CH683634A5 - Valve fitted in micro-pump - Google Patents

Abstract

The value (32, 42) has a first wafer (18) in which a deformable membrane (34, 44) is made, and a second wafer (2) bonded to the first. A sealing ring (38, 46) on the face of one wafer has a free surface to contact the face of the other wafer (valve closed) or to be spaced apart from the other (valve open), according to the position of the membrane. The membrane has at least one layer of other material (40, 40a, 40b) inducing a mechanical strain keeping the value in the closed position in the asbence of external influence. At least one of the wafers is machined so that if the layer or layers would be omitted the value would be in the open position in absence of external influence.

Description

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Description

The present invention relates to micropumps of the type in which at least part of the pump mechanism is produced by machining a silicon wafer using photolithography techniques, and more particularly to a valve for such a micropump.

These pumps can 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 to receive a pump directly implanted in the body. Furthermore, such pumps allow precise dosing of small quantities of fluid to be injected.

In an article entitled "A piezoelectric micropump based on micromachining of Silicon" published in "Sensors and Actuators" N ° 15 (1988), pages 153 to 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 machined silicon wafer disposed between two glass wafers. Another embodiment is described in Swiss patent 680 009.

In this article, the silicon wafer defines a pumping chamber with one of the glass wafers, the part of which coincides 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 alternating voltage source, cause the crystal to deform and, as a result of the glass plate, this, in turn, varying the volume of the pumping chamber.

The pumping chamber is connected on either side respectively to non-return valves of which a membrane and a shutter are machined in silicon and whose seat is formed by the other glass plate.

The realization of such a valve comprises two stages. A first step of etching the silicon wafer to form the membrane, a part of the wafer being protected from etching to define the shutter, and a second step during which a thin layer of oxide is produced on the obturator and possibly on part of the membrane. This gives the membrane a certain mechanical prestress, or pretension, when the seat of the valve is applied against the shutter.

One of the drawbacks of this type of micropump is that the apparently identical flow rates of micropumps are not the same. This results from the fact that while it is relatively easy to control the etching depth of the silicon, it is more difficult to control the thickness of the membranes, since the thickness of a silicon wafer is not constant over its entire length. surface but on the contrary has a certain dispersion. However, the thickness of the membrane partially conditions the intensity of the prestressing, and therefore ultimately the conditions for opening and closing the valve. This is particularly important for the outlet valve, which requires greater preload.

The object of the invention is to eliminate this drawback in particular.

This object is achieved by a valve according to claims 1 and 7. Claim 8 defines a method of manufacturing such a valve and claim 9 a micropump provided with at least one valve # according to the invention.

The characteristics and advantages of the invention will emerge more clearly from the description which follows,

given by way of illustration but not limitation, in reference *

Refer to the accompanying drawings, in which:

- fig. 1 illustrates a schematic section of a micropump according to the invention,

- fig. 2 illustrates a bottom view of the intermediate plate of the micropump shown in FIG. 1,

- fig. 3A, 3B and 3C show in section the production of a valve according to the invention, and

- fig. 4 shows in section another valve according to the invention.

We will first refer to fig. 1 and 2 which represent a micropump comprising a valve according to the invention.

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

The micropump of figs. 1 and 2 comprises a base plate 2 made of glass for example, which is pierced with two channels 4 and 6 respectively forming the suction pipe and the delivery pipe of the pump. These channels 4 and 6 communicate with respective connections 8 and 10.

The connector 8 is connected to a pipe 12 itself connected to a reservoir 14 in which is the liquid substance to be pumped. The reservoir is closed by a pierced cap, a movable piston isolating the useful volume of the reservoir 14 from the outside. This reservoir can contain a medicine, for example in case the pump is used for the injection of this medicine into the human body with a precise dosage. In this application, the micropump can be worn on the patient's body, or even be implanted.

The discharge connection 10 can be connected to an injection needle (not shown) which is connected to it by a pipe 16.

The use in this way of the micropump is particularly suitable for the treatment with the aid of peptides of certain forms of cancers the medication of which is preferably carried out by precise and repeated dosing at small intervals of small quantities of the drug. . Another application can be considered for the treatment *

diabetics having to periodically receive low doses of medication during the day, the dosage being determinable, for example, by means known per se measuring the blood sugar level and automatically controlling the pump so that an appropriate dose of insulin can be injected.

A wafer 18 made of silicon or another material that can be machined by etching using techniques

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photolithography is attached to the glass plate 2. This silicon plate is itself surmounted by a glass closure plate 20. In the plate 18 is formed a membrane 22 whose thickness is such that it can be deformed by a control element 24 which, in the application of the invention described here, is a piezoelectric pad provided with electrodes 26a and 26b connected to a generator 28 of alternating voltage. This pellet can be that manufactured by the Philips Company under the name PXE-52 and it can be glued to the wafer 18 using an appropriate glue.

By way of example, the intermediate wafer 18 made of silicon can have a crystal orientation <100>, in order to lend itself well to etching and to have the necessary solidity. The inserts 2 and 20 are preferably carefully polished.

The plates 2 and 18 together define first of all a pumping chamber 30 of substantially circular shape located below the membrane 22.

Between the suction pipe 4 and the pumping chamber 30 is interposed a first valve 32 of the non-return type machined in the silicon wafer 18. This valve comprises a membrane 34 of generally circular shape and pierced in its center with a passage orifice 36 which, in the embodiment shown, is rectangular. On the side of the pipe 4, the valve 32 has a rib 38 of annular shape and of roughly trapezoidal section forming a shutter. This rib surrounds the orifice 36 and is coated with a thin layer of oxide 40 also obtained by photolithography techniques. This gives the membrane 34 a certain prestress or pretension when the top of the rib 38 is applied against the glass plate 2, the latter thus serving as a seat for the valve 32.

The discharge line 6 of the pump communicates with the pumping chamber 30 by means of a valve 42 whose construction is identical to that of the valve 32, except however that, for example by making a layer d oxide on a part of the membrane and / or by difference in thickness of the layer 40 relative to that of the valve 32, the prestress provided by this oxide layer 40 may be different from that used for the valve 32. The valve 42 therefore comprises a membrane 44 and an annular rib 46, forming a shutter, coated with an oxide layer 40. Furthermore, it can be seen in FIG. 1 that this valve does not have a central orifice such as the orifice 36 of the valve 32.

It will be noted that the pumping chamber 30 communicates with the valve 32 and with the valve 42 respectively via an orifice 48 and a passage 50 both machined in the silicon wafer 18.

To fix the ideas, the thicknesses of the plates 2, 18 and 20 can respectively be around 0.6 mm, 0.3 mm and 0.6 mm for a surface dimension of the plates of the order of 15 by 20 mm .

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

The valves 32 and 42 have a pretension tending to apply the annular rib against the valve seat, in the absence of any external stress. This pretension depends on the thickness of the oxide layer on the membrane, which induces a curvature of the membrane, on the thickness of this membrane and on the height of the annular rib.

By way of example, we will describe the process for producing the outlet valve with reference to FIGS. 3A-3C. The same process can be used to make the inlet valve. However, since the preload required for the inlet valve is lower than for the outlet valve, an oxide layer is generally not deposited on the membrane of the inlet valve.

The outlet valve is therefore produced in accordance with the invention in the following manner. The silicon wafer 18 is etched on at least one of its faces, for example by dipping in a KOH solution, to form the membrane 44. During this phase, part of the wafer is protected from etching to define the annular rib 46 (fig. 3A).

An over-etching 52 is then produced so that, in the absence of an oxide layer and without any external stress, the annular rib does not come into contact with the valve seat. This over-etching can be carried out in the silicon wafer 18 before or after the etching (it results in a reduction in the thickness of the membrane, see fig. 3A); it can also be carried out in the part of the glass plate forming the valve seat.

An oxide layer 40 is then produced by thermal oxidation on a part of the membrane. This oxide layer induces shear forces in the membrane, which causes its curvature (fig. 3B). The thickness of the oxide layer is chosen to be sufficient so that, when the glass wafer 2 is attached to the silicon wafer 18, the rib 46 is applied against this glass wafer in the absence of any other external stress ( fig. 3C). For example, for an etching depth of 2 to 3 nm, an oxide layer of approximately 1.5 μm is produced. This oxide layer can be produced, as shown in FIG. 3B, on the front face of the membrane, that is to say on the side of the rib. It is possible to choose to oxidize the rear face instead of the front face. However, in order for the membrane to be curved in the same direction, it is then necessary to produce the oxide at the periphery of the membrane, in the form of a ring.

One could of course use a material other than silicon oxide to cause this curvature. However, this is the simplest solution since it suffices to subject the wafer to thermal oxidation.

The oxide layer or another layer of another suitable material can also advantageously cover the rib 46 (FIG. 3B) and thus form

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a protective layer to prevent adhesion of the rib on the glass plate.

This protective layer increases the height of the rib; it therefore modifies the pretension due to the rib. It is in fact understood that, in the absence of oxide on the membrane, no pretension is created by the rib when its height (called nominal height) is such that the top of the rib is flush with the valve seat, in l absence of external solicitation. This case corresponds to fig. 3A, before the over-etching 52 is carried out.

When the height of the rib is greater than its nominal height, for example because an oxide layer covers the rib, the latter is applied with a certain pretension against the valve seat. The value of this pretension depends in particular on the difference in height of the rib relative to the nominal height and on the elasticity, and therefore on the thickness, of the membrane. This pretension is added to that which is caused by the oxide layer which curves the membrane, and which also depends on the thickness of the membrane. A variation in the thickness of the membrane induces, in this classic case, variations in the same direction of the pretension due to the rib and of the pretension due to the curvature of the membrane, and consequently a variation of the total pretension.

Conversely, when the height of the rib is less than its nominal height, for example as a result of an over-etching of the plate 18 and a deposit of an oxide layer on the rib thinner than the depth from the overprint, the rib is not in contact with the valve seat. We can consider, by symmetry with the previous case, that the rib creates a negative pretension whose absolute value is equal to the pressure that would have to be exerted on the membrane so that the rib is flush with the valve seat. When, in addition, an oxide layer is produced on the membrane, the pretension to which the valve is subjected is equal to the pretension due to the curvature of the membrane reduced by this negative pretension. A variation in the thickness of the membrane induces, in this case in accordance with the invention, variations in the pretension due to the rib and in the pretension due to the curvature of the membrane in the same direction in absolute value. However, since these pretensions are subtracted from each other, the total pretension remains substantially constant.

Tests have shown that micropumps fitted with an outlet valve in accordance with the invention exhibited substantially the same pretension, and therefore had the same behavior, despite a dispersion of ± 2.5 μm in thickness for valve membranes having an average thickness equal to 25 µm (overprinting depth about 3 µm; oxide layer about 1.5 µm).

The oxidation of the wafer 18 to form the oxide layer 40 is a relatively long step since the thickness of the oxide layer increases as the square root of the oxidation time. The duration of this operation can be divided by four. It suffices for this, as shown in FIG. 4, to oxidize the two faces of the membrane. Indeed, if one carries out oxide layers 40a and 40b with a thickness of 0.5 μm for example, one obtains a prestress identical to that caused by a layer 40 formed on a single face of the membrane with a thickness of 1 (im.

It may be added that, even without resorting to the over-etching mentioned in connection with FIG. 3A, the oxidation of the two faces of the membrane contributes to better reproducibility of the characteristics of the micropump. This results from the fact that the height of the rib is increased less, compared with the case where one oxide of the membrane is oxidized, which reduces the influence of the rib on the pretension of the valve.

It can also be emphasized that the oxidation of the two faces of the membrane makes it easier to adjust the pretension to a desired value by choosing the radius of the oxide layer appropriately.

Claims (9)

Claims 1. Integrated valve (32, 42) comprising a first plate (18) made of a material capable of being machined by photolithographic techniques, in which a deformable membrane (34, 44) is formed, and a second plate (2 ) attached to the first plate (18), a shutter (38, 46) being further produced on the face of one of the plates and having a free surface which can be brought into contact with the face of the other plate (valve closed ) or away from it (valve open), depending on the position of the deformable membrane, the membrane being partially covered with a layer of a second material (40) inducing mechanical stress maintaining the valve (32, 42 ) in the closed position in the absence of external stresses, said valve (32, 42) being characterized in that the deformable membrane (34, 44), the shutter (38, 46) and the plate facing the shutter (38, 46) are shaped so that the valve is placed in position closed only by the stress induced by said layer of a second material. 2. A valve according to claim 1, characterized in that the shutter (38, 46) is formed on the membrane (34, 44) of the first plate (18). 3. Valve according to any one of claims 1 and 2, characterized in that each face of the membrane (44) is partially covered with a layer (40a, 40b) of the second material. 4. Valve according to any one of claims 1 to 3, characterized in that the first plate (18) is made of silicon and the second material is silicon oxide. 5. Valve according to any one of claims 1 to 4, characterized in that the free surface of the shutter (38, 46) is covered with a layer of a third material to prevent adhesion of said shutter on the face of the plate opposite. 6. Valve according to claim 5, characterized in that said third material is identical to the second material. 7. Integrated valve comprising a first plate (18) of material capable of being machined by photolithographic techniques, in which 5 10 15 20 25 30 35 40 45 50 55 60 65 7 CH 683 634 A5 is formed a deformable membrane (34, 44) and a second plate (2) attached to the first plate (18), a shutter (38, 46) being further formed on the face of one of the plates with a free surface capable of be brought into contact with the face of the other plate (valve closed) or distant from it (valve open), depending on the position of the deformable membrane, said valve being characterized in that each face of the membrane (44) is partially covered with a layer (40a, 40b) of a second material inducing mechanical stress keeping the valve in the closed position in the absence of external stresses. 8. A method of manufacturing an integrated valve according to one of claims 1 to 6 comprising a first plate (18) of a material capable of being machined by photolithographic techniques, in which is formed a deformable membrane (34, 44 ), and a second plate (2) attached to the first plate (18), a shutter (38, 46) being further produced on the face of one of the plates and having a free surface which can be brought into contact with the face from the other plate (valve closed) or away from it (valve open), depending on the position of the deformable membrane, the membrane being partially covered with a layer of a second material (40) inducing mechanical stress now the valve (32, 42) in the closed position in the absence of external stresses, the method being characterized in that at least one of the plates is machined so that, before the layer of the second material (40) be carried out, said valve (32, 42) is in the open position in the absence of external stresses. 9. Micropump comprising a first plate (18) made of a material capable of being machined by photolithographic techniques so as to define, with at least a second support plate (2) placed side by side with the first plate, a pumping chamber (30), at least a first valve (32) through which said pumping chamber (30) can selectively communicate with an inlet (4) of the micropump and at least a second valve (42) through which said pumping chamber (30) can selectively communicate with an output (6) of the micropump, means (24, 26a, 26b, 28) being provided to cause a periodic variation in volume of said pumping chamber (30), said micropump being characterized in that at least one of the valves (32, 42) conforms to any one of claims 1 to 7. 5 10 15 20 25 30 35 40 45 50 55 60 65 5