MEMS device including spurious mode suppression and corresponding operating method

Abstract

A MEMS device and a corresponding operating method. The MEMS device is equipped with an oscillatory micromechanical system, which is excitable in a plurality of useful modes, the oscillatory micromechanical system including at least one system component, which is excitable in at least one parasitic spurious mode by a superposition of the useful modes. An adjusting device is provided, which is configured in such a way that it counteracts the parasitic spurious mode by application of an electromagnetic interaction to the system component.

Claims

1. A MEMS device, comprising: an oscillatory micromechanical system, which is excitable in a plurality of useful modes, wherein the oscillatory micromechanical system includes at least one system component, which is excitable in at least one parasitic spurious mode by superposing the useful modes; and an adjusting device, which is configured so that it counteracts the superposition with the parasitic spurious mode by application of an electromagnetic interaction to the system component; wherein the adjusting device includes a DC voltage generating unit for generating a DC voltage and at least one or more electrodes, which is configured so that an electrostatic field is applied to the system component via the electrodes.

2. The MEMS device of claim 1, wherein the DC voltage generating unit is controllable.

3. A MEMS device, comprising: an oscillatory micromechanical system, which is excitable in a plurality of useful modes, wherein the oscillatory micromechanical system includes at least one system component, which is excitable in at least one parasitic spurious mode by superposing the useful modes; and an adjusting device, which is configured so that it counteracts the superposition with the parasitic spurious mode by application of an electromagnetic interaction to the system component; wherein the adjusting device includes an AC voltage generating unit for generating an AC voltage and one or multiple electrodes, which are configured so that an electrodynamic field may be applied to the system component via the electrodes.

4. The MEMS device of claim 3, wherein the AC voltage generating unit is controllable.

5. The MEMS device of claim 1, wherein the one or more electrodes are situated perpendicularly to an oscillation direction of the system component.

6. The MEMS device of claim 1, wherein the one or more electrodes are situated in parallel to an oscillation direction of the system component.

7. The MEMS device of claim 1, wherein the system component includes one or more counter electrodes, which interact with the one or more electrodes.

8. The MEMS device of claim 3, wherein the counter electrodes are molded at the system component.

9. The MEMS device of claim 3, wherein the counter electrodes are applied as a coating to the system component.

10. A MEMS device, comprising: an oscillatory micromechanical system, which is excitable in a plurality of useful modes, wherein the oscillatory micromechanical system includes at least one system component, which is excitable in at least one parasitic spurious mode by superposing the useful modes; and an adjusting device, which is configured so that it counteracts the superposition with the parasitic spurious mode by application of an electromagnetic interaction to the system component; wherein the system component includes a spring unit or a bar unit.

11. The MEMS device of claim 2, wherein the DC voltage generating unit and/or the AC voltage generating unit are controllable proportionally to an oscillation deflection or oscillation speed of the system component.

12. An operating method for a MEMS device, which includes an oscillatory micromechanical system, the method comprising: exciting the oscillatory micromechanical system in a plurality of useful modes, wherein the oscillatory micromechanical system includes at least one system component, which is excitable in at least one parasitic spurious mode by superposing the useful modes; setting a resonant frequency of the system component with an adjusting device, which is configured so that it counteracts the superposition with at least one parasitic spurious mode by applying an electromagnetic interaction to the system component; wherein the parasitic spurious mode is ascertained during the operation by a detection unit.

13. The operating method of claim 12, wherein the parasitic spurious mode is ascertained in a calibration mode or a simulation tool.

14. An operating method for a MEMS device, which includes an oscillatory micromechanical system, the method comprising: exciting the oscillatory micromechanical system in a plurality of useful modes, wherein the oscillatory micromechanical system includes at least one system component, which is excitable in at least one parasitic spurious mode by superposing the useful modes; setting a resonant frequency of the system component with an adjusting device, which is configured so that it counteracts the superposition with at least one parasitic spurious mode by applying an electromagnetic interaction to the system component; wherein the parasitic spurious mode is ascertained during the operation by a detection unit, which includes at least one electrode or at least one piezoelectric layer, at least one piezoresistive layer, or at least one magnetic layer, or at least one current-conducting conductor on the at least one system component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic view to explain the underlying functional principle of the present invention.

(2) FIGS. 2a) and 2b) show schematic partial cross-sectional views of a MEMS device according to a first specific embodiment of the present invention.

(3) FIG. 3 shows a schematic partial cross-sectional view of a MEMS device according to a second specific embodiment of the present invention.

(4) FIG. 4 shows a schematic partial cross-sectional view of a MEMS device according to a third specific embodiment of the present invention.

(5) FIG. 5 shows a schematic partial cross-sectional view of a MEMS device according to a fourth specific embodiment of the present invention.

(6) FIG. 6 shows a schematic partial cross-sectional view of a MEMS device according to a fifth specific embodiment of the present invention.

(7) FIG. 7 shows a schematic partial cross-sectional view of a MEMS device according to a sixth specific embodiment of the present invention.

DETAILED DESCRIPTION

(8) FIG. 1 shows a schematic view to explain the underlying functional principle of the present invention.

(9) In FIG. 1, reference numeral 100 generally identifies an oscillatory micromechanical system, which may be excited in a plurality of useful modes, for example, a rotation rate sensor or a micromirror, oscillatory micromechanical system 100 including a functional block 10 and a system component 1. System component 1 is, for example, an insulated element, e.g., a spring or a bar or a combination of multiple components of functional block 10.

(10) An adjusting device 50 is provided in the area of system component 1, which is configured in such a way that by applying an electromagnetic interaction W to system component 1, it counteracts a parasitic spurious mode to which system component 1 is susceptible.

(11) Adjusting device 50 may be, as already mentioned above, electrostatic, electrodynamic, magnetostatic, magnetodynamic, electromagnetostatic, or electromagnetodynamic, or also piezoelectric, inter alia. In the specific embodiments described hereafter, only an electrostatic and an electrodynamic interaction are described as the electromagnetic interaction to simplify the description.

(12) Adjusting device 50 may either be preprogrammed or be controllable or regulatable.

(13) FIGS. 2a), b) show schematic partial cross-sectional views of a MEMS device according to a first specific embodiment of the present invention.

(14) In FIGS. 2a), b), reference numeral 1a identifies a system component of oscillatory micromechanical system 100 according to FIG. 1, for example, a micromechanical spring. SR identifies the oscillation direction in which system component 1a is excitable.

(15) A first electrode 31 and a second electrode 32 are provided in their plate plane perpendicular to oscillation direction SR on opposing sides adjacent to system component 1a.

(16) Furthermore, a DC voltage generating unit 30 is provided for generating a DC voltage, which is connected to electrodes 31, 32 in such a way that an electrostatic field may be applied to system component 1a via electrodes 31, 32. DC voltage generating unit 30 may be settable or controllable or regulatable, as schematically shown by the arrow. However, this is not necessarily required, but rather is to be considered optional.

(17) DC voltage generating unit 30 and the two electrodes 31, 32 form adjusting device 51 in this first specific embodiment.

(18) As shown in FIG. 2b), counter electrodes S1, S2 are provided as a coating on the surface of system component 1a opposite to the two electrodes 31, 32. These counter electrodes S1, S2 may either be set to a predetermined potential by an electrical connection (not shown) or operated floating. If system component 1a should itself be conductive, counter electrodes S1, S2 may also be omitted.

(19) An adaptation of the resonant frequency of system component 1a is carried out during operation by adjusting device 51, whereby the influence of the parasitic spurious modes is eliminated or strongly reduced. In particular, the rigidity of system component 1a becomes less due to the electrostatic interaction and the resulting resonant frequency becomes smaller. It may be set in such a way that the resonant frequency is no longer at a multiple of the drive frequency or does not meet the internal resonance condition, due to which excitation to spurious oscillations cannot take place.

(20) FIG. 3 shows a schematic partial cross-sectional view of a MEMS device according to a second specific embodiment of the present invention.

(21) In the second specific embodiment according to FIG. 3, instead of DC voltage generating unit 30, an AC voltage generating unit 40 is provided for generating an AC voltage at electrodes 31, 32, which are configured in such a way that an electrodynamic field may be applied to system component 1a via electrodes 31, 32.

(22) As in the first specific embodiment, AC voltage generating unit 40 changes the rigidity of system component 1a in the form of the spring, in order to shift the resonant frequency to eliminate the spurious mode.

(23) The AC voltage generating unit 40 may optionally be settable or controllable or regulatable, but may also be set to a constant value established empirically or by simulation.

(24) AC voltage generating unit 40 and the two electrodes 31, 32 form adjusting device 52 in this example.

(25) Furthermore, it is possible both in the first and in the second specific embodiment and also in the specific embodiments described hereafter to configure DC voltage generating unit 30 or AC voltage generating unit 40 to be regulatable in such a way that the applied DC voltage or AC voltage, respectively, is proportional to the deflection or proportional to the speed of the spurious parasitic oscillations of system component 1a. Further electrodes (not shown) for detecting the deflection or speed may be provided for this purpose.

(26) FIG. 4 shows a schematic partial cross-sectional view of a MEMS device according to a third specific embodiment of the present invention.

(27) In the third specific embodiment, system component 1b is a bar, which is connected via springs 101, 102 to remaining oscillatory micromechanical system 100 according to FIG. 1. The electrodes are identified here by reference numerals 31′, 32′ and corresponding counter electrodes (not shown) may also be provided on system component 1b. In the third specific embodiment, adjusting device 53 again contains a DC voltage generating unit 30, as already described above.

(28) FIG. 5 shows a schematic partial cross-sectional view of a MEMS device according to a fourth specific embodiment of the present invention.

(29) In the fourth specific embodiment, in contrast to the third specific embodiment, an analog AC voltage generating unit 40 is provided as part of adjusting device 54 as in the second specific embodiment. Otherwise, the fourth specific embodiment corresponds to the third specific embodiment.

(30) FIG. 6 shows a schematic partial cross-sectional view of a MEMS device according to a fifth specific embodiment of the present invention.

(31) According to FIG. 6, system component 1a is again a spring, however, an electrode 31″ is provided with its plate plane parallel to oscillation direction SR at the free end of the spring, whereby the electrostatic field of DC voltage generating unit 30 acts perpendicularly to oscillation direction SR.

(32) In the fifth specific embodiment, adjusting device 55 is formed by DC voltage generating unit 30 and electrode 31″.

(33) In this fifth specific embodiment, it is advantageous that in the case of the arrangement in parallel to oscillation direction SR of system component 1a (in the form of the spring), the distance to system component 1a may be small in relation to the above specific embodiments, which results in a strong electrostatic attractive force.

(34) In the fifth specific embodiment, the distance may thus be selected to be smaller. If the attractive force is nonetheless not sufficient in the fifth specific embodiment, it may be increased by a counter electrode which is also moved, as described hereafter.

(35) FIG. 7 shows a schematic partial cross-sectional view of a MEMS device according to a sixth specific embodiment of the present invention.

(36) In FIG. 7, reference numeral 31′″ identifies an electrode which is connected to DC voltage generating unit 30. A counter electrode 32′″ molded at system component 1a may be configured to be enlarged in comparison to the fifth specific embodiment, so that the attractive force is increased.

(37) In the sixth specific embodiment, adjusting device 56 is formed by the DC voltage generating unit and electrodes 31′″, 32′″.

(38) Otherwise, the structure of the sixth specific embodiment is identical to that of the fifth specific embodiment.

(39) Although the present invention was described on the basis of exemplary embodiments, it is not restricted thereto. In particular, the mentioned materials and topologies are only by way of example and are not restricted to the explained examples.

(40) As already mentioned above, in addition to electrostatic and electrodynamic interaction, other electromagnetic interactions may also be used, for example, piezoelectric layers or magnetic layers or current-conducting conductors being applied to corresponding system components of the oscillatory micromechanical structure.

(41) The present invention is also not restricted to the system components shown, but rather is applicable to any arbitrary one-piece or multipart system components.

(42) The ascertainment of the spurious resonances to be eliminated may be carried out either empirically in a calibration mode or by a corresponding simulation.

(43) The present invention is also applicable not only to rotation rate sensors or micromirrors, but rather to any arbitrary oscillatory micromechanical systems.