Patent Publication Number: US-10779101-B2

Title: MEMS device

Description:
This application is a divisional of U.S. patent application Ser. No. 16/200,072, filed Nov. 26, 2018, which application is a divisional of U.S. patent application Ser. No. 15/452,058, filed Mar. 7, 2017, now U.S. Pat. No. 10,171,925, which is a continuation of U.S. patent application Ser. No. 14/275,337, filed on May 12, 2014, now U.S. Pat. No. 9,628,886, which application claims the benefit of U.S. Provisional Application No. 61/870,112 filed Aug. 26, 2013, which applications are hereby incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the invention refer to a MEMS device, to an electrostatic transducer and to a method for manufacturing a MEMS device. 
     BACKGROUND 
     A double backplate microphone in MEMS device technology comprises a top backplate electrode and a bottom backplate electrode being arranged in parallel to each other, and a membrane being disposed between the top backplate electrode and bottom backplate electrode in parallel. The top backplate electrode, bottom backplate electrode and membrane are supported by a support structure. This arrangement is supported by a substrate. 
     In order to transmit sound pressure waves, for example speech, to the membrane interposed between the top backplate electrode and bottom backplate electrode, these electrodes may be perforated. Sound pressure waves cause the membrane to vibrate due to a pressure difference over both planes of the membrane. Hence, the air gap between the membrane and each of the backplate electrodes varies. The backplate electrodes and the membrane may comprise electrically conductive material(s). The variation of the membrane in relation to the backplate electrodes causes variation in the capacitances between the membrane and the bottom backplate electrode as well as between the membrane and the top backplate electrode. This variation in the capacitances is transformed into an output signal responsive to the movement of the membrane. The membrane may be biased by a bias voltage relative to the bottom backplate electrode and the top backplate electrode. 
     The double backplate microphone as described above schematically, suffers from parasitic capacitances, created inside the support structure. A first parasitic capacitance can be created inside the support structure between the membrane and the top backplate electrode. A second parasitic capacitance can be created inside the support structure between the membrane and the bottom backplate electrode. A third parasitic capacitance can be created inside the support structure between the bottom backplate electrode and the substrate. The substrate can be grounded. In other words, parasitic capacitances tend to be created between the top backplate electrode, membrane and bottom backplate electrode in combination, inside the support structure, i.e., in portions of the MEMS device excluding the air gap between the membrane and the top backplate electrode, as well as the air gap between the membrane and the bottom backplate electrode. 
     Parasitic capacitances are usually unwanted capacitances interfering with capacitances between both the membrane and the top backplate electrode as well as between the membrane and the bottom backplate electrode. Hence, capacitance values, intended to be transformed into electrical signals responsive to the movement of the membrane are interfered. In case the MEMS device is embodied as a double backplate microphone, for example, parasitic capacitances may influence the MEMS device such that the (electrical) output does not correspond to a correct reproduction of the (audible) input. While not mentioned, further sources of parasitic capacitances are conceivable. 
     SUMMARY 
     An embodiment of the invention provides a MEMS device comprising a backplate electrode. A membrane is disposed spaced apart from the backplate electrode. The membrane comprises a displaceable portion and a fixed portion. The backplate electrode and the membrane are arranged such that an overlapping area of the fixed portion of the membrane with the backplate electrode is less than maximum overlapping. 
     A further embodiment provides an electrostatic transducer comprising a backplate electrode. A membrane is disposed spaced apart from the backplate electrode. The membrane comprises a displaceable portion and a fixed portion. The backplate electrode and the membrane are arranged such that an overlapping area of the fixed portion of the membrane with the backplate electrode is less than maximum overlapping. The electrostatic transducer is configured to produce an output signal responsive to a movement of the membrane in relation to the backplate electrode. 
     A further embodiment provides a method for manufacturing a MEMS device that comprises a backplate. A membrane is disposed spaced apart from the backplate electrode, wherein the membrane comprises a displaceable portion and a fixed portion. The method comprises providing the backplate electrode and the membrane such that an overlapping area of the fixed portion of the membrane with the backplate electrode is less than maximum overlapping. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are described in the following with respect to the figures. 
         FIG. 1 a    shows a schematic MEMS device in cross-section; 
         FIG. 1 b    shows a schematic circuit diagram of the MEMS device depicted in  FIG. 1   a;    
         FIG. 2 a    shows a further schematic MEMS device in cross-section; 
         FIG. 2 b    shows a schematic circuit diagram of the MEMS device depicted in  FIG. 2   a;    
         FIG. 3 a    shows a plan view of a MEMS device; 
         FIG. 3 b    shows a schematic cross-sectional view of the MEMS device depicted in  FIG. 3   a;    
         FIG. 4 a    shows a further plan view of a MEMS device; 
         FIG. 4 b    shows a schematic cross-sectional view of the MEMS device depicted in  FIG. 4   a;    
         FIG. 5 a    shows a further plan view of a MEMS device; 
         FIG. 5 b    shows a schematic cross-sectional view of the MEMS device depicted in  FIG. 5   a;    
         FIG. 6  shows a schematic diagram of a MEMS device in a cross-sectional view; 
         FIG. 7  shows a schematic plan view of a backplate electrode of the MEMS device; 
         FIG. 8 a    shows a further plan view of a MEMS device; 
         FIG. 8 b    shows a schematic cross-sectional view of the MEMS device depicted in  FIG. 8   a;    
         FIG. 8 c    shows in a schematic diagram a plan view of the arrangement of a top backplate electrode, a membrane and a bottom backplate electrode in relation to each other; 
         FIG. 9 a    shows in a cross-sectional view a schematic diagram of a MEMS device comprising a guard ring; 
         FIG. 9 b    shows in a schematic diagram a plan view of the arrangement of a top backplate electrode, a membrane, a bottom backplate electrode and associated guard rings in relation to each other; and 
         FIGS. 10 a -10 p    schematically illustrate a process flow of a method for manufacturing the MEMS device. 
     
    
    
     Different embodiments of the teachings disclosed herein will subsequently be discussed referring to  FIG. 1  to  FIG. 10 p   . In the drawings, identical reference numerals are provided to objects having identical or similar functions so that objects referred to by identical reference numerals within the different embodiments are interchangeable and the description is mutually applicable. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Referring to  FIG. 1 a   , a MEMS device  10  comprises a backplate electrode  12  and a second backplate electrode  14  being arranged in parallel to each other. Some implementation examples (e.g., so called single backplate microphones) may not comprise the second backplate electrode  14 , i.e., the second backplate electrode  14  may be optional. The backplate electrode  12  may also be referred to as the top backplate electrode. The second backplate electrode  14  may also be referred to as the bottom backplate electrode. The attributes “top” and “bottom” mainly serve to distinguish the two backplate electrodes  12  and  14  regarding their graphical representation in  FIG. 1 a    and possibly further figures, and should not to be construed as limiting. In the following description and figures, the index “T” typically refers to the top backplate electrode  12 , the index “B” typically refers to the bottom backplate electrode  14 , the index “M” typically refers to the membrane  16 , and the index “S” typically refers to the substrate  20 _ 1 ,  20 _ 2 . The MEMS device  10  further comprises a membrane  16 . The membrane  16  is disposed between the backplate electrode  12  and the second backplate electrode  14  in parallel. The membrane  16  can comprise a displaceable portion and a fixed portion. The displaceable portion may be able to move in response to an incident sound wave. For example, the displaceable portion may be deflected or deformed. Alternatively, the displaceable portion may be displaced by a translation. The backplate electrode  12 , second backplate electrode  14  and membrane  16  can comprise electrical conductive material. 
     The backplate electrode  12 , the second backplate electrode  14  and the membrane  16  may be supported by a support structure  18 _ 1 ,  18 _ 2 . The material of the support structure  18 _ 1 ,  18 _ 2  can be made of oxide. The support structure  18 _ 1 ,  18 _ 2  itself may be supported on a substrate  20 _ 1 ,  20 _ 2 . 
     The backplate electrode  12  may comprise perforations to allow sound pressure to pass through the backplate electrode  12  to arrive at the membrane  16 . The second backplate electrode  14  may be arranged on the side of the membrane  16  facing away from the direction of sound pressure arrival. Some of the air in the gap between the membrane  16  and the second backplate  14  may be pushed by the membrane  16  when moved as a consequence of sound pressure arrival. To allow the volume between the membrane  16  and the second backplate electrode  14  to escape, the second backplate electrode  14  may be provided with perforations as well. A backside cavity  22  may be provided allowing the air volume to expand which is pushed by the membrane  16 . 
     The MEMS device  10  may suffer from parasitic capacitances created inside the support structure  18 _ 1 ,  18 _ 2 . As shown in  FIG. 1 a   , a first parasitic capacitance C TM  may be observed in at least a portion of the support structure  18 _ 1 ,  18 _ 2  between the backplate electrode  12  and the membrane  16 . A second parasitic capacitance C MB  may be observed in at least a portion of the support structure  18 _ 1 ,  18 _ 2  between the membrane  16  and the second backplate electrode  14 . A further parasitic capacitance C BS  may be observed in at least a portion of the support structure  18 _ 1 ,  18 _ 2  between the second backplate electrode  14  and the substrate  20 _ 1 ,  20 _ 2 . While not mentioned, further parasitic capacitances can be observed in specific portions of the support structure  18 _ 1 ,  18 _ 2  between different ones of the backplate electrode  12 , the membrane  16  and the second backplate electrode  14 . 
       FIG. 1 b    shows a schematic circuit diagram of the MEMS device depicted in  FIG. 1 a   . The substrate may be grounded. The membrane may be biased by a bias voltage V bias . A voltage level Vp of the electrically conductive top backplate electrode  12  may be output. Further, a voltage level Vm of the electrically conductive (bottom) second backplate electrode  14  may be output. The voltage level outputs Vp and Vm vary in relation to the movement of the voltage biased membrane  16 . 
     In other words, the MEMS device may be able to produce output signals Vp and Vm responsive to the movement of the membrane in relation to the backplate electrode and the second backplate electrode (refer to  FIG. 1 a   ). This feature is schematically indicated by variable capacitors CA and CB, also referred to as active capacitances CA and CB. The active capacitances CA, CB are variable in relation to the movement of the membrane in relation to the backplate electrode and the second backplate electrode, respectively. 
     The circuit diagram shown in  FIG. 1 b    further indicates parasitic capacitances C TM , C MB  and C BS  observed in specific portions of the support structure between different ones of at least the backplate electrode  12 , the membrane  16 , the second backplate electrode  14  and the substrate  20 _ 1 ,  20 _ 2 . 
       FIG. 2 a    shows a schematic diagram of a MEMS device  10  in a cross-sectional view. This schematic diagram differs from the schematic diagram shown in  FIG. 1 a    in that further parasitic capacitances C_MS and C_BT may be observed inside the support structure  18 _ 1  and  18 _ 2 . The parasitic capacitance C_MS may be observed inside portions of the support structure  18 _ 1  disposed between the membrane  16  and the substrate  20 _ 1 . The parasitic capacitance C_BT may be observed between the second backplate electrode  14  and the backplate electrode  12  in portions of the support structure  18 _ 2  disposed between the second backplate electrode  14  and the backplate electrode  12 . Variable active capacitances CA and CB are observed between the membrane  16  and the backplate electrode  12  and the second backplate electrode  14 , respectively. 
       FIG. 2 b    shows a schematic circuit diagram of the MEMS device  10  comprising the further parasitic capacitances C_MS, C_BT. In this circuit diagram, the parasitic capacitance C_MS may be observed between the input bias voltage V bias  and ground gnd. Further, the parasitic capacitance C_BT may be observed between the voltage level outputs Vp and Vm. Variable active capacitances CA and CB are observed between the membrane and the backplate electrode and the second backplate electrode, respectively (refer to  FIG. 2 a   ). The membrane is movable in relation to both the backplate electrode and the second backplate electrode. Hence, active capacitances CA and CB vary in relation to this membrane movement, generated by sound pressure arrival, etc., for example. 
     Referring back to  FIG. 2 a    and in comparison with  FIG. 1 a   , the support structure  18 _ 1  may comprise a portion disposed between the membrane  16  and the substrate  20 _ 1  having no second backplate electrode  14  interposed. Hence, in said portion the parasitic capacitance C_MS may be provided between the membrane  16  and the substrate  20 _ 1  directly. Further, the support structure  18 _ 2  may comprise a portion between the backplate electrode  12  and the second backplate electrode  14  having no membrane  16  interposed. Hence, in said portion the parasitic capacitances C_BT may be provided between the backplate electrode  12  and the second backplate electrode  14  directly. 
       FIG. 3 a    shows a plan view of a MEMS device  10 , and  FIG. 3 b    shows the MEMS device  10  in cross-section in a schematic view. In contrast to the schematic view depicted in  FIG. 2 a   , the backplate electrode  12 , the membrane  16  and the second backplate electrode  14  may have all substantially same dimensions and may be stacked in relation to each other substantially without any offset. In other words, the backplate electrode  12 , the membrane  16  and the second backplate electrode  14  may be arranged such to achieve maximum overlapping. This arrangement can be regarded as a worst case situation, since parasitic capacitances C_TM, C_MB and C_BS may be high compared to the arrangements depicted in  FIGS. 1 a  and 2 a   . For example, parasitic capacitance C_TM may be about 1.0 pF, parasitic capacitance C_MB may be about 1.0 pF and parasitic capacitance C_BS may be about 4.1 pF. Since the membrane  16  is fully disposed between the backplate electrode  12  and the second backplate electrode  14 , the parasitic capacitance C_BT can be regarded as negligible. Further, since the second backplate electrode  14  is disposed fully between the membrane  16  and the substrate  20 _ 1 ,  20 _ 2 , the parasitic capacitance C_MS can be regarded as negligible, too. 
       FIG. 4 a    shows a MEMS device  10  in a plan view, and  FIG. 4 b    shows a schematic diagram of the MEMS device  10  depicted in  FIG. 4 a    in a cross-sectional view. In this arrangement, as can be best seen in  FIG. 4 a   , the circumference of the backplate electrode  12  may comprise recesses  24 . The recesses  24  may be arranged along the circumference of the backplate electrode  12  in an equidistant manner. While not shown in  FIG. 4 a   , also the second backplate electrode can comprise a circumference provided with recesses, wherein the recesses can be arranged along the circumference in an equidistant manner (or uniformly), too. Further, while not shown in  FIG. 4 a   , also the membrane  16  can comprise a circumference provided with recesses, wherein the recesses can be arranged along the circumference in an equidistant manner, as well. The recesses mentioned above are adapted to reduce the overlapping area in relation to each other. 
     Referring to  FIG. 4 b   , this arrangement is likely to achieve reduced parasitic capacitances C_TM, C_MB and C_BS as well as reduced parasitic capacitances C_BT and C_MS, compared to parasitic capacitances created in the support structure of MEMS devices schematically shown in  FIGS. 1 a , 2 a  and 3 b   . For example, parasitic capacitance C_TM is 0.12 pF, parasitic capacitance C_MB is 0.12 pF and parasitic capacitance C_BS is 0.82 pF. 
     Compared to the arrangement shown in  FIG. 3 b   , these parasitic capacitances are all reduced. In the MEMS device  10  as shown in  FIG. 4 b   , in the support structure  18 _ 2 , portions of the backplate electrode  12  and the second backplate electrode  14  may be overlapped, without having the membrane  16  interposed. Hence, in this portion of the support structure  18 _ 2  between the backplate electrode  12  and second backplate electrode  14 , parasitic capacitance C_BT is created. However, this parasitic capacitance C_BT is reduced when compared to the arrangement shown in  FIG. 3 b   , for example. In the arrangement shown in  FIG. 4 b   , in the support structure  18 _ 1 , a portion of the membrane  16  projects beyond the backplate electrode  12  and second backplate electrode  14 . In this configuration, parasitic capacitance C_MS is created in such portions of the support structure  18 _ 1  having no second backplate electrode  14  interposed. However, this parasitic capacitance C_MS may be as small as 0.25% C_BS in some implementation examples. 
       FIG. 5 a    shows a MEMS device  10  in a plan view, and  FIG. 5 b    shows a schematic diagram of the MEMS device  10  depicted in  FIG. 5 a    in a cross-sectional view. In this arrangement, as can be best seen in  FIG. 5 a   , the circumference of the backplate electrode  12  may comprise recesses  24 . The recesses  24  may be arranged along the circumference of the backplate electrode  12  uniformly or in an equidistant manner. Compared to the arrangement shown in  FIG. 4 a   , the recesses  24  may be structured to comprise a larger radius of curvature. While not shown in  FIG. 5 a   , also the second backplate electrode can comprise a circumference provided with recesses, wherein the recesses can be arranged along the circumference uniformly or in an equidistant manner. Further, while not shown in  FIG. 5 a   , also the membrane can comprise a circumference provided with recesses, wherein the recesses can be arranged along the circumference in an equidistant manner. 
     Referring to  FIG. 5 b   , this arrangement may provide reduced parasitic capacitances C_TM, C_MB and C_BS as well as reduced parasitic capacitances C_BT and C_MS compared to parasitic capacitances created in the support structure of MEMS devices schematically shown in  FIGS. 1 a , 2 a , 3 b  and 4 b   . For example, parasitic capacitance C_TM may be about 0.5 pF, parasitic capacitance C_MB may be about 0.5 pF and parasitic capacitance C_BS may be about 0.3 pF. 
     Compared to the arrangement shown in  FIG. 3 b   , for example, these parasitic capacitances may be reduced. In the MEMS device  10  as shown in  FIG. 5 b   , in the support structure  18 _ 2 , portions of the backplate electrode  12  and the second backplate electrode  14  may overlap, without having the membrane  16  interposed. Hence, in this portion of the support structure  18 _ 2  between the backplate electrode  12  and second backplate electrode  14 , parasitic capacitance C_BT is created. However, this parasitic capacitance C_BT can be considered negligible. In the arrangement shown in  FIG. 5 b   , in the support structure  18 _ 1 , a portion of the membrane  16  may project beyond the backplate electrode  12  and the second backplate electrode  14 . In this configuration, parasitic capacitance C_MS may be created in such portions of the support structure  18 _ 1  having no second backplate electrode  14  interposed. However, this parasitic capacitance C_MS may be as small as about 0.25% C_BS. 
       FIG. 6  shows a MEMS device  10  in a cross-sectional view. In general, this MEMS device  10  has substantially the same arrangement as compared to the MEMS devices depicted in  FIGS. 4 b  and 5 b   . However, the MEMS device  10  shown in  FIG. 6  comprises a backplate electrode  12  and a second backplate electrode  14  which comprise segmentations  12 S and  14 S. In particular, the backplate electrode  12  may comprise a segmentation  12 S. Further, the second backplate electrode  14  may comprise a segmentation  14 S. The MEMS device  10  further may comprise a membrane  16  disposed spaced apart from the backplate electrode  12  and the second backplate electrode  14 . The membrane  16  may comprise a displaceable portion and a fixed portion. The fixed portion may be defined to comprise at least a portion of the membrane  16  fixed by the support structure  18 _ 1 ,  18 _ 2 . The displaceable portion may be defined to comprise a portion of the membrane  16  being deflectable. 
     In the backplate electrode  12 , the segmentation  12 S may be arranged to provide an electrical isolation between an active backplate portion  12 ABP and a further backplate portion  12 FBP, the active backplate portion  12 ABP facing the displaceable portion of the membrane  16 . In the second electrode  14 , the segmentation  14 S is arranged to provide an electrical isolation between an active backplate portion  14 ABP and a further backplate portion  14 FBP, the active backplate portion  14 ABP facing the displaceable portion of the membrane  16 . 
     Variable active capacitances CA and CB are observed between the displaceable portion of the membrane  16  and the active backplate portion  12 ABP of the backplate electrode  12  and the active backplate portion  14 ABP of the second backplate electrode  14 , respectively. Hence, active capacitances CA and CB vary in relation to the movement of the displaceable portion of the membrane  16  in relation to both the active backplate portion  12 ABP of the backplate electrode  12  and the active backplate portion  14 ABP of the second backplate electrode  14 , respectively. This membrane  16  movement is generated by, for example, sound pressure arrival caused by speech, etc. 
     In case the MEMS device  10  comprises the backplate electrode  12 , the membrane  16  and the second backplate electrode  14  having a circular shape, also the segmentations  12 S and  14 S may be formed circularly. The segmentations  12 S and  14 S may be arranged to extend in the vicinity of the support structure  18 _ 1 ,  18 _ 2  in order to segment the backplate electrode  12  and the second backplate electrode  14  into the active backplate portions  12 ABP,  14 ABP and the further backplate portion  12 FBP,  14 FBP. Summarized, the active backplate portions  12 ABP and  14 ABP may be central portions (medium portions) and the further backplate portions  12 FBP and  14 FBP may be fringe portions of each the backplate electrode  12  and the second backplate electrode  14 . 
     The backplate electrode  12  and second backplate electrode  14  may be made of, or comprise, an electrically conductive material, for example poly-silicon. By the provision of the segmentations  12 S,  14 S, the parasitic capacitances may be reduced greatly since the isolated (separated) further backplate portions  12 FBP,  14 FBP do not contribute to the creation of parasitic capacitances. Each of the segmentations  12 S,  14 S can be regarded as a fringing capacitance C_F which limits the parasitic coupling. Hence, the capacitance of the MEMS device  10  as a whole may comprise an active capacitance CA created between the active backplate portion  12 ABP of the backplate electrode  12  and the displaceable portion of the membrane  16 , as well as an active capacitance CB created between the active backplate portion  14 ABP of the second backplate electrode  14  and the displaceable portion of the membrane  16 . 
     Note, that both the active backplate portion  12 ABP of the backplate electrode  12  as well as the active backplate portion  14 ABP of the second backplate electrode  14  may be connected to signal outputs via electrical conductive lead-throughs (not shown), respectively. The further backplate portion  12 FBP of the backplate electrode  12  may be isolated in the immediate vicinity. Further, the further backplate portion  14 FBP of the second backplate electrode  14  may be isolated in the immediate vicinity. Hence, parasitic capacitances C_TM, C_MB and C_BS may be substantially eliminated. Further, parasitic capacitances C_MS and C_BT may be substantially eliminated, too. 
     Both, the backplate electrode  12  as well as the second backplate electrode  14  may comprise bonding layers  12 B,  14 B, respectively. The bonding layers  12 B,  14 B may be arranged to support the active backplate portions  12 ABP and  14 ABP to the further backplate portions  12 FBP and  14 FBP. The bonding layers  12 B,  14 B may be arranged to pull the backplate electrode  12  and second backplate electrode  14  flat. 
     The material of the bonding layers  12 B,  14 B may comprise a dielectric material. For example, the dielectric material may comprise SiN. The bonding layers  12 B,  14 B may be bonded to surfaces of the backplate electrode  12  and the second backplate electrode  14 , respectively, facing each other. This feature may provide a symmetrization. In another example, the bonding layers  12 B,  14 B can be bonded to surfaces of the backplate electrode  12  and the second backplate electrode  14 , respectively, facing opposite directions. This feature may provide a symmetrization, as well. It may also be possible that the backplate electrode  12  is bonded to a surface of the bonding layer  12 B, and that the second backplate electrode  14  is bonded to a surface of the bonding layer  14 B. 
       FIG. 7  shows a plan view of the backplate electrode  12  or  14  (backplate electrode  12  or second backplate electrode  14 ). This backplate electrode  12  or  14  may comprise the active backplate portion  12 ABP or  14 ABP (medium portion) surrounded by the further backplate portion  12 FBP or  14 FBP (fringe portion). Both portions may be isolated (separated) from each other via the segmentation  12 S or  14 S. A bonding layer  12 B or  14 B may be provided to bond the active backplate portion  12 ABP or  14 ABP to the further backplate portion  12 FBP or  14 FBP which may be itself supported circumferentially by means of a support structure (not shown). A lead-through  26  may be provided which connects the active backplate portion  12 ABP or  14 ABP to a pad  28  serving as a contact point. Due to the segmentation  12 S or  14 S, the further backplate portion  12 FBP or  14 FBP may be completely isolated from the pad  28  and vice versa. The backplate electrode  12  or  14  may be perforated to allow transmission of sound pressure to the membrane (not shown) in case the backplate electrode is embodied as top backplate electrode. 
       FIG. 8 a    shows a MEMS device  10  in a plan view and  FIG. 8 b    shows the MEMS device  10  in a cross-sectional view. In this arrangement, the circumferences of the backplate electrode  12 , the membrane  16  and the second backplate electrode  14  may be formed such to comprise recesses adapted to, in the support structure, reduce overlapping areas in relation to each other. The recesses are arranged along the circumferences in an equidistant manner. 
     Further, the backplate electrode  12 , the second backplate electrode  14  and the membrane  16  may comprise the same number of recesses. Furthermore, the recesses of the top backplate electrode  12 , the bottom backplate electrode  14  and the membrane  16 , respectively, may be arranged such to be offset to each other angularly. 
       FIG. 8 b    shows a cross-sectional view of the MEMS device  10 . In this configuration, the backplate electrode  12 , the membrane  16  and the second backplate electrode  14  may comprise recesses. This configuration allows for reduced parasitic capacitances. In particular, the parasitic capacitance C_TM, created inside the support structure  18 _ 1  (i.e., the capacitance between the fixed portion of the membrane  16  and the corresponding portion of the top backplate electrode  12 ) equals about 0.0 pF, since the backplate electrode  12  and the membrane  16  do not overlap inside the support structure  18 _ 1 . Further, the parasitic capacitance C_MB created inside the support structure  18 _ 1  equals about 0.0 pF, since the membrane  16  and the second backplate electrode  14  do not overlap inside the support structure  18 _ 1 , as well. In other words, the fixed portion of the membrane  16  does not (or only little) overlap with the corresponding portion of the second backplate electrode  14 . The portions of the backplate electrode  12  and of the second backplate electrode  14  that correspond to the fixed portion of the membrane  16  may be regarded as the clamped portions of the backplate electrode  12 ,  14 , as opposed to their exposed portions which may correspond substantially to the displaceable portion of the membrane  16 . Further, the parasitic capacitance C_BS created between the second backplate electrode  14  and the substrate  20 _ 1  equals about 0.58 pF. 
     In addition, the parasitic capacitance C_BT created between the backplate electrode  12  and the second backplate electrode  14  may be negligible. Further, the parasitic capacitance C_MS may equal about 25% of C_BS. Furthermore, the parasitic capacitance C_TS created between the backplate electrode  12  and the substrate  20 _ 2 , inside the support structure  18 _ 2 , may equal about 14% of C_BS. Hence, parasitic capacitances typically may be reduced significantly. 
     For a better overview,  FIG. 8 c    shows the angular offset arrangement between the backplate electrode  12 , the second backplate electrode  14  and the membrane  16  in a schematic view. In this case, the second backplate electrode  14  is offset from the backplate electrode  12  by an angular offset of 30°. Further, the membrane  16  is offset from the second backplate electrode  14  by an angular offset of 30°. 
     Due to this arrangement the backplate electrode  12 , the second backplate electrode  14  and the membrane  16  may be arranged such that in an area corresponding to the fixed portion (i.e., inside the support structure) of the membrane  16  the overlapping area in relation to each other exhibits substantially minimum overlapping. Further, the membrane  16  may be arranged such that in the fixed portion the overlapping area in relation to both the backplate electrode  12  and second backplate electrode  14  may be less than maximum overlapping. Furthermore, the angular offsets of the recesses of the backplate electrode  12 , the second backplate electrode  14  and the membrane  16  may comprise a value resulting in minimum overlapping with each other. Furthermore, the backplate electrode  12 , the second backplate electrode  14  and the membrane  16  may be arranged such that in an area corresponding to the displaceable portion of the membrane  16  (e.g., central portion of the membrane) the overlapping area in relation to each other exhibits substantially maximum overlapping. 
     The recesses can be shaped to have a semi-circular shape, a circle segment shape, a castellation shape or other shape. 
       FIG. 9 a    shows a schematic diagram of a MEMS device  10  in a cross-sectional view. Similar to the arrangements shown in  FIGS. 4 b , 5 b   ,  6  and  8   b , the backplate electrode  12 , the membrane  16  and the second backplate electrode  14  may be arranged such that an overlapping area of the fixed portion of the membrane  16  with the backplate electrodes  12 ,  14  is less than maximum overlapping. In the MEMS device  10  in the arrangement shown in  FIG. 9 a   , a guard ring  30  may be interposed between the substrate  20 _ 1 ,  20 _ 2  and the support structure  18 _ 1 ,  18 _ 2 . The guard ring  3   o  may be associated with the second backplate electrode  14  and adapted to reduce parasitic capacitance in the support structure  18 _ 1 ,  18 _ 2  (i.e., fixed portion of the membrane  16  with the backplate electrodes  12 ,  14 ). In particular, the guard ring  30  may be adapted to reduce parasitic capacitances between the second backplate electrode  14  and the guard ring  30  itself. The guard ring  30  may be interposed circumferentially. 
     Further, as depicted in  FIG. 9 b   , additional guard rings  30 _ 1  to  30 _ 3  can be provided, wherein each guard ring is associated with the backplate electrode  12 , the membrane  16  and the second backplate electrode  14 , respectively. In particular, each guard ring  30 _ 1  to  30 _ 3  may be associated with one protruding arm of the backplate electrode  12 , the membrane  16 , or the second backplate electrode  14 , wherein each protruding arm may mechanically connect a corresponding central portion (e.g., a suspended portion) of the backplate electrode  12 , the membrane  16 , and the second backplate electrode  14 , respectively, with the support structure. In this case, each guard ring  30 _ 1  to  30 _ 3  may be associated with the respective one of the backplate electrode  12 , the membrane  16  and the second backplate electrode  14 . Due to the provision of the guard rings  30 _ 1  to  30 _ 3 , large reductions in parasitic capacitances can be achieved. 
       FIGS. 10 a  to 10 p    show schematic cross-sections associated during various stages or steps of an example manufacturing process of a MEMS device as described above. 
       FIG. 10 a    shows the substrate  100  which can be made of a silicon wafer. 
     As shown in  FIG. 10 b   , a lower etch stop layer  102  is deposited onto the upper surface of the substrate  100 . The lower etch stop layer  102  may provide a reliable stop of an etching process. The lower etch stop layer  102  may typically be made from a stop oxide TEOS (tetraethyl orthosilicate). The thickness of the lower etch stop layer  102  may be typically about 600 nm. 
       FIG. 10 c    shows a schematic cross-sectional view of the arrangement upon depositing a SiN layer  104  onto the surface of the lower etch stop layer  102  and upon depositing a poly-silicon layer  106  onto the surface of the deposited SiN layer  104 . The SiN layer  104  may have a thickness of about 140 nm. The poly-silicon layer  106  may have a typical thickness of about 330 nm. 
       FIG. 10 d    shows a schematic cross-sectional view after a multilayer arrangement comprising the three layers  102 ,  104  and  106  have been deposited onto the substrate  100  and the poly-silicon layer  106  has been structured, for example by etching, to provide a poly-silicon layer  106  segmentation. 
       FIG. 10 e    shows a schematic cross-sectional view after a multilayer arrangement comprising the SiN layer  104 , poly-silicon layer  106  and a further SiN layer  108  has been structured. In particular, openings or trenches may be formed in the multilayer arrangement, wherein said openings extend to the oxide layer  102 . 
       FIG. 10 f    shows a schematic cross-section after filling the whole substrate  100  surface with a TEOS deposition layer no by means of a deposition process, for example. In particular, the TEOS deposition layer no may have been filled into the openings. Afterwards, the TEOS layer no may have been annealed. A chemical mechanical polishing (CMP) process may have been applied to the TEOS layer no, subsequently. 
       FIG. 10 g    shows a schematic cross-sectional view of the arrangement after a further TEOS layer  112  may have been applied on top of the polished TEOS layer  110 . Afterwards, this TEOS layer  112  may have also been annealed. 
       FIG. 10 h    shows a schematic cross-sectional view of the arrangement after the additional TEOS layer  112  may have been subjected to a process of forming recesses  114 . The recesses  114  may be used for a subsequent formation of anti-sticking bumps. The anti-sticking bumps may be arranged to reduce the risk that a membrane element (not shown) gets stuck to an underlying electrode due to an adhesive force. The anti-sticking bumps  114  may be formed by etching, for example. 
       FIG. 10 i    shows a schematic cross-sectional view of the arrangement after a membrane layer  116  may have been deposited onto the TEOS layer  112 . In particular, the membrane layer  116  may have been deposited onto the TEOS layer  112  to fill the recesses  114  in order to form respective anti-sticking bumps. The membrane layer  116  may have a thickness of about 330 nm and comprises poly-silicon, for example. 
       FIG. 10 j    shows a schematic cross-sectional view of the arrangement after a TEOS layer  118  may have been deposited on top of the TEOS layer  112  as well as on top of the membrane layer  116 . After deposition of the TEOS layer  118 , this layer is etched to form recesses  120  to be used for a subsequent formation of anti-sticking bumps in the (top) backplate electrode  12 . 
       FIG. 10 k    shows a schematic cross-sectional view of the arrangement after a bonding layer  122  may have been deposited on top of the TEOS layer  118 . The bonding layer  122  may comprise SiN. The bonding layer  122  may be deposited such to fill the whole surface as well as the recesses  120  for obtaining respective anti-sticking bumps (refer to  FIG. 10 j   ). After this process, a poly-silicon layer  124  may be deposited on top of the SiN layer  122 . Subsequently, the poly-silicon layer  124  may be segmented, for example, by etching. 
       FIG. 10 l    shows a schematic cross-sectional view of the arrangement after deposition of a SiN layer  126  on top of the arrangement shown in  FIG. 10 k   . In particular, the SiN layer  126  may be deposited on top of the poly-silicon layer  124 . After deposition of the SiN layer  126 , this layered arrangement comprising the SiN layer  122 , the poly-silicon layer  124  and the SiN layer  126  may be etched to form a plurality of openings or trenches, which extend to the TEOS layer  118 . 
       FIG. 10 m    shows a schematic cross-sectional view of the arrangement after deposition of a TEOS layer  128  on top of the layered arrangement comprising the SiN layer  122 , the poly-silicon layer  124  and the SiN layer  126  as mentioned above. The TEOS layer  128  has a thickness of 100 nm, for example. 
     Subsequent to this process, a contact hole  130  may be formed by means of photolithography. This contact hole  130  may be formed to extend across the SiN layer  126  and the TEOS layer  128  until reaching the poly-silicon layer  124 . Further, as shown on the right-hand side of  FIG. 10 m   , first to third trenches  132 ,  134  and  136  may be formed such to extend across respective TEOS layers of the TEOS layers  110 ,  112 ,  118 . 
     In particular, the first trench  132  may be formed to extend across the TEOS layer  118  such to reach the membrane layer  116  (refer to  FIG. 10 p   . Further, the second trench  134  may be formed to extend across the TEOS layers  118  and  112  such to reach the poly-silicon layer  106  (refer to  FIG. 10 e   ). Further, the third trench  136  may be formed to extend across the TEOS layers  110 ,  112  and  118 , as well as the lower etch stop layer  102  such as to reach the substrate  100 . 
       FIG. 10 n    shows a schematic cross-sectional view of the arrangement after filling of electrically conductive material into the contact hole  130  and into the first to third trenches  132 ,  134  and  136 . In doing so, contacts  138 ,  140 ,  142  and  144  may be created, connected to surface-mounted pads  146 ,  148 ,  150  and  152 , respectively. 
     In particular, the contacts  138 ,  14   o ,  142  and  144  may be formed such that the respective contact pads  146 ,  148 ,  150  and  152  may be electrically connected to the respective layers, respectively, i.e., the poly-silicon layer  124 , the membrane layer  116 , the poly-silicon layer  106  and the substrate  100 . In general, connections may be created to achieve electrical connections to the second backplate electrode, the membrane, the backplate electrode and the substrate, respectively. The material of the contacts  138 ,  14   o ,  142  and  144  can be titanium, platinum, or gold, for example. Of course, other materials having good electrical conductivity can be selected. 
       FIG. 10 o    shows a schematic cross-sectional view of the MEMS device  10  after backside etching of a backside cavity  154 . In this etching step, the lower etch stop layer  102  may act as an etch stop element preventing the etching agent to reach the second backplate electrode. 
       FIG. 10 p    shows a schematic cross sectional view of the MEMS device  10  after removal of parts of the TEOS layers  110 ,  112  and  118  inside operation portions of the backplate/membrane/backplate-arrangement. This step may be assisted by a front side protection mask opening the perforations of the backplate electrode. 
     Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. 
     The above described is merely illustrative, and it is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending claims and not by the specific details presented by way of description and explanation above.