Abstract:
The present invention provides a method for manufacturing a fully wafer-level-packaged MEMS microphone and a microphone manufactured with the same, the method comprises: separately manufacturing a first packaging wafer, an MEMS microphone wafer and a second packaging wafer; performing wafer-to-wafer bonding for the three wafers to form a plurality of fully wafer-level-packaged MEMS microphone units; singulating the fully wafer-level-packaged MEMS microphone units to form a plurality of fully wafer-level-packaged MEMS microphones, which are fully packaged at wafer level and do not need any further process after die singulation. The method can improve cost-effectiveness, performance consistency, manufacturability, quality, scaling capability of the packaged MEMS microphone.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of microphone technology, and more specifically, to a packaged MEMS microphone and a method for manufacturing the same. 
       BACKGROUND 
       [0002]    The silicon based MEMS (Microelectromechanical System) microphones, also known as acoustic transducers, are playing a more and more important role in the hearing instrument, mobile communication system, digital camera, video camera and toy industry. Usually, a silicon based MEMS microphone chip needs to be packaged before it can be tested, shipped and utilized. U.S. Pat. No. 6,781,231 disclosed a typical MEMS package as shown in  FIG. 1 , which comprises surface mountable components  12  (e.g., a silicon based MEMS microphone chip, integrated circuits), substrate  14 , and a cover  20 , wherein the combination of the substrate  14  and the cover  20  forms a housing  22  in which the surface mountable components  12  are located and electrically connected. 
         [0003]    However, there are several drawbacks to this MEMS package and its like. Firstly, it is not cost-effective. Packaging cost generally takes a major portion of the total cost for such a conventional packaged MEMS microphone, for example, for a typical 6 mm 2  package size, the minimum packaging cost may exceed $0.1, whilst a typical MEMS microphone chip costs much less than $0.1. Especially, when package size is further reduced, which is a growing trend, packaging cost will become a cost-down bottle neck. Secondly, it is disadvantageous in manufacturability and mass production, since the singulated MEMS microphone chips needs to be packaged separately. Thirdly, performance consistency may not be guaranteed, particle and organic contaminations may not be easily prevented. Fourthly, size reduction of the MEMS package is highly limited due to its incompact structure. 
         [0004]    To overcome the above drawbacks to the conventional packaged MEMS microphone, the present invention suggests a fully wafer-level-packaging technique for packaging a silicon based MEMS microphone. Actually, U.S. Pat. No. 8,368,153 discloses a wafer level package of MEMS microphone, as shown in  FIG. 2 , and manufacturing method thereof. However, the US patent application only discloses a chip structure of an MEMS microphone and a wafer process flow for manufacturing the same, the structure is actually not a packaged MEMS microphone which is surface mountable, and still requires traditional acoustic packaging after wafer process. Therefore, a fully wafer-level-packaged MEMS microphone, which is fully packaged at wafer level and does not need any further process after die singulation, and a method for manufacturing the same are still not applicable. 
       SUMMARY 
       [0005]    In view of the above, the present invention provides a fully wafer-level-packaged MEMS microphone and a method for manufacturing the same with an objective of improving cost-effectiveness, performance consistency, manufacturability, quality, scaling capability of the packaged MEMS microphone. 
         [0006]    According to an aspect of the present invention, there is provided a method for manufacturing a fully wafer-level-packaged MEMS microphone, comprising: separately manufacturing a first packaging wafer, an MEMS microphone wafer and a second packaging wafer, wherein the first packaging wafer comprises a plurality of first packaging units, the second packaging wafer comprises a plurality of second packaging units, and the MEMS microphone wafer comprises a plurality of MEMS microphone units, each of which comprises a silicon substrate formed with a back hole therein and an acoustic sensing part supported on the silicon substrate and aligned with the back hole, and wherein the first packaging units and/or the second packaging units and/or the MEMS microphone units comprise ASICs, and the first packaging units or the second packaging units also comprise acoustic ports; performing wafer-to-wafer bonding for the MEMS microphone wafer and the first packaging wafer and for the second packaging wafer and the MEMS microphone wafer, such that the first packaging units, the MEMS microphone units and the second packaging units are correspondingly aligned to form a plurality of fully wafer-level-packaged MEMS microphone units, in each of which the electrical connections among the acoustic sensing part, the ASICs and surface mountable pads formed on the outer side of the first packaging unit and/or the outer side of the second packaging unit are realized by interconnection wires or conductive pads or through-silicon-vias or the combination thereof; and singulating the fully wafer-level-packaged MEMS microphone units to form a plurality of fully wafer-level-packaged MEMS microphones. 
         [0007]    Preferably, the acoustic sensing part may at least includes: a compliant diaphragm; a perforated backplate; and an air gap formed between the diaphragm and the backplate, wherein the diaphragm and the backplate are used to form electrode plates of a variable condenser. 
         [0008]    Preferably, the wafer-to-wafer bonding may be realized by any of metal-metal bonding, metal eutectic bonding, soldering, and conductive adhesive bonding. 
         [0009]    In one embodiment, preferably, in each of the fully wafer-level-packaged MEMS microphone units, the first packaging unit may comprise the ASICs and an acoustic port, the second packaging unit may comprise a cavity, the back hole in the MEMS microphone unit and the cavity may be merged to form a back chamber, and the surface mountable pads may be formed on the outer side of the first packaging unit. Further preferably, the acoustic sensing part may include a perforated backplate supported on the silicon substrate and a compliant diaphragm supported on the backplate with an air gap sandwiched inbetween, and dimples may be formed on the inner side of the first packaging unit to protect the diaphragm from sticking thereto. 
         [0010]    In another embodiment, preferably, in each of the fully wafer-level-packaged MEMS microphone units, the first packaging unit may comprise an acoustic port, the second packaging unit may comprise the ASICs, and the surface mountable pads may be formed on the outer side of the first packaging unit. Further preferably, the acoustic sensing part may include a perforated backplate supported on the silicon substrate and a compliant diaphragm supported on the backplate with an air gap sandwiched inbetween, and dimples may be formed on the inner side of the first packaging unit to protect the diaphragm from sticking thereto. 
         [0011]    According to another aspect of the present invention, there is provided a fully wafer-level-packaged MEMS microphone, comprising: a first packaging unit; an MEMS microphone unit, comprising a silicon substrate formed with a back hole therein and an acoustic sensing part supported on the silicon substrate and aligned with the back hole; and a second packaging unit, wherein the first packaging unit and/or the second packaging unit and/or the MEMS microphone unit comprise ASICs, and the first packaging unit or the second packaging unit also comprises an acoustic port, wherein the first packaging unit, the MEMS microphone unit and the second packaging unit are aligned, the MEMS microphone unit is bonded to the first packaging unit and the second packaging unit is bonded to the MEMS microphone unit, and wherein the electrical connections among the acoustic sensing part, the ASICs and surface mountable pads formed on the outer side of the first packaging unit and/or the outer side of the second packaging unit are realized by interconnection wires or conductive pads or through-silicon-vias or the combination thereof. 
         [0012]    According to still another aspect of the present invention, there is provided a method for manufacturing a fully wafer-level-packaged MEMS microphone, comprising: separately manufacturing a first packaging wafer, an MEMS microphone wafer, wherein the first packaging wafer comprises a plurality of first packaging units, and the MEMS microphone wafer comprises a plurality of MEMS microphone units, each of which comprises a silicon substrate formed with a back hole therein and an acoustic sensing part supported on the silicon substrate and aligned with the back hole, and wherein the first packaging units and/or the MEMS microphone units comprise ASICs; performing wafer-to-wafer bonding for the MEMS microphone wafer and the first packaging wafer with the back hole side of the MEMS microphone wafer being away from the first packaging wafer, such that the first packaging units and the MEMS microphone units are correspondingly aligned to form a plurality of fully wafer-level-packaged MEMS microphone units, in each of which the electrical connections among the acoustic sensing part, the ASICs and surface mountable pads formed on the outer side of the first packaging unit are realized by interconnection wires or conductive pads or through-silicon-vias or the combination thereof; and singulating the fully wafer-level-packaged MEMS microphone units to form a plurality of fully wafer-level-packaged MEMS microphones. 
         [0013]    Preferably, in each of the fully wafer-level-packaged MEMS microphone units, the acoustic sensing part and the ASICs may be integrally formed on the MEMS microphone unit, and the surface mountable pads may be formed on the outer side of the first packaging unit. Further, the first packaging unit may comprise a cavity. 
         [0014]    According to the yet still another aspect of the present invention, there is provided a fully wafer-level-packaged MEMS microphone, comprising: an MEMS microphone unit, comprising a silicon substrate formed with a back hole therein and an acoustic sensing part supported on the silicon substrate and aligned with the back hole; and a first packaging unit, wherein the MEMS microphone unit and/or the first packaging unit comprise ASICs, wherein the MEMS microphone unit and the first packaging unit are aligned, the MEMS microphone unit is bonded to the first packaging unit with the back hole side of the MEMS microphone unit being away from the first packaging unit, and wherein the electrical connections among the acoustic sensing part, the ASICs and surface mountable pads formed on the outer side of the first packaging unit are realized by interconnection wires or conductive pads or through-silicon-vias or the combination thereof. 
         [0015]    The method for manufacturing the fully wafer-level-packaged MEMS microphone according to the present invention is totally compatible with CMOS MEMS process flow, thus it can guarantee better manufacturability, quality and mass production, and reduce the risk of particle and organic contaminations. The method adopts a parallel multi-wafer process followed by wafer-bonding, thus, minimum yield loss can be ensured due to optimized process flows on different wafers, better performance matching from part to part can be easily achieved, and mechanical robustness can be enhanced by wafer bonding instead of wire bonding. Since a batch of fully wafer-level-packaged MEMS microphones according to the present invention are manufactured in a same process, the performance consistency and the yield thereof can be highly guaranteed. Also, the fully wafer-level-packaged MEMS microphones according to the present invention are fully packaged at wafer level and do not need any further process after die singulation, thus they are cost effective, that is, the total fabrication cost thereof can be much reduced, particularly for small package size, e.g. 6 mm 2  or less. Furthermore, the fully wafer-level-packaged MEMS microphones according to the present invention can easily shrink in package size and can fully comply with state-of-the-art customer package specifications. 
         [0016]    While various embodiments have been discussed in the summary above, it should be appreciated that not necessarily all embodiments include the same features and some of the features described above are not necessary but can be desirable in some embodiments. Numerous additional features, embodiments and benefits are discussed in the detailed description which follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The objectives and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which: 
           [0018]      FIG. 1  is a cross-sectional view showing the structure of an MEMS system package in the prior art; 
           [0019]      FIG. 2  is a cross-sectional view showing the structure of a wafer level package of MEMS microphone in the prior art; 
           [0020]      FIG. 3 a  through 3 c    are cross-sectional views showing a method for manufacturing a fully wafer-level-packaged MEMS microphone according to an embodiment of the present invention; 
           [0021]      FIG. 4  is an enlarged cross-sectional view showing the structures of the first packaging unit, the MEMS microphone unit and the second packaging unit of  FIG. 3   a;    
           [0022]      FIG. 5  is a cross-sectional view showing the structure of the fully wafer-level-packaged MEMS microphone according to an embodiment of the present invention; 
           [0023]      FIG. 6  is a cross-sectional view showing the structure of the fully wafer-level-packaged MEMS microphone according to another embodiment of the present invention; 
           [0024]      FIG. 7 a  through 7 c    are cross-sectional views showing a method for manufacturing a fully wafer-level-packaged MEMS microphone according to another embodiment of the present invention; 
           [0025]      FIG. 8  is a cross-sectional view showing the structure of the fully wafer-level-packaged MEMS microphone according to still another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Various aspects of the claimed subject matter are now described with reference to the drawings, wherein the illustrations in the drawings are schematic and not to scale, and like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be evident, however, that such aspect(s) may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diaphragm form in order to facilitate describing one or more aspects. 
         [0027]    In the description and the appended claims, it will be understood that, when a layer, a region, or a component is referred to as being “on” or “under” another layer, another region, or another component, it can be “directly” or “indirectly” on or under the another layer, region, or component, or one or more intervening layers may also be present. 
         [0028]      FIG. 3 a  through 3 c    are cross-sectional views showing a method for manufacturing a fully wafer-level-packaged MEMS microphone according to an embodiment of the present invention. As shown in  FIG. 3 a  through 3 c   , the method comprises following steps. 
         [0029]    First, as shown in  FIG. 3 a   , separately manufacture a first packaging wafer  1 , an MEMS microphone wafer  3  and a second packaging wafer  2 , wherein the first packaging wafer  1  comprises a plurality of first packaging units  10 , the second packaging wafer  2  comprises a plurality of second packaging units  20 , and the MEMS microphone wafer  3  comprises a plurality of MEMS microphone units  30 . 
         [0030]      FIG. 4  is an enlarged cross-sectional view showing the structures of the first packaging unit, the MEMS microphone unit and the second packaging unit of  FIG. 3 a   . As shown in  FIG. 3 a    and  FIG. 4 , each of the MEMS microphone units  30 , which is disposed upside down in the figures, may comprise a silicon substrate  301  formed with a back hole  302  therein and an acoustic sensing part supported on the silicon substrate  301  and aligned with the back hole  302 . The acoustic sensing part may receive an external acoustic signal and transform the received acoustic signal into an electrical signal, and preferably may at least include: a compliant diaphragm  303 ; a perforated backplate  304 ; and an air gap  305  formed between the diaphragm  303  and the backplate  304 , wherein the diaphragm  303  and the backplate  304  are used to form electrode plates of a variable condenser. An example of the acoustic sensing part is described in details, for example, in the international application No. PCT/CN2010/075514, and detailed description thereof will be omitted herein. 
         [0031]    In the present embodiment, the acoustic sensing part includes a perforated backplate  304  supported on the silicon substrate  301  and a compliant diaphragm  303  supported on the backplate  304  with an air gap  305  sandwiched in between, however, the present invention is not limited thereto. In other embodiment, the acoustic sensing part may includes a compliant diaphragm  303  supported on the silicon substrate  301  and a perforated backplate  304  supported on the diaphragm  303  with an air gap  305  sandwiched in between. 
         [0032]    In the present embodiment, the first packaging unit  10  may comprise the ASICs (Application Specific Integrated Circuits)  101  and an acoustic port  102 . The ASICs  101  may process the electrical signal output by the acoustic sensing part and perform other functions. The acoustic port  102  allows the external acoustic wave reach the acoustic sensing part from the one side thereof. Also, in the present embodiment, the second packaging unit  20  may comprise a cavity  201 , and the surface mountable pads  401  are formed on the outer side of the first packaging unit  10 . Further preferably, dimples  103  may be formed on the inner side of the first packaging unit  10  to protect the diaphragm  303  from sticking thereto, as described later on. 
         [0033]    However, the present invention is not limited thereto. Actually, the ASICs can located on any one or two of the first packaging unit, the second packaging unit, and the MEMS microphone unit, or located on three of them according to device design and performance matching consideration. Also, the acoustic port can dwelt on either the first packaging unit or the second packaging unit according to the structure and orientation of the acoustic sensing part. In addition, the surface mountable pads may be formed on the outer side of the first packaging unit and/or the outer side of the second packaging unit for sake of convenient electrical connections. 
         [0034]    For example, in another embodiment of the present invention, the first packaging unit may comprise an acoustic port, the second packaging unit may comprise the ASICs, and the surface mountable pads may be formed on the outer side of the first packaging unit. Furthermore, the acoustic sensing part may include a perforated backplate supported on the silicon substrate and a compliant diaphragm supported on the backplate with an air gap sandwiched in between, and dimples may be formed on the inner side of the first packaging unit to protect the diaphragm from sticking thereto. 
         [0035]    Referring to the  FIG. 3 b   , after the first packaging wafer  1 , the MEMS microphone wafer  3  and the second packaging wafer  2  are manufactured separately, perform wafer-to-wafer bonding for the MEMS microphone wafer  3  and the first packaging wafer  1  and for the second packaging wafer  2  and the MEMS microphone wafer  3 , such that the first packaging units  10 , the MEMS microphone units  30  and the second packaging units  20  are correspondingly aligned to form a plurality of fully wafer-level-packaged MEMS microphone units  50 . The wafer-to-wafer bonding may be realized by any of metal-metal bonding (e.g. Au—Au, Al—Al or Cu—Cu bonding, etc), metal eutectic bonding (e.g. SnAu eutectic, etc), soldering, and conductive adhesive bonding, i.e. the bonding rings  402  formed on the first packaging units  10 , the MEMS microphone units  30  and the second packaging units  20  can be made of metal, solders, or conductive adhesives. 
         [0036]    In each of fully wafer-level-packaged MEMS microphone units  50 , the electrical connections among the acoustic sensing part, the ASICs  101  and surface mountable pads  401  may be realized by interconnection wires  403  or conductive pads  404  or through-silicon-vias  405  or the combination thereof. Bonding rings  402  may or may not be involved in the electrical connections. 
         [0037]    Referring to the  FIG. 3 c   , after the wafer-to-wafer bonding step, singulate the fully wafer-level-packaged MEMS microphone units  50  to form a plurality of fully wafer-level-packaged MEMS microphones  100 . The fully wafer-level-packaged MEMS microphones  100  are ready for testing or shipping, and do not need any further process for final utilization. 
         [0038]    Hereinafter, embodiments of the fully wafer-level-packaged MEMS microphone manufactured by the above method of the present invention will be described with reference to  FIG. 5  and  FIG. 6 . In the following description, for sake of clarity and conciseness, a lot of processing details, such as equipments, conditions, parameters and so on, are omitted in considering that they are well known by those skilled in the art. 
         [0039]    A fully wafer-level-packaged MEMS microphone manufactured by the method of the present invention may comprise: a first packaging unit; an MEMS microphone unit, comprising a silicon substrate formed with a back hole therein and an acoustic sensing part supported on the silicon substrate and aligned with the back hole, and a second packaging unit, wherein the first packaging unit and/or the second packaging unit and/or the MEMS microphone unit comprise ASICs, and the first packaging unit or the second packaging unit also comprises an acoustic port, wherein the first packaging unit, the MEMS microphone unit and the second packaging unit are aligned, the MEMS microphone unit is bonded to the first packaging unit and the second packaging unit is bonded to the MEMS microphone unit, and wherein the electrical connections among the acoustic sensing part, the ASICs and surface mountable pads formed on the outer side of the first packaging unit and/or the outer side of the second packaging unit are realized by interconnection wires or conductive pads or through-silicon-vias or the combination thereof. 
         [0040]    Preferably, the acoustic sensing part may at least include: a compliant diaphragm; a perforated backplate; and an air gap formed between the diaphragm and the backplate, wherein the diaphragm and the backplate are used to form electrode plates of a variable condenser. 
         [0041]      FIG. 5  is a cross-sectional view showing the structure of the fully wafer-level-packaged MEMS microphone according to an embodiment of the present invention. As shown in  FIG. 5 , in the fully wafer-level-packaged MEMS microphone  100  according to an embodiment of the present invention, specifically, the first packaging unit  10  comprises the ASICs  101  and an acoustic port  102 , the second packaging unit  20  comprises a cavity  201 , the back hole  302  in the MEMS microphone unit  30  and the cavity  201  are merged to form a back chamber, and the surface mountable pads  401  are formed on the outer side of the first packaging unit  10 . The MEMS microphone unit  30  and the first packaging unit  10  as well as the second packaging unit  20  and the MEMS microphone unit  30  are bonded by bonding rings  402 . 
         [0042]    In addition, the acoustic sensing part includes a perforated backplate  304  supported on the silicon substrate  301  and a compliant diaphragm  303  supported on the backplate  304  with an air gap  305  sandwiched in between. Furthermore, dimples  103  are formed on the inner side of the first packaging unit  10  to protect the diaphragm  303  from sticking thereto. 
         [0043]    The electrical connections among the acoustic sensing part, the ASICs  101  and surface mountable pads  401  are realized by interconnection wires  403  or conductive pads  404  or through-silicon-vias  405  or the combination thereof. 
         [0044]      FIG. 6  is a cross-sectional view showing the structure of the fully wafer-level-packaged MEMS microphone according to another embodiment of the present invention. As shown in  FIG. 6 , in the fully wafer-level-packaged MEMS microphone  100 ′ according to another embodiment of the present invention, specifically, the first packaging unit  10 ′ comprises an acoustic port  102 , the second packaging unit  20 ′ comprises the ASICs  101 , and the surface mountable pads  401  are formed on the outer side of the first packaging unit  10 ′. The MEMS microphone unit  30 ′ and the first packaging unit  10 ′ as well as the second packaging unit  20 ′ and the MEMS microphone unit  30 ′ are bonded by bonding rings  402 . 
         [0045]    In addition, the acoustic sensing part includes a perforated backplate  304  supported on the silicon substrate  301  and a compliant diaphragm  303  supported on the backplate  304  with an air gap  305  sandwiched in between. Furthermore, dimples  103  are formed on the inner side of the first packaging unit  10 ′ to protect the diaphragm  303  from sticking thereto. 
         [0046]    The electrical connections among the acoustic sensing part, the ASICs  101  and surface mountable pads  401  are realized by interconnection wires  403  or conductive pads  404  or through-silicon-vias  405  or the combination thereof. 
         [0047]    The above described method of the present invention and the fully wafer-level-packaged MEMS microphone manufactured with the same can be further simplified. 
         [0048]      FIG. 7 a  through 7 c    are cross-sectional views showing a method for manufacturing a fully wafer-level-packaged MEMS microphone according to another embodiment of the present invention. As shown in  FIG. 7 a  through 7 c   , the method comprises following steps. 
         [0049]    First, as shown in  FIG. 7 a   , separately manufacture a first packaging wafer  1 ′, an MEMS microphone wafer  3 ′, wherein the first packaging wafer  1 ′ comprises a plurality of first packaging units  10 ″, and the MEMS microphone wafer  3 ′ comprises a plurality of MEMS microphone units  30 ″. 
         [0050]    Each of the MEMS microphone units  30 ″, which is disposed upside down in  FIG. 7 a   , may comprises a silicon substrate formed with a back hole therein and an acoustic sensing part supported on the silicon substrate and aligned with the back hole, as described above. Also, the MEMS microphone unit  30 ″ comprises ASICs  101 , which are integrated with the acoustic sensing part on the MEMS microphone unit  30 ′. However, the present invention is not limited thereto. Actually, according to the present invention, ASICs can be located on the first packaging units and/or the MEMS microphone units. 
         [0051]    The surface mountable pads  401  are formed on the outer side of the first packaging unit  10 ″. In addition, preferably, the first packaging unit  10 ″ may comprises a cavity. 
         [0052]    Referring to  FIG. 7 b   , after the first packaging wafer  1 ′ and the MEMS microphone wafer  3 ′ are manufactured separately, perform wafer-to-wafer bonding for the MEMS microphone wafer  3 ′ and the first packaging wafer  1 ′ with the back hole side of the MEMS microphone wafer  3 ′ being away from the first packaging wafer  1 ′ (i.e. the back hole is on the top, and the acoustic sensing part is closed to the first packaging wafer  1 ′), such that the first packaging units  1 ′ and the MEMS microphone units  3 ′ are correspondingly aligned to form a plurality of fully wafer-level-packaged MEMS microphone units  50 ″. 
         [0053]    In each of the fully wafer-level-packaged MEMS microphone units  50 ″, the electrical connections among the acoustic sensing part, the ASICs and surface mountable pads formed on the outer side of the first packaging unit  1 ′ are realized by interconnection wires or conductive pads or through-silicon-vias or the combination thereof. 
         [0054]    Referring to  FIG. 7 c   , after the wafer-to-wafer bonding step, singulate the fully wafer-level-packaged MEMS microphone units  50 ″ to form a plurality of fully wafer-level-packaged MEMS microphones  100 ″. The fully wafer-level-packaged MEMS microphones  100 ″ are ready for testing or shipping, and do not need any further process for final utilization. 
         [0055]    Hereinafter, an embodiment of the fully wafer-level-packaged MEMS microphone manufactured by the method shown in  FIG. 7 a -7 c    will be briefly described with reference to  FIG. 8 . In the following description, for sake of clarity and conciseness, details elaborated hereinbefore will not be repeated. 
         [0056]      FIG. 8  is a cross-sectional view showing the structure of the fully wafer-level-packaged MEMS microphone according to still another embodiment of the present invention. As shown in  FIG. 8 , a fully wafer-level-packaged MEMS microphone  100 ″ according to still another embodiment of the present invention may comprise: a first packaging unit  10 ″; and an MEMS microphone unit  30 ″ comprising a silicon substrate  301  formed with a back hole  302  therein and an acoustic sensing part supported on the silicon substrate  301  and aligned with the back hole  302 . The acoustic sensing part may include: a compliant diaphragm  303 ; a perforated backplate  304 ; and an air gap  305  formed in between, the diaphragm  303  and the backplate  304  are used to form electrode plates of a variable condenser. 
         [0057]    The acoustic sensing part and the ASICs  101  are integrally formed on the MEMS microphone unit  30 ″, however, the present invention is not limited thereto. In other embodiments, the ASICs  101  may located on the MEMS microphone unit and/or the first packaging unit according to device design. 
         [0058]    The MEMS microphone unit  30 ″ and the first packaging unit  10 ″ are aligned, the MEMS microphone unit  30 ″ is bonded to the first packaging unit  10 ″ through the bonding rings  402  with the back hole side of the MEMS microphone unit  30 ″ being away from the first packaging unit  10 ″, that is, the back hole  302  of the MEMS microphone unit  30 ″ is on the top, and the acoustic sensing part is closed to the first packaging unit  10 ″. 
         [0059]    The electrical connections among the acoustic sensing part, the ASICs  101  and surface mountable pads  401  formed on the outer side of the first packaging unit  10 ″ are realized by interconnection wires  403  or conductive pads  404  or through-silicon-vias  405  or the combination thereof. 
         [0060]    In addition, a cavity  104  and dimples  103  may be formed on the first packaging unit  10 ″ to improve the acoustic performance and the robustness of the microphone  100 ″. 
         [0061]    The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.