Flow sensor with self-aligned flow channel

• US 20050022594A1
• Filed: 08/31/2004
• Published: 02/03/2005
• Est. Priority Date: 12/07/1998
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Bonne, Ulrich, Padmanabhan, Aravind, Marchini, Michael G.
• Granted Patent: US 7,258,003 B2
• Time in Patent Office: Days
• US Class Current: 73/204.260
• CPC Class Codes: G01F 1/684 Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/6847 where sensing or heating elements are not disturbing the fluid flow, e.g. elements mounted outside the flow duct
• CPC Class Codes: G01F 15/14 Casings, e.g. of special material
• CPC Class Codes: G01F 15/18 Supports or connecting means for meters
• CPC Class Codes: G01F 15/185 Connecting means, e.g. bypass conduits
• CPC Class Codes: G01F 5/00 Measuring a proportion of the volume flow
• CPC Class Codes: G01N 1/2247 Sampling from a flowing stream of gas
• CPC Class Codes: G01N 2001/2285 Details of probe structures
• CPC Class Codes: G01N 25/18 by investigating thermal conductivity by calorimetry G01N25/20; by measuring change of resistance of an electrically-heated body G01N27/18
• CPC Class Codes: G01N 25/488 Details
• CPC Class Codes: G01N 33/0014 by eliminating a gas G01N33/0013 and G01N33/0024 take precedence
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing
• CPC Class Codes: Y10T 29/4913 Assembling to base an electrical component, e.g., capacitor, etc.
• CPC Class Codes: Y10T 29/49135 and shaping, e.g., cutting or bending, etc.
• CPC Class Codes: Y10T 29/49147 Assembling terminal to base
• CPC Class Codes: Y10T 29/49798 Dividing sequentially from leading end, e.g., by cutting or breaking

Abstract

A flow sensor is provided having a substrate with a sensing element and flow channel aligned over the sensing element. The sensing element senses at least one property of a fluid. The flow channel is aligned by one or more guide elements formed in an alignment layer. The flow channel across the sensing area is accurately and precisely aligned due to the guide elements provided at the wafer-level, facilitating reliable, low-cost, and consistent results among multiple flow sensors. The flow sensor is adapted for use in harsh environments.

Claims

1. A flow sensor comprising:

a substrate having a sensing element thereon, said sensing element configured to sense at least one property of a fluid;

an alignment layer deposited on the substrate, the alignment layer defining one or more guide elements; and

a flow channel;

wherein the guide elements align the flow channel over the sensing element.

2. The flow sensor of claim 1, comprising first and second guide elements, wherein the first and second guide elements define the flow channel.

3. The flow sensor of claim 1, wherein said alignment layer includes a polymer.

4. The flow sensor of claim 1, wherein said sensing element includes a heater and at least one thermal sensor.

5. The flow sensor of claim 1, wherein said substrate is selected from the group consisting of quartz, silicon, ceramic, glass, metal, and polymer, which are generally chosen to have a relatively low value of thermal conductivity.

6. The flow sensor of claim 3, wherein said polymer is poly(methyl methacrylate).

7. The flow sensor of claim 3, wherein said polymer is a photoresist.

8. The flow sensor of claim 7, wherein said photoresist is SU8.

9. The flow sensor of claim 2, further comprising a molded element positioned over the guide elements, the molded element defining first and second flow channel extensions;

wherein the first flow channel extension is in fluid communication with a first end of the flow channel and the second flow channel extension is in fluid communication with a second end of the flow channel.

10. The flow sensor of claim 9, wherein the substrate forms a bottom of the flow channel, the guide elements forms sides of the flow channel, and the molded element forms a top of the flow channel.

11. The flow sensor of claim 9, wherein the first and second flow channel extensions are connected to the flow channel at an angle.

12. The flow sensor of claim 11, wherein the angle is a substantially right angle.

13. The flow sensor of claim 12, wherein the first and second flow channel extensions have a diameter and a distance between the angle and the sensing element is greater than or equal to 10 times the diameter of the second flow channel extension.

14. The flow sensor of claim 9, wherein the molded element is attached to the substrate and alignment layer with adhesive, wherein the alignment layer prevents the adhesive from entering the flow channel.

15. The flow sensor of claim 1, wherein the flow channel is a conduit positioned within the flow channel.

16. The flow sensor of claim 15, wherein the conduit is disposable.

17. The flow sensor of claim 15, wherein the conduit is made of one or more materials selected from the group consisting of glass, ceramic, fused silica, polymer, metal, and mixtures thereof.

18. The flow sensor of claim 17, wherein the conduit is stainless steel, and wherein oil is added to a junction between the flow channel and the conduit.

19. The flow sensor of claim 15, further comprising a molded element positioned over the alignment layer, the molded element extending beyond the alignment layer along the flow path, the molded element aligning the conduit over the sensing element.

20. The flow sensor of claim 19, further comprising a cap positioned over the molded element.

21. The flow sensor of claim 20, wherein the cap and molded element are attached with adhesive.

22. The flow sensor of claim 1, further comprising a molded channel positioned within the flow channel.

23. The flow sensor of claim 22, further comprising a cap positioned over the molded channel;

wherein the molded channel forms a bottom and sides of the flow path and the cap forms a top of the flow path.

24. The flow sensor of claim 1, comprising a single guide element adjacent the sensing element;

wherein the flow channel is a molded element positioned over the guide element and substrate.

25. A flow sensor comprising:

a substrate having a sensing element thereon, said sensing element configured to sense at least one property of a fluid;

an alignment layer deposited on the substrate, the alignment layer defining a location channel aligned over the sensing element; and

a flow tube positioned within the location channel.

26. A flow sensor comprising:

a substrate having a sensing element thereon, said sensing element configured to sense at least one property of a fluid;

a polymer structure positioned on the substrate, the polymer structure defining a location channel aligned over the sensing element;

a molded structure defining a flow channel, the molded structure configured to be at least partially received within the location channel such that the flow channel is aligned over the sensing element.

27. The flow sensor of claim 26, further comprising a cap positioned over the molded structure.

28. The flow sensor of claim 27, wherein the molded structure defines a bottom and walls of the flow channel and the cap defines a top of the flow channel.

29. A method of making a plurality of flow sensors each having a flow channel aligned with a sensing element, the method comprising:

providing a substrate having a plurality of sensing elements aligned in a pattern;

forming a plurality of guide elements on the substrate, wherein each guide element is aligned adjacent a sensing element;

dicing the substrate into a plurality of chips, wherein each chip has a sensing element and at least one guide element.

30. The method of claim 29, wherein the step of forming a plurality of guide elements includes depositing a polymer layer onto the substrate and forming the guide elements in the polymer layer.

31. The method of claim 30, further comprising applying a cap over the polymer layer on each chip.

32. The method of claim 30, wherein the polymer layer is a photoresist.

33. The method of claim 29, wherein the flow channels are formed by etching.

34. The method of claim 32, wherein the resist is poly(methyl methacrylate).

35. The method of claim 32, wherein the resist is SU-8.

36. The method of claim 29, wherein the substrate is selected from the group consisting of quartz, silicon, ceramic, glass, metal, and polymer.

37. A sensor comprising:

sensor means for sensing at least one property of a fluid;

flow channel alignment means positioned to direct fluid flow over the sensor means; and

flow directing means for directing fluid flow into the flow channel alignment means.

38. The sensor of claim 37, wherein the sensor means includes a heating element.

39. The sensor of claim 38, wherein the sensor means includes at least one thermal sensing element.

40. The sensor of claim 37, further comprising a cap positioned over the flow channel alignment means.

41. The sensor of claim 37, wherein the flow channel alignment means includes a polymer layer forming walls of a flow channel.

42. The sensor of claim 41, wherein the polymer is a photoresist.

43. The sensor of claim 42, wherein the resist is a poly(methyl methacrylate).

44. The sensor of claim 42, wherein the resist is SU-8.

45. A sensor for measuring one or more physical properties of a fluid comprising:

a sensor die made up of a substantially solid insulating sensor body and a plurality of sensing elements;

a polymer substrate attached to the sensor die, the polymer substrate defining a plurality of flow channels positioned over the sensing elements; and

a plurality of flow tubes in fluid communication with the flow channels.

46. A method of making a plurality of flow sensors each having a flow channel aligned over a sensing element, the method comprising:

(a) providing a substrate having a plurality of sensing elements aligned in a pattern;

(b) depositing an alignment layer onto the substrate;

(c) forming a plurality of guide elements in the alignment layer, wherein at least one guide element is aligned adjacent each sensing element, and the guide elements are substantially the same distance from each sensing element;

(d) dicing the substrate to form a plurality of pieces, each piece having a sensing element and at least one guide element; and

(e) placing a molded element containing a flow channel on the guide element of each piece such that the flow channel is aligned over the sensing element.

47. The method of claim 46, wherein step (e) involves placing a different size flow channel on each piece to achieve a plurality of flow sensors, each having a different sized flow channel aligned over the sensing element.

48. The method of claim 46, wherein the alignment layer is a polymer and the guide elements are formed by photolithography.

49. The method of claim 46, further comprising placing a cap on the molded element, wherein the molded element forms a bottom and sides of the flow channel and the cap forms a top of the flow channel.

50. The method of claim 46, wherein the molded element includes a flow channel region and at least one outwardly protruding arm, wherein the at least one arm extends over the guide element and the flow channel region is aligned over the sensing element, wherein the molded element is sized such that at least a portion of a bottom surface of the flow channel contacts the substrate.

51. The method of claim 50, wherein a bottom wall of the flow channel has a thin area in contact with the substrate over the sensing element, wherein the remaining area of the bottom wall is spaced from the substrate.

52. The method of claim 49, wherein the cap includes a protrusion extending into the flow channel to reduce the volume of the flow channel.

53. The method of claim 49, wherein the cap is attached to the molded element before the molded element is placed on the guide elements.

54. A method of measuring one or more physical properties of a plurality of fluids comprising:

(a) providing a flow sensor including a substrate having a sensing element thereon configured to sense at least one property of a fluid, one or more guide elements on the substrate defining a location channel aligned over the sensing element, and a first disposable flow tube disposed in the location channel such that the flow tube defines a flow path across the sensing element;

(b) directing a first fluid through the first flow tube and across the sensing element;

(c) sensing one or more properties of the first fluid;

(d) removing the first flow tube from the location channel;

(e) positioning a second flow tube in the location channel;

(f) directing a second fluid through the second flow tube and across the sensing element;

(g) sensing one or more properties of the second fluid; and

(h) repeating steps (e) through (g) for additional fluids.