IE902122L - 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. [CH680009A5]

Description

IE 902122 - -m- IMPROVED MICROPUMP The present invention relates to micropumps in which at least part of the pump mechanism is made by machining a silicon 05 wafer using photolithographic technology.

Pumps of this type can be used notably for the in situ administration of medicaments whereby miniaturization of the pump enables the patient to wear it on his person or possibly to have a pump directly implanted in his body. In addition, using ^ pumps of this type, small quantities of liquid to be injected can be accurately metered.

In an article entitled "A piezoelectric micropump based on micromachining of silicon" which appeared in "Sensors and Actuators" No. 15 (1988), pages 153 to 167, H. van Lintel et al 15 describe two embodiments of a micropump each comprising a stack of three wafers, i.e. a wafer of machined silicon arranged between two wafers of glass.

The silicon wafer defines a pumping chamber with one of the glass wafers, it being possible for the part coinciding with 20 this chamber to be deformed by drive means, in the present case a piezoelectric crystal. The latter comprises electrodes which, when connected to a source of alternative potential, cause deformation of the crystal and thus of the glass wafer, the latter in turn causing variation in the volume of the pumping 25 chamber.

The pumping chamber is connected on one side and on the other side respectively to check valves machined from silicon the seat of which is composed of the other glass wafer.

Study of the mode of operation of the pump according to the 30 first embodiment (Figure la) described in the above mentioned article shows that the fluid output delivered by this pump depends greatly on the outlet pressure over the entire operating range. It was found that this relationship between output and pressure is virtually linear, the output falling as pressure 35 rises.

IE 902122 In other words, a pump of this type cannot be used for the above mentioned medical applications in which, in contrast, the output from the pump outlet must be independent of the pressure, at least in the normal operating range of the pump. 05 For this reason the authors propose in this same article (second embodiment shown in Figure 1b) adding a regulating valve to the above described assembly disposed between the second valve downstream from the pumping chamber and the pump outlet. This valve isolates the pump from the outlet when it is closed. 10 Since the regulating valve has a certain degree of mechanical bias against opening the outlet pressure is only able to open the valve after reaching a certain value. As a result, a form of independence of output in relation to outlet pressure develops in the useful operating range of the pump, ie. 15 when the regulating valve is not kept open by the outlet pressure.

Thus, although this second design gives a favourable output pressure diagram, it should nevertheless be noted that a pump manufactured in this manner still has disadvantages. 20 The regulating valve further increase the size of the pump since it must be situated with the silicon wafer and thus takes up additional surface area. It therefore increases the cost price of the pump.

It should also be noted that the regulating valve increases 25 the complexity of the pump and thus the risk of incorrect functioning or manufacturing error.

It is an object of the invention to provide a micropump of the type set out above which avoids the disadvantages of the pumps described in the above mentioned article whilst presenting 30 good characteristics in relation to the outlet pressure over the useful operating range of the pump.

It is thus an object of the invention to provide a micropump having a first wafer of a material capable of being machined using photolithographic technology in such a way as to define 35 with at least one second support wafer bonded face to face with IE 902122 the first wafer a pumping chamber, a first valve of the check type through which said pumping chamber is able to communicate selectively with a pump inlet and a second valve of the membrane type through which said pumping chamber can 05 communicate selectively with an outlet of the pump, means being provided to cause a periodic variation in the volume of said pumping chamber, wherein said outlet communicates directly with an isolated volume of said pumping chamber by means of said second valve and situated on the same side of this valve as the 10 channel through which this valve communicates with the pumping chamber in such a way that both the pressures prevailing in this pumping chamber and this outlet act in the direction of opening on said second valve and in that said second valve is in open communication with said first valve via said pumping chamber in 15 such a way that, during the outlet phase of the pump, this chamber communicates directly with said outlet through said second valve in the open position.

By virtue of these characteristics, said second valve not only regulates output in such a way as to render the latter 20 virtually independent of the pressure in the pump outlet over its entire normal operating range, but it also acts as the element closing the pumping chamber during the inlet phase of the pump.

Other characteristics and advantages of the invention are 25 better illustrated by the following description of several embodiments of the micropump according to the invention, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic sectional view of the micropump of the invention; - Figure 2 shows a plan view of the intermediate wafer of the pump shown in Figure 1; Figure 3 is a view showing the lower face of the intermediate wafer of a micropump designed according to a second embodiment of the invention, the view being taken along the line 35 iii-iii of Figure 4; IE 902122 Figures 4 and 5 are sectional views taken along the lines IV-IV and V-V respectively of Figure 3; Figure 6 is a sectional view of a micropump constructed according to a third embodiment of the invention; 05 - Figure 7 is a view of the lower face of the intermediate wafer 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 lower face of an intermediate wafer of a micropump constructed according to a fourth 10 embodiment of the invention; Figures 9 and 10 are sectional views taken along the lines IX-IX and X-X respectively of Figure 8; Figure 11 shows a partial sectional view of a fifth embodiment of the invention; - Figure 12 is a partial plan view of the micropump shown in Figure 11; and Figure 13 is a graph showing the characteristics of the output as a function of the pressure measured in a micropump designed according to the invention where the inlet pressure 20 equals zero.

Reference will first be made to Figures 1 and 2 which show a first embodiment of the micropump according to the invention.

It should be noted that the thicknesses of the various wafers comprising the micropump have been greatly exaggerated in 25 the drawings in the interest of clarity.

The micropump of Figures 1 and 2 has a base wafer 1 of, for example, glass, which is pierced by two holes or channels 2 and 3 forming the inlet channel and the outlet channel of the pump respectively. These channels 2 and 3 communicate with connectors 30 4 and 5 respectively.

The connector 4 is connected to a tube 6 which in turn is connected to a reservoir 7 containing the liquid to be pumped. The reservoir is closed by a pierced cap, a movable piston isolating the working volume of the reservoir 7 from the 35 outside. This reservoir can, for example, contain a medicament IE 902122 if the pump is used to inject a precise dose of this medicament into the human body. In this application the micropump can be worn on the body of the patient or implanted therein.

The outlet connector 5 may be connected to an injection 05 needle (not shown) joined thereto by a tube 10.

Use of the micropump of the invention in this manner is particularly suitable for treating certain forms of cancer with peptides where medication should preferably be in the form of accurate and repeated doses of small amounts of the medicament 10 at regular intervals. Another potential application could be for the treatment of diabetics who need regular low doses of a medicament in the course of the day, the dose being determined for example by methods known per se, measuring the blood sugar level and automatically instructing the pump to inject a 15 suitable dose of insulin.

A wafer 11 of silicon or other material capable of being machined using photolithographic engraving technology is bonded to the glass wafer 1. Above this silicon wafer is a glass closure wafer 12, the thickness of which is such that it can be 20 deformed by a control element 13 which, in the application of the invention described herein, is a piezoelectric disc provided with electrodes 13a and 13b connected to an alternating current generator 14. This disc may be that manufactured by Philips under the reference number PXE-52 and may be bonded to the wafer 25 12 using a suitable adhesive.

For purposes of example, the intermediate silicon wafer 11 can have a <100> crystalline orientation so as to render it suitable for etching and to give it the requisite strength. The wafers 1 and 12 are preferably carefully polished. 30 The wafers 11 and 12 together define first of all a pumping chamber 15 (see also Figure 2) for example circular in shape, this chamber being situated below an area of the wafer 12 which can be flexed by the control element 13.

IE 902122 A first valve 16 of the check type machined out of the silicon wafer 11 is interposed between the inlet channel 2 and the pumping chamber 15. This valve is located under the pumping chamber and comprises a membrane 16a substantially circular in 05 shape and pierced in its centre by an opening 16b which is square in the embodiment shown. On the side of the channel 2, the valve 16 has an annular rib 16c which is substantially triangular in section. This rib 16c surrounds the opening 16b and is covered by a thin oxide layer 17 also obtained, using 10 photolithographic technology. This oxide layer gives an extra thickness which subjects the membrane 16a to a certain degree or bias or pretension while the top of the rib 16c bears against the glass wafer 1, the latter thus acting as seat for the valve 16.

The outlet channel 3 of the pump communicates with the 15 pumping chamber 15 via the intermediary of a valve 18, the design of which is identical to that of the valve 16 except for the size of the layer 17 compared to that of the valve 16, the bias imposed by this oxide layer 17 can differ from that used for the valve 16. Figure 1 shows that this valve does not 20 have a central opening similar to the opening 16b of the valve 16.

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

The valve 18 thus comprises a membrane 18a partially covered and an annular rib 13c covered by an oxide layer 17 and defines above the channel 3 a volume 18d in which the outlet pressure prevails.

The oxide layer of membrane 18a develops shearing stress which produce a bending of the membrane (oxide layer is on the convex side of the membrane). This induces and additional pretension of the valve to the closure, with respect to the pretension caused by the oxide layer cohering rib 18c.

When the valve 18 is opened, this volume communicates directly with the inlet valve 16 through the pumping chamber 15 with the result that a minimum of flow resistance is imposed on the fluid driven out of the pump during the outlet phase. Moreover, when the valve 18 is closed, the outlet pressure only acts on a small area of the membrane 18a compared to the substantially larger area on which the pressure prevailing in the pumping chamber is able to act. This results in regulation of the outlet output 902122 which becomes virtually independent of the outlet pressure (see Figure 13), this effect being produced by the pretension provided by the oxide layer 17.

By way of example, the thickness of the wafers 1, 11 and 12 may be about 1 mm, 0.3 mm and 0.2 mm respectively for a surface area of the wafers of the order of 15 by 20 mm.

The wafers may also be fixed to one another using various conventional bonding technology such as adhesion or, for example, the technology known as anodic bondinq.

Figures 3 to 5 show a second embodiment of the micropump of the invention which is substantially identical in design to the micropump shown in Figures 1 and 2. The identical elements consequently bear the same reference numerals given earlier. However it differs in that the annular chamber 16e (Figure 4) surrounding the annular rib 16c of the inlet valve 16 is not only connected to the inlet channel 2, but also to a compensation chamber 21 defined in the wafer 11 above the valve 18 and closed by the closure wafer 12, this latter in this case covering the entire surface of the pump. This connection is provided by the intermediary of a communicating channel 22 machined in the silicon and composed of three branches 22a, 22b and 22c disposed at right angles in the wafer 11. It should be noted that the branch 22c of this channel is not at the same level as the two other branches 22a and 22b, the branches 22b and 22c communicating with one another via a communicating opening 23 provided in the wafer 11. In addition, the branch 22c (Figure 5) communicates with the inlet channel 2 via a communicating opening 24 which connects this branch to a small cavity 25 provided in the silicon wafer 11 just above the inlet channel 2.

The channel 22 is designed to provide a communication between the channel 2 of the pump and the chamber 21 provided above the membrane 18a of the outlet valve 18 in such a way as to keep this closed if there is overpressure at the entrance to the pump. This arrangement serves to guard against overpressure.

IE 902122 Figures 6 and 7 to which reference will now be made represent a third embodiment of the micropump of the invention. In this case, the above described design principle remains the same except that the pumping chamber 15 is disposed 05 asymmetrically in respect of the inlet and outlet valves.

This pump is also composed of three wafers, namely a support wafer 26, of, for example, glass, a wafer 27 of, for example silicon or other suitable material, and a closing wafer 28 of, for example, flexible glass, located in a zone above the pumping 10 chamber 15 with the aid of a piezoelectric disc 29 or other suitable control element.

The pumping chamber 15 is defined by the wafer 27 and the wafer 28, these two wafers also defining an inlet chamber 30 (shown only on Figure 6) into which opens an inlet opening 30a 15 which is provided in the wafer 28.

The chamber 30 communicates with a channel 31 (shown only in Figure 7) located in the upper part of the wafer 27 and this channel 31 communicates with a second channel 32 provided in the wafer 27 on the side of the wafer 26. The channel 32 opens into 20 an annular chamber 33 of an inlet valve 34 of identical design to that of the valve 16 previously described. This inlet valve communicates with the chamber 15 through a central opening 35.

The chamber 15 also communicates with an outlet valve 36 via the intermediary of an opening 37 and of a channel 38 both 25 provided in the wafer 27. In addition, the outlet valve 36 which is designed to close the outlet opening 36a (Figure 6) is designed in the same way as the outlet valve of the preceding embodiments except that it has a projection 39 on the side of its membrane opposite the closing rib of the valve. This 30 projection 39 which is at the centre of the membrane is designed to limit the amplitude of movement thereof thanks to the effect of the stop which it can exert on the wafer 28 in the event that the outlet pressure exceeds a predetermined permissible value.

IE 902122 In the embodiment that has just been described the inlet opening 30a opens into the chamber 30 which is located above the outlet valve 36 and thus serves as compensation chamber similar to the chamber 21 of the preceding embodiment. This design 05 consequently also provides a protection against overpressure.

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

In this case the micropump also has three wafers 40, 41 and 42. The wafer 40 is made for example of glass and has an outlet 10 channel 43. The wafer 41 is made of silicon or of another suitable material using photolithographic processes in such a way as to define a pumping chamber 44, an inlet valve 45 and an outlet valve 46 communicating with the pumping chamber 44 via channels 47 and 48 respectively.

In this embodiment, a control element such as a piezoelectric disc 49 is placed directly on the silicon disc 41 in the zone which coincides with the pumping chamber 44 so that, to obtain a pumping effect, it is this wafer 41 which is flexed to change the volume of the pumping chamber. It is also 20 desirable to provide a thin layer of silicon oxide 49a between the wafer 41 and the crystal 49 so as to insulate the corresponding electrode of the disc in respect of this wafer.

The wafer 42 only partially covers the wafer 41 and comprises an inlet opening 50 which opens into an annular 25 compensation chamber 51 provided above the outlet valve 46. It will be noted that this valve is provided with a projection 52 making it possible to limit the amplitude of the membrane of this valve, the projection being able to bear against the lower face of the wafer 42 should the outlet pressure against the 30 valve become excessive.

It will also be noted that the positions of the inlet and outlet valves 45 and 46 are reversed, the seat of the inlet valve being composed of the wafer 42 whereas the seat of the valve 46 is composed, as in the other embodiments, of the wafer 35 40. This arrangement has no special influence on the working of the pump.

IE 902122 Figure 11 shows another embodiment of the invention in which a chamber 54 above the outlet valve 53 is closed by a connection organ 55 made for example of plastic and bonded to the silicon wafer 56. The chamber 54 which, in effect, communicates with the 05 inlet of the pump is totally insulated from the outer atmosphere. An advantage of this construction is that there is no need to use a special closing wafer.

As in the case of the pump of Figures 8-10 (channel 57) and in that of Figure 11 (chamber 54), the outlet valves are 10 connected to the pump inlet so as to guard against overpressure.

The mode of operation of the micropump of the invention will now be examined with particular reference to the diagram of Figure 13 which shows output as a function of pressure in the outlet channel. it will be noted that the operation is the same in all the above described embodiments. For purposes of simplification the following description therefore relates only to the embodiment of Figures 1 and 2.

When no electric potential is applied to the piezoelectric 20 disc 13, the inlet valves 16 and outlet valves 18 are in the closed position. When an electric potential is applied, the piezoelectric disc 13 flexes, causing the wafer 12 to bend towards the inside. The pressure in the pumping chamber 15 therefore rises, actuating the opening of the outlet valve 18 as 25 long as the force acting on the membrane as a result of the pressure in the chamber 15 is greater than the difference between the force created by the pretension of the valve 18, ensured by the layer of silicon oxide 17 and the force resulting from the pressure in the outlet channel 3. The fluid contained 30 in the pumping chamber is thus driven towards the outlet channel 3 by displacement of the flexible zone of the wafer 12. During this phase, the inlet valve 16 is kept closed by the pressure prevailing in the pumping chamber 15. The fluid runs without encountering noteworthy resistance so that the pumping chamber 35 15 then communicates directly with the outlet channel 3.

IE 902122 In contrast, when the electrical potential is released the piezoelectric disc 13 resumes its initial shape or is flexed in the other direction so that the pressure in the pumping chamber 15 falls. This causes the outlet valve 18 to close as soon as 05 the force induced by the pressure in the pumping chamber 15 is lower than the difference between the force created by the pretension of the valve and the force due to the pressure in the outlet channel 3. The inlet valve 16 opens as soon as the sum of the force due to the pressure in the pumping chamber and of the 10 force created by the pretension of the valve 16 is lower than the force due to the pressure in the inlet channel 2. There is then aspiration of the fluid in the pumping chamber 15 via the inlet channel 2 as a result of displacement of the flexible zone of the wafer 12.

By choosing a large ratio between the diameter of the membrane of the outlet valve 18 and its seat, the pressure in the outlet channel 3 has little influence on the pressure in the pumping chamber needed to open and /or keep opened the outlet valve. As a result, by carefully choosing this ratio as well as the control frequency 20 of the piezoelectric disc, it is possible to ensure that the outlet pressure has only very little influence on the outlet output. It is thus possible to determine the outlet output/pressure curves such as those shown in Figure 13. In this figure the curve A was obtained by applying a voltage at 2 Hz to 25 the piezoelectric disc of a micropump according to Figures 3 to 5 having approximately the dimensions stated hereinabove, the outlet output remaining virtually constant at a value of 30 ul/min (most favourable choice). If one controls the piezoelectric disc with a voltage at 5 Hz, this outlet is 30 brought to about 64 ^ul/min. Thus, as can be seen from the graphs of Figure 13, the choice of a given pretension on the membrane of the outlet valve keeps the output constant at the values shown over an outlet pressure range from 0 to 70 cm H2O. In addition, the graphs show that the output remains 35 constant even for the negative values of the difference between IE 902122 the outlet pressure and the inlet pressure (parts C and D respectively of the graphs). This situation can, for example, arise when there is overpressure at the pump inlet.

It will be noted that the micropump, regardless of the 05 embodiment described hereinabove, is compact and simple, presents little resistance to flow and makes it possible to determine with very good approximation a constant output as a function of the outlet pressure.

In all these embodiments, except those of Figures 1 and 2, 10 the pump was designed to guard against overpressure since the inlet of the pump communicates with a chamber situated above the outlet valve. Consequently, if such overpressure occurs, it acts on the outlet valve in the direction of closure, thereby insulating the outlet channel from the pumping chamber. This 15 property of the pump can be important when the pump is worn by a patient who also wears a flexible reservoir. If the latter compresses the reservoir (for example by knocking it against an obstacle) the overpressure in the pump aspiration does not cause a fluid flow on the outlet side thereof. in addition, due to the communication between the compensation chamber and the pump inlet, variation in the inlet pressure has only very little influence on the outlet output in the normal operating range of the pump.

It should be noted that the communication can also be 25 effected by a connection outside the pump. For example, the pump of Figures 1 and 2 could be provided with a tube connecting the inlet to the outlet.

Finally, Figure 1 shows that it is possible to connect an operating control element to the silicon wafer for example in 30 the form of a strain gauge 11 A, the variation in the resistance of which could be measured to show that the pump is operating correctly or else the membrane on which the gauge is bonded has ruptured. One or several of these control elements may of course be provided in all the embodiments described.

IE 902122

Claims (12)

1. A micropump having a first wafer (11; 27; 41; 56) of a material capable of being machined using photolithographic technology in such a way as to define with at least one second 05 support wafer (1; 26; 40) adhered face to face to the first wafer a pumping chamber (15; 44), a first valve of the check type (16; 33; 45) through which said pumping chamber (15; 44) is able to selectively communicate with a inlet (2; 30; 50) of the pump and a second valve of the membrane type (18; 10 36; 46) through which said pumping chamber can selectively communicate with an outlet (3; 36a; 43) of the pump, means (13; 14; 29; 49) being provided to cause a periodic variation in the volume of said pumping chamber (15; 44), wherein said outlet (3; 36a; 43) communicates directly with an isolated volume (18d) of 15 said pumping chamber (15; 44) by means of said second valve (18; 36; 46) and situated on the same side of this valve as the channel (19; 20) through which this valve communicates with the pumping chamber in such a way that the pressures prevailing respectively in this pumping chamber and this outlet act in the 20 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) via said pumping chamber (15; 44) in such a way that, during the outlet phase of the pump this chamber communicates directly with said outlet (3; 36a; 43) via 25 the second valve in open position.

2. A micropump according to claim 1 which comprises a third wafer (12; 28; 42; 55) covering said first wafer (11; 27; 41) at least over part of its surface and delimiting therewith at least one chamber (15; 21; 51; 54) designed to form an active 30 cavity of the pump.

3. A micropump according to claim 2 in which said means provided for causing a periodic variation in the volume of the pumping chamber comprise a piezoelectric disc (13; 29) fixed to said third wafer (12; 28) in a zone coinciding with said pumping 35 chamber (15). 'E 902122 - 14 -

4. A micropump according to claim 2 wherein said means provided for causing a periodic variation in the volume of the pumping chamber comprise a piezoelectric disc (49), in that said pumping chamber (44) is delimited by said first (41) and second 05 (40) wafers and in that said piezoelectric disc is fixed to said first wafer in a zone coinciding with said pumping chamber (44).

5. A micropump according to any one of claims 2 to 4, wherein said third wafer (55) is so designed also to form at least one of the connections by which the pump can be 10 connected to an outside means (Figure 11).

6. A micropump according to any one of claims 1 to 5, wherein a detector such as a strain gauge (11A) is fixed to said first wafer (11) to monitor the correct working of the pump.

7. A micropump according to any one of the preceding 15 claims, wherein said first valve (16; 33; 45) and/or said second value (18; 36; 46) comprise a membrane (16a) provided in the plan of said first wafer in the centre of which is provided an annular rib (16c), the top of which is designed to bear against another wafer (1; 12; 26; 28; 40; 41) serving as seating for 20 this valve and wherein at least said rib (16c) is covered by an oxide layer (17) inducing in the membrane a predetermined pretension so that the valve is normally closed.

8. A micropump according to claim 7, wherein the membrane (18a) of the second valve is at least partially covered with a layer of a material developing shearing stress in the membrane, thereby inducing an additional pretension in it. IE 902122 -14a- 0

9. A micropump according to claim 7 or 8 wherein on the side opposite said rib (16c), said membrane (16a) is provided with a 25 projection (39; Figure 6) extending towards another wafer (28) of the pump and designed to limit the travel of the membrane (16) in the event that this is subjected to an excess pressure.

10. A micropump according to any of claims 7 to 9 wherein the ribs (16c) provided respectively on the membranes 30 (16a) of said valves are disposed on the opposing faces of these membranes (valves 45 and 46, Figures 8, 9 and 10).

11. A micropump according to any of the preceding claims, wherein the pump inlet (2; 30; 50) communicates with a compensation chamber (21; 30; 51; 54) disposed above said second 35 valve (18; 36; 46) so as to close the latter under the influence of the pressure prevailing at said inlet.

12. A micropump substantially as hereinbefore described with reference to the accompanying drawings. Dated this 13th day of June 1990 Dublin 2.