Noise reduction MEMS device with force feedback

Abstract

The present invention relates to a noise reduction MEMS device with force feedback. A micro-electromechanical system MEMS device includes a diaphragm assembly and a force feedback system. The diaphragm assembly includes a first diaphragm and a second diaphragm facing the first diaphragm, and a low-pressure area is defined between the first diaphragm and the second diaphragm. The diaphragm assembly also includes a first plurality of electrodes, a second plurality of electrodes, and a third plurality of electrodes. A solid dielectric is spaced between the first diaphragm and the second diaphragm and includes a plurality of holes. Each of the first plurality of electrodes, the second plurality of electrodes, and the third plurality of electrodes is at least partially disposed in one of the plurality of holes. The force feedback system receives an output from the diaphragm assembly and generates a feedback voltage, which is applied to the diaphragm assembly to generate an electrostatic force on the diaphragm assembly, and the electrostatic force offsets the low-frequency pressure across the diaphragm assembly.

Description

Technical Field

[0001] The present disclosure relates generally to noise reducing micro-electromechanical systems (MEMS) devices, and more particularly to MEMS devices having noise reducing structures and force feedback systems. Background Art

[0002] MEMS devices are used in a variety of applications. For example, many types of acoustic sensors include a MEMS die with a diaphragm and a backplate, and an integrated circuit, where relative motion between the backplate and diaphragm results in a change in capacitance that is detected by the integrated circuit and ultimately interpreted as sound. As with any acoustic sensor, minimizing noise is often a design goal. Summary of the invention

[0003] One aspect of the present invention relates to a micro-electromechanical system device, the micro-electromechanical system device comprising: a diaphragm assembly, the diaphragm assembly comprising: a first diaphragm, the first diaphragm having a first surface and a second surface; a second diaphragm, the first surface of the second diaphragm faces the first surface of the first diaphragm, and the second surface of the second diaphragm faces away from the first diaphragm, and a low-voltage area is defined between the first surface of the first diaphragm and the first surface of the second diaphragm; a first plurality of electrodes, each of the first plurality of electrodes having a first end connected to the first surface of the first diaphragm and a second end connected to the first surface of the second diaphragm; and a second plurality of electrodes, each of the second plurality of electrodes having a first end connected to the first surface of the first diaphragm, and a second free end; a third plurality of electrodes, the third plurality of electrodes Each electrode in the pole has a first free end and a second end connected to the first surface of the second diaphragm; and a solid dielectric, the solid dielectric is spaced between the first diaphragm and the second diaphragm, and the solid dielectric includes a plurality of holes, wherein each electrode of the first plurality of electrodes, the second plurality of electrodes and the third plurality of electrodes is at least partially disposed in one of the plurality of holes, and the solid dielectric surrounds the second end of each electrode of the second plurality of electrodes and the first end of each electrode of the third plurality of electrodes; and a force feedback system, the force feedback system receives an output from the diaphragm assembly and generates a feedback voltage, the feedback voltage is applied to the diaphragm assembly to generate an electrostatic force on the diaphragm assembly, and the electrostatic force offsets the low-frequency pressure across the diaphragm assembly.

[0004] Another aspect of the present invention relates to a micro-electromechanical system device, the micro-electromechanical system device comprising: a diaphragm assembly, the diaphragm assembly comprising: a first diaphragm, the first diaphragm having a first surface and a second surface; a second diaphragm, the first surface of the second diaphragm faces the first surface of the first diaphragm, the second surface of the second diaphragm faces away from the first diaphragm, and a low-voltage area is defined between the first surface of the first diaphragm and the first surface of the second diaphragm; a first plurality of electrodes, each of the first plurality of electrodes having a first end connected to the first surface of the first diaphragm and a second end connected to the first surface of the second diaphragm; a second plurality of electrodes, each of the second plurality of electrodes having a first end connected to the first surface of the first diaphragm, and a second free end; a third plurality of electrodes, each of the third plurality of electrodes having a first free end and a second free end connected to the first surface of the first diaphragm. A second end of the first surface of the second diaphragm; and a solid dielectric, which is spaced between the first diaphragm and the second diaphragm and includes a plurality of holes, wherein each of the first plurality of electrodes, the second plurality of electrodes, and the third plurality of electrodes is at least partially disposed in one of the plurality of holes, and the solid dielectric surrounds the second end of each electrode of the second plurality of electrodes and the first end of each electrode of the third plurality of electrodes; a channel structure, which is disposed through the first diaphragm and the second diaphragm, wherein the channel structure provides fluid communication between the second surface of the first diaphragm and the second surface of the second diaphragm, and wherein the channel structure is configured to keep the low pressure area disposed between the first surface of the first diaphragm and the first surface of the second diaphragm outside the channel structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The foregoing and other features of the present disclosure will become more apparent from the following description and appended claims taken in conjunction with the accompanying drawings. These drawings depict only several embodiments in accordance with the present disclosure and therefore should not be considered limiting of its scope.

[0006] Figure 1 is a cross-sectional view of a MEMS die according to one embodiment.

[0007] Figure 2 yes Figure 1 A cross-sectional view of the MEMS die shows the Figure 1 An enlarged view of the portion within the dotted circle 2.

[0008] Figure 3 is a partially cutaway schematic diagram of an exemplary arrangement of electrodes according to one embodiment.

[0009] Figure 4 is another partially cutaway schematic diagram of an exemplary arrangement of electrodes according to one embodiment.

[0010] Figure 5 is a cross-sectional schematic perspective view of a MEMS die according to one embodiment.

[0011] Figure 6 is a schematic cross-sectional view of a portion of a MEMS die showing a passage through a diaphragm assembly according to one embodiment.

[0012] Figure 7 is a cross-sectional schematic perspective view of a housing according to one embodiment.

[0013] Figure 8 is a cross-sectional schematic perspective view of a housing according to another embodiment.

[0014] Fig. 9 is a cross-sectional view of a microphone assembly according to one embodiment.

[0015] Fig.10 is an electrical diagram of a first embodiment of a force feedback system.

[0016] Fig.11 is an electrical diagram of a second embodiment of a force feedback system.

[0017] In the following detailed description, various embodiments are described with reference to the accompanying drawings. It will be appreciated by those skilled in the art that the accompanying drawings are schematic and simplified for clarity. The same reference numerals always refer to the same elements or components. Therefore, similar elements or components will not necessarily be described in detail for each figure. DETAILED DESCRIPTION

[0018] According to various embodiments described herein, a MEMS die may include a dual diaphragm having one or more electrodes disposed in a low pressure region located between the dual diaphragms, for example, as shown in U.S. Application No. 17 / 133,506, filed on December 23, 2020, and incorporated herein in its entirety. This diaphragm structure arrangement can be used to reduce acoustic damping noise typically associated with air within a MEMS structure. A MEMS die having a miniaturized back cavity volume for reducing thermal boundary layer noise in the back cavity volume is shown in U.S. Application No. 17 / 037,959, filed on September 30, 2020, and incorporated herein in its entirety. A MEMS die consisting of a combination of a low pressure diaphragm structure and a miniaturized back cavity volume and used as, for example, a transducer can still generate acoustic noise that can be reduced using various embodiments described herein.

[0019] According to one embodiment, a microelectromechanical system (MEMS) device includes a diaphragm assembly and a housing disposed on one side of the diaphragm assembly, the diaphragm assembly including a first diaphragm, a second diaphragm facing the first diaphragm, and a low-pressure area is defined between the first diaphragm and the second diaphragm. The diaphragm assembly also includes: a first plurality of electrodes, each electrode in the first plurality of electrodes having a first end connected to the first side of the first diaphragm and a second end connected to the second diaphragm; a second plurality of electrodes, each electrode in the second plurality of electrodes having a first end connected to the first diaphragm, and a second free end; and a third plurality of electrodes, each electrode in the third plurality of electrodes having a first free end and a second end connected to the second diaphragm. A solid dielectric is spaced between the first diaphragm and the second diaphragm and includes a plurality of holes. Each of the first plurality of electrodes, the second plurality of electrodes, and the third plurality of electrodes is at least partially disposed in one of the plurality of holes, and the dielectric surrounds the second end of each electrode in the second plurality of electrodes and the first end of each electrode in the third plurality of electrodes. The MEMS device also includes a force feedback system that receives the output from the diaphragm assembly and generates a feedback voltage that is applied to the diaphragm assembly to generate an electrostatic force on the diaphragm assembly that counteracts low frequency pressure across the diaphragm assembly.

[0020] In one embodiment, the MEMS device includes a housing disposed on a second side of the first diaphragm opposite to the first side, the housing defining a boundary of a back volume, wherein all points within the back volume are less than a single thermal boundary layer thickness from a nearest surface of the housing.

[0021] According to one embodiment, the MEMS device also includes a channel structure arranged through the first diaphragm and the second diaphragm, wherein the channel structure provides fluid communication between the second surface of the first diaphragm and the second surface of the second diaphragm, and wherein the channel structure is configured to maintain a low pressure area arranged between the first surface of the first diaphragm and the first surface of the second diaphragm outside the channel structure.

[0022] In one embodiment, the MEMS device further includes a force feedback system, which includes a differential amplifier. The force feedback system also includes: a first electrical connection between a first end of at least a first subset of the second plurality of electrodes and a first input of the differential amplifier; and a second electrical connection between a second end of at least a first subset of the third plurality of electrodes and a second input of the differential amplifier. A frequency filtering circuit is included, and an input of the frequency filtering circuit is connected to an output of the differential amplifier. The force feedback system also includes a feedback amplifier, whose input is connected to an output of the frequency filtering circuit and whose output is connected to an output of a second subset of the first plurality of electrodes that is not connected to a voltage source. The movement of the diaphragm assembly in response to the pressure generates a voltage signal at the output of the differential amplifier, the voltage signal is filtered by the frequency filtering circuit to select a portion of the signal below a predetermined frequency, and the selected portion of the signal is provided to the feedback amplifier to generate a feedback voltage, which is applied to a second subset of the first plurality of electrodes. The feedback voltage generates an electrostatic force on the diaphragm assembly, and the electrostatic force counteracts the pressure.

[0023] Go to Figure 1 , schematically illustrates a MEMS die in cross-section according to one embodiment. The MEMS die, generally designated 100, includes a substrate 110 having an opening 116 formed therein. In one embodiment, the substrate 110 is a rectangular parallelepiped, but in other embodiments, it can be any shape. In one embodiment, the diaphragm assembly 106 is attached to the substrate 110 around its perimeter and over the opening 116. The opening 116 is typically circular, but can be any shape. In one embodiment, the substrate 110 is made of silicon.

[0024] refer to Figure 2 , Figure 1 A portion of the MEMS die 100 is shown slightly enlarged. In one embodiment, the diaphragm assembly 106 includes a first diaphragm 106A having a first face 124 and a second face 125. The diaphragm assembly 106 also includes a second diaphragm 106B having a first face 128 and a second face 129, wherein the first face 128 faces the first face 124 of the first diaphragm 106A and the second face 129 faces away from the first diaphragm 106A. The low pressure region is defined in the space 112 between the first face 124 of the first diaphragm 106A and the first face 128 of the second diaphragm 106B. In one embodiment, the pressure of the low pressure region is less than about 0.003 atmospheres. In another embodiment, the pressure of the low pressure region is less than about 0.001 atmospheres.

[0025] In one embodiment, the first plurality of electrodes 120 are disposed between the first diaphragm 106A and the second diaphragm 106B. Each electrode of the first plurality of electrodes 120 has a first end 122 connected to the first side 124 of the first diaphragm 106A and a second end 126 connected to the first side 128 of the second diaphragm 106B. In one embodiment, the diaphragm assembly 106 further includes a second plurality of electrodes 130 disposed between the first diaphragm 106A and the second diaphragm 106B. Each electrode of the second plurality of electrodes 130 has a first end 132 connected to the first side 124 of the first diaphragm 106A, and a second free end 134. In one embodiment, the diaphragm assembly 106 further includes a third plurality of electrodes 140 disposed between the first diaphragm 106A and the second diaphragm 106B. Each electrode of the third plurality of electrodes 140 has a first free end 142 and a second end 144 connected to the first side 128 of the second diaphragm 106B.

[0026] Still reference Figure 2 In one embodiment, the solid dielectric 150 is spaced between the first diaphragm 106A and the second diaphragm 106B and includes a plurality of holes 160. Each of the first plurality of electrodes 120, the second plurality of electrodes 130, and the third plurality of electrodes 140 is at least partially disposed within one of the plurality of holes 160. The solid dielectric 150 surrounds the second end 134 of each electrode in the second plurality of electrodes 130 and the first end 142 of each electrode in the plurality of third electrodes 140. The first plurality of electrodes 120, the second plurality of electrodes 130, and the third plurality of electrodes 140 may be electrodes of cylinders, plates, cuboids, prisms, polyhedrons, or other shapes, and may be made of any conductive material.

[0027] In one embodiment, each of the first diaphragm 106A, the second diaphragm 106B and the solid dielectric 150 includes at least an insulating material layer 107. The insulating material 107 can be any insulating material known in the art that will not be damaged in the sacrificial layer removal process. For example, but not limited to, the insulating material 107 can be silicon nitride, silicon oxynitride, metal oxide, polymer, a material that is not damaged by the sacrificial layer removal process, and a combination thereof.

[0028] Reference again Figure 1 In one embodiment, the solid dielectric 150 is arranged such that its periphery is attached between the first diaphragm 106A and the second diaphragm 106B through a spacer layer 182. In one embodiment, the periphery of the second diaphragm 106B is attached through a spacer layer 184 ( Figure 1 Not shown - see Figure 5) is further attached to the substrate 110. In one embodiment, the first diaphragm layer 106A is attached to a housing 170 that defines a back cavity volume 175 (see below). In one embodiment, the attachment between the first diaphragm layer 106A and the housing 170 is as follows Figure 1 In another embodiment, the attachment between the first diaphragm layer 106A and the housing 170 is via an optional spacer layer (not shown but for example Figure 5 The spacer layer 184 shown is made.

[0029] In one embodiment, the diaphragm assembly 106 and the solid dielectric 150 are both circular in plan view (eg, Figure 1 184 are shown along the arrow marked A in the figure, but can be any shape in other embodiments. In one embodiment, the spacer layer 182 has a curved inner wall 182A. The substrate 110 also has a curved inner wall 110A, which defines an opening 116 extending through the substrate 110 to the surrounding environment. The spacer layers 182, 184 are made of any insulating material 107 as described above.

[0030] In one embodiment, the solid dielectric 150 is relatively thick and rigid compared to the first diaphragm 106A and the second diaphragm 106B, and remains relatively stationary when the first diaphragm 106A and the second diaphragm 106B are deflected. The deflection of the first diaphragm 106A and the second diaphragm 106B causes the first plurality of electrodes 120, the second plurality of electrodes 130, and the third plurality of electrodes 140 to move relative to the solid dielectric 150.

[0031] In one embodiment, the solid dielectric 150 has a thickness of about 3 microns; however, in other embodiments, the solid dielectric 150 may have a thickness in a range between about 1 micron and about 10 microns. In addition, in one embodiment, the solid dielectric has a hole that is cylindrical and has a diameter of about 3 microns; however, in other embodiments, the hole may have any cross-sectional shape and / or may have a maximum cross-sectional dimension in a range between about 0.6 microns and about 6 microns. In one embodiment, the thickness of the spacer layers 182, 184 is about 1.5 microns; however, in other embodiments, the thickness of the spacer layers 182, 184 may be in a range between about 0.1 microns and about 10 microns. In one embodiment, the first diaphragm 106A and the second diaphragm 106B are about 0.5 microns thick; however, in other embodiments, the first diaphragm 106A and the second diaphragm 106B may have a thickness in a range between about 0.1 microns and 2 microns. In one embodiment, the first plurality of electrodes 120, the second plurality of electrodes 130, and the third plurality of electrodes 140 are made of polysilicon and are cylindrical and have a diameter of approximately 2 microns; however, in other embodiments, the first plurality of electrodes, the second plurality of electrodes, and the third plurality of electrodes 140 may be made of other conductive materials and may have other shapes and / or have a maximum cross-sectional dimension between approximately 0.5 microns and 5 microns.

[0032] Reference Figure 3 , schematically shows an exemplary arrangement of the first plurality of electrodes 120 and the third plurality of electrodes 140 and a portion of the second diaphragm 106B. Figure 3 As shown, in one embodiment, each electrode of the first plurality of electrodes 120 is connected to the second diaphragm 106B, for example, by an electrical trace or wire 121 (and / or an electrical trace or wire 123 that can be laminated to or in the first diaphragm 106A - see Figure 4 ) are electrically connected to each other. In other embodiments, each electrode in the first subset of the first plurality of electrodes 120 is electrically connected to each other, and each electrode in the second subset of the first plurality of electrodes 120 is connected to each other, for example, by electrical traces or wires 121, such as Figure 3 As shown, however, the first subset is not electrically connected to the second subset.

[0033] Similarly, still refer to Figure 3 In one embodiment, each electrode in the third plurality of electrodes 140 is electrically connected to each other, for example, by electrical traces or wires 141 that can be laminated to or in the second diaphragm 106B. In other embodiments, each electrode in a first subset of the third plurality of electrodes 140 is electrically connected to each other, and each electrode in a second subset of the third plurality of electrodes 140 is electrically connected to each other, for example, by electrical traces or wires 141 that can be laminated to or in the second diaphragm 106B. Figure 3The electrical traces or wires 141 are shown connected to each other, but a first subset is not electrically connected to a second subset.

[0034] refer to Figure 4 , an exemplary arrangement of the first plurality of electrodes 120 and the second plurality of electrodes 130 and a portion of the first diaphragm 106A are schematically shown. Figure 4 As shown, in one embodiment, each electrode in the first plurality of electrodes 120 is electrically connected to each other, for example, by electrical traces or wires 123 that can be laminated to or in the first diaphragm 106A. In other embodiments, each electrode in a first subset of the first plurality of electrodes 120 is electrically connected to each other, and each electrode in a second subset of the first plurality of electrodes 120 is electrically connected to each other, for example, by electrical traces or wires 123 that can be laminated to or in the first diaphragm 106A. Figure 4 The electrical traces or wires 123 are shown connected to each other, but the first subset is not electrically connected to the second subset. Figure 4 In one embodiment, each electrode in the second plurality of electrodes 130 is electrically connected to each other, for example, by electrical traces or wires 131 that can be laminated to or in the first diaphragm 106A. In other embodiments, each electrode in the first subset of the second plurality of electrodes 130 is electrically connected to each other, and each electrode in the second subset of the second plurality of electrodes 130 is electrically connected to each other, for example, by electrical traces or wires 131 that can be laminated to or in the first diaphragm 106A. Figure 4 The electrical traces or wires 131 are shown connected to each other, but a first subset is not electrically connected to a second subset.

[0035] refer to Figure 5 In one embodiment, one or more electrodes in the second plurality of electrodes 130 are coaxially disposed with one or more electrodes in the third plurality of electrodes 140. In one embodiment, the second end 134 of one or more electrodes in the second plurality of electrodes 130 is connected to the first end 142 of one or more electrodes in the third plurality of electrodes 140 via a dielectric support layer 152. In one embodiment, the dielectric support layer 152 is made of the same material as the solid dielectric 150.

[0036] refer to Figure 6 In one embodiment, at least one channel 114 is disposed completely through the diaphragm assembly 106, providing fluid communication 106 between an opening 116 on one side of the diaphragm assembly 106 and a back cavity volume 175 on an opposite side of the diaphragm assembly 106. In one embodiment, a first through-hole 114A of any cross-sectional shape desired or known in the art is disposed through the first diaphragm 106A, and a second through-hole 114B of any cross-sectional shape desired or known in the art is disposed through the second diaphragm 106B.

[0037] Still refer to Figure 6, centerline C and radial axis R have been added for reference to the following description. In one embodiment, the channel structure 118 is disposed completely through the first diaphragm 106A and the second diaphragm 106B. The channel structure 118 provides fluid communication between the second side 125 of the first diaphragm 106A and the second side 129 of the second diaphragm 106B, respectively. The channel structure 118 is configured to maintain a low pressure area within a space 112 between the first side 124 of the first diaphragm 106A and the first side 128 of the second diaphragm 106B, respectively. For example, in one embodiment, the channel structure 118 is sealed to the material of the diaphragm layer 106A at a first end and to the material of the diaphragm layer 106B at a second opposite end.

[0038] In one embodiment, if Figure 6 As schematically shown, the channel structure 118 is manufactured as a solid wall of a hollow tubular structure, which is one electrode of the first plurality of electrodes 120 connected between the first diaphragm 106A and the second diaphragm 106B. The first perforation 114A and the second perforation 114B are disposed within the wall of the hollow tubular structure. In one embodiment, the first perforation 114A and the second perforation 114B extend across the entire open end of the channel structure 118. In other embodiments, the first perforation and the second perforation extend across only a portion of the open end of the channel structure 118 and / or are bounded by the material of the first diaphragm layer 106A and the second diaphragm layer 106B, respectively. In one embodiment, the channel structure 118 comprises a right circular cylinder; however, in other embodiments, the channel structure may have different shapes, including varying cross-sections between its open ends.

[0039] At least one channel 114 allows pressure equalization between the back volume 175 and the surrounding environment. The at least one channel 114 is important for the low frequency roll-off (LFRO) performance of the device ultimately made from the MEMS die 100, and in some embodiments, there may be more than one channel 114 disposed through the diaphragm assembly 106.

[0040] Reference again Figure 1 and Figure 2 In one embodiment, the housing 170 is disposed on the second face 125 of the first diaphragm 106A opposite the first face 124. The housing 170 defines a back volume 175, wherein all points within the back volume 175 are less than a single thermal boundary layer thickness T from the nearest surface of the housing 175. bl The boundary layer thickness is given by:

[0041]

[0042] Wherein, ω is the operating angular frequency of the diaphragm assembly 106, κ is the thermal conductivity, ρ is the density and Cp is the specific heat of the gas in the back cavity volume 175 at constant pressure.

[0043] Figure 1 The cross-sectional view of the housing 170 shown in FIG. 1 may represent two different embodiments of the housing 170. For example, in one embodiment (see also FIG. 1 ), Figure 7 ), the housing 170 includes a rear wall 172 disposed substantially parallel to the diaphragm assembly 106 and a rear wall 172 extending from the rear wall 172 and oriented substantially perpendicular to the diaphragm assembly 106 ( Figure 7 In another embodiment, Figure 1 It can also be represented that the housing 170 has a plurality of elongated channels 176 disposed therein, wherein the plurality of channels 176 are oriented substantially perpendicular to the diaphragm assembly 106, are open at the end facing the diaphragm assembly 106, and are closed at the end facing away from the diaphragm assembly 106. In another embodiment, the housing 170 includes a porous material 178, such as Figure 8 shown.

[0044] Go to Fig. 9 , an embodiment of the MEMS die 100 is used as an acoustic transducer 100 and is configured to be assembled within a microphone assembly generally designated 300. Assembly 300 includes a housing including a base 302 having a first surface 305 and an opposite second surface 307. The housing also includes a cover 304 (e.g., a housing cover) and an acoustic port 306. In one embodiment, the port 306 extends between the first surface 305 and the second surface 307. In one implementation, the base 302 is a printed circuit board. The cover 304 is coupled to the base 302 (e.g., the cover 304 can be mounted to the peripheral edge of the base 302). The cover 304 and the base 302 together define a housing interior having an enclosed volume 308. The acoustic transducer 100 including the diaphragm assembly 106 and the housing 170 is disposed within the housing such that the second diaphragm 106B is above the port 306 and the housing 170 is above the diaphragm assembly 106.

[0045] like Fig. 9 As shown, an acoustic port 306 is disposed on the base 302 and is configured to transmit sound waves to the MEMS acoustic transducer 100 located within the enclosed volume 308. In some embodiments, the assembly 300 forms part of a compact computing device (e.g., a portable communication device, a smartphone, a smart speaker, an Internet of Things (IoT) device, etc.), wherein one, two, three or more components may be integrated for picking up and processing various types of acoustic signals, such as speech and music.

[0046] Assembly 300 includes a circuit disposed within enclosed volume 308. In one embodiment, the circuit includes an integrated circuit (IC) 310. In one embodiment, IC 310 is disposed on a first surface 305 of base 302, for example, inside a housing, and is electrically connected to diaphragm assembly 106. IC 310 may be an application specific integrated circuit (ASIC). Alternatively, IC 310 may include a semiconductor die integrating various analog, analog-to-digital, and / or digital circuits. In one embodiment, cover 304 is disposed on first surface 305 of base 302, covering MEMS acoustic transducer 100 and IC 310.

[0047] The enclosed volume portion 308 between the cover 304 and the outer surface of the MEMS transducer 100 is not acoustically active. The cover 304 is typically welded to the base 302 in an area around its perimeter, which will cause the pressure within the enclosed volume portion 308 to increase dramatically during welding. To prevent solder from being blown out of the welding area, in one embodiment, the cover 304 includes a vent 316 to the outside atmosphere and / or the welding area is discontinuous, for example, having one or more openings 318 disposed therethrough, so that air between the cover 304 and the base 302 can escape.

[0048] exist Fig. 9 In the assembly 300 of FIG. 3 , the MEMS acoustic transducer 100 is shown disposed on a first surface 305 of a base 302. The MEMS acoustic transducer 100 converts acoustic waves received through an acoustic port 306 into corresponding electrical microphone signals and generates an electrical signal (e.g., voltage) at the transducer output in response to acoustic activity incident on the port 306. Fig. 9 As shown, the diaphragm assembly 106 is electrically connected to the circuit via one or more bonding wires. Fig. 9 The assembly 300 also includes electrical contacts, schematically shown as contacts 314, generally disposed on the bottom surface of the base 302. The contacts 314 are electrically coupled to the circuit. The contacts 314 are configured to electrically connect the assembly 300 to one of a variety of host devices.

[0049] Structural aspects of MEMS die 100 have been described above. Implementations of circuits connected to MEMS die 100 (and included, for example, within IC 310) are described below.

[0050] refer to Fig.10 In one embodiment, the voltage source 405 is electrically connected to at least a first subset of the first plurality of electrodes 120 to provide a voltage bias relative to ground to the first subset of the first plurality of electrodes 120. Fig.10, the force feedback system 400 is electrically connected to the diaphragm assembly 106. In one embodiment, the force feedback system 400 is a circuit including a differential amplifier 410 that receives input from electrodes of the diaphragm assembly 106. In particular, in one embodiment, there is a first electrical connection 420 between the first end 132 of the first subset of the second plurality of electrodes 130 and the first input 430 of the differential amplifier 410. In one embodiment, there is also a second electrical connection 440 between the second end 144 of the first subset of the third plurality of electrodes 140 and the second input 450 of the differential amplifier 410.

[0051] Still reference Fig.10 In one embodiment, the force feedback system 400 further includes a frequency filtering circuit 460 (labeled as LPF, which stands for low pass filter) having an input connected to the output of the differential amplifier 410. The force feedback system 400 includes a feedback amplifier 470 having an input connected to the output of the frequency filtering circuit 460. In one embodiment, the force feedback system 400 optionally includes a pulse width modulation (PWM) circuit 480 having an input connected to the output of the feedback amplifier 470 and an output connected to the output of the second subset of the first plurality of electrodes 120 that is not connected to the voltage source 405. In the absence of the optional PWM circuit 480, the output of the feedback amplifier 470 is directly connected to the second subset of the first plurality of electrodes 120 that is not connected to the voltage source 405. The second subset of the second plurality of electrodes 130 is connected to the voltage source 405, and the second subset of the third plurality of electrodes 140 is grounded.

[0052] In operation, about Fig.10 The described MEMS device combining the MEMS die 100 and the force feedback system 400 processes the electrical signal generated by the movement of the diaphragm assembly 106 while also providing feedback force to the diaphragm assembly 106. Specifically, in one embodiment, the movement of the diaphragm assembly 106 generates a voltage signal at the output of the differential amplifier 410. The voltage signal is filtered by the frequency filtering circuit 460 to select a portion of the signal below a predetermined frequency. In one embodiment, the predetermined frequency is 35 Hz. In other embodiments, any different predetermined frequencies can be used as desired, for example, the predetermined frequency can be 10 Hz, 15 Hz, 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz, 45 Hz, 50 Hz, 55 Hz, 60 Hz, 65 Hz, 70 Hz, 75 Hz, 80 Hz, 85 Hz, 90 Hz, 95 Hz, 100 Hz, any frequency between these listed values, a frequency below 10 Hz, or a frequency above 100 Hz.

[0053] The acoustic low pass frequency determined by the resistance of the perforations 114A and 114B and the effective compatibility of the back cavity volume 175 should be lower than the predetermined frequency set by the frequency filtering circuit 460. The acoustic low pass frequency is typically less than 20 Hz, such as 10 Hz, 5 Hz, 1 Hz, 0.1 Hz, or 0.01 Hz. By reducing the acoustic low pass frequency, the overall acoustic noise of the MEMS device (e.g., microphone) is reduced. By using a force feedback with a predetermined frequency higher than the acoustic low pass frequency, the microphone output is limited to the common audio band and potential overload from sub-audible signals is avoided.

[0054] The selected portion of the signal is provided to a feedback amplifier 470 and an optional PWM circuit 480 to generate a feedback voltage that is applied to a second subset of the first plurality of electrodes 120. The feedback voltage generates an electrostatic force on the diaphragm assembly 106 that counteracts the pressure. For example, by utilizing a frequency of 35 Hz, large acoustic pulses at frequencies of 35 Hz and below that may overload the diaphragm assembly can be removed by force feedback provided by the desired circuit.

[0055] refer to Fig.11 In another embodiment, the force feedback system 500 connected to the MEMS die 100 is connected to the Fig.10 The force feedback system 400 described is somewhat different. Fig.11 In the illustrated embodiment, a first voltage source 505 is electrically connected to the first end 132 of the second plurality of electrodes 130 to provide a voltage bias relative to ground to the second plurality of electrodes 130. A second voltage source 510 is electrically connected to the second end 144 of the third plurality of electrodes 140 to provide a voltage bias relative to ground to the third plurality of electrodes 140. The force feedback system 500 includes a first amplifier 520 that receives input from electrodes of the diaphragm assembly 106. In particular, in one embodiment, a first electrical connection 530 exists between at least a first subset of the first plurality of electrodes 120 and an input of the first amplifier 520.

[0056] Still reference Fig.11 In one embodiment, the force feedback system 500 further includes a frequency filtering circuit 540 (labeled as LPF, which stands for low pass filter) whose input is connected to the output of the first amplifier 520. The circuit includes a second amplifier 550 whose input is connected to the output of the frequency filtering circuit 540. The output of the second amplifier 550 is connected to a second subset of the first plurality of electrodes 120.

[0057] In operation, about Fig.11The described MEMS device combining the MEMS die 100 and the force feedback system 500 processes the electrical signal generated by the movement of the diaphragm assembly 106 while also providing feedback force to the diaphragm assembly 106. In particular, by also filtering the voltage signal from the first amplifier 520 to select the signal below a predetermined frequency (the predetermined frequency can be any frequency, as described above with respect to Fig.10 part of the above, Fig.11 The circuit in the embodiment is like about Fig.10 The force feedback system 400 described herein functions as described above.

[0058] Again, a selected portion of the signal is provided to a second amplifier 550 to generate a feedback voltage that is applied to a second subset of the first plurality of electrodes 120. The feedback voltage generates an electrostatic force on the diaphragm assembly 106 that counteracts the pressure that causes the diaphragm assembly 106 to move.

[0059] In About Fig.10 and Fig.11 The components described in the circuit of are only examples, and other combinations of components can be used to perform force feedback. For example, the amplifier can be any type of amplifier with unity gain or other gain.

[0060] The steps in the production process for producing the MEMS die 100 as described above include etching, masking, patterning, cutting, drilling and / or releasing steps performed on the workpiece. Therefore, all steps will not be described in detail herein. However, typically the final termination of the MEMS die 100 is layered onto the workpiece using sacrificial materials as part of the space 112 and the back cavity volume 175, or drilled or etched out of a solid block of material.

[0061] With respect to the plural and / or singular terms used herein, those skilled in the art may translate from the plural to the singular and / or from the singular to the plural as appropriate, depending on the context and / or application. For clarity, various singular / plural permutations may be expressly set forth herein.

[0062] Unless otherwise indicated, the use of the terms "approximately," "about," "approximately," "substantially," etc. means plus or minus 10%.

[0063] The foregoing description of illustrative embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or limiting as to the precise forms disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. The scope of the invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A micro-electromechanical system device, comprising: A diaphragm assembly, the diaphragm assembly comprising: A first diaphragm, the first diaphragm having a first surface and a second surface; a second diaphragm, wherein a first surface of the second diaphragm faces the first surface of the first diaphragm, and a second surface of the second diaphragm faces away from the first diaphragm, and a low pressure area is defined between the first surface of the first diaphragm and the first surface of the second diaphragm; a first plurality of electrodes, each electrode of the first plurality of electrodes having a first end connected to the first side of the first diaphragm and a second end connected to the first side of the second diaphragm; and a second plurality of electrodes, each electrode of the second plurality of electrodes having a first end connected to the first side of the first diaphragm, and a second free end; a third plurality of electrodes, each electrode of the third plurality of electrodes having a first free end and a second end connected to the first side of the second diaphragm; and a solid dielectric, the solid dielectric being spaced between the first diaphragm and the second diaphragm, and the solid dielectric comprising a plurality of holes, wherein each of the first plurality of electrodes, the second plurality of electrodes, and the third plurality of electrodes is at least partially disposed within one of the plurality of holes, and the solid dielectric surrounds a second end of each of the second plurality of electrodes and a first end of each of the third plurality of electrodes; and A force feedback system receives the output from the diaphragm assembly and generates a feedback voltage, which is applied to the diaphragm assembly to generate an electrostatic force on the diaphragm assembly, which counteracts the low frequency pressure across the diaphragm assembly.

2. The MEMS device according to claim 1, wherein: The force feedback system receives output from a first subset of the first plurality of electrodes, and the feedback voltage is applied to a second subset of the first plurality of electrodes to generate the electrostatic force.

3. The MEMS device according to claim 1, wherein: The force feedback system receives outputs from a subset of the second plurality of electrodes and a subset of the third plurality of electrodes, and the feedback voltage is applied to a subset of the first plurality of electrodes to generate the electrostatic force.

4. The MEMS device according to claim 1, wherein: The first plurality of electrodes, the second plurality of electrodes, and the third plurality of electrodes are movable relative to the solid dielectric.

5. The MEMS device according to claim 1, wherein at least a subset of said first plurality of electrodes are electrically connected to each other, At least a subset of the second plurality of electrodes are electrically connected to each other, and At least a subset of the third plurality of electrodes are electrically connected to each other.

6. The MEMS device according to claim 1, wherein: One or more electrodes of the second plurality of electrodes are coaxially disposed with one or more electrodes of the third plurality of electrodes.

7. The MEMS device according to claim 6, wherein: Second ends of one or more electrodes of the second plurality of electrodes are connected to first ends of one or more electrodes of the third plurality of electrodes through a dielectric support layer.

8. The MEMS device according to claim 1, further comprising a channel structure disposed through the first diaphragm and the second diaphragm, wherein: The channel structure provides fluid communication between the second surface of the first diaphragm and the second surface of the second diaphragm, and wherein the channel structure is configured to maintain the low pressure region disposed between the first surface of the first diaphragm and the first surface of the second diaphragm outside the channel structure.

9. The MEMS device according to claim 1, further comprising: integrated circuit; A housing, the housing comprising: a base having a first surface, an opposing second surface, and a port; a cover attached to the first surface of the base, wherein the cover and the base define an interior of the housing, wherein the port extends between the first surface and the second surface, and the diaphragm assembly is disposed inside the housing such that the second diaphragm is located above the port; and Wherein, the integrated circuit is arranged inside the housing and is electrically connected to the diaphragm assembly.

10. The MEMS device of claim 9, further comprising an opening selected from the group consisting of a vent hole disposed through the cover, one or more openings disposed between the cover and the base, and combinations thereof.

11. The MEMS device according to claim 1, further comprising a housing disposed on a second surface of the first diaphragm opposite to the first surface, the housing defining a back cavity volume, wherein: All points within the rear cavity volume are located less than a single thermal boundary layer thickness from a nearest surface of the housing.

12. The MEMS device according to claim 11, wherein: The housing includes a rear wall disposed parallel to the diaphragm assembly and a plurality of elongated posts extending from the rear wall and oriented perpendicular to the diaphragm assembly.

13. The MEMS device according to claim 11, wherein: The shell includes a plurality of elongated channels disposed in the shell, wherein the plurality of elongated channels are oriented perpendicular to the diaphragm assembly, are open at an end facing the diaphragm assembly, and are closed at an end facing away from the diaphragm assembly.

14. The MEMS device according to claim 11, wherein: The housing comprises a porous material.

15. The MEMS device according to claim 1, further comprising: a voltage source electrically connected to at least a first subset of the first plurality of electrodes to provide a voltage bias relative to ground to the first subset of the first plurality of electrodes, Wherein, the force feedback system comprises: Differential amplifier; a first electrical connection between a first end of at least a first subset of the second plurality of electrodes and a first input of the differential amplifier; and A second electrical connection is provided between a second end of at least a first subset of the third plurality of electrodes and a second input of the differential amplifier.

16. The MEMS device according to claim 15, wherein: The force feedback system further comprises: a frequency filtering circuit, wherein an input terminal of the frequency filtering circuit is connected to an output terminal of the differential amplifier; and A feedback amplifier, wherein the input end of the feedback amplifier is connected to the output end of the frequency filtering circuit.

17. The MEMS device of claim 16, wherein: An output of the feedback amplifier is connected to a second subset of the first plurality of electrodes that are not connected to the voltage source; and The movement of the diaphragm assembly in response to pressure generates a voltage signal at the output end of the differential amplifier, the voltage signal is filtered by the frequency filtering circuit to select a portion of the voltage signal below a predetermined frequency, and the selected portion of the voltage signal is provided to the feedback amplifier to generate a feedback voltage, which is applied to a second subset of the first plurality of electrodes, wherein the feedback voltage generates an electrostatic force on the diaphragm assembly, and the electrostatic force offsets the pressure.

18. The MEMS device according to claim 1, further comprising: a first voltage source electrically connected to first ends of the second plurality of electrodes to provide a voltage bias relative to ground to the second plurality of electrodes; a second voltage source electrically connected to second ends of the third plurality of electrodes to provide a voltage bias relative to ground to the third plurality of electrodes; Wherein, the force feedback system comprises: a first amplifier; and A first electrical connection is provided between at least a first subset of the first plurality of electrodes and an input of the first amplifier.

19. The MEMS device of claim 18, wherein: The force feedback system further includes: a frequency filtering circuit, an input end of the frequency filtering circuit being connected to an output end of the first amplifier; and a second amplifier, an input end of the second amplifier being connected to an output end of the frequency filtering circuit; and An output of the second amplifier is connected to a second subset of the first plurality of electrodes.

20. A micro-electromechanical system device, comprising: A diaphragm assembly, the diaphragm assembly comprising: A first diaphragm, the first diaphragm having a first surface and a second surface; a second diaphragm, wherein a first surface of the second diaphragm faces the first surface of the first diaphragm, a second surface of the second diaphragm faces away from the first diaphragm, and a low pressure area is defined between the first surface of the first diaphragm and the first surface of the second diaphragm; a first plurality of electrodes, each electrode of the first plurality of electrodes having a first end connected to the first side of the first diaphragm and a second end connected to the first side of the second diaphragm; a second plurality of electrodes, each electrode of the second plurality of electrodes having a first end connected to the first side of the first diaphragm, and a second free end; a third plurality of electrodes, each electrode of the third plurality of electrodes having a first free end and a second end connected to the first side of the second diaphragm; and a solid dielectric, the solid dielectric being spaced between the first diaphragm and the second diaphragm and comprising a plurality of holes, wherein each of the first plurality of electrodes, the second plurality of electrodes, and the third plurality of electrodes is at least partially disposed within one of the plurality of holes, and the solid dielectric surrounds a second end of each of the second plurality of electrodes and a first end of each of the third plurality of electrodes; A channel structure is arranged through the first diaphragm and the second diaphragm, wherein the channel structure provides fluid communication between the second surface of the first diaphragm and the second surface of the second diaphragm, and wherein the channel structure is configured to maintain the low pressure area arranged between the first surface of the first diaphragm and the first surface of the second diaphragm outside the channel structure.

21. The MEMS device according to claim 20, further comprising: a voltage source electrically connected to at least a first subset of the first plurality of electrodes to provide a voltage bias relative to ground to the first subset of the first plurality of electrodes; A force feedback system, the force feedback system comprising: Differential amplifier; a first electrical connection between a first end of at least a first subset of the second plurality of electrodes and a first input of the differential amplifier; a second electrical connection between a second end of at least a first subset of the third plurality of electrodes and a second input of the differential amplifier; a frequency filtering circuit, wherein an input terminal of the frequency filtering circuit is connected to an output terminal of the differential amplifier; and a feedback amplifier having an input connected to the output of the frequency filtering circuit and an output connected to a second subset of the first plurality of electrodes that are not connected to the voltage source; The movement of the diaphragm assembly in response to pressure generates a voltage signal at the output end of the differential amplifier, the voltage signal is filtered by the frequency filtering circuit to select a portion of the voltage signal below a predetermined frequency, the selected portion of the voltage signal is provided to the feedback amplifier to generate a feedback voltage, and the feedback voltage is applied to the second subset of the first plurality of electrodes, wherein the feedback voltage generates an electrostatic force on the diaphragm assembly, and the electrostatic force offsets the pressure.

22. The MEMS device according to claim 21, wherein: The predetermined frequency is 35 Hz.

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