Micromechanical device with mechanical stop

Abstract

The invention relates to a micromechanical device comprising a substrate (1) having a main plane of extension (x, y), a thin first functional layer (5) on the substrate, a thick second functional layer (10) on the first functional layer, in which second functional layer a fixed functional element (110) and a movable functional element (120) are formed, the movable functional element can be deflected in a first direction parallel to the main extension plane. The core of the invention is that the micromechanical device has a fixed stop element (51) in the first functional layer, the movable functional element is also formed in the first functional layer, and there is a movable stop element (52), the movable stop element can act on the fixed stop element when the movable functional element is deflected in a first direction.

Description

Technical Field

[0001] The invention relates to a micromechanical device having a mechanical stop. Background Art

[0002] MEMS (micro-electromechanical system) rotation rate sensors have moderate to poor impact resistance, depending on their design. If a smartphone with a rotation rate sensor falls to the ground, the rotation rate sensor usually remains intact if the fall height is not too high. However, particles may form in the rotation rate sensor due to mechanical impacts, which, however, may lead to failure of the rotation rate sensor over a long period of time. It is desirable that the rotation rate sensor does not become damaged even under high loads and is not prone to particle formation even under medium loads. Summary of the invention

[0003] The present invention starts from a micromechanical device, which has a substrate with a main extension plane, a thin first functional layer on the substrate, and a thick second functional layer on the first functional layer, wherein fixed functional elements and movable functional elements are formed in the second functional layer, wherein the movable functional element can be deflected in a first direction parallel to the main extension plane.

[0004] The publication DE 19537814 A1 describes a method for producing surface micromechanical (OMM) sensors, such as acceleration and rotation rate sensors. This method and similar methods are used to produce movable silicon structures, the movement of which is measured by determining a change in capacitance (see also Figure 1 ).

[0005] Known OMM rotation rate sensors are based on the concept of linearly deflected seismic masses. Two masses, i.e. movable OMM structures, are deflected in antiparallel directions. The masses are deflected perpendicularly to the direction of movement by the Coriolis force. This deflection is measured and corresponds to the rotation rate to be measured. Figure 2 An example for a three-axis rotation rate sensor is shown in . Figure 3 A cross section through a detection comb of such a rotation rate sensor in the Y direction is shown. The distance between the movable structure and the counter-electrode attached to the substrate is kept as small as possible in order to achieve a large capacitive signal. The suspension of the counter-electrode on the substrate is kept as narrow as possible in order to be able to arrange as many detection combs as possible on a small surface.

[0006] In order to achieve high sensitivity, on the one hand the movable mass must be softly supported in the Y direction in order to be able to achieve large deflections. On the other hand the distance between the movable mass and the fixed electrode must be small in order to achieve a large capacitive signal. In addition, the functional layers forming the movable structure and the fixed electrode should have the greatest possible thickness in order to be able to achieve a large mass in the movable structure in order to generate a correspondingly large Coriolis force and to achieve the largest possible electrode surface in order to obtain a large capacitive signal.

[0007] In order to form movable structures and fixed structures from the functional layer, preferably a trench process with a negative profile, i.e. a trench width in the upper etching area, which widens downwards. It is known that such an etching process is particularly insensitive to process scattering, for example due to different etching environments. In addition, such an etching process can be very well controlled, because in this case the upper area of ​​the etching, i.e. the area with the narrowest opening, can be monitored very well with the aid of a microscope or a scanning electron microscope. In contrast, monitoring of the etching process is difficult in other forms of trench etching.

[0008] The key to this arrangement is that the movable structure collides with the fixed electrode during impact loading and tears off its anchoring to the substrate. This effect is particularly pronounced at small electrode distances, at narrow suspensions, at high functional layer thicknesses and at negative groove profiles. All of these desirable properties lead to a preferential breakage of the fixed electrode during impact loading.

[0009] The object of the present invention is to find a micromechanical device having a robust stop element for stopping a movable functional element.

[0010] The invention proceeds from a micromechanical device having a substrate with a main extension plane, a thin first functional layer on the substrate, a thick second functional layer on the first functional layer, wherein a fixed functional element and a movable functional element are formed in the second functional layer, wherein the movable functional element can be deflected in a first direction parallel to the main extension plane. The core of the invention is that the micromechanical device has a fixed stop element in the first functional layer, the movable functional element is also formed in the first functional layer and has a movable stop element there, wherein the movable stop element can act on the fixed stop element when the movable functional element is deflected in the first direction.

[0011] An advantageous embodiment of the invention provides that the fixed stop element is fixed to the substrate or also to the fixed functional element. Advantageously, this allows a large degree of design freedom in the embodiment of the micromechanical device.

[0012] An advantageous configuration of the invention provides that the fixed stop or the movable stop is elastically configured in the first direction by means of a spring element. Advantageously, a soft stop or a combination of a soft stop and a hard stop can thus be realized. Advantageously, the spring element can be configured very softly in the thin first functional layer.

[0013] An advantageous embodiment of the invention provides that the micromechanical device has a further fixed stop element in the second functional layer, which is arranged on the fixed functional element, or has a further movable stop element, which is arranged on the movable functional element, wherein the movable functional element can act on the fixed functional element when deflected in the first direction. Advantageously, a combined stop can thus be achieved. Advantageously, a torque acting on the fixed functional element is avoided, in particular when the stop element and the further stop element simultaneously stop on each other.

[0014] An advantageous embodiment of the invention provides that the device is a rotation rate sensor, wherein the movable functional element is a sensor mass and the first direction is a deflection direction of the sensor mass for indicating the rotation rate. Advantageously, the sensor mass of the rotation rate sensor, which is very softly elastically suspended for high sensitivity, can be protected from damage due to impact events by the stop element according to the invention.

[0015] Advantageously, the distance between the fixed stop element and the movable stop element is selected to be at least 5% smaller than the groove width between the fixed functional element and the movable functional element, in particular between the movable electrode and the fixed electrode.

[0016] Advantageously, the second functional layer is at least three times thicker than the first functional layer.

[0017] Advantageously, the fixed stop element and the movable stop element are designed in the first functional layer in such a way that after the soft stop, at least the second harder stop element is activated before the stop occurs between the movable electrode and the fixed electrode.

[0018] Advantageously, the stop is produced by means of the production method known from DE 10 2011 080 978 B4.

[0019] Advantageously, the thickness of the first functional layer is greater than the upward and downward distance of the movable functional element and thus the degree of freedom of movement.

[0020] The new stop is very strong since it rests against the substrate and therefore only very low torques are transmitted to the suspension when the stop occurs.

[0021] Since the stop is first implemented elastically, the spring can first absorb the energy in the event of an impact. As a result, the maximum impact force can be well reduced, so that the breakage of the stop structure and the breakage of the parts of the stop structure and thus the formation of particles in the micromechanical device can be avoided.

[0022] Due to the elastic design of the stop, the movement of the yaw rate sensor in its drive direction is not braked suddenly in the event of an impact, but is slowly decelerated by the elastic stop. The energy contained in the drive movement of the yaw rate sensor is thus slowly and definedly dissipated in the event of an impact.

[0023] The elastic stop increases the restoring force for an impact process in which the movable structure is driven against the second, harder stop and possibly gets stuck there.

[0024] The stop element according to the invention can be designed to be spatially neutral below the functional layer.

[0025] During the MEMS production process, thin functional layers are already produced underneath thick functional layers, and the stop element according to the invention can be installed without additional process effort.

[0026] Since the first functional layer is significantly thinner than the second functional layer, a significantly more precise and smaller groove width can be defined in the first functional layer. For the production of the rotation rate sensor, this means that the groove width and therefore the distance between the movable functional element and the opposite detection electrode do not have to be widened in order to be able to produce a stop. As a result, the capacitive structure remains highly sensitive.

[0027] The suspensions of the fixed electrodes can be designed to be significantly smaller, since they no longer have to be designed to abut against the movable structure.

[0028] With the aid of the invention, a rotation rate sensor can be designed to be particularly impact-resistant. It is thus possible to produce a rotation rate sensor which is not damaged even under high loads and which is not prone to particle formation under medium loads. Today, the first functional layer is already present in mature MEMS production processes. Therefore, no additional process steps and thus additional costs are required for producing the new stop element proposed here. The mature production process allows the production of stops in the first functional layer which are precisely adapted to the preferred groove width. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A side view showing the structure of a micromechanical device in the prior art.

[0030] Figure 2 The top view shows the structure and operation of a MEMS rotation rate sensor in the prior art.

[0031] Figure 3 a to c show details of a micromechanical device with a mechanical stop according to the prior art.

[0032] Figure 4 a to c show details of a first exemplary embodiment of a micromechanical device according to the invention having a mechanical stop.

[0033] Figure 5 a to c show details of a second exemplary embodiment of the micromechanical device according to the invention having a mechanical stop.

[0034] Figure 6 a and b show details of a third exemplary embodiment of a micromechanical device according to the invention having a mechanical stop. DETAILED DESCRIPTION

[0035] Figure 1 A side view of the structure of a micromechanical device in the prior art is shown. A surface micromechanical device is shown, having a substrate 1 with a main extension plane (x, y), a thin first functional layer 5 on the substrate, a thick second functional layer 10 on the first functional layer, wherein a fixed functional element 110 and a movable functional element 120 are formed in the second functional layer, wherein the movable functional element can be deflected in a first direction parallel to the main extension plane.

[0036] The movable silicon structure 120 can be produced in a first step by an etching method, wherein a trench 2 is produced in the silicon layer with a high aspect ratio, as disclosed in DE 4241045. In a second step, a sacrificial layer 3, usually an oxide layer, is removed below the thick silicon layer 10, as is known from DE 4317274 and DE 1970445. Thus, a freely movable silicon structure is obtained relative to the substrate. A thin polysilicon layer 5 can be arranged below the movable structure. The polysilicon layer can be used as a suspension device 6 for a movable or fixed silicon structure, or as an electrode 7 below the movable structure, or as a conductor track 8.

[0037] Figure 2 A top view showing the structure and working mode of a MEMS rotation rate sensor in the prior art is shown. The two-piece drive frame 13 is driven by an electrostatically driven comb structure 14 to move in an antiparallel manner in the X direction. In order to detect the rotation rate in the Z direction, the two masses 11 and 12 are moved in the X direction via coupling springs. Typically, the masses are excited to vibrate with a deflection between 10 and 20 μm. The movable MEMS structure is arranged in the sensor in a negative pressure so that the two masses 11, 12 form a high-quality oscillator and can be excited to vibrate in the X direction by resonant excitation.

[0038] If the rotation rate acts in the Z direction, the mass is deflected by the Coriolis force in the Y direction. This deflection can be measured by electrodes located below the two masses. The deflection of the detection mass can be determined electrostatically by means of electrode pairs 15 fixed to the substrate and arranged at a small distance in the Y direction.

[0039] Figure 3 a to 3c show in detail a rotation rate sensor with a mechanical stop according to the prior art.

[0040] Figure 3 3a and 3b show a top view of the structure and mode of operation of a stop in the prior art. The stop 20 in the thick functional layer 10 limits the path of the movable structure 120 before it can collide with the fixed detection electrode 23 .

[0041] Figure 3 c shows a side view (at the cut line) of the mode of operation of the stop in the prior art. In particular, the negative groove profile open toward the substrate and the resulting point-shaped stop 21 in the upper region of the functional layer of the movable functional element 120 can be seen, which in the case of the stop leads to a high torque acting on the suspension device of the fixed functional element 110 on the substrate 1. High torques can lead to the breakage of the fixed functional element. The point-shaped stop 21 can lead to the detachment of the material of the upper functional layer 10 and thus the formation of particles. It can also be seen that such a stop is arranged only laterally next to the detection electrode 23 and thus, on the one hand, creates additional space requirements in the sensor and, on the other hand, in the event of very strong impact events, the connection area up to the stop point can be twisted and thus, for example, a stop can also occur between the electrodes.

[0042] Figure 4 Figures a to 4c partially show a first embodiment of a micromechanical device according to the present invention with a mechanical stop. On a substrate 1 having a main extension plane (x, y), a thin first functional layer 5 is arranged with the aid of other layers. A thick second functional layer 10 is arranged on the first functional layer, wherein a fixed functional element 110 and a movable functional element 120 are formed in the second functional layer. The movable functional element can be deflected in a first direction y parallel to the main extension plane. The micromechanical device has a fixed stop element 51 in the first functional layer. The movable functional element has a driven stop element 52 in the first functional layer, which can act on the fixed stop element when the movable functional element is deflected along the first direction y.

[0043] Figure 4c shows a partial side view of the micromechanical device according to the invention in the region of the stop element. The fixed stop element 51 simultaneously forms an anchoring portion of the fixed functional element 110 on the substrate 1. Alternatively (not shown), the fixed stop element can also be connected only to the fixed functional element located above it or only to the substrate located below it. The movable stop element 52 is fixedly connected to the movable functional element 120 located above it.

[0044] It is advantageous if the thickness of the first functional layer 5 is greater than the movability of the movable functional element 120 upward and downward, i.e. perpendicularly to the main extension plane (x, y) of the substrate. It is thus possible to avoid that the stops get stuck during out-of-plane movements. In this example, the downward movability is given by the distance 36 between the first functional layer 5 and the substrate 1 located below it. The upward movability can be correspondingly limited by a stop in a cover (not shown) arranged above it and can be selected so that jamming can also be avoided in this direction.

[0045] Figure 5 5 a to 5 c show details of a second exemplary embodiment of the micromechanical device according to the invention having a mechanical stop. Figure 5 5a and 5b show a top view of an embodiment of a micromechanical device with a stop element according to the present invention, and the stop element has a combined soft and hard stop. A particularly advantageous embodiment is shown here, in which both functions are realized in one element. When the movable functional element 120 is deflected to the fixed functional element 110 along the first direction y, the fixed stop element 51 and the movable stop element 52 are in mechanical contact at the first stop point 40. This is a soft stop. By braking the spring element 62 integrated in the movable stop element 52, the movable functional element 120 is further deflected. When further deflected, the stop between the two parts of the movable stop element 52 occurs at the second stop point 42. This is a hard stop, and the movable functional element stops. This arrangement is particularly conducive to the manufacturing method according to DE 10 2011080978B4. With the help of this manufacturing method, narrow grooves can be manufactured in the first functional layer. Medium groove widths cannot be manufactured. Large groove widths can be manufactured again. Thus, with this arrangement, a hard stop can be produced in an advantageous manner, which enters the stop only after twice the width of the small groove width that can be produced. The method can be extended accordingly to more times the width of the small groove. Figure 5 c shows a side view of the stop element according to the invention with a combined soft and hard stop.

[0046] Figure 6 6a and 6b show in detail a third exemplary embodiment of a micromechanical device according to the invention having a mechanical stop. Figure 6A top view of an embodiment of a micromechanical device with a stop element of a combined soft and hard stop and other conventional stop elements according to the present invention is shown. For this purpose, the micromechanical device has an additional fixed stop element 53 arranged on a fixed functional element 110 and an additional entrained stop element 54 arranged on a movable functional element 120 in the second functional layer 10. When the movable functional element deflects along the first direction y, the movable stop element 52 first acts on the fixed stop element 51. When further deflected along the first direction y, the spring element of the movable stop element is compressed. The movable functional element 120 can act on the fixed functional element 110 when further deflected along the first direction y. In particular, when the groove width is approximately the same, the two stop elements 51, 52 and two conventional additional stop elements 53, 54 can contact each other at the same time during an impact event. This is also possible for non-elastic stops. Stopping occurs simultaneously in the first and second functional layers. Therefore, almost no torque is generated in the impact situation.

[0047] Figure 6 b shows a side view of a stop element according to the invention with a soft stop and a hard stop in combination with a conventional stop element.

[0048] It is clear that the new stop can be arranged independently of the second functional layer above. Thus, for example, it is possible to move the stop closer to the detection electrode in order to protect the detection electrode particularly well in the event of a particularly hard impact.

[0049] Even though only the movable stop element 52 is shown here in an elastic embodiment with a spring element 62, of course, alternatively or additionally, the fixed stop element 51 can also be designed elastically. This is advantageous, for example, if a particularly small, compact stop element is to be realized on the movable functional element 120.

[0050] Reference numerals list

[0051] 1 Substrate

[0052] 2 Grooves

[0053] 3 Sacrificial layer

[0054] 5 Thin first functional layer

[0055] 6 Anchor

[0056] 7 Electrodes

[0057] 10 thick second functional layer

[0058] 20 Stop

[0059] 21 Dot stop

[0060] 23 Detection electrode

[0061] 40 First stop point

[0062] 42 Second stop point

[0063] 51 Fixed stop element

[0064] 52 Movable stop element

[0065] 53 Additional fixed stop element

[0066] 54 Additional movable stop element

[0067] 62 Spring element

[0068] 110 Fixed functional elements

[0069] 120 Movable functional elements

Claims

1. A micromechanical device comprising a substrate (1) having a main extension plane (x, y), a thin first functional layer (5) on the substrate, a thick second functional layer (10) on the first functional layer, wherein: A fixed functional element (110) and a movable functional element (120) are formed in the second functional layer, wherein the movable functional element is pivotable in a first direction parallel to the main extension plane, It is characterized in that The micromechanical device has a fixed stop element (51) in the first functional layer, the movable functional element is also formed in the first functional layer and has a movable stop element (52) in the first functional layer, wherein the movable stop element can act on the fixed stop element when the movable functional element is deflected along the first direction.

2. The micromechanical device according to claim 1, characterized in that The fixed stop element (51) is fixed to the substrate (1) and / or to the fixed functional element (110).

3. The micromechanical device according to claim 1 or 2, characterized in that The fixed stop element (51) and / or the movable stop element (52) are / is elastically embodied in the first direction by means of a spring element (62).

4. The micromechanical device according to any one of claims 1 to 3, characterized in that The micromechanical device has an additional fixed stop element (53) and / or an additional movable stop element (54) in the second functional layer (10), wherein the additional fixed stop element is arranged on the fixed functional element (110) and the additional movable stop element is arranged on the movable functional element (120), wherein the movable functional element is capable of acting on the fixed functional element when deflected along a first direction.

5. The micromechanical device according to any one of claims 1 to 4, characterized in that: The device is a rotation rate sensor, wherein the movable functional element (120) is a sensor mass and the first direction is a deflection direction of the sensor mass for indicating the rotation rate.

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