US20080075613A1

US20080075613A1 - Motivating fluid vacuum pump

Info

Publication number: US20080075613A1
Application number: US11/796,505
Authority: US
Inventors: Marco Doms; Jorg Muller
Original assignee: Technische Universitaet Hamburg Harburg; Tutech Innovation GmbH
Current assignee: Bayer AG
Priority date: 2004-10-29
Filing date: 2007-04-27
Publication date: 2008-03-27
Also published as: EP1805420A1; DE502005009877D1; DE102004053006A1; EP1805420B1; ATE473374T1; WO2006045634A1

Abstract

The invention relates to a driving agent vacuum pump used in microsystems technology, comprising an evaporator chamber and a pump chamber that are separated by a jet arrangement. The design of the driving agent vacuum pump is improved by: a planar arrangement of at least one jet, which extends vertically in depth and which is situated between two, in particular, parallel plates, these plates closing the evaporator chamber and the pump chamber; an opening in the pump chamber, preferably above the jet arrangement, for drawing in a medium to be pumped, and; an opening for expelling a preferably compressed gas underneath the jet arrangement.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to International Patent Application No. PCT/EP2005/011660 filed on Oct. 31, 2005, which claims priority to German Patent Application No. 10 2004 053 006.8 filed on Oct. 29, 2004, subject matter of these patent documents is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention concerns a miniaturized driving agent vacuum pump which uses preferably planar jet and pump wall geometries structured in keeping with microsystem technology and a suitable driving agent for vacuum creation. It is distinguished by simple manufacturability, small size and thereby good integration capability, for example into mobile systems, operation in a pressure region extending from about one atmosphere to several Pascal, higher suction efficiency and position independent functionality.

BACKGROUND OF THE INVENTION

Pumps for the transport of gases or for the creation of a vacuum exist in macroscopic scale in a number of type variations: displacement pumps, molecular pumps, sorption pumps, condensors, kyro pumps and driving agent pumps. Each of these varieties is suited for application within a specific pressure region; to create a pregiven pressure it can be necessary to operate a number of these pumps in series. The sizes of these customary vacuum pumps even in their smallest construction forms lie in the area of several tens of cubic centimeters. Therefore these pumps cannot be sensibly integrated into systems with microcomponents (for example, sensors). The application of, for example, miniaturized analysis devices, which for their function require a vacuum pressure or a constant gas flow is therefore closely coupled to the development of suitable micro gas pumps.
Micropumps use different physical or chemical principles to create a pumping effect (see: Nam-Trung Nguyen, Xiaoyang Huang, Toh Kok Chuan, MEMS-Micropumps: A Review, Transactions of the ASME, Vol. 124 (June 2002), 384-392; P. Woias, Micropumps—summarizing the first two decades, Proc. SPIE, Vol. 4560 (2001), 39-52). Many of the systems are limited in their application to liquid medium; only a few suit themselves to the pumping of gases or to the creation of a vacuum.
A scaling of the customary pump principles with rotating parts for the displacement of gases is, because of the very small measures and the required rotational speeds for the creation of the displacement, nearly impossible. Most of the realized microvacuum pumps are based however on mechanically movable parts which considerably influence the long time stability of such systems, such as membranes, which through their movement create by way of different actuators the evoked pumping effect or in part require active or passive valves (see: R. Rapp, W. K. Schomburg, D. Mass, J. Schulz, W. Stark, LIGA micropump for gases and liquids, Sens. Act. A. Vol. 40 (January 1994), 57-61; R. Linnemann, P. Wias-P, C. D. Senfft, J. A. Ditte rich, A self-priming and bubble-tolerant piezoelectric silicon micropump for liquids and gases, Proc. MEMS 1998 Heidelberg, 532-537; C. G. J. Schabmueller, M. Koch, A. G. R. Evans, A. Brunnschweiler, M. Kraft, Design and fabrication of a self-aligning gas/liquid micropump, Proc. SPIE-Int. Soc. Opt. Eng. (USA), Vol. 4177 (2000), 282-90).
Also capable of finding application are alternative pumps without mechanical parts and which are based on the principle of Knudsen compressors (thermal transpiration, thermal molecular pressure): between the two volumes at different temperatures which are connected to one another by way of a channel with a small cross sectional area, there exists a pressure difference which can be used for the creation of a pumping effect. Disadvantageous of this however is the relatively complicated construction and the high surface area requirement of such systems, indeed because of the low achievable compression ratio, many such pumps need to be driven in a series in order to create the desired suction performance and pressure difference (see: R. M. Young, Analysis of a micromachine based vacuum pump on a chip actuated by thermal transpiration effect, J. Vac. Sci. Technol B17(2), March/April 1999; J. P. Hobson, D. B. Salzman, Review of pumping by thermal molecular pressure, J. Vac. Sci. Technol. A 18(4), July/August 2000, S. E. Vargo, E. P. Muntz, Initial Results from the first MEMS fabricated thermal transpiration-driven vacuum pump, Rerefied Gas Dynamics: 22. Int. Symposium, 2001).
The use of the pumping principle forming the basis of the invention is not known in micropumps.

SUMMARY OF THE INVENTION

The micropump of the invention uses the functional principle of driving agent pumps described in DIN 28 400, part 2, which principle is based on a rapidly flowing vapor phase or liquid driving agent expanded by moving through a jet. The gas particles in the container to be evacuated move into this driving agent stream and while in that stream receive impacts with the driving agent molecules giving them impulses in the pumping direction.
A special standing among driving medium pumps is taken by diffusion pumps, in the case of which, in contrast to other stream pumps, the mixing process of the driving agent with the gas to be evacuated does not occur in a turbulent boundary layer, but takes place by diffusion of the gas into the driving stream.
In FIG. 1, by way of example the pumping principle for all driving agent pumps is illustrated by the aid of the construction of a diffusion pump: in a boiling space 12, by way of a heater 11, a suitable driving agent (for example silicon oil) is heated; the resulting driving agent vapor 14, escapes at supersonic speed from the jets 15, and transmits downwardly directed impulses onto the molecules of the gas 18 to be evacuated. The driving agent vapor stream 17 condenses on the cooled walls of the pump body 16 and is returned again to the supply container 12.
The gas molecules retain their impulses and moving with the vapor stream reach the next lower jet stage. Below these last jets the gas is taken away through the fore vacuum pipe 13, by means of a fore pump. The pumped away gas is further compressed from stage to stage, so that in the case of a constant mass flow its volume flow is correspondingly reduced; the pump area between the jets and the wall likewise diminishes accordingly from top to bottom, and the highest permissible pressure at the fore vacuum side is hereby increased (see: Wutz, Adam, Walcher, Theorie und Praxis der Vakuumtechnik, Vieweg Verlag Braunschweig, 5. Edition (1992)).
The novelty of the invention lies in the conversion of this principle into a miniaturized form, preferably into a planar form adequate for microsystem techniques. Resulting from this utilization of miniaturization are further advantages. Here, in the case of the driving agent vacuum pump, consisting of an evaporating chamber at high pressure and a pump chamber at low pressure, separated by a jet arrangement, it is provided that the pumping effect is achieved by a flow at high speed through a preferably planar arrangement of jets vertical in depth and located between two parallel plates which close the chambers in the jet region. Further an opening is provided in the pump chamber above the jet arrangement to draw in the medium to be pumped and an opening for the discharge of the compressed gas is provided below the jet arrangement. A planar jet arrangement made of, for example, one or two Laval jets is used, for a purpose of expanding and accelerating selectively up to supersonic speed a liquid, gas or vapor phase driving agent under pressure. With this the jet stream can achieve supersonic speed.
Because of its small dimensions the driving agent vacuum pump is usable at high pressures from about one atmosphere. By choice of the number of jets arranged below one another and therewith a number of pressure steps, high compression ratios are achievable. Furthermore by the choice of suitable dimensions for the pump, of the driving agent and of the evaporating temperature, the working pressure range can be varied widely.
A condensable medium or a gaseous medium is used as the driving agent. Further, as the driving agent a liquid is used with in one implementation the liquid driving agent being evaporated by a heater in the form of an electrically heated coil arranged in the evaporating chamber. Alternatively the driving agent is already delivered to the evaporating chamber in gaseous form.
The increased pressure of the driving agent inside of the jet arrangement can be achieved either by suitable measures outside of the micropump or in the case of a vapor phase driving means by way of a heater and evaporator integrated in the pump so that a liquid can be achieved. The scaling of the measurements of the pump into the region of the free path of the gas molecules in the pressure region makes possible an operation in a pressure region of about one atmosphere down to several Pascal.
To achieve a high as possible pressure difference with only one microdriving agent pump several jet stages can be operated behind one another so that the evacuated gas in each stage is further compressed. A variation of the used driving agent and of the used evaporation temperature likewise makes possible an operation in different pressure regions.
To avoid a contamination of the jets or of the jet delivery channels by small particles, a particle filter can, for example, be integrated in the evaporation chamber. A similar filter can also be integrated into the delivery and discharge channels at the input and output of the evaporating chamber.
The driving agent ejected from the jets, which produces the actual pumping effect, in the case of the use of gases or liquids can be transported in a suitable way from the pump, and in the case of the use of a vapor phase driving agent it can be condensed on the pump walls and, as the case may or may not be, can then be returned to the heater integrated in the pump. There it is again vaporized and it transitions into a driving agent circuit to make possible a closed system supplied outwardly with only energy for the heater.
To condense a gaseous driving medium the vacuum pump is provided with cooling of the outer wall of the pump chamber. The condensation of the vapor phase driving agent can for example be accomplished by way of channels in the walls or by cooling ribs, which are filled with a liquid or a gas which removes heat from the sidewalls used for the condensation; alternatively for this also Peltier elements can be used.
Moreover, in a further development a connection is provided between the evaporating chamber and a pump chamber through which a condensed driving agent is returned and which connection at the same time serves as a pressure stage. A return of the condensed driving agent from the pump chamber to the evaporating chamber can, for example, be carried out by one or more capillary shaped channels which is or are covered by a layer having an outer surface energy higher than that of the pump chamber. These measures make it possible to operate the micropump independently of its position.
For monitoring the pumping function in the pump chamber at its input or output, or in the evaporating chamber or in several or all positions a pressure measurement is integrated with the pump. To monitor the operation of the micro driving agent pump and, as the case may be, to control or regulate it, several pressure sensors can be integrated into the pump. These pressure sensors can be applied to the pumping chamber at the high vacuum side and the fore vacuum side, as well as to the evaporating chamber and by means of suitable switching technology measures can detect the pressure difference between the mentioned measuring points.
Because of their good reliability and applicability to different pressure regions, as pressure sensors are offered, for example, a system based the Pirani principle which measures the pressure dependent heat conductibility of the surrounding medium (see: Wutz, Adam, Walcher, Theorie und Praxis der Vakuumtechnik, Vieweg Verlag Braunschweig, 5. Edition (1992); Mastrangelo, Muller, Microfabricated Thermal Absolute-Pressure Sensor with on-Chip Digital Front-End Processor, IEEE J. Solid State Circuits, Vol. 65 No. 2 (1994), 492-499, Puers, Reyntjens, Bruyker, The NanoPirani—an extremely miniaturized pressure sensor fabricated by focused ion beam rapid prototyping, Sens. & Act. A. Vol. 97-98 (2002), 208-214). With this, there results a pressure measurement by way of a Pirani arrangement integrated into a microsystem technique.
Likewise for monitoring the pump and for determining the suction performance a flow measurement based for example on a microsystem technique realized heating wire principle can be made at the suction intake pipe (suction intake region) and/or possibly at the outlet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectioned schematic illustration of a diffusion pump.
FIG. 2 is a schematic perspective view of a micro agent driving pump.

DETAILED DESCRIPTION

The construction of the invention consists, for example, of three substrates of which the middle substrate contains the jet structures and it is distinguished by a high heat conductibility in order to facilitate the evaporation and condensation of a liquid driving agent.
In one implementation the system or the driving agent vacuum pump is made of three substrates, the middle substrate of which because of its good heat conductibility, mechanical and chemical stability as well as its structurabilty is preferably structured by way of anisotropic etching methods, is silicon and the substrates which close its two sides are preferably because of its low thermal conductivity made of anodically bonded glass.
Moreover, in this further implementation it is advantageous if the middle substrate because of its good heat conduction is made of a galvanic metal structure, for example one made by UV-Liga technique, preferably galvanically washed on to a lower glass substrate and an upper glass substrate as a seal.
The two outer substrates can contain needed connection channels and, as the case may be, can serve as carriers for the integrated pressure or flow sensors and to close the evaporating chamber and the pumping space. To serve as substrates silicon, preferably anisotropically structured boron silicate glass, can be used because of its good chemical and mechanical stability, and even galvanically finished metal structures and glass substrates or structures made by injection molding processes and polymer substrates can be used.
The driving agent vacuum pump according to the invention is preferably closed by polymer substrates and also the jet arrangement is created by, for example, an injection molded structure.
Because of its small size the microdriving agent pump has the following advantages: the pump can be used for existing or in the future developed miniaturized systems, without necessarily increasing their construction shape.
Further, the micro driving agent pump because of its small internal measurements can be used below a pressure of about one atmosphere and, according to its implementation with several jet stages and a suitable driving agent, a pressure of down to several Pascal can be reached.
The system distinguishes itself by a simple way of being manufactured: in the first case the micro driving agent pump consists of a silicon substrate structured by plasma etching methods and two anodically bonded boron silicate glass substrates as covers above and below the silicon substrate, one of which boron silicate glass substrates provides an access from the outside into the evaporating chamber for the external supply of a driving agent.
One such system is shown in FIG. 2 by way of example: through the opening 3, a vapor phase driving agent is delivered, which is expanded through the jets 5, and provides impulses onto the gas molecules delivered to the high vacuum side 6, through channel 7, connected to a volume. The driving agent condenses on the water cooled side walls of the pump 3, and the evacuated gas molecules move out of the micropump through the vacuum fore side 2, and the outlet 1.
Typically the side length of the system has a value of about 15 mm.

Claims

1. A driving agent vacuum pump, especially of microsystem technique, comprising; an evaporation chamber and a pumping chamber, which are separated by a jet arrangement; a planar arrangement of at least one jet running obliquely, preferably vertically, in depth between two, especially parallel, plates, with the plates covering the evaporation chamber and the pumping chamber, and by an opening in the pumping chamber preferably above the jet arrangement, for taking in an agent to be pumped and by an opening for driving out a, preferably compressed, gas below the jet arrangement, said driving agent vacuum pump further including a heater, preferably in the form of an electrically heated coil arranged in the evaporation chamber.

2. A driving agent vacuum pump according to claim 1, wherein at least one jet is formed as a Laval jet.

3. A driving agent vacuum pump according to claim 1, wherein the jet arrangement has several jets.

4. A driving agent vacuum pump according to claim 1, wherein the driving agent is at least one of a condensable medium, a gaseous medium and a liquid.

5. A driving agent vacuum pump according to claim 1, wherein the driving agent is delivered into the evaporation chamber as a gas.

6. A driving agent vacuum pump according to claim 1, wherein the pumping chamber is provided with cooling.

7. A driving agent vacuum pump according to claim 6, wherein the cooling includes channels or cooling ribs.

8. A driving agent vacuum pump according to claim 6, wherein the cooling is formed by at least one Peltier element.

9. A driving agent vacuum pump according to claim 1, wherein between the evaporation chamber and the pumping chamber is a connection through which a condensed driving agent is returned.

10. A driving agent vacuum pump according to claim 9, wherein the connection is formed capillarily.

11. A driving agent vacuum pump according to claim 9, wherein the capillaries are covered by a layer having a higher outer surface energy than the pumping chamber to control the return flow of the driving agent.

12. A driving agent vacuum pump according to claim 1, wherein a pressure sensor for monitoring the pumping function in the pumping chamber, said pressure sensor being integrated into the pump and located in at least one of the pump input, the pump output and in the evaporating chamber.

13. A driving agent vacuum pump according to claim 12, wherein the pressure sensor measures pressure using a Pirani arrangement preferably integrated into the microsystem.

14. A driving agent vacuum pump according to claim 1, further including a flow measurement for determining the vacuum performance, the flow measurement being provided, in at least one of the vacuum intake region and the output region.

15. A driving agent vacuum pump according to claim 14, wherein the flow measurement is made using a heated wire principle, preferably integrated into the microsystem.

16. A driving agent vacuum pump according to claim 1, further including at least one particle filter for reducing contamination, the particle filter being located in at least one of the jet supply channels, the evaporation chamber and the delivery and exhaust channels at the input and output.

17. A driving agent vacuum pump according to claim 1, wherein the pump is made of three substrates.

18. A driving agent vacuum pump according to claim 17, wherein a middle substrate consists of a silicon substrate, preferably structured according to an anisotropic plasma etching method, and in that two side substrates are made of glass, preferably anodically bonded.

19. A driving agent vacuum pump according to claim 18, wherein the middle substrate is made of a metal structure, preferably galvanically finished.

20. A driving agent vacuum pump according to claim 19, wherein the middle substrate is galvanically washed onto a lower glass substrate and has an upper glass substrate as a closure.