level to implement a magnetic prestress, see Fig. 10 (b).

[0015] Another option for adjusting the resonance frequency is to operate the vibratory harvester at a preset ambient pressure and / or in different gases. This is described in US Pat. No. 8,188,622 B1 for a macroscopic vibratory harvester and in [4] for a MEMS-based vibratory harvester. The change in the resonance frequency is limited to a few percent.

[0016] Alternatively, the weight of the seismic mass can be changed. The following designs are known in connection with macroscopic components. In US 8,987,924 B2, the seismic mass is modified using numerous electrically adjustable elements on the movable structure. This control requires energy, which must be generated by the harvester. CN 110212810 B describes a vibrating harvester with a container at the free end of the bending beam, which is filled with a liquid to adjust the seismic mass. In US 8,188,622 B1, the seismic mass has a cavity that can be filled with liquid or gas via a suitable supply line to change the weight. In US 9,106,160 B2, the resonance frequency is adjusted by inserting additional weights into designated openings in the seismic mass.

[0017] In [5], an array of cavities in the seismic mass of a macroscopic vibratory harvester is filled with tungsten powder and then a capping layer is applied to prevent the loose particles from falling out, see Fig. 11 (a). If all cavities are filled, the resonance frequency of the component drops from approximately 50 Hz to approximately 20 Hz. Depending on the degree of filling of all or individual cavities of the array, the resonance frequency can be adjusted.

[0018] Fig. Figure 11 shows (a) a schematic view of a macroscopic vibratory harvester from [5] with an array of cavities in the seismic mass that can be filled with tungsten powder and (b) a schematic view of a macroscopic vibratory harvester according to US7626316B2 (with reference numerals belonging to the document). Fig. 11 (b) further shows: 122, 124 - transfer elements, 128 - piezo or a piezo element.

[0019] A modification of both the mass and the dimensions of the movable structure is achieved in US 7,626,316 B2, Fig. 11 (b). Thanks to movable bearings on transfer elements, this macroscopic harvester adjusts itself to the excitation frequency passively. However, this concept is not transferable to MEMS. Another self-adapting system is described in US 2014 / 0035438 A1. This system exploits the fact that, in a rotating system, centrifugal forces lead to a stiffening of a radially oriented cantilever beam, allowing its resonance frequency to adapt to the rotation speed.

[0020] In the case of MEMS components, modifications of the seismic mass are only described at the chip level. To lower the resonance frequency and increase the energy yield, the silicon of the seismic mass is replaced with tungsten in [6]. The component is fabricated at the substrate level, but the tungsten mass is mounted at the chip level. The chip is then hermetically encapsulated, see Fig. 12 (a).

[0021] Fig. Figure 12 shows (a) a schematic view of a MEMS-based vibration harvester from [6] with a seismic mass made of tungsten and (b) a schematic view of a concept of a MEMS-based vibration harvester according to EP 3 185 320 B1 (with reference numerals belonging to the document). Fig. 12 (b) shows seismic mass 24 and piezo layer 30.

[0022] EP 3 185 320 B1 discloses a special manufacturing process to better utilize the volume beneath the movable structure of a MEMS-based vibration harvester, see Fig. 12 (b). Compared to the classic design according to Fig. 9 (a) and Fig. 9 (b) significantly less chip area is required for a Si mass of the same size. However, implementing the described features involves considerable effort.

[0023] To avoid having to individually adjust the resonance frequency to the excitation for each application, the bandwidth of the harvester can be extended by introducing bistability or nonlinearity. This allows for the compensation of minor fluctuations in the resonance frequency. In US 10,224,835 B1, bistability is induced by magnetic forces, see Fig. 13 (a).

[0024] Fig. Figure 13 shows (a) a schematic representation of a bistable vibration harvester based on magnetic repulsion according to US 10,224,835 B1, (b) a schematic representation of the principle of a vibration harvester with two mechanically coupled elements according to US 10,033,305 B2 (with reference numerals belonging to the document) and (c) a schematic representation of an alternative embodiment of a harvester based on the principle of mechanical coupling of movable microstructures [8]. Fig. 13 (b) also shows: piezo layer 316, bending beam 302, seismic mass 304.

[0025] Due to the repulsive forces of the magnets, the bending beam is Fig. 11 (a) and / or in Fig. 13 (a) either deflected far upwards or far downwards. Alternatively, a multiply clamped movable structure can be subjected to compressive stress to achieve bistability [7]. Stress-induced bistability can be realized relatively easily in MEMS devices by a suitable design of the movable structure. A higher bandwidth through nonlinearity is achieved, for example, by connecting two bending beams with a soft spring, as described in US 10,033,305 B2, see Fig. 13 (b). Another possibility is described in [8], see Fig. 13 (c). In [9], a further improvement is achieved by combining the principle of coupled cantilever beams with permanent magnets for contactless preloading of the moving structures.

[0026] In summary, there are many ways to influence the resonance frequency of vibration harvesters. Most of the concepts mentioned for macroscopic components cannot, in principle, be reproduced using semiconductor and MEMS technology, especially when mechanical contact between moving components is required. Such microstructures would fail within a very short time due to wear effects. Contactless methods with active control place a strain on the already very low energy yield of MEMS-based vibration harvesters. The concepts according to Fig. 10 (b) and Fig. 12 and Fig. 13 are complex to manufacture or require special materials, and are therefore difficult to implement cost-effectively. The only feasible method using MEMS technologies for tuning the resonant frequency of MEMS-based vibration harvesters during their manufacturing without significant changes to the process or component design is based on adjusting the pressure in the package during wafer-level bonding [4]. However, this type of tuning is limited to a very narrow frequency range. Furthermore, the highest energy yield is achieved in vacuum; with increasing pressure, it decreases by several factors due to damping effects.

[0027] Based on this, there is a need for an improved concept for a micromechanical system that has a low complexity and at the same time a high degree of adaptability with regard to characteristic properties of the system, while at the same time being mass-producible.

[0028] Such a concept is provided by the subject matter of the independent claims of the present invention. Further developments of the invention are defined in the subclaims. Summary of the invention

[0029] Embodiments according to the present invention comprise a micromechanical system having a substrate and a mass element suspended from the substrate in an oscillating manner, wherein the mass element comprises a particle mixture and wherein first particles of the particle mixture have a first mass density and wherein second particles of the particle mixture have a second mass density.

[0030] Embodiments according to the present invention are based on the finding that a characteristic property of a micromechanical system comprising a mass element suspended from a substrate in an oscillating manner can be adjusted by adjusting a ratio of first and second particles of a particle mixture of the mass element. The first particles have a first mass density (mass per volume of the particle body, approximately specified in the unit g / cm 3 ) and the second particles have a second mass density.

[0031] The characteristic property can, for example, comprise a vibration property, such as a resonance frequency of a spring-mass system formed by the mass element suspended from a substrate in a vibration-capable manner. In the case of a single-mass oscillator and neglecting damping, the resonance frequency can be determined, for example, via the relationship ω0=cm and / or f0=ω0π where ω o Where f0 is the natural frequency or natural angular frequency, c is the spring stiffness, and m is the mass of the single-mass oscillator. It should be noted that the exemplary embodiments are in no way limited to MMS (micromechanical systems) or MEMS (micro-electro-mechanical systems) with a single-mass oscillator, but can also include higher-order oscillating systems. However, it is immediately apparent from the context presented that mass has a direct influence on the resonance frequency of an MMS / MEMS.

[0032] According to embodiments, by applying a consistent, even identical, manufacturing process in which the mass element is produced using a particle mixture with particles of different mass densities, a precisely adapted mass element can be obtained by adjusting the mixing ratios. This advantageously avoids the need to adapt the manufacturing process itself, for example, the MMS / MEMS process. In other words, mass elements with identical volumes but different masses can be produced by using different mixing ratios. The mixing ratio can be changed by using different materials and / or by changing at least a portion of the respective material.

[0033] According to embodiments, a mass of the mass element and thus a resonance frequency of the spring-mass system can be determined by a suitable choice of the composition of the particle mixture, for example by a suitable choice of the composition of a powder mixture which is solidified or partially solidified to form the mass element.

[0034] The particle mixture can in particular be adjusted such that the micromechanical system, or for example a corresponding spring-mass system of the micromechanical system, has an absorption peak for signals (e.g. excitation signals, e.g. vibrations) with a certain frequency, or signals (e.g. excitation signals, e.g. vibrations) in a certain frequency range, so that for example the resonance frequency of the spring-mass system or of the micromechanical system in general corresponds to the certain frequency, or lies in the certain frequency range.

[0035] It should be noted here that a corresponding spring-mass system can also be actively controlled, e.g., piezoelectrically. Thus, examples can also be used in loudspeaker applications.

[0036] The inventors have recognized that based on an adaptation of such a particle mixture, an adjustment possibility for a corresponding micromechanical system is provided without, or at least without a significant, increase in the complexity of the system.

[0037] Thus, embodiments enable the manufacture of components according to the invention without, or without significant, adjustments to the manufacturing process. Thus, despite changes to component characteristics, such as a resonance frequency, geometric dimensions and / or a shape of the system can remain unaffected. Thus, micromechanical systems according to the invention can be produced in an individually adapted manner by adjusting the mixing ratio of the particle mixture, without fundamentally changing the corresponding production process.

[0038] In other words, a corresponding system design, for example, a layer sequence, a geometric arrangement of materials and / or cavities, as well as a geometry and / or shape of the system, can remain unchanged despite system-specific adaptation of characteristics (e.g., resonance frequency) by adjusting the particle mixture. Thus, despite corresponding adaptations, the same manufacturing tools, for example, machines, lithographic masks, etching processes, and / or, in particular, associated process parameters, can be used. Thus, embodiments enable an improved compromise with regard to component complexity and the customizability of micromechanical systems, thus enabling adaptable, i.e., individually adjustable, mass production.

[0039] At the same time, embodiments also have integrative advantages, since any interfaces to other systems can remain unchanged despite the advantageously enabled system adaptations (e.g. adaptation of resonance frequencies).

[0040] Specifically, embodiments include methods that enable the resonant frequency of vibration harvesters and other MMS oscillators to be specifically adjusted over a wide range at the wafer level, for example, without having to change the design and / or the manufacturing process. As explained above, the manufacturing process can remain unchanged, in particular, in that no adaptation of manufacturing machines, tools, or other aids such as lithographic masks is necessary.

[0041] Thus, embodiments enable micromechanical systems that offer an improved compromise with regard to component complexity and individual adaptability of the system compared to known approaches, while at the same time allowing for mass production of the design.

[0042] With reference to further exemplary embodiments discussed below, it should be noted that a particle mixture according to the invention can also comprise, in particular, more than two “types” of particles. In the following, reference is made to “particles of the particle mixture,” which generally means any particles of the particle mixture, but in particular, for example, first particles and / or second particles. According to exemplary embodiments which, in addition to the first and second particles, also comprise further “particle types,” such further particles of the particle mixture can also fall under “particles of the particle mixture.” Different particle types are understood to be particles with different material densities, regardless of whether the particle size is the same or different.A wide range of adjustable mass of the mass element, and thus the resonance frequency of the spring-mass system, can be achieved by varying the masses of at least two particle types as much as possible. Such a comparatively large difference can be achieved, for example, by choosing silicon (di)oxide SiO2 on the one hand and tungsten on the other. A smaller mass density difference, on the other hand, can offer more precise adjustment within the overall spectrum, since differences in the particle proportions could have a comparatively small impact on the resonance frequency.

[0043] Particle mixtures that can be used in the embodiments described herein comprise particles with at least two different average mass densities of the materials from which the particles consist (or by means of which the particles are formed). In addition to the materials SiO2 and tungsten mentioned, other metals, such as iron particles, copper particles, aluminum particles, other semiconductor material particles in oxidized and / or unoxidized form, carbon particles, dielectric particles, or other suitable materials can also be used: It should be noted that the mass density refers to the density of the material of the particles, i.e. the material from which the particles are formed (and, for example, in this context, not to the “density” of a porous body formed from the particles (e.g. a porous mass body) after agglomeration).

[0044] Furthermore, it should be noted that application examples can also be applied without restriction to the field of vibration dampers, which also benefit from precise adjustment of the natural frequency or resonance frequency. In this respect, the devices described herein are preferably, but not necessarily, MEMS devices, but can generally also be implemented as micromechanical systems (MMS).

[0045] According to some embodiments of the present invention, particles of the particle mixture are bonded together by means of a coating. Thus, particles of the particle mixture can be bonded together robustly, for example, with respect to vibration loading, in order to maintain functionality and, in particular, appropriate system characteristics over the service life of the system. Simply put, this prevents individual particles from "dispersing" within the component during vibration.

[0046] According to embodiments of the present invention, the mass element comprises a porous body. This porous body can be at least partially formed by particles of the particle mixture, which are firmly bonded to one another by means of the coating. Thus, the mass element can be formed, or at least partially formed, by means of solidified particles of the particle mixture. In other words, the particle mixture, for example, a powder mixture, can be solidified by means of the coating to form the mass element.

[0047] According to embodiments of the present invention, the micromechanical system comprises a structural element suspended from the substrate in an oscillating manner, wherein the structural element has a cavity in which the mass element is arranged and wherein the mass element is fixed in the cavity by means of the coating.

[0048] The inventors have recognized that, simply put, by embedding the particle mixture in a cavity, a particularly robust micromechanical system can be provided due to the at least partial enclosure of the particle mixture in the cavity. Furthermore, a corresponding system design offers manufacturing advantages, particularly with regard to the provision of a defined amount of the particle mixture and subsequent optional solidification or partial solidification of the particles. Thus, the cavities can be used to reproducibly define the volume available for the particle mixture.

[0049] Optionally, the structural element together with the mass element can form, for example, a seismic mass of the system or an associated spring-mass system.

[0050] According to embodiments of the present invention, loose particles of the particle mixture are enclosed in the cavity by the porous body. The inventors have recognized that the entire particle mixture does not necessarily have to be solidified to provide a robust, oscillatable system. For example, a portion of the particle mixture facing the cavity opening can be bonded by the coating, thereby forming a solidified portion of the mass element. Remaining, "loose" particles can be held in the cavity by the solidified portion of the mass element, like a plug.

[0051] Thus, embodiments enable the use of cavities with high aspect ratios, or simply "deep" cavities. Since embodiments do not rely on complete coating deposition down to the lowest particles in a cavity, a variety of deposition processes can still be used. At the same time, with the associated synergy, the large or deep cavities can be filled with a comparatively light particle mixture, if necessary, to produce a comparatively light mass element overall; at the same time, a heavy mass element can be produced using the same process using a heavy particle mixture.

[0052] According to embodiments of the present invention, the micromechanical system comprises a plurality of mass elements, wherein the structural element comprises a plurality of cavities, wherein a respective mass element of the plurality of mass elements is arranged in a respective cavity of the plurality of cavities, and wherein each mass element of the plurality of mass elements comprises the particle mixture.

[0053] The inventors have recognized that a component characteristic can thus be adapted over a wider range with little additional complexity of the system (and in particular of an associated manufacturing process).

[0054] Specifically, for example, a total cavity volume can be increased by providing a higher number of cavities (e.g. instead of a single cavity of the same size), whereby a larger amount of the particle mixture can be used while maintaining the same mechanical properties of the individual mass body, on the basis of which the component characteristics can be adjusted by adjusting the mixing ratio.

[0055] In particular, the inventors have recognized that, in terms of component integrity and manufacturing complexity, the provision of a plurality of smaller cavities may have advantages over the provision of a single large cavity of the same volume.

[0056] Furthermore, one reason or even the main reason for using a large number of small cavities instead of a large single cavity can be to minimize stress effects due to different thermal expansion coefficients of the materials involved (e.g. 7.6 for Si; 4.4 for W; 23.1 for Al; 0.5 for SiO2; all times 10 -6 / K). Accordingly, with large individual cavities, cracks or delamination of the porous body can occur much more quickly (e.g., more easily) than with a large number of smaller cavities.

[0057] The penetration depth of the coating can, for example, be independent of the size of the cavity. In terms of volume or particle quantity, a large number of cavities with the same surface area can be inferior, or even consistently inferior, to a large single cavity.

[0058] It should be noted, however, that exemplary embodiments may nevertheless also include micromechanical systems with spring-mass systems with individual cavities. One advantage of individual cavities may be, for example, that if a single cavity is replaced by a plurality of cavities, the volume can be smaller for the same surface area, or even always smaller, and the amount of the particle mixture is correspondingly smaller as well. In particular, the webs between the individual small cavities take up space, which can be saved by using a single cavity (or at least a small number of cavities instead of a large number).

[0059] Furthermore, the use of the same or identical particle mixture, e.g. a particle mixture with the same mixing ratio of particles with different mass densities, enables a simple production of the plurality of mass elements, which can take place in particular in a common process step.

[0060] Furthermore, a mass element can optionally be arranged in each cavity of a structural element according to the invention, wherein all mass elements in turn have the same particle mixture.

[0061] According to embodiments of the present invention, the cavities of the plurality of cavities each have an equal volume fill factor by arranging a respective mass element in the respective cavity. Simply put, the respective cavities can each be "equally filled."

[0062] Embodiments allow the adjustment of a system characteristic within a wide adjustment interval based on the selection of the mixing ratio of the particle mixture. Based on this, changing volume fill factors can be omitted, which can simplify the associated manufacturing process and, on the other hand, enables the use of the same manufacturing process for different instances of the micromechanical system with different characteristics.

[0063] According to embodiments of the present invention, particles of the particle mixture of the mass elements are bonded together by a matching coating to form a respective mass element, wherein the matching coating of the particles originates from a same deposition process.

[0064] A matching coating, for example, is a coating created in a single coating process or even a matching step. This allows the particles that then form the respective mass elements to be solidified together in a single step. The matching coating can be interrupted between different mass elements, for example, through the use of masks and / or physical or chemical regression. Simply put, the same or identical coating, i.e., a matching coating, can be deposited on the particles of different cavities, whereby the resulting coating can optionally contain interruptions.

[0065] In general, a coating according to the invention, and in particular a matching coating, does not necessarily have to be a continuous coating. The coating can even be arranged on particles of the mixture in such a way that the particles are "glued" to form a porous element, but the coating is not continuous (i.e., even "within" a single mass element) between the solidified particles.

[0066] According to embodiments of the present invention, the coating or the conformal coating comprises a vapor-deposited layer, e.g., a layer produced or deposited by atomic layer deposition, e.g., an atomic layer deposited layer.

[0067] The inventors have recognized that such a coating enables the particularly efficient production of porous mass elements using particle mixtures, and in particular powder mixtures. In particular, the use of atomic layer deposited coatings enables the production of particularly robust mass elements. Such coatings can, for example, penetrate particularly deeply into a corresponding particle mixture, e.g., in a cavity, and solidify it to form the mass element.

[0068] According to embodiments of the present invention, the first mass density of the material from which the particles consist (or by means of which the particles are formed) is at least a factor of 2, at least a factor of 3, at least a factor of 5 or at least a factor of 7 greater than the second mass density.

[0069] The inventors have recognized that system properties can be adjusted over a wide adjustment interval based on the above density differences.

[0070] According to embodiments of the present invention, the micromechanical system is configured as an energy harvester to provide electrical energy based on a vibration of the mass element.

[0071] The inventors have recognized that a system according to the invention is particularly suitable as an energy harvester. The system can optionally be configured to generate energy based on an external excitation of the mass element suspended from the substrate in a vibrating manner.

[0072] According to embodiments of the present invention, the particle mixture comprises third particles having a third mass density.

[0073] As previously explained, additional particles with different densities compared to the first and second mass densities can be used according to embodiments. For example, a third material can be used, which, for example, has small and light particles, to fine-tune the mass.

[0074] Embodiments according to the present invention further comprise wafers having a plurality of micromechanical systems according to any of the embodiments disclosed herein, wherein respective mass elements of the plurality of micromechanical systems comprise a same particle mixture.

[0075] The inventors have recognized that a plurality of micromechanical systems according to the invention can be manufactured in parallel on a common wafer using the same particle mixture. This parallelizes and simplifies the manufacturing process.

[0076] According to embodiments of the present invention, particles of the particle mixture of the mass elements are bonded together by a matching coating to form the respective mass element, and the matching coating of the particles originates from a same deposition process.

[0077] The inventors have recognized that the advantages of a consistent, i.e., common, coating of different cavities can also be achieved across different systems at the wafer level.

[0078] Manufacturing methods according to exemplary embodiments are discussed below. It should be noted that features of previously explained micromechanical systems can form corresponding features of corresponding manufacturing methods, both individually and in combination. Conversely, features of manufacturing methods disclosed below can form features of systems according to the invention, individually or in combination.

[0079] Furthermore, it should be noted that the following exemplary embodiments of the invention, which are discussed in the context of methods, may accordingly also be based on similar or identical considerations as the devices disclosed above and may thus have the same or similar features, functionalities, and details as corresponding devices, both individually and in combination. The same applies conversely.

[0080] Methods according to preferred embodiments can in particular enable a design-independent adaptation of the resonance frequency of micromechanical oscillators.

[0081] Embodiments include a method for manufacturing a micromechanical system. The method comprises providing a substrate and forming a mass element suspended from the substrate in an oscillating manner. Forming the mass element comprises creating a cavity in the substrate and filling the cavity with a particle mixture to form the mass element. First particles of the particle mixture have a first mass density, and second particles of the particle mixture have a second mass density.

[0082] The inventors have recognized that manufacturing according to the invention makes it possible to change properties of the micromechanical system for individual micromechanical systems or individual batches of micromechanical systems without fundamentally changing the manufacturing process. In other words, as previously explained, for example, a resonant frequency of a spring-mass system of a micromechanical system, which includes the oscillatory suspended mass element, can be changed by changing the mixing ratio of the first and second particles of the particle mixture, without – in simple terms – the micromechanical system having to be structurally modified. Thus, for example, only the particle mixture used in the manufacturing process needs to be adapted, with no or at least only a few changes being made to other process boundary conditions.

[0083] Thus, the structural design of the micromechanical system can remain unchanged, so that for different instances of the manufacturing process for producing micromechanical systems with different properties, for example, the same, or at least the same, machine tools, as well as associated processing heads, and / or lithographic masks, and / or etching agents and / or manufacturing parameters, such as etching times (e.g. with regard to cavity depth and / or volume), can always be used.

[0084] This provides a flexible and scalable manufacturing process for individually adaptable micromechanical systems.

[0085] According to embodiments of the present invention, the method further comprises determining a mass value of the mass element based on a resonant frequency to be set of a spring-mass system of the micromechanical system comprising the mass element, determining a mixing ratio of the first and second particles of the particle mixture in order to obtain the mass value of the mass element, and adjusting the mixing ratio of the first and second particles of the particle mixture such that the mass element with the mass value is formed by means of the particle mixture with the adjusted mixing ratio.

[0086] As explained above, a property of a produced system can be altered with minor changes to the manufacturing process. The inventors have recognized that such an adaptation is particularly suitable for adjusting such a resonant frequency.

[0087] According to embodiments of the present invention, the resonant frequency is selected in a range from at least 10 Hz to at most 200 kHz, from at least 40 Hz to at most 10 kHz, and / or from at least 50 Hz to at most 2.5 kHz. According to the invention, a wide range of resonant frequencies can be addressed.

[0088] It should be noted here that the resonance frequency of a micromechanical system, such as a corresponding spring-mass system, can differ from the corresponding or application-specific excitation frequency tuned to it. For example, a narrowband excitation frequency matching at least one of the resonance frequencies can be used, as can a broader-band excitation frequency with components matching the resonance frequency or a harmonic. For example, an energy harvester used in a car tire control system can be excited by cyclic tire rotations at frequencies well below the resonance frequency.

[0089] According to embodiments of the present invention, the method further comprises bonding particles of the particle mixture by means of a coating.

[0090] According to embodiments of the present invention, the provision of the substrate, the creation of the cavity, and the filling of the cavity with the particle mixture are performed at the wafer level, prior to singulation of the micromechanical system. Thus, methods according to the invention can implement an adaptation of system properties prior to a post-processing step, making the method applicable at the substrate level, prior to post-processing.

[0091] According to embodiments of the present invention, in various instances of the method for generating micromechanical systems that are identical for each instance and different across the various instances and have instance-specific resonance frequencies, a respective cavity of a respective substrate is filled with a particle mixture assigned to the instance, with a mixing ratio of the first and second particles assigned to the instance. Furthermore, the respective substrates and cavities of the various micromechanical systems of the various instances are of identical design. It should be noted that the substrate can, for example, form the smallest unit on which the various instances can always be of identical design. The instances can vary from substrate to substrate.

[0092] Respective substrates can, for example, form a common (overall) substrate, e.g., at the wafer level, wherein a plurality of micromechanical systems according to the invention of a first instance can be formed on the common substrate (e.g., prior to singulation). In other words, a specific region or the entire wafer on a wafer can serve as a common substrate for a plurality of micromechanical systems of a first instance before they are singulated.

[0093] On another common substrate, for example a different wafer, a second instance of the method according to the invention can be carried out, so that a plurality of micromechanical systems according to the invention can be produced, for example with a particle mixture that differs from the first instance.

[0094] Simply put, the individual resonance frequencies of individual micromechanical systems can be adjusted independently of the respective structure and process steps of the manufacturing process. To simplify matters, but clearly illustrate, switching between systems with different resonance frequencies in a manufacturing machine that fills the cavities can simply be done by changing the particle mixture, for example, by adding a different powder mixture with a different mixing ratio of first and second particles. This provides a simple yet adaptable manufacturing process.

[0095] In simple terms, a generic substrate with optionally pre-processed oscillators can be used for different instances of the process, which is individualized by the particle mixture.

[0096] According to embodiments of the present invention, the cavity is filled to a predetermined filling level regardless of the mixing ratio of the first and second particles of the particle mixture.

[0097] The inventors have recognized that, regardless of a set property of the system (e.g., resonance frequency adjusted based on the mass of the particle mixture), further processing can be maintained between different instances of the process. For example, if cavities are filled differently (e.g., to adjust the resonance frequency based on a fill level instead of adjusting it based on the mixing ratio of the first and second particles of the particle mixture at the same fill level), it may be necessary to individually adapt subsequent deposition processes and / or to provide individual processing masks depending on the fill level and thus structure.

[0098] The filling height is, for example, a height starting from a substrate-side bottom surface of the cavity, perpendicular to a substrate plane and parallel to wall structures of the cavity.

[0099] According to embodiments of the present invention, the particle mixture comprises particles with particle sizes in a first particle size range and particles with particle sizes in a second particle size range. The method further comprises determining a volume fill factor of the cavity to be adjusted and adjusting a mixing ratio of particles with particle sizes in the first and second particle size range of the particle mixture to adjust the volume fill factor.

[0100] The inventors have recognized that by adjusting a volume filling factor in addition to the adjustment using particles with different mass densities, an adjustment of the mass element and thus, for example, a resonance frequency of an associated spring-mass system can be made.

[0101] The inventors have recognized that this provides an additional adjustment option without structural changes to the specific component and thus to the manufacturing process. This allows subsequent processing to be carried out independently of the volume fill factor set for the process instance. If two cavities of different systems of different process instances are filled, for example, with different fill factors but, for example, to the same fill level, additional layers can subsequently be created on the particle mixtures using the same lithographic masks, for example, without process changes.

[0102] However, it should be noted that embodiments can optionally also include manufacturing processes with cavity filling at different fill levels in different instances, without changing the process. However, process adaptation for different fill levels may be unavoidable in some applications, so embodiments that manage with the same fill levels may offer advantages.

[0103] According to embodiments of the present invention, the method further comprises forming a spring element between a substrate region provided for the mass element and a region of the substrate which provides clamping of the spring element, such that the spring element provides the oscillatable suspension of the mass element.

[0104] The exemplary embodiments are not limited to a specific process sequence. For example, a corresponding cavity can be filled first, and then the oscillating suspension, such as the spring element, can be released along with the mass element formed by the cavity and the particle mixture.

[0105] Alternatively, the oscillating suspension could be released first and the cavity formed afterwards.

[0106] According to embodiments of the present invention, the cavity is dimensioned and a mass density difference between the first and second particles is adjusted such that an adjustment range of a resonance frequency of the micromechanical system, based on an adjustment of the mixing ratio of the particle mixture, is at least + / - 10%, at least + / - 25% and / or at least + / - 40% relative to a mean frequency value. The mean frequency value is associated with a mean mass of the predetermined mass range. Optionally, a corresponding adjustment range can also be defined relative to a reference mass with the same volume as the mass element but made of substrate material, e.g., silicon. Thus, a mean frequency or even a lower frequency limit can be defined using such a reference. Short character description

[0107] 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 a schematic side view of a micromechanical system according to embodiments; Fig. 2 a schematic side view of a micromechanical system without a cavity according to embodiments; Fig. 3 a schematic side view of a micromechanical system with loose particles according to embodiments; Fig. 4 a schematic side view of a micromechanical system with a plurality of cavities according to embodiments; Fig. 5 is a schematic block diagram of a method for manufacturing a micromechanical system according to embodiments; Fig. 6 (a), (b), (c) schematic views of various micromechanical systems produced by different instances of manufacturing methods according to embodiments; Fig. 7 a schematic representation of a production of three-dimensional microstructures according to embodiments; Fig. 8 (a) a schematic view of a finite element model of a cantilevered micromechanical oscillator with seismic mass at the free end of the bending beam according to embodiments of the present invention and (b) a plot of a variation of the resonance frequency as a function of the powder mixture according to embodiments of the present invention; Fig. 9 (a) a schematic cross-section through a piezoelectric vibration harvester according to the state of the art, (b) a representation of an implementation by Microgen [2] and (c) a representation of a piezoelectric energy harvester by Fraunhofer ISIT; Fig. 10 (a) a schematic view of a macroscopic vibratory harvester from EP2677656B1 and (b) a schematic view of a hybrid mounted vibratory harvester; Fig. 11 (a) a schematic view of a macroscopic vibratory harvester from [5] with an array of cavities in the seismic mass and (b) a schematic view of a macroscopic vibratory harvester according to US7626316B2; Fig. 12 (a) a schematic view of a MEMS-based vibration harvester from [6] and (b) a schematic view of a concept of a MEMS-based vibration harvester according to EP3185320B1; and Fig. 13 (a) a schematic representation of a bistable vibration harvester, (b) a schematic representation of the principle of a vibration harvester with two mechanically coupled elements and (c) a schematic representation of an alternative design of a harvester based on the principle of mechanical coupling of movable microstructures [8]. Detailed description of the examples according to the figures

[0108] 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 according to exemplary embodiments 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. It should be noted that the reference numerals of the Fig. 10 (a), Fig. 11 (b), Fig. 12 (b) and Fig. 13 (b), in contrast, are merely taken from the relevant reference documents.

[0109] Fig. 1 shows a schematic side view of a micromechanical system according to embodiments. Fig. 1 shows the micromechanical system 100, which comprises a substrate 110 and a mass element 120 suspended from the substrate in an oscillating manner. As an optional feature, the oscillating suspension of the mass element 120 is embodied as a spring element 125. The mass element 120 comprises a particle mixture 130, wherein the particle mixture 130 comprises first particles 130a and second particles 130b. First particles 130a of the particle mixture have a first mass density, and second particles 130b of the particle mixture have a second mass density.

[0110] Furthermore, the system 100 has, as an optional feature, a structural element 160 suspended from the substrate in a vibratable manner, which comprises a cavity 140. It should be noted that the arrangement of the particle mixture in the cavity 140 is also to be considered merely optional, as will be explained in more detail in the exemplary embodiments discussed below.

[0111] Based on an adjustment of the mixing ratio of first and second particles of the particle mixture 130, the mass of the mass element 120 can thus be adjusted, for example, whereby, for example, a resonance frequency of a spring-mass system comprising spring element 125 and structural element 160 with mass element 120 can be adjusted. The structural element 160, together with the mass element 120, can form, for example, a seismic mass of the spring-mass system, wherein the spring-mass system forms, for example, an oscillator.

[0112] It should be noted that such a spring-mass system can optionally contain additional functional layers, e.g. Fig. 9 (a). For example, a voltage can be measured piezoelectrically, or an oscillation of the spring-mass system can be induced.

[0113] The first mass density may, for example, differ from the second mass density by at least a factor of 2, at least a factor of 3, at least a factor of 5 or at least a factor of 7.

[0114] The inventors have recognized that this allows for the adjustment of a system characteristic, e.g., a resonant frequency of the spring-mass system, which can be adjusted independently of the structure of the system 100. For example, despite a constant cavity geometry, spring length, and / or spring thickness, and / or unchanged substrate geometry due to manufacturing, a resonant frequency of the system 100 can be adjusted based on adjusting the mixing ratio of the particle mixture. In other words, while maintaining the spring parameters and adjusting the mass element, an adjustment can be achieved across different process implementations.

[0115] Fig. 2 shows a schematic side view of a micromechanical system without a cavity according to embodiments. Fig. Figure 2 shows the micromechanical system 200, which comprises a substrate 210 and a mass element 220 suspended from the substrate in an oscillating manner. As an optional feature, the oscillating suspension of the mass element 220 is again designed as a spring element 225. The mass element 220 comprises a particle mixture 230, wherein the particle mixture 230 comprises first particles 230a and second particles 230b. First particles 230a of the particle mixture have a first mass density, and second particles 230b of the particle mixture have a second mass density.

[0116] Compared to Fig. 1, the particle mixture 230 is not arranged in a cavity, and the system 200 also does not include a structural element that would have said cavity. A corresponding structural element can be removed, for example, after the particle mixture 230 has solidified, so that no cavity is present.

[0117] Furthermore, the system 200 has a coating 250. The particles 230a and 230b are bonded together by the coating 250. It should be noted again that the coating does not have to be a continuous coating, but can be.

[0118] For example, as in Fig. As shown in Figure 2, a porous body is formed by means of the particle mixture 230 and the coating 250, which forms the mass element 220. Thus, the solidified particle mixture can be attached to the remaining substrate by means of the coating, e.g., in embodiments without a cavity.

[0119] Fig. 3 shows a schematic side view of a micromechanical system with loose particles according to embodiments. Fig. Figure 3 shows the micromechanical system 300, which comprises a substrate 310 and a mass element 320 suspended from the substrate in an oscillating manner. As an optional feature, the oscillating suspension of the mass element 320 is again designed as a spring element 325. The mass element 320 has a particle mixture 330, wherein the particle mixture 330 has first particles 330a and second particles 330b. First particles 330a of the particle mixture have a first mass density, and second particles 330b of the particle mixture have a second mass density.

[0120] As in Fig. 3, embodiments optionally have a structural element 360 suspended from the substrate in an oscillating manner, which in turn has a cavity 340.

[0121] As an optional feature, the particle mixture is again arranged in the cavity 340, so that the mass element 320 is arranged in the cavity 340. As in Fig. 3, optionally only a part of the particle mixture can be bonded together by means of a coating 360, so that a porous body, for example in the form of a porous structure 335a, is formed.

[0122] Furthermore, the mass element 320 comprises, in addition to the porous structure 335a, loose particles 335b of the particle mixture, which are enclosed by the porous body in the cavity 360. Thus, embodiments are not limited to deep coatings 350. The mass element can have both solidified and loose portions, wherein the solidified portions can, in simple terms, serve as plugs or stoppers for the loose particles.

[0123] By means of the coating 360, as an optional feature in Fig. 3, the mass element is secured in the cavity. It should be noted that, for example, only a portion of the mass element 320, such as the portion of the mass element connected by the coating 360 in the case shown, can be secured directly in the cavity. However, as shown, a loose portion of the mass element can also be indirectly secured in the cavity by means of the coating. Optionally, however, the entire mass element can also be secured directly in the cavity by means of the coating.

[0124] Fig. 4 shows a schematic side view of a micromechanical system with a plurality of cavities according to embodiments. Fig. 4 shows the micromechanical system 400, which comprises a substrate 410 and a first and second mass element 4201 and 4202 suspended from the substrate in a vibratable manner. As an optional feature, the vibratable suspension of the mass element 420 is again designed as a spring element 425. The mass element 420 has a particle mixture 430, wherein the particle mixture 430 has first particles 430a and second particles 430b. First particles 430a of the particle mixture have a first mass density, and second particles 430b of the particle mixture have a second mass density.

[0125] As an optional feature, the particle mixture 430 also comprises third particles 430c with a third mass density. Furthermore, the system 400 optionally comprises particles 430a-c with particle sizes within a first range of particle sizes and particles 435 with particle sizes within a second range of particle sizes. Particles 435 can, for example, be fourth particles with a fourth mass density, or particles with the first, second, or third mass density, but with different, e.g., smaller, particle sizes as shown. Correspondingly different particles can be obtained, for example, by sieving.

[0126] As an optional feature, the system 400 again comprises a structural element 460 with a plurality of cavities 4401 and 4402, wherein a respective mass element 4201 and 4202 is arranged in a respective cavity. The mass elements comprise the same particle mixture 430.

[0127] As a further optional feature, cavities 4401 and 4402 have an equal volume fill factor. In other words, both cavities are essentially equally "full," or in other words, equally filled with particle mixture 430 in terms of their volume.

[0128] Furthermore, particles of the particle mixture of the mass elements 4201 and 4202 are bonded together to form a respective mass element by a matching coating 450. Such a coating 450 can, for example, originate from the same deposition process. As shown in Fig. However, as shown in Figure 4, a matching coating does not necessarily mean a continuous coating. Such a coating 450 can be interrupted both between individual mass elements 4201 and 4202 and within a single mass element.

[0129] The coating may optionally comprise, in particular, a layer deposited from a gas phase, e.g., an atomic layer deposited layer.

[0130] The system 400 can, for example, be configured as an energy harvester to provide electrical energy based on a vibration of the mass element. For this purpose, the system 400 can comprise additional layers, e.g., piezoelectric layers.

[0131] At this point, it should be noted that an oscillatable suspension according to the invention is not limited to specific designs of the illustrated spring elements 125, 225, 325, and 425. Thus, any conventional suspensions that allow a oscillatable attachment of the mass element to the substrate can be used.

[0132] Based on Fig. 5 are referred to below with reference to the Fig. 1 to 4, manufacturing methods according to exemplary embodiments are explained in more detail.

[0133] Fig. 5 shows a schematic block diagram of a method for manufacturing a micromechanical system according to embodiments. Fig. 5 shows the method 500 comprising providing, 510, a substrate and forming, 520, a mass element suspended from the substrate in an oscillating manner.

[0134] Thus, for example, in a first step, a substrate 110, 210, 310 and / or 410 can be provided, for example as a solid area on a wafer, e.g., before singulation of a corresponding system.

[0135] The formation, 520, of the mass element suspended from the substrate in a vibratable manner, carried out in a subsequent step, further comprises creating a cavity in the substrate and filling the cavity with a particle mixture to form the mass element.

[0136] As previously explained, first particles of the particle mixture have a first mass density and second particles of the particle mixture have a second mass density.

[0137] For example, starting from a solid substrate, one cavity 140, 340, or several cavities 4401, 4402 can be formed. Then, in a subsequent process step, the cavities 140, 340, 4401, 4402 are filled with the particle mixture 130, 230, 430.

[0138] This can be done, for example, in particular before the formation of the oscillatable suspension, for example in the form of a structural element 160, 360, 460 and a spring element 125, 225, 425, but is by no means necessary.

[0139] A corresponding manufacturing method 500 can further be used, e.g., as a preprocessing step, e.g. B. before physical production of the micromechanical system, optionally determining a mass value of the mass element 120, 220, 320 (or e.g. a total mass value of several mass elements 4201, 4202 or a corresponding seismic mass) based on a resonant frequency to be set of a spring-mass system comprising the mass element (e.g. spring element 125, 225, 425 with structural element 160, 260, 460 and mass element 120, 320, 4201+4202) of the micromechanical system, determining a mixing ratio of the first and second particles (e.g. 130a and 130b, e.g. 230a and 230b, e.g. 330a and 330b, e.g. 430a, 430b, 430c and if necessary(if fourth particles) 435) of the particle mixture to obtain the mass value of the mass element and adjusting the mixing ratio of the first and second (and optionally third and optionally fourth) particles of the particle mixture so that the mass element with the mass value is formed by means of the particle mixture with the adjusted mixing ratio.

[0140] In a corresponding method 500, for example, the resonance frequency can be selected within a wide range, for example, from at least 10 Hz to at most 200 kHz, from at least 40 Hz to at most 10 kHz, and / or from at least 50 Hz to at most 2.5 kHz. Embodiments thus enable adaptation over a wide frequency range.

[0141] As in Fig. 2 to 4, methods 500 according to embodiments further optionally comprise bonding particles of the particle mixture by means of a coating (e.g., 250, 350, 450).

[0142] At this point, it should be noted that the previously described steps of providing the substrate, creating the cavity and filling the cavity with the particle mixture can optionally be carried out at wafer level, before singulating the micromechanical system.

[0143] Thus, embodiments particularly also include wafers with a plurality of micromechanical systems (e.g., 100, 200, 300, 400), wherein respective mass elements of the plurality of micromechanical systems comprise the same particle mixture. Thus, the same particle mixture can be used for an entire wafer batch of systems in order to provide, in parallel, a plurality of systems with a property adjusted by means of the mixing ratio of the particle mixture.

[0144] Accordingly, mass elements of several systems can also be formed at wafer level using a matching, for example, common coating.

[0145] For example, particles of the particle mixture of the mass elements can optionally be bonded together by a matching coating to form the respective mass element. This matching coating can, in turn, originate from the same deposition process.

[0146] In other words, the context of Fig. The matching coating 450 explained in Figure 4 can be used not only within a system 400, but also across systems, i.e., for multiple micromechanical systems on a common wafer. Thus, embodiments enable mass production of micromechanical systems that can still be adjusted at the wafer level.

[0147] Furthermore, according to embodiments in the method according to the invention, the cavity can be filled up to a predetermined filling level regardless of the mixing ratio of the first and second particles of the particle mixture. This optionally applies to cavities within a system, as shown, for example, by the height h for the cavities 4401 and 4402, but optionally also to cavities of different systems, e.g., on a common wafer. Such a filling level can also apply, in particular, to micromechanical systems of different instances, e.g., for different resonance frequencies, as, for example, in Fig. 6 shown.

[0148] Optionally, methods according to the invention can further comprise determining a volume fill factor of the cavity to be adjusted and adjusting a mixing ratio of particles with particle sizes of the first and second interval of the particle mixture to adjust the volume fill factor. Thus, for example, mixing ratios of particles 430a-c to particles 435 can be adjusted to achieve a desired volume fill factor. Using the volume fill factor, a fine-scale mass adjustment can be performed, for example, using small and optionally additionally light particles.

[0149] Furthermore, according to embodiments, the method 500 further optionally comprises forming a spring element (e.g., 125, 225, 325, 425) between a substrate region provided for the mass element and a region of the substrate that provides clamping of the spring element, such that the spring element provides the oscillatable suspension of the mass element.

[0150] Fig. 6 shows schematic views of various micromechanical systems produced by various instances of manufacturing methods according to embodiments.

[0151] Fig. 6 shows, in a), b), and c), a system 6001, 6002, 6003 comprising different instances of a manufacturing method according to the invention. According to exemplary embodiments, in order to generate micromechanical systems 6001, 6002, 6003 that are identical for each instance and different across the different instances, with instance-specific resonance frequencies, optionally at different instances of the method, the filling of a respective cavity 640 of a respective substrate 610 with a particle mixture 6301, 6302, 6303 assigned to the instance with a mixing ratio of the first and second particles 630a, 630b assigned to the instance is carried out. The respective substrates 610 and cavities 640 of the various micromechanical systems of the different instances are designed identically.

[0152] In other words, different instances, e.g., modifications, of the manufacturing process can be used to produce individual systems 6001, 6002, 6003. The special feature here is, for example, the use of a "generic," optionally preprocessed, substrate 610. Simply put, regardless of the instance of the process, an identical substrate 610 with the same dimensions and a structural element 660, including the spring element and cavity 640, which is already exposed or still to be exposed after the mass element has been created, can be used.

[0153] In other words, the systems 6001, 6002, 6003 are structurally identical, but differ in the resonance frequency of their respective spring-mass systems due to a different mass element 6201, 6202, 6203, which is formed by the particle mixtures 6301, 6302, 6303 with different mixing ratios of the particles 630a and 630b. Fig. 6 elements shown without index 1 to 3 can therefore be the same across instances.

[0154] In general, it should be noted that according to embodiments, the cavity 140, 340, 4401, 4402, 640 is optionally dimensioned and a mass density difference between the first and second (and optionally further) particles is adjusted such that an adjustment range of a resonance frequency of the micromechanical system 100, 200, 400, 600, based on adjusting the mixing ratio of the particle mixture, is at least + / - 10%, at least + / - 25% and / or at least + / - 40% based on an average frequency value, wherein the average frequency value is associated with an average mass of the predetermined mass range.

[0155] In the following, further embodiments are discussed, and previously explained embodiments are explained in other words.

[0156] One solution approach according to exemplary embodiments is based on the use of powder-based technology according to EP 2 670 880 B1 (or US Pat. No. 9,221,217 B2), a method for producing integrated three-dimensional microstructures on planar substrates, hereinafter referred to as the PowderMEMS method. This method is suitable for integrating powders of a wide variety of materials into MEMS components in a consistent manner.

[0157] At this point, it should be noted that embodiments according to the present invention may include features of the above-mentioned documents, both individually and in combination. In particular, embodiments may include features relating to the production of a particle mixture and subsequent solidification, e.g., in a cavity.

[0158] Fig. 7 shows a schematic representation of the production of three-dimensional microstructures according to embodiments, for example using powder according to EP 2 670 880 B1. In the first step, for example, cavities 740 in a planar substrate 710 can be filled with a loose particle mixture, for example in the form of a loose, micrometer-sized powder 730. In a subsequent, for example, second step, the loose powder can be agglomerated into porous bodies, i.e., for example, mechanically strong structures 770, by means of a coating, e.g., atomic layer deposition, for example, by means of a specially adapted atomic layer deposition (ALD).

[0159] As from Fig. As can be seen in Figure 7, cavities 740 in the substrate 710 can, for example, first be filled with loose powder. The loose powder 730 can then be agglomerated into mechanically strong microstructures 770 by means of a coating, e.g., by means of atomic layer deposition (ALD)

[10] . Substrates with such structures are compatible with standard MEMS and semiconductor manufacturing processes and can be further processed in a clean room.

[0160] The starting material is, for example, a pre-processed, planar substrate with a multitude of components of one or more oscillator designs. This substrate can contain cavities suitable for accommodating loose microfine powder, depending on the component design(s). The resonant frequency of the oscillators on this substrate can be adjusted by adjusting the weight of the seismic mass using the PowderMEMS process. For this purpose, a mixture of powders of different densities matching the desired resonant frequency can be introduced into the cavities within the seismic mass and solidified by coating, e.g., using ALD, as described in

[15] for NdFeB powder. By mixing a low-density substance, e.g., SiO2 with p=2.65 g / cm 3 , and a high-density material, e.g., tungsten p=19.3 g / cm 3, a continuous or quasi-continuous, or at least discrete, finely graded adjustment of the overall density can be achieved via the volume ratio of the various particles, for example, in powder form, and thus the weight of the seismic mass. The cavities within the seismic mass into which the powder is introduced optionally remain unchanged at all times, for example, between different instances of a manufacturing process according to the invention. The density of the powder mixture required for a specific resonance frequency can therefore be calculated simulatively, e.g., within a few minutes, using FEM simulation.

[0161] It should be noted that simulation tools can generally be used to determine the resonant frequencies to be set, e.g., by adjusting the mass of the mass element. In particular, manufacturing methods according to the invention can optionally include finite element simulations, on the basis of which a parameter, e.g., the mass of the mass element, can be determined.

[0162] According to embodiments, it is optionally taken into account that a corresponding particle mixture, for example the powder-based structure, can have or has a fill factor of less than 100%.

[0163] Fig. Figure 8 shows (a) a schematic view of a finite element model of a cantilevered micromechanical oscillator with seismic mass at the free end of the cantilever beam and (b) a plot of a variation of the resonance frequency as a function of the powder mixture from 100% SiO2 to 100% tungsten according to embodiments of the present invention.

[0164] For the example in Fig. 8, a volume fill factor of 50% is assumed as an example. Thus, the resonance frequency of a vibration harvester with a cantilevered bending beam of a given design, Fig. 8 (a), can be adjusted continuously, or quasi-continuously or at least discretely finely graded, by various mixtures of SiO2 and tungsten in the range from 700 Hz (100% tungsten) to 1800 Hz (100% SiO2), Fig.In this example, the resonance frequency of a MEMS-based vibration harvester can be adjusted or tuned by more than + / - 40% relative to the mean frequency value of 1250 Hz.

[0165] Apart from the mixing ratio of the particle mixture, e.g., the powder, the entire remaining manufacturing process, including photomasks, can remain unchanged. This eliminates the need for development effort for component design or the establishment of new processes, saving material costs and time.

[0166] The seismic mass can be generated, for example, approximately two-thirds of the way through the manufacturing process, and optionally only the movable structure can be defined afterward. Since the substrates with the oscillators can be pre-processed accordingly, it is possible to manufacture customized components in the shortest possible time.

[0167] The described procedure is not limited to standard substrates made of silicon or glass for semiconductor and MEMS manufacturing, but can be applied to any planar substrate made of ceramic, metal or plastic.

[0168] Alternatively or additionally, embodiments may include, among others, the following advantages: Adaptation of the resonance frequency of a MEMS oscillator of a given design, e.g., with a given structure, over a wide range at the substrate level, i.e., in the application, without any (e.g., structural) changes to the component design and manufacturing process (e.g., with the exception of the particle mixture used). This allows for minimal additional development time or production time and / or production costs (e.g., in connection with the definition and production of a powder mixture with a specific density, or even only in connection with the definition and production of a powder mixture with a specific density), a particularly rapid response to customer orders, since the substrates can be pre-processed for approximately two-thirds of the overall process before the seismic mass is generated, and cost-effective production of both mass products and small series.

[0169] Furthermore, embodiments enable the solution of one of the biggest problems in the field of MEMS energy harvesting, the adaptation of the resonance frequency of a vibration harvester to specific mechanical energy sources under the conditions of mass production.

[0170] Furthermore, the described procedure can be applied to any planar substrate made of silicon, glass, ceramic, metal, or plastic. In other words, embodiments further include methods according to the invention using substrates made of silicon, glass, ceramic, metal, and / or plastic.

[0171] Preferred technical application areas of exemplary embodiments include, in particular, micro-energy sources for sensors, e.g., for the Internet of Things, machine monitoring, monitoring of technical systems and components, e.g., car tires, engines, transmissions, and power-free standby of sensor nodes and other electronic components.

[0172] Embodiments according to the present invention further comprise, in particular, methods comprising a design-independent adaptation of the resonance frequency of micromechanical oscillators (e.g. in the form of spring-mass systems) within a wide frequency range, for example by setting the weight of the seismic masses of a plurality of components on a substrate to a specific value in the MEMS manufacturing process optionally only by applying PowderMEMS technology in combination with particle mixtures, e.g. in the form of powders or powder mixtures of different densities.

[0173] Furthermore, according to embodiments, each individual substrate can be processed with a specific particle mixture, for example, in the form of a specific powder mixture with a defined overall density. Accordingly, each component of a specific design on a substrate or wafer can have the same resonant frequency. On different substrates or wafers, components of the same design can have different resonant frequencies by adjusting the particle mixture, for example, the powder mixtures.

[0174] Furthermore, in embodiments, the adjustment of the resonance frequency can be integrated into the MEMS manufacturing process of the component, i.e., the substrate is subsequently further processed, for example, in a clean room. Thus, according to the invention, this optionally does not involve pure post-processing; therefore, an adjustment of the resonance frequency according to embodiments does not occur, for example, in the course of pure post-processing.

[0175] Furthermore, according to embodiments, based on an average frequency value, the adjustment range of the resonance frequency, for example for a specific, fixed design, is at least + / - 10%, preferably at least + / - 25% and particularly preferably at least + / - 40% of the average frequency value.

[0176] Furthermore, according to embodiments, several different designs can be used, each of which covers a different frequency range, so that MEMS devices with any resonance frequencies in the range 10 Hz - 200 kHz, preferably 40 Hz - 10 kHz and particularly preferably 50 Hz - 2.5 kHz can be realized.

[0177] For each design, substrates can also be optionally pre-processed up to the definition of the seismic mass, so that a customer-specific component with a specific resonance frequency can be completed in a particularly short time.

[0178] In particular, embodiments include oscillators for converting mechanical energy into electrical energy (vibration harvesters). Energy conversion can be carried out, in particular, using piezoelectric materials.

[0179] Furthermore, embodiments optionally include the use of individual powders, in particular comprising materials with a higher density than silicon, such as tungsten.

[0180] Furthermore, embodiments include the use of powder mixtures comprising two or more substances having different densities. In particular, light substances can be used mixed with heavy substances in variable proportions. In particular, powder mixtures comprising aluminum or silicon, as well as their oxides and nitrides, mixed with tungsten can be used. Particularly preferably, for example, any tungsten-containing powder or powder mixture can be used, since tungsten has both a high density and is resistant to process parameters such as temperature.

[0181] All lists of materials, environmental influences, electrical properties and optical properties listed herein are to be considered exemplary and not exhaustive.

[0182] Although some aspects have been described in connection with a device, it is 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. Similarly, aspects described in connection with or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device.

[0183] 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 / Literature [1] https: / / assets.websitefiles.com / 6225ec4d016842cb92dle5d3 / 629151680aab97765 5aaad2_Conflow-Energy-Harvesting-Report.pdf [2] BOLT™R0120 data sheet, V2.0, MicroGen Systems, Inc. June 2013 [3] P. Podder, P. Constantinou, A. Amann, S. Roy: Frequency adjustable MEMS vibration energy harvester. In: Journal of Physics, Conference Series 757 (2016) 012037 [4] R. Elfrink, M. Renaud, T. M. Kamel, C. de Nooijer, M. Jambunathan, M. Goedbloed: Vacuum-packaged piezoelectric vibration energy harvesters: damping contributions and autonomy for a wireless sensor system. In: J. Micromech. Microeng. 20 (2010) S. 104001. DOI: 10.1088 / 0960-1317 / 20 / 10 / 104001 [5] R. Adhikari, N. Jackson: Passive frequency tuning of piezoelectric energy harvester using embedded masses. In: IEEE PowerMEMS 2021 Virtual Conference, 6 - 8.12.2021 [6] E. E. Aktakka, R. L. Peterson, K. Najafi: Thinned-PZT on SOI process and design optimization for piezoelectric inertial energy harvesting. In: 2011 16th International Solid-State Sensors, Actuators and Microsystems Conference. Beijing, China, 05.06.2011 - 09.06.2011: IEEE, S. 1649-1652 [7] F. Cottone, L. Gammaitoni, H. Vocca, M. Ferrari, V. Ferrari: Piezoelectric buckled beams for random vibration energy harvesting. In: Smart Mater. Struct. 21 (2012) 035021 (11pp), doi:10.1088 / 0964-1726 / 21 / 3 / 035021 [8] Z. Wang, S. Matova, R. Elfrink, M. Jambunathan, C. de Nooijer, R. van Schaijk, R. J. M. Vullers: A piezoelectric vibration harvester based on clamped-guided beams. In: IEEE MEMS 2012, Paris, FRANCE, 29 January - 2 February 2012 [9] S. Bouhedma, Y. Zheng, F. Lange, D. Hohlfeld: Magnetic Frequency Tuning of a Multimodal Vibration Energy Harvester. In: Sensors 2019 (Basel, Switzerland) 19 (5), S. 1149. DOI: 10.3390 / s19051149

[10] T. Lisec et al.:PowderMEMS - A generic microfabrication technology for integrated threedimensional functional microstructures. In: Micromachines 2022, 13, 398. https: / / doi.org / 10.3390 / mi13030398

[11] M. T. Bodduluri, B. Gojdka, N. Wolff, L. Kienle, T. Lisec, F. Lofink: Investigation of waferlevel fabricated permanent micromagnets for MEMS. In: Micromachines 2022,13, 742. https: / / doi.org / 10.3390 / mi13050742

[12] M. Paesler, T. Lisec, H. Kapels: Novel integrated BEOL compatible inductances for power converter applications. In: IEEE Applied Power Electronics Conference and Exposition (APEC), 25 June 2020, New Orleans, LA, USA. DOI: 10.1109 / APEC39645.2020.9124474

[13] O. Behrmann, T. Lisec, G. Piechotta, B. Gojdka: A microfluidic porous solid phase suitable for mass production. In: MikroSystemTechnik Congress, 08-10 November 2021, Stuttgart- Ludwigsburg, Germany, ISBN:978-3-8007-5656-8

[15] M. T. Bodduluri, T. Dankwort, T. Lisec, S. Grünzig, A. Khare, M. Ahmed, B. Gojdka: Fully integrated high-performance MEMS energy harvester for mechanical and contactless magnetic excitation in resonance and at low frequencies. In: Micromachines 2022, 13,863. https: / / doi.org / 10.3390 / mi13060863

Claims

[1] Micromechanical system (100, 200, 300, 400, 600 1-3 ) with: a substrate (110, 210, 310, 410, 610, 710); a mass element suspended from the substrate in an oscillating manner (120, 220, 320, 420 1-2 , 620 1-3 ), wherein the mass element is a particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770); and wherein first particles (130a, 230a, 330a, 430a, 630a) of the particle mixture have a first mass density and wherein second particles (130b, 230b, 330b, 430b, 630b) of the particle mixture have a second mass density. [2] Micromechanical system (200, 300, 400) according to claim 1, wherein particles of the particle mixture are connected to one another by means of a coating (250, 350, 450). [3] Micromechanical system (200, 300, 400) according to claim 2, wherein the mass element (220, 320, 420 1-2) comprises a porous body (335a) and wherein particles of the particle mixture (230, 330, 430, 770) are firmly bonded to one another by means of the coating (250, 350, 450) in order to form the porous body. [4] Micromechanical system (300, 400) according to one of claims 2 to 3, comprising a structural element (360, 460) suspended from the substrate (310, 410) in an oscillating manner; wherein the structural element comprises a cavity (340, 440 1-2 ), in which the mass element (320, 420 1-2 ) is arranged; and wherein the mass element is fixed in the cavity by means of the coating (350, 450). [5] Micromechanical system (300) according to claim 4, as far as dependent on claim 3, wherein loose particles (335b) of the particle mixture (330) are enclosed in the cavity (340) by the porous body (335a). [6] Micromechanical system (400) according to one of claims 4 to 5, wherein the micromechanical system comprises a plurality of mass elements (420 1-2 ); wherein the structural element (460) has a plurality of cavities (440 1-2 ); wherein a respective mass element of the plurality of mass elements is arranged in a respective cavity of the plurality of cavities; and wherein each mass element of the plurality of mass elements comprises the particle mixture (430). [7] Micromechanical system (400) according to claim 6, wherein the cavities (440 1-2 ) of the plurality of cavities, by means of the arrangement of a respective mass element (420 1-2 ) in the respective cavity, each have the same volume filling factor. [8] Micromechanical system (400) according to one of claims 6 or 7, wherein particles of the particle mixture (430) of the mass elements (420 1-2) are connected to one another by a matching coating (450) to form a respective mass element; and where the matching coating of particles originates from the same deposition process. [9] Micromechanical system (200, 300, 400) according to one of claims 2 to 8, wherein the coating or the matching coating comprises a layer deposited from a gas phase, e.g. a layer produced by atomic layer deposition. [10] Micromechanical system (100, 200, 300, 400, 600 1-3 ) according to one of the preceding claims, wherein the first mass density is at least a factor of 2, at least a factor of 3, at least a factor of 5 or at least a factor of 7 greater than the second mass density. [11] Micromechanical system (100, 200, 300, 400, 600 1-3) according to one of the preceding claims, which is designed as an energy harvester to, based on an oscillation of the mass element (120, 220, 320, 420 1-2 , 620 1-3 ) to provide electrical energy. [12] Micromechanical system (400) according to one of the preceding claims, wherein the particle mixture (430) comprises third particles (430c) with a third mass density. [13] Wafers with: a variety of micromechanical systems (100, 200, 300, 400, 600 1-3 ) according to any one of the preceding claims; where respective mass elements (120, 220, 320, 420 1-2 , 620 1-3 ) the multitude of micromechanical systems use the same particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770). [14] Wafer according to claim 13, where particles of the particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770) of the mass elements (120, 220, 320, 420 1-2 , 620 1-3), to form the respective mass element, are connected to one another by a matching coating (250, 350, 450); and where the matching coating of particles originates from the same deposition process. [15] Method (500) for producing a micromechanical system (100, 200, 300, 400, 600 1-3 ), including: Providing (510) a substrate (110, 210, 310, 410, 610, 710); Forming (520) a mass element (120, 220, 320, 420) suspended from the substrate in an oscillating manner 1-2 , 620 1-3 ); wherein the formation of the mass element creating a cavity (140, 340, 440 1-2 , 640, 740) in the substrate; and filling the cavity with a particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770) to form the mass element includes, wherein first particles (130a, 230a, 330a, 430a, 630a) of the particle mixture have a first mass density and wherein second particles (130b, 230b, 330b, 430b, 630b) of the particle mixture have a second mass density. [16] The method of claim 15, further comprising: Determine a mass value of the mass element (120, 220, 320, 420 1-2 , 620 1-3 ) based on a resonant frequency to be set of a spring-mass system of the micromechanical system comprising the mass element; Determining a mixing ratio of the first and second particles of the particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770) to obtain the mass value of the mass element; and Adjusting the mixing ratio of the first and second particles of the particle mixture so that the mass element with the mass value is formed by means of the particle mixture with the adjusted mixing ratio. [17] Method according to claim 16, wherein the resonance frequency is selected in a range of at least 10 Hz to at most 200 kHz, of at least 40 Hz to at most 10 kHz and / or of at least 50 Hz to at most 2.5 kHz. [18] A method according to any one of claims 15 to 17, further comprising: Connecting particles of the particle mixture (230, 330, 430, 770) by means of a coating (250, 350, 450). [19] Method according to one of claims 15 to 18, wherein the provision of the substrate (110, 210, 310, 410, 610, 710), the creation of the cavity (140, 340, 440 1-2 , 640, 740) and filling the cavity with the particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770) at wafer level, prior to singulation of the micromechanical system. [20] Method according to one of claims 15 to 19, where, at different instances of the process, to generate instance-specific identical and across the different instances different micromechanical systems (600 1-3 ) with instance-specific resonance frequencies, filling a respective cavity (640) of a respective substrate (610) with a particle mixture (630) assigned to the instance 1-3 ) with a mixing ratio of the first and second particles assigned to the instance; wherein the respective substrates (610) and cavities (640) of the different micromechanical systems of the different instances are of the same design. [21] Method according to one of claims 15 to 20, wherein the cavity (140, 340, 440 1-2 , 640, 740) regardless of the mixing ratio of the first and second particles of the particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770) is filled to a predetermined fill level. [22] Method according to one of claims 15 to 21, wherein the particle mixture (430) comprises particles (430a-c) with particle sizes of a first interval of particle sizes and particles (435) with particle sizes of a second interval of particle sizes; and wherein the method further comprises determining a volume filling factor of the cavity (440 1-2 ) and adjusting a mixing ratio of particles having particle sizes of the first and second interval of the particle mixture to adjust the volume fill factor. [23] A method according to any one of claims 15 to 22, further comprising: Formation of a spring element between a for the mass element (120, 220, 320, 420 1-2 , 620 1-3) and a region of the substrate (110, 210, 310, 410, 610, 710) which provides clamping of the spring element, so that the spring element provides the oscillatable suspension of the mass element. [24] Method according to one of claims 15 to 23, in which the cavity (140, 340, 440 1-2 , 640, 740) is dimensioned and a mass density difference between the first and second particles is set; that an adjustment range of a resonance frequency of the micromechanical system (100, 200, 300, 400, 600 1-3 ), based on adjusting the mixing ratio of the particle mixture (130, 230, 330, 430, 630 1-3 , 730, 770), at least + / - 10%, at least + / - 25% and / or at least + / -40% relative to an average frequency value, wherein the mean frequency value is associated with a mean mass of the predetermined mass range. [25] Method according to one of claims 15 to 24, wherein the first mass density is greater than the second mass density by at least a factor of 2, at least a factor of 3, at least a factor of 5 or at least a factor of 7.

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