IE65193B1 - Improved micropump - Google Patents

Abstract

The micro-pump uses a piezo-electric pad (13) to produce deformation of a plate (12), causing variation of volume in a chamber (15) formed inside a plate (11). The plate is of a material which can be photolithographically machined. The pump outlet (3) is closed, selectively, by a membrane check-valve (18). The outlet membrane has a layer of oxide (17) that provides a pretension on closing, so the check-valve has a regulatory effect on pump operation, making flow almost independent of outlet (3) pressure.

Description

The present invention is concerned with a micropump including a first thin slab of a material which can be etched by photolithography techniques in such a manner as to define with at least a second thin support slab bonded by one face to the first thin slab, a pumping cham5 ber, a first valve of the nonreturn type through which said pumping chamber can communicate selectively with an inlet of the pump and a second valve of the membrane type through which said pumping chamber can communicate selectively with an outlet of the pump, means being provided for generating a periodical variation of the volume of said pumping >0 chamber, the second valve being controlled by the pressure of the fluid to be discharged by the pump.

Such pumps can be used in particular for the in situ administration of medicinal drugs, the miniaturization of the pump enabling the patient to carry it on his body, or even possibly to receive a pump di15 rectly implanted inside his body. Furthermore, such pumps make possible an accurate metering of small amounts of the fluid to be administered.

Micropumps of this type are known from an article entitled "A piezoelectric micropump based on micromachining of silicon" and published in ’’Sensors and Actuators" No 15 (1988), pages 153 to 167, in which H.

Van Lintel et al. give a description of two embodiments of a micropump, each including a stacking of three thin slabs, i. e. a thin machined silicon slab placed between two thin glass slabs.

The thin silicon slab defines a pumping chamber with one of the thin glass slabs, of which the portion coinciding with this chamber can be deformed by an actuator member, which in this case, is a piezoelectric crystal. The latter includes electrodes which, when they are connected to a source of alternating tension, cause the deformation of the crystal and consequently of the thin glass slab, to vary as a result the volume of the pumping chamber.

The pumping chamber is connected on each side to respective nonreturn valves formed in the silicon and the seats of which are provided by the other thin glass slab.

An analysis of the operations of this pump according to a first embodiment (figure la) described in the above-mentioned article shows that this pump delivers a flow of fluid which is strongly dependent upon the outlet pressure over the whole operational range. In fact, it - 2 was found that this relationship output - pressure is substantially linear, with the output decreasing as the pressure increases.

In other words, such a pump is of no use for the medical applications mentioned above, in which, on the contrary, the output of the pump must be independent of the pressure, at least in the normal operational range of the pump.

This is why the authors propose in the same article (second embodiment shown in figure lb) to complement the assembly just described with a regulator valve which is placed between the second valve downstream of the pumping chamber and the outlet of the pump. This valve isolates the pump from the outlet when it is closed.

Furthermore, this regulator valve is biased into the closed position by a certain force, so that the outlet pressure can open the valve only when it exceeds a certain value. As a result, in the useful operational range of the pump, the output is substantially independent of the outlet pressure, as long as the regulator valve is not held open by the outlet pressure.

If by means of this second construction, one obtains a favourable output - pressure diagram, it should however be noted that a pump constructed in this manner still has dawbacks. The regulator valve increases the bulk of the pump, because it must be made within the thin silicon slab and thus requires an additional surface. This results in an increase of the cost of the pump.

It should also be noted that the regulator valve increases the complexity of the pump and thus the risks of a defective functioning or of being discarded during quality control.

Mention should be made of the patent FR 2 127 774 describing a conventional membrane type pump which does not use the etching by photolithography techniques of thin slabs of silicon and which includes a pumping chamber located between an inlet valve and an outlet valve. The outlet channel of this pump is furthermore connected to a chamber located on the opposite side of the membrane, relatively to the pumping chamber. Accordingly, the fluid output of this pump is strongly dependent on the outlet pressure.

The present invention is aimed at providing a micropump of the type described above, which avoids the drawbacks indicated above, while ex- 3 hibiting favourable output versus outlet pressure characteristics within the useful operational range of the pump.

To this end, the invention is characterized in that said outlet is in direct communication with a volume isolated from said pumping chamber by said second valve and located on the same side of this valve as the channel through which this valve communicates with the pumping chamber, so that the pressure prevailing respectively in this pumping chamber and in this volume act in a direction to open said second valve, and in that said second valve is in open communication with said first valve through said pumping chamber, so that during the discharge phase of the pump, this chamber communicates directly with said outlet through said second valve in its open position.

Owing to these characteristics, said second valve not only ensures a regulation of the flow in such a manner as to render the same substantially independent of the pressure in the outlet of the pump, throughout its normal operational range, but also acts as a closing member for the pumping chamber during the intake phase of the pump.

Other characteristics and advantages of the invention will become apparent from the following description of several embodiments of the micropump according to the invention, which description is made with reference to the appended drawings, in which : - figure i is a schematic cross-sectional view of a micropump according to the invention; - figure 2 is a bottom view of the thin intermediate slab of the pump shown in figure 1; - figure 3 is a view showing the lower face of the intermediate thin slab of a micropump constructed according to a second embodiment of the invention, the view being taken along line III-ΠΙ of figure 4; - figures 4 and 5 are cross-sectional views taken respectively along lines IV-IV and V-V of figure 3; - figure 6 is a cross-sectional view of a micropump constructed according to a third embodiment of the invention; - figure 7 is a view of the lower face of the intermediate thin slab of the pump shown in figure 6, this view being taken along line VII-VII of figure 6; - figure 8 is a view of the lower face of an intermediate thin slab be- 4 longing to a micropump constructed according to a fourth embodiment of the invention; - figures 9 and 10 are cross-sectional views taken respectively along lines IX-IX and X-X of figure 8; - figure 11 is a partial cross-sectional view of a fifth embodiment of the invention; - figure 12 is a partial top view of the micropump shown in figure 11; et - figure 13 is a graph illustrating the variation of the output versus the measured pressure of a micropump constructed according to the invention, the inlet pressure being equal to zero.

Reference will be made first to figures 1 and 2 which represent a first embodiment of the micropump of the invention.

It should be noted that for sake of clarity, the thickness of the various thin slabs forming the micropump has been considerably exaggerated in the drawings.

The micropump of figures 1 and 2 includes a thin base slab 1 made for example of glass, which is provided with two channels 2 and 3 extending therethrough to provide respectively the intake conduit and the discharge conduit of the pump. These channels 2 and 3 are in communication respectively with the connectors 4 and 5.

The connector 4 is connected to a conduit 6, which in turn is connected to a container 7 which contains the substance to be pumped. The container is closed by a cap having a through hole, with a moving piston isolating the useful volume of the container 7 from the outside. This container can contain a medicinal drug, for example when the pump is used for administering accurately metered amounts of this drug into the body of a human. In this application, the micropump can be carried by the patient on his body, or be implanted inside his body.

The discharge connector 5 can be connected to an injection needle (not shown), via a conduit 10.

This method of using the micropump of the invention is particularly well suited for the treatment with peptides of certain types of cancers, wherein preferably precisely metered small amounts of the medicinal drug are administered repeatedly at regular intervals of time. Another application envisaged is the treatment of diabetics, by the pe- 5 riodical administration of small amounts of medication throughout the day, the doses being adjusted by various means known per se, involving the measurement of the sugar level in the blood and the automatic actuation of the pump in such a manner that an appropriate dose of insulin be injected.

A thin slab 11 made of silicon or some other material which can be etched by photolithography techniques is bonded to the thin glass slab 1. This thin slab of silicon receives on top of it a thin closing slab of glass 12, of which the thickness is such that it may be deformed by an actuator member 13, which in the embodiment of the invention described here is a piezoelectric wafer provided with electrodes 13a and 13b connected to a generator of alternating tension 14. This wafer may be the one manufactured by the firm Philips under the reference PXE-52 and it can be bonded to the thin slab 12 by means of an appropriate adhesive.

By way of example, the intermediate thin slab 11 made of silicon can have a <100> crystalline orientation, in order to facilitate the etching and ensure the solidity required. The thin slabs 1 and 12 are preferably carefully polished.

To start, the thin slabs 11 and 12 define together a pumping chamber 15 (see also figure 2), for example of a circular shape, this chamber being located beneath an area of the thin slab 12 which is deformable by the actuator member 13.

Between the intake conduit 2 and the pumping chamber 15, there is provided a first valve 16 of the nonreturn type, made in the thin slab of silicon 11. This valve is located beneath the pumping chamber and includes a membrane 16a of a generally circular shape provided at its center with an orifice 16b extending therethrough, which is of a square shape in the embodiment illustrated. On the side of the channel 2, the valve 16 includes a rib 16c of an annular shape and of an approximately triangular cross-section. This rib 16c surrounds the opening 16b and is coated with a thin film of oxide 17, also obtained by photolithography techniques. This layer of oxide produces an extra thickness which imparts to the membrane 16a a certain level of prestressing or pretensioning when the top of the rib 16c is applied against the thin glass slab 1, the latter acting as a seat for the valve 16. - 6 The discharge channel 3 of the pump communicates with the pumping chamber 15 via a valve 18, of which the construction is identical to that of the valve 16, except however that owing to the difference of the size of the layer 17 with that of valve 16, the prestressing provided by this oxide layer 17 can be different from that prevailing in the valve 16. Furthermore, one can see in figure 1 that this valve is devoid of any central orifice such as the orifice 16b of valve 16.

It will be noted that the pumping chamber communicates with the valve 18 via an orifice 19 and a passage 20, which are both made in the thin silicon slab 11.

The valve 18 also has a partly coated membrane 18a including an annular rib 18c coated with a layer of oxide 17 and defining above the channel 3 a volume 18d in which prevails the outlet pressure. The oxide layer of the membrane 18a creates shearing forces therein, which induce a bulging of this membrane (the oxide layer is on the convex side of the membrane). This causes an additional pretensioning of the valve in the closing direction, relatively to the pretension induced by the layer of oxide covering the rib 18c. When the valve 18 is open, this volume is in direct communication with the intake valve 16 via the pumping chamber 15, with the result that a minimum resistance to flow is offered to the fluid discharged from the pump during the discharge phase. Furthermore, when the valve 18 is closed, the outlet pressure acts only on a small surface of the membrane 18a, by comparison with the significantly larger surface on which can act the pressure prevailing in the pumping chamber. This has the effect of regulating the output which becomes substantially independent of the outlet pressure (see figure 13), this effect being due to the pretensioning brought about by the layer of oxide 17.

For illustrative purposes, the thin slabs 1, 11 and 12 can have a thickness respectively of about 1 mm, 0.3 mm and 0.2 mm, for a surface area of the thin slabs in the order of 15 to 20 mm.

Furthermore, the thin slabs can be fastened together by various known fastening techniques, such as for example adhesive bonding or the technique known as anodic welding.

Figures 3 and 5 show a second embodiment of the micropump of the invention, which is in substance of the same construction as that of the micropump shown in figures 1 and 2. Identical components are indicated by the same reference numerals as previously. However, it differs in that the annular chamber 16e (figure 4) which surrounds the annular rib 16c of the intake valve 16 is connected not only to the intake 5 channel 2, but also to a compensation chamber 21 defined in the thin slab 11 above the valve 18, and closed by the thin closing slab 12, the latter covering here the totality of the surface of the pump. This connexion is made via a communication channel 22 made in the silicon and comprised of three branches 22a, 22b et 22c arranged perpendiculario ly in the thin slab 11. It is to be noted, that the branch 22c of this channel is not at the same level as the two other branches 22a and 22b, and that the branches 22b and 22c communicate together through a communication orifice 23 provided in the thin slab 11. Furthermore, the branch 22c (figure 5) is in communication with the intake channel 2 via a communication orifice 24 which connects this branch to a small cavity 25 hollowed in the thin silicon slab 11 just above the intake channel 2.

The channel 22 is designed for making the channel 2 of the pump communicate with the chamber 21 provided above the membrane 18a of the discharge valve 18, in such a manner as to maintain the latter closed in the case of an excessive pressure occurring at the inlet of the pump. Hence, this arrangement acts as a safety against excessive pressures.

Figures 6 and 7, to which reference will now be made, illustrate a 25 third embodiment of the micropump according to the invention. In this case, the basic construction described above remains the same, except the fact however that the pumping chamber 15 is arranged in an asymmetrical manner relative to the intake and discharge valves.

This pump is also comprised of three thin slabs, specifically of a thin support slab 26 made of glass for example, of a thin slab 27 made of silicon for example or of some other suitable material, and of a thin closing slab 28 made of glass for example, which is deformable in an area located above the pumping chamber 15, by a piezoelectric wafer 29, or by some other appropriate actuator means.

The pumping chamber 15 is defined by the thin slab 27 and by the thin slab 28, these two thin slabs also defining an inlet chamber 30 - 8 (which can be seen only in figure 6) into which opens an inlet orifice 30a formed in the thin slab 28.

The chamber 30 communicates with a channel 31 (which can only be seen in figure 7) located in the upper part of the thin slab 27, and this channel 31 communicates with a second channel 32 which is provided in the thin slab 27 on the side of the thin slab 26. The channel 32 opens into an annular chamber 33 of an intake valve 34, of which the construction is identical to that of the valve 16 described previously. This intake valve communicates with the chamber 15, via a central orifice 35.

Chamber 15 communicates also with a discharge valve 36 via an orifice 37 and a channel 38 both provided in the thin slab 27. Furthermore, the discharge valve 36 which is designed for closing an outlet orifice 36a (figure 6) is constructed in the same manner as the discharge valve of the preceding embodiments, except that it includes a boss 39 on the side of the membrane opposite to the closing rib of the valve. This boss 39, which is located in the middle of the membrane, is designed for limiting its amplitude of movement, by acting as a stop for the thin slab 28 in case of the discharge pressure exceeding a predetermined admissible value.

In the arrangement which has just been described, the inlet orifice 30a opens into the chamber 30 which is located above the discharge valve 36 and which therefore acts as a compensation chamber, as was the case of chamber 21 of the preceding embodiment. Consequently, this construction also provides a protection against excessive pressures.

Reference will now be made to figures 8 and 10, which represent a fourth embodiment of the invention.

In this case, the micropump also comprises three thin slabs 40, 41 and 42. The thin slab 40 is made of glass for example and includes a discharge channel 43. The thin slab 41 is made of silicon or of some other suitable material and is etched by photolithography techniques so as to define a pumping chamber 44, an intake valve 45 and a discharge valve 46 communicating with the pumping chamber 44 via the conduits 47 and 48, respectively.

In the present embodiment, an actuator member such as a piezoelectric wafer 49 is placed directly upon the thin silicon slab 41 in the area coinciding with the pumping chamber 44, and to achieve a pumping action, this thin slab 41 is deformed to modify the volume of the pumping chamber. Furthermore, it is desirable to provide between the thin slab 41 and the crystal 49 a thin layer of silicon oxide 49a, so as to insulate the corresponding electrode of the wafer from this thin slab.

The thin slab 42 covers only partly the slab 41 and it includes an intake orifice 50 which opens on an annular compensation chamber 51 arranged above the discharge valve 46. It can be seen that this valve is provided with a boss 52 for limiting the amplitude of the membrane of this valve, the boss being arranged for abutting against the lower face of the thin slab 42, should the discharge pressure beneath the valve become excessive.

It will also be noted that the positions of the intake and discharge valves 45 and 46 are inverted, the intake valve having its seat provided for by the thin slab 42, whereas the seat of the valve 46 is provided for, as is the case of the other embodiments, by the thin slab 40. This arrangement has no particular influence on the functioning of the pump.

Another embodiment of the invention is shown in figure 11, in which, above the discharge valve 53, there is provided a chamber 54 which is closed by a connexion member 55 made for example of a plastic material and adhesively bonded to the thin silicon slab 56. Thus, the chamber 54 which actually communicates with the intake of the pump is totally insulated from the outer atmosphere. This construction has the advantage that it makes it possible to avoid the use of a specific closing slab.

Both in the pump according to figures 8 to 10 (conduit 57) and in that of figure 11 (chamber 54), the discharge valves are connected to the inlet of the pump so as to ensure in these cases also, a protection against excessive pressures.

We shall now examine the functioning of the micropump according to the invention, with reference in particular to the diagram of figure 13 which illustrates the variation of the output as a function of the pressure inside the discharge channel.

It will be noted that the functioning is identical in all the embodiments described above. For convenience sake, the following descrip10 tion will be limited solely to the embodiment of figures 1 and 2.

When no electric tension is applied to the piezoelectric wafer 13, the intake and the discharge valves 16 and 18 are in their closed position. When an electric tension is applied, the piezoelectric wafer 13 is deformed to deflect the thin slab 12 inwards. An increase in the pressure then occurs in the pumping chamber 15, which causes the opening of the discharge valve 18, as soon as the force acting on the membrane and produced by the pressure in the pumping chamber 15 exceeds the difference between the force created by the pretensioning of the valve 18 provided by the silicon oxide layer 17 and the force resulting from the pressure in the outlet channel 3. The fluid contained in the pumping chamber is then expelled into the outlet channel 3 by the displacement of the deformable area of the thin slab 12. During this phase, the intake valve 16 is kept closed by the pressure prevailing in the pumping chamber 15. The fluid flows without encountering any noticeable resistance, owing to the fact that the pumping chamber 15 is then in direct communication with the outlet channel 3.

Conversely, when the application of the electric tension is discontinued, the piezoelectric wafer 13 resumes its initial shape, or even deforms in the opposite direction, so that the pressure in the pumping chamber 15 decreases. This causes the closing of the discharge valve 18, as soon as the force due to the pressure in the pumping chamber 15 is lower than the difference between the force created by the pretensioning of the valve and the force due to the pressure in the discharge channel 3. The opening of the intake valve 16 takes place as soon as the force from the pressure in the pumping chamber plus the force generated by the pretensioning of the valve 16 is lesser than the force from the pressure inside the inlet channel 2. The fluid is then sucked into the pumping chamber 15 through the inlet channel 2 owing to the displacement of the deformable area of the thin slab 12.

By setting the ratio of the diameter of the membrane of the discharge valve 18 to that of its seat at a high value, the pressure in the discharge channel 3 has little influence on the pressure of the pumping chamber necessary for opening the discharge valve. Consequently, by selecting properly this ratio and the operational frequency of the piezoelectric wafer, one can ensure that the outlet pres11 sure has only little influence on the output. One can thus establish the output versus outlet pressure curves such as those illustrated in figure 13. In this figure, curve A was obtained by applying a 2 Hz tension to the piezoelectric wafer of a micropump according to figures 3 to 5 and having approximately the dimensions given above : the output remained substantially constant at a value of 30 μΐ/min (these conditions are the most favourable). When the piezoelectric wafer is operated with a 5 Hz tension, the output is increased to about 64 μΐ/min. As can be seen from the curves in figure 13, the choice of a given pretensioning of the membrane of the discharge valve keeps the output constant, at the values indicated, while the outlet pressure can vary from 0 to 70 cm HO. Furthermore, the curves also show that the output remains constant even for negatives values of the difference between the outlet pressure and the inlet pressure (parts C and D of the respective curves). This can occur for example in the case of an excessive pressure at the pump inlet.

One will note that the micropump, in all the embodiments described above, is compact and simple, offers a low resistance to flow and makes it possible to achieve with a very good level of accuracy a flow rate which remains constant when the outlet pressure changes.

In all the embodiments except that of figures 1 and 2, the pump was designed for providing a protection against excessive pressures by virtue of the pump inlet being in communication with a chamber located above the discharge valve. Consequently, should such an excessive pressure occur, it would act on the discharge valve to close it and thus isolate the discharge channel from the pumping chamber. This feature of the pump can be important in the case of the pump being carried by a patient who also carries a flexible container. Should he compress the container (for example by an impact against an obstacle), the excessive pressure at the intake of the pump would not cause any flow on the discharge side thereof.

Furthermore, owing to the communication of the compensation chamber with the inlet of the pump, a variation of the inlet pressure has only very little influence on the output in the normal operational range of the pump.

It is to be noted that the communication can also be established by - 12 a connexion external to the pump. For example, the pump of figures 1 and 2 could also be provided with a conduit connecting the inlet to the outlet.

Finally, figure 1 shows that one can associate the thin silicon 5 slab with a means for controlling the operation of the pump, such as for example a strain gauge 11 A, wherein the variation of the resistance can be measured for controlling the proper functioning of the pump or for checking that the membrane upon which the gauge is bonded is not ruptured. Clearly, one or several such control means can be mounted in all the embodiments described.

Claims (12)

1. A micropump including a first thin slab (11; 27; 41; 56) of a material which can be etched by photolithography techniques in such a manner as to define with at least a second thin support slab (1; 26; 40) bonded 5 by one face to the first thin slab, a pumping chamber (15; 44), a first valve of the nonreturn type (16; 33; 45) through which said pumping chamber (15; 44) can communicate selectively with an inlet (2; 30; 50) of the pump and a second valve of the membrane type (18; 36; 46) through which said pumping chamber can communicate selectively with an outlet (3; 36a; io 43) of the pump, means (13; 14; 29; 49) being provided for generating a periodical variation of the volume of said pumping chamber (15; 44), the second valve being controlled by the pressure of the fluid to be discharged by the pump, characterized in that said outlet (3; 36a; 43) is in direct communication with a volume (18d) isolated from said pumping chamber is (15; 44) by said second valve (18; 36; 46) and located on the same side of this valve as the channel (19; 20) through which this valve communicates with the pumping chamber, so that the pressures prevailing respectively in this pumping chamber and in the outlet channel act in a direction to open said second valve, and in that said second valve (18; 36; 46) is 20 in open communication with said first valve (16; 33, 45) through said pumping chamber (15; 44), so that during the discharge phase of the pump, this chamber communicates directly with said outlet (3; 36a; 43) through said second valve in its open position.

2. A micropump according to claim 1, characterized in that it includes a 25 third thin slab (12; 28; 42; 55) covering said first thin slab (11; 27; 41) at least on one part of its surface while defining therewith at least one chamber (15, 21; 51; 54) designed for providing an active cavity of the pump.

3. A micropump according to claim 2, characterized in that said means 30 provided for generating a periodical variation of the volume of the pumping chamber include a piezoelectric wafer (13; 29) affixed to said third thin slab (12; 28), in a zone which coincides with said pumping chamber (15),

4. A micropump according to claim 2, characterized in that said means provided for generating a peridiodical variation of the volume of the pumping chamber include a piezoelectric wafer (49), in that said pumping chamber (44) is defined by said first (41) and second (40) thin slabs and in that said piezoelectric wafer is affixed to said first thin slab in an exposed zone thereof coinciding with said pumping chamber (44).

5. A micropump according to any one of claims 2 to 4, characterized in that said third thin slab (55) is formed so as to provide also one of the connections by which the pump can be connected to an external circuit (figure 11).

6. A micropump according to any one of claims 1 to 5, characterized in that a detector member, such as a strain gauge (11A), is affixed to said first thin slab (11) for controlling that the pump functions correctly.

7. A micropump according to any one of the preceding claims, characterized in that said first valve (16; 33; 45) and/or said second valve (18; 36; 46) include(s) a membrane (16a; 18a) arranged in the plane of said first thin slab, at the center of which is provided an annular rib (16c; 18c), the ridge of which is designed for application against another thin slab (1; 12; 26; 28; 40; 41) acting as the seat of this valve, and in that at least said rib (16c; 18c) is coated with a layer of oxide (17) for biasing the membrane with a predetermined pretension in such a manner that the valve be normally closed.

8. A micropump according to claim 7, characterized in that the membrane (18a) of the second valve is at least partly coated with a material generating within the membrane shearing forces inducing an additional pretension.

9. A micropump according to one of claims 7 and 8, characterized in that on the side opposed to said rib (16c), said membrane (16a) is provided with a boss (39; figure 6) extending towards another thin slab (28) of the pump and designed for limiting the motion of the membrane (16), should the same be exposed to an excessive pressure.

10. A micropump according to any one of claims 7 to 9, characterized in that the ribs (16c) provided respectively on the membranes (16a) of said valves are provided on opposite faces of these membranes (valves 45 and 5 46, figures 8, 9 and 10).

11. A micropump according to any one of the preceding claims, characterized in that the inlet (2; 30, 50) of the pump is in communication with a compensation chamber (21; 30; 51; 54) formed above said second valve (18; 36; 46), to bias the latter to close under the effect of the pressure io prevailing at said inlet.

12. A micropump substantially as hereinbefore described with reference to the accompanying drawings.