Encapsulated MEMS switching element, device and manufacturing method

Description

[0001] The present invention relates to a microelectromechanical switching element comprising a multilayer carrier substrate with a first layer serving as a carrier layer, an electrically insulating second layer, and a third layer formed as a semiconductor layer. The switching element has a deflectable bending element formed by an exposed portion of the semiconductor layer. Furthermore, the invention relates to a device having such a switching element and a method for producing such a switching element.

[0002] Microelectromechanical switching elements are generally known from the prior art and are also referred to in the technical world as MEMS switching elements. These are mechanical solid-state switching elements structured in the micrometer to nanometer range and comprise electrostatically actuated bending elements so that they can be switched by changing an electrical voltage. A plurality of such individual MEMS switches are often arranged in an array, in particular to achieve a sufficiently high current-carrying capacity and / or dielectric strength. Such MEMS switches and switching devices based thereon are described, for example, in DE 10 2017 215 236 A1, DE 43 02 204 A1, US 2016 / 268084 A1, and WO 2018 028 947 A1. The subject of DE102017215236A1 is a MEMS switch which is built on a silicon-on-insulator (SOI) substrate.With this manufacturing technology, the specified switching times can be set with particular precision thanks to the sophisticated and reproducible manufacturing processes. The flexure element is exposed using subtractive manufacturing, with the SOI substrate being processed on both sides (top and bottom). The carrier layer of the SOI substrate is completely removed from the back of the substrate in the area of the flexure beam, allowing the flexure beam to deflect vertically. A cover substrate is typically arranged on the front side of the SOI substrate (the side with the flexure element), which also has a recess in the area of the flexure beam. A control electrode and one or more counter contacts for the switching process can be arranged in this area of the cover substrate.

[0003] A disadvantage of these known SOI-MEMS switches is that, due to the processing of the SOI substrate from both sides, damage to the active silicon layer can occur relatively easily during manufacturing. Another disadvantage is that the flexural element is initially not protected from chemical and mechanical environmental influences due to the exposed backside. While it is fundamentally possible to encapsulate such an SOI-MEMS switch in a higher-level housing, this requires additional manufacturing steps and results in a relatively large component, which requires a correspondingly large amount of installation space in a higher-level device.

[0004] Other types of MEMS switching elements are also known from the state of the art, for example, with metallic cantilevers. However, with this technology, the desired predetermined switching properties are typically less precisely adjustable. Here, too, encapsulation in a separate housing is usually necessary for protection against external environmental influences, which also leads to comparatively large dimensions.

[0005] The object of the invention is therefore to provide a switching element that overcomes the aforementioned disadvantages. In particular, a switching element is to be provided that is robust against external environmental influences and, at the same time, can be designed as compactly as possible. In particular, the predetermined switching properties should also be able to be adjusted as precisely as possible. A further object is to provide a device with such a switching element and a method for producing such a switching element.

[0006] These objects are achieved by the switching element described in claim 1, the device described in claim 8 and the manufacturing method described in claim 12.

[0007] The microelectromechanical switching element according to the invention comprises a multi-layer carrier substrate with a first layer serving as a carrier layer, an electrically insulating second layer and a third layer designed as a semiconductor layer. The switching element has a bending element which is formed by an exposed partial region of the semiconductor layer (i.e. the third layer). In addition, the switching element comprises a flat cover substrate connected to the multi-layer carrier substrate. The carrier substrate, in particular its carrier layer, has a recess in the region of the bending element. In addition, the cover substrate also has either a recess and / or a spacer layer running around the region of the bending element in the region of the bending element, so that the interaction of the two recesses orThe one recess and the surrounding spacer layer form a superordinate cavity in which the bending element is arranged in a deflectable manner. This superordinate cavity is delimited by the carrier layer and the cover substrate in such a way that it is hermetically sealed from the external environment.

[0008] A microelectromechanical switching element is understood here to be a switching element manufactured using microsystem technology. The term microsystem technology generally refers to technology capable of producing microscopically small, mechanically active components capable of movement, such as switches or gears. In a broader sense, the term microsystem technology also includes nanosystem technology, which enables corresponding structures in the submicrometer to nanometer range. In general, technologies fundamentally familiar from semiconductor manufacturing are used here. Such MEMS switches can be manufactured on glass, sapphire, and / or semiconductor substrates (so-called wafers), for example, made of silicon or gallium arsenide.The length of a MEMS switching element is less than 1 mm, preferably less than 500 µm. The largest structural element of an individual MEMS switching element is typically the flexure. This flexure is preferably elongated to enable a defined, resilient deflection similar to a straight leaf spring. The flexure is therefore often referred to in technical circles as a flexure beam or switching tongue. However, other shapes and proportions are also possible.

[0009] By manufacturing the bending element as an exposed portion of the semiconductor layer (located at the top of the layer system), the switching properties of the bending element can be adjusted particularly precisely, similar to conventional SOI-MEMS switching elements.

[0010] The bending element is located in a higher-level cavity of the component, which is composed of two flat substrates, namely the multilayer carrier substrate and the cover substrate. When aligned horizontally, this cavity is bounded "upward" (on the side of the semiconductor layer, i.e., the third layer of the carrier substrate) by the cover substrate. The outer surface of the cover substrate hermetically seals the cavity from the outside environment. Similarly, the cavity is sealed "downward" (toward the opposite side) by the carrier layer. For this purpose, the carrier layer is designed to be continuous and full-surface on its lower outer side and, at least in the area of the cavity, has no through holes facing the outside environment.In addition, the multilayer carrier substrate and the cover substrate are connected to each other in such a way that the cavity is also hermetically encapsulated to the outside all around the cavity.

[0011] The movement of the bending element on the side of the carrier substrate is made possible in particular by the fact that the carrier layer has a recess in the area of the bending element. It is important that this recess is not continuous (i.e., it does not penetrate the entire carrier layer), but rather represents only a partial cavity. This partial cavity is therefore a type of shallow blind hole and not a hole that extends through to the outside. In other words, the carrier layer is only thinner in the area of the cavity than in the surrounding areas, yet it is still fully covered on the outside.

[0012] In contrast to conventional SOI-MEMS switching elements, hermetic encapsulation of the active region of the switching element is achieved by connecting only two substrates, namely the multilayer carrier substrate and the cover substrate. A key advantage of the invention is that this hermetic encapsulation does not require an additional housing or other (third) substrate; instead, the encapsulation is achieved by two substrates bonded together at the wafer level. This allows the entire structure to be implemented in a particularly compact manner.

[0013] The device according to the invention comprises a switching element according to the invention or an array of several such switching elements according to the invention as subelement(s). Regardless of the specific application of the device, its advantages are analogous to the advantages of the switching element according to the invention described above, in particular with regard to protection against environmental influences, a compact design, and / or precise adjustment of the desired switching properties.

[0014] The method according to the invention serves to produce a switching element according to the invention. a) a prefabricated multilayer carrier substrate with a prefabricated cavity in the carrier layer is provided, b) the bending element is cut out of this prefabricated carrier substrate by subtractive manufacturing and c) in a wafer bonding step the cover substrate is permanently bonded to the carrier substrate, whereby the overarching cavity is hermetically encapsulated.

[0015] The described "exposing" of the bending element is to be understood as meaning that the adjacent regions of the semiconductor layer are removed at least over a predominant part of the longitudinal extent of the bending element.

[0016] As described above, the prefabricated cavity in the first carrier layer should be a partial cavity, i.e., a hole that does not penetrate to the opposite side. A continuous semiconductor layer is arranged in the prefabricated carrier substrate, particularly above this prefabricated cavity. The bending element is then cut out of this continuous semiconductor layer, whereby the multilayer carrier substrate as a whole only needs to be processed from the top side (the side of the semiconductor layer) and not from the back. Such prefabricated carrier substrates with buried partial cavities in the carrier layer are known from the prior art. As a special variant of SOI substrates, these are offered by numerous manufacturers under the designation C-SOI substrates (for cavity silicon-on-insulator substrates).For the production of arrays with a large number of MEMS switching elements, C-SOI substrates with a large number of such cavities can also be used, with at least one released bending element being assigned to each cavity.

[0017] Due to the prefabricated cavity, the bending element is already exposed towards the underside before step b), since the cavity already forms part of the higher-level cavity required for the deflection. The hermetic encapsulation of the overall formed higher-level cavity is then achieved in step c) by connecting the carrier substrate to the cover substrate using a wafer bonding step. The method according to the invention thus enables particularly simple production of the switching element according to the invention, whereby the already described advantages with regard to encapsulation and compact design are realized. In optional further steps (e.g., before or after step b), additional elements can also be applied and, if necessary, structured using surface micromechanics techniques.

[0018] Advantageous embodiments and further developments of the invention emerge from the claims dependent on claims 1, 8, and 12, as well as from the following description. The described embodiments of the switching element, the device, and the manufacturing method can generally be advantageously combined with one another.

[0019] Thus, the deflection direction of the bending element can advantageously be oriented essentially perpendicular to the layer plane of the multilayer carrier substrate. In other words, the bending element can be deflected upwards and downwards when the overall flat component is horizontally aligned. Such mobility out of the layer plane of the bending element is particularly easy to achieve with a leaf spring-shaped bending element. The deflection of the bending element can then occur either in the direction of the recess in the carrier layer or in the opposite direction, in the direction of the recess in the cover substrate or the cavity formed by the surrounding spacer layer.

[0020] According to the invention, the multilayer carrier substrate is a silicon-on-insulator layer system or comprises such a layer system. A silicon-on-insulator (abbreviated: SOI) layer system comprises, in particular, a silicon-insulator-silicon layer sequence, wherein the carrier layer (the first layer of the layer system) is formed by the lower silicon layer, the second layer by the insulator, and the third layer by the upper silicon layer. Advantageously, one of the two silicon layers, and particularly preferably both silicon layers, can be monocrystalline silicon. The insulator layer can preferably be formed essentially by a silicon dioxide layer (SiO 2 ). It can be implemented, in particular, as a so-called buried oxide layer (BOX layer for short).SOI technology, known per se, enables particularly precise definition of the layer thicknesses and other material properties of the individual layers. The semiconductor layer from which the bending element is cut out is, in particular, the thinner of the two silicon layers of a typical SOI substrate. The mechanical connection of the bending element to the remaining regions of the component can be mediated, in particular, via the insulator layer of the SOI substrate. In other words, the bending element can be coupled in its base region to a mechanically supporting part of the switching element via the insulator layer. These and other advantageous features and embodiments of the SOI layer system and its processing are described in more detail in DE102017215236A1, which is therefore intended to be incorporated in its entirety into the disclosure of the present application.

[0021] As an alternative to the SOI layer sequence described above, the carrier layer can also be formed, for example, by a sapphire layer.

[0022] According to a particularly preferred embodiment of an SOI-MEMS switching element, the recess in the carrier substrate comprises a recess in the carrier layer, and this recess is formed by a prefabricated cavity in the SOI layer system. In other words, the switching element is constructed on a cavity-SOI wafer (abbreviated: C-SOI wafer). According to a first alternative, this prefabricated recess is a partial cavity in the lower silicon layer, and the buried oxide layer is also interrupted in this region. According to a second alternative, however, it can also be a partial cavity in the lower silicon layer, which is lined with a corresponding oxide layer in the bottom region.Both types of C-SOI substrates are suitable for providing the required overhead cavity for the movement of the bending element with comparatively little process effort and still enable hermetic encapsulation at the bottom within the wafer layer system.

[0023] However, the use of a C-SOI substrate with a prefabricated cavity is not absolutely necessary. Alternatively, the partial cavity can be created in the carrier substrate during the manufacturing process for the switching element. In this case, the cavity can be limited to the insulating second layer, and the carrier layer can be retained in its full thickness. Such a hole in the second layer (i.e., the buried oxide layer) can be formed, for example, by hydrogen fluoride etching. The cavity for the movement of the flexure element is then limited to the thickness of the oxide layer and may be less deep. However, this can also be sufficient for the vertical movement required during the switching process, especially if the opposite cavity in the area of the cover substrate is comparatively deeper.

[0024] Generally advantageously, the hermetic encapsulation of the superordinate cavity in the lateral direction can be achieved by a permanent, fluid-tight, planar connection between the multilayer carrier substrate and the cover substrate. In other words, these two substrates can be connected by a so-called "wafer bond." This permanent connection can be realized, in particular, circumferentially around the superordinate cavity, so that the cavity as a whole is hermetically encapsulated to the outside. Numerous methods are known from the prior art for such a wafer bonding step. For example, a gold-silicon bond, a germanium-aluminum bond, or another type of eutectic bond can be used. Alternatively, the planar connection can also be realized by a glass frit, an anodic bond, thermocompression bonding, adhesive bonding, and / or fusion bonding.

[0025] According to a further generally advantageous embodiment, the cover substrate can be functionally designed as an electrically insulating cover substrate and in particular can be formed essentially from glass or silicon. This should be understood to mean that the glass or silicon forms the main component of the cover substrate and additional elements, in particular in the form of local coatings, should not be excluded. In particular, a control electrode and additional contact elements can be applied as further elements to the surface of the cover substrate. In particular, the control electrode and / or contact element(s) can be arranged on the side of the cover substrate facing the bending element. However, metallizations in the form of conduction elements and / or contact elements and / or other components can also be present on the outside of the cover substrate.Electrical feedthroughs can be provided between the two main surfaces of the cover substrate, particularly in the form of so-called vias, which extend perpendicular to the substrate surface through the substrate to electrically connect elements on the top and bottom sides. Alternatively, however, a cover substrate made of a conductive material can be used, which is coated with an electrically insulating layer on the side facing the bending element, so that a purely functionally electrically insulating cover substrate is formed. Such an electrically insulating layer can be, for example, a silicon dioxide layer or a polymer layer.

[0026] It is generally advantageous to arrange a switching contact on the bending element. This switching contact can be formed, for example, by a structured metallization on the bending element. Optionally, the bending element can also carry additional functional elements; it need not consist solely of the aforementioned semiconductor layer.

[0027] Furthermore, the cover substrate can carry a first mating contact, which can be contacted with the switching contact of the flexural element depending on a deflection of the flexural element. Thus, when the flexural element is deflected toward the cover substrate and is in contact with it in its end region, an electrical contact can be established between the switching contact of the flexural element and a mating contact arranged opposite one another on the cover substrate. Particularly preferably, the cover substrate even carries a pair of mating contacts, both of which can be contacted with the switching contact of the flexural element. In this way, the pair of mating contacts is electrically connected to one another in the position deflected toward the cover substrate. These two mating contacts can be designed as so-called load contacts of a first load circuit.The load circuit can be closed using the switching contact, and the switching element is in an "ON" position. When the switching contact and the counter contact(s) are not connected, the switching element is in an "OFF" position.

[0028] According to a further generally advantageous embodiment, the cover substrate can have a control electrode with which the deflection of the bending element can be influenced. This control electrode is expediently placed opposite the bending element, and the switching voltage can be applied to it during operation. Such a control electrode is sometimes also referred to in the prior art as a gate electrode. The bending element can be deflected by electrostatic interaction between the control electrode and the bending element. For example, it can be moved towards the cover substrate due to electrostatic attraction, so that this deflection results in the formation of an electrical contact between a contact element of the bending beam and a contact element of the cover substrate.

[0029] In general, and regardless of the precise design of the individual switching element, the higher-level device can have an array of a plurality of switching elements according to the invention. Such an array can be a parallel connection and / or a series connection of a plurality of such switching elements. A parallel connection of a plurality of switching elements can serve, in particular, to increase the current-carrying capacity of the entire device compared to a single switching element. A series connection of a plurality of switching elements can serve, in particular, to increase the dielectric strength compared to a single switching element. In this way, the use of an array can help the device meet the specifications of a circuit breaker of an electrical power distribution line—in particular in a low-voltage or medium-voltage network.The number of individual switching elements in the array can be tailored to the respective specifications. For example, it can range from a few tens to a few thousand switching elements, and for higher performance ranges, even several hundred thousand.

[0030] According to a further advantageous embodiment of the device, in addition to the at least one switching element, it can comprise one or more semiconductor elements electrically connected in series or parallel thereto. These can be, for example, transistors or other semiconductor switching elements, as described in WO2018028947A1. The additional semiconductor elements can in principle be manufactured on the same substrate as the bending element, i.e., monolithically integrated, or they can in principle also be manufactured on a different substrate and subsequently connected to the switching element.

[0031] The higher-level device can be designed for use in a wide variety of applications. For example, it can be configured as a switching device or contactor, a converter or inverter, a logic circuit, and / or a logic gate. The switching device or contactor can, in particular, be a device for a low-voltage or medium-voltage network. The device can also generally be a programmable logic controller, in particular a controller for an industrial plant. Switching elements according to the invention can be used, for example, in an input stage, an output stage, and / or in a safety relay of such a plant control system.

[0032] Generally advantageously, the device can be designed as a surface-mountable component. In other words, it can be an SMD or SMT component (SMD for "surface-mounted device" or SMT for "surface-mounting technology"). For this purpose, the device can be provided with solderable, flat SMD contact points in the area of at least one of its substrate outer surfaces.

[0033] In connection with this embodiment, it is particularly advantageous if the cover substrate and / or the carrier substrate has one or more feedthroughs for electrically contacting the at least one switching element. In other words, so-called "vias" can be provided, which extend perpendicular to the substrate surface through the respective substrate in order to electrically connect elements on the top and bottom sides. In particular, such vias are designed such that they do not breach the hermetic encapsulation of the superordinate cavity. Various methods are known from the prior art with which such vias can be routed, for example, through a glass or semiconductor substrate while maintaining hermetic encapsulation.

[0034] According to an advantageous development of the manufacturing method, the bending element can be obtained by subtractive manufacturing from a silicon-on-insulator layer system, as already described above for the corresponding embodiment of the switching element. In particular, the bending element can be formed by exposing part of a silicon layer of the SOI layer system. The manufacturing method can comprise a multitude of further optional manufacturing steps, which are generally known, in particular, from MEMS and semiconductor processing. For example, additional metallization steps, e.g., in the form of a coating by vapor deposition, sputtering, or galvanic deposition, can be provided.The metallic layers for the electrodes and / or contact elements can include gold, chromium, or silver, or other metals commonly used in semiconductor manufacturing, as well as less common metals, particularly precious metals. The (complete or partial) removal of individual layers can be achieved, for example, by etching and / or mechanical / chemical polishing and / or a lift-off process. Etching processes such as chemical etching with hydrofluoric acid and reactive ion etching (RIE, or DRIE, or deep reactive ion etching) can be used for the defined removal of (partial) layers. Precise structuring can be achieved using conventional lithographic structuring methods.

[0035] According to a particularly preferred embodiment of the method, the subtractive production of the bending element in step b) takes place by exclusively one-sided processing of the multilayer carrier substrate. Particularly preferably, only one-sided processing of a prefabricated carrier substrate takes place. In other words, processing in the rear side region is avoided. This has the advantage that damage in the area of the upper semiconductor layer (i.e., the third layer of the multilayer carrier substrate) can be avoided. This exclusively one-sided processing is made possible in particular by the use of prefabricated C-SOI substrates, since this allows a sufficiently large cavity for the movement of the bending element to be created without rear-side etching.

[0036] The invention will now be described by way of some preferred embodiments with reference to the attached drawings, in which: Figure 1 shows a schematic cross-sectional view of a switching element according to the prior art, Figure 2 shows a schematic plan view of another known switching element, Figure 3 shows a schematic sectional view of a conventional switching element with a housing, Figures 4 to 6 show several process stages in the production of a switching element according to the invention, Figure 7 shows a prefabricated carrier substrate for producing a switching element according to the invention and Figure 8 shows a switching element according to a further example of the invention.

[0037] In the figures, identical or functionally identical elements are provided with the same reference symbols.

[0038] Figure 1shows a microelectromechanical switching element 1, which is known from the prior art. This switching element has an overall similar structure to that described in DE 10 2017 215 236 A1, but is shown here in a somewhat simplified manner for the sake of clarity. The switching element has a silicon-on-insulator layer system 100, which here comprises a first silicon layer 110, followed by a buried oxide layer 120, and then a further silicon layer 130. A second oxide layer can also additionally follow layer 130 as part of the SOI layer system 100 or at least have been present there during production. A bending element 135 has been defined and exposed from the upper semiconductor layer 130 using subtractive manufacturing.The production of the bending element comprises the removal of the surrounding regions of the silicon layer 130 and the local removal of the parts of the layers 110 and 120 adjacent to the bending element 135. Thus, a bending element 135 deflectable in the thickness direction d was produced here, similar to that described in DE 10 2017 215 236 A1. The remaining manufacturing steps can also be carried out analogously to DE 10 2017 215 236 A1. The base region 135a of the bending element, in which it is mechanically connected to the other parts of the SOI layer system, is designed or shown here in a somewhat simplified manner. As an alternative to this simpler implementation, the base region 135a can also be designed analogously to DE 10 2017 215 236 A1 or the as yet unpublished European patent application 20182568.4.

[0039] The component is covered at the top by a cover substrate 200, which can be made of glass, for example. This cover substrate 200 can be connected to the SOI layer system 100, for example, by a wafer bonding step. In the region of the bending beam, the cover substrate has a recess 250 so that, together with the opening 150 in the layers 110 and 120, a higher-level cavity 350 is formed in which the bending element 135 can be deflected. The carrier layer 110 has been completely etched away from the underside of the substrate in the region of the opening 150, so that the bending element is freely accessible from the side shown below.

[0040] To effect the deflection of the flexural element, a control electrode 210 is provided on the cover substrate 200 in the region above the flexural element 135. By applying voltage to the control electrode 210, a deflection of the flexural element can be electrostatically actuated. When the flexural element 135 is deflected upward in direction d, its end region can be brought into contact with the cover substrate to such an extent that a switching contact 140 applied to the flexural element 135 and a mating contact 240 applied in the recess of the cover substrate 200 make electrical contact. In this way, the switching element can be switched to "ON," and an associated load circuit can be closed with the switching element 1.

[0041] The switching element 1 shown can be present as part of a higher-level device, which can in particular comprise an array of similar switching elements. Such a MEMS array can be constructed monolithically from the same SOI substrate. In this case, the Figure 1 The area shown is to be understood as a section of a larger component, whereby the lateral layers extend further to the right and left (and of course also perpendicular to the plane of the paper) and can include further similarly constructed switching elements in these spatial directions.

[0042] Figure 2 shows a schematic plan view of such a conventional switching element, which is particularly similar to the switching element of the Figure 1can be constructed. However, the deflection direction r here is perpendicular to the plane of the drawing, and both elements of the SOI substrate 100 and elements of the cover substrate 200 are shown superimposed. The metallizations of the control electrode 210 and the two mating contacts 240 arranged on the cover substrate 200 partially conceal the underlying layers.

[0043] In the base region 135a of the flexure element, it is connected to the remaining layers of the SOI layer system 100 and to the cover substrate 200 via the planar wafer connection. In the middle region, the flexure element interacts electrostatically with the control electrode 210 located above it on the cover substrate, particularly when a switching voltage is applied to it. In the end region, the flexure element carries a switching contact 140. Opposite, in this example, on the cover substrate, there is a pair of adjacent counter contacts 240. Upon deflection of the flexure element, these two contacts 240 are electrically connected to the switching contact 140 of the flexure element and, through this, to each other; the switching element is then in the ON position. Figure 1 The basic position shown with the bending element not deflected corresponds to the OFF position of the switching element.

[0044] Figure 3shows a similar conventional switching element, which, however, in contrast to the switching element of the Figure 1 is hermetically encapsulated by a housing, which protects the area of the switching element 135 from external environmental influences. The internal structure is generally analogous to the Figure 1, whereby, however, the cover substrate 200 is larger in the lateral direction than the SOI substrate and accordingly projects laterally beyond the latter. In this edge zone, the cover substrate 200 is connected by a circumferential connection 310 to a cap-like housing cover 300, which is designed, for example, as a glass cover. The circumferential connection 310 can, for example, be a hermetically sealed solder or welded connection. In this example, the higher-level cavity 350, in which the bending element moves, is hermetically encapsulated from the external environment, specifically at the top by the cover substrate 200 and at the bottom by the housing cover 300. In this way, the switching element 1 is protected as a whole from damage by external environmental influences. However, the structure with the two substrates 100, 200 and the housing cover 300 is comparatively voluminous both in the thickness direction and laterally due to the wide circumferential edge.In the edge area, contact points 190 for bonding wires 195 can be provided next to the housing cover, which also require additional space. Only one such bonding pad 190 is shown here as an example. It can be connected to one of the electrodes of the switching element (e.g., 210, 240) by a connecting line not shown in detail here.

[0045] In the Figures 4 to 6 several process stages in the production of a switching element 1 according to the present invention are shown. Figure 6 shows the essentially finished switching element 1 or a lateral section of a corresponding device with several such switching elements. In Figure 4A prefabricated multilayer carrier substrate 100 is shown, which is used for the production of this switching element. This prefabricated carrier substrate 100 is also an SOI substrate with a carrier layer 110 made of silicon, an electrically insulating layer 120 made of buried silicon oxide, and a third layer 130 on top, which is also a silicon layer. Inside this layer structure lies a prefabricated cavity 150, which represents a recess in the oxide layer 120 and in a part of the carrier layer 110. However, this cavity 150 is only a partial cavity; in particular, it is not open to the underside 100b of the carrier substrate; rather, the carrier layer 110 nevertheless forms a continuous, planar layer on the underside 100b. On the top side 100a, however, this cavity 150 is delimited by the semiconductor layer 130 on top. This creates a closed, internal cave.Such prefabricated SOI substrates with buried cavities are well known in the art and are offered by numerous manufacturers under the designation C-SOI. Several such buried cavities can also be arranged side by side, particularly when an array of several similar switching elements is to be produced. Each cavity 150 then contributes to forming the overarching cavity necessary for the movement of the respective flexure element.

[0046] In Figure 5a more advanced process stage is shown, in which the carrier substrate 100 has already undergone several process steps. The implementation of these individual process steps can be designed in detail, for example, analogously to the already cited DE102017215236A1. The materials and thicknesses of the individual layers and further elements can also be selected analogously, for example. What is essential in connection with the present invention is that the processing advantageously takes place only from the top side 100a, i.e. that no lithography or etching steps have to be carried out on the bottom side 100b and the carrier substrate 100 accordingly only has to be held from this bottom side 100b during processing. As a result, the top side 100a is advantageously protected from mechanical damage compared to a double-sided process.

[0047] At the process stage of Figure 5A metallic switching contact 140 has been applied in a structured manner in the end region of the bending element 135. In addition, the upper semiconductor layer 130 has been opened in the regions 130a and 130b. These two openings 130a, 130b can in particular actually be a single opening in the layer 130 that runs annularly around the bending element. Alternatively, the layer 130 can also be removed only in the central region and in the end region of the bending element (corresponding to opening 130a), and the opening 130b in the base region of the bending element can be omitted, so that the bending element in the base region can be similar to the Figure 1remains connected to the remaining layer stack via layer 130. A variety of designs are conceivable for the configuration and mechanical coupling of the base region. The only essential requirement is that the bending element 135 is separated from the layer system 100 by subtractive manufacturing to such an extent that it can be deflected perpendicular to the layer plane. In the direction of the carrier layer, this deflection is enabled by the cavity 150 already present in the prefabricated layer system 100.

[0048] In Figure 6 The essentially fully processed switching element 1 is shown. In contrast to the Figure 5 Here, the oxide layer 120 in the areas 120a and 120b was also removed circumferentially around the bending element. Subsequently, the layer system on the substrate top side 100a was connected to a cover substrate 200 by a circumferential planar wafer bond connection 270, similar to the conventional switching element of the Figure 1 . The cover substrate 200 is constructed similarly to that shown there and also has a recess 250 which, together with the cavity 150 already described, forms the superordinate cavity 350 for the movement of the bending element 135. The essential difference to the conventional switching element of the Figure 1 is that the superior cavity 350 is not exposed to the substrate underside 100b, but is closed. In this way, a hermetic encapsulation of the cavity 350 is achieved by the permanent planar connection between the carrier substrate 100 and the cover substrate 200, without the need for any additional sealing elements (as in Figure 3 ) would require an additional housing cover. The key advantage of this inventive design is that it allows for a simple, highly compact component that is nevertheless robust against external environmental influences, since the area of the flexural element is hermetically sealed to the outside.

[0049] Another difference in the switching element of the Figure 6 to the conventional component of the Figure 3 is given by the fact that the electrical contacting is not made by wire bonds, but by vias 400 in the cover substrate and corresponding solderable contact points 410. In other words, it can be an SMD component. However, this additional difference is optional, and in principle, contacting via bond wires could also be used, similar to the Figure 3 According to a further possible embodiment, the feedthroughs 400 can alternatively also be led through the carrier substrate 100 to the underside 100b, or corresponding vias and contact points could be arranged on both the top side and the bottom side. By way of example only, Figure 6A via 400 for connecting the bending element (for its electrical grounding) and another via 400 for contacting one of the mating contacts 240 are shown. Of course, other elements, such as the control electrode 210 and the second mating contact not visible here, can also be contacted in a corresponding manner.

[0050] In Figure 7 Another prefabricated carrier substrate 100 for producing a switching element according to the invention is shown. In contrast to the carrier substrate of Figure 4This carrier substrate does not have just one cavity, but an array of several adjacent buried cavities 150. In other words, a device with an array of several switching elements can be manufactured from it. A further difference is that the respective cavity is lined with an oxide layer in the bottom region. In other words, the oxide layer 120 is not interrupted here, but only locally laid in the bottom of the individual cavities 150. This variant of a C-SOI substrate is also commercially available from various manufacturers and can otherwise be manufactured in a similar way to the substrate of the Figure 4 be used to produce a switching element according to the invention.

[0051] In Figure 8 A switching element 1 according to a further example of the present invention is shown. This switching element 1 is constructed similarly to the example of Figure 6. However, one difference is that the cover substrate does not have a cave-like recess in its base material (e.g., in the glass), but that the corresponding cavity is formed by a spacer layer 260 surrounding the area of the bending element. However, the open area within this surrounding spacer layer 260 effectively forms a recess 250 in the cover substrate, which, together with the opposite recess in the carrier substrate, forms the superior cavity 350 for the bending element. Otherwise, the switching element of the Figure 8 analogous to the example of Figure 6 and can advantageously also be manufactured in an analogous manner using a prefabricated C-SOI substrate. List of reference symbols

[0052] 1 MEMS switching element 100 multilayer carrier substrate (SOI substrate) 100a substrate top (front) 100b substrate bottom (back) 110 first layer (carrier layer) 120 second layer (buried oxide) 120a opening of the second layer 120b opening of the second layer 130 third layer (semiconductor layer) 130a opening of the third layer 130b opening of the third layer 135 bending element 135a foot area 140 switching contact 150 recess (cavity) or opening 190 contact point 195 bond wire 200 cover substrate 210 control electrode 240 counter contact 250 recess 260 surrounding spacer layer 270 connection (wafer bond) 300Housing cover 310Connection 350Superordinate cavity 400Feedthrough (Via) 410Contact point dThickness direction rDeflection direction

Claims

1. Microelectromechanical switching element (1), comprising - a multi-layer carrier substrate (100) comprising a first layer (110) serving as carrier layer, an electrically insulating second layer (120) and a third layer (130) configured as semiconductor layer, wherein the multi-layer carrier substrate (100) is a silicon-on-insulator layer system, - a deflectable bending element (135) which is formed by a freed subregion of the semiconductor layer (130), - and an areal cover substrate (200) which is connected to the carrier substrate (100), characterized in that - the carrier substrate (100) and in particular the carrier layer (110) thereof comprises a cutout (150) in the region of the bending element (135), - wherein the cover substrate (200) also comprises a cutout (250) and / or an encircling spacer layer (260) in the region of the bending element (135), such that a superordinate hollow space (350) is formed overall, in which the bending element (135) is arranged so as to be deflectable, and - wherein the superordinate hollow space (350) is delimited by the carrier layer (110) and by the cover substrate (200) in such a way that it is hermetically encapsulated toward the external environment.

2. Switching element (1) according to Claim 1, wherein the deflection direction (r) of the bending element (135) is oriented substantially perpendicularly with respect to the layer plane of the multi-layer carrier substrate (100).

3. Switching element (1) according to Claim 1 or 2, wherein the cutout (150) in the carrier layer (110) is formed by a prefabricated cavity in the silicon-on-insulator layer system (100).

4. Switching element (1) according to one of the preceding claims, wherein the hermetic encapsulation of the superordinate hollow space (350) is effected by a permanent, fluid-tight, areal connection (270) between the multi-layer carrier substrate (100) and the cover substrate (200).

5. Switching element (1) according to one of the preceding claims, wherein the cover substrate (200) is configured functionally as electrically insulating cover substrate and is in particular formed substantially of glass or silicon.

6. Switching element (1) according to one of the preceding claims, wherein a switching contact (140) is arranged on the bending element (135) and wherein the cover substrate (200) bears at least one mating contact (240) which is able to be contacted with the switching contact (140) of the bending element (135) in dependence on a deflection of the bending element (135).

7. Switching element (1) according to one of the preceding claims, wherein the cover substrate (200) comprises a control electrode (210) which can be used to influence the deflection of the bending element (135).

8. Apparatus comprising a microelectromechanical switching element (1) or an array of multiple microelectromechanical switching elements (1) according to one of the preceding claims.

9. Apparatus according to Claim 8, which is configured as a switching apparatus, as a converter or inverter, as a logic circuit and / or as a logic gate.

10. Apparatus according to either of Claims 8 and 9, which is configured as a surface-mountable component.

11. Apparatus according to one of Claims 8 to 10, wherein the cover substrate (200) and / or the carrier substrate (100) comprises one or more leadthroughs (400) for electrical contacting of the at least one switching element (1).

12. Method for producing a switching element (1) according to one of Claims 1 to 7, wherein a) a prefabricated multi-layer carrier substrate (100) is used, which multi-layer carrier substrate (100) is a silicon-on-insulator layer system, characterized in that the prefabricated multi-layer carrier substrate (100) with a prefabricated cavity (150) in the first carrier layer (110) is used, b) the bending element (135) is freed from this prefabricated carrier substrate (100) by subtractive manufacturing, and, c) in a wafer bonding step, the cover substrate (200) is permanently connected to the carrier substrate (100), as a result of which the superordinate hollow space (350) is hermetically encapsulated.

13. Method according to Claim 12, wherein the subtractive manufacturing in step b) is effected by processing the multi-layer carrier substrate (100) exclusively on one side.