Pumping structure, particle detector and method for pumping

Abstract

A pumping structure comprises at least two membranes, at least two actuation chambers, one evaluation chamber comprising an opening to the outside of the pumping structure, and at least three electrodes. Each membrane is arranged between two electrodes in a vertical direction which is perpendicular to the main plane of extension of the pumping structure, each actuation chamber is arranged between one of the membranes and one of the electrodes in vertical direction, and each actuation chamber is connected to the evaluation chamber via a channel. Furthermore, a particle detector and a method for pumping are provided.

Claims

1. A pumping structure comprising: at least two membranes, at least two actuation chambers, and one evaluation chamber comprising an opening to an outside of the pumping structure, wherein within each actuation chamber, one lower electrode is arranged at a bottom side of the actuation chamber; the pumping structure comprises one upper electrode which is arranged at a side of said least two membranes which faces away from said least two actuation chambers; each of the at least two membranes is arranged between said one lower electrode and said one upper electrode in a vertical direction which is perpendicular to a pumping surface of the at least two membranes; each of the at least two actuation chambers is directly connected to the one evaluation chamber via a channel, the channel being arranged at a side of the evaluation chamber that faces away from a side where the opening is arranged, wherein said one upper electrode is configured to exert a force on said at least two membranes.

2. The pumping structure according to claim 1, wherein the channels extend parallel to a main direction of extension of the evaluation chamber.

3. The pumping structure according to claim 1, wherein the evaluation chamber has a symmetry axis which is parallel to a main direction of extension of the evaluation chamber and the actuation chambers are arranged axisymmetrically with respect to the symmetry axis of the evaluation chamber.

4. The pumping structure according to claim 1, wherein each actuation chamber comprises a pumping volume given by the difference between the volume of the respective actuation chamber for the case that the membranes are not deflected and the volume of the respective actuation chamber for the case that the membranes are fully deflected.

5. The pumping structure according to claim 4, wherein the volume of the evaluation chamber equals the summed pumping volumes of the actuation chambers.

6. The pumping structure according to claim 1, wherein the pumping structure is configured to pump gases.

7. The pumping structure according to claim 1, wherein the membranes comprise an electrically conductive material.

8. The pumping structure according to claim 1, wherein the pumping structure is free of valves.

9. A particle detector comprising the pumping structure according to claim 1.

10. The particle detector according to claim 9, wherein a light source is arranged within the evaluation chamber.

11. The particle detector according to claim 9, wherein a photodetector is arranged within the evaluation chamber.

12. The particle detector according to claim 9, which is configured to detect particles within the evaluation chamber.

13. The pumping structure according to claim 1, wherein the evaluation chamber is arranged below the at least two actuation chambers in the vertical direction.

14. The pumping structure according to claim 1, wherein the channel between each of the at least two actuation chambers and the evaluation chamber is the only opening of the respective actuation chamber.

15. A method for pumping, the method comprising: providing at least two membranes, providing at least two actuation chambers, which are each arranged between one of the at least two membranes and a respective lower electrode, providing one evaluation chamber comprising an opening to an outside of the evaluation chamber, providing one upper electrode which is arranged at a side of said at least two membranes which faces away from said at least two actuation chambers such that each of the at least two membranes is arranged between said respective lower electrode and said one upper electrode in a vertical direction which is perpendicular to a pumping surface of the at least two membranes; applying a voltage to the lower electrodes simultaneously, and applying a voltage to said upper electrode, wherein each actuation chamber is directly connected to the evaluation chamber via a channel, the channel being arranged at a side of the evaluation chamber that faces away from a side where the opening is arranged, wherein said one upper electrode is configured to exert a force on said at least two membranes.

16. The method according to claim 15, wherein the voltage applied is set in such a way that the membranes are deflected when the voltage is applied to a respective electrode.

17. The method according to claim 15, wherein voltage application is alternated between the lower electrodes simultaneously and said upper electrode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following description of figures may further illustrate and explain exemplary embodiments. Components that are functionally identical or have an identical effect are denoted by identical references. Identical or effectively identical components might be described only with respect to the figures where they occur first. Their description is not necessarily repeated in successive figures.

(2) In FIG. 1 a cutaway view of an exemplary embodiment of a particle detector with a pumping structure is shown.

(3) In FIGS. 2A, 2B and 2C top views on an exemplary embodiment of a particle detector with a pumping structure are shown.

(4) With FIGS. 3A and 3B an exemplary embodiment of the method for pumping is described.

(5) With FIGS. 4, 5, 6, 7A and 7B simulation results for the particle flow in an exemplary embodiment of a particle detector with a pumping structure are shown.

(6) With FIGS. 8A, 8B, 8C, 8D and 9 the setup of an exemplary embodiment of a particle detector with a pumping structure is described.

(7) With FIG. 10 an exemplary embodiment of the method for pumping is described.

DETAILED DESCRIPTION

(8) In FIG. 1 a cutaway view of an embodiment of a particle detector 27 comprising a pumping structure 20 is shown. The pumping structure 20 comprises two actuation chambers 22 and one evaluation chamber 23. Each actuation chamber 22 is formed by a membrane 21 which is suspended over walls 39. The membranes 21 comprise an electrically conductive material. The walls 39 delimit the actuation chamber 22 in lateral directions x, y which are parallel to the main plane of extension of the pumping structure 20. The actuation chambers 22 are arranged on a first substrate 36. At a bottom side 34 of the actuation chambers 22, which faces away from the membrane 21, an electrode 25 is arranged. The first substrate 36 can comprise a semiconductor material, as for example silicon. Furthermore, the first substrate 36 can comprise an integrated circuit. On the side of the electrodes 25 which faces away from the first substrate 36 an insulating layer 32 is arranged. In this way, each actuation chamber 22 comprises a first volume of gas and it is delimited by the membrane 21, the walls 39 and the first substrate 36. At the bottom side 34 of each actuation chamber 22 a channel 26 is arranged. The channels 26 directly connect the actuation chambers 22 with the evaluation chamber 23.

(9) The evaluation chamber 23 comprises an opening 24 to the outside of the pumping structure 20. The opening 24 is arranged within a second substrate 37. The second substrate 37 is arranged at a bottom side 34 of the evaluation chamber 23, where the bottom side 34 of the evaluation chamber 23 faces away from the channels 26. The second substrate 37 is connected with the first substrate 36 via spacers 38. The spacers 38 can for example be polystyrene spheres incorporated in a medium or dispended on the second substrate 37.

(10) The channels 26 extend parallel to a main direction of extension of the evaluation chamber 23. The main direction of extension of the evaluation chamber 23 is parallel to a vertical direction z which is perpendicular to the main plane of extension of the pumping structure 20. Furthermore, the evaluation chamber 23 has a symmetry axis which is parallel to the main direction of extension of the evaluation chamber 23 and the actuation chambers 22 are arranged axisymmetrically with respect to the symmetry axis of the evaluation chamber 23. The symmetry axis of the evaluation chamber 23 is parallel to the vertical direction z and runs through the opening 24. Thus, on both sides of this symmetry axis one actuation chamber 22 is arranged.

(11) The pumping structure 20 further comprises a third electrode 25 which is arranged at the side of the membranes 21 which faces away from the actuation chambers 22. The electrodes 25 arranged on the first substrate 36 are referred to as lower electrodes 30. The electrode 25 which is arranged at the side of the membranes 21 which faces away from the activation chambers 22 is referred to as upper electrode 31. The upper electrode 31 is attached to a covering body 35. The covering body 35 extends parallel to the main plane of extension of the first substrate 36 and of the second substrate 37. The covering body 35 is attached to the first substrate 36 via spacers 38. On top of the upper electrode 31 an insulating layer 32 is arranged, such that the insulating layer 32 is arranged between the upper electrode 31 and the membranes 21. If the membranes 21 are not deflected, they are not in direct contact with either the insulating layers 32 nor with the electrodes 25.

(12) This means, each membrane 21 is arranged between two electrodes 25 in the vertical direction z. Furthermore, each actuation chamber 22 is arranged between one of the membranes 21 and one of the electrodes 25 in vertical direction z.

(13) Advantageously, the pumping structure 20 is free of valves. The actuation chambers 22 are directly connected with the evaluation chamber 23 via the channels 26.

(14) The particle detector 27 further comprises a light source 28 which is arranged within the evaluation chamber 23. The light source 28 can for example be a light emitting diode or a laser. The light source 28 is arranged at a top side 33 of the evaluation chamber 23, where the top side 33 faces away from the opening 24. The light source 28 is arranged to emit electromagnetic radiation during operation of the particle detector 27.

(15) The particle detector 27 further comprises a photodetector 29 which is arranged within the evaluation chamber 23. The photodetector 29 comprises a plurality of photodetectors 29. The plurality of photodetectors 29 is arranged at the bottom side 34 of the evaluation chamber 23. In this way, the particle detector 27 is configured to detect particles within the evaluation chamber 23.

(16) With FIGS. 2A, 2B and 2C top views on an exemplary embodiment of the particle detector 27 with the pumping structure 20 are shown for different vertical positions. In FIG. 2A the upper electrode 31 and the size of the evaluation chamber 23 are shown. The dashed line marks the cross section shown in FIG. 1.

(17) In FIG. 2B the upper electrode 31 above the two membranes 21 is shown. Furthermore, the two channels 26 and the light source 28 are shown.

(18) In FIG. 2C the photodetectors 29, the second substrate 37 and the opening 24 are shown.

(19) FIG. 3A the voltages applied to one of the membranes 21 are plotted. On the x-axis the time is plotted in arbitrary units and on the y-axis the voltage is plotted in arbitrary units. At first, a voltage is applied which moves the membrane 21 towards the lower electrode 30. In a next step, a higher voltage is applied in order to move the membrane 21 towards the upper electrode 31. These two steps can be repeated alternatingly.

(20) With FIG. 3B it is shown where the voltages are applied. A cutaway view of one of the actuation chambers 22 is shown with a schematic circuit diagram. In the upper case, which corresponds to the first step shown in FIG. 3A, a voltage is applied between the membrane 21 and the lower electrode 30. Therefore, the volume of the actuation chamber 22 is decreased and gases or fluids within the actuation chamber 22 are moved out of the actuation chamber 22 through the channel 26. In the lower case, which corresponds to the second step shown in FIG. 3A, a voltage is applied between the membrane 21 and the upper electrode 31. Therefore, the volume of the actuation chamber 22 is increased and gas or fluids are pumped from the evaluation chamber 23 through the channel 26 to the actuation chamber 22. Each actuation chamber 22 comprises a pumping volume given by the difference between the volume of the respective actuation chamber 22 for the case that the membrane 21 is not deflected and the volume of the respective actuation chamber 22 for the case that the membrane 21 is fully deflected. The pumping volume is the volume of gas and/or fluid which can be pumped out of each actuation chamber 22.

(21) In FIG. 4 simulations of the movement of the membrane 21 of an exemplary embodiment of the pumping structure 20 are shown. On the x-axis the time is plotted in μs. The lower line shows the displacement of the membrane 21 in vertical direction z in μm. The upper line shows the velocity of the membrane 21 in vertical direction z in m/s. At 0 μs the membrane 21 is in direct contact with the insulating layer 32 which is arranged on the upper electrode 31. At 0 μs a voltage of 10 V is applied between the membrane 21 and the lower electrode 30. Therefore, the membrane 21 is deflected towards the lower electrode 30. At approximately 115 μs the membrane 21 is in direct contact with the insulating layer 32 which is arranged on the lower electrode 30. The displacement of the membrane 21 in vertical direction z amounts to 8 μm. The velocity of the membrane 21 in vertical direction z increases with increasing displacement in vertical direction z. If voltages smaller than 10 V are applied between the membrane 21 and the lower electrode 30 the time required for the membrane 21 to reach the insulating layer 32 which is arranged on the lower electrode 30 is increased.

(22) In FIG. 5 a simulation of the displacement of a fully deflected membrane 21 is shown. On the x-axis and on the y-axis the extension of the membrane 21 in lateral directions x, y is given in mm. On the z-axis the displacement of the membrane 21 in vertical direction z is plotted in μm. Most of the membrane 21 is in direct contact with the insulating layer 32 which is arranged on the lower electrode 30.

(23) In FIG. 6 the flow of particles is shown schematically for the setup of the pumping structure 20 shown in FIG. 1. It is further shown schematically, that a voltage is applied between the membranes 21 and the respective lower electrode 30. Therefore, the membranes 21 are deflected towards the lower electrodes 30. The gas and/or fluid within the actuation chambers 22 is pumped through the channels 26 because of the movement of the membranes 21. Within the evaluation chamber 23 a unidirectional flow of the gas and/or the fluid is established. The gas and/or the fluid can comprise particles, as for example dust or pollen which is schematically shown in FIG. 6. The flow of the gas and/or fluid is directed towards the opening 24. The gas and/or fluid which is arranged within the evaluation chamber 23 is pumped out of the evaluation chamber 23 through the opening 24. As the volume of the evaluation chamber 23 equals the summed pumping volumes of the actuation chambers 22, the volume of gas and/or fluid within the evaluation chamber 23 can be pumped out of the pumping structure 20 completely.

(24) FIG. 7A shows a simulation of the flow of gas within the evaluation chamber 23. On the x-axis the extent in the lateral direction x is plotted in mm. On the z-axis the extent in vertical direction z is plotted in mm. Gases and/or fluids from the actuation chambers 22 enter the evaluation chamber 23 through the channels 26. The arrows symbolize the flow of the gas and/or fluid. The size of each arrow is proportional to the magnitude of the velocity of the gas and/or fluid at their respective position. The larger the arrow, the larger is the velocity of the gas and/or fluid. Furthermore, the scale bar on the right side relates to the velocity of the gas and/or fluid in m/s. The direction of each arrow corresponds to the direction of the flow of gas and/or fluid. The flow rate of the gas and/or fluid can for example amount to 200 mm.sup.3/s.

(25) In FIG. 7B an enlarged view of the plot shown in FIG. 7A is depicted. Within the evaluation chamber 23 the arrows run parallel. This means, that the flow of gas and/or fluid is laminar. Therefore, all the gas and/or fluid is directed to flow in the same direction towards the opening 24.

(26) With FIGS. 8A, 8B, 8C and 8D the setup of an exemplary embodiment of a particle detector 27 with a pumping structure 20 is described. The particle detector 27 with the pumping structure 20 can be produced as described in the following. In FIG. 8A the second substrate 37 is shown which comprises the opening 24. The opening 24 can be formed by micro fabrication techniques as for example deep ion etching. The second substrate 37 can comprise silicon. Within the second substrate 37 the photodetectors 29 and integrated circuits 40 are formed. The integrated circuits 40 can for example be employed to control the photodetectors 29.

(27) In FIG. 8B the first substrate 36 is shown. The first substrate 36 can comprise silicon. Two channels 26 are formed within the first substrate 36 by micro fabrication techniques. On top of the first substrate 36 microelectromechanical systems are formed which form the actuation chambers 22. Walls 39 are formed on the first substrate 36. Two membranes 21 are suspended over the walls 39 such that two actuation chambers 22 comprising each a volume of gas are formed. Each actuation chamber 22 comprises a top side 33 where the membrane 21 is arranged and a bottom side 34 where one of the channels 26 is arranged. Furthermore, at the bottom side 34 of each actuation chamber 22 a lower electrode 30 is arranged on the first substrate 36. On the lower electrode 30 an insulating layer 32 is arranged, such that the lower electrode 30 is arranged between the insulating layer 32 and the first substrate 36. Consequently, each actuation chamber 22 is delimited by one membrane 21, walls 39, the first substrate 36 and the insulation layer 32.

(28) In FIG. 8C the covering body 35 is shown. On the covering body 35 the upper electrode 31 is arranged and on the upper electrode 31 the insulating layer 32 is arranged. The upper electrode 31 is arranged between the covering body 35 and the insulating layer 32. The covering body 35 can comprise silicon. The upper electrode 31 can be a thin metal layer.

(29) In FIG. 8D it is shown that the particle detector 27 with the pumping structure 20 is obtained by arranging the parts shown in FIGS. 8A, 8B and 8C on top of each other. A cross section through the particle detector 27 is shown. The first substrate 36 with the actuation chambers 22 is arranged between the second substrate 37 and the covering body 35 in vertical direction z. The second substrate 37 and the first substrate 36 are connected with each other via spacers 38. The first substrate 36 and the covering body 35 are connected with each other via spacers 38 as well. The distances between the first substrate 36, the second substrate 37 and the covering body 35 can be controlled via the thickness of the spacers 38, respectively. Furthermore, the light source 28 is arranged within the evaluation chamber 23 which is formed between the first substrate 36 and the second substrate 37.

(30) In FIG. 9 a section of an exemplary embodiment of the pumping structure 20 is shown in detail. A part of one actuation chamber 22 with the membrane 21 and the lower electrode 30 are shown. Via an integrated circuit 40 which is arranged within the first substrate 36 both the lower electrodes 30 and the membrane 21 can be electrically contacted. Therefore, electrical connections 41 are arranged within the first substrate 36. The electrical connections 41 comprise an electrically conductive material.

(31) With FIG. 10 an exemplary embodiment of the method for pumping is described. On the x-axis the time is plotted in arbitrary units and on the y-axis the voltage is plotted in arbitrary units. The bottom line plotted on the y-axis corresponds to the voltage applied to the lower electrodes 30. The top line plotted on the y-axis corresponds to the voltage applied to the upper electrode 31.

(32) In a first step S1 of the method for pumping gases and/or fluids are pumped out of the evaluation chamber 23. Therefore, at a time t1 a voltage is applied to the lower electrodes 30 simultaneously. Consequently, the membranes 21 are deflected towards the lower electrodes 30 such that the membranes 21 are in direct contact with the insulating layers 32 which are arranged on the lower electrodes 30. Gases and/or fluids are pumped out of the actuation chambers 22 towards the evaluation chamber 23. Gases and/or fluids within the evaluation chamber 23 are pumped out of the evaluation chamber 23 through the opening 24. At a time t2 a voltage is applied to the upper electrode 31. Consequently, the membranes 21 are deflected towards the upper electrode 31 such that the membranes 21 are in direct contact with the insulating layer 32 which is arranged on the upper electrode 31. Gases and/or fluids are pumped from the evaluation chamber 23 towards the actuation chambers 22 through the channels 26 because of the increased volume of the actuation chambers 22. Furthermore, gases and/or fluids from the environment of the pumping structure 20 are pumped in the evaluation chamber 23. At next, at a time t1 a voltage is applied to the lower electrodes 30 simultaneously again.

(33) Therefore, the membranes 21 are again deflected towards the lower electrodes 30. During the first step S1 alternatingly a voltage is applied to the lower electrodes 30 simultaneously and to the upper electrode 31. Thus, the membranes 21 are deflected up and down in vertical direction z during pumping. In this way, gases and/or fluids from the environment of the pumping structure 20 or the particle detector 27 are pumped into the evaluation chamber 23. The number of cycles of the membranes 21 moving up and down can be adapted.

(34) In a second step S2 at least one property of the gases and/or fluids within the evaluation chamber 23 is measured. During the second step no voltage is applied to the lower electrodes 30 and the upper electrode 31. For example the number of particles within the evaluation chamber 23 is determined during the second step.

(35) In a third step S3 gases and/or fluids are pumped out of the evaluation chamber 23 again as described for the first step S1.