阅读说明：本技术 具有低压区以及有增强柔度的振膜的声学换能器 (Acoustic transducer having a low pressure region and a diaphragm with enhanced compliance ) 是由 M·昆特兹曼 M·佩德森 桑·博克·李 余兵 V·纳德瑞恩 彼得·洛佩特 于 2019-10-04 设计创作，主要内容包括：一种响应于声学信号来生成电信号的声学换能器,该声学换能器包括第一振膜,在该第一振膜中形成有第一皱纹。在第二振膜中形成有第二皱纹,并且第二振膜与第一振膜间隔开,使得在第二振膜与第一振膜之间形成空腔,该空腔的压力低于大气压。在第一振膜与第二振膜之间设置有背板。一个或更多个支柱从第一振膜和第二振膜中的至少一个振膜起朝着另一振膜延伸穿过背板。所述一个或更多个支柱防止第一振膜和第二振膜中的各个振膜因第一振膜和/或第二振膜朝着背板移动而接触到背板。第一皱纹和第二皱纹中的各个皱纹远离背板,分别从第一振膜和第二振膜起向外突出。(An acoustic transducer that generates an electrical signal in response to an acoustic signal includes a first diaphragm having a first wrinkle formed therein. A second corrugation is formed in the second diaphragm, and the second diaphragm is spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure lower than atmospheric pressure. A back plate is arranged between the first vibrating diaphragm and the second vibrating diaphragm. One or more support posts extend from at least one of the first and second diaphragms through the backplate toward the other diaphragm. The one or more posts prevent each of the first and second diaphragms from contacting the backplate as the first and/or second diaphragms move toward the backplate. Each of the first wrinkles and the second wrinkles is away from the back plate and protrudes outward from the first diaphragm and the second diaphragm, respectively.)

1. An acoustic transducer that generates an electrical signal in response to an acoustic signal, the acoustic transducer comprising:

a first diaphragm in which first wrinkles are formed;

a second diaphragm having second corrugations formed therein, the second diaphragm being spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure lower than atmospheric pressure;

a back plate disposed in the cavity between the first diaphragm and the second diaphragm; and

one or more support posts extending from at least one of the first and second diaphragms toward the other of the first and second diaphragms through corresponding apertures defined in the backplate, the one or more support posts configured to prevent each of the first and second diaphragms from contacting the backplate as the first and/or second diaphragms move toward the backplate,

wherein each of the first wrinkles and the second wrinkles protrudes outward from the first diaphragm and the second diaphragm, respectively, in a direction away from the backplate.

2. The acoustic transducer of claim 1, wherein each of the first and second diaphragms includes a plurality of outwardly projecting corrugations.

3. The acoustic transducer of claim 1, wherein the one or more struts extend from the second diaphragm toward the first diaphragm such that tips of the one or more struts are disposed on and coupled to the first diaphragm.

4. The acoustic transducer of claim 1, wherein the one or more struts extend from the second diaphragm toward the first diaphragm such that a tip of the one or more struts is spaced apart from the first diaphragm, the tip configured to contact the first diaphragm in response to at least one of the first and second diaphragms moving toward the other diaphragm.

5. The acoustic transducer of claim 1, further comprising: anchor posts extending from the second diaphragm toward the first diaphragm through corresponding holes in the backplate, apexes of the anchor posts contacting the first diaphragm and coupled to the first diaphragm; a through-hole defined through the apex; and a perforation defined through the first diaphragm, the perforation at least partially overlapping the through-hole.

6. The acoustic transducer of claim 1, further comprising:

a substrate defining a first aperture therein; and

a support structure disposed on the substrate and defining a second aperture corresponding to the first aperture of the substrate,

wherein at least a portion of the first diaphragm is disposed on the support structure.

7. The acoustic transducer according to claim 6, wherein the support structure comprises a glass layer, the glass layer being free of phosphorus or having a phosphorus content in the range of 0.01 wt% to 10 wt%.

8. The acoustic transducer of claim 1, further comprising a perimeter support structure attached to and supporting at least a portion of a perimeter of the first and/or second diaphragms, the perimeter support structure being positioned adjacent to edges of the first and second diaphragms.

9. The acoustic transducer of claim 8, wherein the perimeter support structure comprises at least a first layer and a second layer, each of the first layer and the second layer comprising glass that is free of phosphorus or has a phosphorus content in a range of 0.01 wt% to 10 wt%.

10. The acoustic transducer of claim 9, wherein the first layer has a first phosphorous content and the second layer has a second phosphorous content different from the first phosphorous content.

11. The acoustic transducer of claim 10, wherein a radially inner side wall of the peripheral support structure has a conical profile.

12. The acoustic transducer of claim 1, wherein at least one of the first and second diaphragms comprises: the vibration film comprises a first vibration film layer and a second vibration film layer arranged on the first vibration film layer.

13. The acoustic transducer of claim 1, wherein at least one of the first and second diaphragms further comprises a stress relief structure adjacent a perimeter of the respective first or second diaphragm, the stress relief structure having a thickness greater than a thickness of a portion of the respective first or second diaphragm adjacent a center of the respective first or second diaphragm.

14. The acoustic transducer according to claim 13, wherein the stress relief structure comprises glass embedded between two silicon nitride layers, the glass being free of phosphorus or having a phosphorus content in the range of 0.01 wt% to 10 wt%.

15. The acoustic transducer of claim 13, wherein the stress relief structure comprises silicon nitride.

16. The acoustic transducer of claim 1, wherein the pressure in the cavity is in a range of 1mTorr to 1 Torr.

17. The acoustic transducer of claim 1, further comprising an overpressure stop formed in at least one of the first diaphragm, the second diaphragm, and the back plate.

18. A microphone assembly, the microphone assembly comprising:

a base;

a lid disposed on the base, a port being defined in one of the base and the lid;

an acoustic transducer disposed on the base or the lid and separating a front volume and a back volume of the microphone assembly, the front volume in fluid communication with the port, the acoustic transducer comprising:

a first diaphragm in which first wrinkles are formed;

a second diaphragm having second corrugations formed therein, the second diaphragm being spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure lower than atmospheric pressure;

a back plate disposed in the cavity between the first diaphragm and the second diaphragm; and

one or more support posts extending from at least one of the first and second diaphragms through corresponding apertures defined in the backplate toward the other of the first and second diaphragms, the one or more support posts configured to prevent each of the first and second diaphragms from contacting the backplate as the first and/or second diaphragms move toward the backplate,

wherein each of the first wrinkles and the second wrinkles protrudes outward from the first diaphragm and the second diaphragm, respectively, in a direction away from the backplate; and

an integrated circuit electrically coupled to the acoustic transducer, the integrated circuit configured to measure a change in capacitance between the first diaphragm and the backplate and between the second diaphragm and the backplate in response to receiving an acoustic signal through the port, the change in capacitance corresponding to the acoustic signal.

19. An acoustic transducer that generates an electrical signal in response to an acoustic signal, the acoustic transducer comprising:

a first diaphragm in which first wrinkles are formed;

a second diaphragm having second corrugations formed therein, the second diaphragm being spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure lower than atmospheric pressure;

a back plate disposed in the cavity between the first diaphragm and the second diaphragm;

one or more posts extending from at least one of the first and second diaphragms through corresponding apertures defined in the backplate toward the other of the first and second diaphragms, the one or more posts configured to prevent each of the first and second diaphragms from contacting the backplate as the first and/or second diaphragms move toward the backplate;

a perimeter support structure attached to and supporting at least a portion of the perimeters of the first and second diaphragms, the perimeter support structure being positioned adjacent to edges of the first and second diaphragms;

a substrate defining a first aperture therein; and

a support structure disposed on the substrate and defining a second opening corresponding to the first opening of the substrate, at least a portion of the first diaphragm being disposed on the support structure,

wherein each of the first wrinkles and the second wrinkles protrudes outward from the first diaphragm and the second diaphragm, respectively, in a direction away from the backplate.

20. The acoustic transducer of claim 19, wherein each of the first and second diaphragms includes a plurality of outwardly projecting corrugations.

21. The acoustic transducer of claim 19, wherein the perimeter support structure comprises a plurality of layers, each of the plurality of layers comprising glass, the glass being free of phosphorous or having a phosphorous content in a range of 0.01 wt% to 10 wt%.

Technical Field

The present disclosure relates generally to systems and methods for improving the compliance (compliance) of a diaphragm (diaphragm) included in an acoustic transducer (acoustic transducer).

Background

Microphone assemblies are commonly used in electronic devices to convert acoustic energy into electrical signals. A microphone typically includes a diaphragm that converts an acoustic signal into an electrical signal. The pressure sensor may also comprise such a diaphragm. Advances in micro-and nano-scale manufacturing technologies have led to the development of smaller and smaller micro-electromechanical system (MEMS) microphone assemblies and pressure sensors.

Disclosure of Invention

Embodiments described herein relate generally to systems and methods for increasing the compliance of the top and bottom diaphragms of a dual diaphragm acoustic transducer and/or preventing collapse (collapse) of either or both diaphragms. In particular, some embodiments described herein relate to a dual-diaphragm acoustic transducer comprising: one or more outwardly facing corrugations (corrugations) for increasing compliance are defined in the diaphragm, and/or one or more non-rigid connecting or non-anchoring struts extending from at least one of the dual diaphragms toward the other diaphragm to act as stops (stoppers) to prevent the dual diaphragms from collapsing.

In some embodiments, there is provided an acoustic transducer for generating an electrical signal in response to an acoustic signal, the acoustic transducer comprising: a first diaphragm in which first wrinkles are formed; and a second diaphragm in which second wrinkles are formed. The second diaphragm is spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure less than atmospheric pressure. The backplate is disposed in the cavity between the first diaphragm and the second diaphragm. One or more support posts extend from at least one of the first or second diaphragms through corresponding apertures defined in the backplate toward the other of the first or second diaphragms. The one or more posts are configured to prevent each of the first and second diaphragms from contacting the backplate as the first and/or second diaphragms move toward the backplate. Each of the first wrinkles and the second wrinkles protrudes outward from the first diaphragm and the second diaphragm, respectively, in a direction away from the backplate.

In some embodiments, there is provided a microphone assembly comprising: a base and a lid disposed on the base. A port is defined in one of the base and the lid. An acoustic transducer is disposed on the base or lid and separates a front volume of the microphone assembly from a back volume, the front volume being in fluid communication with the port. The acoustic transducer includes: a first diaphragm in which first wrinkles are formed; a second diaphragm having second corrugations formed therein, the second diaphragm being spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure lower than atmospheric pressure. The backplate is disposed in the cavity between the first diaphragm and the second diaphragm. One or more support posts extend from at least one of the first or second diaphragms toward the other of the first or second diaphragms through corresponding apertures defined in the backplate, the one or more support posts configured to prevent each of the first and second diaphragms from contacting the backplate as the first and/or second diaphragms move toward the backplate. Each of the first wrinkles and the second wrinkles protrudes outward from the first diaphragm and the second diaphragm, respectively, in a direction away from the backplate. An integrated circuit is electrically coupled to the acoustic transducer, the integrated circuit configured to measure a change in capacitance between the first diaphragm and the backplate and between the second diaphragm and the backplate in response to receiving an acoustic signal through the port, the change in capacitance corresponding to the acoustic signal.

In some embodiments, an acoustic transducer is provided that generates an electrical signal in response to an acoustic signal, the acoustic transducer including a first diaphragm having a first wrinkle formed therein. A second corrugation is formed in the second diaphragm, spaced apart from the first diaphragm, such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure lower than atmospheric pressure. The backplate is disposed in the cavity between the first diaphragm and the second diaphragm. One or more support posts extend from at least one of the first or second diaphragms toward the other of the first or second diaphragms through corresponding apertures defined in the backplate, the one or more support posts configured to prevent each of the first and second diaphragms from contacting the backplate as the first and/or second diaphragms move toward the backplate. A perimeter support structure is attached to and supports at least a portion of the perimeters (perimeters) of the first and second diaphragms, the perimeter support structure being positioned adjacent (proximate) edges of the first and second diaphragms. The acoustic transducer also includes a substrate defining a first aperture therein. A support structure is disposed on the substrate and defines a second opening corresponding to the first opening of the substrate, at least a portion of the first diaphragm being disposed on the support structure. Each of the first wrinkles and the second wrinkles protrudes outward from the first diaphragm and the second diaphragm, respectively, in a direction away from the backplate.

It should be clear that all combinations of the foregoing concepts and additional concepts discussed in more detail below (provided such concepts are not mutually inconsistent) are contemplated as part of the subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the subject matter disclosed herein.

Drawings

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. Understanding that these drawings depict only several implementations in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

Fig. 1A is a plan view of an acoustic transducer according to an embodiment, and fig. 1B is a side sectional view of the acoustic transducer of fig. 1A taken along the X-X line shown in fig. 1A.

Fig. 2A is a plan view of an acoustic transducer according to an embodiment, and fig. 2B is a side sectional view of the acoustic transducer of fig. 2A taken along the Y-Y line shown in fig. 2A.

Fig. 2C-2E are schematic illustrations of an acoustic transducer according to various embodiments.

Fig. 2F is a plan view of an acoustic transducer according to yet another embodiment, and fig. 2G is a side cross-sectional view of the acoustic transducer of fig. 2F taken along the Z-Z line shown in fig. 2F.

Fig. 3A is a side cross-sectional view of an acoustic transducer according to yet another embodiment.

Fig. 3B is an isometric top view of a portion of the acoustic transducer of fig. 3A.

Fig. 3C shows a portion of the acoustic transducer of fig. 3A, indicated by arrow a in fig. 3A, showing an aperture defined in the second diaphragm of the acoustic transducer and a catch structure positioned below the aperture.

Fig. 3D shows a portion of a second diaphragm of an acoustic transducer according to another embodiment, the portion showing a sealing aperture defined in the second diaphragm of the acoustic transducer.

Fig. 3E illustrates a portion of the acoustic transducer of fig. 3A, indicated by arrow B in fig. 3A, showing a stress relief structure, in accordance with an embodiment.

Fig. 3F illustrates a portion of an acoustic transducer including a first diaphragm and a second diaphragm, both including stress relief structures, in accordance with another embodiment.

Fig. 3G shows a portion of the second diaphragm of the acoustic transducer of fig. 3A, indicated by arrow C in fig. 3A.

Fig. 3H-3J illustrate portions of various acoustic transducers including perimeter support structures according to various embodiments.

Fig. 4 is a schematic illustration of a microphone assembly including the acoustic transducer of fig. 3, according to an embodiment.

Fig. 5 is a simplified circuit diagram of the microphone assembly of fig. 4 according to an embodiment.

Fig. 6 is a schematic illustration of a pressure sensing assembly including the acoustic transducer of fig. 3, according to an embodiment.

Fig. 7 is a simplified circuit diagram of the pressure sensing assembly of fig. 8, according to an embodiment.

Fig. 8 is a schematic flow diagram of a method of forming a dual-diaphragm acoustic transducer according to an embodiment.

Fig. 9 is a side cross-sectional view of an acoustic transducer according to another embodiment.

Fig. 10 is a side cross-sectional view of an acoustic transducer according to yet another embodiment.

The drawings are described throughout the following detailed description. In the drawings, like numerals generally identify like components, unless context dictates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not intended to be limiting. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure.

Detailed Description

Embodiments described herein relate generally to systems and methods for increasing compliance (compliance) of a top diaphragm and a bottom diaphragm and/or preventing collapse (collapse) of either or both diaphragms of a dual diaphragm acoustic transducer. In particular, some embodiments described herein relate to a dual-diaphragm acoustic transducer comprising: one or more outwardly facing corrugations (corrugation) for increased compliance, and/or one or more non-rigid (non-ribbed) connecting or non-anchored struts defined in the diaphragm that extend from at least one of the diaphragms to the other diaphragm to act as stoppers (stoppers) to prevent collapse of the diaphragms.

The dual diaphragm acoustic transducer includes a top diaphragm and a bottom diaphragm with a backplate interposed therebetween. The diaphragm may be sealed under reduced pressure to form a low pressure region between the top and bottom diaphragms that is at a pressure significantly below atmospheric pressure, e.g., in many cases a moderate vacuum in the range of about 1mTorr to 10Torr may be sufficient. The low pressure region significantly reduces the acoustic damping of the backplate (i.e. squeeze film damping), thereby reducing the gap between the diaphragm and backplate, reducing the perforations (penetrations), and may allow for very high sensing capacitance. Moreover, since the volume between the top and bottom diaphragms is sealed, particles (e.g., dust, water droplets, solder or component debris, etc.) cannot penetrate between the diaphragm and the backplate, which is a common cause of failure of a single-diaphragm acoustic transducer. Thus, in some dual-diaphragm acoustic transducer implementations disclosed herein, a protective mesh or membrane that prevents such particles from entering the single-diaphragm acoustic transducer, but that reduces the signal-to-noise ratio (SNR) may be eliminated.

A major challenge of dual diaphragm acoustic transducers is achieving sufficient compliance in the diaphragm. Atmospheric pressure acting on each of the diaphragms may create tension in the diaphragm, resulting in a significant reduction in compliance. Moreover, a sufficiently large pressure differential between the atmospheric pressure and the low pressure region between the two diaphragms may collapse the diaphragms, resulting in acoustic transducer failure.

In contrast, embodiments of the acoustic transducers described herein may provide benefits including, for example: (1) providing outwardly facing corrugations on each of a top diaphragm and a bottom diaphragm of the acoustic transducer to increase average compliance in a diaphragm region of the acoustic transducer; (2) preventing the first and second diaphragms from collapsing towards each other by providing non-rigid connecting and/or non-anchoring struts acting as stoppers, which protrude from at least one of the diaphragms towards the other diaphragm; (3) increasing the robustness of the diaphragm (robustness); and (4) provide increased compliance (e.g., more than 8 times increase at 100kPa pressure differential) relative to a similar acoustic transducer that does not include such wrinkles.

As described herein, the term "unanchored" when used in conjunction with a strut refers to a strut that extends from one diaphragm to another diaphragm of a dual-diaphragm acoustic transducer in such a manner that a gap or space exists between a tip of the strut and the corresponding diaphragm adjacent the tip. The tip is brought into contact with the respective diaphragm only when a sufficiently high force or pressure is applied to one or both of the diaphragms (e.g., ambient pressure or electrostatic force due to bias), so that the non-anchored support posts can slide and rotate relative to the respective diaphragm.

As described herein, the term "non-rigid connected" when used in conjunction with a post refers to a post that extends from one diaphragm to the other diaphragm of a dual diaphragm acoustic transducer in such a manner that the tip of the post is in permanent contact with the opposing diaphragm so as to allow the post to bend or rotate near or adjacent to the point of contact.

As described herein, the term "anchored" when used in conjunction with a strut refers to a strut that includes a tip that contacts an opposing diaphragm in a manner in which the anchor strut is immovable relative to the opposing diaphragm.

Fig. 1A is a plan view of an acoustic transducer 110 according to an embodiment. FIG. 1B is a side cross-sectional view of the acoustic transducer 110 taken along line X-X of FIG. 1A. The acoustic transducer 110 may include, for example: a MEMS acoustic transducer, a MEMS pressure sensor, or a combination thereof for use in a MEMS microphone assembly. The acoustic transducer 110 is configured to generate an electrical signal in response to an acoustic signal or a change in atmospheric pressure.

The acoustic transducer 110 includes a substrate 112 with a first aperture 113 defined in the substrate 112. In some embodiments, the substrate 112 may be formed of silicon, glass, ceramic, or any other suitable material. The support structure 114 is disposed above the substrate 112 and defines a second aperture 115, which second aperture 115 may be axially aligned with the first aperture 113. In various embodiments, the support structure 114 may be formed from glass (e.g., glass or glass having a phosphorous content, such as PSG). In some embodiments, apertures 113 and 115 may have the same cross-section (e.g., the same diameter). In other embodiments, apertures 113 and 115 may have different cross-sections (e.g., different diameters).

The acoustic transducer 110 includes: a bottom diaphragm or first diaphragm 120, a top diaphragm or second diaphragm 130, and a back plate 140 positioned between the first diaphragm 120 and the second diaphragm 130. Each of the first diaphragm 120, the second diaphragm 130, and the back plate 140 is disposed on the substrate 112. At least a portion of the first diaphragm 120 may be disposed on a support structure. In some embodiments, a portion of a radial edge of one or more of the first diaphragm 120, the second diaphragm 130, and the back plate 140 may be embedded within the support structure 114 during the manufacturing process of the acoustic transducer 110, such that forming the second aperture 115 in the support structure 114 results in each of the first diaphragm 120, the second diaphragm 130, and the back plate 140 being suspended in the second aperture 115 above the first aperture 113.

The diaphragms 120 and 130 may be formed of a conductive material or a sandwich of a conductive material and an insulating material. The material used to form the diaphragms 120 and 130 may include, for example, silicon oxide, silicon nitride, silicon carbide, gold, aluminum, platinum, and the like. In response to an acoustic signal received on one of the first or second diaphragms 120, 130, various vibrations (e.g., out of phase vibrations) of the diaphragms 120, 130 relative to the back-plate 140 that are substantially stationary (e.g., substantially non-flexing relative to the diaphragms 120, 130) result in changes in capacitance between the diaphragms 120 and 130 and the back-plate 140, and corresponding changes in the generated electrical signal.

In other embodiments, at least a portion of the first and second diaphragms 120, 130 may be formed using a piezoelectric material, such as quartz, lead titanate, group III-V and group II-VI semiconductors (e.g., gallium nitride, indium nitride, aluminum nitride, zinc oxide, etc.), graphene, ultra-nanocrystalline diamond, a polymer (e.g., polyvinylidene fluoride), or any other suitable piezoelectric material. For example, the piezoelectric material may be deposited as a ring around the perimeter (perimeter) of the first diaphragm 120 or the second diaphragm 130 on top of a base material (e.g., silicon nitride or polysilicon) forming the diaphragms 120 and 130. In such embodiments, the vibration of the diaphragm 120, 130 in response to the acoustic signal may generate an electrical signal (e.g., a piezoelectric current or voltage) representative of the acoustic signal. When operating as a pressure sensor, inward displacement of each of the diaphragms 120 and 130 toward each other as ambient pressure increases or outward displacement away from each other as ambient pressure decreases may generate an electrical signal corresponding to atmospheric pressure. In various embodiments, the first and second diaphragms 120, 130 may be formed of low stress silicon nitride (LSN) or any other suitable material (e.g., silicon oxide, silicon carbide, ceramic, etc.). Also, the backplate 140 may be formed of polysilicon (poly) and silicon nitride or any other suitable material (e.g., silicon oxide, silicon, ceramic, etc.).

The outer surface 123 of the first diaphragm 120 and the outer surface 133 of the second diaphragm 130 are exposed to an atmospheric environment (atmosphere), such as atmospheric air (atmospheric air). The second diaphragm 130 is spaced apart from the first diaphragm 120 such that a cavity or volume 121 is formed between the first diaphragm 120 and the second diaphragm 130. The cavity 121 has a pressure below atmospheric pressure, e.g., in the range of 1mTorr to 10 Torr; however, in some embodiments, limiting the pressure to a range of 1mTorr to 1Torr may provide particular benefits in terms of signal-to-noise ratio (SNR). The back plate 140 is arranged in the cavity 121 between the first diaphragm 120 and the second diaphragm 130. In some embodiments, one or more holes 142 may be defined in the backplate 140 such that a portion of the cavity 121 between the first diaphragm 120 and the backplate 140 is connected to a portion of the cavity 121 between the second diaphragm 130 and the backplate 140.

The large pressure difference between the atmospheric pressure acting on each of the first and second diaphragms 120, 130 and the low pressure in the cavity 121 places the first and second diaphragms 120, 130 in a continuously tensioned state. This significantly reduces the compliance of the diaphragms 120, 130. In order to increase the flexibility, first corrugations 122 and second corrugations 132 are formed on the first diaphragm 120 and the second diaphragm 130, respectively. The first corrugations 122 and the second corrugations 132 protrude outward from the diaphragms 120 and 130, respectively, in a direction away from the back plate 140.

For example, the diaphragms 120, 130 may include one or more circumferential corrugations (as best shown in fig. 1B) that serve to reduce tension and increase compliance in the first and second diaphragms 120, 130, respectively. Although illustrated as including a single wrinkle 122, 132, any number of wrinkles may be formed in the first and second diaphragms 120 and 130 (e.g., 2, 3, or even more wrinkles positioned circumferentially about the longitudinal axis of the acoustic transducer 110). In various embodiments, the height of the corrugations 122 and 132 may be in the range of 0.5 microns to 5 microns (e.g., 0.5 microns, 1 micron, 2 microns, 3 microns, 4 microns, or 5 microns, all ranges and values therebetween also included), and the spacing between the diaphragm 120 and the diaphragm 130 may be in the range of 1 micron to 15 microns (e.g., 1 micron, 2 microns, 3 microns, 5 microns, 7 microns, 9 microns, 12 microns, 14 microns, or 15 microns, all ranges and values therebetween also included).

The atmosphere exerts a force on each of the first and second diaphragms 120, 130 in a direction toward the backplate 140. Since the corrugations 122 and 132 project outwardly from the diaphragms 120 and 130, atmospheric pressure acting on the corrugations 122 and 132 causes the corrugations to flex axially inwardly and radially outwardly toward the backplate 140. This results in an increase in compliance which increases proportionally with a corresponding increase in atmospheric pressure. For example, in some implementations, the acoustic compliance of the acoustic transducer 110 in the region of the diaphragms 120 and 130 is about 2 times the acoustic compliance of a similar baseline acoustic transducer as follows: the baseline acoustic transducer does not include outwardly projecting corrugations 122 and 132 at about a zero pressure difference between atmospheric pressure and the pressure in the cavity 121. At a pressure differential of about 100kPa (which corresponds to an increase in acoustic compliance of over 13 dB), the compliance of the acoustic transducer 110 may increase to over 8 times the acoustic compliance of the baseline acoustic transducer. In this manner, the acoustic transducer 110 has significantly higher sensitivity to acoustic signals or for measuring pressure changes relative to the baseline acoustic transducer.

In some embodiments, the acoustic transducer 110, or any other acoustic transducer described herein, may be operated as a microphone and/or a pressure sensing component. In such an embodiment, atmospheric pressure acts on both diaphragms 120 and 130, and acoustic pressure acts on one of the diaphragms (e.g., on either diaphragm 120 or 130). The change in atmospheric pressure causes the capacitance value of each of the diaphragms 120 and 130 to change in the same direction, thereby generating a common mode signal for pressure sensing. In contrast, the sound pressure causes the two capacitance values to change in opposite directions, thereby generating a differential mode signal for sensing the sound pressure.

Fig. 2A is a plan view of an acoustic transducer 210a according to an embodiment. Fig. 2B is a side cross-sectional view of the acoustic transducer 210a taken along line Y-Y of fig. 2A. The acoustic transducer 210a may include, for example: a MEMS acoustic transducer, or a MEMS pressure sensor, for use in a MEMS microphone assembly. The acoustic transducer 210a is configured to generate an electrical signal in response to an acoustic signal or a change in atmospheric pressure.

The acoustic transducer 210a includes a substrate 212 with a first aperture 213 defined in the substrate 212. The support structure 214 is disposed above the substrate 212 and defines a second aperture 215, which second aperture 115 may be axially aligned with the first aperture 213. The base plate 212 and the support structure 214 may be substantially similar to the base plate 112 and the support structure 114 and, therefore, are not described in further detail herein.

The acoustic transducer 210a includes: a bottom diaphragm or first diaphragm 220, a top diaphragm or second diaphragm 230, and a back plate 240 positioned between the first diaphragm 220 and the second diaphragm 230. Each of the first diaphragm 220, the second diaphragm 230, and the back plate 240 may be formed of the same material as the first diaphragm 120, the second diaphragm 130, and the back plate 140. Outer surface 223 of first diaphragm 220 and outer surface 233 of second diaphragm 230 are exposed to an atmospheric environment (atmosphere), such as, for example, the atmosphere (atmospheric air). Also, the cavity 221 between the first diaphragm 220 and the second diaphragm 230 is at a pressure below atmospheric pressure, for example, in the range of 1mTorr to 10 Torr; however, in some embodiments, limiting the pressure to a range of 1mTorr to 1Torr may provide particular benefits in terms of signal-to-noise ratio (SNR). One or more holes 242 may be defined in the back plate 240 such that a first portion of the cavity 221 between the first diaphragm 220 and the back plate 240 is connected to a second portion of the cavity 221 between the second diaphragm 230 and the back plate 240.

A large pressure difference between the atmospheric pressure acting on each of the first and second diaphragms 220 and 230 and the low pressure in the cavity 221 may become large enough to cause the first and second diaphragms 220 and 230 to collapse. To prevent this from occurring, the second diaphragm 230 includes one or more posts 234a, the one or more posts 234a extending from the second diaphragm 230a toward the first diaphragm 220 through an aperture 242 defined in the backplate, or any other aperture defined in the backplate 240, a portion of the posts 234a being configured to contact the first diaphragm 220 in response to movement of the second diaphragm 230 toward the first diaphragm 220, and vice versa. For example, tips 235a of posts 234a are positioned adjacent to and spaced apart from first diaphragm 220 such that posts 234a become unanchored posts. In other words, tips 235a of posts 234a do not contact first diaphragm 220 at some pressure differentials, but may contact first diaphragm 220 at other pressure differentials to prevent diaphragms 220 and 230 from collapsing. In some embodiments, a default spacing between the tip 235a and the pillar 234a (e.g., when a pressure difference between a pressure inside the cavity 221 and a pressure of an external environment is about zero) may be in a range of 10nm to 2 microns. In some embodiments, one or more non-anchored struts may additionally or alternatively extend from the first diaphragm 220 toward the second diaphragm 230.

When one or both of diaphragms 220, 230 are displaced (e.g., flexed) toward each other due to an ambient pressure load or other loading force (e.g., electrostatic force), tips 235a of posts 234a contact the inner surface of first diaphragm 220 within cavity 221 to limit further displacement of diaphragms 220, 230 toward each other, at least at the locations of diaphragms 220 and 230 where posts 234a are located. In other words, the posts 234a act as stoppers or motion limiters that limit the displacement of the diaphragms 220 and 230 towards the back plate 240, for example due to a static deformation of the first diaphragm 220 and/or the second diaphragm 230 towards the back plate 240, which static deformation is caused by a large pressure difference between the cavity 221 and the external environment and/or vibrations of the diaphragms 220, 230. Portions of the diaphragms 220, 230 between adjacent struts 234a or between the struts 234a and the support structure 214 may still be displaced toward one another, but the smaller radial length of these portions may limit the displacement, thereby preventing collapse.

In some embodiments, if one or both of the diaphragms 220 or 230 deflect enough to contact the backplate 240, an over-pressure stop or ridge may be included in the area between the posts 234a to prevent an electrical short. For example, as shown in FIG. 2A, a first set of stubs (pilars) 227a extends from the first diaphragm 220 toward the back plate 240, and a second set of stubs 237a extends from the second diaphragm toward the back plate 240. The stubs 227a, 237a are formed of a non-conductive material (e.g., silicon oxide or silicon nitride) to prevent electrical shorting in the event that atmospheric pressure is high enough to cause the first diaphragm 220 and/or the second diaphragm 230 to contact the backplate 240. Although illustrated as stubs 227a, 237a, in other embodiments, the overpressure stop may comprise a bump or a depression defined on the first diaphragm 220 and/or the second diaphragm 230. In addition, an overpressure stopper may also be formed in the back plate 240. Alternatively, if the contact region is non-conductive (e.g., an opening in an electrode), the stubs 227a, 237a can be formed from a conductive material (e.g., doped polysilicon, metal, etc.). It should be understood that while fig. 2A illustrates the struts 234a as being vertically aligned with one another, in other embodiments, the struts 234a may be misaligned, staggered, or disposed at any other suitable location relative to one another. Further, although only three struts 234a are shown in fig. 2A, the acoustic transducer 210a or any other acoustic transducer defined herein may include a plurality of struts, e.g., greater than 10, 20, 30, 40, 50 struts, with all ranges and values therebetween also being encompassed. Moreover, although described as "struts," the struts 234a may comprise any suitable structure configured to provide separation of the first and second diaphragms 320, 330 from the backplate 340.

Fig. 2C is a schematic illustration of an acoustic transducer 210b according to another embodiment. The acoustic transducer 210b is substantially similar to the acoustic transducer 210a except for the following differences. The support 234b extends from the second diaphragm 230 toward the first diaphragm 220. Tips 235b of support posts 234b are positioned to contact first diaphragm 220. The shape of the strut 234b is such that it narrows (e.g., forms a cone) at or near the point of connection, so as to allow the strut to rotate or bend relative to the first diaphragm 220 at or near the point of connection (i.e., at the tip 235b of the strut 234 b). Thus, the strut 234b is a non-rigid connecting strut. In some embodiments, one or more non-rigid connecting struts may additionally or alternatively extend from the first diaphragm 220 toward the second diaphragm 230.

Fig. 2D is a schematic illustration of an acoustic transducer 210c according to yet another embodiment. Acoustic transducer 210c is otherwise generally similar to acoustic transducer 210a/b, except that post 234c, which extends from second diaphragm 230 toward first diaphragm 220, includes a flat tip 235c spaced from first diaphragm 220 (e.g., post 234c may be shaped as a truncated cone). Protrusions 237c (e.g., pins) extend from tip 235c and contact first diaphragm 220 such that posts 234c may rotate or flex at or near the point of attachment and thus non-rigidly connect to first diaphragm 220.

Fig. 2E is a schematic illustration of an acoustic transducer 210d according to yet another embodiment. The acoustic transducer 210d is substantially similar to the acoustic transducer 210a except for the following differences. The first pillar 224d extends from the first diaphragm 220 toward the second diaphragm 230, and includes a flat tip 225d (e.g., shaped like a truncated cone). Also, the second support 234d extends from the second diaphragm 230 toward the first support 224 d. The second leg 234d also includes a flat tip 235 d. The tips 225d/235d are positioned adjacent to each other but not in contact with each other, i.e., are non-anchoring struts. Tips 225d of posts 224d and tips 235d of posts and 234d may contact each other in response to movement of diaphragms 220 and 230 toward each other, respectively. In some embodiments, first leg 224d and second leg 234d may be substantially similar to each other in size and shape.

Fig. 2F is a plan view of an acoustic transducer 210e according to yet another embodiment. Fig. 2G is a side cross-sectional view of the acoustic transducer 210e taken along line Z-Z of fig. 2F. The acoustic transducer 210e includes a substrate 212 and a support structure 214. The acoustic transducer 210e also includes: a first diaphragm 220e, in which first wrinkles 222e are formed in the first diaphragm 220 e; and a second diaphragm 230e in which second wrinkles 232e are formed. The second diaphragm 230e is spaced apart from the first diaphragm 220e such that a cavity 221e is formed between the second diaphragm and the first diaphragm. The cavity 221e has a pressure below atmospheric pressure (e.g., in the range of 1mTorr to 10Torr, or 1mTorr to 1 Torr). The back plate 240e is disposed in the cavity 221e between the first diaphragm 220e and the second diaphragm 230 e.

Each of the first wrinkles 222e and the second wrinkles 232e protrudes outward from the first diaphragm 220e and the second diaphragm 230e, respectively. As shown in fig. 2G, corrugations 222e and 232e are closed circumferential structures disposed about a longitudinal axis of acoustic transducer 210e along which diaphragms 220e and 230e vibrate. The anchor posts 234e extend from the second diaphragm 230e toward the first diaphragm 220e through corresponding holes 242e defined in the backplate 240. Tips 235e of posts 234e are configured to contact first diaphragm 220e in response to movement of second diaphragm 230e toward first diaphragm 220e, and vice versa. Thus, the strut 234e is non-anchored. As shown in fig. 2G, the strut 234e is a dot structure. Although shown as including four struts 234e, any number of struts may be provided in the first diaphragm 220e and/or the second diaphragm 230 e. Out-of-plane struts 234e are not shown in fig. 2G for clarity. Moreover, the first diaphragm 220e and/or the second diaphragm 230e may also include non-rigid connecting struts and/or anchoring struts.

Fig. 3A is a side cross-sectional view of an acoustic transducer 310 according to yet another embodiment. Fig. 3B is an isometric top view of a portion of the acoustic transducer 310. The acoustic transducer 310 may include, for example: a MEMS acoustic transducer, or a MEMS pressure sensor, for use in a MEMS microphone assembly. The acoustic transducer 310 is configured to generate an electrical signal in response to an acoustic signal or a change in atmospheric pressure.

The acoustic transducer 310 includes a substrate 312 (e.g., a silicon, glass, or ceramic substrate), the substrate 312 defining a first opening 313 therein. The support structure 314 is disposed over the substrate 312 and defines a second aperture 315 through which second aperture 315 may be axially aligned with the first aperture 313 so as to define at least a portion of the acoustic path of the acoustic transducer 310. In various embodiments, support structure 314 may be formed from glass (e.g., glass having a phosphorous content). In some embodiments, the second aperture 315 may have the same cross-section (e.g., diameter) as the first aperture 313. In other embodiments, the second aperture 315 may have a larger or smaller cross-section relative to the first aperture 313.

The acoustic transducer 310 includes: a bottom or first diaphragm 320, and a top or second diaphragm 330 spaced from the first diaphragm 320, such that a cavity 341 is formed between the first and second diaphragms, the cavity 341 having a pressure below atmospheric pressure, for example, in a range of 1mTorr to 10Torr, or in a range of 1mTorr to 1 Torr. In the cavity 341, a back plate 340 is positioned between the first diaphragm 320 and the second diaphragm 330. The back plate 340 is anchored to the first diaphragm 320 and the second diaphragm 330 is anchored to the back plate 340 at corresponding edge anchors 343 and 333, respectively. The edge anchors 343 and 333 are radially offset from each other. It should be appreciated that the components included in the acoustic transducer 310 may have a circular cross-section as best shown in fig. 3B. At least a portion of first diaphragm 320 (e.g., adjacent to and radially inward from a first peripheral (perimidral) edge 321 of first diaphragm 320) is disposed on support structure 314. A first peripheral edge 321 of the first diaphragm 320 extends beyond the periphery of the support structure 314 and is coupled to the base plate 312. Also, the second peripheral edge 331 of the second diaphragm 330 extends toward and is coupled to the first peripheral edge 321. As shown in FIG. 3A, a portion 314a of the support structure 314 may be embedded in the volume between the edge anchors 333 and 343 and the second peripheral edge 331 of the second diaphragm 330.

A surface of each of the first and second diaphragms 320 and 330, which is located outside the cavity 341, is exposed to an atmospheric environment, such as the atmosphere. A plurality of holes 342 may be defined in the backplate 340 such that a portion of the cavity 341 between the first diaphragm 320 and the backplate 340 is connected to a second portion of the cavity 341 between the second diaphragm 330 and the backplate 340. Although shown as comprising a single layer, in various embodiments, the second diaphragm 330 may comprise multiple layers. For example, the second diaphragm 330 may include a first insulating layer (e.g., a silicon nitride layer) and a second conductive layer (e.g., a polysilicon layer).

In order to increase the flexibility, first corrugations 322 and second corrugations 332 are formed on the first diaphragm 320 and the second diaphragm 330, respectively. First corrugations 322 and second corrugations 332 project outward from diaphragms 320 and 330, respectively, in a direction away from back plate 340 (as previously described with reference to acoustic transducer 110), and aroundLongitudinal axis A of an acoustic transducer_LCircumferentially, as shown in fig. 3B. More than one corrugation may be defined in the first diaphragm 320 and the second diaphragm 330. In some implementations, the first corrugations 322 and the second corrugations 332 may be closer to the outer edges of the first diaphragm 320 and the second diaphragm 330 than the center points of the first diaphragm 320 and the second diaphragm 330. In other embodiments, the first corrugations 322 and/or the second corrugations 332 may be positioned closer to the longitudinal axis a than the outer edges of the first and second diaphragms 320 and 330_LOr equidistant from the outer edge and the longitudinal axis. Moreover, the first corrugations 322 and the second corrugations 332 may be relative to the longitudinal axis a of the acoustic transducer 310_LAxially aligned or axially offset from each other. In various embodiments, the height of the corrugations 322 and 332 may be in the range of 0.5 microns to 5 microns (e.g., 0.5 microns, 1 micron, 2 microns, 3 microns, 4 microns, or 5 microns, with all ranges and values therebetween also included), and the measured separation between the flat region of the diaphragm 320 and the flat region of the diaphragm 330 may be in the range of 1 micron to 15 microns (e.g., 1 micron, 2 microns, 3 microns, 5 microns, 7 microns, 9 microns, 12 microns, 14 microns, or 15 microns, with all ranges and values therebetween also included).

In order to prevent the first diaphragm 320 and the second diaphragm 330 from collapsing due to the large pressure difference between the atmosphere and the low pressure in the cavity 341, the second diaphragm 330 comprises a plurality of support posts 334, which plurality of support posts 334 extend from the second diaphragm towards the first diaphragm 320 through corresponding holes 342 in the back plate 340. The tips 335 of the support posts 334 are positioned adjacent to and spaced apart from the first diaphragm 320 such that the support posts 334 become unanchored. When one or both of the diaphragms 320 and 330 vibrate or are displaced (e.g., bend) toward each other, one or more of the tips 335 of the plurality of posts 334 contact an inner surface of the first diaphragm 320 within the cavity 341 to limit further displacement of the diaphragms 320, 330 toward each other, at least where the posts 334 are located, to prevent collapse of the diaphragms 320, 330, as previously described herein. In various embodiments, the average compliance of the acoustic transducer 310 in the region of the diaphragms 320 and 330 may be more than 8 times the average compliance of a similar acoustic transducer that does not include outward-facing corrugations and non-anchored struts. In some embodiments, the tip of each of the struts 334 may be coupled to the first diaphragm 320. The acoustic transducer 310 may include any number of struts 334, for example, in the range of 20 to 500 struts (e.g., 20, 25, 30, 35, 40, 45, 50, 100, 200, 300, 400, or 500 struts, inclusive). Moreover, although fig. 3A illustrates the struts 334 extending from the second diaphragm 330 toward the first diaphragm 320, in other embodiments, the struts may additionally or alternatively extend from the first diaphragm 320 toward the second diaphragm 330.

In some embodiments, anchor support 336 extends through a corresponding hole 342 in the backplate from the first diaphragm 320 toward the second diaphragm 330. The anchor strut 336 may extend from an inner edge (rim) of the first diaphragm 320 toward the second diaphragm 330. The apex 337 of the anchor support 336 contacts the first diaphragm 320 and is coupled to the first diaphragm such that the anchor support 336 is shaped as an inverted truncated cone. In other embodiments, the anchor posts may have any other suitable shape, such as, for example, a circular, square or rectangular cross-section, rounded S-shaped sidewalls, or any other suitable shape. A through-hole (pierce)324 is defined in the first diaphragm 320, and a through-hole 338 is defined through the apex 337. Through-hole 338 at least partially overlaps with perforations 324 (e.g., is axially aligned with perforations 324) and has the same cross-section (e.g., diameter) as perforations 324. In other embodiments, the cross-section of the through-hole 338 may be substantially larger than the cross-section (e.g., diameter) of the perforation 324. The perforations 324 and the through-holes 338 may allow pressure equalization between the front volume and the back volume of the acoustic transducer 310.

A plurality of openings 339 may also be formed in the second diaphragm 330. Now, referring also to fig. 3C, the plurality of apertures 339 are configured such that during a manufacturing process, an isotropic etchant (e.g., a wet etchant, such as buffered hydrofluoric acid) flows through the apertures to etch and remove portions of the support structure 314 that may be disposed between the first and second diaphragms 320, 330, thereby forming a cavity 341. An aperture 342 defined in the backplate 340 may also allow etchant to flow through the aperture and etch a portion of the support structure 314 that may be located between the backplate 340 and the first diaphragm 320. The plurality of openings 339 may be sealed, for example, with low stress silicon nitride (LSN). Fig. 3C shows a portion of the acoustic transducer 310 indicated by arrow a in fig. 3A, which shows one of the plurality of openings 339 defined in the second diaphragm 330 after being sealed with a plug 364 formed of a sealing material. A catch structure 366 is disposed below the opening 339 in the cavity 341 and is coupled to the second diaphragm 330. The catch structure 366 includes a ledge 367 that extends below the corresponding opening 339. The opening 399 may have a diameter large enough to allow the sealing material to pass through the opening and deposit on the ledge 367. The sealing material builds up on the ledge 367 and eventually forms a plug 364, which plug 364 seals the aperture 339. In some embodiments, the distance between the edge of the aperture 339 and the edge of the cross piece 367 may be in the range of 1um to 10um, and may be non-uniform across the device. By varying the distance between the edge of the opening 339 and the edge of the ledge 367, the etch rate of the structural material near the opening 339 may be adjusted.

In some embodiments, the plurality of apertures 339 defined in the second diaphragm 330 may be sealed without the use of the latching structure 366. For example, fig. 3D is a side cross-sectional view of a portion of an acoustic transducer according to yet another embodiment. This section shows a second diaphragm 330a of the acoustic transducer, showing an aperture 339a defined in the second diaphragm 330 a. The second diaphragm 330a is generally similar to the second diaphragm 330, except that an opening 339a defined therein has a size that is smaller than a similar opening 339 defined in the second diaphragm 330. The aperture 339a may be small enough to allow the sealing material to form a plug 364a around the aperture 339a without the use of a latching structure thereunder, as described with respect to the acoustic transducer 310. In some embodiments, the diameter or cross-section of the pores may be in the range of 50nm to 500 nm.

FIG. 3E shows an acoustic transducer 310, indicated by arrow B in fig. 3A, to illustrate a stress relief structure 350 formed adjacent to the perimeter edge 321 or perimeter of the first diaphragm 320. The stress relief structure 350 may be along the entire perimeter of the first diaphragm 320 (e.g., about the longitudinal axis a)_LIn the circumferential direction). In some other cases, the stress relief structure 350 may extend over only a portion of the perimeter of the first diaphragm 320.

Thickness T of stress relief structure 350_SRMay be greater than the thickness T of the first diaphragm 320 adjacent to the center of the first diaphragm 320_d. In some embodiments, the thickness of the stress relief structure 350 may be from the thickness T of the diaphragm 320_dInitially gradually increases to a thickness T_SR. For example, as shown in FIG. 3B, the thickness of the stress relief structure 350 increases with increasing distance from the center of the first diaphragm 320 until the thickness equals the thickness T_SR. That is, the thickness of the stress relief structure 350 increases according to the distance from the center of the first diaphragm 320.

In some embodiments, the stress relief structure 350 comprises a layer of a first type of material disposed between two layers of a second type of material. For example, as shown in fig. 3E, the stress relief structure 350 includes: a first diaphragm layer 356 embedded between the first diaphragm layer 352 and a second diaphragm layer 354 disposed over the first diaphragm layer, both formed of a second type of material. The diaphragm layers 352 and 354 may at least partially surround the first material layer 356. The first material may include one or more of silicon, silicon nitride, silicon oxynitride, glass with phosphorous content, PSG, and BPSG, or any other material used to form support structure 314. The second type of material may include silicon nitride (e.g., low stress silicon nitride). In other embodiments, the stress relief structure is formed entirely of silicon nitride. That is, the stress relief structure 350 may be a thicker portion of the first diaphragm 320.

The stress relieving feature 350 may reduce the risk of stress risers along the perimeter of the first diaphragm 320. In particular, large pressure transients impinging on first diaphragm 320 may result in increased mechanical stress along the perimeter of first diaphragm 320. This increase in stress increases the risk of cracking or distortion of the first diaphragm 320. The stress relief structure 350 reduces the risk of stress risers and, therefore, increases the robustness of the first diaphragm 320.

Although described with reference to the first diaphragm 320, in various embodiments, the second diaphragm 330 may also include a stress relief structure at its peripheral edge. For example, fig. 3F is a schematic illustration of an acoustic transducer 410 according to another embodiment. The acoustic transducer 410 includes a substrate 412 and a support structure 414. A cavity 441 is formed between the diaphragms 420 and 430 disposed on the substrate 412, the cavity 441 having a pressure lower than atmospheric pressure. Within the cavity 441, a back plate 440 is disposed between the first diaphragm 420 and the second diaphragm 430. Each of the diaphragms 420 and 430 includes outwardly projecting corrugations 422 and 432, as previously described herein. The back plate 440 is anchored to the first diaphragm 420 and the second diaphragm 430 is anchored to the back plate 440 at corresponding edge anchors 443 and 433, respectively. Similar to the acoustic transducer 410, the first diaphragm 420 includes a first stress relief structure 450 at its radial edge, the first stress relief structure 450 gradually increasing in thickness in a tapered manner toward the edge. The first stress relief structure 450 is substantially similar to the stress relief structure 350 previously described herein with reference to fig. 3A and 3E. Moreover, the second diaphragm 430 also includes a second stress relief structure 460 formed at a radial edge of the second diaphragm. The second stress relief structure 460 includes a layer 466 of a first type of material (e.g., PSG or BPSG), the layer 466 of the first type of material being embedded between a first diaphragm 462 and a second diaphragm layer 464 formed of a second type of material (e.g., silicon nitride or low stress nitride). A portion of the first diaphragm layer 462 forms an edge anchor and a portion of the second diaphragm layer 464 is disposed over the edge anchor 433 such that the edge anchor 433 is also embedded with the first type of material. Further expanded, the first diaphragm layer 462 and the second diaphragm layer 464 are disposed on each other to form the second diaphragm 430. The second diaphragm layer 464 is spaced apart from the first diaphragm layer 462 toward the edge of the second diaphragm 430 to form a stress relief structure 460. The tapered sidewall 465 couples the second diaphragm layer 464 to the first diaphragm layer 462.

Fig. 3G shows a portion of the acoustic transducer of fig. 3A indicated by arrow C in fig. 3A. The formation of the cavity 341 may involve: the radially inner side of the edge anchors 333 and 343 is etched of a structural material (e.g., PSG or BPSG, which may be part of the support structure layer forming the support structure 314) disposed between the first diaphragm 320 and the second diaphragm 330. In some embodiments, an isotropic etchant (e.g., a wet etchant) may be used, or the etching may be timed to etch substantially all of the structural material between diaphragm 320 and diaphragm 330 such that cavity 341 is substantially free of any structural material. The etchant enters the cavity 341 through the opening 339, which is then sealed as previously described herein.

In other embodiments, the etching may be timed such that a perimeter support structure is formed in the cavity 341. For example, fig. 3H is a side cross-sectional view of a portion of an acoustic transducer 310a according to another embodiment. The acoustic transducer 310a is substantially similar to the acoustic transducer 310. However, it differs from the acoustic transducer 310 in that a peripheral support structure 317 is formed at the radial edges of the first diaphragm 320 and the second diaphragm 330. Perimeter support structure 317a is attached to and supports at least a portion of the perimeters of first diaphragm 320 and second diaphragm 330, and is positioned within cavity 341 adjacent to the edges of first diaphragm 320 and second diaphragm 330. Perimeter support structure 317a includes: a first layer 317aa (e.g., a first glass portion having a phosphorus content in the range of 0.01 wt% to 10 wt%, such as PSG); and a second layer 317ab (e.g., a second glass portion having a phosphorus content in the range of 0.01 wt% to 10 wt%, such as a PSG portion), both of the first and second layers having the same impurity content (e.g., the same phosphorus content). For example, the etching of the structural material used to form support structure 314 can be performed for a predetermined time and can be stopped before edge anchors 333 and 343 are reached to form perimeter support structure 317 a.

In some embodiments, first, portions of the structural material adjacent to the aperture 339 are etched relative to portions away from the aperture 339 such that the radially inner side wall of the perimeter support structure 317a has a tapered profile. For example, as shown in FIG. 3H, the radially inner sidewalls of peripheral support structure 317a taper from second diaphragm 330 to backplate 340 and from backplate 340 to first diaphragm 320. In other embodiments, the first layer 317aa can have a first phosphorus content (e.g., in the range of 2% to 6%) and the second layer 317ab can have a second phosphorus content that is different from the first phosphorus content (e.g., in the range of 4% to 10%). This can result in uneven etching of the structural material, resulting in a tapered profile. Perimeter support structure 317a may increase the robustness of diaphragms 320 and 330.

In some embodiments, the perimeter support structure may include three or more layers. For example, fig. 3I is a schematic illustration of a portion of an acoustic transducer 310b according to yet another embodiment. Acoustic transducer 310b is substantially similar to acoustic transducer 310 a. Unlike acoustic transducer 310a, acoustic transducer 310b includes a perimeter support structure 317b, which perimeter support structure 317b includes: a first layer 317ba (e.g., a first glass, PSG, or BPSG portion) adjacent a radial edge of the first diaphragm 320; and a second layer 317bb (e.g., a second glass, PSG, or BPSG portion) adjacent a radial edge of the second diaphragm 330, both of which have a relatively low impurity content (e.g., a glass having a phosphorus content in the range of 2% to 4%). The perimeter support structure 317b also includes a third layer 317bc (e.g., a third glass, PSG, or BPSG portion) disposed between the first layer 317ba and the second layer 317bb by 317 bc. The third layer 317bc has a higher impurity content (e.g., glass having a phosphorus content in the range of 4% to 10%) relative to the first layer 317ba and the second layer 317 bb. The etching of the structural material layer may be performed for a predetermined time to stop before reaching the edge anchors 333 and 343 to form the perimeter support structures 317 b. The first 317ba and second layer 317bb, which have a lower impurity content, are etched more slowly than the third layer 317bc, so that the inner sidewalls of each of the first 317ba and second 317bb taper radially inward from the third layer 317bc toward the diaphragms 320 and 330, respectively. This may further increase the robustness of each of the first diaphragm 320 and the second diaphragm 330. In some embodiments, the impurity content within one or more of the layers 317ba/317bb/317bc may also vary along the height of the layer.

Fig. 3J is a side cross-sectional view of a portion of an acoustic transducer 310c according to yet another embodiment. The acoustic transducer 310c includes a first diaphragm 320 disposed on a substrate 312. The second diaphragm 330c is spaced apart from the first diaphragm 320 such that a cavity 341c is formed between the second diaphragm and the first diaphragm, and the pressure of the cavity 314c is lower than the atmospheric pressure. Inside the cavity 341c, a back plate 340c is disposed between the first diaphragm 320 and the second diaphragm 330 c. The difference from the second diaphragm 330 and the backplate 340 is that the second diaphragm 330c and the backplate 340c do not include edge anchors. And, conversely, a perimetric edge 331c of the second diaphragm 330c extends toward and is coupled to a perimetric edge 321 of the first diaphragm 320. In the cavity, a perimeter support structure 317c is disposed above first diaphragm 320 adjacent to a perimeter edge 331c of second diaphragm 330 c. The perimeter of back plate 340c is embedded in perimeter support structure 317 c. Perimeter support structure 317c may comprise a single layer having a single phosphorous content, a variable phosphorous content, or comprise multiple layers, wherein the phosphorous content of each layer is the same or different.

In some implementations, the acoustic transducer 310 can be included in a microphone assembly. For example, fig. 4 is a schematic illustration of a microphone assembly 300a according to an embodiment. The microphone assembly 300a may comprise a MEMS microphone assembly. Microphone assembly 300a may be used to convert acoustic signals into electrical signals in any device, such as, for example, a cellular telephone, a laptop computer, a television remote control, a tablet computer, an audio system, headphones, a wearable device, a portable speaker, an automobile sound system, or any other device that uses a microphone assembly.

Microphone assembly 300a includes a base 302 having a port 304 or sound hole (sound port) defined therein such that microphone assembly 300a is a bottom port microphone assembly. The lid 306 rests on the base 302 and defines an interior volume within which an acoustic transducer 310 and an integrated circuit 308a are disposed. In other embodiments, the port 304 may be defined in the lid 306 rather than in the base 302, such that the microphone assembly 300 comprises a top-port microphone assembly. The lid 306 may be formed from a suitable material, such as, for example, a metal (e.g., aluminum, copper, stainless steel, etc.), a plastic, a polymer, etc., and may be coupled to the base 302, e.g., via an adhesive, solder, or welded thereto. In some embodiments, lid 306 may be a composite of metal and plastic, for example, metal with insert molded or over molded plastic.

The base 302 may be formed of a material (e.g., plastic) used in Printed Circuit Board (PCB) manufacturing. For example, the substrate may include a PCB configured to mount the acoustic transducer 310, the integrated circuit 308a, and the cover 306 thereon. An acoustic transducer 310 is disposed on the port 304 and is configured to generate an electrical signal in response to an acoustic signal. The acoustic transducer 310 separates a front volume 305 of the microphone assembly from a back volume 307, the front volume 305 being in fluid communication with the port 304. For example, the substrate 312 may be positioned on the base 302 around the port 304 such that the aperture 313 of the substrate 302 is axially aligned with the port 304. The bottom diaphragm 320 may be positioned facing the port 304 to receive an acoustic signal through the port 304 via the front volume 305. The top diaphragm 330 faces the back volume 307. Perforations 324 in the diaphragm 320 allow for equalization of air pressure between the front volume 305 and the back volume 307.

In fig. 4, the acoustic transducer 310 and the integrated circuit 308a are shown disposed on a surface of the base 302, but in other implementations, one or more of these components may be disposed on a side wall of the cover 306 (e.g., on an inner surface of the cover 306) or stacked on top of each other on the cover 306. In some implementations, the base 302 can include an external device interface having a plurality of contacts coupled to the integrated circuit 308, such as to connection pads (e.g., solder pads) that can be disposed on the integrated circuit 308 a. In some implementations, the integrated circuit 308a is an Application Specific Integrated Circuit (ASIC). The contacts may be embodied as pins, pads, bumps, or balls, among other known or future mounting structures. The function and number of contacts on the external device interface depends on the protocol or protocols implemented and may include power, ground, data, and clock contacts, among others. The external device interface permits the microphone assembly 300 to be integrated with a host device using reflow soldering, fusion splicing, or other assembly processes.

The integrated circuit 308a is electrically coupled to the acoustic transducer 310, for example, via electrical leads, and may also be coupled to the base 302 (e.g., to traces or other electrical contacts disposed on the base 302). The integrated circuit 308a receives the electrical signal from the acoustic transducer 310 and may amplify and condition the signal before outputting a digital or analog acoustic signal. Integrated circuit 308a may also include a protocol interface (not shown) according to a desired output protocol. Microphone assembly 300a may also be configured to permit programming or querying of the microphone assembly as described herein. Exemplary protocols include, but are not limited to, PDM, PCM, SoundWire, I2C, I2, and SPI, among others.

The microphone assembly 300a may include an external device interface (i.e., an electrical interface) having a plurality of electrical contacts (e.g., power, ground, data, clock) that are electrically integrated with a host device. An external device interface may be disposed on an outer surface of the base 302 and configured to reflow soldering (reflow) to a host device. Alternatively, the interface may be provided on some other surface of the base 302 or the lid 306. Integrated circuit 308a may be covered by an encapsulation material, which may have electrical insulation, electromagnetic shielding, and thermal shielding properties. The integrated circuit 308a receives the electrical signal from the acoustic transducer 310 and may amplify or condition the signal before outputting a digital or analog acoustic signal. For example, the integrated circuit 308a may receive an electrical signal from the acoustic transducer 310 that has a characteristic (e.g., a voltage) that changes in response to a change in capacitance of the acoustic transducer 310 (e.g., a change in capacitance between the diaphragms 320, 330 and the back plate 340 of the acoustic transducer 310); or receive a piezoelectric current representing an acoustic signal from the acoustic transducer 310.

FIG. 5 is a microphone setA simplified circuit diagram of element 300 a. Diaphragms 320 and 330 are at bias voltage V_biasThe lower is biased. In some embodiments, unequal biases may be applied to the capacitance formed by each diaphragm 320 and 330. The change in capacitance of the second diaphragm 330 is out-of-phase with the change in capacitance of the first diaphragm 320 because the acoustic signal impinges on the first diaphragm 320 only after entering the port 304. The mechanical coupling of diaphragms 320 and 330 through the struts causes diaphragms 320, 330 to vibrate in unison so that the diaphragms can be modeled as out-of-phase capacitors. Integrated circuit 308a may include an analog buffer stage to amplify the electrical signals received from diaphragms 320 and 330. Integrated circuit 308a may also include analog-to-digital conversion (ADC) circuitry, such as a sigma-delta modulator (e.g., Σ Δ in fig. 5). However, this process may be performed in the analog domain, so that ADCs may be eliminated. The resultant electrical signal received from integrated circuit 308a is indicative of the acoustic signal detected by acoustic transducer 310.

In some embodiments, the acoustic transducer 310 may be used in a pressure sensing assembly. For example, fig. 6 shows a pressure sensing assembly 300b, the pressure sensing assembly 300b including an acoustic transducer 310 disposed on a base 302, and including a lid 306 and an integrated circuit 308b (e.g., ASIC). However, both the front volume 305 and the back volume 307 of the acoustic transducer 310 may be open to atmospheric or ambient pressure (e.g., via pressure equalization through the perforations 324). This causes ambient or atmospheric pressure to act equally on each of the first and second diaphragms 320, 330 so that the diaphragms 320, 330 experience common-mode or in-phase changes in capacitance due to deflection or bending of the diaphragms 320, 330 in the region between the struts.

Fig. 7 is a simplified circuit diagram of a pressure sensing assembly 300 b. Diaphragms 320 and 330 are at bias voltage V_biasThe lower is biased. In some embodiments, unequal biases may be applied to the capacitances formed by the respective diaphragms. The capacitance change of the second diaphragm 330 is in phase with the change in atmospheric pressure equally acting on each of the diaphragms 320 and 330, so that the diaphragms can be modeled as in-phase capacitances. Integrated circuit 308b may include an analog buffer stage to amplify the electrical signals received from diaphragms 320 and 330. Integrated circuit 308b may also include analog-to-digital conversion (ADC) circuitry, such as a sigma-delta modulator (e.g., Σ Δ in fig. 7). However, this process may be performed in the analog domain, so that ADCs may be eliminated. The integrated circuit 308b may also include a Low Pass Filter (LPF), for example, to reduce noise and/or isolate atmospheric pressure variations from acoustic signals. The resultant electrical signal received from integrated circuit 308b is indicative of the atmospheric pressure detected by acoustic transducer 310.

Fig. 8 is a schematic flow diagram of an example method 500 of manufacturing an acoustic transducer (e.g., acoustic transducer 110, 210e, 310a/310b/310c, 410), according to an embodiment. The method comprises the following steps: at 502, a substrate is provided. The substrate may include, for example: substrate 112, 212, 312, 412, and may be formed of silicon, silicon oxide, glass, ceramic, or any other suitable material.

At 504, a first diaphragm is formed over the substrate such that the first diaphragm is attached to the substrate at a perimeter thereof. The first diaphragm (e.g., first diaphragm 120, 220e, 320, 420) has outward-facing corrugations extending toward the substrate. The first diaphragm may be formed of a low stress material, such as LSN, low stress ceramic or polysilicon.

At 506, a backplate (e.g., backplate 140, 240e, 340c, 440) is formed spaced apart from the first diaphragm in a direction away from the substrate. The backplate material may be substantially inflexible with respect to the first and second diaphragm materials and may, for example, comprise a multi/SiN/multi (poly/SiN/poly) layer stack or other conductor/insulator/conductor layer stack. The backplate may also be formed from a single layer of conductive material such as polysilicon. In some embodiments, a plurality of holes are also formed through the backing plate.

At 508, a second diaphragm (e.g., second diaphragm 130, 230e, 330a, 330c, 430) is formed spaced apart from the backplate in a direction away from the substrate and attached to the substrate at a perimeter of the second diaphragm. The second diaphragm may also be formed of a low stress material, such as LSN, low stress ceramic or polysilicon. In some embodiments, the step of forming the second diaphragm may further include: at 510, struts (e.g., struts 234a, 234b, 234c, 234d, 334) are formed that extend from the second diaphragm toward the first diaphragm. A portion of the post is positioned adjacent to the other diaphragm (e.g., spaced apart from the other diaphragm by a distance of 50nm to 2 microns in a default position, as previously described herein) and is configured to contact the other diaphragm in response to movement of at least one of the first and second diaphragms toward the other diaphragm so as to prevent the first and second diaphragms from collapsing at atmospheric pressure.

In some embodiments, the step of forming the second diaphragm may further include: anchor posts (e.g., anchor posts 336) are formed that extend from the first diaphragm toward the second diaphragm through corresponding holes in the backplate, the apexes of the anchor posts contacting and being coupled to the other diaphragm. A through hole may be defined through the apex and a perforation may be defined in the second diaphragm at least partially overlapping the through hole to equalize pressure between the front and back cavity volumes of the acoustic transducer. In various embodiments, the vias and through holes may be formed by a Deep Reactive Ion Etching (DRIE) process.

At 512, a cavity is formed between the first diaphragm and the second diaphragm by using isotropic etching to remove structural material from between the first diaphragm and the second diaphragm. In some embodiments, the backplate defines at least one aperture therethrough such that a first portion of the cavity between the first diaphragm and the backplate is connected to a portion of the cavity between the second diaphragm and the backplate. In some embodiments, openings are defined in the second diaphragm, for example, openings 339, 339a may be defined in the second diaphragm 330, 330a via a wet or dry etching process. The openings may allow the isotropic etchant to contact and etch a structural material (e.g., a portion of the support structure) disposed between the first diaphragm and the second diaphragm, thereby forming the cavity.

In some embodiments, the structural material (e.g., glass with a phosphorous content in the range of 0.01 wt% to 10 wt%, such as PSG) may be etched such that a portion of the support structure remains attached to and supports at least a portion of the perimeter of the first and second diaphragms above the substrate. Within the cavity, a perimeter support structure is positioned adjacent to edges of the first and second diaphragms.

At 514, a sealing layer (e.g., low stress silicon nitride, metal, etc.) is deposited using a low pressure deposition process (e.g., LPCVD, PECVD, ALD, sputtering, or evaporation) to seal the openings (e.g., openings 339, 339a) with plugs (e.g., plugs 364, 364 a). This operation seals the cavity at a pressure less than atmospheric pressure (e.g., in the range of 1mTorr to 10Torr, or in the range of 1mTorr to 1 Torr).

At 516, an opening (e.g., opening 313) is formed in a substrate (e.g., substrate 312) by etching through the substrate, for example, using a Deep Reactive Ion Etch (DRIE) process. In some embodiments, additional etching (e.g., wet etching using buffered hydrofluoric acid) may occur to define the location of the support structures 314, 414. In some embodiments, the opening in the substrate may be formed prior to forming the cavity between the first and second diaphragms and prior to sealing the cavity at a pressure less than atmospheric pressure (e.g., operation 516 may occur prior to operation 514 or prior to operation 512).

Fig. 9 is a side cross-sectional view of an acoustic transducer 610 according to yet another embodiment. The acoustic transducer 610 may comprise, for example, a MEMS acoustic transducer or a MEMS pressure sensor for use in a MEMS microphone assembly. The acoustic transducer 610 is configured to generate an electrical signal in response to an acoustic signal or a change in atmospheric pressure. The acoustic transducer 610 is similar to the acoustic transducer 310, but with some differences described herein.

The acoustic transducer 610 includes a substrate 312 (e.g., a silicon, glass, or ceramic substrate) having a first opening 313 defined therein. However, it differs from the acoustic transducer 310 in that the support structure 614 is disposed above the substrate 312 and defines a second aperture 315 through which the second aperture 315 may be axially aligned with the first aperture 313 so as to define at least a portion of the acoustic path of the acoustic transducer 310. The support structure 614 includes: support structure first layer 615, support structure second layer 616, and support structure third layer 617. In some embodiments, the support structure first layer 615 comprises silicon oxide (e.g., thermal silicon oxide) having a thickness in the range of 300nm to 900nm (e.g., 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, or 900nm inclusive). In some embodiments, support structure second layer 616 comprises a glass having a phosphorus content in the range of 6 wt% to 8 wt% (e.g., 6 wt%, 7 wt%, or 8 wt% (inclusive)). For example, the glass may comprise phosphosilicate glass. In some embodiments, the support structure third layer 617 comprises silicon oxide { e.g., deposited by Low Pressure Chemical Vapor Deposition (LPCVD) } and has a thickness in the range of 400nm to 700nm (e.g., 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, or 700nm, inclusive).

The acoustic transducer 610 includes a bottom or first diaphragm 620 and a top or second diaphragm 330 spaced apart from the first diaphragm 620 such that a cavity 341 is formed between the first and second diaphragms, the cavity 341 having a pressure below atmospheric pressure, e.g., in the range of 1mTorr to 10Torr, or in the range of 1mTorr to 1 Torr. The difference from the first diaphragm 320 is that the first diaphragm 620 does not include a stress relief structure.

In the cavity 341, the back plate 340 is located between the first diaphragm 620 and the second diaphragm 630. At least a portion of the first diaphragm 620 is disposed on the support structure 614 (e.g., adjacent to and radially inward from a first peripheral edge 621 of the first diaphragm 620). A first peripheral edge 621 of the first diaphragm 620 extends beyond the periphery of the support structure 614 and is coupled to the substrate 312. Also, the second peripheral edge 331 of the second diaphragm 330 extends toward the first peripheral edge 621 and is coupled to the first peripheral edge 621.

A surface of each of the first and second diaphragms 620 and 330, which is located outside the cavity 341, is exposed to an atmospheric environment, for example, the atmosphere. A plurality of holes 342 may be defined in the back plate 340 such that a portion of the cavity 341 between the first diaphragm 620 and the back plate 340 is connected to a second portion of the cavity 341 between the second diaphragm 330 and the back plate 340. Each of the first and second diaphragms 620 and 330 includes outwardly protruding corrugations 622 and 332, respectively, as previously described herein. In various embodiments, the height of corrugations 622 and 332 may be in the range of 0.5 microns to 5 microns (e.g., 0.5 microns, 1 micron, 2 microns, 3 microns, 4 microns, or 5 microns, with all ranges and values therebetween also included), and the measured separation between the flat region of diaphragm 620 and the flat region of diaphragm 330 may be in the range of 1 micron to 15 microns (e.g., 1 micron, 2 microns, 3 microns, 5 microns, 7 microns, 9 microns, 12 microns, 14 microns, or 15 microns, with all ranges and values therebetween also included). It will be appreciated that the corrugations 322, 622 are circumferential and may include a plurality of corrugations.

The second diaphragm 330 includes a plurality of support posts 334, the plurality of support posts 334 extending from the second diaphragm 330 toward the first diaphragm 620 through corresponding holes 342 in the backplate 340. In other embodiments, the strut 334 may extend from the first diaphragm 620 toward the second diaphragm 330. The anchor support 336 extends from the first diaphragm 620 towards the second diaphragm 330 through a corresponding hole 342 in the backplate. A through hole 324 is defined in the first diaphragm 620 and a through hole 338 is defined through the apex 337. Through-hole 338 at least partially overlaps with perforations 324 (e.g., is axially aligned with perforations 324) and may have the same or different cross-section (e.g., diameter) as perforations 324.

A plurality of openings 339 may also be formed in the second diaphragm 330 such that an isotropic etchant (e.g., a wet etchant, such as buffered hydrofluoric acid) flows through the openings to etch and remove a portion of the support structure 314, as previously described herein. The plurality of openings 339 may be sealed, for example, with low stress silicon nitride (LSN). The catch structure 366 is disposed below the aperture 339 in the cavity 341 and is coupled to the second diaphragm 330 as previously described herein. In some embodiments, the latch stop structure 366 can be formed from a conductive material (e.g., polysilicon). The layer used to form the latch structure 366 may double as the top diaphragm electrode. In some embodiments, the plurality of apertures 339 defined in the second diaphragm 330 may be sealed without the use of the latching structure 366.

As shown in FIG. 9, a second support structure 624 and a third support structure 634 may be embedded in the volume between the edge anchors 333 and 343 and the second peripheral edge 331 of the second diaphragm 330. The second support structure 624 is disposed between the first diaphragm 620 and the backplate 340, and includes: a second support structure first layer 625, a second support structure second layer 626, and a second support structure third layer 627. In some embodiments, the second support structure first layer 625 comprises silicon oxide (e.g., LPCVD thermal silicon oxide) having a thickness in the range of 400nm to 700nm (e.g., 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, or 700nm inclusive). In some embodiments, the second support structure second layer 626 comprises glass having a phosphorous content in a range of 6 wt% to 8 wt% (e.g., 6 wt%, 7 wt%, or 8 wt%, inclusive) and a thickness in a range of 1,000nm to 2,000nm (e.g., 1,000nm, 1,100nm, 1,200nm, 1,300nm, 1,400nm, 1,500nm, 1,600nm, 1,700nm, 1,800nm, 1,900nm, or 2,000nm, inclusive). In some embodiments, the second support structure third layer 627 further includes glass having a phosphorous content in the range of 3 wt% to 6 wt% (e.g., 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%, inclusive) and a thickness in the range of 1,000nm to 2,000nm (e.g., 1,000nm, 1,100nm, 1,200nm, 1,300nm, 1,400nm, 1,500nm, 1,600nm, 1,700nm, 1,800nm, 1,900nm, or 2,000nm, inclusive)).

The third support structure 634 is disposed between the second diaphragm 330 and the backplate 340, and includes: a third support structure first layer 635, a third support structure second layer 636, and a third support structure third layer 637. In some embodiments, the third support structure first layer 635 further comprises a glass having a phosphorous content in a range of 3 wt% to 6 wt% (e.g., 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%, inclusive) and a thickness in a range of 500nm to 1,000nm (e.g., 500nm, 600nm, 700nm, 800nm, 900nm, or 1,000nm, inclusive). In some embodiments, the third support structure second layer 636 comprises a glass having a phosphorous content in a range of 6 wt% to 8 wt% (e.g., 6 wt%, 7 wt%, or 8 wt%, inclusive) and a thickness in a range of 2,000nm to 4,000nm (e.g., 1,000nm, 2,200nm, 2,400nm, 2,600nm, 2,800nm, 3,000nm, 3,200nm, 3,400nm, 3,800nm, or 4,000nm, inclusive). In some embodiments, the third support structure third layer 637 further comprises glass having a phosphorus content in the range of 3 wt% to 6 wt% (e.g., 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%, inclusive) and a thickness in the range of 1,000nm to 2,000nm (e.g., 1,000nm, 1,100nm, 1,200nm, 1,300nm, 1,400nm, 1,500nm, 1,600nm, 1,700nm, 1,800nm, 1,900nm, or 2,000nm, inclusive)).

Fig. 10 is a side cross-sectional view of an acoustic transducer 710 according to yet another embodiment. The acoustic transducer 710 may comprise, for example, a MEMS acoustic transducer or a MEMS pressure sensor for use in a MEMS microphone assembly. The acoustic transducer 710 is configured to generate an electrical signal in response to an acoustic signal or a change in atmospheric pressure.

The acoustic transducer 710 includes a substrate 312 (e.g., a silicon substrate, a glass substrate, or a ceramic substrate) having a first opening 313 defined in the substrate 312. The support structure 614 previously described herein with reference to fig. 9 is disposed above the substrate 312 and defines a second aperture 315 through which second aperture 315 may be axially aligned with the first aperture 313 so as to define at least a portion of the acoustic path of the acoustic transducer 710.

The acoustic transducer 710 includes: a bottom or first diaphragm 620 as previously described herein with reference to FIG. 9; and a top or second diaphragm 730 spaced apart from the first diaphragm 620 such that the following cavities 741 are formed therebetween: the cavity is at a pressure below atmospheric pressure, for example, in the range of 1mTorr to 10Torr, or in the range of 1mTorr to 1 Torr.

In the cavity 741, the back plate 740 is located between the first diaphragm 620 and the second diaphragm 730. At least a portion of the first diaphragm 620 is disposed on the support structure 614 (e.g., adjacent to and radially inward from a first peripheral edge 621 of the first diaphragm 620). A first peripheral edge 621 of the first diaphragm 620 extends beyond the periphery of the support structure 614 and is coupled to the substrate 312. Also, the second peripheral edge 737 of the second diaphragm 730 extends toward and is coupled to the first peripheral edge 621.

A surface of each of the first and second diaphragms 620 and 730, which is located outside the cavity 741, is exposed to an atmospheric environment, such as the atmosphere. A plurality of holes 742 may be defined in the back plate 740 such that a portion of the cavity 741 between the first diaphragm 620 and the back plate 740 is connected to a second portion of the cavity 741 between the second diaphragm 730 and the back plate 740. Each of the first and second diaphragms 620 and 730 includes outwardly protruding corrugations 622 and 732, respectively, as previously described herein. In various embodiments, the height of the corrugations 622 and 732 may be in the range of 0.5 microns to 5 microns (e.g., 0.5 microns, 1 micron, 2 microns, 3 microns, 4 microns, or 5 microns, with all ranges and values therebetween also included), and the measured separation between the flat region of the diaphragm 620 and the flat region of the diaphragm 730 may be in the range of 1 micron to 15 microns (e.g., 1 micron, 2 microns, 3 microns, 5 microns, 7 microns, 9 microns, 12 microns, 14 microns, or 15 microns, with all ranges and values therebetween also included). It should be appreciated that the wrinkles 622, 732 are circumferential and may include a plurality of wrinkles.

The second diaphragm 730 includes a plurality of support legs 754, and the plurality of support legs 754 extend from the second diaphragm 730 toward the first diaphragm 620 through corresponding holes 742 in the backplate 740. In other embodiments, the support 754 may extend from the first diaphragm 620 toward the second diaphragm 730. Anchor struts 756 extend from the first diaphragm 620 toward the second diaphragm 730 through corresponding holes 742 in the backplate 740. A through-hole 324 is defined in the first diaphragm 720 and a through-hole 738 is defined through the apex 737 of the anchor post 756. Through-hole 738 at least partially overlaps perforation 324 (e.g., is axially aligned with perforation 324) and may have the same or a different cross-section (e.g., diameter) than perforation 324.

A plurality of openings 739 may also be formed in the second diaphragm 730 such that an isotropic etchant (e.g., a wet etchant, such as buffered hydrofluoric acid) flows through the openings to etch and remove a portion of the sacrificial layer that may be disposed in the cavity 741, as previously described herein. The plurality of openings 739 may be sealed, for example, with low stress silicon nitride (LSN). A catch structure 766 is disposed below the aperture 739 in the cavity 741 and is coupled to the second diaphragm 730 as previously described herein. In some embodiments, the plurality of openings 739 defined in the second diaphragm 730 may be sealed without the use of the latching structure 766. In some embodiments, the catch structure 766 may be formed of a conductive material (e.g., polysilicon). The layer for forming the latch structure 766 may double as an electrode of the second diaphragm 730.

The difference with the second diaphragm 330 and the backplate 340 is that the second diaphragm 730 and the backplate 740 do not include edge anchors. Instead, the peripheral edge 731 of the second diaphragm 730 extends toward and is coupled to the peripheral edge 721 of the first diaphragm 620. In the cavity 741, the first perimeter support structure 324 is disposed between the first diaphragm 620 and the back plate 740 adjacent the perimeter edge 737 of the second diaphragm 730; and a second perimeter support structure 734 is disposed between the second diaphragm 730 and the back plate 740 adjacent the perimeter edge 737 of the second diaphragm 730, within the cavity 741.

The first perimeter support structure 324 includes: first perimeter support structure first layer 725, first perimeter support structure second layer 726, and first perimeter support structure third layer 727. In some embodiments, first perimeter support structure first layer 725 comprises silicon oxide (e.g., LPCVD thermal silicon oxide) having a thickness in the range of 400nm to 700nm (e.g., 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, or 700nm inclusive). In some embodiments, first perimeter support structure second layer 726 comprises a glass having a phosphorous content in a range of 6 wt% to 8 wt% (e.g., 6 wt%, 7 wt%, or 8 wt%, inclusive) and a thickness in a range of 1,000nm to 2,000nm (e.g., 1,000nm, 1,100nm, 1,200nm, 1,300nm, 1,400nm, 1,500nm, 1,600nm, 1,700nm, 1,800nm, 1,900nm, or 2,000nm, inclusive). In some embodiments, the first perimeter support structure third layer 727 further comprises a glass having a phosphorus content in the range of 3 wt% to 6 wt% (e.g., 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%, inclusive) and a thickness in the range of 1,000nm to 2,000nm (e.g., 1,000nm, 1,100nm, 1,200nm, 1,300nm, 1,400nm, 1,500nm, 1,600nm, 1,700nm, 1,800nm, 1,900nm, or 2,000nm, inclusive).

Second perimeter support structure 734 includes: a second perimeter support structure first layer 735, a second perimeter support structure second layer 736, and a second perimeter support structure third layer 737. In some embodiments, second perimeter support structure first layer 735 further comprises a glass having a phosphorous content in the range of 3 wt.% to 6 wt.% (e.g., 3 wt.%, 3.5 wt.%, 4 wt.%, 4.5 wt.%, 5 wt.%, 5.5 wt.%, or 6 wt.%, inclusive) and a thickness in the range of 500nm to 1,000nm (e.g., 500nm, 600nm, 700nm, 800nm, 900nm, or 1,000nm, inclusive). In some embodiments, the second perimeter support structure second layer 736 comprises a glass having a phosphorus content in the range of 6 wt% to 8 wt% (e.g., 6 wt%, 7 wt%, or 8 wt%, inclusive) and a thickness in the range of 2,000nm to 4,000nm (e.g., 1,000nm, 2,200nm, 2,400nm, 2,600nm, 2,800nm, 3,000nm, 3,200nm, 3,400nm, 3,800nm, or 4,000nm, inclusive). In some embodiments, the second perimeter support structure third layer 737 further comprises a glass having a phosphorus content in the range of 3 wt% to 6 wt% (e.g., 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, or 6 wt%, inclusive) and a thickness in the range of 1,000nm to 2,000nm (e.g., 1,000nm, 1,100nm, 1,200nm, 1,300nm, 1,400nm, 1,500nm, 1,600nm, 1,700nm, 1,800nm, 1,900nm, or 2,000nm, inclusive).

In some embodiments, there is provided an acoustic transducer for generating an electrical signal in response to an acoustic signal, the acoustic transducer comprising: the first diaphragm is provided with first wrinkles; and a second diaphragm having second wrinkles formed therein. The second diaphragm is spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure less than atmospheric pressure. A backplate is disposed in the cavity between the first diaphragm and the second diaphragm.

In some embodiments, each of the first wrinkles and the second wrinkles protrudes outward from the first diaphragm and the second diaphragm, respectively, in a direction away from the back plate.

In some embodiments, the backplate defines at least one aperture therethrough such that a portion of the cavity between the first diaphragm and the backplate is connected to a portion of the cavity between the second diaphragm and the backplate.

In some embodiments, the acoustic transducer further comprises: a substrate defining a first aperture therein; and a support structure disposed on the substrate and defining a second aperture corresponding to the first aperture of the substrate. At least a portion of the first diaphragm is disposed on the support structure. In some embodiments, the support structure comprises a phosphosilicate glass layer.

In some embodiments, the acoustic transducer further comprises: a perimeter support structure attached to and supporting at least a portion of the perimeters of the first and second diaphragms, the perimeter support structure being positioned adjacent to edges of the first and second diaphragms. In some embodiments, the perimeter support structure comprises at least a first layer and a second layer, each of the first layer and the second layer comprising phosphosilicate glass (PSG). In some embodiments, the first layer has a first phosphorus content and the second layer has a second phosphorus content different from the first phosphorus content. In some embodiments, the radially inner side wall of the peripheral support structure has a conical profile.

In some embodiments, at least one of the first diaphragm and the second diaphragm includes a first diaphragm layer and a second diaphragm layer disposed on the first diaphragm layer.

In some embodiments, at least one of the first and second diaphragms includes a stress relief structure adjacent a perimeter of the respective first or second diaphragm. The thickness of the stress relief structure is greater than the thickness of the corresponding first diaphragm or the second diaphragm: the portion is adjacent to the center of the respective first or second diaphragm. In some embodiments, the stress relief structure comprises a phosphosilicate glass embedded between two silicon nitride layers. In some embodiments, the stress relief structure comprises silicon nitride.

In some embodiments, there is provided an acoustic transducer for generating an electrical signal in response to an acoustic signal, the acoustic transducer comprising: a first diaphragm; and a second diaphragm spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure less than atmospheric pressure; a back plate disposed in the cavity between the first diaphragm and the second diaphragm; a post extending through an aperture defined in the backplate from the second diaphragm toward the first diaphragm. A portion of the strut is configured to contact the first diaphragm in response to movement of the second diaphragm toward the first diaphragm.

In some embodiments, the acoustic transducer further comprises: a substrate defining a first aperture therein; and a support structure disposed on the substrate and defining a second aperture corresponding to the first aperture of the substrate. At least a portion of the first diaphragm is disposed on the support structure.

In some embodiments, there is provided an acoustic transducer for generating an electrical signal in response to an acoustic signal, the acoustic transducer comprising: the first diaphragm is provided with first wrinkles; and a second diaphragm having second corrugations formed therein, the second diaphragm being spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure less than atmospheric pressure. A backplate is disposed in the cavity between the first diaphragm and the second diaphragm. A post extends from the second diaphragm toward the first diaphragm through an aperture defined in the backplate. A portion of the strut is configured to contact the first diaphragm in response to movement of the second diaphragm toward the first diaphragm.

In some embodiments, each of the first wrinkles and the second wrinkles protrude outward from the first diaphragm and the second diaphragm, respectively, in a direction away from the backplate.

In some embodiments, the acoustic transducer further comprises: anchor posts extending from the second diaphragm toward the first diaphragm through corresponding holes in the backplate. The apex of the anchor post contacts the first diaphragm and is coupled to the first diaphragm. A through-hole is defined through the apex and a perforation is defined through the first diaphragm, the perforation at least partially overlapping the through-hole.

In some embodiments, the acoustic transducer further comprises: a substrate defining a first aperture therein. A support structure is disposed on the substrate and defines a second aperture corresponding to the first aperture of the substrate. At least a portion of the first diaphragm is disposed on the support structure.

In some embodiments, the acoustic transducer further comprises: a perimeter support structure attached to and supporting at least a portion of the perimeters of the first and second diaphragms, the perimeter support structure being positioned adjacent to edges of the first and second diaphragms.

In some embodiments, at least one of the first and second diaphragms further includes a stress relief structure adjacent a perimeter of the respective first or second diaphragm. The stress relief structure has a thickness greater than a thickness of a portion of the respective first or second diaphragm that is proximate a center of the respective first or second diaphragm.

In some embodiments, there is provided a microphone assembly comprising: a base portion. A lid is disposed on the base, with a port defined in one of the base and the lid. An acoustic transducer is disposed on the base and separates a front volume and a back volume of the microphone assembly, the front volume being in fluid communication with the port. The acoustic transducer includes: the first diaphragm is provided with first wrinkles; and a second diaphragm having second corrugations formed therein, the second diaphragm being spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure less than atmospheric pressure. A backplate is disposed in the cavity between the first diaphragm and the second diaphragm. A post extends from the second diaphragm toward the first diaphragm through an aperture defined in the backplate. A portion of the strut is configured to contact the first diaphragm in response to movement of the second diaphragm toward the first diaphragm. An integrated circuit is electrically coupled to the acoustic transducer. The integrated circuit is configured to measure out-of-phase changes (out-of-phase changes) in capacitance between the first diaphragm and the back-plate and between the second diaphragm and the back-plate issued in response to receiving an acoustic signal through the port, the out-of-phase changes in capacitance corresponding to the acoustic signal.

In some embodiments, there is provided a pressure sensing assembly comprising: a base portion. Positioning a lid on the base, a port being defined in one of the base or the lid. Positioning an acoustic transducer on the base and separating a front volume and a back volume of the pressure sensing assembly, the front volume and the port being in fluid communication. The acoustic transducer includes: the first diaphragm is provided with first wrinkles; and a second diaphragm having second corrugations formed therein, the second diaphragm being spaced apart from the first diaphragm such that a cavity is formed between the second diaphragm and the first diaphragm, the cavity having a pressure lower than atmospheric pressure. The back plate is disposed in the cavity between the first diaphragm and the second diaphragm. A post extends from the second diaphragm toward the first diaphragm through an aperture defined in the backplate. A portion of the strut is configured to contact the first diaphragm in response to movement of the second diaphragm toward the first diaphragm. Electrically coupling an integrated circuit to the acoustic transducer, the integrated circuit configured to measure in-phase changes in capacitance between the first diaphragm and the backplate and between the second diaphragm and the backplate in response to changes in atmospheric pressure relative to pressure in the cavity.

In some embodiments, a method is provided, the method comprising the steps of: setting a substrate: forming a first diaphragm attached at a perimeter of the substrate, the first diaphragm having corrugations extending toward the substrate; forming a backplate spaced apart from the first diaphragm in a direction away from the substrate, the first diaphragm attached to the substrate at a perimeter of the first diaphragm; forming a second diaphragm spaced apart from the backplate in a direction away from the substrate, the second diaphragm attached to the substrate at a perimeter of the second diaphragm, the second diaphragm having corrugations extending away from the substrate; and using isotropic etching to remove structural material from between the first and second diaphragms, thereby forming a cavity between the first and second diaphragms; depositing a sealing layer to seal the cavity such that the pressure of the cavity is below atmospheric pressure; and forming an opening in the substrate below the first diaphragm. In some embodiments, the pressure in the cavity is in the range of 1mTorr to 1 Torr.

In some embodiments, the backplate defines at least one aperture therethrough such that a portion of the cavity between the first diaphragm and the backplate is connected to a portion of the cavity between the second diaphragm and the backplate.

In some embodiments, the step of forming the second diaphragm further comprises: a post is formed in the second diaphragm, the post extending through an aperture defined in the backplate towards the first diaphragm. A portion of the strut is configured to contact the first diaphragm in response to movement of the second diaphragm toward the first diaphragm.

In some embodiments, the step of forming the second diaphragm further comprises: anchoring struts are formed in the second diaphragm that extend through corresponding holes in the backplate towards the first diaphragm. The apex of the anchor post contacts the first diaphragm and is coupled to the first diaphragm; a through hole is defined through the apex and a perforation is defined through the first diaphragm, the perforation at least partially overlapping the through hole.

In some embodiments, there is provided an acoustic transducer for generating an electrical signal in response to an acoustic signal, the acoustic transducer comprising: a first diaphragm including a stress relief structure adjacent a perimeter of the first diaphragm, the stress relief structure having a thickness greater than a thickness of a portion of the first diaphragm adjacent a center of the first diaphragm. A second diaphragm is spaced apart from the first diaphragm to define a cavity therebetween, the cavity having a pressure less than atmospheric pressure. In the cavity, a backplate is located between the first diaphragm and the second diaphragm.

In some embodiments, the stress relief structure comprises a phosphosilicate glass embedded between two silicon nitride layers. In some embodiments, the stress relief structure comprises silicon nitride.

In some embodiments, the acoustic transducer further comprises: a perimeter support structure attached to and supporting at least a portion of the perimeters of the first and second diaphragms, the perimeter support structure being positioned adjacent to edges of the first and second diaphragms. In some embodiments, the perimeter support structure comprises at least a first layer and a second layer, each of the first layer and the second layer comprising phosphosilicate glass (PSG). In some embodiments, the first layer has a first phosphorus content and the second layer has a second phosphorus content different from the first phosphorus content.

In some embodiments, the radially inner side wall of the peripheral support structure has a conical profile.

The subject matter described herein sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being "operably couplable," to each other to achieve the desired functionality. Specific examples of operatively coupled include, but are not limited to, physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. Various singular/plural permutations may be expressly set forth herein for clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.).

It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" or "an" should typically be interpreted to mean "at least one" or "one or more"); the same is true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, typically means at least two recitations, or two or more recitations).

Moreover, in those instances where a convention analogous to "A, B, and at least one of C, etc." is used, in general such a construction is intended by one skilled in the art to be understood in the sense intended for such a convention (e.g., "a system having A, B and at least one of C" shall include but not be limited to systems having A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B and C together, etc.). In those instances where a convention analogous to "A, B or at least one of C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having A, B, or at least one of C" would include but not be limited to systems having a alone, B alone, C alone, a and B together, a and C together, B and C together, and/or A, B and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "a or B" should be understood to include the possibility of "a" or "B" or "a and B". Moreover, unless otherwise specified, use of the words "approximately," "about," "approximately," and the like means plus or minus ten percent.

The foregoing description of the exemplary embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to be limited to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the following claims and their equivalents.