Compact pressure-sensing device

• US 7,543,502 B2
• Filed: 04/10/2006
• Issued: 06/09/2009
• Est. Priority Date: 04/08/2005
• Status: Active Grant

• Current Assignee: Analatom Incorporated
• Original Assignee: Analatom Incorporated
• Inventors: Niblock, Trevor Graham Edward
• Primary Examiner(s): Allen; Andre J
• Assistant Examiner(s): JENKINS, JERMAINE L
• Application Number:
  US11/401,692
• Publication Number:
  US 20070016384A1
• Time in Patent Office: 1,156 Days
• Field of Search: 73700-756, 3612831-2834
• US Class Current: 73/727
• CPC Class Codes: F02B 77/085 with sensors measuring combustion processes, e.g. knocking, pressure, ionization, combustion flame
• CPC Class Codes: F02D 35/023 by determining the cylinder pressure
• CPC Class Codes: F02D 35/025 by determining temperatures inside the cylinder, e.g. combustion temperatures
• CPC Class Codes: G01K 2205/00 Application of thermometers in motors, e.g. of a vehicle
• CPC Class Codes: G01K 7/16 using resistive elements resistive elements per se H01C, H01L
• CPC Class Codes: G01L 23/18 by resistance strain gauges
• CPC Class Codes: G01L 9/0052 of piezoresistive elements circuits therefor G01L9/06
• CPC Class Codes: G01M 15/08 by monitoring pressure in cylinders
• CPC Class Codes: Y10T 29/49007 Indicating transducer

Abstract

The invention is a compact sensing device that is capable of measuring the conditions (e,g, pressure, temperature) inside a cylinder of an internal combustion engine. The invention is also a cost-effective method of fabricating the sensing device. The sensing device includes a substrate, a beam, and piezo-resistive sensing elements. The beam, which is formed on the substrate, is capable of deflecting according to different pressures applied to different beam surfaces. The piezo-resistive sensing elements are coupled to the beam and detect beam deflection. The piezo-resistive sensing elements generate an electrical signal corresponding to the beam deflection.

Claims

1. A sensing device comprising:

a planar substrate characterized by a plane;

a beam formed on the substrate, the beam being capable of deflecting in the plane of the substrate according to different pressures applied to the beam by a flow of gas; and

piezo-resistive sensing elements coupled to the beam, the piezo-resistive sensing elements detecting beam deflection and generating an electrical signal corresponding to the beam deflection.

2. The sensing device of claim 1 further comprising a cavity formed in the substrate, wherein the beam deflects according to difference between pressure inside the cavity and pressure outside the cavity.

3. The device of claim 1, wherein the substrate is a silicon substrate and the piezo-resistive sensing elements are doped into the silicon substrate.

4. The device of claim 1, wherein the piezo-resistive sensing elements form a first pair of piezo-electric sensing elements, further comprising a second pair of piezo-resistive sensing elements for detecting temperature.

5. The device of claim 4, wherein the two pairs of piezo-resistive sensing elements are formed on the same surface of the substrate.

6. The device of claim 4, wherein the two pairs of piezo-resistive sensing elements have the same crystal orientation.

7. The device of claim 1 further comprising:

bond pads on the substrate; and

aluminum connections between the piezo-resistive sensing elements and the bond pads.

8. The device of claim 1 further comprising a piezo resistor formed on the substrate for temperature measurement.

9. The device of claim 1 further comprising a p-n diode formed on the substrate for temperature measurement.

10. The device of claim 1, wherein the beam has a fixed end and a free end, the fixed end being coupled to the piezo-resistive sensing elements.

11. The device of claim 1, wherein the beam is a cantilever.

12. The device of claim 1, wherein the beam has two fixed ends.

13. The device of claim 1, wherein the beam has a uniform cross-section through its length.

14. The sensing device of claim 1, wherein the device is no larger than about 10 cm×

about 10 cm×

about 100 μ

m.

15. A sensor comprising:

a flexible material having an electrical interface;

a sensing device mounted on the flexible material, the sensing device including;

a planar substrate characterized by a plane;

a cavity formed in the substrate;

a beam formed on the substrate, wherein a gas flow passage is formed between the beam and the cavity, the beam being capable of deflecting in the plane of the substrate according to a flow of gas in the gas flow passage proportional to a difference between pressure inside the cavity and pressure outside the cavity;

piezo-resistive sensing elements coupled to the beam, the piezo-resistive sensing elements detecting beam deflection and generating an electrical signal corresponding to the beam deflection; and

bond pads electrically coupled to the pair of piezo-resistive sensing elements;

wherein the bond pads are electrically coupled to the electrical interface on the flexible material.

16. A method of fabricating a sensing device, the method comprising:

providing a planar substrate characterized by a plane;

forming a beam on the substrate that is capable of deflecting in the plane of the substrate according to pressure applied to the beam; and

doping a portion of the substrate to form piezo-resistive sensing elements coupled to the beam, the piezo-resistive sensing elements detecting beam deflection and generating an electrical signal corresponding to the beam deflection.

17. The method of claim 16 further comprising etching the substrate to form a cavity so that the piezo-resistive sensing elements detect pressure difference between inside the cavity and outside the cavity.

18. The method of claim 16 further comprising doping a different portion of the substrate to form a temperature-sensing piezo-resistor.

19. The method of claim 16, wherein the piezo-resistive sensing elements are a first pair of piezo-resistive sensing elements, further comprising doping another portion of the substrate to form a second pair of piezo-resistive sensing elements for temperature measurement.

20. The method of claim 19 further comprising forming the two pairs of piezo-resistive sensing elements on the same surface of the substrate.

21. The method of claim 19 further comprising:

forming a bond pad on the substrate; and

electrically coupling the bond pad to the pair of piezo-resistive sensing elements.