CH684286A5 - Valve fitted with a contact position detector and micropump comprising such a valve - Google Patents

Abstract

The valve (26) is made in a silicon wafer (20). A position detector comprising a first electrical contact (54) formed on a glass support (32) bonded to the rear face of the wafer (20), a second electrical contact fixed to the wafer (20) and a circuit for measuring the electrical impedance (resistance or capacitance, depending on the embodiment) between the two electrical contacts is provided in order to detect by mechanical contact the position of the valve and thus detect an operating defect. Application to micropumps intended for injection of medicinal products. <IMAGE>

Description

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Description

The present invention relates to a valve fitted with a position detector of the type in which the valve body is produced by machining a wafer of silicon or of another material which can be machined by etching using techniques such as photolithography. or similar techniques, and a micropump comprising such a valve.

These micropumps can be used in particular for the in situ administration of drugs, the miniaturization of the pump possibly allowing a permanent implantation thereof in the body. These pumps allow precise dosing of small quantities of fluid to be injected.

Such micropumps are described in particular in the article "A piezoelectric micropump based on micromachining of Silicon" by H. van Lintel et al. published in Sensors and Actuators, n ° 15, 1988, pp 153-157. These micropumps essentially comprise a stack of three wafers, that is to say a silicon wafer disposed between two glass wafers.

The silicon wafer is etched to form a cavity, which with one of the glass wafers defines the pumping chamber, a suction valve and a discharge valve putting the pumping chamber in communication respectively with an inlet channel and an outlet channel, and a control valve. A control element, such as for example a piezoelectric pellet, is provided on a wall of the chamber. This piezoelectric pellet can be deformed when it is subjected to an electric voltage, which causes a deformation of the wall of the pumping chamber and, consequently, a variation in volume thereof.

The operation of the micropump is as follows. At rest, the suction and discharge valves are in the closed position. When an electrical voltage is applied, the wall of the pumping chamber deforms and the pressure increases in the latter until the discharge valve opens. The fluid contained in the pumping chamber is then discharged towards the outlet channel. During this phase, the suction valve is kept closed by the pressure prevailing in the pumping chamber. On the contrary, when the electric voltage is removed or reversed, the pressure in it decreases. This induces the closing of the discharge valve and then the opening of the suction valve. There is then suction of the fluid in the pumping chamber.

As already indicated, these micropumps are used in particular for the administration of drugs. It is therefore important to be able to control the proper functioning of these micropumps. In addition, in certain cases the pump flow can drop considerably, for example when the pumping chamber contains air bubbles or when the pressure in the outlet channel becomes too high.

Obviously, such malfunctions must be detected. It has been discovered that the movement of the valve could be used for this purpose. The invention therefore aims to provide a valve with a position detector which, moreover, is simple, reliable and inexpensive.

Specifically, the subject of the invention is a valve comprising a first plate and a second plate, attached to the first plate to define a valve seat, which is characterized in that it comprises a position detector comprising a first contact electric arranged opposite the rear face of the valve body, at a distance such that there is mechanical contact between the valve body and the first electrical contact when the valve is in the open position, a second electrical contact arranged so forming an electrical impedance with said first electrical contact, which is a function of said mechanical contact, and a detection circuit sensitive to the electrical impedance between the two electrical contacts.

The mechanical contact between the valve body and the first electrical contact thus ensures the greatest possible difference in electrical impedance between the open and closed positions of the valve.

The invention also relates to a micropump comprising a valve fitted with such a position detector.

The characteristics and advantages of the invention will emerge more clearly from the description which follows, given by way of illustration but not limitation, with reference to the appended drawings, in which:

- fig. 1 is a diagrammatic section along the line I-I of a micropump comprising a discharge valve according to the invention,

- fig. 2 is a bottom view, along line II-11, of the intermediate plate of the micropump shown in FIG. 1,

- fig. 3 and 4 show in section a valve according to a first embodiment of the invention, respectively in the closed position and in the open position,

- fig. 5 schematically represents a detection circuit adapted to the valve of FIGS. 3 and 4,

- fig. 6 and 7 show in section a valve according to a second embodiment of the invention, respectively in the closed position and in the open position, and

- fig. 8 schematically represents a detection circuit adapted to the valve of FIGS. 6 and 7,

- fig. 9a shows in section a valve according to a third embodiment of the invention, and FIG. 9b shows a bottom view along line IX-IX of FIG. 9a, and

- fig. 10 shows in section a valve according to a fourth embodiment of 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.

This micropump has a base plate 2, for example made of glass, which is pierced by two channels 4 and 6 respectively forming the con5

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suction line and discharge line of the pump. These channels communicate respectively with fittings 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 plug, a movable piston 16 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 connector 10 can be connected to an injection needle (not shown) which is connected to it by a pipe 18.

The use of the micropump in this way is particularly suitable for the treatment with peptides of certain forms of cancer, the medication of which is preferably carried out by precise and repeated dosing at small intervals of small quantities of drugs. . Another application is the injection of insulin for the treatment of diabetes.

A wafer 20 made of silicon or another material that can be machined by etching using photolithography techniques is attached to the glass wafer 2. This wafer 20 is machined to define a suction valve 22, a pumping chamber 24 and a discharge valve 26 (which also constitutes a control valve). A glass closure plate 28 is attached to the plate 20 above the suction valve 22; a piezoelectric pellet 30 at the wall of the pumping chamber 24, and a glass support 32 above the discharge valve.

The suction valve 22 comprises a membrane 34 of generally circular shape pierced in its center with a passage orifice 36 and, on the side of the inlet channel 4, an annular rib 38. The latter is covered with a thin layer oxide which gives the membrane 36 a certain prestress tending to apply the top of the rib against the glass plate 2, the latter thus serving as a seat for the valve 22. When this valve is open, the inlet channel 4 is in communication with the pumping chamber 24 through the orifice 36 and another orifice 40.

The discharge valve 26 also comprises a membrane 42 of generally circular shape, the latter without a passage orifice, and an annular rib 44 which, as for the suction valve, is covered with a thin layer of oxide. The opening of this discharge valve puts the pumping chamber 24 directly in communication with the outlet channel 6.

Finally, it is noted that the piezoelectric pellet, which is used to control the variations in volume of the pumping chamber, is connected by two electrical conductors 46 and 48, on the one hand, to electrodes (not shown) deposited on the faces of the piezoelectric chip and, on the other hand, to a source of electrical voltage 50.

According to the invention, the discharge valve 26 is provided with a contact position detector. The boss 56 visible on the rear face (that which is not in contact with the pump fluid) of the valve as well as the support 32 are part of this contact position detector. Two particular embodiments of this contact position detector will now be described.

A first embodiment in which the position detector is of the capacitive type is shown in FIGS. 3 to 5.

It should be noted that to ensure good control of the shape of the membrane, the actual lateral dimensions of the membrane are defined by engraving on the front face of the valve. A thermal oxide layer is also formed on the valve membrane. This provides sufficient pretension for a thin membrane. With such thin membranes, the deflection of the membrane can be significant.

The support 32, for example made of glass, may have a groove 52 on its face contiguous to the plate 20. An electrode 54, for example made of Au, Al or indium tin oxide (ITO), is formed on the support 32. The distance between the electrode 54 and the upper part of the rear face of the valve 26, that is to say here the surface of the boss 56, is such that there is mechanical contact between the body of valve and the electrode 54, when the valve is in the open position. To reduce the parasitic capacitances between the electrode 54 and the silicon wafer 20, the distance between them is increased by also making a groove 55 in the wafer 20. Similarly, the upper surface of the boss 56 can be isolated, for example by a thin layer of oxide (of the order of approximately 1 μm).

Thus, when the valve 26 is closed (fig. 3), the distance between the valve and the electrode 54 is of the order of 5 μm whereas, when the valve 26 is open (fig. 4), the valve and the electrode are in contact.

The circuit shown in fig. 5 detects the position of the valve. It comprises a resistor 58 connected, on the one hand, to an alternating voltage source and, on the other hand, to the electrode 54; a transistor 60 whose collector is connected to a DC voltage source at 3 V and the base to the electrode 54; and a resistor 62 disposed between the emitter of transistor 60 and the earth. The valve 26 behaves like a switch 64 which, depending on the structure used, can be resistive and / or capacitive. The silicon wafer 20 is connected to ground directly or, as shown, by the conductor 46 of the control circuit of the piezoelectric chip; in this case, the capacitor 66 represents the capacitance between them.

In this embodiment, the conductor 46 forming one of the electrical contacts is fixed to the wafer 20. It could also only be electrically coupled to it, for example to form an air capacitor.

A high frequency signal, for example at 30 kHz (so that the detection signal is sufficiently modulated according to the position of the valve, taking into account the impedances of the components and to avoid interference with the excitation signal

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of the piezoelectric pad) is applied to the electrode 54 through the resistor 58. The signal detected on the emitter of the transistor 60 is a function of the position, open or closed, of the valve.

The duration of the detected signal also makes it possible to distinguish between a malfunction due to the presence of an air bubble in the pumping chamber, which can result in an incomplete opening but also in a rapid closing of the valve after it was opened by a command on the piezoelectric pad, and a malfunction due to a high pressure in the outlet channel of the micropump, which results in a prolonged opening of the valve. The pump can also be constructed or can operate so that, during normal operation, the pump does not reach the open position, but only reaches it when the pressure in the outlet channel is too high. In this case, the invention is mainly used to detect an excessively high outlet pressure or a blockage.

The micropump can also be designed so that the valve does not fully reach the open position in normal operation, but only when the pressure in the outlet channel is too high. In this case, the invention is only used to detect an excessively high outlet pressure or a blockage of the micropump.

A passive type detection circuit can also be used, in certain cases. When a control signal is applied to the piezoelectric pad (continuous signal of about 130 V), a brief interference signal appears on the emitter of transistor 60 when the valve is in the open position (fig. 4). However, this signal does not make it possible to detect the duration during which the valve is in the open position.

A second embodiment in which the contact position detector is of the resistive type is shown in FIGS. 6 to 8.

Figs. 6 and 7 are identical to FIGS. 3 and 4, except that an additional electrode 68 is produced on the rear face of the valve 26, opposite the electrode 54. This electrode is for example made of Au, Al or indium tin oxide, and it is connected to a conductor 70, of the same material, which passes through the groove 52.

A detection circuit is shown diagrammatically in FIG. 8. It comprises a resistor 72 arranged between the electrode 54 and a voltage source, for example alternating voltage at 30 kHz. The presence or absence of an AC voltage signal on the conductor 54 indicates the closed or open position of the valve. As with the circuit in fig. 5, the detection of the closing of the circuit and the measurement of the duration of this closing make it possible to know the presence and the nature of a malfunction of the micropump.

In the embodiment of FIGS. 6 and 7, one of the electrodes is located on the rear face of the valve. It is however possible to avoid forming or depositing the electrodes independently; the two electrodes can simply be placed on the support 32, separated from each other so that they are both in contact with the valve when the latter is in the open position. Such a structure is shown in FIG. 9a, on which the elements identical to those of FIGS. 6 and 7 have the same reference numbers. The electrodes 54 and 74 may have a semi-circular shape, as shown in FIG. 9b; the electrical connections are arranged in grooves (such as groove 52 in figs. 3 and 6) or are made by means of metallized holes 76, 78 in the support 32.

The detection of the open position of the valve, which is defined by the contact of the valve with the electrodes, can be of the resistive or capacitive type. In the latter case, the contact is less critical and has the advantage of a strong reduction in the current through the liquid, compared to the first embodiment.

The micropumps according to the invention are intended to be used in particular for the injection of medicaments. Such micropumps therefore require precise control of the opening and closing of the valves. However, although it is relatively easy to control the etching depth of the silicon wafer, it is much more difficult to control the thickness of the valve membrane, since the thickness of the silicon wafer is not constant over its entire surface, but on the contrary presents certain variations. The thickness of the diaphragm controls the intensity of the pretension and, consequently, the opening and closing parameters of the valves. This is particularly important in the case of the outlet valve, which requires a higher pretension.

The degree of variation of the pretension depends in particular on the pretension due to the thickness of the oxide layer on the annular rib. This pretension depends on the thickness of the membrane and raised to the cube. It is added to the pretension caused, for example, by the oxide layer on the membrane, which is proportional to the thickness of the membrane. In this classic case, an excessively thick membrane simultaneously causes an increase in the pretension due to the oxide on the annular rib and the pretension due to the oxide on the membrane. The variation of the total pretension is the sum of the variations of these two pretensions. The pretension caused by the oxide on the annular rib can play an important role in this variation, because of this dependence of the third order.

Fig. 10 shows a fourth embodiment of the invention in which the pretension is less dependent on the thickness of the membrane, and in which, for this purpose, an additional etching step is implemented to make all or part of the space between the two parts of the detector. By way of example, the detector is of the capacitive type, as in the embodiment of FIGS. 3 to 5, the electrode 54 on the support 32 being connected to the detection circuit through a metallized hole 76 produced in the support 32. In this embodiment, the annular rib is etched during an additional etching step (during which the membrane can equal5

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be etched, and in this case has been etched on both sides) and the oxide layer on it is smaller than the etching depth, so that the effective thickness of the annular rib is more smaller than its nominal thickness. Thus, if the oxide is not deposited on the membrane but only on the annular rib, the latter is not in contact with the valve seat. In the same way as in the classic case, it is clear that the annular rib causes a pretension, which here is negative, the absolute value of which is equal to the pressure which would have to be exerted on the membrane so that the annular rib comes to be flush the valve seat. However, in the case where the oxide layer is also formed on the membrane (the oxide layer can be produced on one side of the membrane, or as shown in FIG. 10, on both sides), the pretension to which the valve is subjected is equal to the pretension caused by the curvature of the membrane minus this negative pretension. In this situation, the change in pretension due to the oxide on the membrane can be roughly compensated for by the change in negative pretension due to the annular rib.

The dimensions are chosen so that the total pretension remains substantially constant over a certain range of thickness of the membrane. In addition, the dimensions can be chosen so as to adjust the space required for the detector with the additional etching, so as to obtain the space required with this same additional etching operation. In this example, the boss 56 is also etched for this purpose, simultaneously.

Simulations have shown that the micropumps fitted with an outlet valve according to the embodiment of FIG. 10 have essentially the same pretension, and thus have practically the same behavior, despite a difference of plus or minus 2.5 μm in the thickness of the diaphragm of the valves for an average thickness of 25 (im (depth of etching of the annular rib about 4 µm; oxide layers about 1 µm).

The position detector according to the invention has the following properties:

- no calibration necessary, since the detector must only distinguish two signal values, which correspond respectively to the open position and to the closed (or partially open) position of the valve,

- not very sensitive to interference with external signals (for example, to the piezoelectric pellet control signal),

- simple and inexpensive components.

With regard to the embodiments described above, it can be added that the capacitive type position detector (FIGS. 3 to 5) works satisfactorily even if there is not a good electrical contact between the valve. and the electrode 54, while the electrical circuit of the resistive type position detector (FIGS. 6 to 8, and 9a, 9b) is particularly simple.

Claims (12)

Claims 1. Valve comprising a first plate (20) machined to define a valve body (26) and a second plate (2) adjoining said first plate to define a valve seat, which is characterized in that it comprises a detector position comprising a first electrical contact (54) disposed opposite the rear face of the valve body, at a distance such that there is mechanical contact between the valve body and said first electrical contact when the valve is in position open, a second electrical contact (46, 68, 74) arranged to form an electrical impedance with said first electrical contact, which depends on said mechanical contact, and a detection circuit (58, 60, 62, 72) sensitive to the electrical impedance between said electrical contacts. 2. Valve according to claim 1, characterized in that a support (32) is fixed on said first plate (20) opposite the rear face of the valve body, this support receiving said first electrical contact (54). 3. Valve according to any one of claims 1 or 2, characterized in that the rear face of the valve has a boss (56) opposite said first electrical contact. 4. Valve according to any one of claims 1 to 3, characterized in that said second electrical contact is fixed or connected to said first wafer. 5. A valve according to claim 4, characterized in that the second electrical contact is an electrode (68) disposed opposite the first electrical contact, the detection circuit (72) being sensitive to the electrical resistance between said electrical contacts. 6. A valve according to claim 4 in which said first plate (20) is made of a semiconductor material, characterized in that said second electrical contact (46) is connected to said first plate and conductively isolated from said first electrical contact (54), and in that the detection circuit is sensitive to the electrical capacitance between said electrical contacts. 7. A valve according to any one of claims 2 and 3, characterized in that said second electrical contact is located on the support (32), facing the rear face of the valve body, and is electrically isolated from said first electrical contact . 8. Valve according to any one of claims 1 to 7, characterized in that the detection circuit comprises an alternating voltage generator. 9. Valve according to any one of claims 1 to 8, comprising a membrane (42) and an annular rib (44), at least the membrane being provided with a layer inducing a pretension, characterized in that the annular rib ( 44) and the plate (2) facing the annular rib are shaped so that in the closed position of the valve, the membrane (42) is curved in the direction of the plate (2) facing the annular rib, said pretension requesting the 5 10 15 20 25 30 35 40 45 50 55 60 65 5 9 CH 684 286 A5 valve in the closed position in the absence of external influence. 10. A method of manufacturing a valve according to claim 9, characterized in that the machining operation of the annular rib is common with the machining operation to form the space between the valve body and said first electric contact. 11. Micropump comprising a first plate (20) machined to define with at least a second plate (2) contiguous facing the first plate, a pumping chamber (24), and comprising means for sucking and discharging a said pumping chamber, characterized in that it comprises, downstream of the pumping chamber, at least one valve according to any one of claims 1 to 9. 12. Micropump comprising a first plate (20) machined to define with at least a second plate (2) placed face to face with the first plate, a pumping chamber (24), a suction valve (22) through which said pumping chamber can selectively communicate with an inlet (4) of the micropump and a discharge valve (26) through which said pumping chamber can selectively communicate with an outlet (6) of the micropump, means (30, 46 , 48, 50) being provided to cause a periodic variation in volume of said pumping chamber, characterized in that the discharge valve (26) conforms to any one of claims 1 to 9. 5 10 15 20 25 30 35 40 45 50 55 60 65 6