Vibrating mesh module with integrated flow chamber

Abstract

The present invention relates to a vibrating mesh module for use in an aerosol generation device, comprising a MEMS membrane with a plurality of through-holes defining perforations in the membrane, and a flow chamber disposed adjacent to the MEMS membrane, the flow chamber defining a volume configured to hold an aerosol-forming substrate and supply the aerosol-forming substrate to the MEMS membrane. The present invention also relates to an aerosol generation device comprising such a vibrating mesh module. The present invention also relates to a method of manufacturing a vibrating mesh module for use in an aerosol generation device, the method comprising: fabricating the membrane from a bulk wafer of a first material using MEMS technology; fabricating the flow chamber from a bulk wafer of a second material using MEMS technology; and attaching the flow chamber to the membrane to form the vibrating mesh module.

Description

[Technical Field]

[0001] The present invention relates to a vibrating mesh module for use in an aerosol generating device. The present invention also relates to an aerosol generating device comprising such a vibrating mesh module. The present invention also relates to a method of manufacturing a membrane for a vibrating mesh module for use in an aerosol generating device. [Background technology]

[0002] Aerosol generators that use a vibrating mesh module are often referred to as vibrating mesh (VM) nebulizers. Such vibrating mesh nebulizers are used to produce inhalable aerosols that can be used, for example, to treat respiratory disorders.

[0003] Vibrating mesh nebulizers use deformation or vibration of a mesh to force the liquid through the mesh. A typical vibrating mesh nebulizer uses a piezoelectric element in contact with the mesh to vibrate the mesh. The mesh is adjacent to and in direct contact with a liquid-containing substrate. The holes in the mesh may have a conical configuration, with the largest cross-section of the cone in contact with the liquid substrate. The deformation of the mesh creates a pressure field within the liquid, which forces the liquid into and fills the holes. The liquid volume displaced through the holes breaks up into droplets and is expelled into the mouthpiece chamber. The droplets mix with air to form an aerosol directly within the mouthpiece chamber. During inhalation, ambient air passes through the mouthpiece chamber, carrying the aerosol to the user.

[0004] Currently, several off-the-shelf vibrating mesh nebulizer devices are commercially available. These devices include a vibrating mesh module, which can be composed of two main parts: an annular piezoelectric element and a circular porous membrane. When the membrane is made of metal or stainless steel, the perforations are typically formed by laser drilling, which produces conical holes with a small cone angle and a relatively high aspect ratio. Membranes made of nickel or nickel alloys are typically perforated by a combination of lithography and electroplating processes. In a first step, such membranes are perforated using a lithography process to obtain the desired hole pattern with a relatively large diameter. Next, the entire membrane is electroplated to deposit material on the surface, thereby reducing the hole size. The resulting hole shape is funnel-shaped, which is generally more favorable in terms of their microfluidic properties. Furthermore, this process can result in a lower aspect ratio, and therefore is preferred over conical laser-drilled holes for this reason.

[0005] The pore size of the membrane used in any of these commercially available devices is limited to approximately 3–4 micrometers. Therefore, the MMAD (median aerodynamic diameter) of the aerosol size distribution that can be obtained by such devices is also in the 3–4 micrometer range, which is too large for inhalation into the deep lungs. Therefore, most of the aerosol is deposited in the upper respiratory tract, which is unfavorable for efficient drug uptake and may cause throat irritation.

[0006] Conventional membranes may not be able to reduce the hole dimensions because a smaller hole diameter requires higher pressure to force the liquid through the holes. This increase can be compensated for by decreasing the hole aspect ratio (hole length divided by hole diameter). However, for mechanical stability reasons, conventional manufacturing methods do not allow for arbitrarily thin membrane thickness. Furthermore, the liquid throughput rate per hole decreases quadratically with decreasing pore size. Therefore, to maintain the desired aerosol throughput, such membranes must contain a significantly larger number of holes.

[0007] Leakage is also an issue when liquid substrates are used to generate aerosols: leaks can occur if the liquid substrate in the supply is pressurized, or for other reasons, more liquid substrate is provided than can be aerosolized by the aerosolization unit of the aerosol generating device.

[0008] To enable reliable and reproducible aerosol formation, it is necessary to ensure that the membrane, and more specifically the entrance to the membrane pores, is always in contact with a homogenous liquid layer while the VM module is operating to generate aerosol.

[0009] It is therefore desirable to provide a VM module that ensures an adequate supply of aerosol-forming substrate to the membrane, while at the same time preventing leakage of the aerosol-forming substrate from the aerosol-generating device.

[0010] It would be further desirable to provide a porous membrane for a vibrating mesh module that overcomes at least one of the above-mentioned drawbacks.

[0011] It would be desirable to provide a porous membrane that allows for the production of aerosol particles with reduced diameter while at the same time maintaining the volume of the aerosol produced.

[0012] It would further be desirable to provide a manufacturing method that allows for the reliable and reproducible production of porous membranes with specific aerosol generating properties. In particular, it would be desirable to provide a method for manufacturing a vibrating mesh module without the need for adhesives or bonding processes.

[0013] In summary, there is a need in the art to produce membranes for VM modules with smaller exit hole diameters, smaller through-hole aspect ratios, increased hole counts, and no adhesives used to assemble the modules. Summary of the Invention

[0014] According to one embodiment of the present invention, there is provided a vibrating mesh module for use in an aerosol generation device, the vibrating mesh module comprising: a MEMS membrane having a plurality of through-holes defining perforations in the membrane; and a flow chamber disposed adjacent to the MEMS membrane, the flow chamber defining a volume configured to hold an aerosol-forming substrate and supply the aerosol-forming substrate to the MEMS membrane.

[0015] As used herein, a "MEMS membrane" is a membrane suitable for use in a vibrating mesh module, the membrane being fabricated by microelectromechanical systems (MEMS) processing techniques, as described in more detail herein below.

[0016] The perforated MEMS membrane has an inlet face facing the flow chamber. The perforated MEMS membrane further has an outlet face through which the aerosol-forming substrate is released into a mouthpiece chamber of the aerosol-generating device. The flow chamber of the vibrating mesh module can be configured such that the liquid aerosol-forming substrate flows through the volume of the flow chamber and in contact with the inlet face of the MEMS membrane.

[0017] Providing a flow chamber adjacent to the inlet face of the MEMS membrane ensures that the membrane, and more specifically the inlet of the membrane's through-hole, is always in contact with a portion of the liquid substrate while the vibrating mesh module is operating to generate the aerosol.

[0018] The flow chamber of the vibrating mesh module may be configured to include an inlet through which the liquid aerosol-forming substrate can flow into the volume of the flow chamber, and the flow chamber may be further configured to include an outlet through which the aerosol-forming substrate can exit the volume of the flow chamber.

[0019] By configuring the flow chamber of the vibrating mesh module not only with an inlet but also with an outlet, any excess aerosol-forming substrate can exit the flow chamber through the outlet, avoiding a pressure buildup in the flow chamber due to an oversupply of aerosol-forming substrate. On the one hand, this ensures that a uniform pressure level is maintained in the flow chamber. On the other hand, this configuration reduces the risk of excess aerosol-forming substrate being supplied through the membrane into the mouthpiece chamber of the aerosol-generating device.

[0020] The outlet of the flow chamber may be configured to have a flow resistance less than the flow resistance through the perforations of the membrane. The flow resistance through the membrane is primarily determined by the cross-sectional dimensions and aspect ratio of the perforations. The flow resistance of the outlet is primarily determined by its cross-sectional flow area. By appropriately configuring the cross-section of the outlet of the flow chamber, a desired low flow resistance can be achieved. The lower the flow resistance of the outlet, the lower the risk of excess liquid substrate being accidentally dispensed through the membrane.

[0021] In conventional vibrating mesh nebulizers, the membrane may be supplied with the liquid substrate using a wick delivery element. To ensure a consistent delivery of the liquid substrate to the membrane, the wick delivery element must be forced into contact with the membrane. This contact can lead to dampening of membrane vibrations and cause excessive power consumption. In contrast, in the vibrating mesh module described herein, the liquid substrate is allowed to flow freely through the flow chamber, and the liquid substrate exerts no adverse pressure or mechanical force on the membrane. This allows for more uniform and reproducible liquid delivery to all through-holes of the membrane and reduces membrane dampening. Therefore, such vibrating mesh modules may exhibit improved aerosolization efficiency.

[0022] The vibrating mesh module may further include a piezoelectric actuator configured to generate vibrations in the MEMS membrane. The piezoelectric actuator may be a conventional piezoelectric element formed from a piezoelectric material. The piezoelectric element may be integrally formed with the remainder of the vibrating mesh module. The piezoelectric element may be integrally formed with the remainder of the vibrating mesh module using MEMS processing techniques. Integral formation of the piezoelectric element using MEMS processing techniques may avoid the tedious and error-prone process of bonding the piezoelectric element to the vibrating mesh module.

[0023] The present invention also relates to an aerosol-generating device having a vibrating mesh module comprising the membrane described herein. As used herein, the term "aerosol-generating device" refers to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-generating device may interact with one or both of an aerosol-generating article including the aerosol-forming substrate and a cartridge including the aerosol-forming substrate. The aerosol-generating device may comprise a housing, an electrical circuit including a controller, a power source, and multiple sensors.

[0024] The aerosol generating device may further comprise a liquid reservoir for storing and supplying the liquid substrate to be aerosolized, the liquid reservoir being in fluid communication with the inlet and outlet of the flow chamber of the vibrating mesh module.

[0025] The aerosol generator can be configured to generate a circulating flow of the liquid substrate from the liquid reservoir to the inlet of the flow chamber, toward the inlet face of the membrane within the flow chamber, and back to the liquid supply through the outlet of the flow chamber. To this end, the aerosol generator can include a pumping device. The pumping device can generate a flow of liquid through the flow chamber of the vibrating mesh module.

[0026] The present invention also relates to a method of fabricating a vibrating mesh module for use in an aerosol generating device, the method comprising the steps of fabricating a membrane from a bulk wafer of a first material using MEMS technology, providing a flow chamber, and attaching the flow chamber to the membrane to form a vibrating mesh module.

[0027] The flow chamber structure may be fabricated using MEMS or micromachining techniques, which allow the flow chamber to be precisely machined to the desired dimensions.

[0028] The flow chamber may be fabricated from a bulk wafer of a second material using MEMS technology. The bulk wafer material used to fabricate the flow chamber may be the same material as the bulk wafer used to fabricate the membrane.

[0029] The attachment of the membrane to the flow chamber can be performed by any suitable attachment method. These components may be attached by bonding or gluing. In this case, gluing may be the preferred method because the bonding point is sufficiently far from the vibrating membrane. Therefore, gluing these two components together is not expected to have any undesirable effect on the vibration behavior of the membrane. Specifically, it is expected that in this case, the bonding will not change the impedance of the membrane.

[0030] A method of fabricating a membrane may include providing a bulk wafer of a first material, the bulk wafer having opposing first and second surfaces; depositing a cover layer of a second material on the first surface of the bulk wafer; providing through holes in the cover layer using MEMS fabrication techniques; etching the second surface of the bulk wafer to define recesses therein; etching the second surface of the bulk wafer until bulk wafer material is removed from the recesses; and cutting out the membrane.

[0031] MEMS fabrication can allow for the incorporation of piezoelectric elements into the vibrating mesh module during the manufacturing process. The piezoelectric elements may be deposited onto the membrane module. Incorporating the piezoelectric elements already during the fabrication of the membrane module facilitates the attachment of the piezoelectric elements to the membrane module. Traditional manufacturing methods require the piezoelectric elements to be glued to the membrane module, which can typically be a tedious and fault-prone manufacturing step.

[0032] Furthermore, growing the piezoelectric elements directly on the membrane module allows for a more targeted geometric design of the piezoelectric elements. The piezoelectric material may be deposited at specific, predetermined locations on the membrane module. Deposition of the piezoelectric material may be done by MEMS techniques, for example, sputtering or coating techniques. A mask may be used to achieve the desired lateral shape of the piezoelectric elements. Alternatively, the desired lateral shape can be achieved by forming an entire layer of piezoelectric material and then removing the piezoelectric material from locations where it is not required. Such removal can again be done by masking and etching or by mechanical removal.

[0033] One or more piezoelectric elements may be deposited on the contact surface of the membrane structure. The contact surface of the membrane structure may be an annular portion located on the periphery of the membrane structure. If deemed useful, contact areas may also be defined on other surface areas of the membrane structure.

[0034] In principle, any material suitable for manufacturing piezoelectric elements can be used, including lead zirconate titanate, zinc oxide, barium titanate, aluminum nitride, scandium aluminum nitride, lithium niobate, ferroelectric ceramics with a perovsite structure, and combinations thereof.

[0035] The membrane may be fabricated using microelectromechanical systems (MEMS) fabrication techniques, including process techniques used in semiconductor device fabrication, which involve depositing a layer of material, patterning it by photolithography, and etching the material to create the required shape.

[0036] Thus, the membrane may be made of a material suitable for processing by MEMS fabrication techniques. The membrane may comprise a bulk layer formed from a material provided in the form of a wafer. The wafer material may be made from silicon, silicon oxide, silicon nitride, aluminum nitride, or a combination thereof.

[0037] The membrane structure may include multiple layers of different materials, which may be applied to a bulk wafer by thin film deposition techniques.

[0038] MEMS technology allows for the tailoring of hole morphology and shape to meet application needs. As mentioned above, this specifically includes the diameter of the through-holes, which is a key parameter for tailoring the size of the resulting aerosol droplets. MEMS technology also allows for the definition of the aspect ratio of the through-holes, which is a key parameter for enabling and controlling microfluidic flow through the through-holes. As described in more detail below, the MEMS fabrication process may include multiple photolithographic masking and etching steps. The lateral size of the mask determines the lateral placement and size of the recesses and through-holes in the membrane structure, making it easily tailored to specific needs. The combination of the etchant, wafer material, and wafer lattice orientation allows for the determination of the cross-sectional shape of the etched recesses and the resulting recess depth. Subsequent etching steps, therefore, enable the fabrication of complex shapes for the recesses and through-holes in the membrane structure.

[0039] The method of fabricating the membrane is also used in MEMS fabrication and may involve multiple manufacturing steps, which may include processes such as depositing a layer of material, patterning by photolithography, and etching the material to create the required shape.

[0040] Thin film deposition can be achieved by techniques such as evaporation, magnetron sputtering, or physical vapor deposition (PVD), including pulsed laser deposition (PLD). Using these techniques, one or more layers of materials can be deposited in a desired sequence on a bulk wafer.

[0041] Photolithography is a well-known technique that uses light to form finely patterned thin films of a suitable material on a bulk substrate, protecting selected areas of the substrate during subsequent etching, deposition, or implantation operations. Typically, ultraviolet light is used to transfer a geometric design from an optical mask to a light-sensitive chemical (photoresist) coated on the substrate. The photoresist dissolves, or hardens, when exposed to light. A suitable solvent is then used to remove the softened portions of the coating, forming a patterned film.

[0042] The etching step may be performed by wet etching or dry etching, or a combination thereof. Dry etching, for example reactive ion etching or plasma etching, may be preferred as it can be used to create perpendicular edges in the substrate, regardless of the crystallographic orientation of the substrate. Wet etching techniques can also be used. However, these techniques are usually anisotropic, and the resulting pattern is not only determined by the mask already applied, but may also depend on the lattice orientation. For example, <100> KOH etching of oriented silicon results in pyramidal shapes throughout the thickness of the film at angles determined by the orientation of the lattice planes.

[0043] The bulk wafer may be made of any first material suitable for processing by MEMS fabrication techniques. The bulk wafer material may be made of silicon, silicon oxide, silicon nitride, aluminum nitride, or a combination thereof. The material of the one or more additional layers applied to the bulk wafer may also be selected from any material suitable for processing by MEMS fabrication techniques. The material of the one or more additional layers applied to the bulk wafer may be selected from silicon, silicon oxide, silicon nitride, aluminum nitride, or a combination thereof. Furthermore, the additional layer may be formed from a material with specific functional properties, such as a selective etch stopper or a material that enhances the flow properties of the aerosolized liquid substrate.

[0044] In a method for fabricating a membrane for a vibrating mesh module for use in an aerosol generating device, a first material, e.g., a bulk wafer of silicon, is provided. Wafer material is commercially available in a variety of dimensions. The final membrane structure may have a thickness of 5 micrometers to 500 micrometers. The membrane may have a thickness of 10 micrometers to 400 micrometers. The membrane may have a thickness of 30 micrometers to 200 micrometers. The thickness of the membrane structure has a significant impact on the mechanical behavior of the membrane. Therefore, the thickness of the membrane can be selected depending on the target operating frequency and the material properties of the membrane. As described in more detail below, the final thickness of the membrane structure may be adjusted by selective etching steps during the fabrication method.

[0045] Deposition of the cover layer on the first side of the bulk wafer may be performed by any of the physical vapor deposition (PVD) techniques described above. The cover layer may be formed from silicon dioxide or silicon nitride.

[0046] The cover layer may have a thickness of 0.1 micrometers to 10 micrometers. The cover layer may have a thickness of 0.2 micrometers to 3 micrometers. The cover layer may have a thickness of 0.3 micrometers to 1 micrometer. The thickness of the cover layer and the dimensions of the through-holes defined therein are important parameters for controlling the resulting MMAD (mass median aerodynamic diameter). A small aspect ratio is desirable for microfluidic characteristics. Therefore, a thin cover layer may be preferred. The final thickness selection may represent a trade-off with mechanical stability, which may set a lower limit for the cover layer thickness. This lower limit depends on the lateral extent of the cover layer and the forces expected to be applied to the cover layer during use.

[0047] Thereafter, through-holes are provided in the cover layer using another MEMS manufacturing technique. The through-holes through the cover layer can be obtained by a combination of photolithography and etching. For this purpose, the cover layer may be provided with a mask that determines the size and position of the through-holes on the cover layer. In a subsequent etching step, the unmasked areas of the cover layer are etched away, resulting in a plurality of through-holes in the cover layer.

[0048] The through-holes formed in the recesses may have a diameter of 0.1 to 4 micrometers, or 0.2 to 3 micrometers.

[0049] In another method step, the second side of the bulk wafer is treated to define recesses therein. These recesses can be obtained, as before, by masking and subsequent etching of the bulk wafer material. Etching of the silicon bulk wafer can be performed using sulfur hexafluoride (SF6). Etching of the second side of the bulk wafer is continued until the bulk wafer material is removed from the recesses. The recesses on the second side are preferably positioned to coincide with the positions of the through holes provided in the cover layer. The bulk wafer and the cover layer combine to form a membrane structure having recesses of reduced thickness.

[0050] Etching the second side of the bulk wafer may determine the final thickness of the membrane structure, which primarily determines the vibration characteristics of the membrane structure.

[0051] The two sides of the membrane may also be referred to as the "inlet face" and "release face" of the membrane. In this regard, the face of the membrane with the recess is the "inlet face," which in use faces the liquid storage portion and through which liquid enters the through-holes. The other face of the membrane forms the "release face" of the membrane, from which droplets are released downstream into the mouthpiece chamber. Therefore, the cover layer with the through-holes is provided on the release face of the membrane structure.

[0052] In the final step, the membrane is cut from the bulk wafer material. The membrane is cut to the required dimensions as needed for this application. Because the bulk wafer size is typically much larger than the required dimensions of the membrane, this manufacturing method allows for multiple membrane structures to be fabricated simultaneously on a single bulk wafer. This parallel processing allows for convenient mass production of membranes.

[0053] One or more additional material layers can be applied to the fabrication of the film. For example, an additional layer can be deposited between the bulk wafer and the cover layer. This additional cover layer can be configured as a selective etch stopper layer. Such a selective etch stopper layer can protect the cover layer on the first side of the bulk wafer when a recess is formed on the second side of the bulk wafer. The selective etch stopper layer ensures that the etching process for forming the recess on the second side of the bulk wafer is terminated when the etching solution removes the bulk wafer material from the recess and reaches the selective etch stopper layer. This is typically achieved by forming the selective etch stopper layer from a material that does not dissolve when in contact with the etching agent used to etch the bulk wafer material. The selective etch stopper layer can then be removed using another etching solution.

[0054] In the above example where sulfur hexafluoride is used to etch a silicon bulk wafer, the selective etch stop layer may be formed from any material that does not dissolve when in contact with sulfur hexafluoride. In this regard, a suitable material is silicon dioxide. Because silicon dioxide does not dissolve when in contact with sulfur hexafluoride, the vertical etching process of the bulk wafer will stop when the etching solution reaches the silicon dioxide layer. This silicon dioxide layer may then be removed by another etchant, such as hydrogen fluoride (HF) or trifluoromethane (CHF).

[0055] Typically, a layer having a predetermined thickness can be provided in a film structure using a technique that uses a selective etching stopper layer. In this way, the material that determines the thickness of the film itself can also be deposited as a layer of material sandwiched between two layers of selective etching stopper material. In this way, a specific thin film can be provided. In this way, a film with a clearly defined thickness can also be provided.

[0056] Fabricating membranes using MEMS technology allows for the construction of membrane structures with desirable surface properties beneficial to the aerosolization process. Specifically, the material properties of the surfaces that form the through-holes and that may come into contact with the liquid substrate to be aerosolized can be engineered to have such desirable surface properties.

[0057] For example, a layer of polycrystalline silicon may be provided below and directly adjacent to the cover layer, such that the inlet faces of the through-holes in the cover layer are covered with the layer of polycrystalline silicon. Polycrystalline silicon is more hydrophilic than single-crystal silicon or silicon nitride, thereby enhancing microfluidic flow through the through-holes.

[0058] The individual method steps described above may also be performed in different orders, and those skilled in the art may vary the order of the individual manufacturing steps as deemed suitable.

[0059] The following provides a non-exhaustive list of non-limiting examples, any one or more of the features of these examples may be combined with any one or more features of any other example, embodiment, or aspect described herein.

[0060] Features described with respect to one embodiment may be equally applied to other embodiments of the invention.

[0061] The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: [Brief explanation of the drawings]

[0062] [Figure 1] FIG. 1 shows the schematic design of a conventional vibrating mesh nebulizer. [Figure 2] 2A-2C show the geometries of through-holes in membranes obtained by various manufacturing methods. [Figure 3] 3A-3C show a detailed view of the MEMS membrane. [Figure 4] FIG. 4 illustrates the steps of a method for manufacturing a MEMS membrane. [Figure 5] FIG. 5 shows a modification of the method of FIG. [Figure 6] FIG. 6 shows a MEMS membrane provided with a hydrophilic layer. [Figure 7] FIG. 7 shows a MEMS membrane with an integrated heater. [Figure 8] FIG. 8 shows a MEMS membrane incorporating a piezoelectric element. [Figure 9] FIG. 9 shows the VM module connecting to the upstream liquid flow chamber. [Figure 10] FIG. 10 shows the connection of the VM module to the liquid supply. DETAILED DESCRIPTION OF THE INVENTION

[0063] FIG. 1 shows an aerosol generating device 10, which may also be referred to as a nebulizer. The nebulizer includes a liquid reservoir 12 that holds a supply of liquid substrate 14 to be aerosolized. A vibrating mesh module 20 is provided that includes an annular piezoelectric element 22 surrounding a circular mesh in direct contact with the liquid substrate 14. The mesh is configured as a membrane 24 with perforations 26. The perforations 26 in the membrane 24 have a conical configuration, with the largest cross-section of the cone in contact with the liquid formulation. Vibration of the membrane 26 forces the liquid substrate 14 through the perforations 26 and into a mouthpiece chamber 28 where it is sprayed. During inhalation, ambient air passes through the mouthpiece chamber 28, carrying the generated aerosol 30 to the user.

[0064] The size of the perforations 26 at the exit surface of the membrane 24, as well as the aspect ratio of the perforations 26, are important parameters for determining the aerosolization process. FIG. 2 shows an enlarged schematic view of a membrane 24 with perforations 26. The membranes 24 are arranged in descending order from left to right according to the aspect ratio AR of their perforations 26. This order is indicated by the arrows pointing from left to right in FIG. 2. Each membrane 24 has the same thickness H, and the perforations 26 have the same minimum diameter d at the exit surface 32 of the membrane 24. The perforations 26 in the membrane 24 can be obtained by various manufacturing methods, each of which results in perforations 26 with different aspect ratios. Generally, the aspect ratio AR of a perforation 26 is determined by dividing its length by its diameter.

[0065] The membrane 24 shown in FIG. 2A is made of stainless steel. Through-holes 26 therein are formed by laser drilling. Laser drilling results in through-holes 26 having a conical shape with a small taper angle. The through-holes 26 thus obtained have a relatively large aspect ratio A R These through holes have an aspect ratio A R may be approximated by the quotient H / d, where H is the thickness of the membrane 24 and d is the smallest diameter of the through-holes 26 at the outlet end of the membrane 24.

[0066] The membrane 24 shown in FIG. 2B is made of a nickel-cobalt alloy. Through-holes 26 therein are formed by lithography and subsequent electroplating. In a first step, lithography is used to form a pattern of through-holes 26 in the membrane 26, each having a relatively large diameter. Subsequently, electroplating is performed across the membrane 24 to deposit material on the membrane surface, thereby reducing the diameter of the through-holes 26. This results in through-holes 26 having a funnel-like shape. These through-holes 26 have an aspect ratio A R may be preferable to laser drilled through holes 26 because they have a slightly smaller

[0067] The membrane 24 shown in Figure 2C is a membrane 24 according to the present disclosure. The membrane 24 includes a recess 34 in which a through-hole 26 is provided. The remaining thickness h of the membrane 24 within the recess 34 is significantly smaller than the total thickness H of the membrane 24. Therefore, the aspect ratio A of the through-hole 26 of such a membrane 24 is R may be expressed as the quotient h / d, which is the aspect ratio A of the through-holes 26 in the membrane 24 shown in FIGS. 2A and 2B. R Much smaller than that.

[0068] In Figure 3, a portion of a membrane 24 according to the present disclosure is shown in more detail. Figure 3A shows an enlarged view of a recess 34 in such membrane 24. Membrane 24 is made of silicon and has an overall thickness H. Recess 34 has a circular cross section with a diameter D and a depth t. The thickness h of the recessed portion of membrane 24 is determined as h = Ht. A plurality of through-holes 26 are provided in recess 34. These through-holes 26 also have a circular cross section and a diameter d that is much smaller than the diameter D of recess 34.

[0069] As shown in FIG. 3B, the membrane 24 may have a plurality of recesses 34, each of which may have a plurality of through-holes 26 through which the liquid substrate 14 is released into the mouthpiece chamber 28 of the aerosol generating device 10.

[0070] Figure 3C shows an electron microscope image of a portion of a membrane comprising recesses 34. The membrane is approximately 100 micrometers thick. The circular recesses 34 have a diameter D of approximately 50 micrometers. The remaining thickness h of the recesses 34 is 1 micrometer. The recesses comprise 14 circular through-holes 26 uniformly distributed in a hexagonal pattern within the recesses 34. The diameter d of the through-holes 26 is approximately 2 micrometers. Thus, the aspect ratio of the through-holes in the membrane shown in Figure 3C is approximately 0.5.

[0071] The membrane 24 shown in FIG. 3 can be manufactured by a series of manufacturing steps involving various MEMS processing techniques. A suitable manufacturing method is illustrated in FIG. 4. In a first step, a bulk wafer 40 made of silicon is provided as a base substrate. On top of a first surface of the bulk wafer 40, two layers of material 42, 44 are formed by thin film deposition. Layer 42 is made of silicon dioxide and serves as a selective etch stop layer. Layer 44 is deposited on top of layer 42, made of silicon nitride. Layer 44 serves as a cover layer for membrane 24.

[0072] In a second step, a mask defining the location and diameter of the through-holes 26 is lithographically applied to the cover layer 44. The cover layer 44 is then dry etched with carbon tetrafluoride (CF4) to locally remove material of the cover layer 44 and form the through-holes 26 in the silicon nitride cover layer 44.

[0073] In a third step, recesses are defined on the second or backside of the silicon bulk wafer 40. For this purpose, a mask defining the location and cross-section of the recesses is applied by lithography to the second side of the bulk wafer 40. The recesses 34 are then formed by etching the second surface of the silicon bulk wafer 40 with sulfur hexafluoride (SF6).

[0074] In a fourth step, the entire second surface of the silicon bulk wafer 40 is further etched until the bulk wafer material is removed from the recess 34. Due to the use of a selective etch stop layer 42 made of silicon dioxide, which does not dissolve when in contact with sulfur hexafluoride, the etching of the recess 34 stops when it reaches the silicon dioxide layer 42. In this step, the bulk wafer material surrounding the recess 34 is etched until the bulk wafer reaches a desired thickness. The thickness of the remaining silicon bulk wafer material surrounding the recess 34 determines the final thickness of the membrane 24.

[0075] In a fifth step, the silicon dioxide layer 42 is removed by etching with hydrogen fluoride (HF). This etching step removes the accessible portions of the silicon dioxide layer 42 within the recesses 34, thereby connecting the through holes 26 in the cover layer 44 to the recesses 34 in the bulk wafer 40. In a final step (not shown), the membrane 24 can be cut to the desired size from the bulk wafer 40.

[0076] 4, a membrane 24 with through-holes 26 is obtained by utilizing a series of MEMS techniques. These techniques are used to obtain a membrane 24 with well-defined through-holes 26 having diameters significantly smaller than those obtainable with currently used manufacturing techniques. The membrane 24 allows for sufficient liquid throughput and has a flow resistance suitable for use in a vibrating mesh module 20 for an aerosol generation device 10.

[0077] FIG. 5 shows another membrane 24, with another silicon layer 46 disposed between two selective etch-stop layers 42A and 42B. The membrane 24 is generally obtained in a manner similar to that described in FIG. 4 , except that in a first manufacturing step, the selective etch-stop layer 42A, silicon layer 46, selective etch-stop layer 42B, and cover layer 44 are deposited on a silicon bulk wafer 40 in this order, as shown in the top view of FIG. 5 . The final structure of the membrane 24 is shown in the bottom diagram of FIG. 5 . Here, the actual thickness of the membrane 24 is determined by the other silicon layer 46, and recesses 34 are formed within this silicon layer 46. Most of the bulk wafer 40 is etched away, leaving only sidewalls 41 as a lateral framework supporting the membrane 24 extending therebetween. These frameworks and recesses 34 are again obtained by the masking and etching sequence described above. While only two recesses 34 are shown in FIG. 5 , the membrane 24 may, of course, include a much larger number of recesses 34. 4, each recess 34 is again covered by a cover layer 44. The cover layer 44 again has through-holes 26 through which the liquid substrate 14 is sprayed into the mouthpiece chamber 28 of the aerosol generating device 10. By using another silicon layer 46 between the two selective etching stopper layers 42A, B, a membrane 24 with a well-defined thickness is obtained. This method therefore allows for more precise control of the membrane thickness.

[0078] Through suitable selection of materials, the membrane structure can be configured to have desired surface properties that may be beneficial to the aerosolization process. In this regard, FIG. 6 illustrates a membrane structure in which another layer of polycrystalline silicon 48 is provided below and directly adjacent to the cover layer 44. In this manner, the surface of the cover layer 44 that contacts the liquid substrate 14 stored in the liquid supply 12 is covered with the layer of polycrystalline silicon 48. Polycrystalline silicon is more hydrophilic compared to single-crystal silicon or silicon nitride, thereby enhancing microfluidic flow through the through-holes 26.

[0079] FIG. 7 illustrates another modification of the membrane structure shown in FIG. 4. The bulk wafer 40, which forms the base substrate of the membrane 24, is patterned with conductive structures 50. Patterning of the membrane material can be performed using any suitable doping method known to those skilled in the art. In the method of FIG. 5, the conductive structures 50 can also be formed during vapor deposition of the material layers forming the membrane 24. As shown in FIG. 7, the conductive structures 50 extend through portions of the membrane material adjacent the recesses 34 and through-holes 26, but are not exposed to the liquid substrate 14 flowing through the membrane 24. Such conductive structures 50 can form built-in resistive heater elements. By passing an electric current through these conductive structures 50, the temperature of the membrane 24 and the aerosolized liquid substrate 14 can be adjusted.

[0080] MEMS technology also allows for the deposition of further functional layers or components on the membrane structure. In this regard, Figure 8 shows yet another modification of the membrane structure described above. The membrane structure incorporates a piezoelectric element 52 formed on an annular contact area 54 of the membrane structure.

[0081] The piezoelectric material, in this case lead zirconate titanate, is deposited on top of the membrane structure during the fabrication process of the membrane 24. As shown in FIG. 8, the piezoelectric material is deposited on annularly extending contact areas 54 located around the periphery of the membrane structure 24. Deposition of the piezoelectric material is performed by a coating technique that includes a masking step to achieve the desired lateral geometry of the piezoelectric elements 52. Forming the piezoelectric elements 52 integrally with the membrane structure 24 simplifies the fabrication of the vibrating mesh module 20 compared to conventional fabrication methods, which require the separately provided piezoelectric elements 52 to be glued to the membrane module, a typically tedious and error-prone manufacturing process.

[0082] The membrane structure 25 may further be provided with contacts for electrically connecting the piezoelectric elements 52 to a controller of the aerosol generating device 10. A membrane structure such as that shown in Figure 8, further provided with one or more integrated piezoelectric elements 52 and electrical contacts, may also be referred to as a vibrating mesh module 20. Such a vibrating mesh module 20 may be used in the manufacture of a vibrating mesh aerosol generating device 10. The vibrating mesh module 20 may be manufactured as a replaceable accessory for such an aerosol generating device 10, or may be configured to be replaceable and replaceable by the user themselves.

[0083] FIG. 9 shows the vibrating mesh module 20 of FIG. 8 coupled to an upstream liquid flow chamber 60. The liquid flow chamber 60 is configured to supply the liquid substrate 14 to the inlet face of the membrane structure 24. The liquid flow chamber 60 is in fluid communication with a liquid supply (not shown) of an aerosol generating device. Fluid communication is established through an inlet 62 and an outlet 64, allowing the liquid substrate 14 to circulate freely between the flow chamber 60 and the liquid supply. This configuration ensures that the inlet face of the membrane 24 is always in contact with the liquid substrate 14. This configuration ensures that excess liquid substrate 14 that is not diffused through the perforations is resupplied into the liquid supply. In this configuration, the liquid substrate 14 is not pressed against or forced through the perforations of the membrane 24. This configuration improves the reproducibility of aerosol formation and avoids unwanted leakage of the liquid substrate 14.

[0084] Figure 10 shows the embodiment of Figure 9 connected to a liquid supply 66 of an aerosol generating device. Liquid supply 66 holds a supply of liquid substrate 14. Liquid substrate 14 is pumped by pumping device 68 along tube 70 toward inlet 62 of liquid flow chamber 60. A portion of the liquid substrate 14 is delivered through membrane 24 and formed into an inhalable aerosol. Excess liquid substrate 14 pumped into flow chamber 60 that is not delivered through membrane 24 exits the flow chamber through outlet 64 and is re-supplied to liquid supply 66 through tube 72.

Claims

1. 1. A vibrating mesh module for use in an aerosol generating device, comprising: a MEMS membrane having a plurality of through holes defining perforations in the membrane; a flow chamber disposed adjacent to the MEMS membrane; the flow chamber defines a volume configured to hold an aerosol-forming substrate and deliver the aerosol-forming substrate to the MEMS membrane; A vibrating mesh module, wherein the flow chamber is configured to have an inlet through which the aerosol-forming substrate flows into the volume of the flow chamber, and the flow chamber is configured to have an outlet through which the aerosol-forming substrate can be discharged from the volume of the flow chamber.

2. 2. The vibrating mesh module of claim 1, wherein the perforated MEMS membrane has an inlet surface facing the flow chamber, and the perforated MEMS membrane has an outlet surface through which the aerosol-forming substrate is released into the aerosolization chamber of the aerosol generating device.

3. 3. The vibrating mesh module of claim 1, wherein the flow chamber is configured such that an aerosol-forming substrate flows through the volume of the flow chamber and in contact with the inlet face of the MEMS membrane.

4. A vibrating mesh module according to any one of claims 1 to 3, wherein the outlet of the flow chamber is configured to have a flow resistance that is much smaller than the flow resistance through the through-holes of the membrane.

5. The vibrating mesh module according to any one of claims 1 to 4, further comprising a piezoelectric actuator configured to generate vibrations of the MEMS membrane.

6. An aerosol generating device comprising the vibrating mesh module according to any one of claims 1 to 5.

7. 7. The aerosol generating device of claim 6, further comprising a pump device for generating a flow of liquid through the integrated cavity, the pump device comprising a liquid storage portion in fluid communication with the inlet and the outlet of the flow chamber of the vibrating mesh module.

8. 1. A method of manufacturing a vibrating mesh module for use in an aerosol generating device, the method comprising: fabricating a membrane from a bulk wafer of a first material using MEMS technology; fabricating a flow chamber from a bulk wafer of the second material using MEMS technology; and attaching the flow chamber to the membrane to form the vibrating mesh module; A method wherein the flow chamber is configured to have an inlet through which the aerosol-forming substrate flows into the volume of the flow chamber, and the flow chamber is configured to have an outlet through which the aerosol-forming substrate can be discharged from the volume of the flow chamber.

9. The method of claim 8 , wherein the bulk wafer material of the membrane is the same material as the bulk wafer used in fabricating the flow chamber.

10. 10. The method of claim 8, wherein the membrane and the flow chamber are attached to each other by adhesive.

11. Manufacture of the membrane providing a bulk wafer of a first material; depositing a cover layer of a second material on the bulk wafer; providing through holes in the cover layer using MEMS fabrication techniques; Etching the bulk wafer to define a recess therein; Etching the bulk wafer until the bulk wafer material is removed from the recess; and cutting out the membrane.

12. The method according to any one of claims 8 to 11, wherein one or more piezoelectric elements are integrally formed on the MEMS membrane.

13. The method of claim 12 , wherein the piezoelectric element is deposited on the contact surface of the membrane structure by sputtering or by a coating technique.

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