WO2011042041A1

WO2011042041A1 - Microelectromechanical sensor with a differential capacitor principle

Info

Publication number: WO2011042041A1
Application number: PCT/EP2009/062887
Authority: WO
Inventors: Marco Dienel; Jörg Schaufuß; Jan Mehner; Dirk Scheibner
Original assignee: Siemens Aktiengesellschaft
Priority date: 2009-10-05
Filing date: 2009-10-05
Publication date: 2011-04-14

Abstract

The invention proposes a microelectromechanical sensor (3) with a differential capacitor principle, which sensor has a capacitor with a moving electrode (4) and with at least one stationary electrode (5). In this case, the moving electrode (4) and the stationary electrode (5) are in the form of flat surfaces at least in a subregion, said flat surfaces being arranged parallel to one another, that is to say there being a gap between them. First means (7) for reducing the gap in an adjustment direction (y) are connected to the moving electrode (4), wherein the adjustment direction (y) has an angle which differs substantially by 90° from the flat surfaces of the electrodes (4, 5). The fingers of the comb-like electrodes are oriented obliquely in relation to the movement direction of the electrodes and to the movement direction of the adjustment means.

Description

description

Microelectromechanical sensor with differential capacitor principle

The invention relates to a microelectromechanical sensor with differential capacitor principle, which has a capacitor with a movable electrode and at least one fixed electrode, wherein the movable and the fixed electrode are formed at least in a partial area as flat surfaces which are arranged parallel to each other, i. between which there is a gap.

Such microelectromechanical sensors are known. It is also known in capacitive sensors to keep the gap as small as possible, since the sensitivity increases with the reduction of the gap distance. There are several methods available for generating small capacitive gap distances. For example, the microelectromechanical structure is produced with technologically easily realizable, relatively large gap distances. After completion, the gap distance is reduced by means of an adjustment actuator. Hitherto, the adjustment direction has always been the same as the detection direction or working direction of the sensor, such as, for example, the sensor. in the document "Micromechanical resonators with submicron capacitive gaps in 2 μτη process" from ELECTRONICS LETTERS, Dec. 6, 2007, Vol.43, No.25 This means that several adjustment actuators have to be integrated in order to reduce counteracting gap spacings of a differential arrangement ,

The invention has for its object to provide a microelectromechanical sensor of the type mentioned above, which allows a reduction in the gap distance in a simple manner.

The object is achieved with the features of claim 1. An advantageous development of the microelectromechanical sensor is when according to claim 2, the first means for gap reduction comprise at least one return spring. Moreover, it is advantageous if according to claim 3, the first means for gap reduction at least one stop umfas ^¬ sen.

An advantageous development of the microelectromechanical sensor is when, according to claim 4 second means are provided by which the movable electrode is movable in an Ar ^¬ beitsrichtung having an angle to the flat surfaces of the electrodes, which differs substantially from 90 °.

It is advantageous if, according to claim 5, the adjustment direction and the working direction are separated from each other. By separating the suspension direction for adjustment and detection, the cross-sensitivity for vibrations in the adjustment direction can be reduced.

Furthermore, it is advantageous if according to claim 6, the adjustment direction and the working direction to each other at an angle of 90 °.

Another very advantageous embodiment is when this is at least partially carried out according to claim 7 as a micromechanical structure made of silicon. In addition, it proves to be advantageous if according to claim 8, the electrodes are formed in the shape of a comb with triangular tips which engage with each other, wherein the inclined surfaces of the triangular tips of the movable electrode at least partially opposite those of the fixed electrode with the gap.

A further particularly advantageous embodiment is when according to claim 9 for detecting the back and forth Movement of the movable electrode in the working direction two fixed electrodes are provided.

Furthermore, it is advantageous if, according to claim 10, the fixed electrodes are designed with a multiplicity of triangular electrode elements which are interconnected by buried conductor tracks. This results in an electrode pair arrangement for detecting the movement of the movable electrode in the forward and reverse directions.

An embodiment of the invention will be explained in more detail below with reference to a drawing. Show it:

1 shows a schematic representation of the basic principle of an inventive sensor,

2 shows a schematic representation of an inventive Sen ^¬ sors with differential capacitor principle,

3 shows a schematic representation of another erfinderi ^¬ rule sensor with differential capacitor principle and 4 different embodiments of electrode structures.

In FIG 1, the basic principle of the inventive micro-electromechanical sensor with differential capacitor principle is shown schematically. The sensor has a capacitor with a movable electrode and at least one fixed electrode.

1 shows the surface 1 of the movable electrode 4 and In parallel, in a gap distance d arranged the surface 2 of the fixed electrode 5. To reduce the slit spacing ^¬ stands d, the movable electrode is moved in the adjustment direction y. The adjustment y has the position of the two surfaces 1.2 an angle ß, which is substantially smaller than 90 °. Depending on the selected angle ß, the ratio of adjustment path to gap reduction changes. Extremely small, previously unattainable gap distances can be resolved by a larger adjustment path, which can be resolved with high accuracy will be realized. The movable electrode can be moved in the working direction x, whose surface 1 is here at an angle = 90 ° to the adjustment direction. This means that in contrast to previous structures, the separation of working direction and adjustment direction is provided. By separating the suspension direction for adjustment and detection, the cross-sensitivity for vibrations in the adjustment direction is changed according to the angle β, preferably reduced by the factor sin (β), whereas the sensitivity in the working direction is changed only by cos (β). For small angles ß, sin (ß) is much smaller than cos (ß).

This explained with reference to FIG 1 Basic principle is applied in the inventive sensor 3 with differential capacitor principle ACCORDING TO FIG 2, the example is suitable for use as Accelerati ^¬ supply sensor.

The sensor 3 has a movable electrode 4 and two fixed electrodes 5. In the profile, these electrodes 4, 5 is made comb-shaped with triangular tips 6 which interlock, wherein the inclined surfaces of the triangular tips 6 of the movable electrode 4 at least in part ^¬ as those of the fixed electrode 5 facing with a gap d. The two fixed electrodes 5 lent a drive on the outward and return path during a movement in the working direction x.

In this embodiment according to FIG. 2, two interconnected combs are provided for the electrodes 4, 5 in each case. In principle, more combs can also be specified according to this principle. The two combs forming the movable electrode 4 are each connected to first gap-reducing means 7 in an adjustment direction y. The working direction x, in which the deflection of the movable electrode 4 is provided, lies at an angle of 90 ° with respect to the adjustment direction y. The separation of the working direction x and the adjustment direction y as well as the beveled shape of the electrodes 4, 5 also causes a gap reduction with only one adjusting actuator. tion simultaneously between two electrode pairs is possible and the use as a differential capacitor is still guaranteed. When executing the microelectromechanical sensor 3 with silicon, due to the requirement of only one adjustment actuator, a reduced silicon area is required.

For the execution of the Justieraktors solutions in micro-electromechanical structure are known. These include, for example:

- electrostatic delivery,

- thermal delivery by means of multi-layer systems,

- stepper,

- bistable snap mechanisms,

- Ratchet mechanism (catch, pawl).

The first means 7 for gap reduction comprise in addition to the Justieraktor two return springs 8 and two stops 9, which can be made fixed or variable. As stops 9, e.g. Serve stopper. The adjustment movement can be stepped, e.g. via the stoppers or latching pawls or continuously. This also allows an adaptive adjustment of the gap distance.

In addition, the two combs which form the movable electrode 4 are connected to second means 10, which are designed here as springs and which ensure the movement of the movable electrode 4 in the working direction x.

The described sensor 3 with first means 7 for gap reduction would be e.g. advantageous used when a vibration excitation occurs at high frequencies. In this case, smaller movement amplitudes result, which require greater sensor sensitivity by adjusting the gap distance.

Another embodiment of an inventive sensor is shown in FIG. In contrast to the embodiment according to FIG. 2, the stationary electrodes 5 are not comb-shaped, but with a plurality of triangular electrode elements El and E2, which enable an electrode pair arrangement for detecting the movement of the movable electrode 4 in the forward and reverse directions. The respective uniform electrode elements El and E2 are each connected by buried conductor tracks, ie in another plane of the microelectromechanical structure. Incidentally, the present embodiment of the ^¬ be described embodiment of Figure 2 corresponds.

It should be noted that the stops 9 are not absolutely necessary, since adjustment movements can also take place in several steps with a predetermined step size or continuously. The adjustment movement can also take place via the stationary electrodes instead of via the inertial mass.

FIG. 4 shows various electrode structures for movable and stationary electrodes 4, 5. For the selection of the electrode structure u.a. to consider the following factors:

- What technology is used (maximum allowable gap distances, undercut or undercut on sharp corners);

Distribution of the seismic mass (the tines or corners can be made larger or smaller in volume depending on the position of the resonance frequency).

Claims

claims

1. A micro-electromechanical sensor (3) with Differentialkon ^¬ densatorprinzip having a capacitor having a movable electrode (4) and having at least one stationary electrode (5), wherein the movable electrode (4) and the stationary electrode (5) at least in a Partial area are formed as flat surfaces which are arranged parallel to each other, that between which there is a gap, characterized in that with the movable electrode (4) first means (7) for gap reduction in an adjustment direction (y) are connected, wherein the adjustment direction (y) has an angle different from the flat surfaces of the electrodes (4, 5) of 90 °.

2. Microelectromechanical sensor according to claim 1, characterized in that the first means (7) for gap reduction comprise at least one return spring (8).

3. Microelectromechanical sensor according to claim 1 or 2, characterized in that the first means (7) for gap reduction comprise at least one stop (9).

4. Microelectromechanical sensor according to one of the above-mentioned claims, characterized in that second means (10) are provided, by means of which the movable electrode (4) is movable in a working direction (x) facing the flat surfaces of the electrodes (10). 4.5) has an angle which we ^¬ sentlich deviates from 90 °.

5. microelectromechanical sensor according to claim 4, characterized in that the adjustment direction (y) and the working ^¬ direction (x) are separated from each other.

6. Microelectromechanical sensor according to claim 5, characterized in that the adjustment direction (y) and the working ^¬ direction (x) to each other at an angle of 90 °.

7. Microelectromechanical sensor according to one of the preceding claims, characterized in that it is at least partially out as a micromechanical structure made of silicon ^¬ leads.

8. Microelectromechanical sensor according to one of the preceding claims, characterized in that the electrodes (4,5) in the form of a comb are formed with triangular tips (6) which engage with each other, wherein the inclined surfaces of the triangular-shaped tips (6) of the movable

Electrode (4) at least partially facing those of the fixed electrode (5) with the gap.

9. Microelectromechanical sensor according to one of the preceding claims, characterized in that for detecting the back and forth movement of the movable electrode (4) in the working direction (x) two fixed electrodes (5) are provided.

10. A micro-electromechanical sensor according to one of vorange ^¬ Henden claims, characterized in that the festste ^¬ Henden electrodes (5) having a plurality of triangular-shaped electrode elements (E1, E2) are executed, which are connected by ver ^¬ buried conductor lines with each other.