Patent Publication Number: US-2020290077-A1

Title: A monolithic integrated mesh device for fluid dispensers and method of making same

Description:
FIELD 
     The disclosure relates to a mesh device. In particular the disclosure relates to a micro-fabricated mesh device for atomization or pumping of a fluid or liquid. 
     BACKGROUND 
     Atomization creates an aerosol from liquid, and is used in numerous applications. During the atomization process the liquid is in contact with mesh which may be excited into mechanical vibration by the actuator (actively vibrating). During this mechanical vibration the liquid is pumped or extruded through a plurality of holes or apertures in the mesh and is output on the other side of the mesh as an aerosol, as the fluid ligaments recoil into spheres of droplets. Alternatively atomisation can be achieved with the mesh facilitating extrusion of liquid provided momentum by a sonotrode or vibrating horn (passive vibrating/static mesh). One application is as a nebulizer (or drug delivery) device. A vibrating mesh device is one of a number of devices currently used in nebulizer technology. Others include ultrasonic and jet nebulizers. 
     Current vibrating mesh devices are fabricated using laser drilling or electroforming. Such devices use bulk commercial piezoelectric actuators to vibrate the mesh in a specific mode which atomizes the liquid. The current devices are expensive to manufacture, poor repeatability and they do not have the capability of integrating piezoelectric actuator, advanced circuitry or sensors. Advanced circuitry is desired to control the oscillations of the plurality of apertures making up the mesh which is complex and difficult to implement. 
     Examples of atomization device assemblies are disclosed in EP2886185; EP0546964; U.S. Pat. No. 4,850,534; JP2004190537; WO0176762; U.S. Pat. Nos. 5,152,456; 6,235,177; WO2008/029216; JP2002318193; EP1022063; JPH0780369; WO2016/150715 A1; WO2011/154394; EP 1 813 428B1; US 2003/0112300 A1; U.S. Pat. No. 7,226,151 B2 and US2013/0120505. 
     In a typical prior-art implementation of a vibrating mesh, as shown in  FIGS. 1 a  and 1 b   , an assembly process is used to create a head of an aerosol generator. In the assembly process the mesh, usually metal, is attached to a metallic holder (also called a washer) by gluing, brazing, or welding, etc. Also a piezoelectric ring actuator is glued to the metallic holder. In practice, an additional two rings within the assembly are required to attach the PZT ring actuator to the holder. It must be conductive material so the bottom side of the PZT can be electrically biased through applying the voltage to the holder that is made of metal, the second ring is just a regular adhesive to attach the mesh to the holder. As shown in  FIG. 1 b    when an AC voltage is applied to the piezoelectric actuator it starts to vibrate laterally and the acoustic energy is transferred through the holder to the mesh that is excited to mechanical vibration causing an aerosol generation. The assembly process requires different components and adhesives to be fabricated by different manufacturers and delivered to the assembly line. This significantly adds to the cost and reliability of the assembly. A number of problems exist with the assembled components, namely reliability issues during operation of the aerosol head because components can dis-assemble or the intermediate layer such as adhesives can change properties during operation and cause device not to perform properly i.e. if the glue changes the properties than the effective device stiffness and its frequency and displacement also change. This directly affects the generated aerosol in operation. 
     It is therefore an object to provide an improved mesh device and method of making same. 
     SUMMARY 
     According to the invention there is provided, as set out in the appended claims, a monolithic integrated mesh device for atomization of a fluid or liquid comprising a plurality of apertures and a piezoelectric material. 
     The invention provides a mesh device which monolithically combines thin film deposited piezoelectric material that can be deposited directly on the mesh and near at least one aperture. Advantageously the integrated mesh device comprises a thin-film piezoelectric actuator integrated directly with the mesh in single micro-fabrication process. Thus monolithic integration between piezo-actuator and mesh is achieved, where monolithic integration is bonding at the atomic level. 
     The invention provides a monolithic integrated mesh as a single-chip device comprising a structural material, such as silicon, electrode materials, e.g. titanium, aluminium, etc., and a piezoelectric material e.g. aluminium nitride, zinc oxide, etc., and is made in a single fabrication process on a base substrate such as standard Silicon or Silicon On Insulator (SOI) substrate. Fabrication comprises a number of photolithography steps for materials, deposition and etching that are used in semiconductor industry. There is no assembly process required, such as using a glue or bonding, as disclosed in the aforementioned prior art technology and overcoming the problems associated with mesh assemblies. 
     The microfabrication technique reduces costs and increase repeatability and reliability. In one embodiment a (Complementary Metal Oxide Semiconductor) CMOS compatible device allows a complete and integrated system can easily incorporate at least one sensor and advanced circuitry. The mesh device can be used for controlling the size and volume of particles. 
     The mesh device, and method of making the device, according to the invention provides a number of advantages; namely reduces the number of steps arising from the assembly process/interconnect of different system components in the prior art. 
     Moreover, a holder is not required and the mechanical energy from the piezo-actuator is directly transferred to the mesh in use. The piezo-actuator does not touch other system components other than the mesh, therefore the overall energy losses in the system is limited to absolute minimum, which is not the case in multi-component assembled devices. This allows for most efficient transfer of electrical energy from a provided bias into mechanical energy acting on the liquid during atomization process. The integrated mesh device can be built on different substrates suitable for thin film piezoelectric materials deposition. One such substrate can be silicon, thus the entire device can be fabricated using standard high volume production methods used in MEMS and CMOS technologies. It will be appreciated that other semiconductor materials, and also metals or polymers can be used if are suitable as a substrate layer for piezoelectric material to be deposited. 
     In one embodiment the mesh device comprises silicon. 
     In one embodiment the piezoelectric material comprises a thin film piezoelectric material deposited on the mesh device. 
     In one embodiment the size of the apertures are selected to control the droplet size of the atomized fluid or liquid. 
     In one embodiment at least one aperture surface is treated to increase the hydrophobic properties of the at least one aperture. 
     In one embodiment the piezoelectric material covers at least a part of the, or a whole, mesh. 
     In one embodiment the piezoelectric material is selected to control a plurality of different resonant modes of the device. 
     In one embodiment application of a voltage to the piezoelectric material induces displacement of the mesh device to control the vibration frequency and/or displacement. 
     In one embodiment the piezoelectric material comprises CMOS compatible piezoelectric material. 
     In one embodiment the mesh comprises an integrated sensor. 
     In one embodiment the piezoelectric material is adapted to be uniquely patterned on the mesh device to control the mode of operation of the mesh device. 
     In one embodiment the mesh device is made using a microfabrication technique. 
     In one embodiment the mesh device comprises at least one of: glass, metal, ceramic or a polymer. 
     In a further embodiment there is provided an integrated vibrating mesh device for atomization of a liquid comprising a plurality of apertures made using a microfabrication process and wherein the mesh device comprises at least one of: silicon, glass, metal, ceramic or a polymer. 
     It will be appreciated that the invention provides a silicon based vibrating mesh device. The silicon mesh offers less expensive devices, increases yield, increases reliability of aperture or hole dimensions, options to optimize aperture or hole size and shape, and increase aperture/hole density for higher flow rate. 
     The micro-fabricated device of the invention can include deposited piezoelectric materials, which will eliminate the need for expensive assembly process. This also has advantage of requiring lower voltage (less complicated circuitry). By depositing the piezoelectric material optimized patterning of the material can be developed. Previously nebulizer industry just use commercial piezoelectric rings not integrated with mesh. 
     In a further embodiment there is provided a method of making a monolithic integrated mesh device comprising the steps of:
         providing a substrate layer;   depositing a piezoelectric material layer on said substrate; and   etching said substrate layer and piezoelectric layer to fabricate a plurality of apertures and form said monolithic integrated mesh device.       

     In another embodiment there is provided a method of making a monolithic integrated mesh device comprising the steps of:
         providing a substrate layer;   depositing at least two layers to form a piezoelectric stack comprising at least one metal layer and at least one piezoelectric layer on said substrate layer; and   patterning of the piezoelectric stack layer and substrate layer to form a piezoelectric actuator and a plurality of apertures to form said monolithic integrated mesh device.       

     By using CMOS compatible piezoelectric materials and silicon-based process one can fabricate the circuitry on the same die as the vibrating mesh, which will cut the cost to make nebulizers significantly by having all the components on one die. The device of the invention can include integrated smart sensors. 
     In one embodiment the invention integrates a thin-film piezoelectric material onto a mesh, and using CMOS compatible materials add functionality such as control circuitry and sensors to the mesh device. 
     The micro-fabrication technique of the invention can be used to manufacture mesh devices from various substrates such as silicon that can directly replace current mesh devices. Alternatively, a monolithic integrated mesh device that will not require the assembly process and have better performance can be used. Using micro-fabrication techniques to create the aperture/holes will reduce pitch size and hole dimensions which may facilitate a higher flow rate and smaller droplets. In nebulizers, this can allow drugs that exhibit unfavourable physicochemical (surface tension and viscosity) properties to be more easily atomized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:— 
         FIGS. 1 a  and 1 b    illustrates a prior art vibrating mesh assembly; 
         FIG. 2 a    illustrates 3D FEM model of an integrated mesh device for atomization of a fluid or liquid, comprising of a silicon membrane with a thin film of piezoelectric material deposited on top;  FIG. 2 b    also illustrates the FEM results showing the device operating in 02 resonance mode; 
         FIG. 3  illustrates results from the 3D model described in  FIG. 2 , and shows the central displacement around the 02 resonance mode for three different diameters of an actuator; 
         FIG. 4  illustrates results from the 3D model; and shows the central displacement around the 02 resonance mode for one diameter of a piezoelectric actuator and for five different amplitudes of driving voltages; 
         FIG. 5 a    illustrates a SEM image of a micro-fabricated mesh device according to one embodiment of the invention. 
         FIG. 5 b    illustrates an image of micro-fabricated integrated mesh device according to other embodiment of the invention; 
         FIG. 6  illustrates a cross sectional view of micro-fabricated mesh device according to one embodiment of the invention; 
         FIG. 7  illustrates a cross sectional view of micro-fabricated mesh device incorporating piezoelectric material, according to one embodiment of the invention 
         FIGS. 8 a , 8 b  and 8 c    illustrates a schematic top-view and cross-sectional view of a device utilizing the mesh in this invention; 
         FIGS. 9 a  and 9 b    illustrates a schematic top-view and cross-sectional view of a device utilizing the mesh in this invention; 
         FIGS. 10 to 15  illustrates the fabrication process steps to make a monolithic integrated mesh device according to one embodiment of the invention; and 
         FIG. 16  illustrates at least one sensor/circuit configured to operate in conjunction with the monolithic integrated mesh device. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The invention provides a vibrating mesh aperture to atomize or pump a fluid or a liquid. The invention makes use of micro-fabrication techniques along with thin film piezoelectric materials to create a monolithic vibrating mesh aperture. Micro-fabrication techniques significantly reduce the cost of manufacturing the devices, the processes are highly repeatable and predictable, and CMOS compatible thin film piezoelectric material can be used to integrate it with at least on sensor. The devices can be made using standard CMOS and MEMS Silicon fabrication techniques, which includes optimization of aperture or hole dimensions and fabrication of the apertures or holes for the aperture device, as well as surface treatment of the aperture to alter the hydrophobicity of the aperture. The device of the invention can be embodied in a number of different ways: 
     Stand-Alone Mesh Aperture Embodiment 
     A vibrating mesh with a plurality of apertures can be micro-fabricated which can directly replace current mesh devices. The device does not include a thin film deposited piezoelectric material that forms the actuator, as reference below, but instead replaces current apertures and can be used with a bulk commercial piezoelectric actuator. The aperture can be fabricated out of various materials like silicon, glass, metals, ceramics, or polymers. An array of apertures/holes are then etched in the substrate with a specific aperture/hole shape and dimension to create micro-sized droplets during the atomization process. 
     The apertures or holes can be wet or dry etched or a combination of the two to control hole shape. For instance a KOH etch of a (100) Si substrate gives a precise etch at 54.7°, which is a repeatable process. Isotropic wet and dry etch techniques can also be used to create unique hole shapes. However, anisotropic dry etch of Si will have a near 80-90° profile. Hole or aperture shapes can be optimized by combining various wet and dry etch techniques. Thin film insulation material can also be included in the aperture as protection from contamination and can include surface treatment to prevent contamination or to control hydrophobicity. 
     The surfaces hydrophobicity of the mesh device can be altered by changing the surface energy through coatings of layers or various treatments. Coatings of hydrophobic or hydrophilic films can be deposited on the surface of the mesh membrane using various methods including chemical vapour deposition, Atomic layer deposition, dip coating, spin coating, aerosol spray, or physical vapour deposition. In addition surface treatments using different compositions of plasma gases and monomers can be used to alter the surface energy by changing surface topography and attachment of various functional groups at the atomic level. 
     Monolithic Vibrating Mesh Aperture Device with Integrated Piezoelectric Material 
     A more advanced device integrates a standalone mesh aperture with a thin film piezoelectric material to create a monolithic vibrating mesh device. The thin film piezoelectric material can cover the entire device or have unique shapes to promote specific resonant modes. 
     An optimal pattern of piezoelectric material can be selected to enhance displacement of the membrane for specific resonant modes. The integration of the thin film piezoelectric material will give similar displacement as the stand alone aperture but with reduced voltage, which makes the circuitry to control the vibration simpler and uses less power. The thin film piezoelectric material can include PZT, PVDF, ZnO, AlN or any other piezo or ferroelectric materials. Aluminium Nitride however, is CMOS compatible so the entire fabrication can be performed in CMOS/MEMS fabrication facility allowing for integration of sensors or advanced circuitry. 
     Integration of Electronics or Sensors Embodiment 
     In an alternative embodiment the device can be combined with integrated electronics or sensors. By using a CMOS compatible piezoelectric material the entire system with built in control electronics and sensors can be developed. The integrated system can be batch fabricated from a single Silicon wafer, which significantly reduces the cost to manufacture the system. In addition sensors can be integrated to increase the functionality and performance of the nebulizer. 
     Example Nebulizer Embodiment 
       FIG. 1 a    a shows a typical nebulizer aperture which consists of a mesh that has specifically designed holes or apertures, it also consists holder and piezoelectric ring actuator. A bulk piezoelectric ring actuator and mesh are attached to the holder forming an aperture. An AC voltage applied to the piezoelectric ring causes the entire aperture to vibrate and this actuates the mesh, as illustrated in  FIG. 1 b   . There are different resonance modes at which the mesh can operate, which is dependent on the frequency of the applied voltage. The resonant frequency of the mesh is dependent on the stiffness of the mesh. 
     A first aspect of the invention, as described above, is to replace the current mesh with a micro-fabricated mesh. The mesh can be made from silicon, glass, polymers, ceramics, or metals. These devices can be used with existing assemblies using bulk piezoelectric ring actuator and holder.  FIG. 5 a    shows a SEM image of the micro-fabricated mesh according to the invention using a silicon-on-insulator (SOI) wafer. The apertures/holes can be developed using either wet etch or dry etch techniques. 
     A second aspect of the invention is the integrated mesh device comprising a piezoelectric actuator formed as a single monolithic block.  FIG. 5 b    shows an image of the micro-fabricated integrated mesh device. 
     The device operation was modelled using Finite Element Modelling (FEM) tool. Typically, for liquid nebulization the device operates optimally in the 02 resonance-mode (or near 02 resonance-mode). 
       FIG. 2 a    illustrates a 3D FEM model of an integrated mesh device for atomization of a fluid or liquid indicated generally by the reference numeral  10 . The mesh device  10  comprises of a silicon membrane  11  with a thin film of piezoelectric material  12  deposited thereon.  FIG. 2 b    demonstrates the FEM model and simulated 02 resonance-mode of the integrated mesh for a 25 um thick silicon membrane of 5 mm diameter. 
       FIG. 3  shows results for three different patterns of the piezo-film actuator deposited on top of the membrane (i.e. the piezo-film patter has diameter of 4.5 mm, 3 mm, and 1.5 mm, as shown in  FIG. 2 a   ). 
       FIG. 3  shows the magnitude of the central deflection of the membrane for each pattern versus the signal frequency applied across the piezo-film indicated by the reference numeral  30 . Note that the maximum deflection occurs at the resonance frequency that, as expected decreases with the piezo-film diameter due to lower effective stiffness of the device, i.e. 67.3 kHz, 67 kHz, and 65.9 kHz for 4.5 mm, 3 mm, and 1.5 mm piezo-film diameter, respectively. However, it was found that the magnitude of maximum displacement at resonance does not follows the same trend, i.e. the larges displacement is obtained for 4.5 mm pattern and the smallest displacement for the 3 mm pattern with the 1.5 mm pattern laying in between. 
     The results indicate that by optimizing the piezo-film pattern deposited on top of the membrane the displacement magnitude and/or the mode shape can be optimized. It is known that the displacement magnitude and mode shape of vibrating mesh devices can affect the flow rate of the device (i.e. liquid volume that is nebulized per unit of time) which is an important parameter from a medicinal efficacy point of view. 
     It is known that the displacement magnitude and mode shape of vibrating meshes can influence the integrity of the mesh and can lead to fractures propagating between apertures. Integration at the atomic level of silicon and piezoelectric material reduces the opportunity for fracture formation. 
       FIG. 4  shows the result for the device with 4.5 mm piezo-film pattern for different voltages indicated by the reference numeral  30 . The results indicate that significant displacements can be achieved for relatively low voltages up to 25V. This low-voltage operation can be beneficial from the power consumption and driving circuit complexity point of view. 
     The ability to apply a variety of voltages and maintain displacement potential allows for the control of atomisation of liquids of varying physicochemical properties to produce a variety of droplet sizes and output rates. 
       FIG. 5 a    illustrates a SEM image of a micro-fabricated mesh device according to the stand-alone mesh aperture embodiment described above.  FIG. 5 b    illustrates an image of micro-fabricated integrated mesh device to provide a monolithic vibrating mesh aperture device with integrated piezoelectric material. 
       FIGS. 6 and 7  illustrates cross sectional views of a stand-alone mesh and integrated monolithic mesh device, according to embodiments of the invention. 
     The process for fabricating the device shown in  FIG. 6  consists of starting with a silicon wafer  41  or silicon on insulator wafer, then patterning the mesh apertures/holes  42  using an etching technique and mask layer. After the apertures/holes are etched the backside silicon is removed and the device is released. 
     The process for fabricating the device shown in  FIG. 7  consists of the same method shown in  FIG. 6  with addition of a stack of metal layers  43  with a thin film piezoelectric material sandwiched in between them on top of the aperture plate. 
     The process has been optimised such that; a) there is maximal integration between layers, facilitating efficient and even energy transfer across the mesh and form an integrated monolithic device structure and b) the potential for liquid ingress between the layers is eliminated thereby mitigating the risk of delamination. 
       FIGS. 8 a , 8 b , 8 c  and 9 a , 9 b    illustrate a number views of the mesh device for carrying out the present invention. 
       FIGS. 8 a , 8 b  and 8 c    shows a schematic top-view and cross-sectional view illustrating a configuration in the case of utilizing a mesh without an integrated piezoelectric actuator but using an external piezoelectric actuator. The device is configured such that a mesh with a plurality of apertures/holes  51  and a bulk-ring  52  around (e.g. mesh support) is attached to a holder  53  and that the top surface of the holder  53  is present against the bottom surface of the mesh support and the bottom surface of an external piezoelectric actuator  54 . The external piezoelectric actuator  54  can be connected to a driving voltage. In such a configuration, the mesh is contactable with fluid from the top or bottom and the fluid can be stored in a tank or container (not shown) also from either side of the device. When the piezoelectric actuator is caused to vibrate it also induces the vibration of mesh. When mesh vibrates the fluid from the tank passes through the plurality of holes in mesh. 
       FIGS. 9 a  and 9 b    shows a schematic top-view and cross-sectional view illustrating a configuration in the case of utilizing a monolithic integrated mesh  60 , incorporating an integrated piezoelectric actuator. The device configuration and operation is similar to that described in  FIG. 8  but in this case the external piezoelectric actuator is not required and the integrated piezoelectric actuator can be connected to the driving voltage  61  to cause the vibration of mesh. 
     The present invention is not limited to the configurations shown in  FIGS. 8 and 9  and the devices can be assembled in a different way for instance the holder can be attached from the other side of the mesh and also the holder could be integrated with the mesh in a single manufacturing process as well so no assembly step to assemble the mesh and holder is required. The mesh and holder form a single object. The driving voltage to the piezoelectric actuator can be delivered using different methods such as wire-bonding, pin-connectors, or can be directly delivered to the mesh through the tracks integrated on the holder. 
       FIGS. 10 to 15  illustrate a fabrication process of a monolithic integrated mesh device on a substrate.  FIG. 10  shows a top view and cross section view of the initial surface of the base substrate, for example a silicon or SOI wafer  70 , which is prepared to deposit and etch a first metal layer.  FIG. 11  shows a top view and cross section view for depositing and etching of a first metal layer  71 . Metal can be deposited by a sputtering process that, on an atomic level, is the process whereby atoms are ejected from a metal target (material source that is to be deposited) and are deposited and bonded to the atoms on the surface of the substrate.  FIG. 12  shows the piezoelectric material layer  71  and etching of the piezoelectric layer  72 .  FIG. 13  shows a second electrode material  73  layer that is deposited and patterned. In  FIG. 14  the desired apertures are then etched in the device silicon and bulk silicon together down to oxide layer level  75 . In  FIG. 15  the oxide layer  75  and bulk silicon  76  is removed. The top and/or bottom electrodes can then be biased with an AC voltage which allows to excite the device into mechanical movement in a controlled manner. 
     In more detail,  FIGS. 10 to 15  describes a typical sequence of processing steps to fabricate the device. In this non-limitative example, a Silicon on Insulator (SOI) substrate is used with a 25 μm thick device silicon layer, a 1 μm thick oxide, and a 535 μm thick bulk silicon layer in  FIG. 10 .  FIG. 11  shows a thin metal layer deposited to act as bottom electrode and patterned using photolithography. In the next step, the piezoelectric material is deposited, in this case the material is an Aluminium Nitride (AlN) layer which is deposited by sputtering and then the layer is patterned, as shown in  FIG. 12 . One alternative method of processing AlN layer is to deposit a bottom metal layer and AlN layer in a single sputtering chamber without breaking vacuum. In that case, the patterning of layers is performed in the reverse order, e.g. AlN layer is etched first followed by an etching of the metal. The materials can be patterned using wet or dry etch techniques. In the next step, illustrated in  FIG. 13 , a top metal layer is deposited and patterned, which acts as the top electrode. This can follow by deposition and pattern of the passivation layer such as silicon dioxide (not illustrated in figures) that may act as a barrier layer for liquid accessing the electrodes. Other layers, for instance to compensate the material stresses, can also be deposited but are not shown here. In the following step, as shown in  FIG. 14 , the device silicon is etched down to the oxide layer using different methods that can, for example, be a wet etching anisotropic or isotropic (e.g. KOH Potassium hydroxide), dry etching (e.g. DRIE—Deep Reactive Ion Etching) or combination of both or other techniques. The density, dimensions and shape (cross section) of the apertures or holes in the device silicon can be modified during processing according to the required droplets size and flow rate for a given application. For instance, the size of the aperture/hole (i.e. diameter of the exit hole) is one of the major factors defining the size of generated droplets to be dispensed. If the target droplet diameter to be produced is 3 um then the size of the exit aperture or hole must be close to 3 um. This will ensure that the majority of all droplets generated by the vibrating mesh are around 3 um in diameter. Similarly, if another application requires aerosol with average droplets of 20 um then the mesh should be fabricated with holes that have 20 um wide exit aperture/hole. Similarly the flow rate of the device can be optimized by changing the holes density and location over the device area. In the final step, as shown in  FIG. 15 , etching of the bulk silicon is performed using wet or dry etching techniques that is followed by the removal of the oxide layer. 
     It will be appreciated that the process described above demonstrates the fabrication of a single device but 10&#39;s to 100&#39;s of devices can be fabricated per single wafer (depending on the wafer size that for instance can be 300 mm in the diameter) as a typical diameter of a single device is approximately 5 mm. The entire wafer can then be diced using a mechanical saw or other dicing method allowing for an individual devices to be released. Note that the sequence of fabrication steps can be different to that described above and used interchangeably. For instance, the process can start with etching of the bulk silicon first so the entire metal/AlN/metal stack is deposited on the bottom surface of the device silicon. Also, the aperture/holes etching could be performed either from the top surface of the device silicon (as described in the example above) or from the bottom surface of the device silicon. 
       FIG. 16  illustrates at least one sensor/circuit configured to operate in conjunction with the monolithic integrated mesh device. The fabrication steps described in  FIGS. 10 to 15  can be a post-CMOS, which means that before the device fabrication starts CMOS circuitry  80  and/or sensors  81  are fabricated within the substrate  76 , for instance in bulk silicon and/or device silicon. Because all materials such as titanium, aluminium nitride, aluminium are CMOS compatible the entire fabrication process can be performed in CMOS/MEMS fabrication facility allowing for integration of advanced circuitry in highly controlled process environment. The circuitry  80  and sensors  81  can be used for device actuation and performance monitoring. For example at least one strain sensor can be integrated with the monolithic integrated mesh device. 
     Advantages of the monolithic approach according to the invention versus prior-art include lower cost fabrication with better tolerance and process uniformity, better reliability as there is no need for assembling of different discreet components as in prior art. Furthermore, with the monolithic approach, the mesh devices can be fabricated in existing CMOS and MEMS fabrication facilities in high volume allowing for integration with IC electronics and sensors. The following table sets out the advantages of using silicon to make the vibrating mesh of the present invention: 
     
       
         
           
               
               
             
               
                   
               
               
                 Standard metal-based process 
                 New class silicon-based process 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Processing 
               
            
           
           
               
               
            
               
                 current metal-based process 
                 silicon processing techniques 
               
               
                 cannot provide sufficient 
                 have better process tolerance 
               
               
                 process uniformity when 
                 thus tighter hole distribution 
               
               
                 producing small holes 
                 can be achieved which results 
               
               
                 (&lt;5 um) in mesh device, 
                 in more uniform droplets/aerosol, 
               
               
                 which results in non- 
                 higher fabrication yield and 
               
               
                 uniform distribution of 
                 lower fabrication cost 
               
               
                 droplets; out of all pro- 
               
               
                 duced meshes only some 
               
               
                 devices pass the test on 
               
               
                 droplets size and only 
               
               
                 these are selected as a 
               
               
                 valid devices; this result 
               
               
                 in reduced production yield 
               
               
                 and higher overall technology cost 
               
            
           
           
               
            
               
                 Electronics integration 
               
            
           
           
               
               
            
               
                 current metal-based process 
                 Silicon is a new class of material 
               
               
                 doesn&#39;t support integration 
                 to be used for liquid atomization, 
               
               
                 of electronic components with 
                 silicon is a semiconductor material 
               
               
                 the mesh such as resistors, 
                 and silicon-based process allows 
               
               
                 capacitors, or transistors 
                 integration of electronic components 
               
               
                 while such integration would 
                 with vibrating mesh, for example, 
               
               
                 allow adding more func- 
                 implanting resistors into the silicon 
               
               
                 tionalities to the devices 
                 mesh in high strain regions (creation 
               
               
                   
                 of a strain gauge) would allow for 
               
               
                   
                 monitoring the device strain and 
               
               
                   
                 displacement level and this infor- 
               
               
                   
                 mation can be used to improve atom- 
               
               
                   
                 ization performance, reliability 
               
               
                   
                 or creation of breath actuated 
               
               
                   
                 nebulizer technology for more 
               
               
                   
                 efficient treatment 
               
            
           
           
               
            
               
                 Piezoelectric material integration (and other materials) 
               
            
           
           
               
               
            
               
                 current metal-based process 
                 In silicon-based process the inte- 
               
               
                 doesn&#39;t support integration 
                 gration of mesh with piezo-actuator 
               
               
                 of piezoelectric actuator when 
                 can be realized in a monolithic 
               
               
                 producing mesh which results 
                 fashion (in a single fabrication 
               
               
                 in post-process assembly of 
                 process), the reliability of such 
               
               
                 mesh and actuator; the exter- 
                 monolithically integrated mesh can 
               
               
                 nal actuator needs to provide 
                 be better than reliability of metal 
               
               
                 significant force to actuate 
                 mesh that is actuated with the ex- 
               
               
                 the mesh and therefore large 
                 ternal piezo-actuator assembled in 
               
               
                 voltages must be used to 
                 a separate process 
               
               
                 generate sufficient displace- 
                 The root cause of fracture in 
               
               
                 ments; this contributes to 
                 silicon plates is different to 
               
               
                 higher power consumption; also 
                 that in metals, and is further 
               
               
                 the assembly process may de- 
                 mitigated by means of 
               
               
                 crease overall reliability of 
                 integration of piezo-material. 
               
               
                 the nebulizer, also the 
                 Integrated mesh has lower power 
               
               
                 reliability of the actuator 
                 required to actuate the mesh, better 
               
               
                 itself may be the limiting 
                 controllability of mesh displacement, 
               
               
                 factor 
                 lower fabrication cost because 
               
               
                 good transfer of 
                 assembly is not required, and better 
               
               
                 mechanical energy from 
                 reliability 
               
               
                 actuator to mesh requires 
                 Integrated mesh with piezo-actuator 
               
               
                 strong bonds 
                 would have lower energy loss to 
               
               
                   
                 the device housing and better 
               
               
                   
                 energy transfer from the 
               
               
                   
                 actuator to mesh 
               
               
                   
                 Silicon processes allows for relatively 
               
               
                   
                 simple integration of other materials 
               
               
                   
                 that can be used to passivated/coat 
               
               
                   
                 the mesh to improve its properties 
               
               
                   
                 (modify surface tension or 
               
               
                   
                 hydrophobicity) 
               
               
                   
               
            
           
         
       
     
     It will be appreciated that a breath sensor can be integrated with silicon-based mesh, so the device only operates during predefined portions of the breath, allowing control of aerosol delivery to the lung. 
     The invention also covers the capability of creating a new assembly using thin film piezoelectric materials which can be deposited directly onto the MEMS aperture using standard CMOS compatible deposition techniques. Various piezoelectric materials could be used including AlN, ZnO, PZT, and PVDF. The idea is that the piezoelectric material can be deposited and patterned on the surface of the aperture substrate using microfabrication methods. The piezoelectric material can be uniquely patterned to control the mode of operation. Then using standard patterning the holes can be patterned in the piezoelectric layer and through the aperture structure, this technique can reduce power as it requires less voltage to create the same amount of displacement as the bulk ring piezoelectric, and the etch process is highly repeatable. 
     Applications of this type of device are many. Aperture plates for atomisation or filtration can be configured to be included in systems such as;
         a) Nebulisers—wherein the aperture plate is either active or static and facilitates the atomisation of liquid fed to the aperture plate, regardless of feed rate. Nebulising systems including this technology could be used for a variety of targeting applications, including, but not limited to nasal, pulmonary, ophthalmic and laparoscopic drug delivery.   b) Such systems could include handheld configurations, for use in combination with facemask, mouthpiece or nasal cannula, or systems designed for inclusion in circuits providing ventilatory support, for example ventilator circuits, circuits making use of a supplementary gas flow and interfacing with the patient by means of endotracheal tube, face mask laryngeal mask, mouthpiece, tracheostomy, nasal mask nasal cannula et cetera. Humidification systems—wherein the aperture plate is either active or static and facilitates the atomisation of liquid fed to the aperture plate, for the purposes of increasing the level of humidification in a system. Such systems may include, but are not limited to, rooms, ventilator circuits as described above, human airways, transport vehicles, storage units et cetera.   c) Calibration equipment—wherein the aperture plate is either active or static and facilitates the atomisation of liquid fed to the aperture plate, for the purposes of generating droplets of a known size for use in the calibration of associated equipment. Such systems may include, but are not limited to, biohazard detection, smoke/particle detectors et cetera.   d) Liquid feed systems—wherein the aperture plate is either active or static and facilitates the atomisation or transport of liquids fed to the aperture plate, for the purposes of transporting a liquid bulk in a timed and controlled fashion. Such systems may include, but are not limited to, mass spectrometry system, liquid pumps, or other systems requiring an increase in the surface area of a liquid formulation for the purposes of reactions.   e) Filtration systems—wherein the aperture plate is either active or static and facilitates the filtration of fluids and separation of components from said fluid. Such systems may include, but are not limited to, food manufacturing (e.g. sugar cane filtration), systems designed to separate particles of varying sizes.   f) Printing systems—wherein the aperture plate is either active or static and facilitates the atomisation of liquid fed to the aperture plate, for the purposes of generating droplets of a known size for use in the printing process. Such systems may include, but are not limited to, ink jet printing and the application of conductive inks.   g) Spray systems—wherein the aperture plate is either active or static and facilitates the atomisation of liquid fed to the aperture plate, for the purposes of generating droplets of a known size for use in applying liquid formulations to the surfaces of target areas. Such systems may include, but are not limited to, systems spraying formulations for; the surface treatment of clothing, surface treatment of solid surfaces, surface application of liquids to medical devices, mixing of liquids, cosmetic sprays, e.g tanning products.   h) Vaporising systems—wherein the aperture plate is either active or static and facilitates the atomisation of and vaporisation of liquid fed to the aperture plate combined with a heated piezoelectric element. Such systems may include, but are not limited to, electronic cigarettes and the like.       

     It will be appreciated the invention provides:
         reduced fabrication cost   smaller apertures (limited by etch choice and material thickness)   the opportunity to manipulate aperture density, location, shape and size can be easily modified with micro-fabrication processes used for MEMS and CMOS, such as wet and dry etching techniques   tighter fabrication tolerance, better repeatability, higher fabrication yield   assembly between actuator-holder-mesh is not required—lower cost of the entire system   better reliability because actuator monolithically integrated with mesh   better energy transfer as there is no need for holder   silicon gives possibility for integration of electronic components such as resistors and transistors that may be used as control electronics and/or sensors   process flexibility in terms of using different materials and processing steps, for instance to passivated the device or coat to modify surface tension properties or hydrophobicity   silicon only device can directly replace current metal-based device and use current assembly process.       

     In the specification the terms “comprise, comprises, comprised and comprising” or any variation thereof and the terms include, includes, included and including” or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa. 
     The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.