Micromachined flow sensor device using a pressure difference and method of manufacturing the same

• US 5,515,735 A
• Filed: 01/03/1995
• Issued: 05/14/1996
• Est. Priority Date: 01/03/1995
• Status: Expired due to Fees

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Sarihan, Vijay
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): NOORI, MAX H
• Application Number:
  US08/367,603
• Time in Patent Office: 497 Days
• Field of Search: 73/861.42, 73/861.47, 73/861.48, 73/861.53, 73/204.21, 73/204.26, 73/861.21, 73/861.22, 73/721, 73/722
• US Class Current: 73/861.47
• CPC Class Codes: G01F 1/383 with electrical or electro-mechanical indication
• CPC Class Codes: G01F 1/44 Venturi tubes

Abstract

A flow sensor device including a body portion that provides a pressure differential when placed in fluid stream and a pressure sensor portion associated with the body portion to sense the pressure differential. In one embodiment, the body portion (13,72,113) includes a channel (16,76,116) that extends from an entrance side (24,44,124) to an exit side (26, 46). The channel (16, 76,116) has an inner portion (27, 47,87) between the entrance side (24, 44,124) and the exit side (26, 46). The channel (16,76,116) has a first cross-sectional area at the entrance side (24,44,124) and a second cross-sectional area at the inner portion (27,47,87), which is less than the first cross-sectional area. The pressure sensor portion (14,74,114) includes a diaphragm (18,38,78,118) and is associated with the body portion (13,72,113) such that when a fluid passes through the channel (16, 76,116), a pressure differential is sensed by the pressure sensor portion (14,74,114).

Claims

1. A flow sensor device comprising:

a body portion that provides a pressure differential when placed in a fluid stream, wherein the body portion has a duct that extends from an entrance side to an exit side, and wherein the duct has a first and a second opposed sides, a first cross-sectional area at the entrance side, an inner portion between the entrance side and the exit side, and a second cross-sectional area at the inner portion, and wherein the second cross-sectional area is less than the first cross-sectional area;

a plate portion coupled to the body portion to form one side of the duct; and

a pressure sensor portion having a diaphragm and piezoresistive elements, the diaphragm associated with the body portion such that the diaphragm deflects based upon the pressure differential, wherein velocity of the fluid stream is determined from the pressure differential.

2. The flow sensor device of claim 1 wherein one of the first and the second opposed sides of the duct has a shape to provide the second cross-sectional area.

3. The flow sensor device of claim 2 wherein the shape is curved.

4. The flow sensor device of claim 1 wherein the plate portion includes a projection that provides the second cross-sectional area.

5. The flow sensor device of claim 1 wherein the body portion and the pressure sensor portion are formed from a semiconductor material, and wherein the diaphragm forms one side of the duct.

6. The flow sensor device of claim 1 wherein the plate portion has a via, the via substantially centrally located over the inner portion, wherein the plate portion is between the pressure sensor portion and the body portion.

7. The flow sensor device of claim 6 wherein the body portion comprises a material having a thermal expansion coefficient close to that of the pressure sensor portion.

8. The flow sensor device of claim 1 wherein the body portion, the pressure sensor portion, and the plate portion are formed from a single piece of material.

9. A micro-machined sensor for sensing flow velocity of a fluid comprising:

a flow constricting portion having a channel, the channel having two opposed side-walls, a first opening at one end, and a second opening at an opposite end, wherein the channel narrows from the first opening to a throat portion and widens from the throat portion to the second opening such that the channel has a first cross-sectional area at the first opening and a second cross-sectional area at the throat portion, the second cross-sectional area less than the first cross-sectional area;

a cover portion forming one side of the channel; and

a pressure sensor portion having a thin partition, the thin partition and piezoresistive elements having a thickness and first and second opposed surfaces, the pressure sensor portion in spaced relationship with the flow constricting portion such that when a fluid passes through the channel, the thin partition deflects as a function of a pressure differential between the first and the second opposed surfaces.

10. The micro-machined sensor of claim 9 wherein the thin partition forms another side of the channel.

11. The micro-machined sensor of claim 10 wherein the thin partition has a span between the two opposed side-walls of the channel, and wherein one of the two opposed side-walls of the channel has a geometry that narrows the channel to provide the second cross-sectional area.

12. The micro-machined sensor of claim 10 wherein the thin partition has a span between the two opposed side-walls, and wherein the cover portion includes a projection portion that narrows the channel to provide the second cross-sectional area, and wherein the span is substantially uniform from the first opening to the second opening.

13. The micro-machined sensor of claim 9 wherein the cover portion includes a hole, and wherein the pressure sensor portion is attached to one side of the cover portion, and wherein the flow constricting portion is attached to an opposite side of the cover portion.

14. The micro-machined sensor of claim 13 wherein the flow constricting portion and the cover portion are formed from a single piece of material.

15. The micro-machined sensor of claim 9 wherein the flow velocity of the fluid is derived from a formula:

##EQU3## wherein V is the flow velocity, P₁ -P₂ is the pressure differential, A₁ is the first cross-sectional area, A₂ is the second cross-sectional area, and ρ

is a fluid density.

16. A method for making a flow sensor device comprising the steps of:

forming a channel in a body portion for passing a fluid, the channel extending from an entrance side to an exit side, wherein the channel has a first and a second opposed sides, and wherein the channel has a first cross-sectional area at the entrance side, and wherein the channel has an throat portion between the entrance side and the exit side, the channel having a second cross-sectional area at the throat portion, wherein the second cross-sectional area is less than the first cross-sectional area;

forming a plate portion, the plate portion being coupled to the body portion, the plate portion forming one side of the channel; and

forming a pressure sensor portion, the pressure sensor portion having a diaphragm, the diaphragm and piezoresistive having first and second opposed surfaces, wherein the second opposed surface is associated with the body portion such that when the fluid passes through the channel, the diaphragm is deflected based on a pressure differential between the first and second opposed surfaces, and wherein flow velocity is determined from the pressure differential, the first cross-sectional area, and the second cross-sectional area.

17. The method of claim 16 wherein the step of forming the body portion includes forming the body portion from a first semiconductor material, and wherein the step of forming the pressure sensor portion includes forming the pressure sensor portion from a second semiconductor material, and wherein the diaphragm forms one side of the channel.

18. The method of claim 16 wherein the step of forming the plate portion includes forming the plate portion having a via, the via substantially centrally located over the throat portion, wherein the plate portion is between the pressure sensor portion and the body portion.