MEMS PRESSURE SENSOR

• US 20170030788A1
• Filed: 01/15/2015
• Published: 02/02/2017
• Est. Priority Date: 04/10/2014
• Status: Abandoned Application

• Current Assignee: Motion Engine inc
• Original Assignee: Motion Engine inc
• Inventors: Boysel, Robert Mark, Ross, Louis
• Application Number:
  US15/302,731
• Publication Number:
  US 20170030788A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0264 Pressure sensors
• CPC Class Codes: B81B 2203/0127 Diaphragms, i.e. structures separating two media that can control the passage from one medium to another; Membranes, i.e. diaphragms with filtering function
• CPC Class Codes: B81B 2207/012 the micromechanical device and the control or processing electronics being separate parts in the same package
• CPC Class Codes: B81B 2207/015 the micromechanical device and the control or processing electronics being integrated on the same substrate
• CPC Class Codes: B81B 2207/07 Interconnects
• CPC Class Codes: B81B 2207/095 through the lid
• CPC Class Codes: B81B 7/007 Interconnections between the MEMS and external electrical signals
• CPC Class Codes: B81C 1/00182 Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer
• CPC Class Codes: B81C 1/00301 Connecting electric signal lines from the MEMS device with external electrical signal lines, e.g. through vias
• CPC Class Codes: B81C 2203/0109 Bonding an individual cap on the substrate
• CPC Class Codes: B81C 2203/0792 Forming interconnections between the electronic processing unit and the micromechanical structure
• CPC Class Codes: G01L 13/025 using diaphragms
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm

Abstract

The present invention provides a MEMS pressure sensor and a manufacturing method. The pressure is formed by a top cap wafer, a MEMS wafer and a bottom cap wafer. The MEMS wafer comprises a frame and a membrane, the frame defining a cavity. The membrane is suspended by the frame over the cavity. The bottom cap wafer closes the cavity. The top cap wafer has a recess defining with the membrane a capacitance gap. The top cap wafer comprises a top cap electrode located over the membrane and forming, together with the membrane, a capacitor to detect a deflection of the membrane. Electrical contacts on the top cap wafer are connected to the top cap electrode. A vent is extends from outside of the sensor into the cavity or the capacitance gap. The pressure sensor can include two cavities and two capacitance gaps, to form a differential pressure sensor.

Claims

1. A MEMS pressure sensor comprising:

a MEMS wafer being electrically conductive and having first and second opposite sides the MEMS wafer having formed therein a frame and a membrane, the frame defining at least one cavity, the membrane being suspended by the frame over said at least one cavity on the first side of the MEMS wafer;

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

at least a first electrical contact and a second electrical contact are provided on the top cap wafer, the first electrical contact being connected to one of said at least one top cap electrode and the second electrical contact being connected to the membrane by way of an insulated conducting pathway extending from the membrane and through the top cap wafer;

a bottom cap wafer having inner and outer sides, the bottom cap wafer being bonded on its inner side to the second side of the MEMS wafer and enclosing the at least one cavity; and

a vent provided in at least one of the top cap, bottom cap and MEMS wafer, the vent extending from outside of the MEMS pressure sensor into one of said at least one cavity and said at least one capacitance gap.

2. The MEMS pressure sensor according to claim 1, wherein the at least one top cap electrode is delimited by corresponding insulated closed-loop channel(s) patterned in the top cap wafer and extending from the inner to the outer side of the top cap wafer, electrically insulating the at least one top cap electrode from the remainder of the top cap wafer.

3. The MEMS pressure sensor according to claim 1, wherein the MEMS wafer 45 a SOI wafer with a device layer, a handle layer and an insulating layer, the insulating layer separating the device layer from the handle layer, the membrane being formed in the device layer.

4. The MEMS pressure sensor according to claim 3, comprising at least one SOI conducting shunt extending in the insulating layer and electrically connecting the device and handle layers, one of said at least one SOI conducting shunt forming part of the insulated conducting pathway connecting the membrane to the second electrical contact of the top cap wafer.

5. The MEMS pressure sensor according to claim 1, wherein the bottom cap wafer is electrically conductive.

6. The MEMS pressure sensor according to claim 1, comprising at least one additional electrical contact provided on the outer side of the bottom cap wafer, connected to one of said electrical contacts on the top cap wafer via an insulated feedthrough extending successively through the top cap wafer, through the MEMS wafer and through the bottom cap wafer.

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

8. The MEMS pressure sensor according to claim 1, wherein the membrane comprises at least one ring of conductive shunt material.

9. The MEMS pressure sensor according to claim 3, wherein the membrane has an outer periphery delimited by a trench etched in the device layer.

10. The MEMS pressure sensor according to claim 9, wherein the outer periphery of the membrane extends beyond the at least one cavity.

11. The MEMS pressure sensor according to claim 1, wherein said MEMS pressure sensor is a differential pressure sensor, and wherein:

in the MEMS 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;

in the top cap wafer, the at least one recess comprises a first recess and a second recess and the at least one capacitance gap comprises a first capacitance gap and a second capacitance gap;

in the top cap wafer, the least one top cap electrode comprises a first electrode and a second electrode, respectively forming, together with the membrane, a first capacitor and a second capacitor; and

wherein

the top 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.

12. The MEMS pressure sensor according to claim 11, wherein the first and the second capacitance gaps and one of the first and second cavities are hermitically sealed under vacuum, the vent extending into the other one of the first and second cavities.

13. A method for manufacturing a MEMS pressure sensor the method comprising:

providing top and bottom cap wafers having respective inner and outer sides, at least the top cap wafer being electrically conductive;

forming in the top cap wafer at least one recess and at least one top cap electrode;

providing a MEMS wafer being electrically conductive and having first and second sides, and patterning a periphery of a membrane on the first side;

bonding the inner side of the top cap wafer to the first side of the MEMS wafer with the at least one recess facing the membrane to form at least one capacitance gap, said at least one top cap electrode being located over the membrane and forming, together with the membrane, at least one capacitor across to detect a deflection of the membrane;

forming at least one cavity on the second side of the MEMS wafer, the at least one cavity delimiting a frame and a bottom surface of the membrane;

forming a vent in at least one of the top cap, bottom cap and MEMS wafer

bonding the inner side of the bottom cap wafer to the second side of the MEMS wafer and enclosing said at least one cavity, the vent extending into one of said at least one cavity and said at least one capacitance gap; and

removing a portion of the outer side of the top cap wafer to isolate the at least one top cap electrode from the remainder of the top cap wafer.

14. The method for manufacturing a MEMS pressure sensor according to claim 13, comprising a step of forming at least first and second electrical contacts on the top cap wafer, the first electrical contact being connected to one of said at least one top cap electrode and the second electrical contact being electrical connected to the membrane via the top cap wafer.

16. The method for manufacturing a MEMS pressure sensor according to 13, wherein the MEMS wafer is a SOI wafer with an insulating layer separating a device layer from a handle layer, and wherein the periphery of the membrane is patterned in the device layer.

17. The method for manufacturing a MEMS pressure sensor according to claim 16, further comprising creating at least one SOI conducting shunt extending in the insulating layer and electrically connecting the device and handle layers, one of said at least one SOI conducting shunt electrically connecting the membrane to the second electrical contact of the top cap wafer.

18. The method for manufacturing a MEMS pressure sensor according to claim 13, wherein the bottom cap wafer is electrically conductive and the method further comprises forming at least one additional electrical contact provided on the outer side of the bottom cap wafer.

19. The method for manufacturing a MEMS pressure sensor according to claim 13, wherein at least one of said at least one cavity and said at least one capacitance gap is hermetically sealed under vacuum.

20. The method for manufacturing a MEMS pressure sensor according to claim 13, further comprising etching at least one ring on the first side of the MEMS wafer and filling the trench with conductive shunt material, to surround at least a portion of the membrane.

21. The method for manufacturing a MEMS pressure sensor according to claim 13, wherein bonding of the top cap wafer or the bottom cap wafer is made with a conductive bond.

15. The method for manufacturing a MEMS pressure sensor according to claim, wherein forming in the top cap wafer at least one recess and at least one top cap electrode comprises etching closed-loop trenches and filing or lining said trenches with an insulated material to electrically insulate the at least one top cap electrode from the remainder of the top cap wafer.