Patent Application
20240253977
This application claims the benefit of European patent application Ser. No. 23/214,127, filed on Dec. 4, 2023 and European patent application Ser. No. 23/153,777, filed Jan. 27, 2023, which applications are hereby incorporated herein by reference.
Embodiments of the present disclosure relate to a method for producing a MEMS device (microelectromechanical system) comprising laser structured nanostructures and a method for manufacturing the same.
MEMS-based systems are miniaturized systems that comprise a very small form factor. For example, pressure transducers may be provided as MEMS devices, wherein a small membrane may transduce mechanical oscillations of the membrane into electric signals, or vice versa. An example of a MEMS pressure transducer may be a tire pressure sensor that monitors air pressure in tires. A further example may be a MEMS microphone that transduces sound waves (as an example of air pressure), such as music or voice, into electric signals, which can then be converted into digital data. In the reverse direction, a MEMS speaker may convert digital data into sound by oscillating the membrane.
Due to their miniaturized size, MEMS pressure transducers require environmental protection because they can be influenced by several environmental ingress from the surrounding environment, for instance dust particles, water and moisture, which can then lead to lower robustness level and shorter operation time.
For example, currently available MEMS-based microphones often have failures when they are exposed to liquids, for example water droplets, salt-containing liquids, sweat or oil. In case water droplets containing conductive particles, such as salts, reach the MEMS microphone membrane via the bottom sound port, these particles can remain on the bottom membrane surface when the water has evaporated, which may often result in device contamination, corrosion and/or electrical shortcut (leakage). If this phenomenon occurs over a long time, the device may not work as it should, leading to lower robustness and shorter lifetime.
The bottom membranes of MEMS microphones typically possess planar surfaces comprising hydrophilic characteristic, which is typical for planar silicon surfaces. Thus, droplets of water or other liquids tend to adsorb onto the membrane surface. After the liquids have evaporated, solid materials (e.g., salts, particles, and other contaminants) that were contained in said evaporated liquids may remain on the membrane.
The commonly implemented solution to protect the membranes of MEMS microphones is by adding external discrete environmental barrier (EB) components, e.g., an EB membrane having hydrophobic/oleophobic characteristics, and which is placed either inside or outside the package lid covering the sound port. This solution has, however, some drawbacks, such as high production cost, large package size, low acoustic performance, and limited usage for applications.
Therefore, it would be desirable to provide a MEMS device with a membrane comprising a liquid repellent membrane surface and an inherent oleophobic and/or hydrophobic characteristic without the above mentioned drawbacks.
Embodiments of the present disclosure include a MEMS device and a corresponding method for fabricating the MEMS device.
One aspect concerns a method for producing a MEMS device, the method comprising a step of providing a substrate comprising a first substrate surface and an opposite second substrate surface, wherein the substrate comprises a sacrificial layer arranged at the first substrate surface. The method further comprises a step of depositing a membrane material layer onto the sacrificial layer, and a step of structuring a cavity into the substrate, the cavity extending between the second substrate surface and the sacrificial layer. The method further comprises a step of releasing the membrane material layer by removing the sacrificial layer from the cavity such that the cavity is adjacent to the membrane material layer, wherein the released membrane material layer forms a free-standing membrane structure covering the cavity. The method further comprises a step of creating nanostructures in at least one of the first and second surfaces of the membrane material layer, wherein the nanostructures protrude from the respective surface of the membrane material layer, wherein the nanostructures are created by applying a laser structuring process.
A further aspect concerns a MEMS-microelectromechanical system-device comprising a substrate having a cavity formed therein, the cavity extending vertically through the substrate, and a membrane material layer being attached to the substrate, said membrane material layer forming a horizontally extending free-standing membrane structure covering the cavity. The membrane material layer comprises a plurality of nanostructures for providing a liquid repellent membrane surface, wherein the nanostructures protrude from at least one of two opposing surfaces of the membrane material layer. The nanostructures are created by laser structuring such that they are monolithically integrated in the membrane material layer.
In the following, embodiments of the present disclosure are described in more detail with reference to the figures, in which
Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals.
Method steps which are depicted by means of a block diagram and which are described with reference to said block diagram may also be executed in an order different from the depicted and/or described order. Furthermore, method steps concerning a particular feature of a device may be replaceable with said feature of said device, and the other way around.
In the following description, a MEMS-based microphone will be mentioned as a non-limiting example for a MEMS device. However, other MEMS devices with a membrane structure comprising a plurality of upright nanostructures also fall under the scope of protection according to the herein described innovative concept. Some embodiments relate to a method for producing a MEMS device comprising a membrane with a liquid repellent membrane surface, where the membrane has at least one of oleophobic and hydrophobic characteristics.
Furthermore, terms like horizontally and vertically will be used in the following description. Of course, these terms are to be understood in relation to each other, but not necessarily in relation to the earth's horizon. Accordingly, the term horizontally may be synonymously used with “extending in a first direction/plane”, while the term vertically may be synonymously used with “extending in a second direction/plane”, the second direction/plane being perpendicular to the first direction/plane. For example, a substrate may comprise a primary extension direction, which may also be referred to as the substrate plane. For example, the term “horizontally” is to be understood as “parallel to the substrate plane” or “in plane”, while the term “vertically” is to be understood as “perpendicular to the substrate plane”.
Furthermore, upright nanostructures may be described, wherein said upright nanostructures may be arranged on a membrane structure. The term “upright” means that the nanostructures may extend away from the membrane structure, for example in an upward direction. For example, if the membrane structure may extend horizontally, the nanostructures may extend substantially vertically from the membrane structure. Whenever the term “vertically extending” is used in the present disclosure, it is within the scope of the present disclosure that the nanostructures may not be perfectly vertical, but that the nanostructures may be slightly tilted. For example, the terms “upright” and “vertically extending” may include that the nanostructures may be skew and may extend away from the membrane structure in an angle of 90°±25°. Furthermore, some embodiments refer to a plurality of nanostructures that may be arranged, for instance, in a nanostructure array. Accordingly, the present disclosure always refers to a majority (i.e. at least 50%) of the nanostructures. For example, if the present disclosure mentions that the nanostructures are upright, it means that at least 50% of the nanostructures are upright. In real life, it may be possible that several hundreds or thousands of nanostructures may be present, wherein most of them are upright, e.g., substantially vertical, while a few percent of them may not be upright (less than 75° or more than 115°). Furthermore, some embodiments may describe horizontally extending membrane structures as non-limiting examples for membrane structures in general. In such embodiments, vertically extending nanostructures may be described as non-limiting examples of upright nanostructures. Accordingly, the terms “vertically extending” and “upright” may be used synonymously in the present disclosure.
The MEMS device 100 further comprises a horizontally extending membrane structure 130. For example, the membrane structure 130 may comprise or be made from polysilicon. The membrane structure 130 covers the cavity 116. As will be described in more detail below, the membrane structure 130 may be created from a membrane material layer 114 being deposited on a sacrificial layer 140 (e.g., TEOS: tetraethoxysilane or tetraethyl orthosilicate). The sacrificial layer 140 may be sandwiched between the substrate 110 and the membrane material layer 114 and may connect the membrane structure 130 with the substrate 110. Alternatively, the membrane structure 130 may be adhered to the substrate 110, e.g., by means of an adhesive.
According to the present innovative concept, a plurality of upright (e.g., vertically extending) nanostructures 150 is created in the membrane material layer 114 by applying a laser structuring process, such that the nanostructures 150 protrude from at least one of two opposing membrane surface 114A, 114B.
In particular, the horizontally extending membrane material layer 114 comprises a first membrane surface 114A facing the cavity 116, and an opposite second membrane surface 114B facing away from the cavity 116. As exemplarily depicted in
According to the herein disclosed innovative concept, the protruding nanostructures 150 are created by applying a laser structuring process, as will be discussed in more detail later with reference to
The protruding nanostructures 150 may extend substantially perpendicular to the membrane structure 130. The protruding nanostructures 150 provide for a self-cleaning surface characteristic exploiting the so-called lotus effect. Accordingly, the protruding nanostructures 150 provide for a liquid repellent membrane surface of the membrane structure 130. In particular, the protruding nanostructures 150 create a rough nanostructured membrane surface 114A, 114B that may provide for at least one of a hydrophobic or an oleophobic surface characteristic of the membrane structure 130.
In contrast, a membrane without these protruding nanostructures 150 may comprise a hydrophilic surface characteristic, i.e., liquids (water, oil, etc.) adhere to the membrane. If the liquid evaporates, solid matters (like salts, particles, and other contaminants) that are solved in said liquids, may remain on the membrane surface which may often result in device contamination, corrosion and/or electrical shortcut (leakage). The membrane structure 130 of the herein described innovative concept, instead, comprises a hydrophobic and/or oleophobic surface characteristic, i.e., liquids (water, oil, etc.) are repelled from the membrane structure 130. Said hydrophobic and/or oleophobic surface characteristics are provided by the protruding nanostructures 150.
The MEMS device 100 as depicted in
The membrane structure 130 may be configured as a microphone membrane that can oscillate in response to acoustic waves. The acoustic waves may enter the microphone package through a so-called sound port. The depicted single backplate microphone 100 may be mounted over the sound port, such that the acoustic waves may enter the vertically extending cavity 116 and arrive at the bottom surface of the membrane structure 130.
As mentioned above, the upright (e.g., vertically extending) nanostructures 150, which protrude from the membrane structure 130, may provide for a hydrophobic/oleophobic surface characteristic of the membrane structure 130. Thus, liquids contained in the air that is transferred by the acoustic waves may be repelled from the hydrophobic and/or oleophobic membrane surface. Accordingly, it is advantageous if the protruding nanostructures 150 are provided at a membrane surface that faces a source of environmental liquids, for example the sound port. Thus, in this non-limiting example, the protruding nanostructures 150 may face the cavity 116 and may vertically extend into the cavity 116. However, as will be explained below, the protruding nanostructures 150 may additionally or alternatively face away from the cavity 116 and may vertically extend away from the cavity 116. In other words, the protruding nanostructures 150 may be arranged on either one of the two membrane surfaces 114A, 114B or on both membrane surfaces 114A, 114B.
At least one of the first and second membrane portions 131, 132 may comprise the above described upright nanostructures 150 that protrude from the respective membrane portion 131, 132. Also in this case, it is advantageous if the protruding nanostructures 150 are provided at a membrane surface that faces a source of environmental liquids, for example the sound port. Thus, in this non-limiting example, the protruding nanostructures 150 may be arranged on the second membrane portion 132 facing the cavity 116.
The protruding nanostructures 150 may be configured as upright (e.g., vertically extending) nanospikes, nanotubes, nanofins, nanopillars, nanowhiskers, nanowalls, nanocircular walls, black silicon, and many more, while various other geometric designs and shapes are possible. In any case, the protruding nanostructures 150 may be configured as single, free-standing 3D elements, that protrude from a plane surface, e.g., from at least one of the two opposing membrane surfaces 114A, 114B of the membrane structure 130. The protruding nanostructures 150 may not be connected to each other, i.e., they are configured as individual unconnected elements. This is a difference compared to meshes and grids, which may sometimes be used as environmental barrier structures. Meshes and grids comprise a plurality of single mesh segments/grid segments that are all connected to each other to form the mesh/grid structure.
Summarizing in a more general terminology, the protruding upright nanostructures 150 may be configured as single unconnected three-dimensional geometric structures extending away from the membrane structure 130. For example, the protruding upright nanostructures 150 may extend into a direction that is substantially perpendicular to the lateral extension of the membrane structure 130.
For example, the single unconnected nanostructures 150 may be configured as single upright nanopillars protruding and extending away from the membrane structure 130. Nanopillars are pillar-shaped nanostructures, approximately a few nanometers (e.g. 10 nm to 1.000 nm) in diameter, that can be grouped together in lattice like arrays. In such an array configuration, the protruding nanostructures 150 may be densely arranged next to each other. According to an embodiment, the plurality of protruding nanostructures 150 may comprise an area density of 106-1010 nanostructures per cm.
In some embodiments, the protruding nanostructures 150 may comprise a geometrical shape similar to a frustum cone. However, various other geometrical shapes are possible, as exemplarily depicted in
Besides different geometrical shapes, further advanced surface chemistry modification can be realized by introducing organic self-assembled monolayers, so-called SAMs. For example,
Different self-assembled monolayers, and in particular silane-based SAMs, may be used for coating the protruding nanostructures 150. For example, the organic self-assembled monolayers may comprise, or may consist of, at least one of:
The inorganic nano-elements 190 may be grown on the surface of the nanostructures 150. For example, a suitable material, for example zinc oxide (ZnO), may be used for creating the nano-elements 190. For example, for creating ZnO nanowires, a zinc oxide film may be deposited onto the surface of the nanostructures 150 using e.g., a sputtering technique for forming ZnO nanoseeds. The growth of the ZnO nanowires can then be realized by employing e.g., a chemical bath deposition (CBD) process. Other alternative methods (e.g., hydrothermal method, vapor-liquid-solid process, spray pyrolysis, chemical vapor deposition, molecular beam epitaxy, electrodeposition, atomic layer deposition, and pulsed laser deposition) can also be opted to grow or deposit ZnO layer and create ZnO nanostructures. This combination with ZnO nanowires is beneficial for the case of coarse nanostructures 150 (e.g. nanostructures 150 with large pitch or distance among them). ZnO nano-elements 190 may be advantageously grown on silicon-based nanostructures 150.
In result, the grown nano-elements 190 may protrude from the nanostructures 150, and they may extend substantially perpendicular from the surface of the nanostructures 150. Accordingly, the nanostructures 150 may comprise a tree-like shape. Each of the tree-like nanostructures 150 may comprise a plurality of inorganic nano-elements 190, e.g., nanowires.
As mentioned above, the nanostructures 150 may provide for a hydrophobic and/or oleophobic and/or superhydrophobic and/or omniphobic surface characteristic of the membrane structure 130. To explain these surface characteristics, imagine an untreated planar silicon surface on which a water droplet is applied. Planar silicon surfaces in general comprise a hydrophilic surface characteristic, i.e., liquids are adhered to the planar surface due to its low surface roughness and, thus, its large surface energy. A hydrophilic surface comprises a small water contact angle. For example, the water contact angle may be around 5° to 20°.
In turn, a nanostructured silicon surface, for example the herein described rough nanostructured membrane surfaces 114A, 114B of the membrane structure 130 with the protruding nanostructures 150, may comprise a larger water contact angle of at least 120° or at least 150°. Therefore, a water droplet being applied to the nanostructured membrane surface 114A, 114B almost stays in a perfect sphere shape. This is due to the higher surface roughness and, thus, lower surface energy provided by the nanostructures 150. Accordingly, the membrane structure 130 comprising the protruding nanostructures 150 may comprise a hydrophobic or even superhydrophobic surface characteristic.
Superhydrophobic surfaces generally show water contact angles of greater than 150° (nearly perfect sphere) along with low contact angle hysteresis. Contact angle hysteresis is defined as the difference between measured values of the advancing and receding contact angles (the highest and lowest contact angles on such a structures).
Additionally or alternatively, the nanostructures 150 protruding from the membrane structure 130 may provide an oleophobic surface characteristic such that oils are repelled from the membrane surface, or even an omniphobic surface characteristic such that almost each and every liquid is repelled from the membrane surface.
Liquids that approach the nanostructured membrane 130 having superhydrophobic/omniphobic surface characteristics will bounce or roll off. Hence, the herein discussed nanostructures 150 are useful for water/liquid repellent and self-cleaning surfaces. The nanostructured membrane surface can be self-cleaning because any water/liquid droplets that contact it will roll off picking up any particles along with the operation of the moving membrane 130.
By adjusting the geometry (e.g., diameter, height, aspect ratio, pitch) of the nanostructures 150, the hydrophobicity/oleophobicity/omniphobicity level of the nanostructures 150 can be varied.
According to some embodiments, the protruding nanostructures 150 may comprise a diameter of 1 μm or less. If the nanostructures 150 may comprise a varying diameter, e.g., if they were configured as frustum cones, the diameter is measured at the thickest portion. Additionally or alternatively, the protruding nanostructures 150 may comprise a pitch, i.e., a distance between the centers of two adjacent nanostructures 150, said pitch comprising a ratio of at least pitch:diameter=2:1. Additionally or alternatively, the protruding nanostructures 150 may comprise an aspect ratio (width-to-height) between 1:3 and 1:40. The authors of this disclosure have found that nanostructures 150 with high aspect ratio (e.g., x>5) produce a larger contact angle (more hydrophobicity/omniphobicity) than those with low aspect ratio (e.g., 1<x<5).
As mentioned above with reference to
The package 200 may further comprise a lid 240 being arranged on the component board 210. The lid 240 may cover the MEMS device 100 and the circuitry 220. The free space or cavity 250 underneath the hollow lid 240 may provide for an acoustic back volume.
The component board 210 may comprise a vertically extending through hole 211. In case the MEMS-based package 200 is a microphone package (as exemplarily depicted here), the through hole 211 may be referred to as a sound port through which acoustic waves may enter the cavity 250.
In this non-limiting example, the MEMS device 100 may be configured as a MEMS-based single backplate (SBP) microphone, as previously discussed above with reference to
As can be seen in
As mentioned above, acoustic waves may enter the package 200 through the sound port 211. Since the sound port 211 is in fluid connection with the cavity 116, the acoustic waves may be further conveyed into the cavity 116 until reaching the membrane structure 130. The membrane structure 130 will be deflected in response to the impinging acoustic waves. The amplitude of deflection will be measured by the electrode structure 160.
The air through which the acoustic waves may travel may comprise moisture, e.g., liquids containing salt particles and the like. Since the herein described innovative membrane structure 130 comprises the protruding nanostructures 150, the membrane structure 130 shows a (super-)hydrophobic/omniphobic surface characteristic. Thus, intruding liquids and or any solid matter (like salts, particles, and other contaminants) contained in said liquids may be repelled from the surface of the membrane structure 130. This provides for a superior protection of the microphone membrane 130.
Furthermore, a MEMS-based microphone 300 is depicted. This MEMS-based microphone 300 may be a MEMS device 100 as discussed above, or a conventional MEMS-based microphone. In this non-limiting example, a conventional SDM microphone is depicted. However, it may also be possible that a SBP microphone may be used instead. The MEMS-based microphone 300 may comprise a microphone sound transducer membrane 310.
As can be seen in
The MEMS device 100 being configured as an environmental barrier structure comprises a horizontally extending environmental barrier membrane or mesh structure. In this non-limiting example, the innovative membrane structure 130 may be configured as the aforementioned environmental barrier membrane or mesh structure.
The membrane structure 130 may comprise the protruding nanostructures 150 as discussed herein. This provides for an improved hydrophobicity/omniphobicity level of the membrane structure 130. Thus, intruding liquids and or any solid matter (like salts, particles, and other contaminants) contained in said liquids may be repelled from the surface of the membrane structure 130. This provides for a superior protection of the downstream arranged microphone membrane 310.
In the previous sections, different embodiments of the MEMS device 100 were described. In the following, examples and embodiments of methods for manufacturing a MEMS device 100 will be discussed.
The applied laser structuring process may use a femtosecond laser or a picosecond laser. This may have the advantage that membrane material may change from solid to gas, without an intermediate liquid state, and heat input may be limited to specific spots. Thus, the nanostructures 150 may be formed from the membrane material layer 114, or in other words, the nanostructures 150 may be monolithically integrated in the membrane material layer 114.
Accordingly, the step of creating the nanostructures 150 may comprise a step of removing portions 118 of the membrane material layer 114 by means of one or more laser beams 180 being used in the applied laser structuring process, wherein the nanostructures 150 remain between the removed portions 118 of the membrane material layer 114, such that the nanostructures 150 are monolithically integrated in the membrane material layer 114.
Additionally or alternatively, the applied laser structuring process may comprise Direct Laser Interference Patterning (DLIP), wherein interference patterns may be directly imprinted into the membrane surface 114A, 114B of the membrane material layer 114. Thereby, a plurality of nanostructures 150 may be created with a single laser beam.
The step of creating the nanostructures 150 may comprise distributing the nanostructures 150 in a random or periodic pattern along the respective membrane surface 114A, 114B of the membrane material layer 114.
The nanostructures 150 that are created according to the herein described innovative principle are not only monolithically integrated in the membrane material layer 114, but they also protrude from the respective membrane surface 114A, 114B of the membrane material layer 114. Thus, the protruding nanostructures 150 provide for an increased surface roughness (compared to unstructured plane membrane surfaces without nanostructures) of the respective membrane surface 114A, 114B thereby increasing the hydrophobicity and/or oleophobicity level of the membrane material layer 114 and, thus, of the membrane structure 130 created therefrom.
In the non-limiting example shown in
As a further alternative, which is not explicitly depicted here, the protruding nanostructures 150 may be created in the first and second membrane surfaces 114A, 114B.
As shown in
The nanopillars 155 created by lithography may comprise an average diameter that is at least ten times larger than an average diameter of the laser structured nanostructures 150. For example, the nanopillars 155 may comprise a diameter of 100 nm, and the laser structured nanostructures 150 may comprise a diameter of 10 nm.
The nanopillars 155 may also be referred to as nanowhiskers. In some embodiments, the above discussed nanopillars 155 may comprise a geometrical shape that is different to a pillar. However, for the sake of easy differentiation from the laser structured nanostructures 150, they may generally be referred to as nanopillars 155 within this disclosure. Furthermore, while the nanopillars 155 have been described as being created by means of lithography, other embodiments may include that the nanopillars 155 are created differently, for example also by means of laser structuring, or the nanopillars 155 may be deposited onto at least one of the membrane surfaces 114A, 114B.
As discussed above, SAMs 180 may provide for an advanced surface chemistry modification of the coated surfaces. For example, nanostructures 150 being coated with SAMs exhibit an enhanced level of hydrophobicity and/or oleophobicity compared to uncoated nanostructures 150. Using this combined chemical/physical method, the SAM-coated nanostructures 150 can increase the resulting water or liquid contact angle on their surface and can repel not only water but also other liquids (e.g., oil) resulting in (super-)hydrophobic or omniphobic surfaces. Different self-assembled monolayers, and in particular silane-based SAMs, may be used for coating the protruding nanostructures 150.
As discussed herein, the laser structured nanostructures 150 improve hydrophobicity and/or oleophobicity of a treated surface, which expresses in a higher contact angle of 120° or more, or even 150° or more. Furthermore, SAMs do also improve hydrophobicity and/or oleophobicity of the treated surface.
However, the authors of the present disclosure surprisingly found out that the laser structured nanostructures 150 can improve the hydrophobicity/oleophobicity effect of SAMs. Accordingly, the laser structured nanostructures 150 in combination with SAMs do provide for an increased hydrophobicity/oleophobicity effect compared to SAMs alone or compared to nanostructures 150 alone. In other words, the combination of laser structured nanostructures 150 with SAMs lead to a higher contact angle compared to SAMs alone or compared to nanostructures 150 alone.
The herein discussed innovative laser structured nanostructures 150 may comprise a characteristic geometrical shape that allows to distinguish them from nanostructures 150 that have been created by methods different from laser structuring. For example, nanostructures 150 may also be created by lithography, deposition or growing, as will be discussed in more detail below with reference to
For example, laser structured nanostructures 150 may comprise a non-flat top section, e.g., a sharp top. Furthermore, due to the laser beams 180 being applied to the membrane material layer 114 in slightly varying angles, the laser structured nanostructures 150 of two different MEMS devices 100 may comprise a similar pattern (in terms of roughness etc.) but with different orientations towards each other, i.e., offsets may not be exactly identical. Nanostructures being created by means of lithography, for instance, may comprise an identical pattern instead. Yet further, nanostructures being created by means of lithography may comprise a shape that is limited to certain angles around 90°. In turn, the shape of laser structured nanostructures 150 may differ from 90° and may vary.
As shown in
Accordingly, the nanoimprints 113 (c.f.
With the method as described with reference to
In some further examples, the first material 114 forming the membrane structure 130 and the integrally formed protruding nanostructures 150 may comprise a dielectric characteristic. For example, the first material 114 may comprise or consist of silicon nitride or one or more oxides. Dielectric nanostructures 150 may be beneficial if electrical leakages shall be avoided.
Accordingly, the horizontally extending membrane structure 130 is made from the subsequently deposited second material 124, and the protruding nanostructures 150 are made from the first material 114. The membrane structure 130 and the protruding nanostructures 150 may be firmly bonded. Furthermore, the protruding nanostructures 150 may face and extend into the cavity 116.
In some examples, the second material 124 forming the membrane structure 130 may comprise a conducting or semiconducting characteristic. For example, the second material 124 may comprise or consist of (poly-)silicon. The first material 114 forming the protruding nanostructures 150 may comprise a dielectric characteristic. For example, the first material 114 may comprise or consist of silicon nitride (Si3N4) or one or more oxides. Dielectric nanostructures 150 may be beneficial if electrical leakages shall be avoided.
Accordingly, with the method as described with reference to
The above embodiments concern methods for creating a horizontally extending membrane structure 130 with protruding upright (e.g., vertically extending) nanostructures 150, wherein said protruding nanostructures 150 faced the cavity 116. In the following, some further embodiments will be described which provide for a method for creating a horizontally extending membrane structure 130 with protruding upright (e.g., vertically extending) nanostructures 150, wherein said protruding nanostructures 150 face away from the cavity 116. It is to be noted that these embodiments may be combined with each other, e.g., for creating a first set of protruding nanostructures 150 facing the cavity 116 in combination with a second set of protruding nanostructures 150 facing away from the cavity 116.
In
The cavity 116 is not structured through the entire substrate 110. Instead, the cavity 116 is structured such that it stops before reaching the nanostructures 150. Accordingly, a substrate portion 110C between the nanostructures 150 and the cavity 116 remains. This remaining substrate portion 110C may later form the horizontally extending membrane structure (c.f.
As mentioned above, the substrate 110 may comprise an optional etch stop layer 117. If the etch stop layer 117 is available, as exemplarily depicted in
As mentioned above, the substrate 110 may be divided into a first substrate portion 110A and a second substrate portion 110B. For example, at least the second substrate portion 110B may comprise or consist of a CMOS-compatible material, e.g., silicon, silicon carbide (SiC), gallium nitride (GaN), carbon, metals, polymers.
While
The method steps as shown in
Then, the method step as shown in
Summarizing,
Furthermore, in the method steps as shown in
In each embodiment discussed herein, the protruding upright nanostructures 150 may be configured as three-dimensional structures, as exemplarily discussed above with reference to
Summarizing, one of the core solutions of the herein described innovative concept is the provision of a nanostructured membrane and its applications on MEMS devices 100, like MEMS microphones and environmental barriers. The integrated nanostructures 150 can result in (super)hydrophobic or omniphobic surface characteristics to repel incoming liquid droplets.
Parts of this disclosure concern design/concept and fabrication processes of upright (e.g., vertical) nanostructure arrays on membranes 130 of MEMS microphones and environmental barriers. MEMS microphones and environmental barriers with integrated upright nanostructure arrays yield (super)omniphobic membrane surfaces.
For example, a MEMS microphone with a superomniphobic nanostructure array-integrated membrane comprises a high environmental robustness. The present innovative concept allows to provide MEMS microphones with integrated nanostructures 150 either directly on the MEMS membrane 130 or on a discrete environmental barrier.
The common approach to increase the environmental robustness of MEMS microphones is by integrating external environmental barriers made of polymer having hydrophobic and oleophobic characteristics into the package. The environmental barrier covering the sound port is located either inside (directly underneath the MEMS microphone) or outside the metal package lid (embedded on the structured printed circuit board (PCB)). Moreover, only SAMs deposited on planar silicon surface might also result in hydrophobic characteristics. However, such organic materials are known to degrade within device operation time. Thus, instead of only using a chemical approach, the present concept combines physical and chemical methods into one (i.e., SAM/Si nanopillars) to reach higher environmental robustness.
The herein described innovative concept has, among others, the following advantages:
Nanostructure arrays can be directly integrated into the MEMS device (e.g. underneath the bottom membrane of an SDM) and allow to directly protect it from the environment. This possibly allows to fabricate a MEMS microphone system that does not need additional environmental barrier components to achieve high water/oil-protection levels.
Compared to planar MEMS membrane, the nanostructure array-integrated MEMS membrane will provide (super)omniphobic surface that is able to repel the water/other liquids. Thus, it can also potentially provide self-cleaning feature because the approaching liquid droplets will bounce or roll off and simultaneously take the particles away from the membrane surface.
Fabrication Process of Nanostructures Adapted from Existing Technology
Despite the required adjusted structure sizes and designs, currently existing technology can be used as a basis for the process development. Thus, the realization and optimization of the proposed upright nanostructures will not start from ‘zero’. However, in terms of producing very small nanostructures (smaller than current MEMS bumps) and large-scale production (productive fabrication in front line), adaptations of lithography tools may be necessary.
Flexible Design Related to Combination with Other Organic or Inorganic Materials
Silicon nanopillars can also be combined with either organic SAMs or other inorganic 1D nanostructures (e.g., ZnO nanowires) to increase the hydrophobicity/omniphobicity level of the membrane surfaces.
The following non limiting examples form part of the present disclosure:
According to a first example, a MEMS-microelectromechanical system-device (100) may be provided, the MEMS device (100) comprising a substrate (110) comprising a vertically extending through hole (120) (wherein the vertically extending through hole corresponds to the above discussed cavity 116) and a horizontally extending membrane structure (130) covering the through hole (120), wherein the membrane structure (130) may comprise a plurality of protruding and/or upright nanostructures (150) for providing a liquid repellent membrane surface.
According to a second example that can be combined with the first example, the upright/protruding nanostructures (150) may be configured as three-dimensional geometric structures extending from the membrane structure (130), and extending into a direction away from the membrane structure (130).
According to a third example that can be combined with one of the first and second examples, the upright/protruding nanostructures (150) may comprise at least one of:
According to a fourth example that can be combined with one of the preceding examples, the plurality of upright/protruding nanostructures (150) provided on the membrane structure (130) may provide a membrane surface comprising at least one of a hydrophobic and an oleophobic surface characteristic.
According to a fifth example that can be combined with one of the preceding examples, the upright/protruding nanostructures (150) may comprise at least one of the following geometrical shapes:
According to a sixth example that can be combined with one of the preceding examples, the upright/protruding nanostructures (150) may be coated with an organic Self Assembled Monolayer—SAM—.
According to a seventh example that can be combined with one of the preceding examples, the upright/protruding nanostructures (150) may comprise inorganic nanodots (190) or nanowires (190) extending from an outer surface of the upright/protruding nanostructures (150).
According to an eighth example that can be combined with one of the preceding examples, the horizontally extending membrane structure (130) may comprise a first membrane surface (130A) facing the through hole (120) and an opposite second membrane surface (130B) facing away from the through hole (120), and the upright/protruding nanostructures (150) may be arranged on at least one of the first and second membrane surfaces (130A, 130B).
According to a ninth example that can be combined with one of the preceding examples, the MEMS device (100) may be configured as a MEMS microphone, in which the horizontally extending membrane structure (130) may be configured as a microphone sound transducer membrane, wherein the upright/protruding nanostructures (150) may be arranged at the microphone sound transducer membrane.
According to a tenth example that can be combined with one of the first to eighth examples, the MEMS device (100) may further comprise a MEMS microphone (300) comprising a microphone sound transducer membrane (310), wherein the MEMS device (100) may be configured as an environmental barrier structure comprising an environmental barrier membrane or mesh structure for protecting the microphone sound transducer membrane (310) from moisture and/or environmental particles, and wherein the horizontally extending membrane structure (130), at which the upright/protruding nanostructures (150) are arranged, may be configured as the environmental barrier membrane or mesh structure.
According to an eleventh example that can be combined with one of the ninth or tenth examples, the MEMS microphone may comprise a sound port (211) through which acoustic waves reach the membrane structure (130), wherein the membrane structure (130) may be positioned such that the upright/protruding nanostructures (150) face the sound port (211).
According to a twelfth example that can be combined with one of the preceding examples, the plurality of upright/protruding nanostructures (150) may comprise an area density of 106-1010 nanostructures per cm.
According to a thirteenth example, a method for fabricating a MEMS device (100) is provided, the method comprising a step of providing a substrate (110) comprising a first substrate surface (111) and an opposite second substrate surface (112), wherein the substrate (110) comprises a sacrificial layer (140) arranged at the first substrate surface (111), and a step of structuring nanoimprints (113) into the sacrificial layer (140), and a step of filling the nanoimprints (113) by depositing a first material (114) onto the structured sacrificial layer (140), and a step of structuring a cavity (116) into the substrate (110), the cavity (116) being positioned opposite to the filled nanoimprints (113) and extending between the second substrate surface (112) and the sacrificial layer (140), and a step of releasing the filled nanoimprints (113) by removing the sacrificial layer (140) through the cavity (116), thereby creating a horizontally extending membrane structure (130) comprising upright/protruding nanostructures (150) that extend into the cavity (116).
According to a fourteenth example that can be combined with the thirteenth example, the horizontally extending membrane (130) and the upright/protruding nanostructures (150) may be made from the deposited first material (114).
According to a fifteenth example that can be combined with the thirteenth example, after the step of depositing the first material (114) onto the structured sacrificial layer (140), the method may further comprise steps of removing the deposited first material (114) from the sacrificial layer (140) while maintaining the deposited first material (114) inside the filled nanoimprints (113), and depositing a different second material (124) onto the sacrificial layer (140) and the filled nanoimprints (113), such that the horizontally extending membrane (130) is made from the deposited second material (124) while the upright/protruding nanostructures (150) are made from the first material (114).
According to a sixteenth example, a method for fabricating a MEMS device (100) is provided, the method comprising a step of providing a substrate (110) having a first substrate surface (111) and an opposite second substrate surface (112), and a step of creating upright/protruding nanostructures (150) in the first substrate surface (111), and a step of structuring a cavity (116) into the substrate (110), the cavity (116) being positioned opposite to the upright/protruding nanostructures (150), and the cavity (116) extending from the second substrate surface (112) up to a remaining substrate portion (110C) between the cavity (116) and the upright/protruding nanostructures (150), thereby creating a membrane structure (130) horizontally extending over the cavity (116) and having the upright/protruding nanostructures (150) integrated therein, wherein the upright/protruding nanostructures (150) face away from the cavity (116).
According to a seventeenth example that can be combined with the sixteenth example, the step of creating the upright/protruding nanostructures (150) in the first substrate surface (111) may comprises at least one of the following steps:
According to an eighteenth example that can be combined with one of the thirteenth to seventeenth examples, the method may further comprise a step of applying a coating onto the upright/protruding nanostructures (150), the coating comprising an organic self-assembled monolayer.
According to an nineteenth example that can be combined with one of the thirteenth to eighteenth examples, the method may further comprise a step of depositing a film of inorganic material onto the upright/protruding nanostructures (150) for forming inorganic nanoseeds, and a step of growing nanowires (190) from the deposited nanoseeds, such that the grown nanowires (190) extend from an outer surface of the upright/protruding nanostructures (150).
Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus.
While this disclosure has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of this disclosure, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23153777 | Jan 2023 | EP | regional |
| 23214127 | Dec 2023 | EP | regional |
