MEMS STRUCTURE FOR FLOW SENSOR

• US 20090158838A1
• Filed: 12/19/2007
• Published: 06/25/2009
• Est. Priority Date: 12/19/2007
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Speldrich, Jamie W.
• Granted Patent: US 7,603,898 B2
• Time in Patent Office: Days
• US Class Current: 73/272.R
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 15/006 characterised by the use of a particular material, e.g. anti-corrosive material G01F15/14 takes precedence

Abstract

A MEMS based flow sensor is disclosed which generally incorporate isolation between a sensing structure and the sensed media. An internal flow channel can be configured by attaching a backing structure with flow openings to the back of the sensing structure. The sensing structure can be composed of a insulating layer with heating element and a dual sensing element which comprises of resistive thin films positioned in a Wheatstone bridge configuration over a backside cavity. The dual sensing element and its associated wirebonds can be isolated from the sensing media by directing the fluid through the internal flow channel. The completed sensing structure can be over packaged with standard processes such as epoxies and seals.

Claims

1. A MEMS flow sensor, comprising:

a backing structure having two openings for fluid flow formed there through;

a sensing structure including an electrically insulating topside layer on a substrate with backside cavity including a heater element and a plurality of dual sensing elements disposed on said electrically insulating topside layer, said topside layer further comprising of a plurality of resistive thin films wherein said plurality of dual sensing elements measure a flow of fluid and wherein two of said plurality of dual sensing elements can be located on both sides of said heating element to indicate flow of fluid direction;

a plurality of layers of silicon nitride deposited over said resistive thin films to provide protection from media and the environment; and

a flow channel formed by bonding said sensing structure to said backing structure wherein said flow of fluid is directed through said flow channel in order to isolate a plurality of wirebonds and said plurality of dual sensing elements from said flow channel.

2. The flow sensor of claim 1 further comprising:

a plurality of electrical conductive leads extending from said sensing structure from said heater element and said plurality of dual sensing elements to said plurality of wirebonds.

3. The flow sensor of claim 2, wherein said plurality of electrical conductive leads and said plurality of wirebonds provide an electrical connection for said heater element and said plurality of dual sensing elements.

4. The flow sensor of claim 2 wherein said plurality of resistive thin films comprise metal selected from nickel and platinum.

5. The flow sensor of claim 2 wherein said plurality of resistive thin films are connected in a Wheatstone bridge configuration.

6. The flow sensor of claim 1 wherein said sensing structure is overpackaged utilizing standard processes comprising epoxies and seals.

7. The sensor of claim 1 wherein said backing structure, said sensing structure and said flow channel are arranged together to comprise a complete assembly.

8. The MEMS flow sensor of claim 1 wherein said backing structure is selected from the group comprising etched silicon, a fabricated glass, and a molded plastic.

20. The MEMS flow sensor of claim 1 wherein said backing structure is selected from a group comprising etched silicon, a fabricated glass, and a molded plastic.

9. A MEMS flow sensor, comprising:

a backing structure having two openings for fluid flow formed there through and a channel disposed between the openings;

a sensing structure including a heater element and a plurality of dual sensing elements said sensing structure further comprising of a plurality of resistive thin films wherein said plurality of dual sensing elements measures a flow of fluid and wherein two of said plurality of dual sensing elements can be located on both sides of said heating element to indicate flow of fluid direction;

a plurality of layers of silicon nitride deposited over said resistive thin films to provide protection from media and the environment;

a plurality of electrical conductive leads extending onto said sensing structure from said heater element and said plurality of dual sensing elements to said plurality of wire bond; and

a flow channel formed by bonding said sensing structure to the said backing structure wherein said flow of fluid is directed through said flow channel in order to isolate a plurality of wire bonds and said plurality of dual sensing elements from said flow channel.

10. The flow sensor of claim 9, wherein said plurality of electrical conductive leads and said plurality of wire bonds provides an electrical connection for said heater element and said plurality of dual sensing elements.

11. The flow sensor of claim 9 wherein said plurality of resistive thin films comprises metal selected from nickel and platinum.

12. The flow sensor of claim 9 wherein said plurality of resistive thin films are connected in a Wheatstone bridge configuration.

13. The flow sensor of claim 9 wherein said sensing structure is overpackaged utilizing standard processes comprising epoxies and seals.

14. The sensor of claim 9 wherein said backing structure, said sensing structure and said flow channel are assembled together into a complete assembly.

15. The MEMS flow sensor of claim 9 wherein said backing structure is selected from the group comprising etched silicon, a fabricated glass, and a molded plastic.

16. A MEMS flow sensor, comprising:

a backing structure having two openings for fluid flow formed there through;

a sensing structure including a backside etched channel and topside electrically insulating layer with heater element and a plurality dual sensing element, said sensing structure further comprising a plurality of resistive thin films further comprised of metals selected from nickel and platinum, wherein said plurality of dual sensing elements measure a flow of fluid and wherein two of said plurality of dual sensing elements can be located on both sides of said heating element to indicate flow of fluid direction;

a plurality of layers of silicon nitride deposited over said resistive thin films to provide protection from media and the environment; and

a flow channel formed by bonding said sensing structure to the back of said backing structure wherein said flow of fluid is directed through said flow channel in order to isolate a plurality of wire bonds and said plurality of dual sensing elements from said flow channel.

17. The flow sensor of claim 16 further comprising:

a plurality of electrical conductive leads extending from said sensing structure from said heater element and said plurality of dual sensing elements to said plurality of wire bonds.

18. The flow sensor of claim 17, wherein said plurality of electrical conductive leads and said plurality of wire bonds provides an electrical connection for said heater element and said plurality of dual sensing elements.

19. The flow sensor of claim 16 wherein said plurality of resistive thin films are connected in a Wheatstone bridge configuration.