Stress reduced diaphragm for a micro-electro-mechanical system sensor

A micro-electro-mechanical system (MEMS) sensor can comprise a substantially rigid layer having a center. The MEMS sensor can further comprise a movable membrane that can be separated by a gap from, and be disposed substantially parallel to, the substantially rigid layer. The MEMS sensor can further include a plurality of pedestals extending into the gap, where a first pedestal of the plurality of pedestals can be of a first size, and be disposed a first distance from the center, and a second pedestal of the plurality of pedestals can be a second size different from the first size, and be disposed at a second distance from the center. In another aspect, the substantially rigid layer and the movable membrane can be suspended by a plurality of suspension points. In another aspect, at least one of the plurality of pedestals can be disposed so as to limit a deformation of the movable membrane.

TECHNICAL FIELD

This disclosure generally relates to embodiments for a device comprising a micro-electro-mechanical systems (MEMS), and more particularly to MEMS sensors.

BACKGROUND

MEMS sensors, include audio and pressure sensors, can be composed of a membrane suspended over a rigid surface. This membrane can be subject to uneven levels of stress in some circumstances. This uneven stress can cause problems, especially when MEMS sensors are exposed to sound or pressure levels approaching or in excess of their pressure level capabilities.

Consequently, conventional MEMS technologies have had some drawbacks, some of which may be noted with reference to the various embodiments described herein.

SUMMARY

The following presents a simplified summary of one or more of the embodiments of the present invention in order to provide a basic understanding of the embodiments. This summary is not an extensive overview of the embodiments described herein, e.g., it is intended to neither identify key or critical elements of the embodiments nor delineate any scope of embodiments or the claims. A purpose of this summary is to present some concepts of the embodiments in a simplified form as a prelude to the more detailed description that is presented later. It will also be appreciated that the detailed description may include additional or alternative embodiments beyond those described in the Summary section.

Generally speaking, the present disclosure recognizes and addresses, in at least certain embodiments, the issue of excessive sound pressure on a MEMS sensor. Some of the disclosed systems and methods provide for a plurality of pedestals of different lengths to reduce the stress on different components of the MEMS sensor, e.g., at edge points where a movable membrane is suspended over the substantially rigid layer.

In one or more embodiments, a MEMS sensor can comprise a substantially rigid layer having a center and a movable membrane separated by a gap from, and disposed substantially parallel to, the substantially rigid layer. In the one or more embodiments, the MEMS sensor can further comprise a plurality of pedestals extending into the gap, where a first pedestal of the plurality of pedestals can be of a first size, and be disposed a first distance from the center, and a second pedestal of the plurality of pedestals can be of a second size different from the first size, and be disposed at a second distance from the center. In another aspect, the plurality of pedestals can be disposed on the substantially rigid layer, extending into the gap. In an alternative embodiment, the plurality of pedestals can be disposed on the movable membrane, extending into the gap. In another aspect, the substantially rigid layer and the movable membrane can be suspended by a plurality of suspension points, and a stress on the movable membrane can be substantially located at a suspension point of the plurality of suspension points. In another aspect, at least one of the plurality of pedestals can be disposed so as to limit a deformation of the movable membrane.

In another aspect, the first size can be selected based on a stress on the movable membrane. In another aspect of one or more embodiments, at least one of the first size the second size can be selected to reduce the stress on the movable membrane. In another aspect, the first pedestal can be shorter than the second pedestal. In another aspect, the first distance can be closer to the center than the second distance. In aspects of additional embodiments, the reduction of the stress on the movable membrane is based on at least one of the plurality of pedestals being disposed so as to limit a deformation of the movable membrane. In another aspect, the MEMS sensor of one or more embodiments can be one of an acoustic sensor or a pressure sensor.

In other embodiments, a method can comprise disposing, on a surface comprising one of a movable membrane or a substantially rigid layer, a plurality of pedestals, with a first pedestal of the plurality of pedestals being a first size, and disposed a first distance from a center of the surface, and a second pedestal of the plurality of pedestals can be of a second size different from the first size, and be disposed at a second distance from the center of the surface. The method can further comprise suspending from a plurality of suspension points, the movable membrane to be substantially parallel to, and separated by a gap from, the substantially rigid layer, with the plurality of pedestals being disposed to extend into the gap. In one or more embodiments, the method can further comprise, disposing a capacitance sensor to detect, in a micro-electro-mechanical system (MEMS), a capacitance change caused by movement of the movable membrane. In another aspect of the method, at least one of the plurality of pedestals are disposed so as to limit a deformation of the movable membrane. In another aspect, the first size can be selected so as to limit a deformation of the movable membrane.

In another aspect, a stress on the movable membrane can be limited based on the limiting the deformation of the movable membrane. In another aspect, the stress on the movable membrane is limited at a suspension point of the plurality of suspension points. In a variation of the one or more embodiments described herein, the first pedestal can be shorter than the second pedestal. In another aspect, the first distance can be closer to the center than the second distance. In one or more embodiments, the MEMS sensor of the method can be one of an acoustic sensor or a pressure sensor.

DETAILED DESCRIPTION

Reference throughout this specification to “one embodiment,” “an embodiment,” or “one or more embodiments” can be an indication that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment,” “in an embodiment,” and “in one or more embodiments” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Furthermore, to the extent that the terms “includes,” “has,” “contains,” and other similar words are used in either the detailed description or the appended claims, such terms are intended to be inclusive—in a manner similar to the term “comprising” as an open transition word—without precluding any additional or other elements. Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

Furthermore, the word “exemplary” and/or “demonstrative” is used herein to mean serving as an example, instance, or illustration. For the avoidance of doubt, the subject matter disclosed herein is not limited by such examples. In addition, any aspect or design described herein as “exemplary” and/or “demonstrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs, nor is it meant to preclude equivalent exemplary structures and techniques known to those of ordinary skill in the art.

FIG. 1depicts a two-dimensional axisymmetric cross-section of MEMS sensor100comprising substantially rigid layer110, movable membrane120suspended from suspension point170, and pedestals130A-D disposed in a gap between substantially rigid layer110and movable membrane120, in accordance with one or more embodiments. As discussed further herein, for illustrative purposes, MEMS sensor100is depicted as having deformed elements, e.g., substantially rigid layer110and movable membrane120are deformed in accordance with force190.

As would be appreciated by one having skill in the relevant art(s), given the disclosure herein, in some implementations, MEMS sensor100can operate when sound or other types of pressure hit movable membrane220, which, depending on the amount of pressure, can cause movable membrane220to move towards and away from substantially rigid layer210, this movement causing a capacitance change which can be detected by different types of sensors.

It should be noted that substantially rigid layer210can also be termed a backplate, a non-moving plate, and a fixed plate, and can also have holes (e.g., termed acoustic holes and other terms) to let pressure through to movable membrane220, these not being depicted in FIGS. of this disclosure. It should also be noted that movable membrane220can also be termed a diaphragm, a movable plate, a conductive plate, and other similar terms.

One having skill in the relevant art(s), given the disclosure herein will appreciate that, because MEMS sensor100is, by design, generally expose to aspects of the environment, force190can a be force to which MEMS sensor100can be exposed, including but not limited to, pressure from acoustic waves (e.g., sound waves propagated through air) and other forces (e.g., air from an air gun used to clean a circuit board upon which MEMS sensor100is disposed). As discussed herein, deformation of movable membrane220can, in some circumstances such as application of a large acoustic pressure, cause movable membrane220to hit substantially rigid layer210. This deformation, particularly at the outer edges where the membrane is suspended or otherwise attached to the MEMS structure, can cause a very low radius of curvature that can lead to stress concentration, e.g., at the outer edges. These stress points, in some cases, being exposed to the highest stress of movable membrane220, are discussed below inFIGS. 6 and 8, along with difference approaches that can be employed by one or more embodiments to reduce these stresses.

As discussed further below,FIG. 1depicts MEMS sensor100with deformations based on a particular level of pressure from force190, with one or more embodiments having various features that can improve how MEMS sensor100handles these different levels of pressure, including levels of pressure that cause a failure of implementations without benefit of the approaches described herein. In a non-limiting example, one implementation of MEMS sensor100has a maximum sound pressure level (max SPL) of 135-145 dB SPL, above which operation of the MEMS sensor can be impaired, and mechanical failure (e.g., of movable membrane220) can occur, e.g., from 160-180 dB SPL being an example excess pressure range. As noted above, with some implementations of MEMS sensors being in integrated circuits on circuit boards commonly subject to cleaning by compressed air, approaches described herein can reduce a likelihood of mechanical damage from pressure overload. In should also be appreciated that, even in non-overload circumstances, by reducing stress on certain parts of MEMS sensors, one or more embodiments can extend the lifespan of these devices.

As depicted inFIG. 1, a portion of MEMS sensor100is shown, e.g., the half of the sensor extending from center point160. As noted above,FIG. 1depicts a two-dimensional 2D axisymmetric cross-section of MEMS sensor100, e.g., in this example substantially rigid layer110and movable membrane120are circular, with other shapes being possible, in accordance with one or more embodiments. In this example, as discussed below in the examples ofFIGS. 3, 7, and 8, pedestals130A-D, are of at least two lengths, e.g., pedestals130A-B are of a first length and pedestals130C-D are of a second length, different than the first length. In addition, pedestals130A-D are different distances from center point160, e.g., pedestal130B is distance150A from center point160and pedestal130C is distance150B from center point160. Example distance from center point160are illustrated by measurements155, e.g., pedestals130B and130D are approximately 270 μm and 320 μm from center point160, respectively.

Generally speaking, in accordance with one or more embodiments, one or more of factors that include, but are not limited to, a number of pedestals130A-D, length of respective pedestals, distance of respective pedestals from center point160, distance of respective pedestals from suspension point170, and distance of respective pedestals from other pedestals, can individually affect, or be combined to affect, the stress on different components of MEMS sensor100based on force190. To illustrate some of these features, example lengths of pedestals and placement distances are discussed withFIGS. 2-5 and 7below, while example changes in stress levels on components of MEMS sensor100based on force190are discussed withFIGS. 6 and 8below.

FIG. 2depicts a block diagram of a cross section of MEMS sensor200comprising pedestals230A-B of substantially equal lengths, in accordance with one or more embodiments. Repetitive description of like elements and/or processes employed in respective embodiments is omitted for sake of brevity.

In contrast to the deformations caused by force190ofFIG. 1, it should be noted that MEMS sensor200is depicted as being under zero or minimal stress, and as a result, rigid layer110and movable membrane120are depicted without deformation. Based on this lack of deformation, example pedestals230A-B are depicted as substantially perpendicular to substantially rigid layer110extending into gap225between substantially rigid layer210and movable membrane220. As noted above, for illustrative purposes, in this example, pedestals230A-B and other pedestals depicted, are of substantially equal length.

It should be noted thatFIG. 2illustrates gap225, which can be an air gap between substantially rigid layer210and movable membrane220, as well as other instances of substantially rigid layer and movable membrane shown in the examples ofFIGS. 3-8described below.

FIG. 3depicts a block diagram of a cross section of MEMS sensor300comprising pedestals330A-C, some having different lengths from other pedestals, in accordance with one or more embodiments. Repetitive description of like elements and/or processes employed in respective embodiments is omitted for sake of brevity.

LikeFIG. 2described above, inFIG. 3, for illustrative purposes, substantially rigid layer310and movable membrane320are depicted as not subject to force (or subject to a minimal force) such that no deformation substantially rigid layer310and movable membrane320is depicted.

It should be noted that, in accordance with one or more embodiments, in an alternative to the examples discussed thus far, any pedestals discussed herein (e.g., in the examples ofFIG. 1-3and additional embodiments discussed below) can be disposed on either substantially rigid layer310as depicted or on movable membrane220(not shown), e.g., affixed to or a part of, movable membrane220extending into gap325toward substantially rigid layer310. It should also be noted that, as described herein, pedestals330A-C (as well as other example pedestals described herein) can also be referred to as dimples, protrusions, standoff elements, and other similar terms.

To illustrate some features of one or more embodiments,FIG. 3includes labels for regular dimple height340(e.g., including pedestal330A and other pedestals of substantially similar height) and extended dimple height350(e.g., including pedestal330C and other pedestals of substantially similar height. As noted above, it should be noted that, although the dimples of the extended dimple height350group are depicted as of a substantially similar length, in one or more embodiments, to achieve various benefits described herein, different heights can be selected for the dimples of extended dimple height350, e.g., increasing in size from the dimples adjacent to the regular dimple height dimples to the opposite end of the group (e.g., pedestal330C). Different benefits of one or more embodiments are discussed withFIGS. 6 and 8below, e.g., changes in stress loads under which different components are subjected based on one or more embodiments described herein.

FIG. 4depicts a block diagram of a cross section of MEMS sensor400that includes a more detailed view of the height430A-B of pedestals410A-D (as well as relative height435) as well as the distances420A-C between pedestals. Repetitive description of like elements and/or processes employed in respective embodiments is omitted for sake of brevity. It should be noted that, as described above, base405, upon which pedestals410A-D are disposed, can, in one or more embodiments, be either substantially rigid layer310as depicted as well as movable membrane320.

In an alternative embodiment, various features and benefits of one or more embodiments can be achieved by individual pedestals410A-D being variously placed on either substantially rigid layer310as depicted as well as movable membrane320, e.g., pedestals410A-B being disposed on base405as substantially rigid layer310, and pedestals410C-D being disposed on a movable membrane320opposite to base405(not shown).

As described above, differences in spacing of pedestals410A-D can affect the results achieved by one or more embodiments, e.g., the selection of substantially similar distances420A-B between pedestals410A-B and distance420C between pedestals410C-D can affect the results of one or more embodiments, e.g., as described withFIGS. 6 and 8below, the stress on movable membrane320at suspension point170, as well as other results.

It should be noted that different distances between individual pedestals, and the length, size, composition, and any other characteristics of the pedestals can be selected for different implementations to achieve different results described and suggested by the present disclosure. For example, as depicted inFIG. 4, while pedestals410A-B are shown with substantially the same length, pedestals410B-D have a gradual transition between the length of pedestal410B and410D, e.g., based on the length of pedestal410C. One having skill in the relevant art(s), given the description herein, would appreciate that the depicted smooth transition, as well as any other transition, can be selected in different implementations of one or more embodiments described herein.

It should be noted that other elements depicted inFIG. 4, including but not limited to, the relative differences in height between pedestals410B-C and410C-D, can also affect the results of one or more embodiments. As discussed further withFIG. 8below, one approach that can be used by one or more embodiments to alter (e.g., maximize) one or more benefits is to select different heights430A-B and distances420A-C, so as to cause different results.

FIG. 5depicts another, more detailed block diagram of a cross section of MEMS sensor500where substantially rigid layer510and movable membrane520are subject to force190, in accordance with one or more embodiments. Repetitive description of like elements and/or processes employed in respective embodiments is omitted for sake of brevity.

For illustrative purposes, it should be noted thatFIG. 5depicts substantially rigid layer and movable membrane before and after force190is applied, e.g., substantially rigid layer210is deformed to be substantially rigid layer510, and movable membrane220is deformed by distance590to be movable membrane520. Example non-limiting sizes of elements can be estimated by vertical scale560and horizontal scale570, though other relative sizes can also have similar results, based on various features of embodiments described herein.

It should be noted that not all pedestals230A-B (extending from substantially rigid layer510) are depicted as contacting movable membrane520, e.g., while pedestal230A is depicted as contacting movable membrane520, a gap is depicted between pedestal230B and movable membrane520. The causes, results, and effects of one or more embodiments on similar gaps are discussed withFIGS. 6 and 8below.

FIG. 6depicts a more detailed view600of MEMS sensor500ofFIG. 5, with stress levels labeled on both movable membrane520and substantially rigid layer510, in accordance with one or more embodiments. Repetitive description of like elements and/or processes employed in respective embodiments is omitted for sake of brevity.

Specifically,FIG. 6depicts pedestals630A-C, with pedestal630A having no gap with movable membrane520, pedestal630B having a gap635A and pedestal630C having a gap635B larger than gap635A. One of the results of MEMS sensor500operating with pedestals630B-C having gaps635A-B is that movable membrane520(e.g., at stress point680) can be subject to stress higher than other parts of movable membrane520.

In some circumstances (e.g., under relatively high force190) the stress at stress point680and other portions of movable membrane520can cause movable membrane520to incur mechanical failure, e.g., rupture or otherwise fail. One of the benefits that can accrue from various features of one or more embodiments (e.g., pedestals of varying heights) is a relative reduction in stress on movable membrane520, e.g., at stress point680and other points, as compared to the embodiments depicted inFIGS. 5 and 6.

FIG. 7depicts a block diagram of a cross section of MEMS sensor700comprising pedestals730A-D disposed on substantially rigid layer710, in accordance with one or more embodiments. Repetitive description of like elements and/or processes employed in respective embodiments is omitted for sake of brevity.

LikeFIG. 5discussed above, for illustrative purposes, it should be noted thatFIG. 7depicts the substantially rigid layer and the movable membrane before and after force190is applied, e.g., substantially rigid layer310is deformed to be substantially rigid layer710, and movable membrane320is deformed by distance790to be movable membrane720.

It should be noted that, unlike pedestals in similar position onFIG. 5, pedestals730B-D are of variable length and have no gap with deformed movable membrane720. Pedestal730A is depicted, in this example, as having gap735with movable membrane720. As noted throughout this disclosure, the existence of a gap between pedestals730A-D is but one factor that can affect the results of one or more embodiments, e.g., stress impressed upon deformed movable membrane720.

As discussed further withFIG. 8below, in this example, the contact between pedestals730B-D and deformed movable membrane720can affect stress imposed by force190on both substantially rigid layer710and deformed movable membrane720.

FIG. 8depicts a more detailed view800of MEMS sensor700ofFIG. 7, with stress areas850A-B and880respectively labeled on substantially rigid layer710and movable membrane720, in accordance with one or more embodiments. Repetitive description of like elements and/or processes employed in respective embodiments is omitted for sake of brevity.

As noted with the discussion ofFIG. 7above, in one or more embodiments, different aspects of pedestals730A-B (e.g., length, placement, whether a gap with movable membrane720exists at different force190levels) can affect stress levels on one or both of substantially rigid layer710and movable membrane720as compared to not employing modified pedestals and pedestal placement (e.g., as described with the examples ofFIG. 6andFIG. 8).

For example, in the example depicted inFIG. 8(e.g., with variable length pedestals730A-D placed, like the distance between pedestals730A-B, at different intervals) stress can be reduced on movable membrane720during the application of force190, as compared to movable membrane520ofFIG. 6. More specifically, inFIG. 6, with an example uniform pedestal height of 0.5 p.m, in some circumstances stress point680can be the point of highest stress during the application of force, e.g., a maximum von mises stress of 0.27 GPa at a force190of 10 kPa.

In contrast to the example stress at stress point680, at stress point880, based on a variable pedestal height from 0.5 μm to 1.85 μm used in the example ofFIG. 8, while stress point880is still the highest stress point of movable membrane720, in this example, the maximum von mises stress at stress point880can be reduced by 33% from the example ofFIG. 6, from 0.27 GPa to 0.18 GPa. In one or more embodiments, the reduction in stress is proportional to the deflection of movable membrane720.

Other differences in stress from the examples ofFIG. 6andFIG. 8include at points810A-B in substantially rigid layer710. For example, in the implementations ofFIGS. 6 and 8, at the application of 10 kPa force190, both stress point610A and810A can be under similar stresses, but stress point810A can have a lower maximum stress, e.g., a maximum von mises stress of 0.2 for stress point880and 0.4 for stress point680.

It is important to note that, in some implementations and configurations, one way that stress can be beneficially reduced on components of MEMS sensor700(e.g., stress point880) is by distributing stress to other components and locations on the same component, e.g., increasing stresses in these areas. For example, comparing stresses in movable membranes520and720associated with pedestals630A and730B, in some implementations the lower side of stress point890can have increased stress applied as compared to a stress point on the lower side of movable membranes520associated with pedestal630A. It would be appreciated by one having skill in the relevant art(s), given the disclosure herein, that one or more embodiments can reduce stress in a high stress area (e.g., stress point880) and balance the benefits of this reduction against potential increases in stress distributed across other parts of MEMS sensor700.

As noted throughout this disclosure, different aspects of one or more embodiments are implementation specific, e.g., the different sizes selected for different pedestals, the number of pedestals, the spacing of the pedestals, and the placement of the pedestals on either or both of substantially rigid layer710and movable membrane720. One approach that can be used by one or more embodiments to configure different aspects is an approach where a constant force190is selected (e.g., 10 kPa used as an example force withFIGS. 1-7above) and stresses associated with different pedestal configurations are measured. In alternative embodiments, the experimental approach (or any other approach) can be used to develop a mathematical model of the operation of different configurations.

FIG. 9illustrates a flow diagram of an example method900that can facilitate forming a MEMS sensor that can reduce stresses sustained by different components of the MEMS sensor during sensor operation, in accordance with one or more embodiments. For purposes of brevity, description of like elements and/or processes employed in other embodiments is omitted. Repetitive description of like elements and/or processes employed in respective embodiments is omitted for sake of brevity.

At910, example method900can dispose, on a surface comprising one of a movable membrane or a substantially rigid layer, a plurality of pedestals, with a first pedestal of the plurality of pedestals being a first size, and disposed a first distance from a center of the surface, and a second pedestal of the plurality of pedestals is of a second size different from the first size, and is disposed at a second distance from the center of the surface. For example, in one or more embodiments, method900can dispose, on a surface comprising one of movable membrane120or substantially rigid layer110, a plurality of pedestals130A-D, with a first pedestal130B of the plurality of pedestals being a first size, and disposed a first distance150A from center160of the surface, and a second pedestal130C of the plurality of pedestals130A-D is of a second size different from the first size (pedestal130B is smaller than pedestal130C), and is disposed at a second distance150B from the center160of the surface.

At920, example method900can suspend from a plurality of suspension points, movable membrane to be substantially parallel to, and separated by gap from, the substantially rigid layer, with the plurality of pedestals being disposed to extend into the gap. For example, in one or more embodiments, method900can suspend from a plurality of suspension points170, movable membrane120to be substantially parallel to, and separated by gap225from, the substantially rigid layer110, with the plurality of pedestals130A-D being disposed to extend into the gap.

At920, example method900can dispose a capacitance sensor to detect, in a micro-electro-mechanical system (MEMS), a capacitance change caused by movement of the movable membrane. For example, in one or more embodiments, method900can dispose a capacitance sensor to detect, in a micro-electro-mechanical system (MEMS)100, a capacitance change caused by movement of movable membrane120.