Micromechanical device with a mechanical stop

Abstract

The invention relates to a micromechanical device with a substrate (1) having a principal extension plane (x,y), with a thin first functional layer (5) over the substrate, with a thick second functional layer (10) over 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 deflectable in a first direction parallel to the principal extension plane. The core of the invention consists in the fact 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) there, wherein the movable stop element can be applied to the fixed stop element when the movable functional element is deflected in the first direction.

Description

[0001] MEMS gyroscopes have moderate to poor shock robustness, depending on their design. If a smartphone with a gyroscope falls to the ground, the gyroscope usually remains intact if the fall is not too great. However, particles can form within the gyroscope due to the mechanical impact, which can eventually lead to its failure. Ideally, gyroscopes would not be destroyed even under higher impacts and would not be prone to particle formation even under moderate impacts. State of the art

[0002] The invention relates to a micromechanical device with a substrate having a principal extension plane (x,y), with a thin first functional layer over the substrate, with a thick second functional layer over 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 is deflectable in a first direction parallel to the principal extension plane.

[0003] Publication DE 19 537 814 A1 describes a method for manufacturing surface micromechanical (OMM) sensors, such as acceleration and angular rate sensors. This and similar methods are used to create movable silicon structures whose movements are measured by determining changes in capacitance (see also Fig. 1).

[0004] Known OMM gyroscopes are based on the concept of linearly deflected seismic masses. Two masses, namely movable OMM structures, are deflected antiparallel. Due to the Coriolis force, the masses are deflected perpendicular to the direction of motion. The deflection is measured and corresponds to the gyroscope rate to be measured. An example of a three-axis gyroscope is shown in Fig. 2 can be seen. Fig. Figure 3 shows a cross-section in the Y-direction through the detection combs of such a rotation rate sensor. The distance between the movable structure and the counter electrodes attached to the substrate is kept as small as possible to achieve a high capacitive signal. The suspension of the counter electrodes on the substrate is kept as narrow as possible to allow for the arrangement of as many detection combs as possible in a small area.

[0005] To achieve high sensitivity, the movable mass must be softly mounted in the Y-direction to allow for a large deflection. Simultaneously, the distance between the movable mass and the stationary electrodes must be small to achieve a strong capacitive signal. Furthermore, the functional layer from which the movable structures and stationary electrodes are fabricated should be as thick as possible. This allows for a large mass in the movable structure to generate a correspondingly large Coriolis force, and also enables the largest possible electrode areas to achieve a strong capacitive signal.

[0006] To isolate the movable and fixed structures from the functional layer, a trench etching process with a negative profile is preferred. This means that the trench has a narrow width in the upper etching area, widening towards the bottom. Such etching processes are known to be particularly insensitive to process variations caused, for example, by different etching environments. Furthermore, this type of etching process can be very well controlled, since the upper etching area, i.e., the area with the narrowest opening, can be easily monitored with a microscope or SEM. In contrast, monitoring the etching process is difficult with other trench etching methods.

[0007] A critical aspect of this arrangement is that, under shock load, the movable structures collide with the stationary electrodes and are torn from their anchorage to the substrate. This effect is particularly pronounced with small electrode spacing, narrow suspensions, thick functional layers, and negative trench profiles. All these desired characteristics ensure that stationary electrodes are preferentially prone to breaking under shock load. Object of the invention

[0008] An arrangement for a micromechanical device with robust stop elements for stopping a movable functional element is sought. Core and advantages of the invention

[0009] The invention relates to a micromechanical device with a substrate having a principal extension plane (x,y), with a thin first functional layer over the substrate, with a thick second functional layer over 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 is deflectable in a first direction parallel to the principal extension plane. The core of the invention consists in the fact 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 be applied to the fixed stop element when the movable functional element is deflected in the first direction.

[0010] An advantageous embodiment of the invention provides that the fixed stop element is attached to the substrate or to the fixed functional element. This advantageously allows for considerable design freedom in the design of the micromechanical device.

[0011] An advantageous embodiment of the invention provides that the fixed or movable stop element is resiliently designed in the first direction by means of a spring element. Advantageously, this allows for the creation of a soft stop or a combination of a soft and a hard stop. Advantageously, the spring element can be designed to be very soft within the thin first functional layer.

[0012] An advantageous embodiment of the invention provides that the micromechanical device in the second functional layer has a further fixed stop element, which is arranged on the fixed functional element, or alternatively, a further movable stop element, which is arranged on the movable functional element, wherein the movable functional element can be pressed against the fixed functional element when deflected in the first direction. Advantageously, this allows for the creation of a combined stop. Particularly advantageous is the avoidance of torques on the fixed functional element when the stop elements and further stop elements simultaneously press against each other.

[0013] An advantageous embodiment of the invention provides that the device is a gyroscope, wherein the movable functional element is a sensor mass and the first direction is a deflection direction of the sensor mass for detecting a gyroscope rate. Advantageously, the sensor mass of a gyroscope, which is very softly spring-mounted for high sensitivity, can be protected from damage by shock events by the stop elements according to the invention. It is advantageous if the distance between the fixed stop element and the movable stop element is chosen to be at least 5% smaller than the trench width between the fixed functional element and the movable functional element, in particular between movable and fixed electrodes. It is advantageous if the second functional layer is at least three times thicker than the first functional layer. It is advantageous to design the fixed stop element and the movable stop element in the first functional layer in such a way that after a soft stop at least a second harder stop becomes active before a stop occurs between the movable and the fixed electrodes. It is advantageous to produce the stops using the manufacturing process known from DE 1020 11 080 978 B4. The advantage is that the first functional layer is made thicker than the distance and thus the freedom of movement of the movable functional element upwards and downwards.

[0014] The new stop is very robust because it is located close to the substrate, meaning that only a small torque is transferred to the suspension in the event of impact.

[0015] Due to the initially spring-like design of the stop, energy can be absorbed in the spring in the event of a shock. This effectively reduces the maximum impact forces, preventing both breakage of the stop structure and the formation of particles within the micromechanical device. The spring-like design also ensures that the movement of the yaw rate sensor in its drive direction is not abruptly stopped in the event of a shock, but rather gradually decelerated by the spring action. This allows the energy contained in the drive movement of the yaw rate sensor to be dissipated slowly and in a controlled manner during a shock. The spring-loaded stop increases the restoring force for shock events where the movable structure is driven into the second, harder stop and could get stuck there. The stop elements according to the invention can be represented below the functional layer in a space-neutral manner. In MEMS manufacturing processes that already create a thin functional layer beneath a thick functional layer, the stop elements according to the invention can be incorporated without additional process effort. In the first functional layer, significantly more precise and smaller trench widths can be defined because this layer is considerably thinner than the second. For the creation of a rotation rate sensor, this means that the trench widths, and thus the distances between the moving functional element and the opposing detection electrodes, do not need to be increased to generate stops. Therefore, the capacitive structures retain high sensitivity. The suspensions of the fixed electrodes can be made significantly smaller because they no longer need to be designed to withstand the impact of the moving structure.

[0016] The invention enables the design of highly shock-resistant gyroscopes. This allows for the production of gyroscopes that are not destroyed even under high loads and that do not tend to form particles under moderate loads. The first functional layer is already present in established MEMS manufacturing processes. Therefore, no additional process steps are required to produce the new stop elements proposed here, and thus no additional costs are associated with their manufacture. The established manufacturing process allows for the production of stops in the first functional layer that are precisely suited to the preferred trench widths. drawing Fig. Figure 1 shows the side view of the structure of a micromechanical device in the prior art. Fig. Figure 2 shows the structure and function of a state-of-the-art MEMS gyroscope. The Fig. Figures 3 a to c show a section of a micromechanical device with a mechanical stop in the prior art. The Fig. Figures 4 a to c show a section of a micromechanical device according to the invention with a mechanical stop in a first embodiment. The Fig. Figures 5 a to c show a section of a micromechanical device according to the invention with a mechanical stop in a second embodiment. The Fig. Figures 6 a and b show in part a micromechanical device according to the invention with a mechanical stop in a third embodiment. Description of the characters

[0017] Fig. Figure 1 shows a side view of the structure of a prior art micromechanical device. The depicted surface micromechanical device comprises a substrate 1 with a principal extension plane (x,y), a thin first functional layer 5 over the substrate, and a thick second functional layer 10 over the first functional layer. A fixed functional element 110 and a movable functional element 120 are formed in the second functional layer, the movable functional element being deflectable in a first direction parallel to the principal extension plane. The movable silicon structures 120 can be produced in a first step by an etching process, whereby grooves 2 are created 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 from beneath the thick silicon layer 10, as described in DE 4317274 and DE 1970445. This results in silicon structures that are freely movable relative to the substrate. A thin polysilicon layer 5 can be arranged beneath the movable structures. The polysilicon layer can be used as a suspension 6 for the movable or fixed silicon structures, as an electrode 7 beneath the movable structures, or as a conductor track 8.

[0018] Fig. Figure 2 shows a top view of the structure and function of a state-of-the-art MEMS gyroscope. A two-part drive frame 13 is driven into an antiparallel movement in the X-direction via electrostatically driven comb structures 14. To detect a rotation rate in the Z-direction, two masses 11 and 12 are moved in the X-direction via coupling springs. Typically, the masses are excited to oscillate with a displacement between 10 and 20 µm. The movable MEMS structures are located in a vacuum within the sensor, allowing the two masses 11 and 12 to form a high-quality oscillator and be excited to oscillate in the X-direction via resonant excitation.

[0019] If a rotational rate is applied in the Z-direction, the masses are deflected in the Y-direction by the Coriolis force. The deflection can be measured via electrodes located beneath the two masses. Electrode pairs 15, fixed to the substrate and arranged close together in the Y-direction, can be used to electrostatically determine the deflection of the detection masses.

[0020] The Fig. Figures 3 a to c show a section of a gyroscope with a mechanical stop in the prior art.

[0021] The Fig. Figures 3a and 3b show the structure and function of the stop in the prior art from above. The stop 20 in the thick functional layer 10 limits the path of the movable structure 120 before it can collide with stationary detection electrodes 23.

[0022] Fig. Figure 3c shows a side view (at the section line) illustrating the operation of a stop in the prior art. In particular, the negative trench profile, which opens towards the substrate, is visible, as is the resulting point-like stop 21 in the upper region of the functional layer of the movable functional element 120. In the event of impact, this stop causes a large torque on the suspension of the fixed functional element 110 on the substrate 1. This high torque can lead to the breakage of the fixed functional element. The point-like stop 21 can cause material from the upper functional layer 10 to be knocked out, resulting in particle formation. Furthermore, it can be seen that such a stop can only be arranged laterally next to the detection electrodes 23, which on the one hand creates an additional space requirement in the sensor and on the other hand, in the case of very strong shock events, the connection area up to the stop point can twist and thus a stop can also occur, for example, between the electrodes.

[0023] The Fig. Figures 4 a to c show a section of a micromechanical device according to the invention with a mechanical stop in a first embodiment. A thin first functional layer 5 is arranged above a substrate 1 with a principal extension plane (x,y) by means of further layers. A thick second functional layer 10 is arranged above 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 is deflectable in a first direction y parallel to the principal extension plane. The micromechanical device has a fixed stop element 51 in the first functional layer. The movable functional element has a co-moving stop element 52 in the first functional layer, which can be applied to the fixed stop element when the movable functional element is deflected in the first direction y.

[0024] Fig. Figure 4c shows a partial side view of the micromechanical device according to the invention in the area of ​​the stop elements. The fixed stop element 51 simultaneously anchors the fixed functional element 110 to the substrate 1. Alternatively (not shown), the fixed stop element can also be connected only to the fixed functional element above it or only to the substrate below it. The movable stop element 52 is fixedly connected to the movable functional element 120 above it.

[0025] It is advantageous if the thickness of the first functional layer 5 is greater than the upward and downward movement of the movable functional element 120, i.e., perpendicular to the principal plane (x,y) of the substrate. This prevents the stop from jamming during out-of-plane movement. In this example, the downward movement is determined by the distance 36 between the first functional layer 5 and the underlying substrate 1. The upward movement can be limited accordingly by a stop in a cap arranged above it (not shown) and selected to prevent jamming in this direction as well.

[0026] The Fig. Figures 5 a to c show a section of a micromechanical device according to the invention with a mechanical stop in a second embodiment. The Fig. Figures 5a and 5b show a top view of an embodiment of the micromechanical device with stop elements according to the invention, featuring a combined soft and hard stop. A particularly advantageous embodiment is shown here in which both functions are realized in a single element. When the movable functional element 120 is deflected in the first direction y towards the fixed functional element 110, the fixed stop element 51 comes into mechanical contact with the movable stop element 52 at a first stop point 40. This is a soft stop. The movable functional element 120 then deflects further, dampened by the spring element 62 integrated into the movable stop element 52. Upon further deflection, a second stop point 42 results in an impact between two parts of the movable stop element 52. This is a hard stop, and the movable functional element comes to a halt.This arrangement is particularly advantageous for a manufacturing process according to DE 10 2011 080 978 B4. With this manufacturing process, narrow trenches can be produced in the first functional layer. Medium trench widths cannot be produced. Large trench widths, however, can. This arrangement therefore allows for the advantageous creation of a hard stop that only engages after twice the width of the smallest producible trench width. The process can be extended accordingly to further multiples of the small trench width. Fig. Figure 5c shows a side view of the stop elements according to the invention with the combined soft and hard stop.

[0027] The Fig. Figures 6 a and b show in part a micromechanical device according to the invention with a mechanical stop in a third embodiment. Fig. Figure 6a shows a top view of an embodiment of the micromechanical device with stop elements according to the invention, including a soft and a hard stop, as well as conventional additional stop elements. The micromechanical device has, in the second functional layer 10, a further fixed stop element 53, which is arranged on the fixed functional element 110, and a further movable stop element 54, which is arranged on the movable functional element 120. When the movable functional element is deflected in the first direction y, the movable stop element 52 is initially pressed against the fixed stop element 51. With further deflection in the first direction y, the spring element of the movable stop element is compressed. With a further deflection in the first direction y, the movable functional element 120 can be pressed against the fixed functional element 110.In particular, if the trench width is approximately the same, the two stop elements 51, 52 and the two conventional additional stop elements 53, 54 can come into contact with each other simultaneously during a shock event. This is also possible for non-spring-loaded stops. The impact occurs simultaneously in the first and second functional layers. Therefore, virtually no torque is generated during impact.

[0028] Fig. Figure 6b shows in side view the stop elements according to the invention with the soft and hard stop combined with the conventional stop elements.

[0029] It is clear that the new stop can be positioned independently of the upper, second functional layer. This makes it possible, for example, to move the stop closer to the detection electrodes in order to provide particularly good protection for the detection electrodes in the event of especially severe shocks.

[0030] Although only the movable stop element 52 in a spring-loaded design with a spring element 62 is shown here, it is self-evident that the fixed stop element 51 can also be designed to be spring-loaded, either alternatively or additionally. This is advantageous, for example, if particularly small, compact stop elements are to be implemented on the movable functional element 120. Reference symbol list 1 substrate 2 trenches 3. Sacrifice layer 5 thin first functional layer 6 Anchoring 7 electrode 10 thick second functional layer 20? 21 point-shaped stop 23 Detection electrode 40 first stop point 42 second stop point 51 fixed stop element 52 movable stop element 53 additional fixed stop element 54 additional movable stop element 62 Spring element 110 fixed functional element 120 movable functional element QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 19 537 814 A1

[0003] DE 1020 11 080 978 B4 [0013, 0026] DE 4241045

[0017] DE 4317274

[0017] DE 1970445

[0017]

Claims

[1] Micromechanical device comprising a substrate (1) with a main extension plane (x,y), with a thin first functional layer (5) above the substrate, with a thick second functional layer (10) above 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 deflectable in a first direction parallel to the main extension plane, characterized by 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) there, wherein the movable stop element can be placed against the fixed stop element upon deflection of the movable functional element in the first direction. [2] Micromechanical device according to claim 1, characterized bythat the fixed stop element (51) is attached to the substrate (1) and / or to the fixed functional element (110). [3] Micromechanical device according to claim 1 or 2, characterized by that the fixed stop element (51) and / or the movable stop element (52) is designed to be resilient in the first direction by means of a spring element (62). [4] Micromechanical device according to one of claims 1 to 3, characterized by in that the micromechanical device has in the second functional layer (10) a further fixed stop element (53) which is arranged on the fixed functional element (110) and / or a further movable stop element (54) which is arranged on the movable functional element (120), wherein the movable functional element can be placed against the fixed functional element upon a deflection in the first direction. [5] Micromechanical device according to one of claims 1 to 4, characterized bythat 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 detecting a rotation rate.

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