Patent Publication Number: US-2023134752-A1

Title: Dual-diaphragm assembly having center constraint

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to a microelectromechanical systems (MEMS) dual-diaphragm assembly, and more particularly to a MEMS dual-diaphragm assembly having a center constraint. 
     BACKGROUND 
     It is known that in the fabrication of MEMS devices often a plurality of devices are manufactured in a single batch process wherein individual portions of the batch process representative of individual MEMS devices are known as dies. Accordingly, a number of MEMS dies can be manufactured in a single batch process and then cut apart or otherwise separated for further fabrication steps or for their ultimate use, which for example without limitation includes use as an acoustic transducer or other portion of a microphone. 
     Existing vacuum sealed MEMS dual-diaphragm assemblies including a stationary electrode assembly disposed between first and second diaphragms do not include a center constraint. The lack of a center constraint can result in a mismatch in gap spacing between each of the first and second diaphragms and the stationary electrode assembly, and such a mismatched gap spacing is detrimental to performance. Conversely, it has been demonstrated that adding a center constraint reduces both the mean and variation in the static deflection of the assembly, which improves the gap matching. Further benefits of adding a center constraint include reducing the damping for a given cavity pressure, which increases the backplate resonance frequency thereby reducing the effect of ringing, and increasing the effective area of the assembly, which allows the same sensitivity to be achieved with lower compliance, resulting in better linearity and lower total harmonic distortion (THD). A need therefore exists for a vacuum sealed MEMS dual-diaphragm assembly having a center constraint. 
    
    
     
       DRAWINGS 
       The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. These drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope. 
         FIG.  1    is a top plan schematic view of a MEMS die, according to an embodiment. 
         FIG.  2 A  is a cross-sectional schematic view of the MEMS die of  FIG.  1    taken generally along the lines  2 - 2  of  FIG.  1   . 
         FIG.  2 B  is a cross-sectional schematic view of another embodiment of the MEMS die of  FIG.  1    taken generally along the lines  2 - 2  of  FIG.  1   . 
         FIG.  3    is a cross-sectional schematic view of a MEMS die, according to another embodiment. 
         FIG.  4    is a cross-sectional schematic view of a MEMS die, according to yet another embodiment. 
         FIG.  5 A  is a cross-sectional schematic view of a MEMS diaphragm assembly, according to an embodiment. 
         FIG.  5 B  is a cross-sectional schematic view of a MEMS diaphragm assembly, according to another embodiment. 
         FIG.  6 A  is a cross-sectional schematic view of a MEMS diaphragm assembly, according to yet another embodiment. 
         FIG.  6 B  is a cross-sectional schematic view of a MEMS diaphragm assembly, according to a further embodiment. 
         FIG.  7    is a cross-sectional schematic view of a MEMS diaphragm assembly, according to yet another embodiment. 
         FIG.  8    is a cross-sectional schematic view of a MEMS diaphragm assembly, according to a further embodiment. 
         FIG.  9    is a cross-sectional schematic view of a MEMS die including a tunnel disposed through the MEMS diaphragm assembly, according to an embodiment. 
         FIG.  10    is a cross-sectional schematic view of a MEMS die including a tunnel disposed through the MEMS diaphragm assembly, according to another embodiment. 
         FIG.  11    is a cross-sectional schematic view of a MEMS die including a tunnel disposed through the MEMS diaphragm assembly, according to a further embodiment. 
         FIG.  12    is a cross-sectional view of a microphone assembly according to an embodiment. 
     
    
    
     In the following detailed description, various embodiments are described with reference to the appended drawings. The skilled person will understand that the accompanying drawings are schematic and simplified for clarity. Like reference numerals refer to like elements or components throughout. Like elements or components will therefore not necessarily be described in detail with respect to each figure. 
     DETAILED DESCRIPTION 
     According to an embodiment, a MEMS diaphragm assembly comprises a first diaphragm, a second diaphragm, and a stationary electrode assembly spaced between the first and second diaphragms and including a plurality of apertures disposed therethrough. Each of a plurality of pillars is disposed through one of the plurality of apertures and connects the first and second diaphragms. At least one of the first and second diaphragms is connected to the stationary electrode assembly at a geometric center of the assembly. 
     According to an embodiment, both of the first and second diaphragms are connected to the stationary electrode assembly at the geometric center of the assembly. According to an embodiment, the at least one of the first and second diaphragms is connected to the stationary electrode assembly at a geometric center of the assembly by an electrically insulative material. According to an embodiment, the at least one of the first and second diaphragms is connected to the stationary electrode assembly at a geometric center of the assembly by an electrically conductive material. According to an embodiment, the at least a portion of the at least one of the first and second diaphragms is connected directly to the stationary electrode assembly. 
     According to an embodiment the first diaphragm and the second diaphragm bound a sealed chamber, and the pressure within the sealed chamber is below atmospheric pressure. According to another embodiment at least one tunnel passes through the first and second diaphragms and the stationary electrode assembly, wherein the at least one tunnel is sealed off from the sealed chamber. In an embodiment the at least one tunnel is sealed off from the sealed chamber and passes through the sealed chamber, and in another embodiment the at least one tunnel is sealed off from the sealed chamber and passes through the geometric center of the assembly. 
     According to an embodiment, a microphone device comprises a MEMS die comprising a substrate having an opening formed therethrough, and a diaphragm assembly attached around a periphery thereof to the substrate and over the opening. The diaphragm assembly comprises a first diaphragm, a second diaphragm, and a stationary electrode assembly spaced between the first and second diaphragms and including a plurality of apertures disposed therethrough. Each of a plurality of pillars is disposed through one of the plurality of apertures and connects the first and second diaphragms, wherein at least one of the first and second diaphragms is connected to the stationary electrode assembly at a geometric center of the assembly. In another embodiment at least a portion of the at least one of the first and second diaphragms is connected directly to the stationary electrode assembly. In a further embodiment the one of the first and second diaphragms having at least a portion thereof connected directly to the stationary electrode assembly is the one of the first and second diaphragms disposed on a side of the diaphragm assembly away from the opening. 
     Referring to  FIGS.  1  and  2 A , an exemplary MEMS die  100  is shown schematically in a top plan view in  FIG.  1   .  FIG.  2 A  illustrates a cross-sectional view taken generally along the lines  2 - 2  of  FIG.  1   . In an embodiment the MEMS die  100  includes a first diaphragm  102  and a second diaphragm  104 . The first diaphragm  102  and the second diaphragm  104  bound a sealed chamber  106 . A stationary electrode assembly  108  is disposed within the sealed chamber  106  between the first diaphragm  102  and the second diaphragm  104 . 
     Referring to  FIGS.  1  and  2 A , in an embodiment the MEMS die  100  includes a substrate  118  having an outer boundary  120  as indicated in  FIG.  1   . In an embodiment the substrate  118  has a generally rectangular perimeter, but in other embodiments it can be any shape. The substrate  118  in an embodiment includes an opening  122  formed therethrough. The geometric center  125  of the MEMS die  100  is also illustrated at an intersection of crossed centerlines in  FIG.  1    and at the left side of the cross-sectional view of  FIG.  2 A . In an embodiment the first and second diaphragms  102 ,  104  extend over the entire substrate  118 . In other embodiments the first and second diaphragms  102 ,  104  extend over a portion but not all of the substrate  118 . 
     Referring to  FIG.  2 A , in an embodiment a MEMS diaphragm assembly  101  comprises the first diaphragm  102 , the second diaphragm  104 , and the stationary electrode assembly  108  spaced between the first and second diaphragms  102 ,  104  and including a plurality of apertures  110  disposed therethrough. A plurality of pillars  112 , each disposed through one of the plurality of apertures  110 , connects the first and second diaphragms  102 ,  104 . In an embodiment the MEMS diaphragm assembly  101  is attached around the outer periphery thereof to the substrate  118  and over the opening  122 . 
     In an embodiment the MEMS diaphragm assembly  101  is attached to the substrate  118  via the second diaphragm  104  over the opening  122  via a spacer layer  124 . However, in other embodiments at least a portion of the second diaphragm  104  is attached directly to the substrate  118 . In some embodiments the spacer layer  124  can be an integral part of the substrate  118  or added onto the substrate  118  as an additional sacrificial layer  124 . The spacer layer  124  can, for example, be made of any insulative material as described hereinbelow. In an embodiment the substrate  118  is made of silicon. 
     According to an embodiment, the first diaphragm  102  includes an insulative layer  102 A and a conductive layer  102 B, and the second diaphragm  104  includes an insulative layer  104 A and a conductive layer  104 B. Each of the conductive layers  102 B and  104 B includes a sensing or electrically active region  20  and a non-sensing or electrically inactive region  30 . The sensing region  20  is disposed radially inward of and separated from the non-sensing region  30  by a first gap  40  in the conductive layer  102 B or  104 B. In embodiments having a connection between the conductive layer  102 B or  104 B and the stationary electrode assembly  108  (or directly between the first and second conductive layers  102 B,  104 B), the sensing region  20  is further separated from the connection by a second gap  42 . The sensing region  20 , the non-sensing region  30 , and the gaps  40 ,  42  are illustrated in  FIGS.  2 A- 4  and  9 - 11   . The sensing region  20  of the conductive layer  102 B of the first diaphragm  102  may be referred to as a first movable electrode. Similarly, the sensing region  20  of the conductive layer  104 B of the second diaphragm  104  may be referred to as a second movable electrode. 
     Still referring to  FIG.  2 A , according to an embodiment, the stationary electrode assembly  108  includes an insulative layer  108 A, a first conductive layer  108 B, and a second conductive layer  108 C. The insulative layer  108 A is sandwiched between the first conductive layer  108 B and the second conductive layer  108 C. In one embodiment, the first conductive layer  108 B and the second conductive layer  108 C are shorted together so as to form a single electrode (also referred to herein as a stationary electrode), which faces the first movable electrode and also faces the second movable electrode. In another embodiment, the first conductive layer  108 B and the second conductive layer  108 C are electrically isolated from one another, and may be respectively referred to as a first stationary electrode (which faces the first movable electrode) and a second stationary electrode (which faces the second movable electrode). In an embodiment, the stationary electrode assembly  108  is relatively thick and/or stiff compared to the first and second diaphragms  102  and  104 , for example by being fabricated using thicker materials or using thin very high stress films to maintain sufficient rigidity. The stationary electrode assembly  108  remains relatively motionless when the first and second diaphragms  102  and  104  are deflected. Referring to  FIG.  2 B , in another embodiment the stationary electrode assembly  108  includes a single conductive layer  108 D surrounded by two dielectric layers  108 E, where the single conductive layer  108 D is sandwiched between the two dielectric layers  108 E. 
     Referring to  FIGS.  2 A and  2 B , in an embodiment a mechanically active area for the first diaphragm  102  is defined by an annular region bounded at an outer radius by the innermost radial boundary (the release front  134 ) of material  117  disposed between the stationary electrode assembly  108  and the first diaphragm  102 , and at an inner radius by the outermost radial boundary of the connection between the first diaphragm  102  and the stationary electrode assembly  108 . Similarly, in an embodiment a mechanically active area for the second diaphragm  104  is defined by an annular region bounded at an outer radius by the innermost radial boundary (the release front  136 ) of material  117  disposed between the stationary electrode assembly  108  and the second diaphragm  104 , and at an inner radius by the outermost radial boundary of the connection between the second diaphragm  104  and the stationary electrode assembly  108 . In an embodiment, the material  117  disposed between the stationary electrode assembly  108  and each of the first and second diaphragms  102 ,  104  can be a sacrificial material and/or can, for example, be made of any insulative material as described hereinbelow. 
     The material of any of the insulative layers  102 A,  104 A, and  108 A can be any insulative material that would not be damaged during a sacrificial layer removal process. For example, without limitation, the insulative material can be silicon nitride, silicon oxynitride, metal oxides, polymers, materials that are not damaged by a sacrificial layer removal process, and combinations thereof. Similarly, the material of any of the conductive layers  102 B,  104 B,  108 B, and  108 C can be any conductive material that would not be damaged during a sacrificial layer removal process. For example, without limitation, the conductive material can be polycrystalline silicon, one or more metals, alloys of metals, carbon, materials that are not damaged by a sacrificial layer removal process, and combinations thereof. The structural geometry of materials comprising the first and second diaphragms  102  and  104  and the stationary electrode assembly  108  can be other than those described hereinabove in other embodiments. 
     Referring now to  FIGS.  2 A- 4   , in various embodiments at least one of the first and second diaphragms  102 ,  104  is connected to the stationary electrode assembly  108  at the geometric center  125  of the assembly  101 . For example,  FIGS.  2 A and  2 B  illustrate an embodiment wherein both of the first and second diaphragms  102 ,  104  are connected to the stationary electrode assembly  108  at the geometric center  125  of the assembly  101 .  FIG.  3    illustrates an embodiment wherein the second diaphragm  104  is connected to the stationary electrode assembly  108  at the geometric center  125  of the assembly  101 , and  FIG.  4    illustrates an embodiment wherein the first diaphragm  102  is connected to the stationary electrode assembly  108  at the geometric center  125  of the assembly  101 . 
     The connection between the at least one of the first and second diaphragms  102 ,  104  and the stationary electrode assembly  108  can be via a direct connection, or via a connecting material  119  as illustrated in  FIGS.  2 A- 4   . The connecting material  119  can be either an electrically insulative material or an electrically conductive material. It is envisioned that in an embodiment where both of the first and second diaphragms  102 ,  104  are connected to the stationary electrode assembly  108  that one of the connections could be via an insulative material and the other of the connections could be via a conductive material. In an embodiment the connection between the at least one of the first and second diaphragms  102 ,  104  and the stationary electrode assembly  108  can be via an electrically insulative material comprising an unreleased sacrificial material  119 . 
       FIGS.  5 A- 8    are exemplary cross-sectional views of a MEMS diaphragm assembly  101  illustrating a direct connection of at least one of the first and second diaphragms  102 ,  104  to the stationary electrode assembly  108  or to the other of the first and second electrodes  102 ,  104  at the geometric center  125  thereof. It is important to note that the first diaphragm  102  and the second diaphragm  104  bound a sealed chamber  106 , and the pressure within the sealed chamber  106  is reduced below atmospheric pressure. The sealed chamber  106  in some embodiments is a low pressure region having a pressure below atmospheric pressure. In an embodiment the sealed chamber  106  has an internal pressure, for example, of less than 100,000 Pa. In another embodiment the sealed chamber  106  has an internal pressure of less than 10,000 Pa. In a further embodiment the sealed chamber  106  has an internal pressure of less than 1,000 Pa, and in yet another embodiment the sealed chamber  106  has an internal pressure of less than 100 Pa. 
     The embodiments shown in  FIGS.  5 A- 8    take advantage of the reduced pressure of the sealed chamber  106  to achieve a direct connection between at least one of the first and second diaphragms  102 ,  104  and the stationary electrode assembly  108  or a direct connection between the first and second electrodes  102 ,  104  at the geometric center  125 . This direct connection is structurally different than the embodiments having a connection via a connecting material  119 . 
     Referring to  FIGS.  5 A and  5 B , in an embodiment at least a portion of the first diaphragm  102  is connected directly to the stationary electrode assembly  108 . In an embodiment as shown in  FIG.  5 A  the second diaphragm  104  is connected to the stationary electrode assembly  108  by a connecting material  119 , which can be an electrically insulative material or electrically conductive material. In an embodiment as shown in  FIG.  5 B  the second diaphragm  104  is not connected to the stationary electrode assembly  108 . 
     Referring to  FIGS.  6 A and  6 B , in an embodiment at least a portion of the second diaphragm  104  is connected directly to the stationary electrode assembly  108 . In an embodiment as shown in  FIG.  6 A  the first diaphragm  102  is connected to the stationary electrode assembly  108  by a connecting material  119 , which can be an electrically insulative material or electrically conductive material. In an embodiment as shown in  FIG.  6 B  the first diaphragm  102  is not connected to the stationary electrode assembly  108   
     Referring to  FIG.  7   , in an embodiment, at least a portion of both of the first and second diaphragms  102 ,  104  is connected directly to the stationary electrode assembly  108 . 
     Referring to  FIG.  8   , in an embodiment a MEMS diaphragm assembly  101  comprises first and second diaphragms  102 ,  104 , and a stationary electrode assembly  108  spaced between the first and second diaphragms  102 ,  104 . The stationary electrode assembly  108  includes a plurality of apertures  110  disposed therethrough, the plurality of apertures including a central aperture  111  disposed through a geometric center  125  of the stationary electrode assembly  108 . A plurality of pillars  112  is each disposed through one of the plurality of apertures  110  except for the central aperture  111 , wherein the plurality of pillars  112  connects the first and second diaphragms  102 ,  104 . In this embodiment the first and second diaphragms  102 ,  104  are connected directly to one another within the central aperture  111 . 
     It should be noted that there are two different types of direct connection that can be made as described hereinabove in regard to  FIGS.  5 A- 8   . As described in paragraph [0036] above, a first type of direct connection between at least one of the first and second diaphragms  102 ,  104  and the stationary electrode assembly  108 , or between the first and second electrodes  102 ,  104  at the geometric center  125 , can be achieved by taking advantage of the reduced pressure of the sealed chamber  106 . This type of direct connection uses ambient pressure of the surroundings against the reduced pressure of the sealed chamber  106  to make the direct connection, so that the first and second electrodes  102 ,  104  are not fabricated to be in contact until sacrificial layers within the chamber  106  are etched away and the resulting chamber  106  is sealed at a pressure below ambient. 
     This type of direct connection is structurally different than the embodiments having a connection established via a connecting material  119 , which are fabricated to have a direct connection by the layering process (as described for  FIGS.  2 A- 4   ), wherein the layers are deposited directly in contact with each other at the time of layer fabrication. 
     Referring to  FIGS.  9 - 11   , in some embodiments the MEMS diaphragm assembly  101  further includes a tunnel  114  that passes through at least a portion of the assembly  101 . Referring to  FIGS.  9  and  10   , in an embodiment the MEMS diaphragm assembly  101  includes at least one tunnel  114  that passes through the first and second diaphragms  102 ,  104 , and the stationary electrode assembly  108 . In an embodiment the at least one tunnel  114  passes through the first and second diaphragms  102 ,  104  and the stationary electrode assembly  108 , and the tunnel  114  is further sealed off from the sealed chamber  106 . The tunnel  114  can be sealed off from the sealed chamber  106  by not passing through the sealed chamber  106  as illustrated in  FIG.  9   . In another embodiment, as illustrated in  FIG.  10   , the tunnel  114  passes through the sealed chamber  106  yet is sealed off from the sealed chamber  106 . In an embodiment as illustrated in  FIG.  11   , the at least one tunnel  114  is sealed off from the sealed chamber  106  and passes through the sealed chamber  106  through the geometric center  125  of the assembly  101 . 
     Still referring to  FIGS.  9 - 11   , in an embodiment the tunnel  114  is defined by a side wall  116  and in another embodiment at least a portion of the side wall  116  is surrounded by sacrificial material  117 . The sacrificial material  117  can, for example, be made of any insulative material as described hereinabove. The pillars  112  and the side wall  116  can be made of any insulative material that would not be damaged during a sacrificial layer removal process. For example, without limitation, the insulative material can be silicon nitride, silicon oxynitride, metal oxides, polymers, materials that are not damaged by a sacrificial layer removal process, and combinations thereof. 
     During operation of the MEMS die  100  described hereinabove, for example as an acoustic transducer  100 , electric charge is applied to the conductive layers  108 B and  108 C of the stationary electrode assembly  108  and the sensing regions  20  of the first and second movable electrodes  102 B and  104 B thereby inducing an electric field between the stationary electrode(s) of the stationary electrode assembly  108  and the first and second movable electrodes  102 B,  104 B. Fluctuations in ambient pressure (e.g., resulting from sound waves) act against the outer surface of the diaphragm  104  facing the opening  122  causing the first and second diaphragms  102 ,  104  to deflect (enter a deflection state) and to deform. This deformation causes a change in the capacitance between the one or more stationary electrodes of the stationary electrode assembly  108  and the first and second diaphragms  102 ,  104 , which can be detected and interpreted as sound. 
     Turning to  FIG.  12   , the MEMS die  100  used as an acoustic transducer  1000  is configured to fit within a microphone assembly, generally labeled  900 . The assembly  900  includes a housing including a base  902  having a first surface  905  and an opposing second surface  907 . The housing further includes a cover  904  (e.g., a housing lid), and an acoustic port  906 . In an embodiment the port  906  extends between the first surface  905  and the second surface  907 . In one implementation, the base  902  is a printed circuit board. The cover  904  is coupled to the base  902  (e.g., the cover  904  may be mounted onto a peripheral edge of the base  902 ). Together, the cover  904  and the base  902  form an enclosed volume  908  for the assembly  900 . In an embodiment, for example, the MEMS die  100  used as an acoustic transducer  1000  includes a diaphragm assembly  101  as illustrated in  FIGS.  5 A or  5 B  wherein the one of the first and second diaphragms  102 ,  104  having at least a portion thereof connected directly to the stationary electrode assembly  108  is the one of the first and second diaphragms  102 ,  104  disposed on a side of the diaphragm assembly  101  away from the opening  122 . In another embodiment, for example, the MEMS die  100  used as an acoustic transducer  1000  includes a diaphragm assembly  101  as illustrated in  FIGS.  6 A or  6 B  wherein the one of the first and second diaphragms  102 ,  104  having at least a portion thereof connected directly to the stationary electrode assembly  108  is the one of the first and second diaphragms  102 ,  104  disposed on a side of the diaphragm assembly  101  facing from the opening  122 . 
     As shown in  FIG.  12   , the acoustic port  906  is disposed on the base  902  and is structured to convey sound waves and/or otherwise be acoustically coupled to the MEMS die  100  used as an acoustic transducer  1000  located within the enclosed volume  908 . In other implementations, the acoustic port  906  is disposed on the cover  904  and/or a side wall of the cover  904 , but is still acoustically coupled to the MEMS die  100 . In an embodiment, the MEMS diaphragm assembly  101  of the MEMS acoustic transducer  1000  is oriented relative to the opening  122  such that one of the first and second diaphragms  102 ,  104  having at least a portion thereof connected directly to the stationary electrode assembly  108  is disposed on a side of the diaphragm assembly  101  facing away from the opening  122 . In another embodiment, the MEMS diaphragm assembly  101  of the MEMS acoustic transducer  1000  is oriented relative to the opening  122  such that one of the first and second diaphragms  102 ,  104  having at least a portion thereof connected directly to the stationary electrode assembly  108  is disposed on a side of the diaphragm assembly  101  facing toward the opening  122 . 
     In some embodiments, the assembly  900  forms part of a compact computing device (e.g., a portable communication device, a smartphone, a smart speaker, an internet of things (IoT) device, etc.), where one, two, three or more assemblies may be integrated for picking-up and processing various types of acoustic signals such as speech and music. 
     The assembly  900  includes an electrical circuit disposed within the enclosed volume  908 . In an embodiment, the electrical circuit includes an integrated circuit (IC)  910 . In an embodiment the IC  910  is disposed on the first surface  905  of the base  902 . The IC  910  may be an application specific integrated circuit (ASIC). Alternatively, the IC  910  may include a semiconductor die integrating various analog, analog-to-digital, and/or digital circuits. In an embodiment the cover  904  is disposed over the first surface  905  of the base  902  covering the MEMS acoustic transducer  1000  and the IC  910 . 
     In the assembly  900  of  FIG.  12   , the MEMS acoustic transducer  1000  is illustrated as being disposed on the first surface  905  of the base  902 . The MEMS acoustic transducer  1000  converts sound waves, received through acoustic port  906 , into a corresponding electrical microphone signal, and generates an electrical signal (e.g., a voltage) at a transducer output in response to acoustic activity incident on the port  906 . As shown in  FIG.  12   , the transducer output includes a pad or terminal of the transducer that is electrically connected to the electrical circuit via one or more bonding wires  912 . The assembly  900  of  FIG.  12    further includes electrical contacts, shown schematically as contacts  914 , typically disposed on a bottom surface of the base  902 . The contacts  914  are electrically coupled to the electrical circuit. The contacts  914  are configured to electrically connect the assembly  900  to one of a variety of host devices. 
     As noted hereinabove, a plurality of MEMS devices can be manufactured in a single batch process. Individual portions of the batch process representative of individual MEMS devices are known as dies. Accordingly, a number of MEMS dies can be manufactured in a single batch process and then cut apart or otherwise separated for further fabrication steps or for their ultimate use, which for example without limitation includes as an acoustic transducer or other portion of a microphone. 
     Steps in a production process utilized to produce the MEMS die  100  as described hereinabove include etching, masking, patterning, cutting, boring, and/or release steps executed on a workpiece. All of the steps are not described in detail herein. However, generally the portions of the MEMS die  100  that ultimately end up as the structure of the vacuum sealed dual diaphragms and the one or more tunnels  114  are layered onto a workpiece using sacrificial material, or otherwise bored or etched out of a solid block of material. 
     With respect to the use of plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     Unless otherwise noted, the use of the words “approximate,” “about,” “around,” “substantially,” etc., mean plus or minus ten percent. 
     The foregoing description of illustrative embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.