EP1227060A2 - Micromechanical device and process for its manufacture - Google Patents

Abstract

The micromechanical component has a substrate in which at least two current channels (10, 10') are provided. The channels have a common input (5) and then branch out separately. The input has a branching with a peak (P) where the inner walls of the channels separate. A first electrode (20) is provided to apply a first electric potential to the inner walls of the channels. A second electrode (30) applies a second electric potential to the outer walls of the channels. The channels may then recombine to have a commom output. Independent claims also cover a method of manufacturing the components by etching.

Description

STATE OF THE ART

The present invention relates to a micromechanical Component, and in particular a micropump for polar Fluids, as well as a corresponding manufacturing process.

Although on any micromechanical components and Structures, sensors and actuators, applicable, are the present invention and the underlying problem with respect to one in the technology of silicon surface micromechanics manufacturable micromechanical micropump explained.

Use micropumps manufactured in micromechanics, for example Pump chambers with check valves or pump chambers with flow channels of different diameters, to create a clear flow direction:

The force effect on dipoles, such as water molecules, in inhomogeneous electrical fields has long been known and is described in standard textbooks of physics.

6 shows a schematic representation of a polar H ₂ O molecule; and FIGS. 7a, b show a schematic representation of the polar H ₂ O molecule under the influence of an electric field, namely FIG. 7a in a first state and FIG. 7b in a second state.

H ₂ O molecules, like many other polar molecules, have a permanent dipole moment due to their molecular structure. Oxygen binds the binding electrons to itself more strongly. This gives the oxygen atom a slightly negative charge and the hydrogen atoms a slightly positive charge. The spatially different position of the charges results in a dipole moment D, as shown in FIG. 6.

As can be seen from Fig. 7a, b, under the influence of electric field F generated by the charge q the dipole D rotated and tightened, the attractive force K ' in the rotated second state greater than the force K in the unrotated first state is.

Spatial leads in inhomogeneous electric fields Separation of the charges to align the dipole D in the field F and the attractive force K 'to the location of the larger one electric field. The positive charge of the Dipoles D attracted, the negative charge repelled. This leads to the rotation of the dipole D. The positive charge of the dipole D is now in a place with larger electrical Field (narrower field lines) than the negative charge. Thereby is the attractive force on the positive charge of the Dipoles D greater than the repulsive force on the negative Charge. This results in an attraction of the dipole D. The attractive force is independent of the sign the electrical charge q, which the inhomogeneous field F caused.

This effect is used in some ship propulsion systems. In the bow of a ship there is an inhomogeneous electric Field created. The attractive power of hull and Water molecules cause the Ship.

Electro-osmotic pumping has already been described (Dasgupta et al., "Electroosmosis: A Reliable Fluid Propulsion System for Flow Injection Analysis ", Anal. Chem. 66 (1994) 1792-1798). Here liquids are pumped by ions in the liquids through electrical fields in the desired directions are drawn while doing the rest Push the liquid along.

Electrohydrodynamic pumping has already been described (Bart et al., "Microfabricated Electrohydrodynamic Pumps", Sensor and Actuators A29 (1990) 193-197; P. J. Zanzucchi et al., US 5,858,193). The pumping effect occurs at high electric fields caused by forces on ions of high fields through dissociation and electrolytic Processes have arisen.

ADVANTAGES OF THE INVENTION

The idea on which the present invention is based exists in that the attractive force on polar molecules (e.g. water) in inhomogeneous electrical fields is going to accelerate these molecules. It takes place the manufacture of channels with electrodes, the corresponding generate inhomogeneous fields.

The micromechanical component according to the invention with the Features of claim 1 and the corresponding manufacturing process according to claim 8 have the advantage that a simple and inexpensive manufacture of a micropump for polar liquids or gases. The Pump is extremely robust because there are no moving parts be used.

The generation is possible through many process variants, and this makes the possibility of integration with others micromechanical or electrical components on one Chip created.

The pumping effect already occurs at low voltages (a few V) because of the small radii (approx. 5 µm) with Micromechanics can be produced, very inhomogeneous electrical Fields can be generated even at low voltages generate sufficient force. In particular voltages as high (> 100 V) are not required as for example in electrohydrodynamic pumps.

Advantageous further developments can be found in the subclaims and improvements of the respective subject of the invention.

According to a preferred development, the flow channels are merged in a common exit area.

According to a further preferred development, the Tip a small radius in the range of a few micrometers on. In this way, particularly inhomogeneous fields can be generated.

According to a further preferred development, the Inner walls of the flow channels in the common exit area a round up. Here is a homogeneous field course desired.

According to a further preferred development, there are two Flow channels branched off from the common entrance area, the flow channels in a common central region are merged, from the central area two more flow channels are branched off, and the others two flow channels in a common exit area are merged, one branch with another Has tip on which the inner walls of the Share flow channels.

According to a further preferred development, the A branch with a curve on both sides of the central area on which the inner walls of the flow channels divide.

According to a further preferred development, a third electrode for applying a third electrical potential to the inner walls of the two further flow channels intended.

DRAWINGS

Embodiments of the invention are in the drawings shown and explained in more detail in the following description.

Fig. 1a,b

eine schematische Darstellung eines mikromechanischen Bauelements in Form einer Mikropumpe als erstes Ausführungsbeispiel der vorliegenden Erfindung, und zwar Fig. 1a im Querschnitt und Fig. 1b eine vergrößerte Ausschnittsdarstellung von Fig. 1a;

Fig. 2

eine schematische Darstellung eines mikromechanischen Bauelements in Form einer Mikropumpe als zweites Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 3a-c

eine schematische Darstellung eines Herstellungs-verfahrens für ein mikromechanisches Bauelement in Form einer Mikropumpe als drittes Ausführungs-beispiel der vorliegenden Erfindung;

Fig. 4

eine Modifikation des Herstellungsverfahrens als viertes Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 5

eine weitere Modifikation des Herstellungsverfahrens als fünftes Ausführungsbeispiel der vorliegenden Erfindung;

Fig. 6

eine schematische Darstellung eines polaren H₂O-Moleküls; und

Fig. 7a,b

eine schematische Darstellung des polaren H₂O-Moleküls unter Einfluß eines elektrischen Feldes, und zwar Fig. 7a in einem ersten Zustand und Fig. 7b in einem zweiten Zustand.

Show it:

Fig. 1a, b

a schematic representation of a micromechanical component in the form of a micropump as the first exemplary embodiment of the present invention, specifically FIG. 1a in cross section and FIG. 1b an enlarged detail representation of FIG. 1a;

Fig. 2

a schematic representation of a micromechanical component in the form of a micropump as a second embodiment of the present invention;

3a-c

a schematic representation of a manufacturing method for a micromechanical component in the form of a micropump as a third embodiment of the present invention;

Fig. 4

a modification of the manufacturing method as a fourth embodiment of the present invention;

Fig. 5

a further modification of the manufacturing method as a fifth embodiment of the present invention;

Fig. 6

a schematic representation of a polar H ₂ O molecule; and

7a, b

is a schematic representation of the polar H ₂ O molecule under the influence of an electric field, namely Fig. 7a in a first state and Fig. 7b in a second state.

DESCRIPTION OF THE EMBODIMENTS

In the figures, the same reference symbols designate the same or functionally identical components.

1a, b show a schematic representation of a micromechanical Component in the form of a micropump first Embodiment of the present invention, and 1a in cross section and Fig. 1b an enlarged Detail view of Fig. 1a.

The effect described with reference to FIGS. 7a, b can be exploited be a micropump for a polar medium or to produce fluid.

The polar medium flows from a branch in the Entrance area 5 into the two flow channels 10, 10 '. By applying a voltage between the center electrode 20, which with the inner walls of the flow channels 10, 10 ' is connected, and the outer electrode 30, which with the outer walls the flow channels 10, 10 'is connected, an electric field is generated. The one with "top" designated area P occurs due to the very small Radius of curvature of the center electrode 20 is a very inhomogeneous Field IF on (Fig. 1b). In the other areas occurs an approximately homogeneous field HF, because in these areas there are relatively large radii of curvature. This highly inhomogeneous field IF causes the polar molecules (such as water) towards "tip" P. To the left and right of the "tip" P is after a very small transition area the area with homogeneous electrical field HF in the respective flow channel 10 or 10 '.

Polar molecules that are relatively close to the "tip" P are traced by subsequent molecules that are still above the "top" P are pushed aside into the area with homogeneous electrical field HF. This creates one clear flow direction S or pumping action. Because by means of Micromechanics made a "tip" P with a very small radius is the electric field in the area the "tip" P is very inhomogeneous. This creates a relative great attraction to the polar molecules.

In contrast, the inner walls 7, 7 'of the flow channels 10, 10 'in the common exit area 6 a rounding R with a relatively homogeneous field.

Of course, several of those shown in Fig. 1a, b Pumps connected sequentially or in parallel in order to achieve a higher pumping effect.

In the embodiment shown in FIGS. 1a, b, a Backflow cannot be stopped. This could be done with a Check valve (not shown) can be prevented.

Fig. 2 shows a schematic representation of a micromechanical Component in the form of a micropump as the second Embodiment of the present invention.

Another option is the combination of two Micropump geometries as shown in Fig. 2. Is to the structure of Fig. 1a, b practically mirrored at the outlet.

The fluid branches at the "tip" in flow direction S1 P1 into the flow channels 10, 10 'and enters at the exit the flow channel 11, which connects the two structures. The flow channel 11 has a branch on both sides with a curve R or R 'on which the inner walls 7 or 7 'of the flow channels 10, 10' or 12, 12 ' divide.

The fluid for branching flows through the flow channel 11 with a round shape (homogeneous field) and then runs through the flow channels 12, 12 'over the "tip" P2 to Exit area 6.

Due to the difference in the electric fields caused by the two center electrodes 20a, 20b can be generated a flow direction S1 or S2 is specified in this example become.

3a-c show a schematic representation of a manufacturing process for a micromechanical component in Shape of a micropump as a third embodiment of the present invention.

3a shows an intermediate state, wherein 70 denotes a silicon substrate, 60 an insulating intermediate layer (eg SiO ₂ ), 50 a micromechanical functional layer (eg polysilicon) and 40 a mask (eg nitride / oxide or photoresist).

The intermediate state in FIG. 3a can be established, for example are achieved by using an SOI substrate (silicone insulator) and applying and patterning the mask 40 or by oxidation of the substrate 70, deposition of the functional layer 50 (e.g. doped polycrystalline silicon) and application and structuring of the mask 40. The intermediate layer 60 between substrate and functional layer necessary to isolate the electrodes.

3b shows the intermediate state after etching the flow channels 80 (e.g. by anisotropic plasma etching), removal the mask 30 and producing the contact pads 90 for the middle or external electrodes. Optionally, the contact pads 90 can also be produced before the mask 30 is applied.

Finally, as shown in Fig. 3c, one is preferred pre-structured cover substrate 100 with the previous structure connected. This can be done, for example, by anodizing Glass bonding is done. The pre-structuring is desirable thus 90 access openings to the contact pads consist.

Optionally, in substrate 70 or in cover substrate 100 Openings to the channels 80 to be made from the Bottom and / or top of the structure the medium to be pumped supply.

Fig. 4 shows a modification of the manufacturing process as a fourth embodiment of the present invention.

This fourth embodiment is made by anodizing. When anodizing, the substrate 70 ', here a p-type wafer substrate with n ⁺ wells 120, is immersed in an etching solution which contains HF. By applying a voltage to two electrodes, between which the substrate is located, small pores are etched into the substrate from one side. The pore size is determined by the anodizing conditions (HF concentration, current density, doping of the substrate, etc.).

By masking the p-doped substrate 70 'with the n ⁺ -doped regions 120, locally limited, porous layer regions 110 can be produced on the substrate 70'. By changing the anodizing conditions (HF concentration, current density, ...), the silicon can be completely detached below these porous layer regions 110 and thus a respective flow channel 80 'can be generated (electropolishing).

Subsequent brief oxidation oxidizes the porous Silicon completely due to its large surface area and converts to silicon oxide. With a suitable choice The volume expansion leads to the porosity of the porous layer regions 110 during oxidation to close the Pores. A sealing layer can optionally be applied become.

It is important that the two electrodes due to the oxidation 90 laterally electrically isolated. To prevent, that a current flow below the respective channel 80 'of one electrode 90 flows to the other electrode 90 the different dopings are used to make a Generate diode in reverse direction.

5 shows a further modification of the manufacturing method as a fifth embodiment of the present Invention.

By changing the anodizing conditions further a porous layer under the respective channel 80 ' 110 'can be generated. One gets one after the oxidation Channel 80 'or a cavity with above and below Oxide 110, 110 'of the electrodes 90 from each other completely isolated.

Although the present invention has been described above in terms of preferred embodiment has been described, it is not limited to this, but can be modified in a variety of ways.

In the above examples, the component according to the invention is in simple forms to explain its basic principles have been explained. Combinations of examples and much more complicated designs using the same basic principles are of course conceivable.

Any micromechanical basic materials can also be used be used, and not just the example Silicon substrate.

Also by masking with a nitride layer certain areas of the substrate are protected from the etching attack become.

Claims (13)

Micromechanical component, in particular micropump for polar fluids, with: a substrate (50, 60, 70; 70 '); at least two flow channels (10, 10 '; 10, 10', 11, 12, 12 ';80;80') provided in the substrate (50, 60, 70; 70 ') which branch off from a common entrance area (5) are; wherein the entrance area has a branching with a tip (P; P1, P2) on which the inner walls (7; 7 ') of the flow channels (10, 10'; 10, 10 ', 11, 12, 12';80; 80 ') share;
a first electrode (20; 20a, 20b) for applying a first electrical potential to the inner walls (7; 7 ') of the flow channels (10, 10'; 10, 10 ', 11, 12, 12';80; 80 ') ; and
a second electrode (10) for applying a second electrical potential to the outer walls (8; 8 ') of the flow channels (10, 10'; 10, 10 ', 11, 12, 12';80; 80 '). Micromechanical component according to claim 1, characterized in that the flow channels (10, 10 '; 10, 10', 11, 12, 12 ';80;80') are brought together in a common output region (6). Micromechanical component according to claim 1 or 2, characterized in that the tip (P; P1, P2) has a small radius in the range of a few micrometers. Micromechanical component according to one of the preceding claims 2 or 3, characterized in that the inner walls (7; 7 ') of the flow channels (10, 10'; 10, 10 ', 11, 12, 12';80; 80 ') in the common exit area (6) have a curve (R; R, R '). Micromechanical component according to Claim 1, characterized in that two flow channels (10, 10 ') are branched off from the common input area (5), the flow channels (10, 10') are brought together in a common central area (11) from the central area ( 11) two further flow channels (12, 12 ') are branched off, and the further two flow channels (12, 12') are brought together in a common exit area (6) which has a branching with a further tip (P; P1, P2) , on which the inner walls (7; 7 ') of the flow channels (12, 12') share. Micromechanical component according to Claim 5, characterized in that the central region (11) has a branching on both sides with a curve (R, R ') on which the inner walls (7; 7') of the flow channels (10, 10 '; 10, 10 ', 11, 12, 12';80; 80 ') share. Micromechanical component according to claim 5, characterized by a third electrode (20b) for applying a third electrical potential to the inner walls (7 ') of the two further flow channels (12, 12'). Method for producing a micromechanical component according to claim 1, characterized by the steps: Providing a substrate (50, 60, 70) with a micromechanical functional layer (50) with an insulation layer (60) interposed on a wafer substrate (70); Etching trenches (80; 80 ') in the micromechanical functional layer (50) to create the first electrode (20; 20a, 20b) and the second electrode (10) and the flow channels (10, 10'; 10, 10 ', 11 , 12, 12 ';80;80'); and Closing the flow channels (10, 10 '; 10, 10', 11, 12, 12 ';80;80') from above. A method according to claim 8, characterized in that to close the flow channels (10, 10 '; 10, 10', 11, 12, 12 ';80;80') from above another substrate (100) on the micromechanical functional layer (50 ) is bonded. Method for producing a micromechanical component according to claim 1, characterized by the steps: Providing a substrate (70 '); Providing masking areas (120) for defining the position of the flow channels (80; 80 '); anodic etching of the flow channels (80; 80 '); Providing the first electrode (20; 20a, 20b) and the second electrode (10) in the masking areas (120); and Closing the flow channels (80; 80 ') from above. Method according to claim 10, characterized in that to close the flow channels (80; 80 ') a porous layer (110) above the flow channels (80; 80') is oxidized from above. Method according to Claim 10 or 11, characterized in that the masking regions (120) are doping regions with a doping type opposite to the substrate (70 '). Method according to Claim 10, 11 or 12, characterized in that porous regions (110; 110 ') are provided in the substrate (70') above and below the flow channels (80; 80 ').

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