MEMS element for moving a mass element of an acoustic transducer for generating and / or receiving acoustic signals, and acoustic transducer having such a MEMS element
Patent Information
- Application Number
- EP2023726992
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-06-01
- Filing Date
- 2023-05-15
- Publication Date
- 2025-04-09
AI Technical Summary
Conventional MEMS elements for sound transducers face accuracy issues in setting depth stops due to design and manufacturing processes, leading to potential actuator element failure and deviations in resonance frequencies.
A MEMS element with an actuator element and connecting element, where the geometry is defined by a substrate cavity, providing a precise depth stop and increased stiffness for precise resonance frequency setting and reduced risk of actuator element failure, using a substrate with a cavity to enhance precision and adjustability.
The solution allows for precise geometry and resonance frequency control, reducing the risk of actuator element failure and enabling efficient movement transmission with minimal loss, while maintaining low manufacturing costs.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] MEMS element for moving a mass element of a sound transducer for generating and / or receiving sound signals and a sound transducer with such a MEMS element
[0003] State of the art
[0004] The invention relates to a MEMS element for moving a mass element of a sound transducer for generating and / or receiving sound signals.
[0005] The idea is to set a mass element of the sound transducer into a reciprocating movement by one or more MEMS elements and thus emit the sound or to be deflected in the opposite direction by a sound and to detect the sound signal via the MEMS element.
[0006] A problem with conventional MEMS elements is that, due to the design of the MEMS element and the associated manufacturing process, the depth stop often deviates significantly from the target specification, resulting in insufficient accuracy for setting the depth stop. This poses the risk of exceeding the actuator element's breaking point, potentially destroying the MEMS element.
[0007] Furthermore, in conventional MEMS elements, the design of the actuator element, which directly affects the resonant frequency, is created using a trench process, whose dimensions can be inaccurate due to tilting and widening. Consequently, state-of-the-art MEMS elements can exhibit significant deviations from one another with regard to their resonant frequencies.
[0008] The invention is intended to solve the problems mentioned.
[0009] Disclosure of the invention The invention relates to a MEMS element for moving a mass element of a sound transducer for generating and / or receiving sound signals.One aspect of the invention is that the MEMS element is produced from a substrate, wherein the MEMS element has an actuator element with at least one piezo element applied to the actuator element for moving the actuator element in the vertical direction relative to the main extension plane of the MEMS element, and wherein the geometry of the actuator element is defined by a cavity of the substrate, and wherein the MEMS element has a connecting element arranged on the actuator element for connecting the actuator element to the mass element of the sound transducer and for transmitting the movement of the actuator element to the mass element, wherein the connecting element has a higher rigidity than the actuator element, and wherein the cavity is designed in the substrate in such a way that the substrate itself forms a depth stop for the actuator element in the vertical direction.
[0010] The advantage here is that both the geometry of the actuator element and the design of the depth stop can be implemented more precisely than in the prior art using the cavity. This, in turn, allows the resonant frequency of the actuator element to be adjusted more precisely and reduces the risk of exceeding the fracture limit of the actuator element.
[0011] A further advantage is that by adjusting the stiffness it is possible to move the actuator element easily and yet, due to the increased stiffness of the connecting element, to enable the movement to be transmitted to the mass element of the sound transducer with as little loss as possible.
[0012] A sound transducer is a system that converts a non-mechanical form of energy, typically electrical energy, into mechanical energy via a piezoelectric element in a suitable manner to generate a sound signal. The conversion effect can typically be reversed, meaning that the mechanical energy of received sound signals is converted into electrical energy, and the resulting electrical signal can be evaluated accordingly. In particular, the sound transducer can be designed as an ultrasonic transducer, for example, and can receive or transmit corresponding ultrasonic signals.
[0013] The sound transducer can be used, for example, in a microphone or a loudspeaker or in an ultrasonic sensor system.
[0014] The emitted sound signal is generated by a mass element of the sound transducer, which is set in motion by the MEMS element, or the mass element is set in motion by the received sound signal, which can be detected by the MEMS element. The mass element can be designed, for example, as a membrane or piston-like.
[0015] In particular, several sound transducers can form a sound sensor array.
[0016] A MEMS element is a micro-electronic-mechanical system that combines or integrates electronic and mechanical components in a very small space.
[0017] The MEMS element has an actuator element, which can be designed, for example, as a cantilever or membrane-like and can be set in motion by the piezo element or can transmit movement to the piezo element for evaluation.
[0018] Here, the actuator element is mounted on a suspension element, which is more rigid than the actuator element and, for example, represents the remaining substrate of the MEMS element. Furthermore, a connecting element is mounted on the actuator element, which serves to connect the actuator element to the mass element and thus enable movement in either direction.
[0019] The connecting element can comprise individual or all layers that are also present in the actuator element and can be designed as a continuation of the actuator element or can extend beyond the actuator element at least in a vertical direction relative to the main extension plane of the actuator element. The piezo element can be designed, for example, as a piezoelectric layer.
[0020] For example, a suitably preprocessed silicon wafer can serve as a substrate, which can then be processed accordingly to obtain the desired configuration of the MEMS element, comprising the suspension element, the actuator element, and the connecting element. A combination of wafers can also serve as a substrate, for example, connected via a wafer bond, each of which can include layer systems and structures. A cavity SOI wafer, for example, would also be conceivable as a substrate.
[0021] Stiffness is a quantity in engineering mechanics that describes the relationship between the load acting on a body and its elastic deformation. The stiffness of a body depends primarily on its material and its geometry.
[0022] A cavity is a hollow space in the substrate.
[0023] The cavity in the substrate runs particularly parallel to the main extension plane below the actuator element.
[0024] A depth stop is also understood to be a stop for the actuator element that stops the movement of the actuator element at a certain point. In this case, the actuator element is particularly designed as a region on the upper side of the cavity, with the depth stop representing a region on the lower side of the cavity.
[0025] One embodiment of the invention provides that the depth stop is defined by a height of the cavity.
[0026] The advantage here is that the height of the cavity in the substrate can be adjusted very precisely in terms of process technology.
[0027] The height of the cavity refers to the distance between the floor and ceiling of the cavity in a state in which the MEMS element is not subjected to load, i.e., when the ceiling and floor of the cavity are essentially parallel to each other. One embodiment of the invention provides that the stiffness of the actuator element and / or the connecting element is adjusted depending on the material and / or thickness and / or structuring of the respective element. This is advantageous because it provides a simple way to adjust the stiffness of the corresponding elements as desired.
[0028] Material refers to the chemical composition of the corresponding element, which can affect its stiffness.
[0029] Structuring refers to the design of an element, which can, for example, have corresponding recesses or openings to change its rigidity. For example, the actuator element can be designed in a spoke-like manner to keep rigidity low, whereas the suspension element and the connecting element can lack corresponding recesses to keep rigidity high in comparison.
[0030] Thickness refers to the vertical dimension of the element relative to the main plane of extension of the MEMS element. This could theoretically also fall under the term structuring, but is explicitly emphasized here due to the particular importance of thickness for the stiffness properties of the element.
[0031] A further embodiment of the invention provides that the connecting element is arranged laterally on the actuator element and forms a stump, wherein the cavity is opened in such a way that the connecting element is separated from the remaining substrate.
[0032] An advantage here is that the geometry of the actuator element, and thus the resonant frequency, is defined by the lateral dimensions of the cavity, which can usually be adjusted very precisely depending on the chosen method for creating the cavity. The height of the depth stop d can, in turn, be defined by the height of the cavity, which can also usually be adjusted very precisely depending on the chosen method for creating the cavity. Furthermore, the MEMS element can be manufactured particularly easily from a substrate with a cavity, thus keeping the costs of the MEMS element low.
[0033] In this case, the corresponding design of the actuator element can, for example, form a so-called cantilever, which can be understood as a movable arm.
[0034] The cavity is open in particular in one direction or on one side and particularly preferably open downwards, whereby the connecting element is only connected to the actuator element and no longer connected to the remaining substrate, which serves as a suspension element.
[0035] Here, the connecting element is arranged, for example, in the main extension plane at one end of the actuator element, for example on the right side, and the actuator element is in turn connected to the suspension element at its other end, i.e. on the left side.
[0036] The term stump can be understood in particular as a so-called stub.
[0037] According to one embodiment of the invention, it is provided that at least two piezo elements are applied to the actuator element, which can be controlled in a phase-shifted manner.
[0038] The advantage here is that an S-shaped deflection can be realized, which in turn can increase the stroke and the breaking strength of the actuator element.
[0039] By means of the phase-shifted control, it can be achieved, for example, that one of the piezo elements is bent to the left, while the other piezo element is bent to the right, whereby a corresponding deformation of the actuator element can occur due to the position of the piezo element on the actuator element.
[0040] According to a further embodiment of the invention, the cavity has regions of different heights, with the region of the cavity with the lowest height serving as a depth stop. Advantageously, the different heights can influence the properties of the elements adjacent to the cavity. For example, the rigidity of the actuator element can be influenced.
[0041] According to a further embodiment of the invention, it is provided that the actuator element and the connecting element are arranged concentrically in the main extension plane of the MEMS element, wherein the connecting element is arranged centrally, and wherein the cavity runs parallel to the main extension plane below the actuator element and connecting element.
[0042] The advantage here is that a different design of the actuator element and the connecting element enables a more uniform transmission of the movement of the actuator element to the mass element of the sound transducer, since the connecting element is moved accordingly from several sides by the actuator element.
[0043] The actuator element can, for example, be designed like a membrane and be arranged accordingly around the connecting element, for example in the form of a circle from a perspective from above on the MEMS element, although another geometry would also be conceivable.
[0044] According to a further embodiment of the invention, it is provided that the cavity has a lower height in the region of the connecting element than in the region of the actuator element, so that an indirect depth stop for the actuator element is formed via the connecting element.
[0045] The advantage here is that the depth stop can be adjusted better due to the lower height of the cavity in the area of the connecting element, whereas in the area of the actuator element an improved damping property of the actuator element can be achieved due to the comparatively greater height.
[0046] The invention also relates to a sound transducer with a MEMS element according to the invention, wherein the actuator element of the MEMS element is connected to a mass element of the sound transducer via the connecting element of the MEMS element. Drawings
[0047] Fig. 1 shows a lateral cross-section of a sound transducer with a first embodiment of a MEMS element designed according to the invention.
[0048] Fig. 2 shows a lateral cross-section of a sound transducer with a second embodiment of a MEMS element designed according to the invention.
[0049] Fig. 3 shows process steps for manufacturing a MEMS element according to the state of the art.
[0050] Fig. 4 shows process steps for producing a MEMS element according to the first embodiment of Fig. 1.
[0051] Description of implementation examples
[0052] Fig. 1 shows a lateral cross-section of a sound transducer with a first embodiment of a MEMS element designed according to the invention. It shows a sound transducer 101 for generating and / or receiving sound signals 120. For this purpose, the sound transducer 101 has a mass element 110 and a MEMS element 11 for moving the mass element 110 of the sound transducer 101. The MEMS element 11 is made of a substrate 21.
[0053] The MEMS element 11 has an actuator element 31 with two piezo elements 35 applied to the actuator element 31 for moving the actuator element 31 in a vertical direction relative to the main extension plane 15 of the MEMS element 11. In principle, a single piezo element 35 would also be conceivable here. In addition, a deflection of the mass element 110 due to a received sound signal 120 by the actuator element 31 and the piezo elements 35 applied there can of course also be detected by means of the MEMS element 11. The piezo elements 35 can be applied to the actuator element 31 as corresponding piezo layers and can be controlled or read out by electronics (not shown). In particular, the piezo elements 35 can be controlled with a phase shift in order to achieve an S-shaped deflection of the actuator element 31.
[0054] Furthermore, the MEMS element 11 has a connecting element 51, which is in particular directly connected to the actuator element 31, for connecting the actuator element 31 to the mass element 110 of the sound transducer 101 and for transmitting the movement of the actuator element 31 to the mass element 110, wherein the connecting element 51 has a higher rigidity than the actuator element 31. The connecting element 51 can be connected to the mass element 110 via a connecting means 111, which is designed, for example, as an adhesive. The higher rigidity of the connecting element 51 compared to the rigidity of the actuator element 31 is achieved by the greater thickness of the connecting element 51 compared to the thickness of the actuator element 31, where thickness means the dimensions of the respective element 31, 51 in the vertical direction.
[0055] The actuator element 31 is also connected to a suspension element 71, which forms the remaining substrate 21 and also has a higher rigidity than the actuator element 31, again achieved by a greater thickness.
[0056] Furthermore, the geometry of the actuator element 31 is defined by a cavity 41 of the substrate 21, wherein the cavity 41 is configured in the substrate 21 such that the substrate 21 itself forms a depth stop 61 for the actuator element 31 in the vertical direction relative to the main extension plane 15. Here, the depth stop 61 is defined by a height h of the cavity 41.
[0057] In particular, the connecting element 51 is arranged laterally on the actuator element 31 and forms a stump, wherein the cavity 41 is open such that the connecting element 51 is separated from the remaining substrate 21 and thus the actuator element 31 and the connecting element 51 are correspondingly movable. Due to the corresponding design, the actuator element 31 can move with the connecting element 51 around the suspension element 71 as a bearing point, which is represented by a corresponding double arrow. Alternatively, a depth stop could also be defined by a width of the opening between the connecting element 51 and the remaining substrate 21.
[0058] The MEMS element 11 can also be connected to a carrier element 130, which is designed as a PCB, for example, via a connection 131, which is again designed as an adhesive, for example.
[0059] Fig. 2 shows a lateral cross-section of a sound transducer with a second embodiment of a MEMS element designed according to the invention.
[0060] Shown is a sound transducer 102 which, like the sound transducer 101 in Fig. 1, serves to generate and / or receive sound signals 120. For this purpose, the sound transducer 102 in turn has a mass element 110 and a MEMS element 12 for moving the mass element 110 of a sound transducer 102. The MEMS element 12 is made of a substrate 22.
[0061] In addition, the MEMS element 12 has an actuator element 32 with two piezo elements 35 applied to the actuator element 32 for moving the actuator element 32 in the vertical direction, represented by the double arrow, relative to the main extension plane 15 of the MEMS element 12. Alternatively, it would also be conceivable to use a single, ring-shaped piezo element instead of the two piezo elements 35. In addition, the MEMS element 12 can of course also be used to detect a deflection of the mass element 110 due to a received sound signal 120 by the actuator element 32 and the piezo elements 35 applied there. The piezo elements 35 can in turn be applied to the actuator element 32 as corresponding piezo layers and can be controlled or read out by electronics (not shown). In particular, the piezo elements 35 can be controlled in a phase-shifted manner in order to achieve an S-shaped deflection of the actuator element 32.Furthermore, the MEMS element 12 has a connecting element 52, which is in particular directly connected to the actuator element 32, for connecting the actuator element 32 to the mass element 110 of the sound transducer 102 and for transmitting the movement of the actuator element 32 to the mass element 110, wherein the connecting element 52 has a higher rigidity than the actuator element 32. The connecting element 52 can be connected to the mass element 110 via a connecting means 111, which is designed, for example, as an adhesive. The higher rigidity of the connecting element 52 compared to the rigidity of the actuator element 32 can be achieved by appropriately structuring the actuator element 32, in that the latter is designed spoke-like in a plan view (not shown) and has corresponding recesses or openings, whereas the connecting element 52 does not have such recesses or openings.
[0062] The actuator element 32 is connected radially outwardly to a circumferential suspension element 72, which forms the remaining substrate 22 and also has a higher rigidity than the actuator element 32, again achieved by the absence of corresponding recesses.
[0063] Furthermore, the geometry of the actuator element 32 is influenced by a cavity 42 of the substrate 22 and can in particular be defined thereby, among other things, wherein the cavity 42 is configured in the substrate 22 such that the substrate 22 itself forms a depth stop 62 for the connecting element 52 and consequently indirectly for the actuator element 32 in the vertical direction relative to the main extension plane 15. The depth stop 62 is defined by a height h of the cavity 42. In particular, the cavity 42 has regions each with a different height h, wherein in particular the region of the cavity 42 with the smallest height h serves as the depth stop 62. Accordingly, the cavity 42 has a lower height h in the region of the connecting element 52 than in the region of the actuator element 32, so that an indirect depth stop 62 for the actuator element 32 is formed via the connecting element 52.The MEMS element 12 can in turn also be connected to a carrier element 130, which is designed as a PCB, for example, via a connection 131, which is designed as an adhesive, for example.
[0064] Fig. 3 shows process steps for manufacturing a MEMS element according to the state of the art.
[0065] Thus, in a method step a), a substrate 220 is provided which is designed as an SOI wafer.
[0066] In a subsequent process step b), a piezo element 35 can then be applied as a piezo layer.
[0067] In a process step c), a trench process is then carried out to produce an actuator element 230 and a connecting element 250.
[0068] Subsequently, in a method step d), a depth stop 260 is produced on one side and a suspension 270 for the actuator element 230 is produced on the other side by bonding the product from method step c) to a carrier element 130 configured as a wafer using a wafer bond 132, thereby obtaining a MEMS element which, similar to the MEMS element 11 according to Fig. 1, is configured as a cantilever. However, this results in the difficulty that very fragile structures on the wafer 130 must be handled and separated during the manufacturing process in the prior art. Furthermore, the vertical distance d for the depth stop 260 can only be adjusted with insufficient precision using the wafer bond 132. Furthermore, the geometry of the actuator element 230, and thus the resonant frequency, is defined according to method step c) by a trench process, the dimensions of which can be inaccurate due to tilting and widening due to process-related factors.
[0069] Fig. 4 shows process steps for manufacturing a MEMS element similar to the first embodiment of Fig. 1.
[0070] In a method step a), a substrate 21 with a cavity 41 is provided, which in this case is a cavity SOI wafer. Alternatively, a substrate with a corresponding cavity can also be realized using a porous silicon process or using a trench process for the cavity. In a method step b), a piezoelement 35 is then deposited and structured as a piezoelectric layer. This can include further layers not shown, such as electrode layers, barrier layers, etc. In a method step c), the cavity 41 is opened downward on one side, creating an opening 45 that separates the actuator element 31 and the connecting element 51 from the rest of the substrate 21 and makes them movable accordingly. This results in a MEMS element that differs from the MEMS element 11 of Fig. 1 only in the number of piezoelements 35.The production process can include further steps, such as creating marks or separating the elements.
Claims
Claims 1. MEMS element (11, 12) for moving a mass element (110) of a sound transducer (101, 102) for generating and / or receiving sound signals (120), wherein the MEMS element is made of a substrate (21, 22), and wherein the MEMS element (11, 12) has an actuator element (31, 32) with at least one piezoelectric element (35) applied to the actuator element (31, 32) for moving the actuator element (31, 32) in a vertical direction with respect to the principal extension plane (15) of the MEMS element (11, 12), and wherein the geometry of the actuator element (31, 32) is influenced by a cavity (41, 42) of the substrate (21), and wherein the MEMS element (11, 12) has a The actuator element (31, 32) has a connecting element (51, 52) arranged for connecting the actuator element (31, 32) to the mass element (110) of the sound transducer (101, 102) and for transmitting the movement of the actuator element (31, 32) to the mass element (110), wherein the connecting element (51,52) has a higher stiffness than the actuator element (31, 32), and wherein the cavity (41, 42) is designed in the substrate (21, 22) such that the substrate (21, 22) itself forms a depth stop (61, 62) for the actuator element (31, 32) in the vertical direction.
2. MEMS element (10, 11) according to claim 1 , characterized in that the depth stop (61 , 62) is defined by a height (h) of the cavity (41 , 42).
3. MEMS element (11 , 12) according to one of the preceding claims, characterized in that the stiffness of the actuator element (31 , 32) and / or the connecting element (51 , 52) is adjusted depending on the material and / or thickness and / or structure of the respective element (31 , 32, 51 , 52).
4. MEMS element (11) according to one of the preceding claims, characterized in that the connecting element (51) is arranged laterally on the actuator element (31) and forms a stub, wherein the cavity (41) is opened in such a way that the connecting element (51) is separated from the remaining substrate (21). MEMS element (11 , 12) according to one of the preceding claims, characterized in that at least two piezo elements (35) are applied to the actuator element (31 , 32) which can be controlled in a phase-shifted manner. MEMS element (11, 12) according to one of the preceding claims, characterized in that the cavity (41, 42) has areas with different heights (h), wherein in particular the area of the cavity (41, 42) with the lowest height (h) serves as a depth stop (61, 62). MEMS element (12) according to one of the preceding claims, characterized in that the actuator element (42) and the connecting element (52) are arranged concentrically in the main extension plane (15) of the MEMS element (12), wherein the connecting element (52) is arranged centrally, and wherein the cavity (42) runs parallel to the main extension plane (15) below the actuator element (42) and connecting element (52).MEMS element (12) according to claim 7, characterized in that the cavity (42) in the region of the connecting element (52) has a lower height (h) than in the region of the actuator element (32), such that an indirect depth stop (62) for the actuator element (32) is formed via the connecting element (52). A transducer (101, 102) with a MEMS element (11, 12) according to one of the preceding claims, wherein the actuator element (31, 32) of the MEMS element (11, 12) is connected to a mass element (110) of the transducer (101, 102) via the connecting element (51, 52) of the MEMS element (11, 12).