MEMS devices and microphones

Abstract

The present disclosure relates to a micro-electromechanical system device and a microphone, the micro-electromechanical system device comprising: a constrained diaphragm including a surface, the diaphragm having a net compressive stress; and a back plate comprising: a surface facing the surface of the diaphragm, the surface of the back plate having a center, and a pillar extending from the surface of the back plate, wherein the pillar is placed at or near the center of the surface and limits the maximum deflection of the diaphragm.

Description

Technical Field

[0001] The present disclosure relates to a micro-electromechanical systems (MEMS) device having a diaphragm with a net compressive stress. Background Art

[0002] It is well-known that micro-electromechanical systems (MEMS) based acoustic sensors require a diaphragm with a net stress of tension, because a diaphragm with a net compressive stress tends to buckle during operation. Summary of the invention

[0003] According to one aspect of the present disclosure, a micro-electromechanical system device is provided, the micro-electromechanical system device comprising:

[0004] a constrained diaphragm, the diaphragm comprising a surface, the diaphragm having a net compressive stress; and

[0005] A back plate, the back plate comprising:

[0006] The surface of the back plate has a center facing the surface of the diaphragm;

[0007] A post extends from the surface of the backplate, wherein the post is positioned at or near the center, wherein the post limits the maximum deflection of the diaphragm.

[0008] According to another aspect of the present disclosure, a micro-electromechanical system device is provided, the micro-electromechanical system device comprising:

[0009] a constrained diaphragm, the diaphragm comprising a surface, wherein the diaphragm has a net compressive stress; and

[0010] A back plate, the back plate comprising:

[0011] The surface facing the surface of the diaphragm,

[0012] A pillar extends from the surface of the back plate, wherein the pillar is arranged at or near the unconstrained maximum deflection point of the diaphragm to limit the actual maximum deflection of the diaphragm during operation of the micro-electromechanical system device.

[0013] According to another aspect of the present disclosure, there is provided a microphone, comprising:

[0014] A micro-electromechanical system device, the micro-electromechanical system device comprising:

[0015] A constrained diaphragm, the diaphragm comprising a surface, wherein the diaphragm has a net compressive stress; and a backplate, the backplate comprising:

[0016] The surface facing the surface of the diaphragm,

[0017] a support post extending from the surface of the back plate, wherein the support post is disposed at or near the centroid of the diaphragm and the back plate; and

[0018] An integrated circuit is electrically connected to the MEMS device. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings.The drawings depict only several embodiments in accordance with the present disclosure and therefore should not be considered limiting of its scope.

[0020] Figure 1A is a side cross-sectional view of a MEMS device according to an embodiment, wherein the MEMS device is in an unbiased state.

[0021] Figure 1B yes Figure 1A A three-dimensional cross-sectional view of a MEMS device in which the diaphragm is in a deflected state.

[0022] Figure 1C yes Figure 1A A perspective cross-sectional view of an alternative embodiment of a MEMS device in which the diaphragm is in a deflected state.

[0023] Figure 2A is a side cross-sectional view of a MEMS device according to another embodiment.

[0024] Figure 2B is a side cross-sectional view of a MEMS device according to yet another embodiment.

[0025] Figure 3 is a side cross-sectional view of a microphone assembly according to an embodiment.

[0026] Figure 4A Graphs depicting inherent stress at different deflections at different distances from the center of a diaphragm are configured in accordance with embodiments.

[0027] Figure 4B Graphs depicting inherent stress at different deflections at different distances from the center of a diaphragm are configured in accordance with embodiments, wherein a backplate has a post at its center.

[0028] In the detailed description below, various embodiments are described with reference to the accompanying drawings. The skilled person will appreciate that the drawings are schematic and simplified for clarity. Throughout the text, the same reference numerals refer to the same elements or components. Therefore, it is not necessary to describe the same elements or components in detail for each of the accompanying drawings. DETAILED DESCRIPTION

[0029] A constrained diaphragm is one that is attached (e.g., to a substrate) so that the exposed edge of the diaphragm cannot move along the x, y, or z axes or rotate about any axis. Such a diaphragm eliminates the possibility of contaminants getting around the edge of the diaphragm, but is very sensitive to residual film stress. It is well known that any residual film stress in the diaphragm should be tensile, because if it is compressive, the diaphragm will wrinkle. However, the stiffness of the diaphragm in operation does not depend solely on its initial stress, but also on the induced stress and bow caused by the electrostatic field between the diaphragm and the backplate. Since the net diaphragm stress is not important when the microphone is not operating, a diaphragm with a net compressive film stress can be used for operation. It is easier and less expensive to manufacture a diaphragm with a net compressive stress than to manufacture a diaphragm with a net tensile stress.

[0030] In general, a MEMS device having a diaphragm with a net compressive stress and a microphone incorporating such a MEMS device are disclosed herein. The details of the disclosure are more fully described with reference to the accompanying drawings.

[0031] According to an embodiment, a MEMS device is provided, comprising: a constrained diaphragm including a surface, the diaphragm having a net compressive stress; and a backplate including a surface facing the surface of the diaphragm, the surface of the backplate having a center; and a pillar extending from the surface of the backplate, wherein the pillar is positioned at or near the center, wherein the pillar limits the maximum deflection of the diaphragm.

[0032] In an embodiment, a MEMS device is provided, comprising: a constrained diaphragm including a surface, wherein the diaphragm has a net compressive stress; and a backplate including a surface facing the surface of the diaphragm, and a post extending from the surface of the backplate, wherein the post is arranged at or near an unconstrained maximum deflection point of the diaphragm so as to limit the actual maximum deflection of the diaphragm during operation of the MEMS device.

[0033] According to an embodiment, a microphone is provided, comprising a MEMS device, the MEMS device comprising a constrained diaphragm, the constrained diaphragm comprising a surface, wherein the diaphragm has a net compressive stress; an integrated circuit electrically connected to the MEMS device; and a backplate, the backplate comprising a surface facing the surface of the diaphragm, and a pillar extending from the surface of the backplate, wherein the pillar is arranged at or near the centroid of the diaphragm and the backplate.

[0034] In an embodiment, the microphone further comprises a housing comprising a base and a cover attached to the base, wherein the housing encloses the MEMS device and the integrated circuit. The housing may further comprise an acoustic port defined in the cover or the base.

[0035] According to an embodiment, the diaphragm (which may be attached to the pillars) includes multiple membrane layers having a combined net compressive stress. For example, one or more of the layers may be compressive or tensile. The diaphragm may be made of a tensile nitride layer and a compressive polysilicon layer.

[0036] Go to Figure 1A and Figure 1B , shows a MEMS device according to an embodiment. The MEMS device, generally designated 100, includes: a back plate 102, a first spacer 104, a diaphragm 106, a second spacer 108, and a substrate 110. The diaphragm 106 and the back plate 102 can be of any shape. The first spacer 104, the second spacer 108, and the substrate 110 can all be part of a single integral body. In an embodiment, the diaphragm 106 is made of polycrystalline silicon (poly-silicon). For ease of reference, Figure 1A-Figure 1C However, it is to be understood that, because the diaphragm 106 has a net compressive stress, the diaphragm 106 is most likely to be bowed (e.g., bowed upward or bowed downward) when the MEMS device 100 is in an unbiased state (i.e., no charge is applied to the diaphragm 106 and the backplate).

[0037] The back plate 102 has a first surface 102a as part of an insulating or dielectric layer, and a second surface 102b opposite to the first surface 102a, which is part of a conductive layer (first electrode). The diaphragm 106 (which has a second electrode or is a second electrode) has a first surface 106a and a second surface 106b opposite to the first surface 106a. The diaphragm 106 is sandwiched between a first spacer 104 (which is in contact with the first surface 106a) and a second spacer 108 (which is in contact with the second surface 106b) and is constrained by the first spacer 104 and the second spacer 108. The first spacer 104 has a curved inner wall 104a. The second surface 102b of the back plate 102, the first surface 106a of the diaphragm 106, and the inner wall 104a of the first spacer 104 define a chamber 112.

[0038] The second spacer 108 has a curved inner wall 108a. The diaphragm 106 is completely constrained (by the first spacer 104 and the second spacer 108) along a boundary defined by the following curve: along this curve, the inner wall 104a of the first spacer 104 intersects the diaphragm 106. The substrate 110 also has a curved inner wall 110a, which defines a hole 116 extending through the substrate 110.

[0039] In an embodiment, the first spacer 104 and the second spacer 108 are part of a sacrificial material of the MEMS device 100 , and the walls 104 a and 108 a of the spacers are made by a time-limited etch front of the sacrificial material.

[0040] There are many possible implementations of the backplate 102 and the diaphragm 106. For example, the backplate 102 may include a dielectric layer and a conductive layer deposited onto or otherwise connected to the dielectric layer. The diaphragm 106 may be made entirely of conductive layers. In other implementations, similar to the backplate 102, the diaphragm 106 includes both an insulating layer and a conductive layer. In yet other implementations, the diaphragm 106 includes both a conductive layer and an insulating layer, and the backplate 102 is formed entirely of conductive layers. The conductive layers of both the backplate 102 and the diaphragm 106 may face each other without any material in between, or may be separated from each other by insulating layers of the diaphragm 106 and / or the backplate 102. The insulating layers of both the backplate 102 and the diaphragm 106 may be made of silicon nitride or other suitable insulating materials. The conductive layers on the backplate 102 and / or the diaphragm 106 may be made of polysilicon, metal, or other suitable conductors.

[0041] During operation of the MEMS device 100, electric charges are applied to the conductive layer of the back plate 102 and the conductive layer of the diaphragm 106, thereby inducing an electric field between the back plate 102 and the diaphragm 106 and generating an electrostatic bias on the diaphragm 106. The movement of air (e.g., caused by sound waves) pushes against the second surface 106b of the diaphragm 106, causing the diaphragm 106 to deflect (enter a deflected state) and deform. This deformation causes a change in capacitance between the back plate 102 and the diaphragm 106, which can be detected and interpreted as sound.

[0042] In an embodiment, the diaphragm 106 has a net compressive stress when in an unbiased state and without an electric field. To fabricate the MEMS device 100 so that the diaphragm 106 has a net compressive stress, the fabricator deposits a film of the diaphragm and (if appropriate) anneals the film so that the net stress in the diaphragm is compressive when the entire structure is complete.

[0043] According to an embodiment, the charge applied to the back plate 102 and the diaphragm 106 is such that the electrostatic bias voltage generated on the diaphragm is greater than the expected peak sound pressure on the diaphragm. This helps prevent the diaphragm 106 from buckling.

[0044] In an embodiment, the stress gradient on the diaphragm 106 causes the diaphragm 106 to bow upward (ie, the concave surface faces away from the backplate 102) when the MEMS device 100 is in an unbiased state. This helps prevent large movements in the diaphragm 106 when the MEMS device 100 is powered on.

[0045] According to an embodiment, the back plate 102 includes a support 118 extending from the second surface 102b. The support 118 is used to limit the maximum deflection of the diaphragm 106. Thus, the tip of the support 118 is arranged at a distance from the first surface 106a of the diaphragm 106, which is sufficient to substantially limit the deflection of the diaphragm 106.

[0046] Since there is pillar 118, Figure 1B As shown, the diaphragm 106 is deformed into an "M" shape.

[0047] In an embodiment, the support post 118 is disposed at or near the unconstrained maximum deflection point of the diaphragm 106 in order to limit the actual maximum deflection of the diaphragm 106 during operation of the MEMS device 100. The center deflection (the deflection at the center of the diaphragm 106) may be between 10% and 90% of the total gap (the gap between the back plate 102 and the diaphragm 106), but is optimally in the range of 10% to 20%, which controls the maximum deflection to the greatest extent without presenting a high risk of the diaphragm 106 sticking to the support post 118.

[0048] Go to Figure 1CIn an embodiment, the support 118 spans the gap between the back plate 102 and the diaphragm 106 and is attached to the diaphragm 106. In this case, there is obviously no gap between the support 118 and the diaphragm 106.

[0049] According to an embodiment, the post 118 is positioned at or near the centroid of the diaphragm 106 and the backplate 102. In some embodiments, the post 118 is part of the diaphragm 106, rather than part of the backplate 102, and extends toward the backplate 102. In such an embodiment, the post 118 will perform the same function as if it were attached to the backplate 102.

[0050] Go to Figure 2A , another embodiment of the MEMS device 100 is shown. In this embodiment, the diaphragm 206 is composed of a first layer 206a and a second layer 206b, wherein one layer is a tensile layer (e.g., a nitride film) and the other layer is a compressive layer (e.g., polysilicon). In one implementation, the first layer 206a is tensile and the second layer 206b is compressive. In another implementation, the first layer 206a is compressive and the second layer 206b is tensile. In both implementations, the diaphragm 206 as a whole is in net compression.

[0051] Go to Figure 2B , shows another embodiment of the MEMS device 100. In this embodiment, the diaphragm 206 is composed of a ring-shaped outer part 206a and a disk-shaped inner part 206b, wherein one part is tensile (e.g., a nitride film) and the other part is compressive (e.g., polysilicon). In one implementation, the outer part 206a is tensile and the inner part 206b is compressive. In another implementation, the outer part 206a is compressive and the inner part 206b is tensile. In both implementations, the diaphragm 206 as a whole is in net compression.

[0052] Go to Figure 3 , the MEMS device is configured to be assembled within a microphone assembly (generally labeled 300). Assembly 300 includes a housing including: a base 302, a cover 304 (e.g., a housing lid), and an acoustic port 306. In one implementation, base 302 is a printed circuit board. Cover 304 is coupled to base 302 (e.g., cover 304 can be mounted to the peripheral edge of base 302). Together, cover 304 and base 302 form an enclosed volume 308 of assembly 300. As shown in FIG. Figure 3As shown, the acoustic port 306 is disposed on the base 302, and the acoustic port is configured to deliver sound waves to the MEMS device 100 disposed in the enclosed volume 308. In other implementations, the acoustic port 306 is disposed on the cover 304 and / or the sidewall of the cover 304. In some embodiments, the assembly 300 forms part of a compact computing device (e.g., a portable communication device, a smart phone, a smart speaker, an Internet of Things (IoT) device, etc.), in which one, two, three or more microphone assemblies can be integrated for picking up and processing various types of acoustic signals such as voice and music.

[0053] Assembly 300 includes circuitry disposed in enclosed volume 308. The circuitry includes integrated circuit (IC) 310. IC 310 may be an application specific integrated circuit (ASIC). Alternatively, IC 310 may include a semiconductor die integrating various analog circuits, analog-to-digital circuits, and / or digital circuits.

[0054] exist Figure 3 In the assembly 300 of FIG. 1 , the MEMS device 100 is a MEMS acoustic transducer that converts acoustic waves received through an acoustic port 306 into a corresponding electrical microphone signal. In response to acoustic activity incident on the port 306, the transducer generates an electrical signal (e.g., a voltage) at the transducer output. Figure 3 As shown, the transducer output includes a pad or terminal of the transducer that is electrically connected to a circuit via one or more bond wires 312 . Figure 3 The assembly 300 also includes electrical contacts (schematically shown as contacts 314) that are typically disposed on the bottom surface of the base 302. The contacts 314 are electrically coupled to the circuit. The contacts 314 are configured to electrically connect the assembly 300 to one of a variety of host devices.

[0055] Figure 4A A graph of the deflection of the diaphragm versus radial distance from the center is depicted. The graph includes various net stress values ​​and the diaphragm is under electrostatic bias. The diaphragm is configured without a center post to limit the maximum deflection. It should be noted that for a net compressive stress of 10 MPa (negative values ​​are compressive stress), the maximum diaphragm bow is just over 3.5 micrometers (μm).

[0056] Figure 4B Depicted with Figure 4A A similar graph, but with a diaphragm constructed in accordance with an embodiment in which the backplate has a post at its center (such as Figure 1A and Figure 1B It should be noted that the maximum deflection of the diaphragm is less than 2.5 μm, which is consistent with the Figure 4AIn contrast, the maximum deflection of the diaphragm without a central pillar is greater than 3.5 μm.

[0057] With respect to the use of plural and / or singular terms herein, those skilled in the art may translate from the plural to the singular and / or from the singular to the plural as appropriate for each situation and / or application. For clarity, various singular / plural permutations may be explicitly set forth herein.

[0058] Unless otherwise indicated, use of the words "approximately," "about," "roughly," "substantially," etc. means plus or minus ten percent.

[0059] The foregoing description of exemplary embodiments is presented for purposes of illustration and description. The description is not intended to be exhaustive or limited to the precise form disclosed, but may be modified and altered in accordance with the above teachings, or may be obtained from the practice of the disclosed embodiments. The scope of protection of the present disclosure is intended to be defined by the appended claims and their equivalents.

Claims

1. A micro-electromechanical system device, comprising: a constrained diaphragm, the diaphragm comprising a surface, the diaphragm having a net compressive stress; as well as A back plate, the back plate comprising: The surface of the back plate has a center facing the surface of the diaphragm; A post extends from a surface of the back plate, wherein the post is positioned at or near the center, wherein the post limits a maximum deflection of the diaphragm.

2. The MEMS device according to claim 1, wherein: The diaphragm is attached to the support.

3. The MEMS device according to claim 1, wherein: The diaphragm includes a plurality of membrane layers, each of the plurality of membrane layers has stress, and a combination of the plurality of membrane layers generates a net compressive stress of the diaphragm.

4. The MEMS device according to claim 1, wherein: The diaphragm comprises: tensile silicon nitride layer; and Compress the polysilicon layer.

5. A micro-electromechanical system device, comprising: a constrained diaphragm, the diaphragm comprising a surface, wherein the diaphragm has a net compressive stress; and A back plate, the back plate comprising: a surface facing the surface of the diaphragm, A pillar extends from the surface of the back plate, wherein the pillar is arranged at or near the unconstrained maximum deflection point of the diaphragm to limit the actual maximum deflection of the diaphragm during operation of the micro-electromechanical system device.

6. The MEMS device according to claim 5, wherein: The diaphragm is attached to the support.

7. The MEMS device according to claim 5, wherein: The diaphragm includes a plurality of membrane layers.

8. The MEMS device according to claim 7, wherein: The plurality of film layers include a film layer having tensile stress.

9. The MEMS device according to claim 7, wherein: The plurality of film layers include a film layer having compressive stress.

10. The MEMS device according to claim 5, wherein: The diaphragm comprises: tensile silicon nitride layer; and Compress the polysilicon layer.

11. A microphone, comprising: A micro-electromechanical system device, the micro-electromechanical system device comprising: a constrained diaphragm, the diaphragm comprising a surface, wherein the diaphragm has a net compressive stress; and A back plate, the back plate comprising: The surface facing the surface of the diaphragm, a support column extending from a surface of the back plate, wherein the support column is disposed at or near the centroid of the diaphragm and the back plate; and An integrated circuit is electrically connected to the MEMS device.

12. The microphone according to claim 11, wherein The microphone further includes a housing including a base and a cover attached to the base, wherein the housing encloses the MEMS device and the integrated circuit.

13. The microphone according to claim 12, wherein: An acoustic port is defined in the cover of the housing.

14. The microphone according to claim 12, wherein: An acoustic port is defined in the base of the housing.

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