Flexible silicon strain gage

• US 6,444,487 B1
• Filed: 02/05/1999
• Issued: 09/03/2002
• Est. Priority Date: 07/28/1998
• Status: Expired due to Fees

• Current Assignee: Rosemount Aerospace, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Rosemount Aerospace, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Bang, Christopher A., Stark, Kevin C., Just, Marcus S., Boggs, Bradley J.
• Primary Examiner(s): MULPURI, SAVITRI
• Application Number:
  US09/245,272
• Time in Patent Office: 1,306 Days
• Field of Search: 438/48-50, 438/51, 438/52, 438/53, 438/977, 438/11, 438/18, 438/5, 438/6, 438/455, 438/459, 438/464, 296/18, 257/417, 737/19, 737/20, 737/21, 737/77, 738/626.5, 338/2, 338/3, 338/4, 338/5, 338/6
• US Class Current: 438/48
• CPC Class Codes: G01L 1/18 using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
• CPC Class Codes: G01L 1/2293 of the semi-conductor type semi-conductor devices controllable by variations of applied mechanical force H01L29/84
• CPC Class Codes: G01L 9/0055 bonded on a diaphragm

Abstract

A generally flexible strain gage comprising a strain sensing element, and a generally flexible substrate supporting the strain sensing element. The strain sensing element is made of single crystal or polycrystalline semiconducting material. The invention also includes a method for forming a generally flexible strain gage comprising the step of selecting a wafer having a portion of a base material and portion of a single crystal or polycrystalline semiconducting material located thereon. The method further comprises the steps of etching a strain sensing element out of the semiconducting material and forming a generally flexible substrate onto said sensing element.

Claims

1. A method for forming a strain sensor on a flexible substrate, the method comprising the steps of:

providing a wafer having a portion of base material and a portion of sensor material that has at least one property that varies with an applied strain;

forming said strain sensor out of said sensor material;

forming said flexible substrate over said strain sensor; and

removing at least part of said base material to expose at least part of said sensor.

2. The method of claim 1 wherein said flexible substrate is polyimide, and wherein said flexible substrate is spun onto said wafer.

3. The method of claim 1 wherein said sensor is flexible.

4. The method of claim 1 wherein said removing step includes removing said base material using deep reactive ion etching.

5. The method of claim 1 wherein said sensor material is a semiconducting material.

6. The method of claim 1 wherein said sensor material is a single crystal semiconductor.

7. The method of claim 1 wherein the step of forming said sensor comprises etching said sensor material.

8. The method of claim 1 wherein said wafer includes an oxide layer between said base material and said sensor material.

9. The method of claim 1 further comprising the steps of fabricating microelectronic circuitry in said wafer, and electrically connecting said electronic component to said sensor.

10. The method of claim 9 wherein said electrically connecting step includes depositing metal on said wafer such that said deposited metal electrically connects said electronic component and said sensor.

11. The method of claim 1 wherein said substrate is directly deposited over said sensor in a liquid form, and wherein the method further comprises the step of curing said substrate.

12. The method of claim 1 wherein said substrate is formed over said sensor such that said substrate is thick enough to support said sensor.

13. The method of claim 1 wherein said wafer includes an oxide layer located between said portion of base material and said portion of sensor material, and wherein said removing step includes removing at least part of said base material located over said sensor to expose at least part of said oxide layer.

14. A method for forming a flexible strain gage comprising the steps of:

selecting a wafer having a portion of a base material and portion of a single crystal semiconducting material or polycrystalline semiconducting material located thereon;

etching a strain sensing element out of said semiconducting material; and

forming a flexible substrate onto said sensing element;

etching away said base material after said forming step.

15. The method of claim 14 wherein said strain sensing element is silicon.

16. The method of claim 14 wherein said base material is etched away using deep reactive ion etching.

17. The method of claim 14 wherein said wafer includes an oxide layer between said base material and said semiconducting material, and wherein said etching step includes removing said base material until at least part of said oxide layer located over said sensor is exposed.

18. The method of claim 14 wherein said wafer includes an oxide layer between said base material and said semiconducting material.

19. The method of claim 14 further comprising the step of electrically connecting a first output pad to said sensing element after said etching step.

20. The method of claim 19 further comprising the step of doping a portion of said strain sensing element, and wherein said output pad is connected to said sensing element at said doped portion.

21. The method of claim 19 wherein said output pad is formed by metal sputtering, and wherein said output pad is connected to said sensing element by a metal lead.

22. The method of claim 19 wherein said wafer includes an oxide layer between said base material and said semiconducting material, and wherein the method further comprises the step of partially etching a portion of said oxide layer before forming said output pad, and wherein said output pad is formed in said partially etched portion of said oxide layer.

23. The method of claim 14 further comprising the steps of fabricating microelectronic circuitry in said wafer, and electrically connecting said microelectronic circuitry to said strain sensing element.

24. A method for forming a strain sensor array comprising the steps of:

providing a wafer having a portion of base material and a portion of sensor material that has at least one property that varies with an applied strain;

forming a plurality of strain sensors out of said sensor material;

forming a flexible substrate over said plurality of strain sensors; and

removing at least part of said base material to expose at least part of each sensor.

25. The method of claim 24 wherein each sensor has an output lead, and wherein said output leads terminate in a common area.

26. The method of claim 24 wherein each sensor has an output lead, and wherein said output leads are connected to an electronic component carried on said substrate.

27. The method of claim 24 further comprising the steps of fabricating microelectronic circuitry in said wafer before forming said sensors, and electrically connecting said circuitry to at least one of said sensors.

28. A method for forming a strain sensor on a flexible substrate, the method comprising the steps of:

selecting a wafer having a portion of base material and a portion of sensor material;

forming said strain sensor by etching said sensor material;

directly depositing said substrate over said sensor in a liquid form;

allowing said substrate to cure such that said substrate is in a solid but flexible form; and

removing at least part of said base material to expose said sensor.

29. A method for manufacturing a flexible strain gage comprising the steps of:

providing a wafer having a portion of base material and a portion of sensor material that has at least one property that varies with an applied strain;

etching said sensor material to form a strain gage;

depositing at least one lead on said wafer, said at least one lead being electrically coupled to said strain gage;

depositing a flexible substrate over said substrate and said at least one lead; and

removing at least part of the base material located over said sensor and located over said at least one lead to expose said at least one lead.

30. A method for forming a strain sensor on a flexible substrate, the method comprising the steps of:

providing a wafer having a portion of base material and a portion of semiconducting material;

forming said strain sensor out of said portion of semiconducting material;

forming said flexible substrate over said sensor; and

removing at least part of said base material to expose at least part of said sensor.

31. The method of claim 30 wherein said semiconducting material is silicon.