Micromechanical sensor device

Abstract

Micromechanical sensor device (100), comprising: - at least one movable detection element (20); and - a stop device (10) for the detection element (20), wherein the stop device (10) is mechanically and electrically connected to the detection element (20), wherein the stop device (10) is designed such that in the event of a movement of the detection element (20), a stop region (11) of the stop device (10) is moved in the opposite direction to the detection element (20).

Description

The invention relates to a micromechanical sensor device and to a method for operating a micromechanical sensor device.Prior ArtLaid-open specification EP 2 439 542 A1 discloses a sensor.In inertial sensor systems, for example, the rotation rate and acceleration sensor systems, movable structures are used to translate measured variables (e.g., rotation rate and acceleration) into a deflection of seismic masses. Such sensors are manufactured, inter alia, in silicon micromechanics.Micromechanical production processes include, among other things, a sequence of deposition and structuring steps. The latter are referred to as etching or trench processes. The mentioned movable structures require a certain freedom of movement in order to enable optimum sensing of the measured variable. On the other hand, these structures must not be deflected too far in order to avoid damage or non-linear behavior.To limit the deflection, what are known as stop structures are used, the object of which is to prevent damage to the utility structure in the event of mechanical overload, for example due to external disturbance acceleration, and in the event of snapping or collapsing processes due to electrical overvoltage.In the prior art, static or resilient stops are known which fulfil this task more or less.However, despite the use of stop structures, problems arise again and again both in the case of rotation rate sensors and in the case of acceleration sensors due to particles becoming free due to the stop.In particular in the case of acceleration sensors, so-called sticking also occurs despite these structures, which means that the movable structure no longer releases mechanically or only with a delay after an impact process. There are several causes and mechanisms for this adhesion problem. In at least one of these mechanisms, the impact velocity plays a predominant role, that is, the higher the velocity in the impact, the higher the probability of sticking.It is therefore the object of the invention to provide an improved micromechanical sensor device.Disclosure of the InventionThe object is achieved with a micromechanical sensor device, having:at least one movable sensing element; anda stop device for the detection element, wherein the stop device is mechanically and electrically connected to the detection element, wherein the stop device is configured such that, in the event of a movement of the detection element, a stop region of the stop device is moved in the opposite direction to the detection element.This prevents a part of the sensor from being able to build up too high a kinetic energy, with the result that the kinetic energy is minimized upon impact, whereby collapse or collapse is advantageous. These can be substantially prevented from occurring in the event of snapping states or other damage or destruction of the sensor devices. Due to the electrical connection of the detection element to the stop device, the mentioned elements are at the same electrical potential, so that no currents can flow between them or forces can act, whereby e.g. welds can be advantageously avoided.The object is furthermore achieved by a method for operating a micromechanical sensor device, having the following steps:moving a sensing element of the sensor device;wherein, by means of a lever device of a stop device, the stop device is moved in the opposite direction to the detection element.Preferred embodiments of the micromechanical sensor device according to the present invention are the subject matter of dependent claims.A preferred embodiment of the micromechanical sensor device is characterized in that the stop device comprises a lever device, wherein a pivot point of the lever device is fixed by means of a fastening device, wherein the lever device is connected to the detection element. By means of the lever device, a deflection mechanism is realized, which easily realizes the opposing movements of the detection element and the stop device.A preferred embodiment of the sensor device according to the invention is characterized in that arms of the lever device are substantially of the same length or of different lengths. In this way, the entire structure can be made more or less sensitive, or a transmission ratio can be set for the movements of the detection element and the stop device.A further preferred embodiment of the sensor device according to the invention is characterized in that a stop device is arranged on one side of the detection element. In this way, a symmetrical structure of the stop device is realized, whereby a stop energy can be distributed or minimized in an advantageous manner.A further preferred specific embodiment of the micromechanical sensor device is characterized in that the fastening device is able to be loaded under tension or under pressure. In this way, different possibilities for the design and arrangement of the fastening device are advantageously provided, as a result of which spatial conditions within the sensor device can be used as well as possible.A further preferred embodiment of the micromechanical sensor device according to the present invention is characterized in that the lever device is strongly dimensioned in relation to the fastening device and has a more weakly dimensioned transition region toward the sensing element. In this way, a relatively rigid deflection mechanism is realized, which, however, is deflectable due to the less heavily dimensioned transition region. The transition region thus forms a type of hinge joint which brings about the mechanical and electrical coupling to the detection element.A further preferred embodiment of the sensor device according to the invention is characterized in that the stop region has a non-planar surface. In this way, a smooth and material-saving abutment of the detection element on the abutment device is made possible because a load distribution is effected over a larger area.The invention is described in detail below with reference to several figures with further features and advantages. All features described or shown form the subject matter of the invention, either alone or in any combination, independently of their summary in the patent claims or their reference, and independently of their formulation or representation in the description or in the figures. The figures are intended above all to illustrate the principles essential to the invention; any orders of magnitude or dimensions therefore cannot be gathered from the figures. Identical or functionally identical elements have the same reference numerals.The figures show: FIG. 1a shows a basic illustration of a plate capacitor for explaining the snap effect; FIG. 1 bshows three force-displacement characteristic curves for different electrical voltages for explaining the snap effect of the capacitor of FIG. 1 a; FIG. 2 ashows a first specific embodiment of the micromechanical sensor device according to the present invention in the unbended state; FIG. 2 b shows the micromechanical sensor device of FIG. 2 a in the deflected state; FIG. 3 shows a further specific embodiment of the micromechanical sensor device according to the present invention; and FIG. 4 shows a basic illustration of an embodiment of the method according to the invention.Embodiments of the InventionFIG. 1a shows a basic illustration of a plate capacitor having two electrodes, which is connected to an electrical voltage source V. The forces acting by the electric field on the electrodes of the plate capacitor are indicated by arrows. One of the electrodes of the capacitor is fixed and a second electrode of the capacitor is resiliently suspended and thereby movable.FIG. 1 bshows a force-displacement characteristic curve for various electrical voltages U 1, U 2 and U 3 applied to the capacitor of FIG. 1 a. On the x-axis, a deflection state of the upper electrode of the plate capacitor is plotted and on the y-axis, a dimensionless representation of the force between the electrodes is plotted. The value 1 on the x-axis corresponds to the deflection state of the capacitor in a rest position.Approximately at the value 0.7 (indicated by a double arrow) on the x-axis, the upper electrode has been pulled down by approximately 30%, whereby the plate capacitor assumes a stable state. Now, when the applied electric voltage is further increased, in the case of U2, at about 0.35, an inflection point is reached at which a force on the upper electrode changes sign, thereby pulling down the upper electrode. In this case, the entire system collapses or snaps, which has the result that the upper electrode of the plate capacitor can no longer be pulled upward by means of the spring from this point in time. In this state, undesirable adverse side effects, such as, for example, electrical welding, material ablation, adhesion, etc., can occur.U3 is the so-called electrical "snap voltage" in which the electrodes of the plate capacitor snap and in which the plate capacitor can never assume a stable state. The starting process begins when about one third of the gap of the plate capacitor has been passed through. In the case of U1 and U2, the structure would snap only if, for example, a deflection greater than approximately 70% or greater than approximately 80% was already caused by an external disturbance acceleration, because in this case the force between the electrodes is directed negatively, that is to say downwards.FIG. 2 ashows a schematic diagram of a first specific embodiment of micromechanical sensor device 100 according to the present invention. A movable sensing element 20 of the sensor device 100 is resiliently suspended. Four fixed electrodes 21, 22, 23, 24 are electrically connected to form a total of two capacitors (not shown) (e.g. the fixed electrodes 21 and 23 and the fixed electrodes 22 and 24), wherein, in the event of a deflection of the detection element 20, capacitance values of the capacitors are evaluated by means of a differential evaluation circuit (e.g. an ASIC, not shown). The number of two of the capacitors is merely exemplary, wherein naturally only one or more capacitors could also be. It can be seen that a deflection between the fixed electrodes 21, 22, 23 and 24 and the detection element 20 is d0in each case. The same extent of the deflection can be seen between a stop region 11 of the stop device 10 and the detection element 20.FIG. 2 ashows the entire structure in an unbended rest state. The stop device 10 is mechanically and electrically connected to the detection element 20 and is externally fastened by means of an elongate fastening device 12 (e.g. made of silicon). A stop device 10 is arranged on one side of the movable detection element 20 and surrounds the latter in the manner of a clamp or anchor. The stop device 10 comprises a lever device with lever arms 10 a, 10 b, whereby a pivot point 13 is formed, to which the stop device 10 is fixed by means of the fastening device 12. By means of the fastening device 12 designed as a fixed suspension, it is ensured that the stop device 10 is pulled in the opposite direction to the detection element 20 via a deflection mechanism.By dimensioning lengths L 1, L 2 of the lever arms 10 a, 10 b, a lever action or a transmission ratio of the lever device of the stop device 10 between movement of the mass and counter movement of the dynamic stop, and thus the effectively effective stop distance, can be set almost arbitrarily and can be dimensioned in a simple manner.In the following, a principle of operation of the stop device 10 is explained in more detail with reference to FIG. 2 b. It can be seen that the movable detection element 20 has been deflected downward by a force in comparison with FIG. 2 a. As a result, a gap width d 1 that is smaller than the gap width d 0 has been set between the fixed electrodes 21, 22, 23, 24 and the detection element 20. Furthermore, as a result, the stop device 10 is deformed such that the stop region 11 of the stop device 10 is moved upward by means of the deflection mechanism of the lever device. Thus, between the detection element 20 and the stop device 10 a gap width d 2 is achieved which is approximately zero. In this way, when the movable sensing element 20 impacts the stop region 11, the kinetic energy of the movable element 20 is significantly reduced or a stop of the movable sensing element 20 on the stop region 11 is carried out more gently. This advantageously results in lower detachments of material particles.In the arrangement of FIG. 2 b, for the case L1=L2, the stop would be reached after passing through approximately 50% of the gap d0, which means that if the original gap width is 1 μm, the stop would act after 500 nm deflection. In principle, however, only a single stop device 10 or more than two stop devices 10 can also be used.FIG. 3 shows a further embodiment of the sensor device 100 according to the invention, in which it is provided that the fastening device 12 can be loaded under pressure. This can be of use in particular when spatial conditions above the stop device 10 are limited. It can also be seen that in this embodiment the lever region of the stop device 10 is dimensioned to be relatively heavy, wherein a transition region to the movable detection element 20 is dimensioned to be relatively thin as a kind of hinge. In this way, mobility of the lever structure of the stop device 10 relative to the sensing element 20 can still be ensured.Furthermore, it can also be provided that the stop region 11 is rounded or otherwise formed with a reduced contact surface against the detection element 20. This advantageously supports a load distribution of the detection element 20 on a slightly enlarged area of the stop region 11 of the stop device 10.It is of course also conceivable to realize all or only individual ones of the features of the stop device 10 of FIG. 3 in the embodiment of FIGS. 2 aand 2 b.Due to the fact that in acceleration sensors usually only approximately 20% of the electrode gap or gap is used as the evaluation range, wherein this value can be even significantly lower in the case of rotation rate sensors, movements exceeding this value can be evaluated. However, these cannot be prevented up to now according to the prior art and in the worst case lead to snapping processes, gluing, damage or to other undesirable effects.FIG. 4 shows in principle a flow chart of the method according to the invention. In a first step S 1, a movement of a detection element 20 of the sensor device 100 is carried out. In a step S 2, the stop device 10 is moved in the opposite direction to the detection element 20 by means of a lever device of a stop device 10.In summary, the present invention provides a micromechanical sensor device which makes it possible to make mechanical stops effectively available at significantly smaller distances than would be possible by technically minimally possible distance rules for static stop structures. Advantageously, it is possible by means of the sensor device according to the invention to effectively set dynamic stops just above the useful range. The invention thus represents a specific implementation of a stop structure in a micromechanical sensor device, with the aid of which it is possible to minimize stop energy on the stop structure.In this case, it is provided, without additional, possibly space-consuming, wiring measures, that the stop structure is connected at the same electrical potential as the structure to be protected.According to the invention, it is provided that the movable mass to be protected activates a deflection mechanism by its movement, which dynamically moves the stop structure towards the movable mass. In this way, mechanical impact occurs already after relatively small deflections, as a result of which the movable mass can absorb significantly less speed and thus kinetic energy than would be the case if the impact were to take place only at a great distance.Advantageously, in this way, a destructive force of the impact and thus the risk of particle formation as a result of, for example, chipping is reduced. The difference between snap (snap) and release (release) voltage can be advantageously reduced, so that the so-called "electrical clamping" is also made weaker. During the stated electrical clamping, a structure still remains in the snapped state even if the applied electrical voltage is already below the actual snap voltage again, but still above the release voltage. As a result, this has the advantageous effect that in the sensor device according to the invention a snap-in state can be released again advantageously more quickly after a reduction in the electrical voltage.Likewise, the reduced impact speed advantageously allows the mentioned tendency to stick to be reduced.A further advantage of the invention is that structures which have already been snapped or collapsed--regardless of the cause of the snap--are available again more quickly for a reasonable signal evaluation after impact because of the only short impact travel and lower clamping effect.This advantageously results in a reduction in measurement times, which results in an optimization of measurement or test series in production processes and thus saves costs. Furthermore, this results in a prolonged operating time of the sensor device.The person skilled in the art will combine the described features with one another without departing from the core of the invention.

Claims

Micromechanical sensor device (100), having: - at least one movable detection element (20); and - a stop device (10) for the detection element (20), wherein the stop device (10) is mechanically and electrically connected to the detection element (20), wherein the stop device (10) is designed such that, in the event of a movement of the detection element (20), a stop region (11) of the stop device (10) is moved in the opposite direction to the detection element (20).Sensor device according to Claim 1, characterized in that the stop device (10) comprises a lever device, wherein a pivot point (13) of the lever device is fixed by means of a fastening device (12), wherein the lever device (10a, 10b) is connected to the detection element (20).Sensor device according to Claim 2, characterized in that arms (10a, 10b) of the lever device are formed substantially of the same length or of different lengths.Sensor device according to one of Claims 1 to 3, characterized in that in each case one stop device (10) is arranged on one side of the detection element (20).Sensor device according to one of Claims 2 to 4, characterized in that the fastening device (12) can be loaded under tension or under pressure.Sensor device according to one of Claims 2, 3 or 5, characterized in that the lever device is of large dimensions in relation to the fastening device (12) and has a region of transition of smaller dimensions towards the detection element (20).Sensor device according to one of the preceding claims, characterized in that the stop region (11) has a non-planar surface.Method for operating a micromechanical sensor device (100), having the steps: - moving a detection element (20) of the sensor device (100); - the stop device (10) being moved in the opposite direction to the detection element (20) by means of a lever device of a stop device (10).

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