Patent Application
20150316425
One subject of the invention is a pump incorporating an assembly for measuring the temperature or flow rate of a fluid. Another subject of the invention is a process for fabricating this pump. The invention especially relates to microassemblies and micropumps, which are microsystems.
MEMS (micro-electromechanical systems) are one example of microsystems. These microsystems differ from macroscopic mechanical systems in their fabrication process, inter alia. These microsystems are produced using the same wafer-scale fabrication processes as those used to produce microelectronic chips. For example, microsystems are produced from wafers of single-crystal silicon that are machined by photolithography and etching (for example deep reactive ion etching (DRIE etching)) and/or structured by epitaxial growth and deposition of metal.
By virtue of these fabrication processes, microsystems are small and generally comprise machined parts or part components with at least one micron-sized dimension. The micron-sized dimension is generally smaller than 200 μm in size and, for example, comprised between 1 and 200 μm in size.
Known pumps comprise:
Such a known pump is described in patent application WO 2011/133014.
Prior art is also known from:
It is necessary to measure with precision the temperature or flow rate of the pumped fluid.
The invention aims to provide such a pump equipped with an assembly for measuring the temperature or flow rate of the pumped fluid while nevertheless not complexifying fabrication of this pump. One of its subjects is therefore a pump as claimed in claim 1.
The measuring assembly incorporated in the above pump allows the pump to be fabricated by machining and joining just two substrates. The above pump therefore remains simple to fabricate even though it incorporates an assembly for measuring the temperature or flow rate of the pumped fluid.
In addition, use of a thermally insulating material housed in a well inside the substrate, and on which the temperature probe is placed, allows the temperature probe to be thermally insulated from the substrate without recourse to a movable membrane suspended above an empty cavity. The measuring assembly thus obtained is therefore more precise than known measuring assemblies because the cross section of the tube or of the chamber through which the fluid passes does not vary above the temperature probe.
Lastly, the above assembly remains simple to produce using the wafer-scale fabrication processes conventionally used to produce microelectronic chips. In particular, this assembly makes it possible to use substrates that are easily machinable and joinable and that are widely used in microelectronics, such as silicon substrates, even if these substrates have a very good thermal conductivity. Moreover, given that the exterior side of the well is flush with that of the substrate, it is simple to connect electrically the temperature probe to other elements produced on the same substrate as there is no height difference to overcome between the temperature probe located on the exterior side of the well and other elements located directly on the substrate.
Embodiments of this pump may comprise one or more of the features of the dependent claims.
These embodiments of the pump furthermore have the following advantages:
Another subject of the invention is a process for fabricating a pump as claimed in claim 9.
Embodiments of this fabrication process may comprise one or more of the features of the dependent claims.
These embodiments of the process furthermore have the following advantages:
The invention will be better understood on reading the following description, which is given merely by way of nonlimiting example and with reference to the appended drawings.
In these figures, the same references are used to designate the same elements.
In the rest of this description, features and functions that are well known to those skilled in the art are not described in detail.
Here, the pump 2 is a microsystem and may therefore be called a micropump. Typically, the largest width of the pump is smaller than 2 or 1 cm. This largest width is generally larger than 1 mm.
Here, the pump 2 is produced from only two substrates 4 and 6, which are bonded one on top of the other. The bonding interface 8 between these two substrates 4 and 6 is shown by an axis in
The substrate 6 is above the substrate 4. The substrate 4 comprises:
The substrate 6 also comprises a horizontal upper side 16 opposite its lower side 12.
The various layers forming each of these substrates will be described in more detail with reference to the process in
The following description of the pump 2 is given with reference to these two figures,
The pump 2 contains a vertical cross-sectional plane 18. Here, this plane 18 is parallel to the Y and Z directions. Below, only the elements of the pump 2 in the left-hand portion of this plane 18 will be described in detail.
The substrate 4 comprises in succession in the flow direction F of the fluid:
One end of the hole 20 opens onto the lower side 14. Here, this end is flared in order to receive, for example, a sleeved tube allowing the pump 2 to be connected to the outlet of a fluidic circuit.
The opposite end of the hole 20 opens onto the upper side 10. This end is blocked by the lower side 12 of the substrate 6.
The hole 28 is the symmetric of the hole 20 with respect to the plane 18.
The channel 22 extends horizontally parallel to the X direction. It extends from an inlet orifice 30 as far as an outlet orifice 32. The orifice 30 opens onto a vertical wall of the hole 20. The orifice 32 opens onto a vertical wall 34 of the chamber 24.
The cross section of the channel 22 is for example rectangular. The upper wall of the channel 22 is here formed by the lower side 12 of the substrate 6. The channel 22 therefore forms a tube.
The channel 26 is the symmetric of the channel 22 with respect to the plane 18. It extends from an inlet orifice 36 as far as an outlet orifice 38. The orifices 36 and 38 open onto a vertical wall 40 of the chamber 24 and onto the hole 28, respectively. The wall 40 is the symmetric of the wall 34 with respect to the plane 18.
The chamber 24 extends on either side of the plane 18. Here, this chamber 24 is a parallelepiped that mainly extends horizontally. The chamber 24 defines a hollow space formed by bringing together:
The cavity is bounded in the substrate 4 by a vertical walls, especially including the walls 34 and 40, and by a horizontal wall 42 also called the bottom of the cavity.
The vertical walls and the bottom of the cavity are integrally formed with the substrate 4 and are unable to move.
The aperture of this cavity opens onto the upper side 10.
Here, the interior of the chamber 24 is empty, i.e. especially devoid of anti-return valve.
The membrane 44 covers the entirety of the aperture of the cavity in order to form the leak-tight chamber 24. The chamber 24 is leak-tight to the pumped fluid.
The membrane 44 deforms elastically between a suction position and an expulsion position. When it moves from the expulsion position to its suction position, it sucks fluid into the chamber 24 via the channel 22. When it moves from its suction position to its expulsion position, it expels fluid from the interior of the chamber 24 toward the exterior via the channel 26.
In
In this embodiment, in the suction position, the membrane 44 is deflected into the interior of the substrate 6. In this position, the apex of the membrane 44 is retracted inside the substrate 6 relative to its location in the rest position of the membrane.
In the expulsion position, the membrane 44 is deflected into the interior of the cavity formed in the substrate 4. The apex of the membrane 44 is then located inside the cavity of the substrate 4. This movement of the membrane on either side of its rest position allows the volume pumped to be maximized and therefore the capacity of the pump to be increased.
Here, the membrane 44 is integrally formed with the substrate 6. Its periphery is therefore secured with no degree of freedom to the rest of the substrate 6.
The pump 2 also comprises an actuator 46 capable of converting the energy that it receives into a movement of the membrane 4 between its suction and expulsion positions. For example, the actuator 46 is a conventional actuator such as an electrostatic actuator or a piezoelectric actuator or a bimetallic actuator, such as a bimetallic strip, or a shape memory actuator or a thermo-pneumatic actuator or an electromagnetic actuator.
In certain cases, the actuator is completely or partially merged with the membrane 44. This is the case when the membrane 44 is made of a piezoelectric material or by a bilayer complex in which each layer has a different expansion coefficient from the other in order to form a bimetallic strip. The energy received by the actuator may be electrical energy or thermal energy. Thermal energy is for example used when the actuator comprises a bimetallic complex. Of course, the actuator according to the invention may also be a device external to the membrane and connected to the latter by a mechanical linking element.
The channel 22 comprises an anti-return valve 50 able to prevent or limit the flow of the fluid in the direction opposite to the direction F. This valve 50 is located upstream of the orifice 32 and downstream of the orifice 30 inside the channel 22. It is movable between an open position and a closed position. In the open position, it allows fluid to flow more easily in the direction F than in its closed position. In its closed position, it prevents the fluid from flowing in the opposite direction to the direction F. Here, in its closed position, the valve 50 extends parallel to the plane 18. In its open position, shown in
The valve 50 is a flexible tongue with the same cross section as the cross section of the channel 22 but slightly smaller in size. Here, the valve 50 therefore has a rectangular cross section. The height of this valve hc in the Z direction and its width Lc in the Y direction are smaller, for example by at least 0.1 μm or 1 μm, respectively, than the height and width of the channel 22 in the same directions.
The valve 50 moves between its open and closed positions via rotation about an axis secured to the substrate 4. Specifically, a proximal side of the valve 50 is anchored with no degree of freedom to one of the walls of the channel 22. Here, this proximal side is anchored to a vertical wall of the channel 22. Thus, the valve 50 is integrally formed with the substrate 4.
The valve 50 is flexible in order to be able to deform elastically between its open and closed positions under the action of the flowing fluid alone. For this purpose, the thickness ec of the valve 50 is at least five or ten times smaller than its width Lc or its height hc. Typically, the width Lc and height hc are larger than 50 or 100 μm. Therefore, typically, the thickness of the valve 50 is smaller than 10 μm or 5 μm.
In its rest position, i.e. in the absence of a difference in the pressure upstream and downstream of the valve 50, the latter is in a position of rest located, for example, between its open position and its closed position.
In the closed position, the free periphery of the valve 50 is separated from the walls of the channel 22 and from the lower side 12 of the substrate 6 by a play. For example, this play is larger than or equal to 0.1 or 1 μm. The free periphery of the valve 50 corresponds to the periphery of the valve 50 minus its anchored side.
More precisely, here, the free periphery of the valve 50 is formed by:
In this embodiment, in order to suppress almost completely leaks via this play, at least during operation, the channel 22 comprises a shoulder 54 against which the free periphery of the valve 50 directly bears mechanically when the latter is in its closed position. This shoulder almost completely obstructs the play when the valve 50 is in its closed position. The shoulder 54 is located upstream of the valve 50.
For example, the shoulder 54 is formed by two abutments 56 and 58. The abutments 56 and 58 are secured, with no degree of freedom, to the substrates 4 and 6, respectively.
Here, the abutment 56 has an “L” shape. The horizontal arm of the “L” extends parallel to the Y direction over the entire length of the bottom of the channel 22. The vertical arm of the “L” extends parallel to the Z direction along the vertical wall of the channel 22, facing the wall of the channel 22 to which the proximal side of the valve 50 is anchored. Here, the vertical arm of the “L” extends over at least 80% of the height of the channel 22.
In the closed position, the lower and distal sides of the valve 50 mechanically rest against the horizontal and vertical arms of the “L” of the abutment 56, respectively.
The abutment 58 extends parallel to the Y direction along the lower side 12. This abutment 58 sides the horizontal bar of the “L” of the abutment 56. Its length is larger than 70 or 80% of the width of the channel 22 in the Y direction. In the closed position, the upper side of the valve 50 rests against the abutment 58.
The channel 26 comprises an anti-return valve 60. In
In its closed position, the free periphery of the valve 60 bears directly against a shoulder 62 of the channel 26 located immediately upstream of this valve 60. The shoulder 62 is for example identical to the shoulder 54.
The pump 2 also comprises an assembly 64 for measuring the flow rate of the pumped fluid. This assembly is described in more detail with reference to
The assembly 64 is connected to an electronic processing unit 65 able to calculate the flow rate from measurements taken by the assembly 64.
In this description, the expression “thermally insulating material” is understood to mean a material the thermal conductivity of which at 20° C. is lower than 5 W·m−1·K−1, and preferably lower than 2 or 1 W·m−1·K−1.
The probe is the active component that is sensitive to temperature. In other words this is the component that allows the measurement to be carried out. In contrast, the probe does not necessarily comprise a control/processing component allowing the signals generated by the probe to be processed. This control/processing component may be placed elsewhere than on the well. Thus, when the probe is said to be placed on the thermally insulating material, this does not necessarily mean that the control/processing component allowing the probe signals to be processed is also placed on this thermally insulating material. Preferably, each probe is entirely and only placed on the thermally insulating material.
The well 66, filled with thermally insulating material, allows the probes 68 and 69 and the resistor 70 to be thermally insulated from the substrate 6. Here, this substrate 6 is made of a thermally conductive material. In this description, the expression “thermally conductive material” is understood to mean a material the thermal conductivity of which at 20° C. is higher than 50 W·m−1·K−1, and preferably higher than 100 or 150 W·m−1·K−1. For example, in this description, the substrate 6 comprises a layer made of silicon, inside of which most of the well 66 is dug.
Here, the well 66 is essentially parallelepipedal in shape. It is dug into the side 12 of the substrate 6. In addition, it is completely encircled, in the XY plane, by the substrate 6.
The depth of the well 66, measured from level with the side 12, is larger than 10 μm and typically larger than 50 or 100 μm. The depth of the well 66 is however smaller than the thickness of the substrate 6 in order to leave a band of the substrate 6 under the well 66. The thickness, in the Z direction, of this band under the well 66 is larger than 100 μm, and preferably larger than 200 or 500 μm.
The well 66 is completely filled with a thermally insulating material 72. For example, the material 72 is silicon oxide glass or borosilicate glass or a polymer.
The material 72 has an exterior side 74 that is flush with the side 12 of the substrate 6. Here, these sides 72 and 12 extend in the same plane to within plus or minus 0.5 μm, and preferably to within plus or minus 0.1 μm.
The thickness of the material 72 is here equal to the depth of the well 66. Thus, to improve the thermal insulation, the well 66 is preferably as deep as possible.
By way of illustration, the length in the X direction of the well 66 is larger than 50 μm and, preferably, larger than 100 or 200 μm. Its width in the Y direction is larger than 50 μm and, preferably, larger than 100 or 200 μm. Thus, the area of the side 74 is larger than 500 or 1000 μm2.
The well 66 is dug into the substrate 6 in a location such that the side 74 makes direct contact with the fluid the flow rate of which must be measured. In this example, the side 74 opens onto the interior of the hole 20.
The probes 68 and 69 are able to convert a temperature variation into a measurable variation in an electrical property. For example, the probes 68 and 69 are thermistors or resistance thermometers. They are therefore essentially formed from a block of material the resistance of which varies as a function of temperature. For example, these resistors are bands made of a material chosen from the group containing silver, copper, nickel, gold, platinum, tungsten, titanium and aluminum, or even of silicon.
The probes 68 and 69 are entirely placed on the side 74 in order to be completely thermally insulated from the substrate by the material 72. Here, the probes 68 and 69 are placed one after the other in the flow direction F of the fluid. Each of these probes is electrically connected by a wired connection to the processing unit 65.
The heating electrical resistor 70 is placed directly on the side 74 between the probes 68 and 69 in the direction F. This resistor heats the fluid when commanded to do so by the unit 65. Preferably, the resistor 70 is entirely placed on the side 74 in order to limit the power consumption of the assembly 64. Here, the resistor 70 is supplied with power by the processing unit 65.
The probes 68 and 69 and the resistor 70 together form a flow rate sensor that delivers signals depending on the flow rate of the fluid pumped by the pump 2.
The processing unit 65 calculates the flow rate of the fluid from temperatures measured at the same time by the probes 68 and 69, respectively. This unit 65 therefore for example functions as described in the following B1 patent: US 2009/078040 or in the following B2 patent application: US 2006/000270. Alternatively, or at the same time, the unit 65 may also calculate the temperature of the pumped fluid from the measurements taken by the probes 68 and 69.
The operating mode of the pump may be deduced from the above explanation and, if necessary, from the explanation given in patent application WO 2011/133014 A1. The operating mode of the assembly 64 is explained in the above B1 and B2 patent applications and will therefore not be described here in further detail. However, it will be noted that the absence of a membrane allows the precision of the measurement of flow rate and temperature to be increased.
A process for fabricating the pump 2 will now be described with reference to the process in
The process in
The phase 80 is a phase of fabrication of the substrate 4 whereas the phase 82 is a phase of fabrication of the substrate 6.
At the start of the phase 80, in a step 86, the substrate 4 is provided. Here, it is a question of a BSOI (bonded silicon-on-insulator) substrate. The substrate 4 comprises a layer 88 (
Next, in a step 94, an oxide layer is deposited on the upper side. For example, this deposition is carried out by plasma-enhanced chemical vapor deposition (PECVD). Next, a step of lithography then etching of this oxide layer is carried out to form a mask 96 (
In a step 98, an oxide layer is deposited on the lower side of the substrate 4. For example, this deposit is produced using a PECVD process. Next, lithography followed by etching of this layer is carried out to form a mask 100 that defines the location of the hole 20 (
In a step 102, a lithography step is carried out in order to form a resist mask 104 (
In a step 106, the upper side is etched through the mask 104 (
In a step 108, the mask 104 is removed (
Next, etching is carried out from the upper side using the mask 96. This etching is for example carried out using a DRIE process. This etching allows the abutment 56 to be formed.
In a step 110, the valve 50 is freed by implementing a wet or vapor phase HF etch (
In parallel, at the start of the phase 82, in a step 116, the substrate 6 is provided (
In a step 124, the measuring assembly 64 is produced (
In a step 128, the abutment 58 (
In a step 132, a metal layer 134 (
Lastly, in a step 136, the membrane 44 is formed by etching the lower side of the substrate 6 through the mask 130 (
Next, once the substrates 4 and 6 have been fabricated, in a step 140, the upper side 10 of the substrate 4 is bonded to the lower side 12 of the substrate 6 (
Next, in a step 152, a rigid sheet 154 made of glass is bonded to the side 12 of the layer 118. This sheet covers the well 66 (
Next, in a melting step 156, a heat treatment is applied to the sheet 154. During this heat treatment, the melting point of the sheet 154 is exceeded so that the sheet melts and fills the well 66 (
In a step 158, the side of the substrate is thinned then polished so as to reexpose the side of the layer 118 and to planarize it. Preferably, the thinning is carried out by grinding. It may also be carried out chemically. The polishing is for example chemical-mechanical polishing. At the end of this step 158 a well 66 filled with material 72 is obtained.
Lastly, in a step 160, the probes 68 and 69 and the resistor 70 are formed on the side 74. For example, the probes in the resistor are fabricated by successively depositing and etching layers on the side 74.
A second process for fabricating the assembly 64 will now be described with reference to the process in
Thus, below, the steps used to fabricate the well are not described in detail.
In a step 170, trenches are dug in the layer 118 so as to bound vertical pillars 172 (
Next, in a step 174, a heat treatment at between 1100 and 1200° is applied in order to oxidize the pillars 172. This oxidation step is carried out so as to grow a layer of silicon oxide that is about 10 μm thick. This layer 174 of silicon oxide then completely fills the trenches that separate the pillars 172. In addition, this thermal oxidation completely converts the pillars 172 of silicon into silicon oxide. Thus, at the end of step 174, a well 66 filled with silicon oxide is obtained.
Lastly, in a step 178, the probes 68, 69 and the resistor 70 are formed on the side 74 (
A third process for fabricating the assembly 64 will now be described with reference to the process in
In a step 180, a well 66 filled with porous silicon 182 is formed. For example, to do this, anodization or dopant implantation is used. More details on this step are given in article A2. The depth of the well is larger than 10 μm and, generally, smaller than 200 μm.
Next, in a step 184, the silicon is oxidized by applying, for example, a heat treatment. This oxidation causes an oxide layer 186 to appear the thickness of which is typically smaller than 5 μm. Given the porous structure of the porous silicon 182, almost all of the porous silicon 182 is oxidized in this step. In addition, the pores of the porous silicon fill with silicon oxide. At the end of this step 184, a well 66 filled with silicon oxide is obtained. Thus, preferably, step 184 is carried out until more than 90% or 95% or 99% or all of the porous silicon 182 has been oxidized. However, as a variant, it is also possible to oxidize only some of the porous silicon 182. For example, only a surface layer of at least 10 μm in thickness of the porous silicon is completely oxidized.
Lastly, in step 188, the probes 68 and 69 and the resistor 70 are formed, for example as described with reference to step 160.
During operation of the pump 200, the actuators 206, 44 and 208 are actuated in succession in this order so as to move a quantity of fluid from the channel 22 into the chamber 24 then from the chamber 24 into the channel 26. Once the membrane 204 has returned to its rest position, the membrane 202 is actuated again in order to expel a new quantity of fluid into the chamber 24. The pump 200 does not require any anti-return valves in order to operate. A process for fabricating this pump 200 may easily be deduced from the explanation given regarding fabrication of the pump 2.
Many other embodiments are possible. For example, other thermally conductive materials may be used for the substrates. Thus, the thermally conductive material may be gallium or gallium nitrate. The thermally conductive material may be homogenous or heterogeneous. It is considered to be heterogeneous when it is formed by an assembly of a plurality of different homogenous materials. This is the case of the substrate 6 described with reference to the process in
Similarly, other thermally insulating materials may be used to fill the well. For example, the material may be a polymer, such as a polymer filled with graphite in order to limit mechanical strain due to differences in the expansion coefficients of the substrate and polymer. The thermally insulating material may also be porous silicon directly. Just like the material of the substrate, the thermally insulating material may be homogenous or heterogeneous. It is heterogeneous when the thermally insulating material is formed by an assembly of a plurality of different thermally insulating materials. For example, it may be formed by an assembly of a plurality of layers of various thermally insulating materials.
The substrate 4 may be bonded to the substrate 6 using various methods such as:
The substrate 6 is not necessarily added to the substrate 4. It may instead be deposited on the substrate 4 in the form of a layer itself deposited on a sacrificial layer filling the various channels and the cavity of the substrate 4. Then, after the substrate 6 has been deposited, the sacrificial layer is removed so as to free the channels and the chamber of the pump.
The temperature probes and the heating resistor may be fabricated independently of the well filled with thermally insulating material, then subsequently added to the exterior side 74.
The measuring assembly described above may be used in other pumps. For example, it may be used in the pump described in the above B1 patent application. It 40 may also be used in pumps devoid of anti-return valves, such as the pump 200. The assembly may also be used in other systems that are not necessarily pumps. For example, the assembly may be used simply to measure the flow rate flowing through a microfluidic duct of a device. The assembly 64 may also be used to measure only the temperature of the fluid. In this case, the resistor 70 may be omitted and a single temperature probe may suffice.
The pump may also be produced by joining more than two substrates.
The measuring assembly may be placed elsewhere in the pump. For example, the measuring assembly may be placed so that the temperature probes and the side 74 are flush in either one of the channels of the pump or in the chamber 24. The measuring assembly may also be produced in the substrate 4 rather than in the substrate 6.
In another embodiment, the channels and the cavity are not dug but formed by depositing successively structured layers one on top of the other.
As a variant, the suction position of the membrane 42 or, alternatively, its expulsion position may be the same as its rest position.
The cavity may have the same cross section as the channels 22 and 26. In this case, the cavity is distinguishable from the channels only insofar as it is covered by the movable membrane, which is not the case for the channels.
The pump 2 may also comprise a plurality of intake channels and a plurality of discharge channels fluidically connected to the same chamber 24. In this case, each of these intake and discharge channels comprises its own anti-return valve.
In another embodiment, the movement of each valve is actuated by an electrical or thermal actuator. For example, the actuator is based on a similar principle to that employed to move the membrane 44.
In a simplified embodiment, the shoulders are omitted. Specifically, if the play between the free periphery of the valve and the walls of the channel is sufficiently small, a negligible leakage of liquid is obtained even in the absence of the shoulders.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1262050 | Dec 2012 | FR | national |
This application is a U.S. National Stage of International Application Number PCT/EP2013/076282, filed Dec. 11, 2013, which claims the benefit of the priority date of French Patent Application FR 1262050, filed Dec. 14, 2012, the contents of which are herein incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/076282 | 12/11/2013 | WO | 00 |
