Micromechanical z-inertial sensor

Abstract

A micromechanical z-inertial sensor includes a substrate; a movable seismic mass in a micromechanical functional layer; a torsion spring connected to the movable seismic mass and about which the seismic mass able to rotate; an electrode layer below the seismic mass and that, in an outer region is connectible to a potential of the substrate and is connected to the seismic mass via an insulating layer; and electrodes at a distance above and below an inner region of the electrode surface.

Claims

1. A micromechanical z-inertial sensor comprising: a substrate; a movable seismic mass in a micromechanical functional layer; a torsion spring that is connected to the movable seismic mass and about which the seismic mass is able to rotate; an electrode layer that is below the seismic mass and that, in an outer region of the electrode layer, is connectible to a potential of the substrate and is connected to the seismic mass via an insulating layer; and electrodes situated at a distance above and below an inner region of the electrode layer.

2. The micromechanical z-inertial sensor of claim 1, wherein the outer and inner regions of the electrode layer are connectible to different electrical potentials and are divided by an insulating channel that is circumferentially around the inner region.

3. The micromechanical z-inertial sensor of claim 1, wherein, at the outer region, at least one of the electrode layer and the seismic mass is unperforated.

4. The micromechanical z-inertial sensor of claim 1, wherein at least one of the electrode layer and the seismic mass is perforated at the outer region.

5. The micromechanical z-inertial sensor of claim 1, wherein the electrode layer is connectible to a potential of the substrate by a spring element.

6. The micromechanical z-inertial sensor of claim 5, wherein a stiffness of the spring element is such that the spring element in a state of rest of the micromechanical z-inertial sensor prevents the rocker from tilting.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a cross-sectional view of a conventional micromechanical z-inertial sensor.

(2) FIG. 2 is a top view onto a conventional micromechanical z-inertial sensor.

(3) FIG. 3 is a sectional view through a conventional micromechanical z-inertial sensor.

(4) FIGS. 4 and 5 are sectional views through a conventional micromechanical z-inertial sensor.

(5) FIG. 6 is a top view onto a conventional micromechanical z-inertial sensor.

(6) FIGS. 7 and 8 are views of a micromechanical z-inertial sensor according to an example embodiment of the present invention.

(7) FIG. 9 is a top view onto the micromechanical z-inertial sensor according to an example embodiment of the present invention.

(8) FIG. 10 is a flowchart of a method for manufacturing a micromechanical z-inertial sensor according to an example embodiment of the present invention.

DETAILED DESCRIPTION

(9) FIG. 7 is a cross-sectional view of a micromechanical z-inertial sensor 100 in a position of rest, according to an example embodiment of the present invention. It can be seen that the electrode layer 13 is situated below the movable rocker and is able to move along with the latter. Furthermore, it can be seen that polysilicon layer 12 is clearly smaller than in the known design and is limited to a central sensing region below the fixed electrodes 14. In this instance, electrode layer 13 is divided into a central region and an outer region by a circumferential continuous perforation channel. In this manner, electrode layer 13 and substrate 10 are able to be brought to the same electrical potential, as a result of which, in the operation of z-inertial sensor 100, electrode layer 13 has different electric potentials in the outer region and in the central sensing region.

(10) This makes it possible that no electrical field occurs in the region of a cavity 15 below electrode layer 13, i.e., that the region is potential-free, and that a deflection of the rocker can be achieved exclusively by mechanical forces.

(11) As can be seen in the cross-sectional view of FIG. 8, this advantageously makes it possible to achieve a greater freedom of movement of the rocker as compared to the conventional system. Below electrode layer 13, etching channels or cavities (not shown) are developed in a production process, which can be produced for example together with the patterning of polysilicon layer 12 of the buried conductor track.

(12) Electrode layer 13 can be advantageously produced also without perforation holes 13a, whereby a rocker can be produced that is completely symmetrical with respect to a vertical gas flow. Optionally, electrode layer 13 can also be produced with perforation holes (not shown). Electrode layer 13 is furthermore coupled in mechanically rigid fashion to the rocker structure of seismic mass 21 via an insulating oxide layer 16.

(13) For this purpose, regions (even without perforation) are provided in the micromechanical functional layer of the rocker structure that are sufficiently large so that an oxide layer 16 remains between the functional layer and electrode layer 13 in the sacrificial layer etching process. This makes it possible for electrode layer 13 to be upwardly mechanically connected to the rocker in the outer region by an insulating layer in the form of oxide layer 16. At the same time, all oxides below electrode layer 13 are completely removed in the sacrificial layer etching process due to the etching channels provided there.

(14) The top view of the provided micromechanical z-inertial sensor 100 of FIG. 9 shows that via thin spring elements 17, which have a lower spring stiffness with respect to a tilting of the rocker, electrical conductor tracks are produced that keep electrode layer 13 at substrate potential. The thin spring elements 17 are advantageously arranged symmetrically with respect to the torsional direction of the rocker. In this manner, movable seismic mass 21 is able to hover potential-free in the outer region and is therefore maximally sensitive to mechanical forces only due to the mass asymmetry.

(15) As a result it is possible advantageously to increase a maximum deflection of the rocker. It can be seen that, in contrast to the conventional system, the electrode surfaces of polysilicon layer 12 are limited to the central region of the rocker. The more central arrangement of fixed counter-electrodes 14 achieved in this manner makes the micromechanical z-inertial sensor 100 less susceptible to a bending of substrate 10, which typically occurs as a result of external influences when the component is soldered onto a circuit board and is thereby exposed to temperature fluctuations or is exposed to mechanical strains induced in other ways.

(16) In the provided z-inertial sensor 100, the mass asymmetry is advantageously increased, as a result of which the sensor can be designed to be markedly more sensitive or a sensor of the same sensitivity can be produced in resource-saving fashion on a smaller surface.

(17) The sensor thus becomes markedly less sensitive to pre-deflections of the rocker. Fundamentally, micromechanical z-acceleration sensors always have a small, statistically distributed pre-deflection due to variances in the manufacturing process. It is possible to compensate for the pre-deflection via a calibration method in an evaluation electronics, but, due to various effects, this results in nonlinearities and other undesired secondary effects. The greater freedom of movement of the rocker advantageously makes it possible to reduce greatly the effects in the signal path caused by the uniform pre-deflections.

(18) The approach provided makes it possible to develop the rocker regions that are not situated below or above fixed electrodes 14 without perforation holes. This advantageously makes it possible markedly to increase a damping of z-acceleration sensor 100. The rocker can be designed to be completely symmetrical with respect to the geometry in the flow of gas from the lower side to the upper side. Static and dynamic effects, which occur when different temperatures or temperature gradients exist at the rocker between the upper side and the lower side and radiometric effects are produced in the sensor, affect the rocker symmetrically and are advantageously able to avoid tilting the rocker.

(19) The provided structure is advantageously able to substantially reduce an adhesion in z-inertial sensors. In sensors having the same torsion spring, the greater maximum deflection of the sensors allows for sensors having a greater restoring force at the end stop, which reduces the adhesion propensity substantially. Advantageously, it is possible to produce smaller and thus more favorable z-acceleration sensors. As a result, an offset behavior of such a z-inertial sensor can be improved markedly.

(20) FIG. 10 shows a basic sequence of a method for manufacturing a micromechanical z-inertial sensor 100. In a step 200, a substrate 10 is provided. In a step 210, a movable seismic mass 21 is provided in a micromechanical functional layer 20. In a step 220, a torsion spring 22 that is connected to the movable seismic mass 21 and about which the seismic mass able to rotate, is provided. In a step 230, an electrode layer 13 is provided below the seismic mass 21, the electrode layer 13 being connectible to the potential of substrate 10 in an outer region and being connected to seismic mass 21 via an insulating layer 16. In a step 240, electrodes 12, 14 are developed at a distance above and below an inner region of electrode surface 13. The order of the mentioned steps can also be switched in a suitable manner.

(21) Although the present invention was described above with reference to concrete example embodiments, one skilled in the art is also able to implement example embodiments that were not disclosed above or that were disclosed above only partially, without deviating from the essence of the invention.