A MEMS microphone having a backplate, a spring, and a membrane. In one embodiment, the membrane is supported in an approximate center of the membrane via a support. The support is connected to the approximate center of the membrane and an approximate center of the backplate. The membrane is connected to a spring that provides an electrical connection. The membrane may be electrically biased via the electrical connection. One or more overtravel stops are fixed to the backplate and pass through an aperture of the membrane. The overtravel stops are configured to prevent movement of the membrane in a radial direction opposite to the backplate. The membrane includes a stress gradient, a corrugation, or another structure that sets or determines a stiffness of the membrane.

BACKGROUND

Embodiments of the disclosure relate to micro-electromechanical system (MEMS) microphones and methods of their construction. In particular, embodiments of the disclosure relate to constructions of a membrane of the MEMS microphone and overtravel stops that support said membrane.

Capacitive MEMS microphones measure sound pressure levels with a pressure-sensitive membrane. The membrane must be of sufficient mechanical strength to withstand various acoustic pressures without being destroyed. In addition to mechanical strength, the membrane must be sensitive to sensing small acoustic pressures. Sensitivity, natural frequency, and response characteristics are affected by the construction and shape of the membrane and the mounting of the membrane to the MEMS microphone die. Therefore, performance of the MEMS microphone is due, at least in part, to the membrane structure and mounting configurations of the membrane.

SUMMARY

Certain embodiments provide a MEMS microphone including a membrane with features that determine a stiffness of the membrane. One particular embodiment provides a MEMS microphone that includes at least one spring having a first end and a second end. The first end of the spring is connected to the membrane. The MEMS microphone also includes a backplate and a support connected to a central region of the membrane. The support is also connected to the backplate. The support is positioned between the membrane and the backplate.

Another embodiment provides a method of limiting the movement of a membrane of a MEMS microphone. The MEMS microphone includes a backplate, an overtravel stop, and a spring. The method includes coupling a first end of the spring to the membrane and coupling a central region of the membrane via a support to a central region of the backplate. An overtravel stop is positioned through an aperture in the membrane.

Other aspects of embodiments of the disclosure will become apparent by consideration of the detailed description and accompanying drawings.

DETAILED DESCRIPTION

A typical MEMS microphone senses acoustic pressure with a flexible member connected with one or more springs to a housing or a rigid member of the MEMS microphone. In one example, the flexible member may be a membrane such as a diaphragm and the rigid member may be a backplate. In another example, the flexible member may be a backplate while the rigid member may be a membrane. In the examples illustrated, the flexible member is the membrane and the rigid member is the backplate. The membrane is biased with a voltage differential relative to the backplate. When the membrane deflects due to acoustic pressure, a distance between the membrane and the backplate varies in proportion to the magnitude of the acoustic pressure. As the distance fluctuates, an amount of capacitance between the membrane and the backplate varies in proportion to the change in distance. The amount of capacitance on across the membrane and the backplate sets a potential that varies proportionally to the change in capacitance. A preamplifier generates an electrical signal indicative of the amount and change of potential and acoustic pressure incident on the membrane.

FIG. 1Aillustrates a cross-sectional view of a MEMS microphone101in accordance with one embodiment. The MEMS microphone101includes a membrane103, a backplate105, and a support member107. The backplate105includes perforations109(e.g., acoustic holes/vents) that allow sound waves to pass through the backplate105. The sound waves impinge on the membrane103and cause deflection of the membrane103with respect to the backplate105. The backplate105and the membrane103may be flat, circular, and/or positioned in parallel layers. The backplate105and the membrane103are spaced a predetermined distance apart in a radial direction of the membrane103and the backplate105. The support member107sets the predetermined distance of spacing between the backplate105and the membrane103. The backplate105may be fabricated as a single layer formed from polysilicon. In some embodiments, the backplate105may be fabricated as a plurality of layers. The materials, in one embodiment, may be gold material deposited on silicon nitride or polysilicon by various types of deposition. Other types of material for forming single or multiple layered backplate are possible, depending on applications. The membrane103may be fabricated from materials such as polysilicon, silicon, or the like. Other types of materials for forming the membrane103are possible, depending on the application.

In some embodiments, the support member107is formed in a substrate and couples an inner region111of the membrane103to the backplate105either directly or indirectly. As a consequence, the membrane103is mechanically connected to the support member107, and the support member107is mechanically connected to the backplate105. As shown, the membrane103coupled to the backplate105via the support member107is suspended freely below the backplate105. The support member107may be non-conductive and/or formed of a metal oxide and may provide electrical isolation between the backplate105and the membrane103. The support member107may be positioned near an approximate center113of the membrane103and/or the backplate105. For example, the support member107may be located at an approximate geographical center located at the inner region111of the membrane103. The approximate center113of the membrane103is positionally fixed relative to the backplate105by the support member107. Although one support member107is illustrated herein, more than one support member may be incorporated into the MEMS microphone101to space the backplate and the membrane apart.

As illustrated inFIG. 1B, a plurality of support members107positioned side by side couple the inner region111of the membrane103to the backplate105either directly or indirectly. The support members107, in some embodiments, have equal height and width. In other embodiments, one of the support members107may have a width greater or lesser than the width of another one of the other support members107without sacrificing the performance of the MEMS microphone101. More than two support members107may be provided between the membrane103and the backplate105, depending on the applications. As illustrated inFIG. 1C, the MEMS microphone101also include a plurality of support members107for coupling the membrane103to the backplate105. As depicted, the support members107are in a stacked configuration which is different from the support members in side-by-side configuration as illustrated inFIG. 1B. Unlike the previous figures, whether a single support member107as illustrated inFIG. 1Aor side-by-side support members107as illustrated inFIG. 1B, the support members107coupled to both the backplate105and the membrane103. As illustrated inFIG. 1C, a top support member107ais coupled to the backplate105whereas a bottom support member107bis coupled to the membrane103. The top support member107aand the bottom support member107bare attached to each other by various fastening techniques. In one example, the support members107a,107bmay be formed of same material. In another example, the support members107a,107bmay be formed of different material. In yet another example, the support members107a,107band the backplate105may be formed from the same material. An optional insulating layer member may be formed between the support members107a,107bto isolate the membrane103and the backplate105. The support members107inFIGS. 1A-1Cmay be in various forms of geometry, size, and shape, depending on the particular application.

FIGS. 2A and 2Bare top views of the membrane103ofFIG. 1A. In these figures, the backplate105has been removed for purposes of illustration.FIG. 2Ais a full top view of the membrane103.FIG. 2Bis a close-up view of a portion of the membrane103. The membrane103includes a spring215. The spring215is formed from a portion of the same structure as the membrane103. A separation217(e.g., a slit) is made between the membrane103and the spring215. The separation217may be formed by slicing along a perimeter of the portion of the membrane103thus decoupling at least part of the spring215from the membrane103. The spring215remains connected to the membrane at a first end219. At a second end221, the spring215is connected to either the backplate105or a part of the housing of the MEMS microphone101. The spring215provides an electrical pathway to generate a bias voltage on the membrane103. In some embodiments, the MEMS microphone101contains only a single spring215. In such embodiments, the spring215provides a single electrical connection point to the membrane103. In some embodiments, as in the illustrated embodiment, the spring215is long and narrow. In other examples, the spring215may be short and wide, depending on the particular application. A spring215that is long and narrow has a low stiffness factor that has reduced or little effect on the overall stiffness of the membrane103. Therefore, in such embodiments, the spring215has little impact on mechanical performance and characteristics of the membrane103. In addition, the spring215has little impact on the responsiveness of the MEMS microphone101to acoustic pressure.

The characteristics of the membrane103, such as shape, size, and material may alter the response of the membrane103to incident sound waves. As such, these characteristics also determine stiffness, natural frequency, and mode shapes of the MEMS microphone101. When the membrane103receives incident acoustic pressure, the membrane flexes around the support member107based on the stiffness of the membrane103. Since the membrane103is not supported from its perimeter, mechanical connections at the perimeter (e.g., springs) do not have an appreciable effect on the performance of the MEMS microphone101. Rather, when the membrane103is fixed at the center, the characteristics of the membrane103may be adjusted by introducing variations into the design and structure of the membrane103. Variants produced by these variations are illustrated by the embodiments shown inFIGS. 3-5.

FIG. 3is a cross-sectional view of a MEMS microphone301according to another embodiment. The MEMS microphone301includes a membrane303, a backplate305, and a support member307. The support member307is formed in a substrate and couples an inner region311of the membrane303to the backplate305either directly or indirectly. The support member307may be fixed to the membrane303at an approximate center313of the membrane303. The MEMS microphone301also includes perforations309in the backplate305that allow sound waves to pass through the backplate305. In this embodiment, the membrane303has a predetermined stress gradient and a curvature of the membrane303. In other respects the MEMS microphone301is the same as the MEMS microphone101. The membrane303coupled to the backplate305via the support member307is suspended freely below the backplate305. The predetermined stress gradient is set at the time of manufacture to achieve a desired curvature of the membrane303. Based on the stress gradient and the curvature, the stiffness of the membrane303is increased by a certain factor as the stress gradient is increased. The membrane303is manufactured to exhibit and maintain the predetermined stress gradient according to design specifications. In one embodiment, the curvature caused from the stress gradient may be induced toward a perimeter310of the backplate305, as depicted inFIG. 3. Alternatively, the curvature may be induced away from the perimeter310of the backplate305. The stress gradient is predetermined such that a desired stiffness, natural frequency, and mode shapes are also predetermined for the MEMS microphone301. Although only one support member307is illustrated, it is understood that a plurality of support members in a stacked configuration, side-by-side configuration, or the like, as illustrated in previous figures, may be used.

FIG. 4Ais a cross-sectional view of a MEMS microphone401according to yet another embodiment. The MEMS microphone401includes a membrane403, a backplate405, and a support member407. The support member407is formed in a substrate and couples an inner region411of the membrane403to the backplate405either directly or indirectly. The support member407may be fixed to the membrane403at an approximate center413of the membrane403. The MEMS microphone401also includes perforations409in the backplate405as in the previously described embodiments. In this embodiment, the membrane403includes a structure412affixed to the membrane403. In other respects, the MEMS microphone401is the same as the MEMS microphones101and301. The membrane403is manufactured such that the structure412is incorporated in the membrane403itself, on a top of the membrane403, or on a bottom of the membrane403. The structure412may take a variety of forms. As illustrated inFIG. 4B, the structure412may be in the form of circle beam. Although only one circle beam is illustrated, more than one circle beam may be incorporated into the MEMS microphone401. For example, an optional inner circle beam may be provided within the structure412. In another example, an optional outer circle beam may surround the structure412. In yet another embodiment, a plurality of circle beams may be formed either within the structure412or surround the outer region of the structure412, or combination thereof. The structure412as illustrated inFIG. 4C, is different from the previous embodiment. InFIG. 4C, the structure is in the form of a radial beam or spokes. The structure412, in the embodiment illustrated inFIG. 4D, may include a plurality of spots affixed to the membrane403. The spots can come in various sizes, shapes, and geometries. For example, the structure412may be a rib, a circle beam, a spot, a spoke or some combination of these forms. The structure412may be formed at the same time as the membrane403such that the structure412forms a single contiguous surface with the membrane403. The membrane403has predetermined response characteristics based on the type and form of the structure412. For example, the MEMS microphone401has its stiffness, natural frequency, and mode shapes determined, at least in part, on the structure412. The size and shape of the structure412is determined such that the desired response characteristics of the MEMS microphone401are achieved. Although only one support member407is illustrated inFIG. 4A, it is understood that a plurality of support members in a stacked configuration, side-by-side configuration, or the like, as illustrated in previous figures may be incorporated into the MEMS microphone401.

FIG. 5is a cross-sectional view of a MEMS microphone501according to yet another embodiment. The MEMS microphone501includes a membrane503, a backplate505, and a support member507. The support member507is formed in a substrate and couples a center region511of the membrane503to the backplate505either directly or indirectly. The support member507may be fixed to the membrane503at an approximate center513of the membrane503. The MEMS microphone501also includes perforations509in the backplate505as in the previously described embodiments. In this embodiment, the membrane503includes a corrugation515on the membrane503. The corrugation515includes one or more grooves or ridges positioned within, on a top, or on a bottom of the membrane503. The corrugation515may include a single groove or ridge or may include multiple grooves or ridges extending radially along the membrane503. The corrugation515may take different forms of size and geometry. The response characteristics of the MEMS microphone501may be tuned, in part, based on the types and sizes of the corrugation515. The membrane503has its stiffness, natural frequency, and mode shapes determined, at least in part, by the type and size of the corrugation515. Although only one support member507is illustrated, it is understood that a plurality of support members107in a stacked configuration, side-by-side configuration, or the like, as illustrated in previous figures may be incorporated into the MEMS microphone501.

FIG. 6is a cross-sectional view of a MEMS microphone601according to yet another embodiment. The MEMS microphone601includes a membrane603(support for the membrane not shown) and a backplate605. As in the previous embodiments, the MEMS microphone601includes perforations609in the backplate605. In this embodiment, the MEMS microphone601includes an overtravel stop617. The overtravel stop617may be used in combination with any or all of the other embodiments. As such, this embodiment provides configurations for bracing the membranes103,303,403,503, as described in other embodiments, against excessive travel in at least an axial direction opposite the backplate605. In some embodiments, the backplate605itself provides an overtravel stop toward the backplate605.

The overtravel stop617passes through an aperture619of the membrane603. The overtravel stop617is positionally fixed relative to the MEMS microphone601. In some embodiments, the overtravel stop617and the backplate605are formed of a single structure (e.g., a substrate). The overtravel stop617includes a first end621affixed to the backplate605and a second end623positioned on an opposite side of the membrane603as the backplate605. Although not illustrated, in some embodiments, the second end623is fixed to a portion of the MEMS microphone601other than the membrane603. In another embodiment, the first end621is a support member similar to the support members107,307,407,507illustrated in other embodiments. In another embodiment, the overtravel stop617includes only the second end623extended at a distance from the membrane603via an optional connecting member625. In yet another embodiment, the overtravel stop617includes only the second end623directly suspended below the membrane603without the connecting member625. At least a portion of the second end623is larger than the aperture619. The second end623prevents the membrane603from moving beyond the position of the overtravel stop617in a direction opposite of the backplate605. The membrane603is free to move with respect to the overtravel stop617until the membrane603reaches a maximum deflection (i.e., a furthest point of travel). At the maximum deflection, the second end623of the overtravel stop617contacts the membrane603and prevents further movement.

The overtravel stop617may be non-conductive and/or formed of a metal oxide and may provide electrical isolation between the backplate605and the membrane603. Other types of material may be used to form the overtravel stop617, depending on the particular application. The overtravel stop617may be positioned in various discrete locations along the membrane603. For example, the overtravel stop617may be positioned proximal to a support member of the membrane603. In some embodiments, a plurality of overtravel stops617may be used. The overtravel stops617may be positioned around the support members107,307,407, and507in various configurations, such as, having multiple overtravel stops617positioned approximately equal radial distances from the support members107,307,407, and507. In this case, the overtravel stops617may also be positioned equal distances from each other, such as, on opposite sides of the support members107,307,407, and507. The overtravel stops617may also be positioned with approximately equal spacing around the perimeter of the membranes103,303,403,503, and603and with approximately equal distances between each of the overtravel stops617.

Based on the acoustic pressure, the membranes103,303,403,503, and603experience differing magnitudes of acceleration in an axial direction (e.g., a direction of applied acoustic pressure). If the acoustic pressure is large enough, the acceleration may exceed the restorative force of the one or more springs215and the resisting force provided by the stiffness of the membranes103,303,403,503, and603. Since the restorative force of the springs215may be minimal, the overtravel stop617provides additional support for the membrane103. In such cases, the overtravel stop617prevents overtravel and, as a consequence, potential damage to the membranes103,303,403,503, and603. Therefore, the overtravel stop617helps protect the membrane103,303,403,503, and603from large changes in acceleration of the MEMS microphone101, as may occur, for example, as a result of impacts, heavy vibrations, and large pressure waves.

FIG. 7illustrates a MEMS microphone701according to one embodiment. The MEMS microphone701is similar in construction to the MEMS microphone101ofFIG. 1. In contrast to the microphone101ofFIG. 1, the membrane703includes a support member707located near an approximate center713of the membrane703and/or the backplate705. The support member707is integrated into the membrane703as a single structure. Optional structures, such as those structures described inFIGS. 4A-4D, may be coupled to and suspended below the membrane703. The height and width of the support member707may be modified according to the particular application.

MEMS microphones101,301,401,501,601,701with centered supported membranes allow radial expansion or contraction to release residual stress, and thereby are compliant with enhanced sensitivity.

Thus, embodiments of the disclosure provide, among other things, a MEMS microphone with a center-supported membrane and one or more overtravel stops. The membrane includes various features that help determine the response characteristics for the membrane and thus, the response characteristics for the MEMS microphone. The overtravel stops restrict movement of the membrane to prevent overtravel and provide support for the center-mounted membrane. Various features and advantages of the disclosure are set forth in the following claims.