3D mems device with hermetic cavity

Abstract

A three dimensional (3D) micro-electro-mechanical system (MEMS) device is provided. The device comprises a central MEMS wafer, and top and bottom cap wafers. The MEMS wafer includes a MEMS structure, such as an inertial sensor. The 5 top cap wafer, the bottom cap wafer and the MEMS wafers are stacked along a stacking axis and together form at least one hermetic cavity enclosing the MEMS structure. At least one of the top cap wafer and the bottom cap wafer is a silicon-on-insulator (SOI) cap wafer comprising a cap device layer, a cap handle layer and a cap insulating layer interposed between the cap device layer and the cap handle layer. At 10 least one electrically conductive path extends through the SOI cap wafer, establishing an electrical convection between an outer electrical contact provided on the SOI cap wafer and the MEMS structure.

The invention claimed is: 
     
         1 . A three dimensional (3D) micro-electro-mechanical system (MEMS) device comprising:
 a MEMS wafer including a MEMS structure, the MEMS wafer having opposed first and second sides;   a top cap wafer and a bottom cap wafer respectively bonded to the first side and the second side of the MEMS wafer, the top cap wafer, the bottom cap wafer and the MEMS wafer being stacked along a stacking axis and together forming to form at least one hermetic cavity enclosing the MEMS structure, at least one of the top cap wafer and the bottom cap wafer being a silicon-on-insulator (SOI) cap wafer comprising a cap device layer, a conductive silicon cap handle layer and a cap insulating layer interposed between the cap device layer and the conductive silicon cap handle layer, one of the conductive silicon cap handle layer and of the cap device layer of the SOI cap wafer having an inner side bonded to the MEMS wafer, and the other one of the cap handle layer and the cap device layer the conductive silicon cap handle layer having an outer side with outer electrical contacts form thereon; and   an electrically conductive path extending through the conductive silicon cap handle layer and through the cap device layer of the SOI cap wafer and comprising a conducting shunt formed through the cap insulating layer, the electrically conductive path establishing an electrical connection between one of the outer electrical contacts and said at least one of MEMS structure and connecting wherein the conducting shunt electrically connects the conductive silicon cap handle layer and the cap device layer to conduct signals through the conduction shunt and at least a portion of the conductive silicon cap handle layer.    
     
     
         2 . The 3D MEMS device of  claim 1 , wherein said electrically conductive path comprises a post formed in the cap handle layer, the post being delineated by a closed-loop trench patterned through an entire thickness of the cap handle layer, said one of the outer electrical contacts being located on top of said post. 
     
     
         3 . The 3D MEMS device of  claim 2 , wherein said electrically conductive path comprises a pad formed in the cap device layer, the pad being delineated by a trench patterned through an entire thickness of the cap device layer, the pad being aligned along the stacking axis with said post. 
     
     
         4 . The 3D MEMS device according to  claim 1 , wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer. 
     
     
         5 . The 3D MEMS device of  claim 4 , wherein said electrically conductive path comprises a pad formed in the MEMS device layer, delineated by a trench, the pad being electrically connected to the MEMS structure, the pad formed in the MEMS device layer being aligned along the stacking axis with athe pad formed in the cap device layer. 
     
     
         6 . The 3D MEMS device of claim  5   1 , wherein the MEMS wafer comprises an outer frame, the MEMS structure comprising at least one proof mass suspended by springs, the at least one proof mass being patterned in both the MEMS handle and device layers, the springs being patterned in the MEMS device layer, the at least one proof mass including conductive shunts electrically connecting the MEMS device and handle layers, the electrically conductive path connecting said one of the outer electrical contacts to the MEMS structure via at least one of the springs. 
     
     
         7 . The 3D MEMS device according to  claim 1 , wherein the cap device layer comprises a plurality of cap electrodes patterned therein, the 3D MEMS device comprising additional electrically conducting paths extending through the conductive cap handle layer and the cap device layer, at least one of said additional electrically conducting paths establishing an electrical connection between a subset of the outer electrical contacts and at least a portion of said plurality of cap electrodes. 
     
     
         8 . The 3D MEMS device of  claim 7 , wherein the cap device layer comprises leads patterned therein, the leads being electrically connected to the cap electrodes, the leads extending orthogonally to the stacking axis and forming part of corresponding ones of said additional electrically conducting paths. 
     
     
         9 . The 3D MEMS device according to  claim 1 , comprising a device feedthrough extending along the stacking axis, the device feedthrough comprising a cap feedthrough and a MEMS feedthrough aligned with one another, wherein the cap feedthrough comprises:
 a cap feedthrough post patterned through the entire thickness of the cap handle layer, the cap feedthrough post being electrically connected to one of the outer electrical contacts;   a cap feedthrough pad patterned through the entire thickness of the cap device layer; and   a conductive shunt formed through the cap insulating layer, electrically connecting the cap feedthrough post and the cap feedthrough pad;   wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer, the MEMS feedthrough comprising:   a MEMS feedthrough post patterned through an entire thickness of the MEMS handle layer;   a MEMS feedthrough pad patterned through an entire thickness of the MEMS device layer; and   a conductive shunt formed through the MEMS insulating layer, electrically connecting the MEMS feedthrough post and the MEMS feedthrough pad, thereby establishing an electrical connection between said one of the outer electrical contacts on top of the cap feedthrough post and the MEMS feedthrough, through the cap feedthrough.   
     
     
         10 . The 3D MEMS device of  claim 9 , wherein trenches delineating posts in at least one of the SOI cap wafer and the SOI MEMS wafer are left unfilled. 
     
     
         11 . The 3D MEMS device of  claim 9 , wherein the cap feedthrough post and the MEMS feedthrough post have respective cross-sections taken orthogonally with respect to the stacking axis, said cross-sections being of different sizes. 
     
     
         12 . The 3D MEMS device of  claim 9 , wherein the device feedthrough comprises aone or more bond padpads on the outer side of the SOI cap wafer, the bond pads being electrically connected to said cap feedthrough post and configured to bond with an integrated circuit chip that receives electrical signals from the 3D MEMS device. 
     
     
         13 . The 3D MEMS device according to  claim 9 , wherein both the top and the bottom cap wafers are SOI wafers. 
     
     
         14 . The 3D MEMS device of  claim 13 , wherein the cap feedthrough is a top cap feedthrough formed in the top cap wafer, and the bottom cap wafer comprises a bottom cap feedthrough aligned and electrically connected to the top cap feedthrough via the MEMS feedthrough. 
     
     
         15 . The 3D MEMS device of claim  13   7 , wherein the cap electrodes comprise top cap electrodes formed in the device layer of the top cap wafer, and bottom cap electrodes formed in the device layer of the bottom cap wafer. 
     
     
         16 . The 3D MEMS device according to  claim 1 , wherein the cap device layer is a single crystal silicon layer. 
     
     
         17 . The 3D MEMS device according to  claim 1 , wherein the cap handle layer has a thickness between 100 micrometers and 800 micrometers. 
     
     
         18 . The 3D MEMS device according to  claim 1 , wherein the hermetic cavity enclosing the MEMS structure is a first cavity and wherein the MEMS structure is a first MEMS structure, the 3D MEMS device comprising at least a second cavity enclosing at least a second MEMS structure, said first and second cavities having different internal pressures. 
     
     
         19 . The 3D MEMS device of  claim 18 , further comprising a vent extending through one of the top and bottom cap wafers, the vent defining a gas communication path between the second cavity and an exterior of the MEMS device. 
     
     
         20 . The 3D MEMS device of  claim 18 , wherein the first cavity is a hermetically sealed vacuum cavity. 
     
     
       21. A micro-electro-mechanical system (MEMS) device comprising:
 a silicon-on-insulator (SOI) MEMS wafer including an SOI MEMS structure, the SOI MEMS wafer including a MEMS device layer, a MEMS handle layer and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer and having opposed first and second sides;   a top cap wafer and a bottom cap wafer respectively bonded relative to the first side and the second side of the SOI MEMS wafer, respectively, the SOI MEMS structure being positioned in a cavity between the top cap wafer and the bottom cap wafer such that the SOI MEMS structure moves within the cavity, at least one of the top cap wafer and the bottom cap wafer being a silicon-on-insulator (SOI) cap wafer comprising a cap device layer, a conductive cap handle layer and a cap insulating layer interposed between the cap device layer and the conductive cap handle layer, and wherein the conductive cap handle layer has an outer side with outer electrical contacts, and the cap device layer includes at least one sensing electrode connected to at least one of the outer electrical contacts; and   an electrically conductive path extending through an insulated feedthrough of the conductive cap handle layer, through the cap insulating layer and through the cap device layer of the SOI cap wafer, the electrically conductive path establishing an electrical connection between at least one of the outer electrical contacts and said MEMS structure that includes at least a portion of the MEMS device layer and the conductive cap handle layer.    
     
     
       22. The MEMS device of  claim 21 , wherein said electrically conductive path comprises the insulated feedthrough with a post formed in the cap handle layer, the post being delineated by a closed-loop trench patterned through an entire thickness of the conductive cap handle layer wherein the electrically conductive pathway is insulated, said one of the outer electrical contacts being located on top of said post, and wherein said electrically conductive path comprises a pad formed in the cap device layer, the pad being delineated by a trench patterned through an entire thickness of the cap device layer, the pad being aligned along a wafer stacking axis with said post.  
     
     
       23. The MEMS device of  claim 21 , wherein the SOI MEMS wafer comprises a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer, wherein said electrically conductive path comprises a pad formed in the MEMS device layer, delineated by a trench, the pad being electrically connected to the MEMS structure, the pad formed in the MEMS device layer being aligned along the stacking axis with the pad formed in the cap device layer and wherein the SOI MEMS wafer comprises an outer frame, the MEMS structure comprising at least one proof mass suspended by springs, the at least one proof mass being patterned in both the MEMS handle and device layers, the springs being patterned in the MEMS device layer, the at least one proof mass including conductive shunts electrically connecting the MEMS device and handle layers, the electrically conductive path connecting said one of the outer electrical contacts to the MEMS structure via at least one of the springs.  
     
     
       24. The MEMS device according to  claim 21 , wherein the cap device layer comprises a plurality of cap electrodes patterned therein, the MEMS device comprising additional electrically conducting paths extending through the conductive cap handle layer and the cap device layer, at least one of said additional electrically conducting paths establishing an electrical connection between a subset of the electrical contacts and at least a portion of said plurality of cap electrodes and wherein the cap device layer comprises leads patterned therein, the leads being electrically connected to the cap electrodes, the leads extending orthogonally to the stacking axis and forming part of corresponding ones of said additional electrically conducting paths.  
     
     
       25. The MEMS device according to  claim 21 , comprising a device feedthrough extending along a stacking axis, the device feedthrough comprising the insulated feedthrough and a MEMS feedthrough aligned with one another, wherein the insulated feedthrough comprises:
 a cap feedthrough post patterned through an entire thickness of the conductive cap handle layer, the cap feedthrough post being electrically connected to one of the outer electrical contacts;   a cap feedthrough pad patterned through the entire thickness of the cap device layer; and   a conductive shunt formed through the cap insulating layer, electrically connecting the cap feedthrough post and the cap feedthrough pad;   wherein SOI MEMS wafer comprises a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer, the MEMS feedthrough comprising:   a MEMS feedthrough post patterned through an entire thickness of the MEMS handle layer;   a MEMS feedthrough pad patterned through an entire thickness of the MEMS device layer;   a conductive shunt formed through the MEMS insulating layer, electrically connecting the MEMS feedthrough post and the MEMS feedthrough pad, thereby establishing an electrical connection between said one of the outer electrical contacts on top of the cap feedthrough post and the MEMS feedthrough, through the cap feedthrough;   wherein trenches in at least one of the SOI cap wafer and the SOI MEMS wafer are unfilled;   wherein the cap feedthrough post and the MEMS feedthrough post have respective cross-sections taken orthogonally with respect to the stacking axis, said cross-sections being of different sizes;   wherein the device feedthrough comprises a bond pad on the outer side of the SOI cap wafer, the bond pad being electrically connected to said cap feedthrough post; and   wherein the cap feedthrough is a top cap feedthrough formed in the top cap wafer, and the bottom cap wafer comprises a bottom cap feedthrough aligned and electrically connected to the top cap feedthrough via the MEMS feedthrough.    
     
     
       26. The MEMS device of  claim 21 , wherein both the top and the bottom cap wafers are SOI wafers, one of the conductive cap handle layer and the cap device layer having an inner side bonded to the SOI MEMS wafer, the MEMS device being connected to an integrated circuit of an inertial measurement unit and wherein the cap electrodes comprise top cap electrodes formed in the device layer of the top cap wafer, and bottom cap electrodes formed in the device layer of the bottom cap wafer.  
     
     
       27. The MEMS device of  claim 21 , wherein the conductive silicon cap device layer is a single crystal silicon layer and wherein the conductive silicon cap handle layer has a thickness between 100 micrometers and 800 micrometers.  
     
     
       28. The MEMS device of  claim 21 , wherein the hermetic cavity enclosing the MEMS structure is a first cavity and wherein the MEMS structure is a first MEMS structure, the MEMS device comprising at least a second cavity enclosing at least a second MEMS structure, said first and second cavities having different internal pressures and further comprising a vent extending through at least one of the top and bottom cap wafers, the vent defining a gas communication path between the second cavity and an exterior of the MEMS device.  
     
     
       29. A micro-electro-mechanical system (MEMS) device comprising:
 a MEMS wafer including a MEMS structure, the MEMS wafer having opposed first and second sides;   a top cap wafer and a bottom cap wafer respectively bonded to the first side and the second side of the MEMS wafer, the top cap wafer, the bottom cap wafer and the MEMS wafer being stacked along a stacking axis to form at least one hermetic cavity enclosing the MEMS structure, at least one of the top cap wafer and the bottom cap wafer being a silicon-on-insulator (SOI) cap wafer comprising a conductive silicon cap handle layer, a conductive silicon cap device layer and a cap insulating layer interposed between the cap device layer and the cap handle layer, the SOI cap wafer having a plurality of outer electrical contacts, the cap device layer including at least one sensor electrode to sense a motion of the MEMS structure and at least one drive electrode to actuate motion of the MEMS structure; and   an electrically conductive path extending within an insulated feedthrough of the conductive silicon cap handle layer, through the cap insulating layer, and within the conductive silicon cap device layer of the SOI cap wafer, the electrically conductive path establishing an electrical connection between at least one of the plurality of the outer electrical contacts and said MEMS structure.    
     
     
       30. The MEMS device of  claim 29 , wherein said electrically conductive path comprises the feedthrough with a post formed in the cap handle layer, the post being delineated by a closed-loop trench patterned through an entire thickness of the conductive silicon cap handle layer, said outer electrical contact being located on top of said post and wherein said electrically conductive path conducts electrical signals with the post and further comprises a pad formed in the conductive silicon cap device layer, the pad being delineated by a trench patterned through an entire thickness of the conductive silicon cap device layer, the pad being aligned along a wafer stacking axis with the post.  
     
     
       31. The MEMS device of  claim 29 , wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer and wherein said electrically conductive path comprises a pad formed in the MEMS device layer, delineated by a trench, the pad being electrically connected to the MEMS structure, the pad formed in the MEMS device layer being aligned along the stacking axis with the pad formed in the cap device layer.  
     
     
       32. The MEMS device of  claim 29 , wherein the MEMS wafer comprises an outer frame, the MEMS structure comprising at least one proof mass suspended by springs, the at least one proof mass being patterned in both the MEMS handle and device layers, the springs being patterned in the MEMS device layer, the at least one proof mass including conductive shunts electrically connecting the MEMS device and handle layers, the electrically conductive path connecting said outer electrical contact to the MEMS structure via at least one of the springs.  
     
     
       33. The MEMS device of  claim 29 , wherein the conductive silicon cap device layer comprises a plurality of cap electrodes patterned therein, the MEMS device comprising additional electrically conducting paths extending through the conductive silicon cap handle layer and the conductive silicon cap device layer, at least one of said additional electrically conducting paths establishing an electrical connection between the outer electrical contact and at least a portion of said plurality of cap electrodes and wherein the conductive silicon cap device layer comprises leads patterned therein, the leads being electrically connected to the cap electrodes, the leads extending orthogonally to the stacking axis and forming part of corresponding ones of said additional electrically conducting paths.  
     
     
       34. The MEMS device according to  claim 29 , comprising a device feedthrough extends along a wafer stacking axis, the device feedthrough comprising the insulated feedthrough and a MEMS feedthrough aligned with the insulated feedthrough that comprises:
 a cap feedthrough post patterned through an entire thickness of the cap handle layer, the cap feedthrough post being electrically connected to one of the outer electrical contacts;   a cap feedthrough pad patterned through the entire thickness of the cap device layer; and   a conductive shunt formed through the cap insulating layer, electrically connecting the cap feedthrough post and the cap feedthrough pad;   wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer, the MEMS feedthrough comprising:   a MEMS feedthrough post patterned through an entire thickness of the MEMS handle layer;   a MEMS feedthrough pad patterned through an entire thickness of the MEMS device layer;   a conductive shunt formed through the MEMS insulating layer, electrically connecting the MEMS feedthrough post and the MEMS feedthrough pad, thereby establishing an electrical connection between said one of the outer electrical contacts on top of the cap feedthrough post and the MEMS feedthrough, through the cap feedthrough;   wherein trenches in at least one of the SOI cap wafer and the SOI MEMS wafer are unfilled;   wherein the cap feedthrough post and the MEMS feedthrough post have respective cross-sections taken orthogonally with respect to the stacking axis, said cross-sections being of different sizes; and   wherein the device feedthrough comprises a bond pad on the outer side of the SOI cap wafer, the bond pad being electrically connected to said cap feedthrough post.    
     
     
       35. The MEMS device of  claim 29 , wherein one of the cap handle layer and the cap device layer has an inner side bonded to the MEMS wafer, and the other one of the cap handle layer and the cap device layer has an outer side bonded to the MEMS wafer, the MEMS device being connected to an integrated circuit of an inertial measurement unit.  
     
     
       36. The MEMS device of  claim 29 , wherein the top cap wafer and the bottom cap wafer comprise SOI cap wafers and further comprising cap electrodes including top cap electrodes formed in a device layer of the top cap wafer, and bottom cap electrodes formed in a device layer of the bottom cap wafer.  
     
     
       37. The MEMS device of  claim 29 , wherein the cap device layer is a single crystal silicon layer and wherein the cap handle layer has a thickness between 100 micrometers and 800 micrometers.  
     
     
       38. The MEMS device of  claim 29 , wherein the cavity enclosing the MEMS structure is a first cavity and wherein the MEMS structure is a first MEMS structure, the MEMS device comprising at least a second cavity enclosing at least a second MEMS structure, said first and second cavities having different internal pressures and further comprising a vent extending through one of the top and bottom cap wafers, the vent defining a gas communication path between the second cavity and an exterior of the MEMS device.  
     
     
       39. A micro-electro-mechanical system (MEMS) device comprising:
 a MEMS wafer including a MEMS structure, the MEMS wafer having opposed first and second sides;   a top cap wafer and a bottom cap wafer respectively bonded relative to the first side and the second side of the MEMS wafer to form a wafer stack, at least the top cap wafer, the bottom cap wafer and the MEMS wafer being stacked to form at least one cavity wherein the MEMS structure is within the cavity, the top cap wafer and the bottom cap wafer respectively being first and second silicon-on-insulator (SOI) cap wafers, each SOI cap wafer comprising a conductive silicon cap device layer, a conductive silicon cap handle layer and a cap insulating layer interposed between the conductive silicon cap device layer and the conductive silicon cap handle layer; and   an electrically conductive path extending through an insulated feedthrough of the conductive silicon cap handle layer, through the cap insulating wafer, and through the conductive silicon cap device layer of the top SOI cap wafer and through at least a portion of the MEMS wafer to electrically contact the cap device layer of the bottom SOI cap wafer, the electrically conductive path establishing an electrical connection between a first outer electrical contact and the bottom cap device layer and a further electrically conductive path establishing an electrical connection between a second outer electrical contact and said MEMS structure.    
     
     
       40. The MEMS device of  claim 39 , wherein said insulated feedthrough comprises a post formed in the conductive silicon cap handle layer, the post being delineated by a closed-loop trench patterned through an entire thickness of the conductive silicon cap handle layer, said outer electrical contact being located on top of said post and wherein said electrically conductive path includes a single crystal silicon material and a polysilicon material and further comprises a pad formed in the conductive silicon cap device layer, the pad being delineated by a trench patterned through an entire thickness of the conductive silicon cap device layer, the pad being aligned along a wafer stacking axis with said post.  
     
     
       41. The MEMS device of  claim 39 , wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer.  
     
     
       42. The MEMS device of  claim 41 , wherein said electrically conductive path comprises a pad formed in the MEMS device layer, delineated by a trench, the pad being electrically connected to the MEMS structure, the pad formed in the MEMS device layer being aligned along the stacking axis with the pad formed in the cap device layer.  
     
     
       43. The MEMS device of  claim 39 , wherein the MEMS wafer comprises an outer frame, the MEMS structure comprising at least one proof mass suspended by a spring and wherein the at least one proof mass being patterned in MEMS handle and device layers of an SOI MEMS wafer, the spring being patterned in the MEMS device layer, the at least one proof mass including conductive shunts electrically connecting the MEMS device and handle layers, the electrically conductive path connecting said outer electrical contact to the MEMS structure via at least one of the springs.  
     
     
       44. The MEMS device of  claim 39 , wherein each cap device layer comprises a plurality of cap electrodes patterned therein, the MEMS device comprising additional electrically conducting paths extending through the cap handle layer and the cap device layer, at least one of said additional electrically conducting paths establishing an electrical connection between the outer electrical contact and at least a portion of a plurality of cap electrodes and wherein the cap device layer comprises leads patterned therein, the leads being electrically connected to the cap electrodes, the leads extending orthogonally to a stacking axis and forming part of corresponding ones of said additional electrically conducting paths.  
     
     
       45. The MEMS device according to  claim 39 , comprising a device feedthrough extends along a stacking axis, the device feedthrough comprising the insulated feedthrough and a MEMS feedthrough aligned with the insulated feedthrough that comprises:
 a cap feedthrough post patterned through an entire thickness of the cap handle layer, the cap feedthrough post being electrically connected to the outer electrical contact;   a cap feedthrough pad patterned through the entire thickness of the cap device layer; and   a conductive shunt formed through the cap insulating layer, electrically connecting the cap feedthrough post and the cap feedthrough pad;   wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer, the MEMS feedthrough comprising:   a MEMS feedthrough post patterned through an entire thickness of the MEMS handle layer;   a MEMS feedthrough pad patterned through an entire thickness of the MEMS device layer;   a conductive shunt formed through the MEMS insulating layer, electrically connecting the MEMS feedthrough post and the MEMS feedthrough pad, thereby establishing an electrical connection between said outer electrical contact on top of the cap feedthrough post and the MEMS feedthrough, through the cap feedthrough;   wherein trenches in at least one of the SOI cap wafer and the SOI MEMS wafer are unfilled;   wherein the cap feedthrough post and the MEMS feedthrough post have respective cross-sections taken orthogonally with respect to the stacking axis, said cross-sections being of different sizes and   wherein the device feedthrough comprises a bond pad on the outer side of the SOI cap wafer, the bond pad being electrically connected to said cap feedthrough post.    
     
     
       46. The MEMS device of  claim 39 , wherein one of the cap handle layer and the cap device layer has an inner side bonded to the MEMS wafer, and the other one of the cap handle layer and the cap device layer has an outer side bonded to the MEMS wafer, the MEMS device being connected to an integrated circuit of an inertial measurement unit.  
     
     
       47. The MEMS device of  claim 46 , wherein the cap feedthrough is a top cap feedthrough formed in the top cap wafer, and the bottom cap wafer comprises a bottom cap feedthrough aligned and electrically connected to the top cap feedthrough via the MEMS feedthrough and wherein the cap electrodes comprise top cap electrodes formed in the device layer of the top cap wafer, and bottom cap electrodes formed in the device layer of the bottom cap wafer.  
     
     
       48. The MEMS device of  claim 39 , wherein the conductive silicon cap device layer is a single crystal silicon layer and wherein the conductive silicon cap handle layer has a thickness between 100 micrometers and 800 micrometers.  
     
     
       49. The MEMS device of  claim 39 , wherein the cavity for the MEMS structure is a first hermetically sealed cavity and wherein the MEMS structure is a first MEMS structure, the MEMS device comprising at least a second cavity enclosing at least a second MEMS structure, said first and second cavities having different internal pressures and further comprising a vent extending through one of the top and bottom cap wafers, the vent defining a gas communication path between the second cavity and an exterior of the MEMS device.  
     
     
       50. A micro-electro-mechanical system (MEMS) device comprising:
 a MEMS wafer including a MEMS structure, the MEMS wafer having opposed first and second sides;   a top cap wafer and a bottom cap wafer respectively bonded on the first side and the second side of the MEMS wafer, respectively, the top cap wafer, the bottom cap wafer and the MEMS wafer being stacked along a stacking axis to form at least one hermetic cavity that houses the MEMS structure, at least one of the top cap wafer and the bottom cap wafer being a silicon-on- insulator (SOI) cap wafer comprising a conductive silicon cap handle layer, a conductive silicon cap device layer and a cap insulating layer interposed between the conductive silicon cap device layer and the conductive silicon cap handle layer, the SOI cap wafer having a plurality of outer electrical contacts, the conductive silicon cap device layer including at least one sensor electrode to sense a motion of the MEMS structure and at least one drive electrode to actuate motion of the MEMS structure; and   an electrically conductive path extending within an insulated feedthrough of the conductive silicon cap handle layer, through the cap insulating layer, and within the conductive silicon cap device layer of the SOI cap wafer, the insulated feedthrough defined by a trench extending through an entire thickness of the conductive silicon cap handle layer that provides an electrical connection between at least one of the plurality of the outer electrical contacts and said MEMS structure.    
     
     
       51. The MEMS device of  claim 50 , wherein said insulated feedthrough comprises a post formed in the conductive silicon cap handle layer, the post being delineated by the trench formed as a closed-loop trench patterned through an entire thickness of the conductive silicon cap handle layer, said outer electrical contact being located on top of said post and wherein said electrically conductive path comprises a pad formed in the conductive silicon cap device layer, the pad being aligned along a wafer stacking axis with the post.  
     
     
       52. The MEMS device of  claim 50 , wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer.  
     
     
       53. The MEMS device of  claim 50 , wherein the MEMS wafer comprises a frame, the MEMS structure comprising at least one proof mass suspended one or more springs, the at least one proof mass being patterned in both the MEMS handle and device layers, the one or more springs being patterned in the MEMS device layer, the at least one proof mass including conductive shunts electrically connecting the MEMS device and handle layers, the electrically conductive path connecting said outer electrical contact to the MEMS structure via the at least one spring.  
     
     
       54. The MEMS device of  claim 50 , wherein the cap device layer comprises a plurality of cap electrodes patterned therein, the MEMS device comprising additional electrically conducting paths extending through the conductive silicon cap handle layer and the conductive silicon cap device layer, at least one of said additional electrically conducting paths establishing an electrical connection between the outer electrical contact and at least a portion of said plurality of cap electrodes and wherein the conductive silicon cap device layer comprises leads patterned therein, the leads being electrically connected to the cap electrodes, the leads extending orthogonally to the stacking axis and forming part of corresponding ones of said additional electrically conducting paths.  
     
     
       55. The MEMS device according to  claim 50 , comprising a device feedthrough extending along a wafer stacking axis, the device feedthrough comprising the insulated feedthrough and a MEMS feedthrough aligned with one another, wherein the insulated feedthrough comprises:
 a cap feedthrough post patterned through an entire thickness of the cap handle layer, the cap feedthrough post being electrically connected to one of the outer electrical contacts;   a cap feedthrough pad patterned through the entire thickness of the cap device layer; and   a conductive shunt formed through the cap insulating layer, electrically connecting the cap feedthrough post and the cap feedthrough pad;   wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer, the MEMS feedthrough comprising:   a MEMS feedthrough post patterned through an entire thickness of the MEMS handle layer;   a MEMS feedthrough pad patterned through an entire thickness of the MEMS device layer;   a conductive shunt formed through the MEMS insulating layer, electrically connecting the MEMS feedthrough post and the MEMS feedthrough pad, thereby establishing an electrical connection between said one of the outer electrical contacts on top of the cap feedthrough post and the MEMS feedthrough, through the cap feedthrough;   wherein trenches in at least one of the SOI cap wafer and the SOI MEMS wafer are unfilled;   wherein the cap feedthrough post and the MEMS feedthrough post have respective cross-sections taken orthogonally with respect to the stacking axis, said cross-sections being of different sizes and   wherein the device feedthrough comprises a bond pad on the outer side of the SOI cap wafer, the bond pad being electrically connected to said cap feedthrough post.    
     
     
       56. The MEMS device of  claim 50 , wherein one of the cap handle layer and the cap device layer has an inner side bonded to the MEMS wafer, and the other one of the cap handle layer and the cap device layer has an outer side bonded to the MEMS wafer, the MEMS device being connected to an integrated circuit of an inertial measurement unit.  
     
     
       57. The MEMS device of  claim 50 , wherein the top cap wafer and the bottom cap wafer comprise SOI cap wafers and further comprising cap electrodes including top cap electrodes formed in a device layer of the top cap wafer, and bottom cap electrodes formed in a device layer of the bottom cap wafer.  
     
     
       58. The MEMS device of  claim 50 , wherein the conductive silicon cap device layer is a single crystal silicon layer and wherein the conductive silicon cap handle layer has a thickness between 100 micrometers and 800 micrometers.  
     
     
       59. The MEMS device of  claim 50 , wherein the cavity enclosing the MEMS structure is a first cavity and wherein the MEMS structure is a first MEMS structure, the MEMS device comprising at least a second cavity enclosing at least a second MEMS structure, said first and second cavities having different internal pressures and further comprising a vent extending through one of the top and bottom cap wafers, the vent defining a gas communication path between the second cavity and an exterior of the MEMS device.  
     
     
       60. A micro-electro-mechanical system (MEMS) device comprising:
 a MEMS wafer including a MEMS structure, the MEMS wafer having opposed first and second sides;   a top cap wafer and a bottom cap wafer respectively bonded relative to the first side and the second side, respectively, of the MEMS wafer to form a wafer stack, at least the top cap wafer, the bottom cap wafer and the MEMS wafer being stacked to form at least one cavity wherein the MEMS structure is within the cavity, the top cap wafer and the bottom cap wafer, respectively, being a top silicon-on-insulator (SOI) cap wafer and a bottom SOI cap wafer, the top SOI cap wafer and the bottom SOI cap wafer each comprising a conductive silicon cap device layer, a conductive silicon cap handle layer and a cap insulating layer interposed between the conductive silicon cap device layer and the conductive silicon cap handle layer; and   a first insulated electrically conductive path extending through an insulated feedthrough of the conductive silicon cap handle layer, through the cap insulating wafer, and through the conductive silicon cap device layer of the top SOI cap wafer and through at least a portion of the MEMS wafer to electrically contact the conductive silicon cap device layer of the bottom SOI cap wafer, the electrically conductive path establishing an electrical connection between a first outer electrical contact and the bottom cap device layer and a second electrically conductive path establishing an electrical connection between a second outer electrical contact and said MEMS structure.    
     
     
       61. The MEMS device of  claim 60 , wherein said insulated feedthrough comprises a post formed in the cap handle layer, the post being delineated by a closed-loop trench patterned through an entire thickness of the cap handle layer, said outer electrical contact being located on top of said post and wherein said electrically conductive path comprises a pad formed in the cap device layer, the pad being delineated by a trench patterned through an entire thickness of the cap device layer, the pad being aligned along a wafer stacking axis with said post.  
     
     
       62. The MEMS device of  claim 60 , wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer.  
     
     
       63. The MEMS device of  claim 60 , wherein said electrically conductive path comprises a pad formed in the MEMS device layer, delineated by a trench, the pad being electrically connected to the MEMS structure, the pad formed in the MEMS device layer being aligned along the stacking axis with the pad formed in the conductive silicon cap device layer.  
     
     
       64. The MEMS device of  claim 60 , wherein the MEMS wafer comprises an outer frame, the MEMS structure comprising at least one proof mass suspended by a spring and wherein the at least one proof mass being patterned in MEMS handle and device layers of an SOI MEMS wafer, the spring being patterned in the MEMS device layer, the at least one proof mass including conductive shunts electrically connecting the MEMS device and handle layers, the electrically conductive path connecting said outer electrical contact to the MEMS structure via at least one of the springs.  
     
     
       65. The MEMS device of  claim 60 , wherein each conductive silicon cap device layer comprises a plurality of cap electrodes patterned therein, the MEMS device comprising additional electrically conducting paths extending through the conductive silicon cap handle layer and the conductive silicon cap device layer, at least one of said additional electrically conducting paths establishing an electrical connection between the outer electrical contact and at least a portion of a plurality of cap electrodes and wherein the conductive silicon cap device layer comprises leads patterned therein, the leads being electrically connected to the cap electrodes, the leads extending orthogonally to a stacking axis and forming part of corresponding ones of said additional electrically conducting paths.  
     
     
       66. The MEMS device according to  claim 60 , comprising a device feedthrough extending along a stacking axis, the device feedthrough comprising the insulated feedthrough and a MEMS feedthrough aligned with one another, wherein the insulated feedthrough comprises:
 a cap feedthrough post patterned through an entire thickness of the cap handle layer, the cap feedthrough post being electrically connected to the outer electrical contact;   a cap feedthrough pad patterned through the entire thickness of the cap device layer; and   a conductive shunt formed through the cap insulating layer, electrically connecting the cap feedthrough post and the cap feedthrough pad;   wherein the MEMS wafer is an SOI MEMS wafer comprising a MEMS device layer bonded to the top cap wafer, a MEMS handle layer bonded to the bottom cap wafer, and a MEMS insulating layer interposed between the MEMS device layer and the MEMS handle layer, the MEMS feedthrough comprising:   a MEMS feedthrough post patterned through an entire thickness of the MEMS handle layer;   a MEMS feedthrough pad patterned through an entire thickness of the MEMS device layer;   a conductive shunt formed through the MEMS insulating layer, electrically connecting the MEMS feedthrough post and the MEMS feedthrough pad, thereby establishing an electrical connection between said outer electrical contact on top of the cap feedthrough post and the MEMS feedthrough, through the cap feedthrough;   wherein trenches in at least one of the SOI cap wafer and the SOI MEMS wafer are unfilled;   wherein the cap feedthrough post and the MEMS feedthrough post have respective cross-sections taken orthogonally with respect to the stacking axis, said cross-sections being of different sizes; and   wherein the device feedthrough comprises a bond pad on the outer side of the SOI cap wafer, the bond pad being electrically connected to said cap feedthrough post.   
     
     
       67. The MEMS device of  claim 60 , wherein one of the conductive silicon cap handle layer and the conductive silicon cap device layer has an inner side bonded to the MEMS wafer, and the other one of the conductive silicon cap handle layers and the conductive silicon cap device layer has an outer side bonded to the MEMS wafer, the MEMS device being connected to an integrated circuit of an inertial measurement unit.  
     
     
       68. The MEMS device of  claim 66 , wherein the insulated feedthrough is a top cap feedthrough formed in the top cap wafer, and the bottom cap wafer comprises a bottom cap feedthrough aligned and electrically connected to the top cap feedthrough via the MEMS feedthrough and wherein the cap electrodes comprise top cap electrodes formed in the conductive silicon device layer of the top cap wafer, and bottom cap electrodes formed in the conductive silicon device layer of the bottom cap wafer.  
     
     
       69. The MEMS device of  claim 60 , wherein the conductive silicon cap device layer is a single crystal silicon layer and wherein the conductive silicon cap handle layer has a thickness between 100 micrometers and 800 micrometers.  
     
     
       70. The MEMS device of  claim 60 , wherein the cavity for the MEMS structure is a first hermetically sealed cavity and wherein the MEMS structure is a first MEMS structure, the MEMS device comprising at least a second cavity enclosing at least a second MEMS structure, said first and second cavities having different internal pressures and further comprising a vent extending through one of the top and bottom cap wafers, the vent defining a gas communication path between the second cavity and an exterior of the MEMS device.