MEMS pressure sensor

1 . A MEMS pressure sensor comprising:

a MEMS electrically conductive silicon wafer having first and second opposite sides, the MEMS electrically conductive silicon wafer having formed therein a frame and a membrane sealed to the frame, the frame defining at least one cavity, the membrane being suspended by the frame relative to said at least one cavity on the second side of the MEMS electrically conductive silicon wafer, the membrane being deflected in response to a change in fluid pressure in the at least one cavity;

an electrically conductive silicon cap wafer having inner and outer sides, the electrically conductive silicon cap wafer being fusion bonded on the inner side to the first side of the MEMS electrically conductive silicon wafer, the inner side of the electrically conductive silicon cap wafer having at least one recess defining, with the membrane, at least one capacitance gap, the electrically conductive silicon cap wafer having formed therein at least one cap electrode located over the membrane and forming, together with the membrane, at least one capacitor to detect a deflection of the membrane and wherein the at least one cap electrode is delimited by a corresponding insulated closed-loop channel patterned in the electrically conductive silicon cap wafer;

at least a first electrical contact and a second electrical contact on the electrically conductive cap wafer, the first electrical contact being connected to the at least one cap electrode and the second electrical contact being connected to the membrane by way of an insulated conducting pathway extending from the MEMS electrically conductive silicon wafer that includes a deflecting portion of the membrane and through the electrically conductive silicon cap wafer;

a vent provided in the electrically conductive silicon cap wafer in fluid communication with the capacitance gap or wherein the vent is in fluid communication with the at least one cavity on the second side of the MEMS electrically conductive silicon wafer.

2 . The MEMS pressure sensor according to claim 1 , further comprising a second cap silicon wafer having inner and outer sides, the second cap silicon wafer being bonded on its inner side to the second side of the MEMS electrically conductive silicon wafer and enclosing the at least one cavity; at least one conducting shunt extending through an insulating layer in the frame, the at least one conducting shunt forming part of the insulated conducting pathway connecting the membrane to the second electrical contact of the electrically conductive silicon cap wafer.

3 . The MEMS pressure sensor according to claim 2 , wherein the second cap silicon wafer is electrically conductive.

4 . The MEMS pressure sensor according to claim 3 , comprising at least one additional electrical contact provided on the outer side of the second cap silicon wafer, connected to one of said first and second electrical contacts on the electrically conductive silicon cap wafer via an insulated feedthrough extending successively through the electrically conductive silicon cap wafer, through the MEMS electrically conductive silicon wafer and through second cap semiconductor wafer.

5 . The MEMS pressure sensor according to claim 1 , wherein said at least one cavity and said at least one capacitance gap is hermetically sealed under vacuum.

6 . The MEMS pressure sensor according to claim 1 , wherein the MEMS electrically conductive silicon wafer comprises a silicon-on-insulator (SOI) wafer including a device layer, and insulating layer and a handle layer, the device layer including the membrane having at least one ring of conductive shunt material.

7 . The MEMS pressure sensor according to claim 6 , wherein the membrane has an outer periphery delimited by a trench etched in the device layer.

8 . The MEMS pressure sensor according to claim 7 , wherein the outer periphery of the membrane extends beyond the at least one cavity.

9 . The MEMS pressure sensor according to claim 6 , wherein said MEMS pressure sensor is a differential pressure sensor, and wherein:

in the MEMS SOI wafer, the frame comprises an outer lateral section and an inner section, and said at least one cavity comprises a first cavity and a second cavity, the membrane being suspended over the first and the second cavities by the outer lateral section and by the inner section of the frame;

wherein the electrically conductive silicon cap wafer includes the at least one recess comprising a first recess and a second recess and the at least one capacitance gap comprises a first capacitance gap and a second capacitance gap; and

wherein the electrically conductive silicon cap wafer having the least one cap electrode that comprises a first electrode and a second electrode, respectively forming, together with the membrane, a first capacitor and a second capacitor; and wherein the electrically conductive silicon cap wafer comprises a third electrical contact, the first electrical contact being connected to the first electrode and the third electrical contact being connected to the second electrode.

10 . The MEMS pressure sensor according to claim 9 , wherein the first and the second capacitance gaps and one of the first and second cavities are hermetically sealed under vacuum, the vent extending into the other one of the first and second cavities.

11 . The MEMS pressure sensor of claim 6 , wherein the electrically conductive silicon cap wafer is conductively bonded to the MEMS SOI wafer.

12 . The MEMS pressure sensor of claim 1 , wherein the membrane is formed of silicon material.

13 . The MEMS pressure sensor of claim 1 further comprising an inertial sensor.

14 . The MEMS pressure sensor of claim 13 wherein the inertial sensor comprises an accelerometer.

15 . The MEMS pressure sensor of claim 1 wherein the electrically conductive silicon cap wafer further comprises an insulating layer.

16 . The MEMS pressure sensor of claim 1 wherein membrane has a change in capacitance in a range of 0.1-1 pF.

17 . The MEMS pressure sensor of claim 1 wherein the MEMS pressure sensor comprises a pressure sensor chip bonded to a circuit board and connected to a CMOS integrated circuit.

18 . A MEMS pressure sensor comprising:

a MEMS electrically conductive silicon wafer having first and second opposite sides, the MEMS electrically conductive silicon wafer having formed therein a frame and a membrane that separates at least one cavity from a recess with a hermetic seal, the membrane being deflectable in response to a change in fluid pressure on at least one of a first side and a second side of the membrane;

an electrically conductive silicon cap wafer having inner and outer sides, the electrically conductive silicon cap wafer being fusion bonded on the inner side to the first side of the MEMS electrically conductive silicon wafer, the inner side of the electrically conductive silicon cap wafer having the recess defining, with the membrane, at least one capacitance gap, the electrically conductive silicon cap wafer having formed therein at least one cap electrode located relative to the membrane and forming, together with the membrane, at least one capacitor to detect a deflection of the membrane and wherein the at least one cap electrode is defined by an insulated region patterned in the electrically conductive silicon cap wafer;

at least a first electrical contact and a second electrical contact on or over the electrically conductive cap wafer, the first electrical contact being connected to the at least one cap electrode and the second electrical contact being connected to the membrane with an insulated conducting pathway extending through the MEMS conductive silicon wafer and that includes a deflecting portion of the membrane and through a portion of the electrically conductive silicon cap wafer that is electrically insulated from the at least one cap electrode;

a vent in fluid communication with the capacitance gap on the first side of the membrane or in fluid communication with the at least one cavity on the second side of the membrane.

19 . The MEMS pressure sensor of claim 18 wherein the electrically conductive silicon cap wafer further comprises an insulating layer.

20 . The MEMS pressure sensor of claim 18 , further comprising a second cap silicon wafer having inner side and an outer side, the second cap silicon wafer being bonded on the inner side to the second side of the MEMS electrically conductive silicon wafer and enclosing the at least one cavity; at least one conducting shunt extending through an insulating layer in the frame, the at least one conducting shunt forming of the insulated conducting pathway connecting the membrane to the second electrical contact of the electrically conductive silicon cap wafer.

21 . The MEMS pressure sensor of claim 18 , further comprising a second cap silicon wafer that is electrically conductive.

22 . The MEMS pressure sensor of claim 18 , wherein the MEMS electrically conductive silicon wafer comprises a silicon-on-insulator (SOI) wafer including a device layer, and insulating layer and a handle layer.

23 . The MEMS pressure sensor of claim 22 , wherein the membrane has an outer periphery delimited by a trench etched in the device layer.

24 . A method of measuring pressure comprising:

measuring pressure with a MEMS pressure sensor comprising:

a MEMS electrically conductive wafer having first and second opposite sides, the MEMS electrically conductive wafer having a frame and a pressure sensor membrane, the frame defining at least one cavity, the pressure sensor membrane suspended by the frame to define a portion of said at least one cavity on the first side of the MEMS electrically conductive wafer;

an electrically conductive cap wafer having an inner side and an outer side, the electrically conductive cap wafer being bonded on the inner side to the first side of the MEMS electrically conductive wafer, the inner side of the electrically conductive cap wafer having at least one recess defining, with the pressure sensor membrane, at least one capacitance gap, the electrically conductive cap wafer having formed therein at least one cap electrode located relative to the pressure sensor membrane and forming, together with the pressure sensor membrane, at least one capacitor to detect a deflection of the pressure sensor membrane;

at least a first electrical contact and a second electrical contact positioned on or over the electrically conductive cap wafer, the first electrical contact being connected to said at least one cap electrode and the second electrical contact being connected to the pressure sensor membrane by an insulated conducting pathway extending from the pressure sensor membrane and through the electrically conductive cap wafer; and

a vent extending from outside of the MEMS pressure sensor into one of said at least one cavity and said at least one capacitance gap; and

processing pressure sensor signals generated by the MEMS pressure sensor with processing circuitry connected to the electrical contacts.

25 . The method of claim 24 , wherein the at least one cap electrode is delimited by corresponding insulated closed-loop channel patterned in the electrically conductive cap wafer and extending from the inner to the outer side of the electrically conductive cap wafer, electrically insulating the at least one cap electrode from the remainder of the electrically conductive cap wafer.

26 . The method of claim 24 , wherein the MEMS electrically conductive wafer comprises a MEMS SOI wafer having a device layer, a handle layer, and an insulating layer, the insulating layer separating the device layer from the handle layer.

27 . The method of claim 26 , further comprising measuring pressure sensor signals wherein the pressure sensor is hermetically sealed under vacuum in at least one of said at least one cavity and said at least one capacitance gap wherein the pressure sensor membrane has an outer periphery delimited by a trench etched in the device layer.

28 . The method of claim 24 , comprising conducting signals with at least one additional electrical contact provided on an outer side of a second cap semiconductor wafer and connected to one of said first and second electrical contacts on the electrically conductive cap wafer via an insulated feedthrough extending successively through the electrically conductive cap wafer, through the MEMS SOI wafer and through the second cap semiconductor wafer.

29 . The method of claim 24 further comprising processing pressure sensor signals with the processing circuit that comprises an integrated circuit connected to the first electrical contact and the second electrical contact.

30 . The method of claim 24 wherein the MEMS pressure sensor comprises a first pressure sensor and a second pressure sensor and further comprising processing pressure sensor signals from the first pressure sensor and the second pressure sensor, the second pressure sensor having a vent.

31 . The method of claim 24 further comprising processing pressure sensor signals from the MEMS pressure sensor and processing motion sensor signals from a MEMS motion sensor with the processing circuitry wherein the MEMS pressure sensor and the MEMS motion sensor are mounted on a printed circuit board.