FR2650634A1 - Improved micropump - Google Patents

Abstract

In this micropump, pumping is obtained by virtue of the deformation of a small plate 12 with the aid of a piezoelectric pellet 13. Deformation gives rise to a variation in volume of a pumping chamber 15 delimited in a small plate 11 made from a material capable of being machined by photolithography methods. The outlet 3 of the pump is selectively closed off by a diaphragm valve 18 which is in direct communication with another valve 16 through the pumping chamber. The said valve 16 selectively makes this pumping chamber communicate with the inlet 2 of the pump. The membrane of the outlet valve 18 is associated with a layer of oxide 17 which prestresses it in the closed direction. In this way, the valve exerts a regulation effect on the operation of the pump making the output practically independent of the pressure of the outlet 3. Application to the injection of medicinal products in precise doses.

Description

PERFECTED MICROPUMP
The present invention relates to micropumps of the type in which
at least a part of the pump mechanism is produced by machining a silicon wafer using
photolithography.

 Such pumps -may be used in particular for the in-situ administration of drugs, the miniaturization of the pump allowing a patient to carry it on himself, or even possibly receive a pump directly implanted in the body. Moreover, such pumps allow accurate dosing of small amounts of fluid to be injected.

In an article titled "A piezoelectric micropump based on micromachining of silicon" and appeared in "Sensors and Actuators"
No. 15 (1988), 153-167, H. van Lintel et al. give a description of two embodiments of a micropump, each comprising a stack of three wafers, that is to say a silicon wafer disposed between two plates of glass.

 The silicon wafer defines one. pumping chamber with one of the glass plates whose part coinciding with this chamber can be deformed by a motor element which is, in this case, a piezoelectric crystal. The latter has electrodes which, when connected to an AC voltage source, cause deformation of the crystal and hence the glass wafer thereof, in turn, varying the volume of the pumping chamber.

 The pumping chamber is connected on either side respectively to factory check valves in the silicon and whose seat is constituted by the other glass plate.

 An analysis of the operation of the pump according to the first embodiment (FIG. 1a) described in the aforementioned article shows that this pump delivers a fluid flow rate that is highly dependent on the outlet pressure over the entire operating range. Indeed, it has been found that this flow-pressure relationship is practically linear, the flow rate being all the lower as the pressure is higher.

In other words, such a pump is unusable for the aforementioned medical applications in which, on the contrary, the output flow of the pump must be independent of the pressure,
at least in the normal operating range of the pump,
This is why the authors propose in this same article
(second embodiment shown in FIG. 1b) of adjoin
to the assembly that has just been described a regulating valve
interposed between the second valve which follows the chamber of
pumping, and the output of the pump. This valve isolates the pump from the
exit when closed.

Moreover, the regulator valve having a certain
prestressing at closing, the outlet pressure can not open
the flapper only from a certain value. This results in
in the useful range of operation of the pump, a quasi
flow rate independence from the outlet pressure,
that is, as long as the regulating valve is not kept open
by the outlet pressure.

 If, thanks to this second construction, a favorable pressure-flow diagram is obtained, it must however be observed that a pump produced in this way still has disadvantages.

 The regulator valve increases the size of the pump, because it must be made in the thickness of the silicon wafer and thus occupies the additional surface. This also results in an increase in the cost price of the pump.

It should also be noted that the regulator valve increases the
complexity of the pump and thus the risks of malfunction or waste in the manufacture.

The object of the invention is to provide a micropump of the type indicated above, which makes it possible to avoid the disadvantages of the pumps described in the aforementioned article while presenting a characteristic
flow rate as a function of the favorable outlet pressure in
the useful operating range of the pump.

The subject of the invention is therefore a micropump comprising a
first wafer material capable of being machined by photolithographic techniques so as to define with at least a second support plate contiguous facing the first wafer, a pumping chamber, a first valve, anti return type through which said pump chamber can selectively communicate with a pump inlet and a second diaphragm type valve through which said pump chamber can selectively communicate with an outlet of the pump, means being provided to cause a periodic change in volume of the pump. said pumping chamber, characterized in that said outlet is in
direct communication with an isolated volume of said chamber of
pumping by said second valve and located on the same side of this valve
that the channel through which this valve communicates with the pumping chamber, so that the pressures respectively in this pumping chamber and this volume act in the direction of
opening on said second valve, and in that said second valve is in open communication with said first valve by
via said pumping chamber, so that, during the discharge phase of the pump, this chamber communicates directly with said outlet, through said second valve in the open position.

Thanks to these characteristics, said second valve not only regulates the flow rate so as to make the latter almost independent of the pressure in the pump outlet over its entire normal operating range, but it also acts as
the organ closing the pumping chamber during the aspi phase
ration of the pump.

Other features and advantages of the invention appear
during the following description of several embodiments of the micropump according to the invention, a description referring to the appended drawings in which
- Figure 1 is a schematic sectional view of a micropump according to the invention;
- Figure 2 shows a bottom view of the plate
intermediate of the pump-shown in Figure 1;
- Figure 3 is a view showing the underside of the intermediate plate of a micropump constructed according to a second embodiment of the invention, the view being taken along line III-III of Figure 4 ;.

- Figures 4 and 5 are sectional views taken respectively along the lines IV-IV and VV of Figure 3;
FIG. 6 is a 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 plate of the pump shown in Figure 6, this view being taken along the line VII-VII of Figure 6;
Figure 8 is a view of the underside of an intermediate wafer belonging to a micropump constructed according to a fourth embodiment of the invention;
- Figures 9 and 10 are sectional views taken respectively along the lines IX-IX and XX of Figure 8;
- Figure 11 shows a partial sectional view of a fifth embodiment of the invention;
- Figure 12 is a partial top view of the micropump shown in Figure 11; and
- Figure 13 is a graph showing the characteristic of the flow as a function of the pressure measured on a micropump constructed according to the invention, the inlet pressure being zero.

 We will first refer to Figures 1 and 2 which show a first embodiment of the micropump according to the invention.

 It should be noted that for the sake of clarity, the thicknesses of the various platelets comprising the micropump have been greatly exaggerated in the drawings.

 The micropump of Figures 1 and 2 comprises a base plate 1 glass for example, which is pierced with two channels 2 and 3 respectively forming the suction pipe and the discharge pipe of the pump. These channels 2 and 3 communicate with respective connectors 4 and 5.

 The connector 4 is connected to a pipe 6 itself connected to a reservoir 7 in which the liquid substance to be pumped is located. The reservoir is closed by a pierced cap, a movable piston isolating the useful volume of the reservoir 7 from the outside. This reservoir may contain a drug for example, in case the pump is used for the injection of this drug into the human body with a precise dosage. In this application, the micropump can be worn on the body of the patient or even be implanted.

 The discharge connection 5 can be connected to an injection needle (not shown) connected to it by a pipe 10.

 The use in this way of the micropump of the invention is particularly suitable for the treatment with peptides of certain forms of cancers whose medication is carried out, preferably, by a precise and repeated dosing at regular intervals. small amounts of the drug. Another application can be envisaged for the treatment of diabetics to periodically receive low doses of drug during the day, the dosage can be determined for example by means known per se, measuring the blood sugar level and automatically controlling the pump so that a suitable dose of insulin can be injected.

 A wafer 11 made of silicon or of another material machinable by etching using photolithographic techniques, is contiguous to the glass wafer 1. This wafer is itself surmounted by a glass closure wafer 12 of which the thickness is such that it can be deformed by a control element 13 which, in the application of the invention described here is a piezoelectric pellet provided with electrodes 13a and 13b connected to a voltage generator 14 alternative. This pellet may be that manufactured by the Philips Company under the name PXE-52 and may be glued to the wafer 12 by means of a suitable glue.

 For example, the intermediate wafer 11 in silicon can have a crystalline orientation <100>, in order to be well suited to etching and to have the necessary strength. Platelets 1 and 12 are preferably carefully polished.

 The plates 11 and 12 delimit firstly together a pumping chamber 15 (see also FIG. 2), of circular shape for example, this chamber being situated below an area of the plate 12 which is deformable. by the control element 13.

Between the suction pipe 2 and the pumping chamber 15 is interposed a first valve 16 of the non-return type machined in the silicon wafer 11. This valve is located under the pumping chamber and has a membrane 16a of generally circular shape and pierced at its center with a through hole 16b which, in the
of embodiment represents, is of square shape. On the side of
pipe 2, the valve 16 has a rib 16c shaped
annular and of approximately triangular section.This rib 16c
surrounds the orifice 16b and is coated with a thin oxide layer 17
also obtained by photolithography techniques and conferred
to the membrane 16a some prestress or pretension
tending to apply the top of the rib 16c against the wafer
glass 1, the latter thus serving as seat valve 16.

The pipeline of. discharge 3 of the pump communicates with the
pumping chamber 15 via a valve 18 whose
construction is identical to that of the flap 16, except that
as a difference in thickness of the layer 17 relative to that of the valve 16, the prestress provided by this layer
oxide 17 may be different from that used for the valve 16.

In addition, we see in Figure 1 that this valve is devoid of a
central orifice such as orifice 16b of the valve 16.

It will be noted that the pumping chamber communicates with the valve 18
through an orifice 19 and a passage 20 both
machined in the silicon wafer 11.

The valve 18 thus comprises a membrane 18a and a rib
annular 18c coated with an oxide layer 17 and bounded above
of the pipe 3 a volume 18 of which reigns the pressure of
exit. When the valve 18 is open, this volume is in communica
direct connection with the suction valve 16 through the chamber of
pumping 15 with the result that a minimum of resistance to
is imposed on the fluid pumped out of the pump during the
discharge. In addition, when the valve 18 is closed, the pressure
output only acts on a small surface of the membrane 18a
compared to the much larger area over which can
act on the pressure prevailing in the pumping chamber. This has for
effect an output flow regulation that virtually becomes
independent of the outlet pressure (see Figure 13), this effect
being caused by the pre-tension provided by the oxide layer 17.

To fix the ideas, the thicknesses of the plates 1, 11 and 12
can respectively be about 1 mm, 0.3 mm and 0.2 mm for
a surface dimension of the wafers of the order of 15 by 20 mm.

 Furthermore, the wafers can be fixed to each other by various known bonding techniques such as gluing or the technique known as anodic solder, for example.

 FIGS. 3 to 5 show a second embodiment of the micropump according to the invention, which is essentially of identical construction to that of the micropump shown in FIGS. 1 and 2. The identical elements have therefore been identified by the same references as before. However; it differs in that the annular chamber 16e (Figure 4) surrounding the annular rib 16c of the suction valve 16 is connected not only to the suction pipe 2, but also to a compensation chamber 21 defined in the plate 11 above the valve 18, and closed by the closure plate 12, the latter covering the entire surface of the pump here. This connection is achieved by means of a communication channel 22 machined in the silicon and formed of three branches 22a, 22b and 22c arranged at right angles in the plate 11. It should be noted that the branch 22c of this pipe is not at the same level as''the other two branches 22a and 22b, the branches 22b and 22c being in communication with one another through a communication orifice 23 formed in the wafer 11.By the other hand, the branch 22c (FIG. 5) is in communication with the suction pipe 2 by the intermediate of an orif communicating ice 24 which connects this branch to a small cavity 25, dug in the silicon wafer 11 just above the suction pipe 2.

 The pipe 22 is intended to communicate the channel 2 of the pump, with the chamber 21 formed, above the diaphragm 18a of the discharge valve 18 so as to keep it closed if an overpressure occurs to the pump. input of the pump. This arrangement therefore acts as a safety against overpressures.

 Figures 6 and 7 which will be referred to now represent a third embodiment of the micropump according to the invention. In this case, the principle of the construction, described above, remains the same however that the pumping chamber 15 is disposed. asymmetrically with respect to the suction and discharge valves.

 This pump is also composed of three plates, namely a support plate 26, for example glass, a wafer 27, made of silicon for example or in another suitable material, and a closure plate 28 of glass for example which is deformable in an area above the pumping chamber 15, using a piezoelectric pellet 29 or other suitable control element.

 The pumping chamber 15 is delimited by the wafer 27 and the wafer 28, these two wafers also defining an inlet chamber 30 (visible in FIG. 6 only) into which an inlet orifice 30a opens which is formed in the wafer 28.

 The chamber 30 communicates with a channel 31 (which is visible only in FIG. 7) situated in the upper part of the plate 27 and this pipe 31 communicates with a second pipe 32 which is formed in the plate 27 on the side of the plate. plate 26. The pipe 32 opens into an annular chamber 33 of a suction valve 34 whose construction is identical to that of the valve 16 described above. This suction valve communicates with the chamber 15 through a central orifice 35.

 The chamber 15 also communicates with a delivery valve 36 via an orifice 37 and a pipe 38 both formed in the wafer 27. Furthermore, the discharge valve 36 which is intended to close an orifice outlet 36a (Figure 6) is constructed in the same manner as the discharge valve of the previous embodiments except that it has a boss 39 on the side of its diaphragm opposite to the shutter valve rib. This boss 39, which is located in the center of the membrane, is intended to limit the amplitude of the movement thereof through the abutment effect that it can exert on the wafer 28 in the case where the outlet pressure exceeds a predefined permissible value.

 In the arrangement just described, the inlet orifice 30a opens into the chamber 30 which is located above the discharge valve 36 and thus serves as a compensation chamber, such as the chamber 21 of the previous embodiment. Therefore, this construction also provides safety against overpressure.

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

 In this case, the micropump also comprises three plates 40, 41 and 42. The wafer 40 is made of glass for example and comprises a discharge line 43. The wafer 41 is made of silicon or another material suitable and shaped, at the same time. using photolithographic processes, so as to define a pumping chamber 44, a suction valve 45 and a discharge valve 46 respectively communicating with the pumping chamber 44 via conduits 47 and 48.

 In the present embodiment, a control element such as a piezoelectric pellet 49 is placed directly on the silicon wafer 41 in the area coinciding with the pumping chamber 44 so that to obtain the effect pumping, it is this plate 41 which is deformed to change the volume of the pumping chamber. It is further desirable to provide between the wafer 41 and crystal 49 a thin layer of silicon oxide 49a to isolate the corresponding electrode from the wafer with respect to this wafer.

 The wafer 42 covers only partially the wafer 41 and has a suction orifice 50 which opens into an annular compensation chamber 51 provided above the discharge valve 46. It can be seen that this valve is provided with a boss 52 to limit the amplitude of the membrane of the valve, the boss may come to rest against the lower face of the wafer 42 in case the outlet pressure under the valve becomes excessive.

 Note also that the positions of the suction and discharge valves 45 and 46 are reversed, the suction valve having its seat is formed by the wafer 42, while the seat of the valve 46 is constituted, as in the other modes This arrangement has no particular influence on the operation of the pump.

FIG. 11 shows another embodiment of the invention in which ', above the discharge valve 53, is
provided a chamber 54 which is closed by a connecting member 55
made of plastic material for example and glued on the plate
in silicon 56. Thus, the chamber 54 which is actually in communica
with the suction of the pump is totally isolated from the atmosphere
outdoor lighthouse. This construction has the advantage of allowing
to avoid the use of a particular closure plate.

Both in the pump according to FIGS. 8 to 10 (line 57)
that in that of Figure 11 (chamber 54), the check valves
are connected to the inlet of the pump so as to ensure
these cases also, the safety against overpressures.

We will now examine the operation of the micropump
according to the invention with particular reference to the dia
gram of Figure 13 which represents # the flow rate according to the
pressure in the discharge pipe.

Note that the operation is the same regardless of the
embodiments described above. For convenience, the
The following description therefore refers only to the embodiment of FIGS. 1 and 2.

When no voltage is applied to the patch
piezoelectric 13, the suction valves 16 and discharge
18 are in closed position. When a voltage is applied
the piezoelectric chip 13 deforms, causing the
plate 12 inwards. It then occurs an increase
of pressure in the pumping chamber 15 which causes the opening
of the discharge valve 18 that the force acting on the mem
brane because of the pressure in the chamber 15 is greater than
the difference between the force created by the prensensiùn of the valve 18,
ensured by the silicon oxide layer 17 and the force due to the
pressure in the outlet channel 3.The fluid contained in the
pumping chamber is then forced back to the outlet channel 3 by
the displacement of the deformable zone of the wafer 12. During
this phase, the suction valve 16 is kept closed by the
pressure prevailing in the pumping chamber 15 The fluid flows
without encountering significant resistance, because the
pumping 15 is then directly in communication with the channel of
exit 3.

 On the other hand, when the electrical voltage is reversed, the piezoelectric chip 13 returns to its original shape, or even deforms in the other 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 less than the difference between the force created by the pre-tension of the valve and the force due to the pressure in the outlet channel. 3. The opening of the suction valve 16 takes place as soon as the sum of the force due to the pressure in the pumping chamber and the force created by the pretension of the valve 16 is less than the force due to the pressure in the chamber. the inlet channel 2. There is then suction of fluid in the pumping chamber 15 through the inlet channel 2 as a result of the displacement of the deformable zone 'of the wafer 12.

 By choosing a large ratio of the diameter of the diaphragm of the discharge valve 18 and its seat, the pressure in the discharge channel 3 has little influence on the pressure of the pressure port. pumping chamber, necessary to open the discharge valve. Therefore, by judiciously choosing this ratio, as well as the control frequency of the piezoelectric pellet, it can be obtained that the output pressure influences very little the output flow. It is thus possible to determine output flow / pressure curves such as those shown in FIG. 13. In this figure, the curve A has been obtained by applying to the piezoelectric pellet a micropump according to FIGS. 3 to 5, having about the dimensions indicated above, a voltage at 2 Hz, the output flow remaining substantially constant at a value of 30 pl / min (most favorable choice). If the piezoelectric pellet is controlled with a voltage at 5 Hz, this flow rate is increased to about 64 μl / min. As can be seen in the curves of FIG. 13, the choice of a given pretension on the diaphragm of the discharge valve keeps the flow rate constant at the indicated values while the outlet pressure can vary from 0 to 70 cm. H20.In addition, the curves also show that the flow remains constant even for negative values of the difference between the output pressure and the inlet pressure (parts C and D of the respective curves).

This case can occur for example in the presence of an overpressure at the inlet of the pump.

 It will be noted that the micropump, whatever its embodiment described above, is compact and simple, has a low resistance to flow and makes it possible to determine with a very good approximation a constant flow rate as a function of the pressure of exit.

 In all the embodiments, except that of FIGS. 1 and 2, the pump has been designed to ensure safety against overpressures thanks to the fact that the inlet of the pump is in communication with a chamber situated above the valve of repression.

Therefore, if such an overpressure occurs, it acts on the discharge valve in the direction of the isolating closure-thus the discharge channel of the pumping chamber. This property of the pump can be important when it comes to a pump carried by a patient who also carries a bladder. If the latter then compresses the reservoir (for example because it encounters an obstacle), the overpressure in the suction of the pump does not cause any flow on the discharge side thereof.

 In addition, thanks to the communication of the compensation chamber with the pump inlet, a variation of the inlet pressure has, in the normal operating range of the pump, very little influence on the output flow.

 It should be noted that the communication can also be carried out by an external connection to the pump. For example, the pump of Figures 1 and 2 could be provided with a pipe connecting the inlet to the outlet.

 Finally, FIG. 1 shows that the silicon wafer can be associated with an operating control element, for example, in the form of a strain gauge 11A whose variation in resistance can be measured to testify to the good operation of the pump or rupture of the membrane on which the gauge is glued. Of course, one or more of these control elements can be provided in all the embodiments described.

Claims (10)

 1. Micropump comprising a first plate (11; 27; 41; 56) of material capable of being machined by photolithographic techniques so as to define with at least a second support plate (1; 26; 40) contiguous face to face at the first wafer, a pumping chamber (15; 44), a first non-return valve (16; 33; 45) through which said pumping chamber (15; 44) can selectively communicate with an inlet ( 2; 30; 50) of the pump and a second diaphragm type valve (18; 36; 46) through which said pump chamber can selectively communicate with an outlet (3; 36a; 43) of the pump; means (13; 14; 29; 49) being provided for causing a periodic volume change of said pumping chamber (15; 44), characterized in that said output (3; 36a; 43) is in direct communication with a volume (18d) isolated from said pumping chamber (15; 44) by said second valve (18; 36; 46) and located in the same the side of this valve that the channel (19, 20) by which the valve communicates with the pumping chamber, so ~ that the pressures prevailing respectively in this pumping chamber and this volume act in the direction of opening on said second valve, and in that said second valve (18; 36; 46) is in open communication with said first valve (16; 33; 45) through said pumping chamber (15; 44) so that, during the delivery phase of the pump, this chamber communicates directly with said first valve (16; with said outlet (3; 36a; 43), through said second valve in the open position.  2. Micropump according to claim 1, characterized in that it comprises a third plate (12; 28; 42; 55) covering said first plate, (11; 27; 41) at least over a portion of its surface and defining with it at least one chamber (15; 21; 51; 54) for forming an active cavity of the pump.  Micropump according to claim 2, characterized in that said means for causing a periodic volume change of the pumping chamber comprise a piezoelectric pellet (13; 29) fixed on said third plate (12; zone which coincides with said pumping chamber (15).  4. Micropump according to claim 2; characterized in that said means for causing a periodic volume change of the pumping chamber comprises a piezoelectric pellet (49), in that said pumping chamber (44) is delimited by said first (41) and second (40) ) and said piezoelectric pellet is attached to said first wafer in an open area thereof coinciding with said pumping chamber (44).  5. Micropump according to any one of claims 2 to 4, characterized in that said third plate (55) is arranged to also form at least one of the connections by means of which the pump can be connected to an external circuit (Figure 11).  6. Micropump according to any one of claims 1 to 5, characterized in that a sensor element, such as a. strain gauge (11A) is fixed on said first plate (11) to allow monitoring of the proper operation of the pump.  7. Micropump according to any one of the claims. previous, characterized in that said first valve (16; 33; 45) and / or said second valve (18; 36; 46) comprises a membrane (16a) provided in the plane of said first wafer to which is provided an annular rib (16c) whose apex is intended to bear against another plate (1; 12; 26; 28; 40; 41) serving as seat of this valve, and in that at least said rib (16c) is covered with an oxide layer (17) biasing the membrane with a predetermined pre-tension so that the flap is normally closed.  8. Micropump according to claim 7, characterized in that on the opposite side to said rib (16c), said membrane (16a) is provided with a boss (39, figure 6) extending towards another plate (28) of the pump and intended to limit the absorption of the membrane (16) in the case where it is subjected to excessive pressure.  9. Micropump according to any one of claims 7 and 8, characterized in that the ribs (16c), respectively provided on the membranes (16a) of said valves are deposited on opposite sides of these membranes (valves 45 and 46, figures 8, 9 and 10).  Micropump according to one of the claims  previous, characterized in that the inlet (2; 30; 50) of the pump -is in communication with a compensation chamber (21; 30; 51;  54) arranged above said second valve (18; 36; 46) in order to  to urge the latter to close under the influence of the pressure at the inlet.