CN219003514U - Microfluidic device - Google Patents

Abstract

The present disclosure relates to microfluidic devices. The microfluidic device comprises: a monolithic body having a peripheral surface defining a first face, a fluid chamber in the monolithic body, a first fluid opening extending from the peripheral surface of the monolithic body and in fluid communication with the fluid chamber, a cap element extending over the monolithic body and attached to the first face, an actuator chamber extending between the cap element and the first face of the monolithic body, a membrane region extending in the monolithic body between the first face and the fluid chamber, and a piezoelectric actuator element extending on the first face, over the membrane region, inside the actuator chamber. The at least one first region of the film region includes a first portion of polysilicon and a second portion of polysilicon. The second region of the film region includes a third portion of polysilicon. The first crystal structure of the first portion has a smaller average grain size than the second crystal structure of the second portion and the third crystal structure of the third portion.

Description

Microfluidic device

Technical Field

The present disclosure relates to a microfluidic MEMS device including buried cavities and a process for fabricating the same. In particular, in the following description, reference will be made to a fluid ejection device based on piezoelectric technology (such as an inkjet head for printing applications), a micro-actuator (such as a micro-pump), and the like.

Background

However, with suitable modifications, the microfluidic device may also be used for the emission of fluids other than ink, for example for applications in the biological or biomedical field, for the local application of biological materials (e.g. DNA) in the manufacture of sensors for biological analysis, for textile or ceramic decoration, and for 3D printing and additive manufacturing applications.

Furthermore, it may be a different micro-actuator, such as a micro-switch or the like.

Various types of fluid ejection devices are known that are handled by MEMS (microelectromechanical systems) technology.

These devices are currently formed by coupling a large number of pre-processed and assembled components in a final manufacturing step.

For example, fig. 1 shows a spraying apparatus 1, which spraying apparatus 1 comprises a nozzle section 2, a chamber section 3 and a dispensing section 4, formed from respective semiconductor wafers which are stacked and bonded to each other.

The nozzle portion 2 has a spray channel 10 (also referred to as nozzle 10) and defines a fluid containing chamber 11 downwardly.

The chamber portion 3 is formed by a body 5 of silicon and a film 6 of, for example, silicon oxide. The fluid containing chamber 11 is laterally delimited by the body 5 and upwardly delimited by the membrane layer 6. The region of the membrane layer 6 above the fluid containment chamber 11 forms the membrane 7. The membrane layer 6 has a thickness such that it can deflect.

The dispensing portion 4 is made of silicon and delimits upwards an actuator chamber 12, which actuator chamber 12 is closed downwards by the membrane layer 5 and is superimposed on the fluid containing chamber 11 and the membrane 7. The dispensing portion 4 has a supply channel 13 communicating with the fluid containing chamber 11 through a corresponding opening 14 in the membrane layer 6.

The piezoelectric actuator 15 is arranged above the membrane 7 in the actuator chamber 12. The piezoelectric actuator 15 includes a pair of electrodes 21, 22 stacked on each other, provided onPiezoelectric layers 20 extending therebetween, e.g. PZT (Pb, zr, tiO) ₃ )。

The ejection device 1 may comprise a plurality of fluid containing chambers 11 extending side by side, the plurality of fluid containing chambers 11 being laterally spaced apart by walls 19 but being interconnected at the ends, as shown in fig. 2, which fig. 2 shows a plurality of feed channels 13 in dashed lines and a plurality of ejection channels 10 in solid lines.

In use, fluid or liquid to be ejected is supplied to the fluid containing chamber 11 through the supply channel 13 (arrow 23); the piezoelectric actuator 15 is controlled by the electrodes 21, 22 (appropriately biased) in such a way that a deflection of the membrane 7 towards the inside of the fluid containing chamber 11 and a movement of the fluid towards the nozzle 10 are produced, resulting in a controlled ejection of droplets towards the outside of the ejection device 1 (arrow 24).

Then, the piezoelectric actuator 15 is controlled in the opposite direction, thereby increasing the volume of the fluid containing chamber 11 and causing further fluid to be drawn out.

By periodically repeating the actuation of the piezoelectric actuator 15, more drops are ejected.

The injection device 1 may be manufactured as described in patent application US 2017/182778. The manufacturing process described therein provides three couplings for at least partial pretreatment.

This coupling (e.g., by bonding techniques) generally requires high precision in order to obtain good alignment between the wafers and between the functional elements formed therein.

Furthermore, the use of three wafers is expensive and, in some cases, may lead to yield problems and technical difficulties.

Patent application US 2020/032545 describes a process for manufacturing a fluid ejection device using two silicon wafers and a nozzle plate formed from a dry film. Although this solution solves the problem of using three silicon wafers, it remains to be improved because the material of the nozzle plate is not always able to ensure reproducibility and uniformity of the technical process, which is useful in some applications and may be incompatible with some liquids. Furthermore, the use of polymeric materials for the nozzle plate may be incompatible with applications where the part is operated at low or high temperatures.

Disclosure of Invention

According to the present disclosure, a microfluidic device and a process for manufacturing the same are provided.

The present disclosure relates to a microfluidic device comprising: a monolithic body having a peripheral surface defining a first face; a fluid chamber in the monolithic body; a first fluid opening extending from the peripheral surface of the monolithic body and in fluid communication with the fluid chamber; a cap element extending over the monolithic body and attached to the first face; an actuator chamber extending between the cap element and the first face of the monolithic body; a membrane region in the monolithic body extending between the first face and the fluid chamber; and a piezoelectric actuator element extending on the first face over the membrane region inside the actuator chamber, wherein the membrane region comprises at least one first region comprising a first portion of polysilicon facing the fluid chamber and having a first crystal structure and one second region covering the first portion and having a second crystal structure, and having a third portion of polysilicon facing the fluid chamber and having a third crystal structure, the first crystal structure having a smaller average grain size than the second crystal structure and the third crystal structure.

In some embodiments, the at least one first region is surrounded by the second region.

In some embodiments, the at least one first region comprises a plurality of first regions and the second region comprises a plurality of apertures, each aperture surrounding a respective first region.

In some embodiments, the film region comprises a laminate comprising a silicon carrier layer, a silicon permeable layer, a silicon sealing layer, and an insulating layer of insulating material, wherein at the first region the permeable layer forms the first portion, the insulating layer covers the permeable layer, and the sealing layer forms the second portion and covers the insulating layer, and at the second region the carrier layer forms the third portion, the permeable layer covers the carrier layer, and the insulating layer covers the permeable layer.

In some embodiments, the sealing layer covers the insulating layer at the second region.

In some embodiments, the at least one first region forms a step protruding toward the interior of the fluid chamber relative to the second region.

In some embodiments, the first fluid opening extends between the fluid chamber and the first face of the monolithic body, the microfluidic device further comprising a second fluid opening extending through the monolithic body between the second face of the monolithic body and the fluid chamber.

In some embodiments, the microfluidic device forms a fluid ejection device, a micropump, a microswitch, or a fluid buffer device.

Drawings

For a better understanding of the present disclosure, some embodiments thereof are now described, purely by way of non-limiting example, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-section of a known fluid ejection device;

FIG. 2 is a horizontal cross-sectional view taken along section line II-II of FIG. 1;

fig. 3A-3I are cross-sections through a fluid ejection device in a subsequent manufacturing step according to an embodiment;

fig. 4A to 4D are top plan views of the apparatus of fig. 3A to 3I, respectively, in the manufacturing steps of fig. 3A, 3B, 3C and 3I;

FIGS. 5A-5I are cross-sections through a fluid ejection device in a subsequent manufacturing step according to another embodiment;

fig. 6A to 6I are top plan views on a reduced scale of the apparatus of fig. 5A to 5I in manufacturing steps corresponding to the figures having the same letters a to I;

fig. 7A-7D are cross-sections of the apparatus of fig. 5A-5I taken along section lines 7A-7A, 7B-7B, 7C-7C and 7D-7D of fig. 6B, 6G, 6H and 6I, respectively, in manufacturing steps corresponding to fig. 5B, 5G, 5H and 5I;

FIG. 8 shows an enlarged detail of FIG. 3D; and

fig. 9A and 9B are respectively cross-sections of variants of the device of fig. 3A to 3I in a manufacturing step subsequent to fig. 3C and in a manufacturing step corresponding to fig. 3D.

Detailed Description

The following description relates to the arrangement shown; thus, expressions such as "above", "below", "top", "bottom", "right", "left" are related to the drawings and are not intended to be limiting.

Fig. 3A-3I and 4A-4C relate to manufacturing steps for manufacturing a first microfluidic device (e.g., an ink or other liquid ejection head).

Fig. 3A shows a first wafer 30 that has undergone an initial processing step to form a sacrificial layer 32 over a substrate 31; the carrier layer 33 extends over the sacrificial layer 32 and has a portion 34 extending through the sacrificial layer 32 down to the substrate 31.

The portion 34 of the carrier layer 33 forms a closing wall (hereinafter also referred to as blocking wall 34) which laterally surrounds a sacrificial portion of the sacrificial layer 32 indicated by 32A, at which a cavity is to be formed, as will be explained in detail below.

For example, the blocking wall 34 forms a hollow rectangular wall, as indicated by the dashed line in the top view of fig. 4A.

In particular, to form the structure of fig. 3A and 4A, the substrate 31, here monocrystalline silicon, may be subjected to oxidation to form the sacrificial layer 32, here silicon oxide. The sacrificial layer 32 is selectively etched where it is desired to form the barrier wall 34. The carrier layer 33 is epitaxially grown on the sacrificial layer 32 and in the removed region directly on the substrate 31, forming a barrier wall 34.

As described below, the sacrificial layer 32 may have a thickness comprised between 0.5 μm and 5 μm, depending on the desired depth of the structure to be formed.

The carrier layer 33 may have a thickness comprised between 1 μm and 20 μm, depending on the desired design features.

In fig. 3B and 4B, the carrier layer 33 is etched to form release holes 36, for example, by dry etching.

The release holes 36 extend through the thickness of the carrier layer 33 and have a circular area, for example, a diameter d comprised between 0.5 μm and 2 μm. The number and distance of the release holes 36 are such that they allow a uniform flow of the Xu Shike agent during the subsequent release step and maintain a sufficient mechanical robustness of the carrier layer 33. For example, in order to obtain a film with a length equal to 25 μm, four release holes 36 arranged along the line may be formed.

In general, the relief holes 36 may be distributed throughout the area of the sacrificial portion 32A where it is desired to form the cavity, based on technical considerations.

In fig. 3C and 4C, a permeable layer 37 is deposited on the surface of the first wafer 30. The permeable layer 37 is, for example, permeable polysilicon deposited by LPCVD (low pressure chemical vapor deposition) and has a thickness comprised between 0.06 μm and 0.2 μm. For example, as described in US 5,919,364A, polysilicon deposited by LPCVD has a structure featuring micro-holes that make it permeable and allow the flow of liquids and vapors (in particular etchants such as HF-hydrofluoric acid vapor).

In particular, the permeable layer 37 covers the walls and bottom of the release hole 36.

Then, an etchant (e.g., gas phase HF) is used to etch the sacrificial portion 32A. Due to the permeability of the permeable layer 37, the etchant passes through the permeable layer 37 and removes the sacrificial portion 32A disposed under the release hole 36. In this way, the buried cavity 38 is formed.

The barrier wall 34 here laterally stops the etching of the sacrificial layer 32, confining it to the sacrificial portion 32A and thus forming a wall defining the buried cavity 38.

Subsequently, as shown in fig. 3D, the buried cavity 38 is sealed by epitaxially depositing a sealing layer 39, the sealing layer 39 covering the carrier layer 33 and filling the release hole 36.

To this end, for example, a polysilicon layer having a thickness comprised between 2 μm and 25 μm is deposited, which can then be planarized and thinned to obtain the desired final thickness, for example a thickness varying between 1 μm and 24 μm.

During sealing of the release hole 36, the permeable layer 37 forms a barrier against polysilicon deposition inside the buried cavity 38.

In this step, permeable layer 37 generally changes crystalline state and at the end of the sealing process it assumes a structure that is no longer permeable, but rather a polycrystalline structure.

Further, at the end of the sealing process, the permeable layer 37 (hereinafter referred to as impermeable polycrystalline layer 37') has grains of smaller size than the carrier layer 33 and the sealing layer 39.

In particular, it may have grains that are an order of magnitude smaller than the carrier layer 33 and the sealing layer 39 on average. For example, the grains of impermeable polycrystalline layer 37' may have a size of 100-500nm, while the grains of carrier layer 33 and sealing layer 39 may be 500-5000nm.

Furthermore, as shown in the detail of fig. 8, due to the growth process of the sealing layer 39, the bottom of the impermeable polycrystalline layer 37' may protrude slightly with respect to the bottom surface of the carrier layer 33, where various very small steps 43 are formed.

In fig. 3E, an insulating layer 40 is deposited over the sealing layer 39.

For example, the insulating layer 40 may be a silicon oxide layer by CVD, chemical vapor deposition, such as TEOS (tetraethyl orthosilicate), having a thickness of about 0.5 μm.

The carrier layer 33, the impermeable polycrystalline layer 37', the sealing layer 39 and the insulating layer 40 form a film layer 41, which film layer 41 forms a film 42 on the buried cavity 38.

In fig. 3F, an actuator element 45 having a structure such as that shown in the piezoelectric actuator 15 of fig. 1 is formed on the film 42.

In particular, the bottom electrode layer (e.g. comprising TiO between 5nm and 50nm by a thickness deposited thereon ₂ Layer and thickness including Pt layer formation between 30nm and 300 nm) is deposited on the insulating layer 40. Then, a piezoelectric layer (e.g., PZT-Pb, zr, tiO) ₃ -a layer) having a thickness comprised between 0.5 μm and 3.0 μm (typically 1 μm or 2 μm). Subsequently, a top electrode layer, e.g. Pt or Ir or IrO, is deposited over the piezoelectric layer ₂ Or TiW or Ru, the thickness being comprised between 30nm and 300 nm. The top electrode, piezoelectric layer and bottom electrode layer are then patterned to form a stack 46 comprising the bottom electrode and top electrode in a known and not shown manner.

In particular, the laminate 46 covers almost the entire membrane 42, except for the peripheral frame.

One or more insulating and protective layers, e.g. USG, siO, are then deposited ₂ Or SiN or Al ₂ O ₃ A layer, monolayer or stack, of thickness comprised between 10nm and 1000nm, forms the protective layer 47.

Selectively removing the protective layer 47 to form a contact opening; a metal layer is then deposited and patterned in a manner known per se to form contact regions 48 in direct electrical contact with the top and bottom electrodes of stack 46. The metal layer also forms conductive traces and pads 50, only schematically shown, for electrical connection of the actuator element 45.

In fig. 3G, a fluid opening 51 is formed in the first wafer 30 over the buried cavity 38.

To this end, the film layer 41 is etched in a selective manner, firstly by etching the oxide of the insulating layer 40 through a mask and then by dry etching the silicon of the sealing layer 39, the impermeable polycrystalline layer 37' and the carrier layer 33 until the buried cavity 38 is reached.

For example, the fluid opening 51 is formed at a first end of the buried cavity 38 such that it is accessible from the outside.

In addition, bonding and sealing regions 53 are formed on the top surface of wafer 30, insulating layer 40 and/or sealing layer 39.

The bonding and sealing region 53 may be a polymeric material such as BCB (benzocyclobutene) or other suitable material and may be deposited and defined or formed by molding.

Then, in fig. 3H, the pretreated cap wafer 55 is bonded to the top face of the first wafer 30 by bonding and sealing region 53.

Thereby forming a composite wafer 60.

The cap wafer 55 has been pre-treated so as to have a recess 56 of larger area than the actuator element 45 and is delimited by a protruding edge 57 intended to be coupled to the bonding and sealing area 53.

Furthermore, the cap wafer 55 has already had a through opening 58 outside the recess 56.

The recess 56 and the through opening 58 are arranged such that when the cap wafer 55 is bonded to the first wafer 30, the recess 56 is arranged above the actuator element 45 forming an actuator chamber again indicated by 56, and the through opening 58 is arranged continuous with the fluid opening 51 forming a first fluid channel 59, typically a supply channel.

Cap wafer 55 may also have openings 61 for access to pads 50.

Further, the first wafer 30 is etched from the back side, for example, by dry etching the material of the substrate 31.

A second fluid channel 62, here an outlet nozzle, is thus formed which passes completely through the substrate 31 and reaches the buried cavity 38, for example at its second end opposite the fluid opening 51.

Thus, the buried cavity 38 is now connected to the outside by both the first fluid channel 59 and the second fluid channel 62 and forms a fluid cavity chamber again indicated by 38.

Since the fluid chamber 38 is obtained by partially removing the sacrificial layer 32, the thickness of the sacrificial layer 32 is determined for the desired depth of the fluid chamber 38.

As shown in fig. 3I and 4D, the composite wafer 60 may then be diced to form microfluidic devices 65.

After dicing, the microfluidic device 65 of fig. 3I and 4D thus comprises a monolithic body 80 formed by the substrate 31, the sacrificial layer 32, the carrier layer 33 and the insulating layer 40.

The monolithic body 80 has a peripheral surface defining a first face 80A (top face in the drawing) and a second face 80B (bottom face in the drawing).

The cap element 81 extends over the monolithic body 80 and is attached to the first face 80A.

The film 42 includes a bottom layer including a plurality of first polycrystalline regions 90 and a plurality of second polycrystalline regions 91.

The first polycrystalline region 90 is formed by the impermeable polycrystalline layer 37 'and the filled portion of the sealing layer 39, and includes a portion having a finer crystal structure (at the impermeable polycrystalline layer 37') facing the fluid chamber 38 and a cover portion having a coarser crystal structure.

The second polycrystalline region 91 (which is typically contiguous) is formed from the carrier layer 33 and has a relatively coarse crystal structure. In this way, the microfluidic device 65 is formed of only two wafers (the first wafer 30 and the cap wafer 55), and thus has a simplified structure, and can be formed with simpler steps and reduced cost.

In use, and in a manner known to those skilled in the art, fluid may enter the first fluid passage 59, pass through the fluid chamber 38, and exit the second fluid passage 62 (or vice versa) due to deformation of the membrane 42 caused by actuation of the actuator element 45.

In particular, by arranging one of the bonding and sealing areas 53 such that it surrounds the recess 56, after the first wafer 30 and the cap wafer 55 are bonded to each other, the actuator chamber 56 is tightly closed and the actuator element 45 is safely insulated from the external environment.

Furthermore, by arranging one of the bonding and sealing areas 53 such that it surrounds the fluid opening 51, the first fluid channel 59 is tightly closed with respect to the rest of the device, in particular the actuator chamber 56, after the first wafer 30 and the cap wafer 55 are bonded to each other.

Fig. 5A-5I, 6A-6H, and 7A-7D relate to manufacturing steps for manufacturing another microfluidic device (e.g., a micropump).

Fig. 5A and 6A show a first wafer 130 that has undergone an initial processing step to form a sacrificial layer 132 over a substrate 131 and a carrier layer 133 thereon.

Substrate 131 may be, for example, monocrystalline silicon; the sacrificial layer 132 may be silicon oxide obtained by thermal oxidation and has a thickness comprised between 0.5 μm and 5 μm (based on the desired depth of the fluid chamber to be formed); and the carrier layer 133 may be epitaxially grown and may have a thickness comprised between 1 μm and 20 μm based on the desired elasticity and resistance characteristics of the film.

In fig. 5B, 6B, and 7A, the carrier layer 133 is etched to form release holes 136A-136C.

In particular, here, a film release hole 136A, a plurality of inlet release holes 136B, and a plurality of passage release holes 136C are formed. The etching may be dry etching.

In the example shown, as seen in the top view of fig. 6B, the film release hole 136A has a circular shape with a diameter D1 approximately equal to the diameter of the film to be formed and comprised between 1 μm and 10 μm, for example.

The inlet release hole 136B is arranged outside the film release hole 136A along the closing line. The inlet relief holes 136B may have any shape, such as circular, square, rectangular (or other shape), with a diameter or side length comprised between 0.5 μm and 2 μm, and may be arranged at a mutual distance of a few μm (typically from 0.1 μm to 0.2 μm), similar to that described for the relief holes 36 of fig. 3B. In the illustrated example, the inlet release holes 136B have a circular ring sector shape and are arranged along a circumference concentric with the membrane release holes 136A. For example, the circumference (here the inner circumference) may have a diameter D2 comprised between 20 μm and 100 μm.

The passage release holes 136C are arranged in a radial direction connecting the membrane release holes 136A to the circumference of the inlet release holes 136B. In this embodiment, the channel release holes 136C are arranged along four radial lines, placed at 45 ° to each other, but other arrangements are also possible. The channel release holes 136C may also have a circular or square shape (or other shape) with a diameter or side length comprised between 0.5 μm and 2 μm, and may be arranged at a mutual distance (e.g. between 0.2 μm and 0.4 μm).

In fig. 5C and 6C, a permeable layer 137 is deposited on the surface of the first wafer 130. The permeable layer 137 is, for example, polysilicon deposited by LPCVD (low pressure chemical vapor deposition) and has a thickness comprised between 0.06 μm and 0.2 μm.

As described above, the permeable layer 137 has a structure featuring micro-holes, and is thus permeable to liquid and vapor.

Here, the permeable layer 137 covers the walls and bottoms of the membrane release holes 136A, the inlet release holes 136B, and the channel release holes 136C.

In fig. 5D and 6D, an etchant (e.g., gas phase HF) is used to etch the sacrificial layer 132. For example, time etching is performed.

Due to the permeability of the permeable layer 137, the etchant passes through the permeable layer 137 and removes the portion of the sacrificial layer 132 disposed below the release holes 136A-136C, and partially laterally removes the portion of the sacrificial layer 132 (in a manner not shown in fig. 5D for simplicity).

In this way, the buried cavity 138 is formed below the film release hole 136A.

An inlet groove 170 is formed below the inlet release hole 136B; in fact, they are close enough to each other to remove material of the sacrificial layer 132 along a continuous line (here, a circumference) having an inlet relief hole 136B extending therealong.

Further, connection passages 171 (four in fig. 6D) are formed below the passage release holes 136C. Also here, the channel release holes 136C are close enough to each other such that the material of the sacrificial layer 132 is seamlessly removed along the four radial directions of the channel release holes 136C. Then, a connection channel 171 extends between the buried cavity 138 and the inlet groove 170, and fluidly connects the buried cavity 138 and the inlet groove 170.

This is shown in fig. 6D, where the buried cavity 138, the inlet trench 170 are shown in solid lines for clarity of illustration. The connecting channel 171 is indicated by a dashed line.

Subsequently, as shown in fig. 5E and 6E, the buried cavity 138 is sealed by epitaxially growing a sealing layer 139, which sealing layer 139 covers the carrier layer 133 and fills the release holes 136A-136C.

To this end, for example, a polysilicon layer having a thickness comprised between 2 μm and 25 μm is deposited, which can then be planarized and thinned. In the illustrated embodiment, the silicon of the sealing layer 139 outside of the release holes 136A-136C is completely removed.

In general, removal of the sealing layer 139 outside of the release holes 136A-136C may not be complete, similar to what happens with the sealing layer 39 of FIG. 3E.

Also here, in this step, the permeable layer 137 forms a barrier to polysilicon deposition inside the buried cavity 138 and changes its crystal structure into an impermeable polycrystalline layer having a smaller grain size than the sealing layer 139, and is indicated by 137' hereinafter.

In fig. 5F and 6F, an insulating layer 140 is deposited over the sealing layer 139; the actuator element 145 is formed and an electrical connection is made, as discussed in detail below.

The insulating layer 140 may here also be a TEOS (tetraethyl orthosilicate) layer with a thickness of about 0.5 μm.

The carrier layer 133, the impermeable polycrystalline layer 137', the sealing layer 139 and the insulating layer 140 thus form a film layer 141, which film layer 141 forms a film 142 on the buried cavity 138.

The actuator element 145 may be formed in the manner described in the above aspects with reference to fig. 3F, and thus includes a bottom electrode, a piezoelectric layer, and a top electrode, which are not shown.

Here, as can be seen from fig. 6F, the actuator element 145 has a generally annular shape, which includes a plurality of sections circumferentially spaced apart from one another, and extends along the peripheral (circumferential) edge of the membrane 142 (fig. 6F).

In fig. 5F, a protective layer 147 is deposited over the actuator element 145 and opened where contacts are to be formed, as described previously with reference to fig. 3F.

A metal layer is then deposited and patterned to form contact regions (indicated generally by 148 in fig. 5F, and indicated by 148A for contact with the bottom electrode and indicated by 148B for contact with the top electrode in fig. 6F). Conductive trace 149 and pads 150A, 150B are also formed in a manner apparent to those skilled in the art (fig. 6F).

In fig. 5G, 6G, and 7B, a fluid opening 151 is formed in the first wafer 130.

The fluid openings 151 extend annularly into the membrane layer 141 and are arranged in vertical alignment with the inlet grooves 170. Alternatively, a single fluid opening 151 may be formed in a complete ring shape.

To this end, the film layer 141 is etched in a selective manner, first by etching the protective layer 147 and the insulating layer 140, and then by dry etching the silicon of the sealing layer 139 and the impermeable polycrystalline layer 137' at the inlet release holes 136B (fig. 5F), until the inlet trenches 170 are reached.

Thereby forming the connection channel 171 and allowing the buried cavity 138 to communicate with the outside through the groove 170 (fig. 6G, 7B).

In fig. 5H, 6H and 7C, a bonding and sealing region 153 is formed on the top surface of the wafer 130.

The previously processed cap wafer 155 is then bonded to the top face of the first wafer 130 through the bonding and sealing region 153, thereby forming a composite wafer 160.

In particular, cap wafer 155 has a recess 156 that is larger in area than actuator element 145; the recess 156 is defined by a protruding edge 157 coupled to the bonding and sealing region 153.

Further, cap wafer 155 has been provided with a plurality of through openings 158 disposed outside of recess 156 and spanning protruding edge 157.

The recess 156 and the fluid opening 151 are arranged such that when the cap wafer 155 is bonded to the first wafer 130, the recess 156 is arranged above the actuator element 145, forming an actuator chamber again indicated by 156, and is arranged continuous with the fluid opening 151 through the opening 158. Together, the opening 158 and the fluid opening 151 form a first fluid channel 159, typically a supply channel, which is directly connected to the fluid chamber 138 via an inlet channel 170 and a connecting channel 171.

Cap wafer 155 may also have openings for accessing pads 150 in a manner not shown.

In this way, the actuator chamber 156 is sealed from the exterior and the fluid path defined by the fluid chamber 138, the connecting channel 171 and the first fluid channel 159, and tightly encloses the actuator element 145.

In fig. 5I, 6I and 7D, the first wafer 130 is etched from the back side, for example, by dry etching.

A second fluid channel 162, typically an outlet opening, is thereby formed, completely across the substrate 131 and to the fluid chamber 138, e.g. centrally.

Thus, the fluid chamber 138 is now connected to the outside through both the first fluid paths 171-170-159 and the second fluid passage 162.

The composite wafer 160 may then be diced to form microfluidic devices 165.

After dicing, the microfluidic device 165 of fig. 5I, 6I, and 7D includes a monolithic body 180, the monolithic body 180 having a peripheral surface defining a first face 180A (top face in fig. 5I) and a second face 180B (bottom face in fig. 5I).

The monolithic body 180 is here formed by a substrate 131, a sacrificial layer 132, a carrier layer 133 and an insulating layer 140.

The cap element 181 extends over the monolithic body 180 and is attached to the first face 180A of the monolithic body 180.

In this case, the film 142 is formed of the first polycrystalline region 190 and the second polycrystalline region 191.

The first polycrystalline region 190 includes a filled portion of the impermeable polycrystalline layer 137' having a finer crystal structure and the sealing layer 139 having a coarser crystal structure.

Similar to the sealing layer 139, the second polycrystalline region 191 is formed of the carrier layer 133, surrounds the first polycrystalline region 190, and has a thicker crystal structure.

In use, and in a manner known to those skilled in the art, by actuating the actuator element 145, the membrane 142 may be deflected to draw fluid toward the fluid chamber 138 through the first fluid passage 159 and the connecting passage 170; the liquid may then be pumped outwardly through the second fluid passage 162 (and vice versa).

In particular, during use, actuator chamber 156 is tightly closed and bonding and sealing region 153 safely insulates actuator element 145 from the external environment.

According to various embodiments, an insulating layer may be deposited on the permeable layer prior to forming the sealing layer.

For example, fig. 9A shows a variation of the microfluidic device of fig. 3A-3I, in an intermediate manufacturing step between the manufacturing steps of fig. 3C and 3D.

In detail, here, after formation of the buried cavity 38, an insulating layer 44, for example of oxide, is deposited over the permeable layer 37.

Then, in fig. 9B, a sealing layer 39 is formed and covers the carrier layer 33, the permeable layer 37 and the insulating layer 44, filling the release hole 36.

In this case, permeable layer 37 tends to maintain the previous permeability and crystalline state characteristics.

Since only two wafers are used, the described microfluidic device can be manufactured in a low cost and simpler manner, reducing alignment operations between wafers, and thus having a high yield.

Furthermore, processing only two wafers allows for a smaller number of masks to be used than a three wafer process.

Finally, it is clear that modifications and variations may be made to the microfluidic device and to the manufacturing process described and illustrated herein, without departing from the scope of the present disclosure as defined in the claims.

For example, the inlet and outlet channels may extend from the same face of the body housing the fluid chambers 38, 138.

Furthermore, the microfluidic device may have a single inlet/outlet channel and operate as a buffer in the fluidic circuit.

As shown in fig. 2, the microfluidic device may comprise a plurality of fluid chambers, in particular in the case of manufacturing inkjet heads, arranged side by side and connected to the ends.

For example, the different embodiments described may be combined to provide further solutions. For example, the variations of fig. 9A and 9B are also applicable to the microfluidic devices of fig. 5A-5I.

The microfluidic device (65; 165) may be summarized as comprising: a monolithic body (80; 180) having a peripheral surface defining a first face (80A; 180A); a fluid chamber (38; 138) in the monolithic body; a first fluid opening (51; 151, 170) extending from the peripheral surface of the monolithic body and in fluid communication with the fluid chamber; a cap element (81; 181) extending over the monolithic body and attached to the first face; an actuator chamber (56; 156) extending between the cap element and the first face of the monolithic body; a membrane region (42; 142) in the monolithic body, the membrane region extending between the first face and the fluid chamber; a piezoelectric actuator element (45; 145) extends on a first face over a membrane region inside an actuator chamber, wherein the membrane region (42; 142) comprises at least one first region (90; 190) and one second region (91; 191), the at least one first region (90; 190) comprises a first portion (37; 137') of polysilicon having a first crystal structure facing the fluid chamber and a second portion (39; 139) of polysilicon covering the first portion and having a second crystal structure, and the second region (91; 191) comprises a third portion (33; 133) of polysilicon having a third crystal structure facing the fluid chamber (38; 138), the first crystal structure having a smaller average grain size than the second crystal structure and the third crystal structure.

At least one first region (90, 190) may be surrounded by a second region (91; 191).

The at least one first region (90) may comprise a plurality of first regions and the second region (91) may comprise a plurality of apertures (36), each aperture surrounding a respective first region (90).

The film region (42; 142) may comprise a laminate comprising a carrier layer (33; 133) of silicon, a permeable layer (37; 137) of silicon, a sealing layer (39; 139) of silicon and an insulating layer (44) of insulating material, wherein in the first region (90, 190) the permeable layer (37; 137) may form a first part, the insulating layer (44; 144) may cover the permeable layer (37; 137) and the sealing layer (39; 139) may form a second part and may cover the insulating layer (44; 144), and in the second region the carrier layer (33; 133) may form a third part, the permeable layer (37; 137) may cover the carrier layer (33; 133) and the insulating layer (44) may cover the permeable layer (37; 137).

The second region (91), the sealing layer (39) may cover the insulating layer (44).

The at least one first region (90, 190) may form a step (43) protruding towards the interior of the fluid chamber (38; 138) relative to the second region (91; 191).

The first fluid opening (51; 151) may extend between the fluid chamber (38; 138) and the first face (80A, 180A) of the monolithic body (80; 180), and the microfluidic device (65; 165) may further include a second fluid opening (62; 162) extending through the monolithic body (80; 180) between the second face (80B; 180B) and the fluid chamber (38; 138).

The microfluidic device may form a fluid ejection device, a micropump, a microswitch, a fluid buffer device.

The process for manufacturing a microfluidic device may be summarized as including: forming a sacrificial layer (32; 132) on a semiconductor substrate (31; 131); forming a carrier layer (33; 133) on the sacrificial layer, the carrier layer being of an impermeable semiconductor material; selectively removing the carrier layer to form at least one release opening (36; 136A) extending through the carrier layer; forming a permeable layer (37; 137) permeable to the semiconductor material in the at least one release opening; selectively removing the sacrificial layer (32; 132) through the permeable layer (37; 137) in the at least one release opening and forming a fluid chamber (38; 138); filling the at least one release opening with an impermeable semiconductor fill material, thereby forming a monolithic body (80; 180) having a peripheral surface defining a first face (80A; 180A) and including a membrane region (42; 142) extending between the first face and the fluid chamber; forming a piezoelectric actuator element on a first face of the monolithic body over the membrane region, forming a first fluid opening (51; 151) extending into the carrier layer (33, 133) up to the fluid chamber; and attaching a cap element to the first face of the monolithic body, the cap element having a recess that together with the monolithic body defines an actuator chamber surrounding the piezoelectric actuator element.

The film region (42; 142) may include at least one first region (90; 190) and one second region (91; 191), the at least one first region (90; 190) including a first portion (37; 137') of polysilicon of a first crystal structure facing the fluid chamber and a second portion (39; 139) of polysilicon covering the first portion and having a second crystal structure, and the second region (91; 191) may include a third portion (33; 133) of polysilicon of a third crystal structure facing the fluid chamber (38; 138), the first crystal structure having a smaller average grain size than the second crystal structure and the third crystal structure.

Forming the permeable layer (37; 137) may include depositing a polysilicon layer by LPCVD.

The permeable layer (37; 137) may have a thickness of between 0.06 μm and 0.2 μm.

Filling the at least one relief opening may include epitaxially growing a sealing layer (39; 139).

The sealing layer (39; 139) may have a thickness of between 2 μm and 25 μm.

The process may further include depositing an insulating layer (44) such as silicon oxide after selectively removing the sacrificial layer (32; 132) and after filling the at least one release opening (34; 134).

The various embodiments described above may be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary, to employ concepts of the various patents, applications and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the present disclosure.

Claims (8)

1. A microfluidic device, comprising:

a monolithic body having a peripheral surface defining a first face;

a fluid chamber in the monolithic body;

a first fluid opening extending from the peripheral surface of the monolithic body and in fluid communication with the fluid chamber;

a cap element extending over the monolithic body and attached to the first face;

an actuator chamber extending between the cap element and the first face of the monolithic body;

a membrane region in the monolithic body extending between the first face and the fluid chamber; and

a piezoelectric actuator element extending on said first face, over said membrane region, inside said actuator chamber,

wherein the membrane region comprises at least one first region comprising a first portion of polysilicon facing the fluid chamber and having a first crystal structure and a second portion of polysilicon covering the first portion and having a second crystal structure, and the second region comprises a third portion of polysilicon facing the fluid chamber and having a third crystal structure, the first crystal structure having a smaller average grain size than the second crystal structure and the third crystal structure.

2. The microfluidic device of claim 1, wherein the at least one first region is surrounded by the second region.

3. The microfluidic device of claim 1, wherein the at least one first region comprises a plurality of first regions and the second region comprises a plurality of holes, each hole surrounding a respective first region.

4. The microfluidic device of claim 1, wherein the membrane region comprises a laminate comprising a silicon carrier layer, a silicon permeable layer, a silicon sealing layer, and an insulating layer of insulating material,

wherein at the first region the permeable layer forms the first portion, the insulating layer covers the permeable layer, and the sealing layer forms the second portion and covers the insulating layer,

and, at the second region, the carrier layer forms the third portion, the permeable layer covers the carrier layer, and the insulating layer covers the permeable layer.

5. The microfluidic device of claim 4, wherein at the second region, the sealing layer covers the insulating layer.

6. The microfluidic device of claim 1, wherein the at least one first region forms a step protruding toward the interior of the fluid chamber relative to the second region.

7. The microfluidic device of claim 1, wherein the first fluid opening extends between the fluid chamber and the first face of the monolithic body, the microfluidic device further comprising a second fluid opening extending through the monolithic body between the second face of the monolithic body and the fluid chamber.

8. The microfluidic device of claim 1, wherein the microfluidic device forms a fluid ejection device, a micropump, a microswitch, or a fluid buffer device.

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