Vibrating mesh module with integrated flow chamber

Abstract

The present invention relates to a vibrating grid module for use in an aerosol-generating device, comprising a MEMS membrane having a plurality of through-holes to define perforations of the membrane; and a flow chamber positioned adjacent to the MEMS membrane, wherein the flow chamber defines a volume configured to hold an aerosol-forming substrate and to feed the aerosol-forming substrate to the MEMS membrane. The invention also relates to an aerosol-generating device comprising such a vibrating grid module. The invention also relates to a method of manufacturing a vibrating mesh module for use in an aerosol-generating device, the method comprising manufacturing a membrane from a bulk wafer of a first material using MEMS technology, manufacturing a flow chamber from a bulk wafer of a second material using MEMS technology, 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 use in a vibrating mesh module for an aerosol generating device. Background Art

[0002] An aerosol generating device using a vibrating mesh module is commonly referred to as a vibrating mesh (VM) nebulizer. Such a vibrating mesh nebulizer is used to generate a breathable aerosol that can be used, for example, to treat respiratory diseases.

[0003] A vibrating mesh nebulizer uses mesh deformation or vibration to push liquid through the mesh. In a typical vibrating mesh nebulizer, a piezoelectric element in contact with the mesh is used to generate the vibration of the mesh. The mesh is adjacent to and in direct contact with a liquid drug-containing substrate. The holes in the mesh can have a tapered structure, where the largest cross-section of the cone contacts the liquid substrate. The mesh deformation generates a pressure field in the liquid, thereby pumping and loading the holes with liquid. The volume of liquid discharged through the holes breaks up into droplets and is ejected into the mouthpiece chamber. The droplets mix with air and directly form an aerosol in the mouthpiece chamber. During inhalation, ambient air passes through the mouthpiece chamber to deliver the aerosol to the user.

[0004] Currently, several off-the-shelf vibrating mesh nebulizer devices are available. These devices include a vibrating mesh module, which can mainly consist of two parts: an annular piezoelectric element and a circular perforated membrane. In the case where the membrane is formed of metal or stainless steel, the perforations are typically produced by laser drilling. Laser drilling produces tapered holes with a small cone angle and a relatively high aspect ratio. Membranes made of nickel or nickel alloys are typically perforated by a combined photolithography and electroplating process. In the first step, such a membrane is perforated using a photolithography process to obtain a desired pattern of holes with a relatively large diameter. Then the entire membrane undergoes electroplating to deposit material on the surface, thereby reducing the size of the holes. The resulting hole shape is funnel-shaped, which is generally more preferred in terms of their microfluidic properties. Additionally, this process may produce a lower aspect ratio and is thus also superior to tapered laser drilling for this reason.

[0005] The size of the holes in the membranes used in these commercially available devices is limited to about 3 to 4 micrometers. Therefore, the MMAD (Median Mass Aerodynamic Diameter) of the aerosol size distribution obtainable by such devices is also in the range of 3 to 4 micrometers, which is too large for deeper lung inhalation. Therefore, most of the aerosol will be deposited in the upper regions of the respiratory tract, which may be disadvantageous for effective drug uptake and may cause throat irritation.

[0006] Reducing the size of the pores in a conventional membrane may not be possible because the reduced pore diameter requires increased pressure to drive the liquid through the pores. This increase can be compensated for by reducing the aspect ratio of the pores (the length of the pore divided by the pore diameter). However, due to mechanical stability reasons, the thickness of the membrane cannot be arbitrarily reduced in conventional manufacturing methods. In addition, the liquid throughput rate per pore decreases quadratically with decreasing pore diameter. Therefore, in order to maintain the desired aerosol flux, such a membrane would have to be provided with a significantly larger number of pores.

[0007] Leakage is also critical when a liquid matrix is used to generate aerosols. Leakage can occur if the liquid matrix in the supply section is pressurized, or if for other reasons more liquid matrix is dispensed than can be aerosolized by the aerosolization unit of the aerosol generating device.

[0008] To allow reliable and reproducible aerosol formation, it is necessary to ensure that the membrane (more specifically, the entrances of the pores in the membrane) is always in contact with a uniform liquid layer when the VM module is operated to generate aerosols. Summary of the Invention

[0009] Therefore, it is desirable to provide a VM module that ensures that the membrane is adequately supplied with the aerosol-forming matrix. It is also desirable to prevent leakage of the aerosol-forming matrix from the aerosol generating device at the same time.

[0010] It is also desirable to provide a perforated membrane for a vibrating mesh module that overcomes at least one of the above disadvantages.

[0011] It is desirable to provide a perforated membrane that allows the generation of aerosol particles with a reduced diameter while maintaining the volume of the generated aerosol.

[0012] It is also desirable to provide a manufacturing method that allows reliable and reproducible manufacture of a perforated membrane with specific aerosol generation properties. In particular, it is desirable to provide a method of manufacturing a vibrating mesh module without the need for glue or gluing steps.

[0013] In summary, there is a need in the art to manufacture a membrane for a VM module that has a reduced outlet pore diameter, a reduced through-hole aspect ratio, an increased number of pores, and avoids gluing to assemble the module.

[0014] According to an embodiment of the present invention, there is provided a vibrating mesh module for use in an aerosol generating device. The vibrating mesh module includes a MEMS membrane having a plurality of through-holes to define the perforations of the membrane; and a flow chamber positioned adjacent to the MEMS membrane. The flow chamber defines a volume configured to hold an aerosol-forming matrix and to feed the aerosol-forming matrix to the MEMS membrane.

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

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

[0017] By providing a flow chamber adjacent to the inlet side of the MEMS membrane, it is ensured that the membrane (more specifically, the inlets of the through-holes in the membrane) is always in contact with a portion of the liquid substrate while the vibrating mesh module is operated to generate an aerosol.

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

[0019] By configuring the flow chamber of the vibrating mesh module to include not only an inlet but also an outlet, any excess aerosol-forming substrate can leave the flow chamber through its outlet, and an increase in pressure in the flow chamber due to an excessive supply of the aerosol-forming substrate can be avoided. 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 distributed through the membrane into the mouthpiece chamber of the aerosol-generating device.

[0020] The outlet of the flow chamber can be configured to have a flow resistance less than the flow resistance through the through-holes of the membrane. The flow resistance through the membrane is mainly determined by the cross-sectional size and aspect ratio of the through-holes. The flow resistance of the outlet is mainly determined by its flow cross-section. By appropriately configuring the cross-section of the outlet of the flow chamber, a desired low flow resistance can be established. The lower the flow resistance of the outlet, the lower the risk of accidental distribution of excess liquid substrate through the membrane.

[0021] In a conventional vibrating mesh atomizer, a liquid substrate can be supplied to a membrane by using a wick feed element. To ensure a permanent supply of the liquid substrate to the membrane, such a wick feed element needs to be in forced contact with the membrane. Such contact results in damping of the membrane vibration and may lead to excessive power consumption. In contrast, in the vibrating mesh module described herein, the liquid substrate can flow freely through the flow chamber, and the liquid substrate does not exert any adverse pressure or mechanical force on the membrane. This allows for a more uniform and reproducible liquid feed into all through-holes in the membrane and also results in lower damping of the membrane. Thus, such a vibrating mesh module can exhibit increased atomization efficiency.

[0022] The vibrating mesh module may also include a piezoelectric actuator configured to generate vibrations of the MEMS membrane. The piezoelectric actuator can be a conventional piezoelectric element formed of a piezoelectric material. The piezoelectric element can be formed integrally with the remainder of the vibrating mesh module. The piezoelectric element can be formed integrally with the remainder of the vibrating mesh module using MEMS processing techniques. By integrally forming the piezoelectric element using MEMS processing techniques, the cumbersome and error-prone step of gluing the piezoelectric element to the vibrating mesh module can be avoided.

[0023] The present invention also relates to an aerosol-generating device having a vibrating mesh module including a membrane as 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 can interact with one or both of an aerosol-generating article including an aerosol-forming substrate and a cartridge including an aerosol-forming substrate. The aerosol-generating device can include a housing, a circuitry including a controller, a power source, and a plurality of sensors.

[0024] The aerosol-generating device may also include a liquid storage portion for storing and providing a supply of the liquid substrate to be atomized. The liquid storage portion can be in fluid communication with the inlet and outlet of the flow chamber of the vibrating mesh module.

[0025] The aerosol-generating device can be configured to generate a circulating flow of the liquid substrate from the liquid storage portion to the inlet of the flow chamber, toward the inlet side of the membrane in the flow chamber, through the outlet of the flow chamber, and back to the liquid supply portion. For this purpose, the aerosol-generating device can include a pumping device. The pumping device can generate a liquid flow through the flow chamber of the vibrating mesh module.

[0026] The present invention also relates to a method of manufacturing a vibrating mesh module for use in an aerosol-generating device. The method includes 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 can be fabricated using MEMS technology or micromachining techniques. These techniques allow the flow chamber to be precisely machined to the desired dimensions.

[0028] The flow chamber can be fabricated from a bulk wafer of a second material using MEMS technology. The bulk wafer material used to fabricate the flow chamber can 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 can be attached by bonding or by gluing. In this case, gluing can be a suitable method because the glue points are sufficiently far from the vibrating membrane. Thus, it is expected that the gluing of these two components will not have any undesirable effect on the vibration behavior of the membrane. In particular, it can be assumed that the gluing does not change the impedance of the membrane in this case.

[0030] The method of fabricating the membrane can include the following steps: providing a bulk wafer of a first material having opposing first and second surfaces, depositing a cover layer of a second material onto the first surface of the bulk wafer, providing vias in the cover layer using MEMS fabrication techniques, etching the second surface of the bulk wafer to define a recess therein, etching the second surface of the bulk wafer until bulk wafer material is removed from the recess, and cutting out the membrane.

[0031] MEMS fabrication can offer the possibility of including piezoelectric elements during the fabrication process of the vibrating grid module. The piezoelectric elements can be deposited on the membrane module. By already including the piezoelectric elements during the fabrication of the membrane module, the attachment of the piezoelectric elements to the membrane module is facilitated. In conventional fabrication methods, the piezoelectric elements have to be glued to the membrane module, which is often a cumbersome and error-prone fabrication step.

[0032] Furthermore, growing the piezoelectric elements directly onto the membrane module allows for a more target-specific geometric design of the piezoelectric elements. The piezoelectric material can be deposited at certain predetermined locations on the membrane module. The deposition of the piezoelectric material can be achieved using MEMS techniques, such as by sputtering or coating techniques. A mask can be used to achieve the desired lateral geometry of the piezoelectric elements. Alternatively, the desired lateral geometry can also be achieved by providing an entire layer of piezoelectric material and subsequently removing the piezoelectric material from the locations where it is not needed. This removal can again be achieved by masking and etching or by mechanical removal.

[0033] One or more piezoelectric elements can be deposited on the contact surface of the membrane structure. The contact surface of the membrane structure can be an annular portion located at the peripheral region of the membrane structure. If considered helpful, the contact portion can also be defined at other surface regions of the membrane structure.

[0034] In principle, any material suitable for manufacturing piezoelectric elements can be used. Such suitable piezoelectric materials may include lead zirconate titanate, zinc oxide, barium titanate, aluminum nitride, scandium aluminum nitride, lithium niobate, ferroelectric ceramics having a perovskite structure, and combinations thereof.

[0035] The membrane can be fabricated by utilizing microelectromechanical systems (MEMS) manufacturing techniques. Such manufacturing techniques include the process technologies used in semiconductor device manufacturing. These techniques include the deposition of material layers, patterning by lithography, and etching of materials in order to produce the desired shape.

[0036] Accordingly, the membrane can be made of materials suitable for processing by MEMS manufacturing techniques. The membrane can include a bulk layer formed from a material provided in wafer form. The wafer material can be made of silicon, silicon oxide, silicon nitride, aluminum nitride, or combinations thereof.

[0037] The membrane structure can include multiple additional material layers. These layers can be applied to the bulk wafer by thin film deposition techniques.

[0038] MEMS technology allows for the customization of hole geometries and shapes to meet the requirements needed for the application. As described above, this particularly includes the diameter of the through holes, which is a key parameter for regulating the size of the resulting aerosol droplets. MEMS technology also allows for the definition of the aspect ratio of the through holes, which is an important parameter for achieving and controlling the microfluidic flow through the through holes. As will be discussed in more detail below, the MEMS manufacturing process can include multiple photolithography masking and etching steps. The lateral dimensions of the masks define the lateral placement and size of the recesses and through holes in the membrane structure and can be easily adapted to specific needs. The combination of the etchant, wafer material, and wafer lattice orientation allows for the definition of the cross-sectional shape of the etched recesses and the depth of the resulting recesses. Subsequent etching steps thus allow for the fabrication of complex shapes of the recesses and through holes of the membrane structure.

[0039] The method of manufacturing the membrane can include multiple manufacturing steps, which are also used in MEMS manufacturing and can include processes such as the deposition of material layers, patterning by lithography, and etching of materials in order to produce the desired shape.

[0040] Thin film deposition can be achieved by physical vapor deposition (PVD), including techniques such as evaporation, magnetron sputtering, or pulsed laser deposition (PLD). These techniques can be used to deposit one or more material layers onto the bulk wafer in a desired sequence.

[0041] Lithography is a well-known technique where light is used to create a tiny patterned film of a suitable material on a bulk substrate to protect 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 photosensitive chemical (photoresist) coated on the substrate. The photoresist decomposes or hardens at the locations where it is exposed to light. Then, a patterned film is created by removing the softer portions of the coating with a suitable solvent.

[0042] The etching step can be accomplished by wet etching, dry etching, or a combination thereof. Dry etching, such as reactive ion etching or plasma etching, may be preferred because it can be used to create vertical edges in the substrate regardless of the crystalline orientation of the substrate. Wet etching techniques can also be used. However, these techniques are generally anisotropic, and the resulting pattern is not only defined by the previously applied mask but can also depend on the lattice orientation. For example, <100>-oriented silicon etched with KOH produces a pyramidal shape through the film thickness with an angle defined by the lattice plane orientation.

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

[0044] In a method of manufacturing a membrane for a vibrating mesh module for use in an aerosol-generating device, a bulk wafer of a first material such as silicon is provided. Commercially available wafer materials have different sizes. The final membrane structure can have a thickness of 5 micrometers to 500 micrometers. The membrane can have a thickness of 10 micrometers to 400 micrometers. The membrane can have a thickness of 30 micrometers to 200 micrometers. The thickness of the membrane structure significantly determines the mechanical behavior of the membrane. Thus, the membrane thickness can be selected based on the target operating frequency and the material properties of the membrane. As discussed in more detail below, the final thickness of the membrane structure can be adjusted during the manufacturing method by a selective etching step.

[0045] Depositing a cover layer onto the first surface of the bulk wafer can be performed by any of the aforementioned physical vapor deposition (PVD) techniques. The cover layer can be formed of silicon dioxide or silicon nitride.

[0046] The cover layer can have a thickness of from 0.1 to 10 micrometers. The cover layer can have a thickness of from 0.2 to 3 micrometers. The cover layer can have a thickness of from 0.3 to 1 micrometer. The thickness of the cover layer and the size of the through-holes defined therein are decisive parameters for controlling the resulting MMAD (Median Mass Aerodynamic Diameter). Due to the microfluidic properties considered, a small aspect ratio is required. Therefore, a cover layer with a small thickness may be preferred. The final choice of thickness can represent a trade-off with mechanical stability, which can form the lower limit of the thickness of the cover layer. This lower limit can also depend on the lateral extent of the cover layer and the expected forces applied to the cover layer during use.

[0047] Subsequently, additional MEMS manufacturing techniques are used to provide through-holes in the cover layer. The through-holes through the cover layer can be obtained by a combination of photolithography and etching. For this purpose, the cover layer can be provided with a mask defining the size and position of the through-holes on the cover layer. In a subsequent etching step, the unmasked areas of the cover layer can be etched away so that the cover layer is provided with a plurality of through-holes.

[0048] The through-holes formed in the recessed portions can have a diameter between 0.1 and 4 micrometers. The through-holes formed in the recessed portions can have a diameter between 0.2 and 3 micrometers.

[0049] In another method step, the second surface of the bulk wafer is processed to define recesses therein. These recesses can again be obtained by masking and subsequent etching of the bulk wafer material. The etching of the silicon bulk wafer can be carried out by using sulfur hexafluoride (SF6). The etching of the second surface of the bulk wafer is continued until the bulk wafer material is removed from the recesses. The recesses in the second surface are preferably positioned such that they coincide with the positions of the through-holes provided in the cover layer. The combination of the bulk wafer and the cover layer forms a membrane structure with recesses of reduced thickness.

[0050] By etching the second surface of the bulk wafer, the final thickness of the membrane structure can be defined. The thickness of the membrane largely determines the vibration characteristics of the membrane structure.

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

[0052] In the final step, the membrane is cut from the bulk wafer material. The membrane is cut into the required sizes needed for the application. Generally, the size of the bulk wafer is significantly larger than the required size of the membrane, such that in the manufacturing method, multiple membrane structures can be fabricated in parallel on a single bulk wafer. This parallel processing allows for the convenient mass production of membranes.

[0053] One or more additional material layers can be applied when manufacturing the membrane. 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 stop layer. When forming a recess at the second surface of the bulk wafer, such a selective etch stop layer can protect the cover layer on the first surface of the bulk wafer. The selective etch stop layer can ensure that the etching process used to form the recess at the second surface of the bulk wafer terminates when the etchant fluid has removed bulk wafer material from the recess and has reached the selective etch stop layer. Generally, this is achieved by forming the selective stop layer from a material that does not dissolve when in contact with the etchant used to etch the bulk wafer material. Subsequently, the selective etch stop layer can be removed by using a different etchant.

[0054] In the above example where sulfur hexafluoride is used to etch a silicon bulk wafer, the selective etch stop layer can be formed from any material that does not dissolve when in contact with sulfur hexafluoride. In this regard, a suitable material is silicon dioxide. Silicon dioxide does not dissolve when in contact with sulfur hexafluoride, such that the vertical etching process of the bulk wafer will stop when the etchant fluid reaches the silicon dioxide layer. This silicon dioxide layer can later be removed by another etchant, such as hydrogen fluoride (HF) or trifluoromethane (CHF3).

[0055] Techniques using a selective etch stop layer can generally be used to provide a layer with a predetermined thickness for a membrane structure. In this way, the material defining the thickness of the membrane itself can also be deposited as a material layer sandwiched between two selective etch stop material layers. In this way, a particularly thin membrane can be provided. In this way, a membrane with a clearly defined thickness can also be provided.

[0056] Manufacturing the membrane using MEMS technology allows the membrane structure to be configured to have desired surface properties that may be beneficial for the aerosolization process. In particular, the material properties of the surface forming the through-holes and the surface that can come into contact with the liquid matrix to be aerosolized can be designed to have such desired surface properties.

[0057] For example, a polysilicon layer can be provided under the cover layer and directly adjacent to the cover layer. In this way, the entrance side of the through-holes in the cover layer is lined with the polysilicon layer. Since polysilicon is more hydrophilic compared to single-crystalline silicon or silicon nitride, the microfluidic flow through the through-holes is enhanced.

[0058] The various method steps discussed above can also be carried out in a different sequence. A person skilled in the art can change the order of the various manufacturing steps according to what is considered appropriate.

[0059] A non-exhaustive list of non-limiting examples is provided below. Any one or more features of these examples can be combined with any one or more features of another example, embodiment, or aspect described herein. Description of the Drawings

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

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

[0062] Figure 1 A schematic design of a conventional vibrating mesh atomizer is shown;

[0063] Figure 2 The geometry of through-holes in a membrane obtainable by different manufacturing methods is shown;

[0064] Figure 3 A detailed view of a MEMS membrane is shown;

[0065] Figure 4 Method steps for manufacturing a MEMS membrane are shown;

[0066] Figure 5 Shows Figure 4 a modification of the method of;

[0067] Figure 6 A MEMS membrane provided with a hydrophilic layer is shown;

[0068] Figure 7 A MEMS membrane provided with an inherent heater is shown;

[0069] Figure 8 A MEMS membrane provided with an integrated piezoelectric element is shown;

[0070] Figure 9 A VM module connected to an upstream liquid flow chamber is shown; and

[0071] Figure 10 The connection of the VM module to the liquid supply section is shown. Detailed Description of the Invention

[0072] Figure 1 An aerosol generating device 10 is shown, which may also be referred to as an atomizer. The atomizer includes a liquid storage section 12 that holds a supply of a liquid substrate 14 to be aerosolized. A vibrating mesh module 20 in direct contact with the liquid substrate 14 is provided, the vibrating mesh module including an annular piezoelectric element 22 that surrounds a circular mesh. The mesh is configured as a membrane 24 that includes through-holes 26. The through-holes 26 in the membrane 24 have a tapered structure, where the largest cross-section of the cone contacts the liquid medicament. By the vibration of the membrane 26, the liquid substrate 14 is pumped through the through-holes 26 and ejected into the mouthpiece chamber 28. During inhalation, ambient air passes through the mouthpiece chamber 28 to deliver the generated aerosol 30 to the user.

[0073] The size of the through - hole 26 at the outlet side of the membrane 24 and the aspect ratio of the through - hole 26 are key parameters that determine the atomization process. Figure 2 An enlarged schematic view of the membrane 24 including the through - hole 26 is shown. The membranes 24 are shown in descending order from left to right according to the aspect ratio AR of their through - holes 26. This order is indicated by Figure 2 the arrow pointing from the left - hand side to the right - hand side in. Each membrane 24 has the same thickness H, and the through - hole 26 has the same minimum diameter d at the outlet side 32 of the membrane 24. The through - holes 26 in the membranes 24 are obtained by different manufacturing methods, where each manufacturing method produces through - holes 26 with different aspect ratios. Generally, the aspect ratio AR of the through - hole 26 is defined by dividing its length by its diameter.

[0074] Figure 2 The membrane 24 shown in A is a membrane 24 made of stainless steel. The through - hole 26 therein is produced by laser drilling. Laser drilling makes the through - hole 26 have a conical shape with a small cone angle. The through - holes 26 obtained in this way have a relatively large aspect ratio A R . The aspect ratio A of these through - holes R can be approximated by the quotient H / d, where H is the thickness of the membrane 24 and d is the minimum diameter of the through - hole 26 at the outlet end of the membrane 24.

[0075] Figure 2 The membrane 24 shown in B is a membrane 24 made of a nickel - cobalt alloy. The through - hole 26 therein is produced by photolithography and subsequent electroplating. In the first step, a pattern of a plurality of through - holes 26 with a relatively large diameter is produced in the membrane 26 using photolithography. Subsequently, the entire membrane 24 undergoes electroplating to deposit material on the membrane surface, thereby reducing the diameter of the through - hole 26. This makes the through - hole 26 have a funnel - like shape. These through - holes 26 have a slightly smaller aspect ratio A R , and thus will be superior to the laser - drilled through - holes 26.

[0076] Figure 2 The membrane 24 shown in C is the membrane 24 according to the present disclosure. The membrane 24 includes a recess 34, and the through - hole 26 is disposed in the recess. The remaining thickness h of the membrane 24 in the recess 34 is significantly less than the total thickness H of the membrane 24. Therefore, the aspect ratio A of the through - hole 26 of this membrane 24 R can be expressed as a quotient h / d that is much smaller than Figure 2 the aspect ratio A of the through - hole 26 of the membranes 24 shown in A and 2B. R

[0077] In Figure 3 , a part of the membrane 24 according to the present disclosure is shown in more detail. Figure 3A shows an enlarged view of the recess 34 of such a membrane 24. The membrane 24 is made of silicon and has a total thickness H. The recess 34 has a circular cross-section with a diameter D and a depth t. The thickness h of the recessed portion of the membrane 24 is determined as h = H - t. A plurality of through-holes 26 are provided at the recess 34. These through-holes 26 also have a circular cross-section and have a diameter d that is much smaller than the diameter D of the recess 34.

[0078] As Figure 3 shown in B, the membrane 24 may include a plurality of recesses 34, and each recess 34 may in turn include a plurality of through-holes 26 through which the liquid matrix 14 is released into the mouthpiece chamber 28 of the aerosol generating device 10.

[0079] Figure 3 C shows an electron microscope image of a part of the membrane including the recess 34. The membrane has a thickness of about 100 micrometers. The circular recess 34 has a diameter D of about 50 micrometers. The remaining thickness h of the recess 34 is equal to 1 micrometer. The recess includes 14 circular through-holes 26 uniformly distributed in the recess 34 in a hexagonal pattern. The diameter d of the through-holes 26 is equal to about 2 micrometers. Thus, Figure 3 the aspect ratio of the through-holes of the membrane shown in C is equal to about 0.5.

[0080] As Figure 3 shown, the membrane 24 can be manufactured by a series of manufacturing steps involving various MEMS processing techniques. A suitable manufacturing method is shown in Figure 4 In the first step, a bulk wafer 40 made of silicon is provided as a base substrate. On top of the first surface of the bulk wafer 40, two material layers 42, 44 are formed by thin film deposition. Layer 42 is formed of silicon dioxide and serves as a selective etch stop layer. On top of layer 42, a layer 44 formed of silicon nitride is deposited. Layer 44 serves as a cover layer for the membrane 24.

[0081] In the second step, a mask defining the positions and diameters of the through-holes 26 is applied to the cover layer 44 by photolithography. Then the cover layer 44 is dry-etched with carbon tetrafluoride (CF4) to locally remove the material of the cover layer 44 and create the through-holes 26 in the silicon nitride cover layer 44.

[0082] In the third step, a recess is defined in the second surface or back side of the silicon bulk wafer 40. For this purpose, a mask defining the position and cross-section of the recess is applied to the second surface of the bulk wafer 40 by photolithography. Subsequently, the recess 34 is formed by etching the second surface of the silicon bulk wafer 40 with sulfur hexafluoride (SF6).

[0083] In the fourth step, the entire second surface of the silicon body wafer 40 is further etched until the body wafer material is removed from the recess 34. Since the selective etch stop layer 42 made of silicon dioxide, which does not dissolve when in contact with sulfur hexafluoride, once the silicon dioxide layer 42 is reached, the etching of the recess 34 stops. In this step, the body wafer material surrounding the recess 34 is etched until the body wafer has reached the desired thickness. The thickness of the remaining silicon body wafer material surrounding the recess 34 defines the final thickness of the membrane 24.

[0084] In the fifth step, the silicon dioxide layer 42 is removed by etching with hydrogen fluoride (HF). By this etching step, the accessible portion of the silicon dioxide layer 42 in the recess 34 is removed, whereby the through hole 26 in the covering layer 44 is connected to the recess 34 in the body wafer 40. In the final step (not shown), the membrane 24 can be cut from the body wafer 40 in the desired size.

[0085] Using Figure 4 the method shown in, the membrane 24 including the through hole 26 is obtained by using a series of MEMS techniques. Using these techniques, a membrane 24 including a clearly defined through hole 26 is obtained, the diameter of which is significantly smaller than the diameter obtainable by currently used manufacturing techniques. The membrane 24 allows sufficient liquid flux and has a flow resistance that makes the membrane 24 suitable for use in the vibrating mesh module 20 for the aerosol generating device 10.

[0086] In Figure 5 another membrane 24 is shown, in which an additional silicon layer 46 is arranged between two selective etch stop layers 42A, 42B. The membrane 24 is generally obtained by a method similar to that Figure 4 described, except that in the first manufacturing step, a sequence of the selective etch stop layer 42A, the silicon layer 46, the selective etch stop layer 42B and the covering layer 44 is deposited on the silicon body wafer 40, as shown in the top view of Figure 5 . In the lower view of Figure 5 the final structure of the membrane 24 is shown. The thickness of the actual membrane 24 is now defined by the additional silicon layer 46, and the recess 34 is formed in this silicon layer 46. Most of the body wafer 40 is etched away, and only the side walls 41 are left as a lateral frame structure supporting the membrane 24 extending therebetween. These frame structures and the recess 34 are again obtained by a sequence of masking and etching as described above. In Figure 5 only two recesses 34 are shown, while the membrane 24 may of course include a greater number of recesses 34. In a manner similar to Figure 4In the same manner, each recess 34 is again covered by a cover layer 44. The cover layer 44 again includes through-holes 26 through which the liquid substrate 14 is ejected into the mouthpiece chamber 28 of the aerosol-generating device 10. By using an additional silicon layer 46 between the two selective etch-stop layers 42A, B, a film 24 with a clearly defined thickness is obtained. Thus, this method allows for more precise control of the film thickness.

[0087] By appropriately selecting materials, the film structure can be configured to have desired surface properties that may be beneficial to the aerosolization process. In this regard, Figure 6 A film structure is shown in which an additional layer 48 of polysilicon is provided below and in direct contact with the cover layer 44. In this way, the surface of the cover layer 44 that contacts the liquid substrate 14 stored in the liquid supply section 12 is lined with the polysilicon layer 48. Since polysilicon is more hydrophilic than single-crystalline silicon or silicon nitride, the microfluidic flow through the through-holes 26 is enhanced.

[0088] Figure 7 A further modification of the film structure shown in Figure 4 is shown. The bulk wafer 40 of the base substrate forming the film 24 is patterned to have a conductive structure 50. The patterning of the film material can be carried out by using any suitable doping method known to those skilled in the art. In the Figure 5 method, the conductive structure 50 can also be formed during the vapor deposition of the material layer forming the film 24. As shown in Figure 7 , the conductive structure 50 extends through the portions of the film material adjacent to the recesses 34 and the through-holes 26, but is not exposed to the liquid substrate 14 flowing through the film 24. Such a conductive structure 50 can form an inherent resistance heater element. By passing an electric current through these conductive structures 50, the temperature of the film 24 and the liquid substrate 14 to be aerosolized can be adjusted.

[0089] MEMS technology also allows for the deposition of additional functional layers or components on the film structure. In this regard,

[0090] Figure 8 A further modification of the previously described film structure is shown. The film structure is provided with an integrated piezoelectric element 52 formed on the annular contact area 54 of the film structure.

[0091] During the manufacturing process of the film 24, a piezoelectric material (in this case lead zirconate titanate) is deposited on top of the film structure. As shown in Figure 8As shown, the piezoelectric material is deposited in an annularly extending contact area 54 located at the peripheral region of the membrane structure 24. The deposition of the piezoelectric material is carried out by a coating technique including a masking step in order to achieve the desired lateral geometry of the piezoelectric element 52. Forming the piezoelectric element 52 integrally with the membrane structure 24 makes the manufacture of the vibrating mesh module 20 easier compared to conventional manufacturing methods. In conventional manufacturing methods, a separately provided piezoelectric element 52 has to be glued to the membrane module, which is generally a cumbersome and error-prone manufacturing step.

[0092] The membrane structure 25 may also be provided with a contact portion for electrically contacting the piezoelectric element 52 to the controller of the aerosol generating device 10. As Figure 8 shown, such a membrane structure additionally provided with one or more integrated piezoelectric elements 52 and electrical contact portions may also be referred to as a vibrating mesh module 20. Such a vibrating mesh module 20 can be used for manufacturing a vibrating mesh aerosol generating device 10. The vibrating mesh module 20 can be manufactured as an interchangeable accessory for such an aerosol generating device 10 and can be configured to be replaced and substituted by the user himself.

[0093] Figure 9 shown is the vibrating mesh module 20 connected to the upstream liquid flow chamber 60. Figure 8 The liquid flow chamber 60 is configured to supply the liquid substrate 14 to the inlet side of the membrane structure 24. The liquid flow chamber 60 is in fluid communication with a liquid supply portion (not shown) of the aerosol generating device. Fluid communication is established via the inlet 62 and the outlet 64, which allows the liquid substrate 14 to freely circulate between the flow chamber 60 and the liquid supply portion. This configuration ensures that the inlet side of the membrane 24 is always in contact with the liquid substrate 14. This configuration also ensures that no excess liquid substrate 14 dispersed through the through-holes is returned to the liquid supply portion. With this configuration, the liquid substrate 14 is not pressed against or through the through-holes of the membrane 24. This configuration allows for enhanced reproducibility of aerosol formation and avoids unwanted leakage of the liquid substrate 14.

[0094] Figure 10 shown is an embodiment connected to the liquid supply portion 66 of the aerosol generating device. Figure 9 The liquid supply portion 66 holds a supply of the liquid substrate 14. The liquid substrate 14 is pumped via a pumping device 68 along a pipe 70 towards the inlet 62 of the liquid flow chamber 60. A portion of the liquid substrate 14 is dispensed through the membrane and forms an inhalable aerosol. The excess liquid substrate 14 pumped into the flow chamber 60 that is not dispensed through the membrane 24 can leave the flow chamber via the outlet 64 and be returned to the liquid supply portion 66 via a pipe 72.

Claims

1. A vibrating mesh module for use in an aerosol generating device, comprising: a MEMS membrane having a plurality of through-holes to define perforations of the membrane, and a flow chamber positioned adjacent to the MEMS membrane, wherein the flow chamber defines a volume configured to hold an aerosol-forming substrate and to feed the aerosol-forming substrate to the MEMS membrane, and wherein the flow chamber is configured to include an inlet through which the aerosol-forming substrate flows into the volume of the flow chamber, and wherein the flow chamber is configured to include an outlet through which the aerosol-forming substrate can leave the volume of the flow chamber.

2. The vibrating mesh module according to claim 1, wherein the perforated MEMS membrane includes an inlet side facing the flow chamber, and wherein the perforated MEMS membrane includes a release side through which the aerosol-forming substrate is released into an aerosolization chamber of the aerosol generating device.

3. The vibrating mesh module according to any one of the preceding claims, wherein the flow chamber is configured such that the aerosol-forming substrate flows through the volume of the flow chamber and contacts the inlet side of the MEMS membrane.

4. The vibrating mesh module according to any one of the preceding claims, wherein the outlet of the flow chamber is configured to have a much lower flow resistance than the flow resistance through the through-holes of the membrane.

5. The vibrating mesh module according to any one of the preceding claims, 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 the preceding claims.

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

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

9. The method according to the previous claim, wherein the bulk wafer material of the membrane is the same material as the bulk wafer used to manufacture the flow chamber.

10. The method according to any one of claims 8 and 9, wherein the membrane and the flow chamber are attached to each other by gluing.

11. The method according to any one of claims 8 to 10, wherein manufacturing the membrane comprises the steps of: providing a bulk wafer of a first material, depositing a cover layer of a second material onto the bulk wafer, Provide vias to the cover layer using MEMS manufacturing techniques, Etch the bulk wafer to define recesses therein, Etch the bulk wafer until the bulk wafer material is removed from the recesses, Cut off 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 according to the previous claim, 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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