Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1999-06-10
2001-01-30
Walberg, Teresa (Department: 3742)
Pumps
Motor driven
Electric or magnetic motor
C417S322000, C604S068000
Reexamination Certificate
active
06179584
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a microejector pump for generating microdrops, consisting of at least one pump chamber configured in a silicon chip, (and) a silicon membrane arranged over the pump chamber and piezoelectrically actuable, the pump chamber being connected to at least one supply line and a discharge line provided with an ejection orifice, in which a glass chip closes off at least the pump chamber from the silicon membrane.
By means of such microejector pumps, the handling of extremely small quantities of fluid is made possible, which may be either pure substances or mixtures of substances, or alternatively contain microparticles suspended in liquids, to be subjected to controlled further processing in chemical analysis, medical technology, biotechnology, etc.
These microejector pumps, in combination with a suitable handling device, for example manipulators, permit the controlled release of these substances at the point of further sample processing or of sample disposal, as the case may be. Using a suitable positioning technique, the points of sampling and sample deposition may be different. The point of sample deposition may be a liquid surface, a solid surface, or else a gas-filled reaction chamber.
A micropump intended for the above purposes is disclosed in U.S. Pat. No. 5,094,594. This patent discloses a micropump which consists of a pump unit having an associated pump chamber and a deformable chamber sector on which an electrically triggerable piezoelement is arranged. The liquid to be delivered is supplied to the pump chamber by way of an inlet capillary (supply line). The force alternately exerted on the deformable chamber sector by the actuation of the piezoelement effects a continuous pressure variation in the pump chamber, so that alternately a loading thereof by way of the inlet capillary and an expulsion of the liquid by way of an outlet capillary in communication with the pump chamber takes place. To achieve an adequate pump action, piezoelectrically actuable valves are provided in each of the inlet and outlet capillaries.
The production of such a micropump in a silicon substrate may be accomplished by the known process of photolithography and anisotropic textural etching. On the silicon substrate so textured, a glass plate is then applied by anodic bonding, thus creating a firm glass-silicon bond.
With such a micropump, it is possible to apply small quantities of fluid, although only a comparatively limited frequency range and hence only a limited delivery rate are available. For example, with the micropump just described, for example a delivery of only about 500 picoliters is attainable. To ensure the requisite functional dependability of this micropump, it is necessary that the liquids or suspensions exhibit as low a viscosity as possible.
In addition, WO A 9419609 shows a micropump containing a pump chamber with variable chamber volume and a liquid inlet as well as a liquid outlet. In order to obtain liquid transport through the pump chamber towards the liquid outlet and at the same time to dispense with the wear-prone valves otherwise required, here a combination of a diffuser with a nozzle is provided. This diffuser is associated with the liquid inlet and the nozzle with the liquid outlet.
SUMMARY OF THE INVENTION
An object of the invention is to create a microejector pump suitable for handling of liquids, suspensions, or liquefiable substances, in the volume range from a few picoliters up to hundreds of microliters, while exhibiting high frequency stability.
According to the invention, the object is accomplished with a microejector pump wherein the supply line is configured at least partially as a diffuser element in the direction of the pump chamber and in that the exit channel opens in an exit plane.
By the interposition of the diffuser element ahead of the pump chamber according to the invention, the frequency stability of the microejector pump is considerably improved. The anisotropy of the diffuser flow resistance supports droplet formation in pump mode, that is, a nozzle effect is produced along the positive pressure gradient, and in loading mode, the liquid backflow into the pump chamber is supported. That is, a diffuser effect is produced along the positive pressure gradient. Furthermore, the diffuser effect in loading mode effectively suppresses the generation of air bubbles in the pump chamber at high frequencies. In this way, extremely high delivery rates up to about 750 mcl/minute can be achieved, at an excitation frequency up to about 6500 Hz. In the use of the microejector pump according to the invention for printing, a higher pressure velocity can be attained by the diffuser.
The outlet passage is further configured as a microcapillary, so that the sample release takes place in the form of individually countable, directed, pulse-accelerated microdroplets of defined drop volume, reproducibly. The volume of the drops and the delivery rate are adjustable through the electrical parameters (frequency, amplitude, pulse shape) of the pump control.
Preferably, the diffuser element is placed immediately ahead of the pump chamber, or extends directly to the pump chamber. In a first variant of the invention, the diffuser element, has a constant aperture angle. The aperture angle of the diffuser element should be at most 10 degrees, with an aperture angle of about 3 to 5 degrees being preferred.
In a second embodiment of the invention, the diffuser element exhibits a continuously varying aperture angle. The aperture angle can for example, increase continuously.
In another embodiment of the invention, the pump chamber has a base outline of straight or curved boundary lines, while the diffuser element opens in an entrance zone of the pump chamber. The outlet is arranged in opposition to the entrance zone.
The outlet passage is further configured as a microcapillary, so that the sample release takes place in a reproducable form of individually countable, directed, pulse-accelerated microdrops of defined drop volume. The volume of the drops and the delivery rate are adjustable by means of the electrical parameters (frequency, amplitude, pulse shape) of the pump control.
In addition, the microcapillary is connectable to other supply passages between the pump chamber and the ejection orifice. Thus it is possible to mix other substances in a controlled manner with the liquid delivered through the pump chamber.
Preferably, the microejector pump consists of a composite of a micromechanically textured silicon chip and a glass chip.
To avoid contamination, the microejector pump, i.e., the composite of silicon chip and glass chip, is diminished in an x- and/or y-direction towards the ejection orifice of the outlet passage. This ensures that upon superficial immersion of the microejector pump in a liquid, only an extremely slight surface contamination will occur, which is easily removable in a following purification step. Thus, contamination can be prevented. The micro-ejector pump according to the invention is therefore especially suitable for manipulation of extremely small quantities of fluid.
The diminution in an x-direction may advantageously be configured during the sawing of the silicon chip, whereas the diminution in y-direction may be configured during the anisotropic textural etching. It is possible also to form the diminutions subsequently by a final grinding operation.
In another embodiment of the invention, the silicon chip is directly heatable under temperature control, i.e. the ohmic resistance of free silicon is utilized, the heating effect being produced due to Joulean heat in the silicon material.
The heating is preferably integrated into the silicon membrane, or acts directly thereupon, the electrical contacts being arranged laterally opposed to the silicon chip.
By the refinement of the invention with heat acting at least on the pump chamber, various possible arrangements of the diffuser element according to the invention are very considerably enlarged, without requiring additional design changes in the microejector pu
Burger Mario
Gehring Thomas
Howitz Steffen
Wegener Thomas
Baker & Botts L.L.P.
Fastovsky Leonid
Gesim Gesellschaft fur Silizium-Mikrosysteme mbH
Walberg Teresa
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