MEMS Microphone

Abstract

The invention relates to a MEMS microphone comprising: a membrane for absorbing sound pressure, a signal conversion element and a lever element which is coupled to the diaphragm and the signal conversion element, wherein the lever element is configured to generate a tilting movement when the diaphragm is deflected and to transmit the generated tilting movement to the signal conversion element.

Description

[0001] The invention relates to a MEMS microphone. State of the art

[0002] The published patent application CN 112383869 A discloses a piezoelectric MEMS transducer.

[0003] The published patent application EP 2 579 616 A1 discloses an acoustic transducer.

[0004] The published patent application DE 10 2021 206 005 A1 discloses a micromechanical component for a microphone device.

[0005] The published patent application DE 10 2014 212 340 A1 discloses a microphone. Disclosure of the invention

[0006] The object underlying the invention is to provide a MEMS microphone.

[0007] This object is achieved by the subject matter of the independent claim. Advantageous embodiments of the invention are the subject matter of dependent subclaims.

[0008] According to one aspect, there is provided a MEMS microphone comprising: a membrane for absorbing sound pressure, a signal conversion element and a lever element which is coupled to the membrane and the signal conversion element, wherein the lever element is configured to generate a tilting movement upon deflection of the membrane and to transmit the generated tilting movement to the signal conversion element.

[0009] The invention is based on and incorporates the finding that the above object is achieved by using a closed or partially closed membrane to detect a deflection due to sound pressure. The membrane is, for example, completely or partially connected to a substrate, generally a carrier, and spans, for example, a cavity in the substrate. It is provided that a lever element is used which is coupled to the membrane and generates a tilting movement which is transmitted to a signal conversion element. Such a signal conversion element generates, for example, a capacitive signal based on the transmitted tilting movement, which signal depends on the deflection and thus on the sound pressure.

[0010] This means that the membrane does not have to move relative to one or two fixed counter electrodes, which means that on the one hand the movement of the membrane in the sound is almost undamped and on the other hand a very good signal quality can be ensured.

[0011] This allows for the creation of a sensitive MEMS microphone with low noise and good linearity. Furthermore, a MEMS microphone with good media robustness can be created. Furthermore, the MEMS microphone can be manufactured easily and cost-effectively.

[0012] Because the lever element transfers the deflection of the membrane to the signal conversion element, the membrane can be anchored, for example, externally to the substrate (generally the carrier), especially all around, allowing the use of a very thin membrane that is nevertheless highly robust. Furthermore, a very thin and therefore lightweight membrane can also be used.

[0013] For example, a polysilicon membrane is provided which has a thickness of less than 4µm, for example a 2µm thick membrane.

[0014] This anchoring allows the use of very large, yet lightweight, and therefore sensitive, membranes. The membrane, as a sound-collecting element, therefore does not need to stabilize itself, but is stabilized, for example, by its suspension from the substrate, generally the support.

[0015] Furthermore, the lever element, for example, can be designed to be light yet rigid. The moving parts of the signal conversion element can also be made light yet robust.

[0016] Light and stiff means in particular that the natural frequency of the pure lever element is high, for example greater than 30kHz.

[0017] Overall, such an arrangement advantageously enables the design of a microphone with a high natural frequency and simultaneously high sensitivity. The natural frequency can be specifically adjusted, for example, by layer stress in the diaphragm and / or by suspension springs between the diaphragm and the substrate, generally the support, so that high natural frequencies, in particular a natural frequency greater than 15 kHz, can be achieved even for large diaphragms. By clamping the diaphragm to the substrate, for example, a bypass for the airflow can be completely or partially prevented. Furthermore, this also makes the component highly robust against particles and liquids.

[0018] The abbreviation “MEMS” stands for “micro-electro-mechanical system”.

[0019] In one embodiment of the MEMS microphone, the lever element is connected to the membrane off-center or centrally relative to the membrane.

[0020] This results in the technical advantage of a particularly efficient connection of the lever element to the membrane.

[0021] With a central arrangement, a correspondingly large deflection of the membrane can be efficiently transmitted to the signal conversion element.

[0022] In one embodiment of the MEMS microphone, recesses are provided in the membrane in the case of a central connection in order to compensate for different tilting movements between the lever element and the membrane.

[0023] This provides the technical advantage that the different tilting movements between the lever element and the membrane can be efficiently compensated.

[0024] In one embodiment of the MEMS microphone, it is provided that the lever element is connected to the membrane at a connection point in such a way that a tilting of the membrane substantially coincides with a tilting movement of the lever element.

[0025] This results in the technical advantage of providing a particularly sensitive MEMS microphone in which no additional stresses are caused in the signal conversion element, the lever element or the membrane when the membrane is deflected.

[0026] In one embodiment of the MEMS microphone, the lever element is coupled to the membrane at a distance from the latter in order to prevent the membrane from striking the lever element.

[0027] This provides the technical advantage that the membrane can be effectively prevented from hitting the lever element during large deflections.

[0028] In one embodiment of the MEMS microphone, the lever element is connected to the diaphragm via a mechanical connecting element, which in a partial area has a height at least three times the thickness of the diaphragm and which covers a surface of the diaphragm by less than 25% relative to the surface of the diaphragm in order to compensate for different tilting movements between the lever element and the diaphragm. Here, the term "surface" refers in particular to the surface of a main plane of extension of the diaphragm. The term "surface" refers in particular to a horizontal surface of the diaphragm when it is in the rest position.

[0029] This provides the technical advantage of compensating for the different tilting movements between the lever and the membrane.

[0030] In one embodiment, the MEMS microphone comprises a carrier, in particular a substrate, on which the membrane, the signal conversion element and the lever element are arranged, wherein the membrane is at least partially connected, in particular suspended, to the carrier via at least one spring.

[0031] This provides the technical advantage, for example, that tension stress can be reduced efficiently.

[0032] In one embodiment of the MEMS microphone, it is provided that the at least one spring is spiral-shaped.

[0033] This provides the technical advantage, for example, that stress in the layer can be compensated for by a rotational movement of the membrane. Thus, the membrane properties are no longer dependent on the layer stress of the membrane. Furthermore, the membrane suspensions can be designed to be particularly soft.

[0034] In one embodiment, the MEMS microphone comprises a stop structure for the membrane in at least one of two deflection directions of the membrane.

[0035] This provides the technical advantage that the membrane can be effectively prevented from hitting the lever element in the event of an overload.

[0036] The phrase “at least one” means “one or more”.

[0037] This means that the phrase “in at least one of two deflection directions of the membrane” means: in one or in two of the two deflection directions of the membrane.

[0038] One deflection direction, which can also be referred to as the first deflection direction, is directed toward the beam. Another deflection direction, also referred to as the second deflection direction, is directed away from the beam.

[0039] In one embodiment of the MEMS microphone, it is provided that the stop structure has a support region of the support formed below the at least one spring as a stop for the membrane in a deflection direction towards the support.

[0040] This results in the technical advantage, for example, that the stop structure can be formed efficiently.

[0041] In one embodiment of the MEMS microphone, it is provided that the stop structure has a cover formed above the at least one spring as a stop for the membrane in a deflection direction away from the carrier.

[0042] This provides the technical advantage that the stop structure can be formed efficiently.

[0043] In one embodiment, the MEMS microphone comprises a carrier, in particular a substrate, on which the membrane, the signal conversion element and the lever element are arranged, wherein the membrane is directly connected to the carrier.

[0044] This provides the technical advantage that the membrane is efficiently bonded to the carrier.

[0045] The signal conversion element can, for example, be the signal conversion element according to DE 10 2021 206 005. Accordingly, the signal conversion element can be a conversion element that generates a capacitive signal within a hermetically sealed area, wherein a pressure is enclosed in this area that is lower than the external pressure.

[0046] The signal conversion element as described converts a tilting movement transmitted by the lever element into a signal, for example a voltage signal. The signal conversion element is configured, for example, to convert a tilting movement transmitted by the lever element into a signal, for example a voltage signal. The signal is, for example, an electrical signal. For example, the signal conversion element comprises two opposing electrodes which form a capacitor, wherein one of the two electrodes is a fixed electrode and the other of the two electrodes is a movable electrode to which the tilting movement is transmitted by the lever element. A voltage applied to the capacitor depends in particular on a distance between the two electrodes.Since the distance changes due to the transmitted tilting movement, the applied voltage changes accordingly, so that the deflection of the membrane can be determined from a voltage measurement. The applied voltage therefore depends on the deflection of the membrane.

[0047] The signal conversion element comprises, for example, two stationary counter electrodes: a first counter electrode and a second counter electrode, arranged on the carrier. The stationary counter electrodes can also be referred to as stator electrodes.

[0048] Above the two counter electrodes, for example, a movable electrode of the signal conversion element is provided, which can perform a tilting movement and whose movement is determined, for example, by measuring the capacitance of each of the two counter electrodes. The movable electrode can also be referred to as an actuator electrode. The lever element is configured, for example, to generate a tilting movement upon deflection of the membrane and to transfer the generated tilting movement to the movable electrode. The deflection of the membrane is thus transferred to the movable electrode of the signal conversion element by means of the lever element.

[0049] The MEMS microphone, for example, includes a sealing layer that closes or seals the two counter electrodes and the movable electrode. The sealing layer thus ensures the closure of this structure consisting of the counter electrodes and the movable electrode, for example, to enclose a vacuum in this area to reduce attenuation.

[0050] A carrier within the meaning of the description is, for example, a substrate.

[0051] A membrane can, for example, be formed as a MEMS functional layer.

[0052] In general, elements of the MEMS microphone, such as membrane, lever element, counter electrode, movable electrode and / or sealing layer, can each be formed as MEMS functional layers.

[0053] The invention is explained in more detail below using preferred embodiments. Fig. 1 a first MEMS microphone in a cross-sectional view, Fig. 2 a second MEMS microphone in a cross-sectional view, Fig. 3 a third MEMS microphone in a cross-sectional view, Fig. 4 a fourth MEMS microphone in a cross-sectional view and Fig. 5 the fourth MEMS microphone in a top view.

[0054] In the following, the same reference symbols may be used for the same features.

[0055] Fig. 1 shows a first MEMS microphone 101 in a cross-sectional view.

[0056] The first MEMS microphone 101 includes a diaphragm 103 for recording sound pressure. The diaphragm 103 is connected to a substrate 105 and spans a cavity 107 in the substrate 105.

[0057] The first MEMS microphone 101 includes a lever element 109 coupled to the diaphragm 103. The lever element 109 is further coupled to a signal conversion element 111 of the first MEMS microphone 101. The lever element 109 is configured to generate a tilting movement upon deflection of the diaphragm 103 and to transmit the generated tilting movement to the signal conversion element 111.

[0058] In other words, the lever element 109 is coupled to the membrane 103 and, when the membrane 103 is deflected, generates a tilting movement which is transmitted to the signal conversion element 111.

[0059] Since the membrane 103 does not have to move relative to one or two fixed counter electrodes, the movement of the membrane 103 in the sound is almost undamped and a very good signal quality can be ensured.

[0060] In the first MEMS microphone 101, the lever element 109 is connected to the diaphragm 103 off-center relative to the diaphragm 103. A connection point 113 of the lever element 109 to the diaphragm 103 is selected such that a tilting of the diaphragm 103 coincides with the tilting movement of the lever element 109, which is fixed to the signal conversion element 111. This makes it possible to provide a particularly sensitive MEMS microphone in which no additional stresses are caused in the signal conversion element 111, the lever element 109, or the diaphragm 103 upon deflection of the diaphragm 103.

[0061] The signal conversion element 111 comprises two stationary counter electrodes: a first counter electrode 115 and a second counter electrode 117, which are arranged on the substrate 105. The stationary counter electrodes 115, 117 can also be referred to as stator electrodes.

[0062] Above the two counter electrodes 115, 117, a movable electrode 119 of the signal conversion element 111 is provided. This movable electrode can perform a tilting movement and its movement is determined by measuring the capacitance of each of the two counter electrodes 115, 117. The movable electrode 119 can also be referred to as an actuator electrode.

[0063] The MEMS microphone 101 comprises a sealing layer 121, which closes or seals the two counter electrodes 115, 117 and the movable electrode 119. The sealing layer 121 thus ensures the closure of this structure consisting of counter electrodes 115, 117 and the movable electrode 119, for example, to enclose a vacuum in this area to reduce attenuation.

[0064] Fig. 2 shows a second MEMS microphone 201 in a cross-sectional view.

[0065] In the second MEMS microphone 201, the lever element 109 is connected in the center of the diaphragm to transmit the greatest possible deflection to the signal conversion element 111. The diaphragm 103 has recesses 203 in the center of the diaphragm, which can compensate for the different tilting movements between the lever element 109 and the diaphragm 103.

[0066] Fig. Figure 3 shows a third MEMS microphone 301 in a cross-sectional view. A distance is created between the diaphragm 103 and the lever element 109 using a connecting element 303 to prevent the diaphragm 103 from striking the lever element 109 during large deflections of the diaphragm 103. The connecting element 303 can be particularly thin and high in order to compensate for the different tilting movements between the lever element 109 and the diaphragm 103.

[0067] It is particularly advantageous to use membranes that are particularly thin but subject to tensile stress. This allows large areas to be covered, and the natural frequency of the membrane can be adjusted via the tensile stress, with the low mass of the membrane resulting in high sensitivity.

[0068] For applications where layers with tensile stress are not available, or for arrangements where the layers are also used to construct the signal conversion element, arrangements such as those shown in the Fig. 4 and Fig. 5 are particularly advantageous.

[0069] Fig. 4 shows a fourth MEMS microphone 401 in a cross-sectional view.

[0070] At the edge of the membrane 103, the membrane 103 is suspended from the substrate 105 via a three-part spring 403. A first spring part 405 designates the part of the spring 403 that is coupled to the substrate 105. The second spring part 407 essentially designates the central part of the spring 403. The third part 409 designates the part of the spring that is coupled to the membrane 103.

[0071] The spring 403, or rather the three spring parts 405, 407, 409, have a spiral shape. This allows stress in the layer to be compensated for by a rotational movement of the membrane 103. The membrane properties are thus no longer dependent on the layer stress of the membrane 103. Furthermore, the suspension of the membrane 103 can be designed to be particularly soft.

[0072] For example, multiple layers are used or employed to set a small distance between the substrate 105 and the spring 403 and between the spring 403 and the diaphragm 103 in order to keep an acoustic leakage path as small as possible.

[0073] A short distance, for example, is a distance between 3 µm and 0.3 µm, including both 3 µm and 0.3 µm. Distances between 3 µm and 0.3 µm, including both 3 µm and 0.3 µm, can therefore be defined as short distances.

[0074] Furthermore, for example, both a substrate region 411 and a cover with a further layer 413 can be provided above and below the springs, wherein the further layer 413 can, for example, be the same layer from which the lever element 109 is formed. This advantageously further reduces an acoustic leakage path and, at the same time, advantageously provides a stop structure for the membrane in both deflection directions, i.e., once toward the substrate 105 and once away from the substrate 105. Furthermore, this advantageously prevents the membrane 103 from striking the lever element 109 in the event of an overload.

[0075] Fig. 5 shows the fourth MEMS microphone 401 in a top view. QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] CN 112383869 A

[0002] EP 2 579 616 A1

[0003] DE 10 2021 206 005 [0004, 0045] DE 10 2014 212 340 A1

[0005]

Claims

[1] MEMS microphone (101, 201, 301, 401), comprising: a membrane (103) for receiving a sound pressure, a signal conversion element (111) and a lever element (109) which is coupled to the membrane (103) and the signal conversion element (111), wherein the lever element (109) is configured to generate a tilting movement upon deflection of the membrane (103) and to transmit the generated tilting movement to the signal conversion element (111). [2] MEMS microphone (101, 201, 301, 401) according to claim 1, wherein the lever element (109) is connected to the membrane (103) off-center or centrally with respect to the membrane (103). [3] MEMS microphone (101, 201, 301, 401) according to claim 2, wherein, in the case of a central connection, recesses (203) are provided in the membrane (103) in order to compensate for different tilting movements between the lever element (109) and the membrane (103). [4] MEMS microphone (101, 201, 301, 401) according to one of the preceding claims, wherein the lever element (109) is connected to the membrane (103) at a connection point (113) such that a tilting of the membrane (103) substantially coincides with a tilting movement of the lever element (109). [5] MEMS microphone (101, 201, 301, 401) according to one of the preceding claims, wherein the lever element (109) is coupled to the membrane (103) at a distance therefrom in order to prevent the membrane (103) from striking the lever element (109). [6] MEMS microphone (101, 201, 301, 401) according to one of the preceding claims, wherein the lever element (109) is connected to the membrane (103) via a mechanical connecting element (303) which has at least three times the height of a membrane thickness in a partial area and which covers an area of the membrane (103) by less than 25% based on the area of the membrane (103) in order to compensate for different tilting movements between the lever element (109) and the membrane (103). [7] MEMS microphone (101, 201, 301, 401) according to one of the preceding claims, comprising a carrier, in particular substrate (105), on which the membrane (103), the signal conversion element (111) and the lever element (109) are arranged, wherein the membrane (103) is at least partially connected, in particular suspended, to the carrier via at least one spring (105). [8] MEMS microphone (101, 201, 301, 401) according to claim 7, wherein the at least one spring (105) is spiral-shaped. [9] MEMS microphone (101, 201, 301, 401) according to claim 7 or 8, comprising a stop structure (411; 413) for the membrane (103) in at least one of two deflection directions of the membrane (103). [10] MEMS microphone (101, 201, 301, 401) according to claim 9, wherein the stop structure (411; 413) has a support region of the support formed below the at least one spring (105) as a stop for the membrane (103) in a deflection direction towards the support. [11] MEMS microphone (101, 201, 301, 401) according to claim 9 or 10, wherein the stop structure (411; 413) has a cover formed above the at least one spring (105) as a stop for the membrane (103) in a deflection direction away from the carrier. [12] MEMS microphone (101, 201, 301, 401) according to one of claims 1 to 6, comprising a carrier, in particular substrate (105), on which the membrane (103), the signal conversion element (111) and the lever element (109) are arranged, wherein the membrane (103) is directly connected to the carrier.

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