Abstract:
A method of fabricating a plurality of MEMS microphone modules by providing a first substrate wafer  62  on which are mounted a plurality of sets comprising an LED  102 , an IC chip  22  and a MEM microphone device  24 , where the LED  102  and IC chip  22  are surrounded and separated by first spacers  104, 64 A,  64 , the spacer  104  being much taller, attaching a second substrate on top of the first spacer elements above the IC chip  22 , mounting a MEMS microphone device  24  to the second substrate  60 , the second substrate not extending over the LED  102 , surrounding the MEMS microphone device by second spacers  32 A,  32 , attaching a cover wafer  28  across the whole first substrate wafer  62  covering all the plurality of sets, forming openings  30  to the MEMS cavities, dividing the substrate wafer  62  into individual MEMS microphone modules through the width of the separating spacers  104, 32, 64 . Conductive traces may extend through the spacers. Also defined are MEMS modules without LED&#39;s, without stacking, on a single substrate, or on either side of a single substrate.

Description:
[0001]    This disclosure relates to MEMS microphone modules and wafer-level fabrication techniques. 
         [0002]    A microphone refers to a transducer or sensor that converts sound into electrical signals. One type of microphone that can be integrated into small electronic devices is fabricated as a micro-electromechanical system (MEMS) and sometimes is referred to as a MEMS microphone or a MEMS condenser microphone. Such microphones can provide superior sound quality and demonstrate greater heat tolerance than some other types of microphones, which facilitates the use of high-volume surface mount manufacturing techniques. MEMS microphones currently are incorporated into a wide range of consumer electronic and other products such as cellphones, laptops, headsets and media tablets, as well as gaming applications, cameras, televisions and hearing aids. In some cases, multiple microphones may be incorporated into a single electronic product. For example, multiple microphones are now being adopted in some smartphones for noise suppression, in which the cancellation of ambient sounds is important for handsets when carrying out voice commands. Likewise, some laptops have three microphones: two are used in the lid on each side of a Webcam to provide clear, noise free communication, and a third is used to suppress the noise from the keys on the keyboard. 
         [0003]    In view of the increasingly widespread use of MEMS microphones in various electronic devices, it is desirable to find ways to improve manufacturing efficiency, reduce costs and reduce the size of the MEMS microphones. 
       SUMMARY 
       [0004]    The present disclosure describes MEMS microphone modules and fabrication techniques that, at least in some implementations, address some or all of the foregoing issues. 
         [0005]    For example, the disclosure describes various wafer-level fabrication techniques. A particular wafer-level method of fabricating multiple MEMS microphone modules includes providing a substrate wafer on which are mounted pairs of devices, each pair including a MEMS microphone device and an integrated circuit device to perform processing of signals from the MEMS microphone device. A cover wafer is provided over the substrate wafer to form a wafer stack, where the cover wafer and substrate wafer are separated by a spacer that serves as a wall surrounding respective pairs of devices. The method includes dividing the wafers into individual MEMS microphone modules each of which includes at least one of the MEMS microphone devices and an associated one of the integrated circuit devices, and wherein each MEMS microphone module has an opening through which sound can enter the MEMS microphone module. The disclosure describes other wafer-level fabrication techniques as well. 
         [0006]    The disclosure also describes various MEMS microphone modules. For example, in one aspect, a MEMS microphone module includes a first substrate and a second substrate on which is mounted a MEMS microphone device. The second substrate is separated from the first substrate by a first spacer. An integrated circuit device is mounted on the first substrate and arranged to perform processing of signals from the MEMS microphone device. A cover is separated from the second substrate by a second spacer. The module has an opening in the cover or in the second spacer through which sound can enter. 
         [0007]    According to another aspect, a MEMS microphone module includes a substrate, a MEMS microphone device mounted on a first surface of the substrate, and an integrated circuit device mounted on a second surface of the substrate, where the second surface is on an opposite side of the substrate from the first surface, and the integrated circuit device is arranged to perform processing of signals from the MEMS microphone device. A cover is separated from the substrate by a first spacer, and a second spacer is on the second surface of the substrate. The module has an opening in the cover or in the first spacer through which sound can enter. 
         [0008]    Some implementations include acoustics-enhancing features on an inner surface of the second spacer or an inner surface of the cover. The acoustics-enhancing features can be composed, for example, of a polymer material, a foam material or a porous material. Some implementations include one or more projections extending from an exterior surface of the cover. The projections can be used, for example, to facilitate positioning of the MEMS microphone module within a housing of an electronic or other device. 
         [0009]    One or more of the following advantages are provided in some implementations. For example, the MEMS microphone modules can, in some cases, improve reliability, performance or ease of manufacturing. The modules can be made to have a compact size with a relatively small footprint, which can be important for applications in which space is at a premium. Furthermore, the modules can be fabricated in wafer-level processes, which can facilitate the manufacture of multiple modules. 
         [0010]    Other aspects, features and advantages will be readily apparent from the following, detailed description, the accompanying drawings and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  illustrates a cross-section of an example of a MEMS microphone module. 
           [0012]      FIGS. 2-4  illustrate steps in an example wafer-level fabrication process. 
           [0013]      FIG. 5  illustrates another example of a MEMS microphone module. 
           [0014]      FIG. 6  illustrates yet another example of a MEMS microphone module. 
           [0015]      FIGS. 7, 8 and 9  illustrates further examples of MEMS microphone modules. 
           [0016]      FIG. 10  illustrates an example of a MEMS microphone module combined with a flash module. 
           [0017]      FIGS. 11-15  illustrate steps in an example wafer-level fabrication process. 
           [0018]      FIG. 16  illustrates another example of a wafer-level fabrication process. 
           [0019]      FIG. 17  illustrates a further example of wafer-level fabrication process. 
           [0020]      FIG. 18  illustrates a wafer stack resulting from the process of  FIG. 17 . 
           [0021]      FIG. 19  is an example of a MEMS microphone module obtained after separating the stack of  FIG. 18 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    As shown in  FIG. 1 , a MEMS microphone module  20  includes an integrated circuit (IC)  22  and a MEMS device  24  mounted on a printed circuit board (PCB) substrate  26 . Electrical wires  27  or electrical pads on the underside of IC  22  and MEMS device  22  can provide connections to PCB substrate  26 . IC  22  can be implemented, for example, as a semiconductor chip device and can include circuitry that performs analog-to-digital processing of signals from MEMS device  24 . The module  20  includes a cover  28  that includes an opening  30  to allow sound to enter the module. Cover  28  can be composed, for example, of a glass material, a plastic material or a printed circuit board (PCB) material such as FR4, which is a grade designation assigned to glass-reinforced epoxy laminate material. PCB substrate  26  and cover  28  are separated by spacers  32  that form sidewalls for the module. Spacers  32  may be formed as a single integral wall that surrounds MEMS microphone device  24  and IC  22 . 
         [0023]    Electrical contacts such as solder balls  29  or contact pads can be provided on the outer, bottom surface of PCB substrate  26 . Conductive vias  31  can provide electrical connections from wiring  27  to solder balls  29 . Module  20  can be mounted, for example, on a printed circuit board, e.g., using surface mount technology (SMT), next to other electronic components. The printed circuit board can be a constituent of an electronic device (e.g., a hand-held communication device such as a cellphone or smartphone), a laptop, a headset, a media tablet, an electronic product for a gaming application, a camera, a television or a hearing aid. Spacers  32  and cover  28  can be coated or lined with a conductive material to provide electromagnetic shielding. 
         [0024]    Module  20  can be made relatively small. For example, in some implementations, module  20  has dimensions on the order of about 5 mm of less (width)×5 mm or less (length)×3 or less mm (height). For example, in a particular implementation, module  20  has dimensions on the order of about 3 mm (width)×3 mm (length)×1 mm (height). Different dimensions may be appropriate for other implementations. 
         [0025]    Multiple MEMS microphone modules  20  can be fabricated at the same time, for example, in a wafer-level process. Generally, a wafer refers to a substantially disk- or plate-like shaped item, its extension in one direction (z-direction or vertical direction) is small with respect to its extension in the other two directions (x- and y-directions or lateral directions). On a (non-blank) wafer, a plurality of similar structures or items can be arranged, or provided therein, for example, on a rectangular grid. A wafer can have openings or holes, and in some cases a wafer may be free of material in a predominant portion of its lateral area. In some implementations, the diameter of a wafer is between 5 cm and 40 cm, and can be, for example between 10 cm and 31 cm. The wafer may be cylindrical with a diameter, for example, of 2, 4, 6, 8 or 12 inches, one inch being about 2.54 cm. The wafer thickness can be, for example, between 0.2 mm and 10 mm, and in some cases, is between 0.4 mm and 6 mm. 
         [0026]    In some implementations of a wafer-level process, there can be provisions for at least ten modules  20  in each lateral direction, and in some cases at least thirty or even fifty or more modules in each lateral direction. Examples of the dimensions of each of the wafers are: laterally at least 5 cm or 10 cm, and up to 30 cm or 40 cm or even 50 cm; and vertically (measured with no components arranged thereon) at least 0.2 mm or 0.4 mm or even 1 mm, and up to 6 mm or 10 mm or even 20 mm. 
         [0027]      FIGS. 2-4  illustrate various steps in an example wafer-level fabrication process. As shown in  FIG. 2 , multiple ICs  22  and MEMS devices  24  are mounted on a PCB substrate wafer  40 , for example, by pick-and-place equipment. Pairs of ICs  22  and MEMS devise  24  are spaced from one another in view of the lateral dimensions of modules. PCB substrate wafer  40  can comprise standard PCB materials (e.g., fiber glass or ceramic). Solder balls  29  can be provided on the side opposite the side on which ICs  22  and MEMS devise  24  are mounted. Conductive vias  31  can be provided through PCB substrate wafer  40  for electrical connection between wires  27  and the solder balls  29  on the exterior surface of the PCB substrate wafer. 
         [0028]    Next, as illustrated in  FIG. 3 , spacers  42  are formed, for example, by a replication or vacuum injection technique. The spacers  42  can be replicated, for example, directly on PCB substrate wafer  40  (or on a cover wafer  46 , described below) by a vacuum injection technique. In some implementations, spacers  42  are composed of a polymer material, for example, a hardenable (e.g., curable) polymer material, such as an epoxy resin. In Other implementations, spacers  42  are made of a PCB material (e.g., fiber glass or ceramic). In some implementations, instead of using a direct replication by a vacuum injection technique to form spacers  42 , a pre-formed spacer wafer is attached to PCB substrate wafer  40 . The pre-formed spacer wafer can be formed, for example, by replication. The spacer wafer can include openings (i.e., through-holes)  44  such that, when the wafers are stacked on one another, ICs  22  and MEMS devices  24  are laterally encircled by sidewalls formed by the spacer wafer. In case of a PCB spacer wafer, openings  44  can be made, for example, by micromachining. 
         [0029]    As illustrated in  FIG. 4 , cover wafer  46  is attached over spacers  42 . Cover wafer  46  includes openings  48  which correspond to the opening  30  in  FIG. 1 . Openings  48  can be formed, for example, by micromachining or by a replication technique. Openings  48  may have a circular, square or other shape. The shape and size of openings  48  can be selected to achieve desired acoustics or sound propagation. 
         [0030]    If a spacer wafer is used to provide spacers  42 , then the wafers (i.e., PCB substrate wafer  40 , spacer wafer and cover wafer  46 ) can be attached to one another, for example, by glue or some other adhesive to form a stack  49 . In some implementations, the wafers can be attached to one another in a different order than the one described above. For example, cover wafer  46  can be attached to the spacer wafer to form a sub-stack, which subsequently is attached to PCB substrate wafer  40 . As also noted above, in some implementations, spacers  42  are formed by a replication or vacuum injection technique, and may be formed directly on PCB substrate wafer  40  or cover wafer  46 . 
         [0031]    After stack  49  is formed, it is separated, for example, by dicing, along imaginary lines  50  (see  FIG. 4 ) into multiple individual modules  20 , each of which includes an IC  22  and associated MEMS microphone  24 , as shown in  FIG. 1 . If desired, the exterior surfaces of sidewalls  32  and cover  28  can be coated (or lined) with a conductive material to provide electromagnetic shielding of the components within module  20 . 
         [0032]    The footprint (i.e., the area coverage) of module  20  is dictated, at least in part, by the combined footprints of IC  22  and MEMS device  24 .  FIGS. 5 and 6  illustrate examples of modules in which IC  22  and MEMS device  24  are disposed one over the other, rather than side-by-side. In some implementations, such arrangements can help reduce the overall footprint of the module. 
         [0033]    For example,  FIG. 5  shows an example of a module  58  in which IC  22  and MEMS device  24  are mounted on different PCB substrates  60 ,  62 . In this example, the first PCB substrate  60 , on which MEMS device  24  is mounted, is disposed between cover  28  and the second PCB substrate  62  (on which IC  22  is mounted). First spacers  32  separate cover  28  and first PCB substrate  60 , and second spacers  64  separate first PCB substrate and second PCB substrate  62 . Electrical connections  68  can extend from wiring  66  through first PCB substrate  60 , through spacers  64  and through second PCB substrate  62  to provide electrical access to MEMS device  24  from outside module  58 . Likewise, an electrical connection  70  can extend from wiring  67  through PCB substrate  62  to provide electrical access to IC  22  from outside module  58 . 
         [0034]      FIG. 6  illustrates an example of a module  76  in which both IC  22  and MEMS device  24  are mounted on opposite sides of the same PCB substrate  72 . In the illustrated example, MEMS device  24  is mounted on surface  78 , which is closer to cover  28 , whereas IC  22  is mounted on the opposite side on surface  80 . First spacers  32  separate cover  28  and PCB substrate  72  from one another, and second spacers  74  are attached to other side of PCB substrate  72 . Electrical connections  83  can extend from wiring  66  through PCB substrate  72  and through spacers  74  to provide electrical access to MEMS device  24  from outside module  76 . Likewise, electrical connections  84  can extend from wiring  67  through PCB substrate  72  and through spacers  74  to provide electrical access to IC  22  from outside module  76 . 
         [0035]    As illustrated in the example of  FIGS. 5 and 6 , portions of the electrical connections are embedded within spacer walls  64 ,  74 . If a PCB spacer wafer is used to provide spacers  64 ,  74 , then electrical connections  68 ,  70 ,  82 ,  84  can be formed, for example, using a plated through-hole (PTH) conductive via process. Electrical connections  68 ,  70 ,  82 ,  84  can be provided, for example, by a plating process using a conductive metal or metal alloy such as copper (Cu), gold (Au), nickel (Ni), tin-silver (SnAg), silver (Ag) or nickel-palladium (NiPd). Other metals or metal alloys may be used in some implementations as well. Furthermore, in some implementations, some or all of the electrical connections are provided on the outer surface of spacers, for example as a conductive coating or conductive tracks, conductive tape, or conductive glue. 
         [0036]    The implementations of  FIGS. 5 and 6  can reduce the overall footprint of the module. Modules  58 ,  76  can be made relatively small. For example, in some implementations, the modules have dimensions on the order of about 3 mm of less (width)×2.5 mm or less (length)×3 or less mm (height). For example, in a particular implementation, the modules have dimensions on the order of about 2 mm (width)×1.5 mm (length)×2 mm (height). Different dimensions may be appropriate for other implementations. In addition, the implementation of  FIG. 6  can reduce the amount of material needed to fabricate the module because only a single PCB substrate  72  is needed (rather than two PCB substrates  60 ,  62  as in the implementation of  FIG. 5 ). 
         [0037]      FIGS. 7, 8 and 9  illustrate various modifications that can be made to module  20  of  FIG. 1 . For example, the module  86  of  FIG. 7  includes an opening  30  in one of the spacer sidewalls  32  instead of in cover  28 . As part of the fabrication of module  86 , spacers  32  can be formed, for example, by replication on PCB substrate  26  and cover  28 . Providing opening  30  in one of spacer sidewalls  32  can be implemented in the embodiments of  FIGS. 5 and 6 , as well. In particular, opening  30  can be provided in spacer  32 . 
         [0038]      FIG. 8  illustrates a module  88  that includes acoustics-enhancing features  90  on inner surfaces of cover  28  and/or spacer sidewalls  32 . Acoustics-enhancing features  90  can be shaped and sized to impact the acoustics or sound propagation in a pre-defined manner. Acoustics-enhancing features  90  on cover  28  can be formed, for example, by a replication or vacuum injection technique. Acoustics-enhancing features  90  on spacers  32  can be formed, for example, by injection molding or by replication. The replication tool for making the cover wafer and spacer wafer can include provisions for forming the acoustics-enhancing features  90 , which can be composed, for example, of a polymer, foam or porous material. Acoustics-enhancing features  90  can be implemented in the embodiments of  FIGS. 5 and 6 , as well. In particular, acoustics-enhancing features  90  can be provided on the inner surfaces of spacers  32  and/or cover  28 . 
         [0039]      FIG. 9  illustrates a module  92  that includes alignment or positioning features  94  in the form of small projections that extend from the outer surface of cover  28 . In the illustrated example, alignment features  94  are located adjacent opening  30 ; however, in other implementations they may be located elsewhere on the outer surface of cover  28 . In some implementations, a single projection surrounds opening  30  to form position feature  94 , whereas other implementations include multiple projections. Features  94  can be used to facilitate positioning of the MEMS microphone module within the housing of an electronic or other device. Alignment features  94  can be fabricated, for example, by a replication technique or by micromachining. Alignment features  90  can be implemented in the embodiments of  FIGS. 5, 6, 7 and 8  as well. 
         [0040]    More than one of the various features of  FIGS. 7-9  (i.e., an opening  30  in a spacer sidewall  32 ; acoustics-enhancing features  90 ; and/or alignment features  94 ) can be incorporated into the same MEMS microphone module. Thus, the modifications illustrated in  FIGS. 8, 9 and 10  can be used separately or in combination with the features of other modules described in this disclosure. The foregoing MEMS microphone modules can be fabricated in a wafer-level process. 
         [0041]    To improve the acoustics or sound propagation in the MEMS microphone modules, polymer materials with mineral fillers and/or foam materials can be used for one or more of the spacers  32 , the internal acoustics-enhancing features  90  or the cover  28 . 
         [0042]    The foregoing MEMS microphone modules can be integrated with other small modules (e.g., a LED flash module, or sensors, such as ambient light sensors) to help reduce the overall footprint of the modules even further. For example,  FIG. 10  illustrates an example of a module  100  that combines the MEMS microphone module  58  of  FIG. 5  with a LED flash module  101  to form a single integrated module in which MEMS microphone module  58  and LED flash module  101  are disposed side-by-side and share spacers  32 A,  64 A in common. Spacers  32 A,  64 A serve as walls that separate the modules  58 ,  101  from one another. 
         [0043]    In the illustrated example of  FIG. 10 , flash module  101  includes a LED device  102  mounted on PCB substrate  62 . Wiring  105  and electrical connection  106  connect LED device  102  to a solder ball  29  on the outer surface of PCB substrate  62 . Electrical connection  106  can be formed, for example, using a plated through-hole (PTH) conductive via process as described above. 
         [0044]    Although  FIG. 10  shows a cover  28  having the same structure for the MEMS microphone portion and for LED flash portion, in some implementations, cover  28  can be structured differently for those portions. For example, cover  28  can incorporate a lens or diffuser for the LED flash portion. 
         [0045]    Module  100  of  FIG. 10  also can be fabricated, for example, in a wafer-level process, an example of which is illustrated by  FIGS. 11-15 . As shown in  FIG. 11 , multiple ICs  22  and LED devices  102  are mounted on a first PCB substrate wafer  110 , for example, by pick-and-place equipment. ICs  22  and LED devices  102  are spaced from one another in view of the lateral dimensions of the modules. 
         [0046]    As illustrated in  FIG. 12 , spacers  64 ,  64 A and  104  are formed, for example, by a replication or vacuum injection technique. In some implementations, spacers  64  and  104  are formed as a single spacer, which is diced vertically during subsequent processing (see  FIG. 15 ). Spacers  64 ,  64 A can be replicated directly on first PCB substrate wafer  110  or on second PCB substrate  112 , described below. Likewise, spacers  104  can be replicated directly on first PCB substrate wafer  110  or on cover wafer  114 ; described below. Alternatively, the spacers can be provided by wafers that are glued or otherwise attached to PCB wafers  110 ,  112  and cover wafer  114 . The spacers can be composed of a polymer material, for example, a hardenable (e.g., curable) polymer material, such as an epoxy resin. In other implementations, the spacers are composed of a PCB material (e.g., fiber glass or ceramic). 
         [0047]    As illustrated in  FIG. 13 , MEMS microphone devices  24  are mounted on a second PCB substrate wafer  112 , which is attached over first PCB substrate  110  such that ICs  22  are housed in an area between first and second PCB substrates  110 ,  112 . Spacers  64 ,  64 A serve as sidewalls surrounding respective ICs  22 . Second PCB substrate  112  has openings corresponding to the area above each LED device  102 . 
         [0048]    As illustrated in  FIG. 14 , spacers  32 ,  32 A also can be formed, for example, by a replication or vacuum injection technique. Spacers  32 ,  32 A can be replicated directly on second PCB substrate wafer  112  or on cover wafer  114 . The spacers can be composed of a polymer material, for example, a hardenable (e.g., curable) polymer material, such as an epoxy resin. In other implementations, the spacers are composed of a PCB material (e.g., fiber glass or ceramic). 
         [0049]    As shown in  FIG. 15 , cover wafer  114  then is attached over second PCB substrate  112 . Cover wafer  112  includes openings  48  each of which corresponds to opening  30  in  FIG. 5 . As explained above, openings  48  can be formed, for example, by micromachining or by a replication technique, and can have a shape and size selected to achieve desired acoustics or sound propagation. In some implementations, cover wafer  114  has different sections composed of different materials that correspond to the various functions of the combined module (e.g., a diffuser for the LED flash portion). The stack of wafers  110 ,  112 ,  114  then can be separated (e.g., by dicing) into multiple modules similar to module  100  in  FIG. 10 . 
         [0050]    Exterior connections (e.g., solder balls or contact pads also can be provided for the implementations of  FIGS. 10-15  as described above. In addition, if a PCB spacer wafer is used to provide spacers  64 ,  64 A, plated through-hole (PTH) conductive vias can be provided as described above. 
         [0051]      FIG. 16  illustrates another wafer-level technique for fabricating module  100  of  FIG. 10 . In this example, a first sub-stack  120  is formed by providing spacers  64 ,  64 A and spacer elements  104 A on first PCB substrate wafer  110  (e.g., by replication (separate spacer wafer) or vacuum injection (replication directly on substrate)). Spacer elements  104 A correspond to roughly the bottom half of spacers  104  in  FIG. 10 . In this example, spacer elements  104 A have about the same height as spacers  64 ,  64 A. In some implementations, spacers  64  and  104 A are formed as a single spacer, which is diced vertically during subsequent processing (see dicing line  124 ). 
         [0052]    A second sub-stack  122  is formed by providing spacers  32 ,  32 A and spacer elements  104 B on cover wafer  114 . Spacer elements  104 B correspond to roughly the top half of spacers  104  in  FIG. 10 . In this example, spacer elements  104 B are slightly longer than spacers  32 ,  32 A (i.e., by an amount equal to the thickness of second substrate wafer  112 . In some implementations, spacers  32  and  104 B are formed as a single spacer, which is diced vertically during subsequent processing (see dicing line  124 ). 
         [0053]    The various spacers and spacer elements in  FIG. 16  can be formed, for example, by replication directly on first substrate wafer  110  and cover wafer  114 , or by providing a separate spacer wafer, as appropriate. 
         [0054]    To complete the wafer stack, second substrate wafer  112  (with MEMS devices  24  mounted thereon) is attached (e.g., by glue or some other adhesive) to first sub-stack  120 . In particular, the underside of second substrate wafer  112  is attached to spacers  64 ,  64 A, thereby forming an intermediate stack. Then, second sub-stack  122  is attached to the intermediate stack. In particular, spacer elements  104 B of the second sub-stack  122  are attached (e.g., by glue or some other adhesive) to corresponding spacer elements  104 A of the first sub-stack  120 , and spacers  32 ,  32 A are attached (e.g., by glue or some other adhesive) to the upper side of second substrate wafer  112 . The resulting wafer stack, which appears similar to  FIG. 15 , then can be separated (e.g., by dicing) into multiple modules similar to module  100  in  FIG. 10 . Exterior connections (e.g., solder balls or contact pads), as well as plated through-hole (PTH) conductive vias, also can be provided, for example, as described above. 
         [0055]      FIGS. 17-18  illustrate yet a further wafer-level technique for fabricating MEMS microphone modules. In this example, a first sub-stack  220  is formed by providing spacers elements  202 A,  204 A on first PCB substrate wafer  110 . The spacer elements  204 A have the same height as spacer elements  202 A. A second sub-stack  222  is formed by providing spacer elements  202 B,  204 B on cover wafer  114  The spacer elements  204 B have the same height as spacer elements  202 B. The spacer elements in  FIG. 17  can be formed, for example, by replication directly on first substrate wafer  110  and cover wafer  114 , or by providing separate spacer wafers. In addition to openings  30 , the cover wafer  114  may include lenses or other beam shaping elements  210  at spaced intervals. When the wafers are stacked, each lens  210  is disposed over a respective one of the LED devices  102 . 
         [0056]    To form the wafer stack, a second substrate wafer  112  (with MEMS devices  24  mounted thereon) is attached (e.g., by glue or some other adhesive) to first sub-stack  220 . In particular, the underside of second substrate wafer  112  is attached to spacers  202 A,  204 A, thereby forming an intermediate stack. Then, second sub-stack  222  is attached to the intermediate stack. In particular, spacer elements  202 B,  204 B of the second sub-stack  222  are attached (e.g., by glue or some other adhesive) to the MEM-side of the second substrate wafer  112 , and spacers elements  202 A,  204 A are attached (e.g., by glue or some other adhesive) to the opposite side of second substrate wafer  112 . The resulting wafer stack (see  FIG. 18 ) then can be separated (e.g., by dicing along lines  230 ) into multiple modules, one of which is shown in  FIG. 19 . Exterior connections (e.g., solder balls or contact pads), as well as plated through-hole (PTH) conductive vias, also can be provided, for example, as described above. 
         [0057]    Although  FIGS. 10-19  illustrate examples in which small MEMS microphone modules are combined with flash LED modules, the MEMS microphone modules can be combined with other small modules, including, for example, proximity sensor modules, time-of-flight (TOF) modules and camera modules. Thus, LED flash module  101  of  FIG. 10  can be replaced by one of these other types of modules in some implementations. By combining the MEMS microphone module with one or more other modules, the overall footprint of the modules can be reduced, thereby allowing the modules to be integrated into small consumer electronic or other products (e.g., cellphones, laptops, headsets and media tablets, gaming applications, cameras, televisions and hearing aids) in which space is at premium. 
         [0058]    Various modifications can be made within the scope of the invention. Accordingly, other implementations are within the scope of the claims.