Pumps – Motor driven – Electric or magnetic motor
Patent
1992-03-04
1994-01-11
Bertsch, Richard A.
Pumps
Motor driven
Electric or magnetic motor
417410A, 137855, F04B 1700
Patent
active
052775569
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to micropumps, and particularly to micropumps of the type in which at least a part of the mechanism of the pump is formed by machining a wafer using micromachining technologies such as photolithographic technology and in particular a valve for such a micropump.
BACKGROUND OF THE INVENTION
Pumps of this type can be used notably for the in situ administration of medicaments whereby miniaturisation of the pump enables the patient to wear it on his person or optionally to have a pump directly implanted in his body. In addition, using pumps of this type small quantities of liquid can be accurately administered.
In an article entitled "A piezoelectric micropump based on micromachining of silicon" published in "Sensors and Actuators" No. 15 (1988), pages 153 to 167, H. van Lintel et al. 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. Another embodiment of such a micropump is described in Swiss Patent Application No. 02 241/89-1 of Jun. 14, 1989.
In this article a silicon wafer defines a pump chamber with one of the glass wafers, it being possible for the part coinciding with this chamber to be deformed by a drive means, in the present case a piezoelectric crystal. The latter comprises electrodes which, when connected to an alternative voltage source, cause deformation of the crystal and thus of the glass wafer, the latter in turn causing variation in the volume of the pump chamber.
The pump chamber is connected on both sides to check valves in which a membrane and a sealing ring are machined from silicon and the seat of which is composed of the other glass wafer.
The construction of such a valve is carried out in two stages. In a first step, the silicon wafer is etched in order to form the membrane, part of the wafer being protected from the etching in order to form the sealing ring and in a second step a thin layer of oxide is formed on the sealing ring and optionally on part of the membrane. This gives to the membrane a certain mechanical preconstraint or pre-tension whereby the seat of the valve is forced towards the sealing ring.
One of the disadvantages of this type of micropump is that the yields of such micropumps, which may seem to be identical, are not the same. This mainly results from the fact that even though it is relatively easy to control the depths of the etching of the silicon, it is more difficult to control the thickness of the membranes since the thickness of a wafer of silicon is not constant over the whole of its surface, but on the contrary shows certain variations. The thickness of the membranes governs the amount of the pre-tension and hence ultimately the parameters for the opening and closing of the valves. This is particularly important in the case of the outlet valve which requires a greater pre-tension.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome this disadvantage. This object is achieved by a valve according to claim 1. Claim 7 also defines a valve according to the invention which reduces this disadvantage. Claim 8 defines a micropump equipped with at least one valve according to the invention.
The layer of other material may be realized on the membrane, so as to cover it for example by thermal oxidation, or in the membrane, for example by a heavy doping the membrane surface.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the invention are better illustrated by the following description given for purposes of example, but which is not limiting and with reference to the accompanying drawings in which:
FIG. 1 shows a schematic cross-section of a micropump according to the invention,
FIG. 2 shows a top view of the intermediate wafer of the micropump shown in FIG. 1, 5 FIGS. 3A, 3B and 3C show a section of an embodiment of the valve according to the invention, and
FIG. 4 shows a section of a further valve according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
Reference is
REFERENCES:
Article entitled "A piezoelectric micropump based on micro-machining of silicon" Sensors and Actuators, vol. 15, #2, pp. 153-167.
International Search Report for PCT/EP91/01240.
Basichas Alfred
Bertsch Richard A.
Westonbridge International Limited
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