A condenser MEMS microphone and its fabrication method

Abstract

This invention relates to the field of acoustic-to-electrical conversion technology, and provides a capacitive MEMS microphone and its manufacturing method. The capacitive MEMS microphone includes a substrate, a diaphragm, a suspension bracket, and a backplate. The backplate is disposed on the substrate; the suspension bracket is disposed on the side of the backplate away from the substrate; the edge of the diaphragm is suspended on the side of the suspension bracket facing the backplate; wherein, a first gap is provided between the upper surface of the diaphragm and the lower surface of the suspension bracket, and a second gap is provided between the lower surface of the diaphragm and the upper surface of the backplate. This capacitive MEMS microphone reduces the stress at the connection point between the diaphragm and the suspension bracket, prevents the diaphragm from cracking due to excessive deformation, and makes the microphone more stable, effectively improving the performance of the MEMS microphone.

Description

Technical Field

[0001] This invention relates to the field of acoustic-to-electric conversion technology, specifically to a capacitive MEMS microphone and its manufacturing method. Background Technology

[0002] With the increasing intelligence of electronic products, the demand for audio interface devices has increased dramatically. Currently, microphones used in electronic products are mainly divided into two categories: ECM (Electret Condenser microphone) microphones and MEMS (Micro Electro Mechanical System) condenser microphones. Among them, MEMS microphones, due to their use of microelectronics technology, have advantages such as small size, lower cost, and better sensitivity consistency, and have been widely used. High-performance and high-reliability MEMS microphones are being extensively researched.

[0003] However, in existing technologies, the diaphragm of a traditional condenser microphone is fixed to the substrate by a sacrificial layer. The position of this sacrificial layer is often difficult to control, leading to instability in the diaphragm's fixed position and consequently, instability in its stiffness, resulting in poor consistency in the microphone's sensitivity. Alternatively, the MEMS diaphragm is fixed by springs around its perimeter. When the diaphragm is subjected to large mechanical or pneumatic shocks, the springs experience significant displacement, stress concentration at the spring locations, and potential spring breakage, causing microphone failure. The reliability failure of condenser microphones is primarily due to the large deformation of the diaphragm under strong airflow or mechanical impacts, leading to breakage. The pneumatic shocks that microphone devices may encounter during use can reach several MPa; therefore, it is necessary to enhance microphone reliability without sacrificing signal-to-noise ratio performance.

[0004] In summary, to solve the above problems and improve the reliability of the microphone, this invention proposes a novel capacitive MEMS microphone and its manufacturing method. Summary of the Invention

[0005] Based on the above description, the present invention provides a capacitive MEMS microphone and its manufacturing method, which solves the technical problem in the prior art where the diaphragm of a MEMS microphone is subjected to large air pressure or mechanical impact, resulting in excessive displacement and diaphragm breakage, thereby improving the reliability of the MEMS microphone.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] In a first aspect, the present invention provides a capacitive MEMS microphone, comprising: a substrate, a diaphragm, a suspension bracket, and a backplate;

[0008] The back plate is disposed on the substrate;

[0009] The suspension bracket is mounted on the side of the back plate away from the substrate;

[0010] The edge of the diaphragm is suspended on the side of the suspension frame facing the back plate;

[0011] The upper surface of the diaphragm and the lower surface of the suspension frame are provided with a first gap, and the lower surface of the diaphragm and the upper surface of the back plate are provided with a second gap.

[0012] Based on the above technical solution, the present invention can be further improved as follows.

[0013] Furthermore, the diaphragm includes a diaphragm body and an elastic portion;

[0014] The elastic part is a plurality of parts, and the plurality of elastic parts are arranged along the circumferential direction of the diaphragm body on the outer periphery of the diaphragm body.

[0015] Furthermore, the elastic portion is bent.

[0016] Furthermore, the suspension frame includes a first mounting part, a second mounting part, and a suspension part;

[0017] The first mounting part is annular and is mounted on the back plate;

[0018] The second mounting part is connected to the side of the first mounting part away from the back plate and is arranged perpendicular to the first mounting part;

[0019] The suspension portion is disposed on the lower surface of the second mounting portion, and the elastic portion is connected to the lower surface of the suspension portion, so that the lower surface of the second mounting portion and the upper surface of the diaphragm body form the first gap.

[0020] Furthermore, there are multiple suspension parts, and the multiple suspension parts are correspondingly arranged with the multiple elastic parts.

[0021] Furthermore, the substrate has a cavity, and the diaphragm is disposed on the cavity. The cavity is used to allow sound pressure to pass through so that the sound pressure acts on the diaphragm.

[0022] Furthermore, at least one of the diaphragm and the backplate has a protrusion on the side facing the other.

[0023] Furthermore, the back plate has multiple through holes; the multiple through holes are arranged in an array.

[0024] In a second aspect, the present invention provides a method for manufacturing a capacitive MEMS microphone as described in any one of the first aspects, comprising:

[0025] A first sacrificial layer is deposited on the substrate;

[0026] Silicon nitride is deposited on the upper surface of the first sacrificial layer and etched through holes to obtain a backplate with multiple through holes;

[0027] A second sacrificial layer is deposited on the back plate and at the through-hole;

[0028] Polycrystalline silicon is deposited on the upper surface of the second sacrificial layer and etched to obtain a diaphragm, forming a substrate-backplate-diaphragm structure;

[0029] A third sacrificial layer is deposited on the upper surface of the substrate-backplate-diaphragm structure and etched to expose a portion of the diaphragm.

[0030] Silicon nitride is deposited on the outer surface of the third sacrificial layer to obtain a suspension frame, which is in contact with the diaphragm.

[0031] The first sacrificial layer, the second sacrificial layer, and the third sacrificial layer are removed to form a capacitive MEMS microphone.

[0032] Based on the above technical solution, the present invention can be further improved as follows.

[0033] Furthermore, before removing the first sacrificial layer, the second sacrificial layer, and the third sacrificial layer, the process further includes:

[0034] The substrate is etched to form a cavity.

[0035] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0036] The capacitive MEMS microphone provided by this invention comprises a substrate, a diaphragm, a suspension bracket, and a backplate. The suspension bracket is located on the side of the backplate away from the substrate, and the edge of the diaphragm is suspended on the side of the suspension bracket facing the backplate. A first gap is provided between the upper surface of the diaphragm and the lower surface of the suspension bracket. By setting the suspension bracket and mounting the diaphragm on the suspension bracket, a suspension structure is provided above the diaphragm. The suspension structure is connected to the edge of the diaphragm, which can reduce the stiffness of the diaphragm around its perimeter. The outer boundary of the diaphragm overlaps with the non-contact portion of the suspension bracket. When the diaphragm is subjected to a large air pressure impact, the non-contact portion of the diaphragm can contact the lower surface of the suspension structure, thereby limiting the further increase of the diaphragm displacement.

[0037] Compared to existing technologies, the capacitive MEMS microphone provided by this invention reduces the stress at the connection point between the diaphragm and the suspension frame, preventing the diaphragm from cracking due to excessive deformation, thus giving the microphone higher stability and effectively improving the performance of the MEMS microphone. Attached Figure Description

[0038] Figure 1This is a schematic diagram of the structure of the capacitive MEMS microphone provided in Embodiment 1 of the present invention;

[0039] Figure 2 This is a partial structural diagram of the capacitive MEMS microphone provided in Embodiment 1 of the present invention;

[0040] Figure 3 This is a top view of the capacitive MEMS microphone provided in Embodiment 1 of the present invention.

[0041] Figure 4 This is a schematic diagram of the manufacturing process of a capacitive MEMS microphone provided in Embodiment 2 of the present invention;

[0042] The attached diagram lists the components represented by each number as follows:

[0043] 1. Substrate;

[0044] 2. Diaphragm; 21. Diaphragm body; 22. Elastic part;

[0045] 3. Suspension bracket; 31. First mounting part; 32. Second mounting part; 33. Suspension part;

[0046] 4. Back panel. Detailed Implementation

[0047] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0048] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0049] In the description of the embodiments of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0050] Furthermore, in the description of the embodiments of the present invention, the term "multiple" refers to a quantity of two or more.

[0051] The following is in conjunction with the appendix Figures 1 to 4The embodiments will be described in further detail below to illustrate the implementation of the present invention. The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of the present invention.

[0052] Example 1

[0053] like Figures 1 to 3 As shown, the capacitive MEMS microphone provided in this embodiment of the invention consists of a substrate 1, a diaphragm 2, a suspension bracket 3, and a backplate 4.

[0054] The back plate 4 is disposed on the substrate 1, the suspension bracket 3 is disposed on the side of the back plate 4 away from the substrate 1, and the edge of the diaphragm 2 is suspended on the side of the suspension bracket 3 facing the back plate 4.

[0055] The upper surface of the diaphragm 2 and the lower surface of the suspension frame 3 are provided with a first gap, and the lower surface of the diaphragm 2 and the upper surface of the back plate 4 are provided with a second gap.

[0056] Specifically, the working principle of a condenser microphone is as follows: A MEMS microphone mainly consists of three parts: a diaphragm, a backplate, and a substrate. The diaphragm and backplate form a parallel-plate capacitor. When a bias voltage is applied to the diaphragm or backplate, the sound pressure acts on the diaphragm, causing a change in the distance between the diaphragm and the backplate, which in turn changes the capacitance, generating a voltage signal output. The corresponding calculation formula is as follows:

[0057]

[0058] Where sensitivity is the sensitivity, and V is the bias voltage. Δ C represents the change in capacitance under sound pressure, and C0 represents the initial capacitance.

[0059] Typically, to reduce the pressure damping between the diaphragm 2 and the back plate 4, the back plate 4 has a through-hole structure.

[0060] Specifically, such as Figure 2 As shown, the back plate 4 has multiple through holes; the array of multiple through holes is arranged in a specific manner. The specific number and arrangement of the through holes are not limited here, and can be set according to actual needs.

[0061] Signal-to-noise ratio (SNR) is a key performance indicator for microphones. Improving SNR is mainly achieved by increasing MEMS sensitivity and reducing MEMS noise.

[0062] The bias voltage V is usually set as the pull-in voltage between the microphone diaphragm and the backplate. pullin At a certain ratio (when a voltage exists between the diaphragm 2 and the back plate, an electrostatic force is generated between the diaphragm and the back plate; when the voltage is large enough, the diaphragm and the back plate will be attracted together under the action of the electrostatic force, V) pullin (This is the maximum voltage at which the diaphragm and backplate do not engage).

[0063] In summary, under the same bias voltage, the capacitance change can be increased. Δ C is used to improve the microphone's sensitivity.

[0064] Among them, capacitance change Δ C is proportional to the effective area of ​​the diaphragm, A. eff Effective area A eff The calculation formula is:

[0065]

[0066] w represents the displacement at various points on the diaphragm. This integral is the integral of the diaphragm displacement over the diaphragm area, where w0 is the displacement at the point of maximum diaphragm displacement.

[0067] The effective area of ​​a diaphragm is generally smaller than its actual area. The more uniform the displacement at all points on the diaphragm, the closer the effective area of ​​the diaphragm is to its actual area, meaning the larger the effective area.

[0068] like Figure 1 As shown, the capacitive MEMS microphone provided in this embodiment of the invention includes a substrate 1, a diaphragm 2, a suspension bracket 3, and a back plate 4. The suspension bracket 3 is located on the side of the back plate 4 away from the substrate 1, and the edge of the diaphragm 2 is suspended on the side of the suspension bracket 3 facing the back plate 4. A first gap is provided between the upper surface of the diaphragm 2 and the lower surface of the suspension bracket 3.

[0069] By setting up a suspension frame 3 and mounting the diaphragm 2 on the suspension frame 3, that is, by setting up a suspension structure above the diaphragm 2 and connecting the suspension structure to the edge of the diaphragm 2, the stiffness of the diaphragm 2 around the perimeter can be reduced.

[0070] The outer boundary of the diaphragm 2 overlaps with the non-contact portion of the suspension frame 3. When the diaphragm 2 is subjected to a large air pressure impact, the non-contact portion of the diaphragm 2 can contact the lower surface of the suspension structure, thereby limiting the further increase of the displacement of the diaphragm 2.

[0071] This condenser MEMS microphone reduces the stress at the connection point between the diaphragm 2 and the suspension bracket 3, preventing the diaphragm 2 from cracking due to excessive deformation, thus giving the microphone higher stability and effectively improving the performance of the MEMS microphone.

[0072] like Figure 1 As shown, the substrate 1 has a cavity, and the diaphragm 2 is disposed on the cavity. The cavity is used to allow sound pressure to pass through so that the sound pressure acts on the diaphragm 2.

[0073] In a preferred example, the diaphragm 2 includes a diaphragm body 21 and an elastic portion 22; both can be integrally formed and are formed in the same process step.

[0074] There are multiple elastic parts 22, and the multiple elastic parts 22 are arranged on the outer periphery of the diaphragm body 21 along the circumferential direction.

[0075] The specific number of elastic parts 22 is not limited here. Figure 3 The arrangement of the eight elastic parts 22 shown is only an example; other numbers are also possible, and the specific number can be set according to actual needs.

[0076] The elastic part 22 is bent, and its shape can be regular or irregular, straight or curved, preferably spring-shaped, but not specifically limited. Various bent elastic structures can achieve the effects of the present invention and can all fall within the protection scope of the embodiments of the present invention.

[0077] In optional embodiments, such as Figure 2 As shown, the suspension frame 3 includes a first mounting part 31, a second mounting part 32, and a suspension part 33.

[0078] The first mounting part 31 is ring-shaped and is mounted on the back plate 4.

[0079] The second mounting part 32 is connected to the side of the first mounting part 31 away from the back plate 4 and is set perpendicular to the first mounting part 31.

[0080] The suspension part 33 is provided on the lower surface of the second mounting part 32, and the elastic part 22 is connected to the lower surface of the suspension part 33 so that the lower surface of the second mounting part 32 and the upper surface of the diaphragm body 21 form a first gap.

[0081] Furthermore, there can be multiple suspension parts 33, and multiple suspension parts 33 are provided corresponding to multiple elastic parts 22. The ends of the elastic parts 22 are connected to the lower surface of the suspension parts 33, thereby reducing the stiffness around the diaphragm 2.

[0082] The location and number of the suspension part 33 can be adapted to the elastic part 22 described above, and there is no limitation on its specific arrangement and number.

[0083] Based on the above embodiments, further, such as Figure 2 As shown, a second gap is provided between the lower surface of the diaphragm 2 and the upper surface of the back plate 4; a first gap is provided between the upper surface of the diaphragm 2 and the lower surface of the suspension part 33, so that the diaphragm 2 can be displaced under the action of sound pressure. The specific dimensions of the first gap and the second gap are not limited here, and can be set according to actual needs.

[0084] The non-elastic portion of the outer boundary of the diaphragm body 21 overlaps with the lower surface of the second mounting portion 32. In actual operation, when the diaphragm 2 is subjected to a large air pressure impact, the non-elastic portion of the outer boundary of the diaphragm body 21 can contact the lower surface of the second mounting portion 32, limiting the displacement of the diaphragm 2 to increase further, thereby reducing the spring position stress of the diaphragm 2 and preventing the diaphragm 2 from breaking due to excessive displacement.

[0085] In an optional embodiment, in order to further improve the stability of the diaphragm 2, the middle part of the diaphragm 2 has an elastic structure, so that the displacement of the diaphragm 2 under the action of sound pressure is more uniform.

[0086] Based on the above embodiments, optionally, at least one of the diaphragm 2 and the back plate 4 has a protrusion on the side facing the other.

[0087] The number of protrusions can be one or more, and they can be evenly distributed or irregularly distributed. Preferably, multiple protrusions are evenly distributed, and the following three methods of arrangement are included:

[0088] 1. A protrusion is provided on the lower surface of diaphragm 2;

[0089] 2. A protrusion is provided on the upper surface of the back plate 4;

[0090] 3. Protrusions are provided on the lower surface of the diaphragm 2 and the upper surface of the back plate 4;

[0091] The purpose of setting the convex part is to effectively prevent the diaphragm 2 from sticking to the back plate 4.

[0092] Example 2

[0093] like Figure 4 As shown, this embodiment of the invention provides a method for manufacturing a capacitive MEMS microphone as described in Embodiment 1, comprising:

[0094] Step S1: Deposit a first sacrificial layer on the substrate, preferably made of silicon oxide.

[0095] Step S2: Deposit silicon nitride on the upper surface of the first sacrificial layer to obtain a silicon nitride backplane layer.

[0096] Step S3: Etch through the silicon nitride backplane layer to obtain a backplane with multiple through holes.

[0097] Step S4: Deposit a second sacrificial layer on the backplate and at the vias to form an air gap between the subsequently generated diaphragm and the backplate. The material of the second sacrificial layer is preferably silicon oxide.

[0098] Step S5: Deposit polycrystalline silicon on the upper surface of the second sacrificial layer to obtain a polycrystalline silicon layer.

[0099] Step S6: Etch the polysilicon layer to form the diaphragm body and elastic part, thus obtaining the diaphragm and forming a substrate-backplate-diaphragm structure.

[0100] Step S7: Deposit a third sacrificial layer on the upper surface of the substrate-backplate-diaphragm structure. The material of the third sacrificial layer is preferably silicon oxide.

[0101] Step S8: Etch the third sacrificial layer to expose part of the diaphragm.

[0102] Step S9: Deposit silicon nitride on the outer surface of the third sacrificial layer to obtain a silicon nitride layer.

[0103] Step S10: Etch the silicon nitride layer to obtain the suspension frame, which then contacts the diaphragm.

[0104] Step S11: Etch the substrate to form a cavity.

[0105] Step S12: Remove the first sacrificial layer, the second sacrificial layer and the third sacrificial layer to form a capacitive MEMS microphone structure.

[0106] Specifically, since this manufacturing method is used to manufacture the capacitive MEMS microphone described in Embodiment 1, it has all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be repeated here.

[0107] In the description of this specification, references to terms such as "specific example" or "some examples" refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example that are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A capacitive MEMS microphone, characterized in that, include: Substrate, diaphragm, suspension bracket and backplate; The back plate is disposed on the substrate; The suspension bracket is mounted on the side of the back plate away from the substrate; The edge of the diaphragm is suspended on the side of the suspension frame facing the back plate; The upper surface of the diaphragm and the lower surface of the suspension frame are provided with a first gap, and the lower surface of the diaphragm and the upper surface of the back plate are provided with a second gap. The diaphragm includes a diaphragm body and an elastic portion; The elastic part is multiple, and the multiple elastic parts are arranged on the outer periphery of the diaphragm body along the circumferential direction of the diaphragm body; The suspension frame includes a first mounting part, a second mounting part, and a suspension part; The first mounting part is annular and is mounted on the back plate; The second mounting part is connected to the side of the first mounting part away from the back plate and is arranged perpendicular to the first mounting part; The suspension part is disposed on the lower surface of the second mounting part, and the elastic part is connected to the lower surface of the suspension part so that the lower surface of the second mounting part and the upper surface of the diaphragm body form the first gap; The substrate has a cavity, and the diaphragm is disposed on the cavity. The cavity is used to allow sound pressure to pass through so that the sound pressure acts on the diaphragm.

2. The capacitive MEMS microphone according to claim 1, characterized in that, The elastic part is bent.

3. The capacitive MEMS microphone according to claim 1, characterized in that, There are multiple suspension parts, and the multiple suspension parts are correspondingly arranged with the multiple elastic parts.

4. The capacitive MEMS microphone according to claim 1, characterized in that, At least one of the diaphragm and the backplate has a protrusion on the side facing the other.

5. The capacitive MEMS microphone according to claim 1, characterized in that, The back plate has multiple through holes; the multiple through holes are arranged in an array.

6. A method for manufacturing a condenser MEMS microphone as described in any one of claims 1 to 5, characterized in that, include: A first sacrificial layer is deposited on the substrate; Silicon nitride is deposited on the upper surface of the first sacrificial layer and etched through holes to obtain a backplate with multiple through holes; A second sacrificial layer is deposited on the back plate and at the through-hole; Polycrystalline silicon is deposited on the upper surface of the second sacrificial layer and etched to obtain a diaphragm, forming a substrate-backplate-diaphragm structure; A third sacrificial layer is deposited on the upper surface of the substrate-backplate-diaphragm structure and etched to expose a portion of the diaphragm. Silicon nitride is deposited on the outer surface of the third sacrificial layer to obtain a suspension frame, which is in contact with the diaphragm. The first sacrificial layer, the second sacrificial layer, and the third sacrificial layer are removed to form a capacitive MEMS microphone.

7. The manufacturing method according to claim 6, characterized in that, Before removing the first sacrificial layer, the second sacrificial layer, and the third sacrificial layer, the method further includes: The substrate is etched to form a cavity.

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