Flexible imaging pressure sensor

• US 7,373,843 B2
• Filed: 06/02/2005
• Issued: 05/20/2008
• Est. Priority Date: 06/02/2005
• Status: Active Grant

• Current Assignee: Lenovo PC International Limited (Lenovo Group Ltd.)
• Original Assignee: Fidelica Microsystems
• Inventors: DeConde, Keith T., Ganapathi, Srinivasan K., Gluck, Randolph S.
• Primary Examiner(s): Lefkowitz; Edward
• Assistant Examiner(s): Kirkland, III; Freddie
• Application Number:
  US11/145,534
• Publication Number:
  US 20060272429A1
• Time in Patent Office: 1,083 Days
• Field of Search: 73862041-862046
• US Class Current: 73/862.046
• CPC Class Codes: G01L 1/142 using capacitors
• CPC Class Codes: G01L 1/205 using distributed sensing elements
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

A sensor for a textured surface (e.g., a fingerprint) is provided. The sensor includes a flexible substrate and a flexible membrane supported above the substrate by one or more spacers. The sensor also includes multiple pressure sensor elements responsive to a separation between parts of the membrane and corresponding parts of the substrate. The membrane is conformable to the textured surface being sensed, so the variation in separation between substrate and membrane is representative of the textured surface being sensed. A preferred sensor array arrangement has a set of parallel substrate electrodes on the substrate facing the membrane and a set of parallel membrane electrodes on the membrane facing the substrate, where the substrate and membrane electrodes are perpendicular. The sensor array is preferably an entirely passive structure including no active electrical devices, to reduce cost. Row and column addressing circuitry can be provided as separate units (e.g., ASIC chips) to be hybrid integrated with the sensor array.

Claims

1. An imaging pressure sensor for providing an image of a textured surface, the sensor comprising:

a) a flexible membrane conformable to the textured surface;

b) a flexible substrate capable of being affixed to a flexible surface without breaking;

c) at least two pressure sensor elements, wherein each pressure sensor element has an electrical resistance greater than 25 kΩ

responsive to a separation between a part of the membrane and a corresponding part of the substrate; and

d) a spacer disposed between and connected to the membrane and the substrate;

wherein each of the separations has a corresponding non-zero nominal value determined in part by the spacer;

wherein said substrate has a flexural rigidity D_S and said membrane has a flexural rigidity D_M, and wherein D _M<

D_S<

10⁶ D_M.

2. The sensor of claim 1, wherein said membrane includes a layer of a material selected from the group consisting of:

polyimides, aromatic fluorine polyesters, polyethersulfone, polysulfones, polyacrylates, polycarbonates, polyetheretherketone, polyethylene naphthalate, blocked isocyanates, silicone based elastomers, polyamides, polyether imides, polymethacrylates, polyolefins, poly (ethylene-acrylate) copolymers, poly(ethylene-methacrylate) copolymers, polyethylene terephthalate, polynaphthalene terephthalate, polydienes, poly(styrene-diene) block copolymers, poly(vinyl halides), polyurethanes, poly(urethane acrylates), poly(urethane methacrylates), poly(dimethyl siloxanes), and ionomers.

3. The sensor of claim 2, wherein said layer comprises particulate inclusions.

4. The sensor of claim 1, wherein said membrane is a laminate including two or more layers of differing composition.

5. The sensor of claim 1, wherein 10⁻

11 N-m≦

D_M≦

10⁻

N-m.

6. The sensor of claim 5, wherein 10⁻

8 N-m≦

D_M≦

10<sup>−

6</sup> N-m.

7. The sensor of claim 1, wherein said substrate includes a layer of a material selected from the group consisting of:

polyimides, aromatic fluorine polyesters, polyethersulfone, polysulfones, polyacrylates, polycarbonates, polyetheretherketone, polyethylene naphthalate, blocked isocyanates, silicone based elastomers, polyamides, polyether imides, polymethacrylates, polyolefins, poly(ethylene-acrylate) copolymers, poly(ethylene-methacrylate) copolymers, polyethylene terephthalate, polynaphthalene terephthalate, polydienes, poly(styrene-diene) block copolymers, poly(vinyl halides), polyurethanes, poly(urethane acrylates), poly(urethane methacrylates), poly(dimethyl siloxanes), and ionomers.

8. The sensor of claim 7, wherein said layer comprises particulate inclusions.

9. The sensor of claim 1, wherein said substrate is a laminate including two or more layers of differing composition.

10. The sensor of claim 1 wherein 10⁻

7 N-m≦

D_S≦

10<sup>−

4</sup> N-m.

11. The sensor of claim 10, wherein 10⁻

6 N-m≦

D_S≦

10<sup>−

5</sup> N-m.

12. The sensor of claim 1, wherein each of said pressure sensor elements provides an analog output signal or a binary output signal.

13. The sensor of claim 1, wherein each of said pressure sensor elements includes two contact electrodes disposed on said substrate and an electrically conductive region disposed on said membrane facing the two contact electrodes.

14. The sensor of claim 1 further comprising:

a plurality of membrane electrodes disposed on said membrane and facing said substrate, wherein the membrane electrodes are substantially parallel;

a plurality of substrate electrodes disposed on said substrate and facing said membrane, wherein the substrate electrodes are substantially parallel;

wherein the membrane electrodes are substantially perpendicular to the substrate electrodes.

15. The sensor of claim 14, wherein each of said pressure sensor elements comprises

a first contact including part of one of said membrane electrodes;

and

a second contact including part of one of said substrate electrodes;

whereby each of said pressure sensor elements are addressable by a corresponding row and column.

16. The sensor of claim 15, wherein each of said pressure sensor elements further includes a component selected from the group consisting of a discrete resistor and a diode.

17. The sensor of claim 16, wherein said component is disposed on said first contact or on said second contact.

18. The sensor of claim 16, wherein an electrically conductive layer is disposed on a surface of said component facing and nominally separated from said first contact or said second contact.

19. The sensor of claim 16, wherein said component is a discrete resistor including a material selected from the group consisting of:

co-sputtered metals and ceramics, tantalum oxide, polysilicon, amorphous silicon, conductive polymer composites, polymer thick film resistors, carbon nanotube composites, composite plastics, composite elastomers, and intrinsically conductive polymers.

20. The sensor of claim 1, wherein said spacer comprises a material selected from the group consisting of:

silicones, polyurethanes, polyamides, polyimides, polyacrylates, polymethacrylates, poly(glycidyl ethers), poly(ethylene-acrylate) copolymers, poly(ethylene-methacrylate) copolymers, polydienes, poly(styrenediene) block copolymers, poly(vinyl halides), polyurethanes, poly(urethane acrylates), poly(urethane methacrylates), and poly(dimethyl siloxanes).

21. The sensor of claim 1, wherein said spacer defines a global cavity including all of said pressure sensor elements.

22. The sensor of claim 1, wherein said spacer defines a plurality of local cavities, each corresponding to one of said pressure sensor elements.

23. The sensor of claim 1, wherein 50 D_M≦

D_S≦

500 D_M.

24. The sensor of claim 1, wherein said substrate is substantially composed of a first material and said membrane is substantially composed of a second material, and wherein said first and second materials have similar elastic properties.

25. The sensor of claim 24, wherein said substrate has a thickness t_S and said membrane has a thickness t_M, and wherein t_M≦

t_S≦

1000 t_M.

26. The sensor of claim 25, wherein t_S≦

t_M≦

10 t_s.

27. The sensor of claim 1, wherein said sensor is a passive device including no active electrical devices.

28. The sensor of claim 1, wherein said sensor includes at least one active electrical device.

29. The sensor of claim 1, further comprising addressing circuitry disposed remotely from said pressure sensor elements.

30. The sensor of claim 1 further comprising a body having a flexible surface to which said flexible substrate is affixed.

31. A method of making an imaging pressure sensor for providing an image of a textured surface, the method comprising:

a) providing a flexible substrate capable of being affixed to a flexible surface without breaking;

b) processing the substrate to form a substrate pattern;

c) providing a flexible membrane conformable to the textured surface;

d) processing the membrane to form a membrane pattern;

e) providing a spacer;

f) bonding the membrane, the spacer and the substrate together such that the spacer is sandwiched between the membrane and the substrate, and wherein the substrate pattern faces the membrane pattern;

wherein the membrane and substrate patterns define at least two pressure sensor elements each having an electrical resistance greater than 25 kΩ

responsive to a separation between a part of the membrane and a corresponding part of the substrate;

wherein each of the separations has a corresponding non-zero nominal value determined in part by the spacer;

wherein said substrate has a flexural rigidity D_S and said membrane has a flexural rigidity D_M, and wherein D _M<

D_S<

10⁶ D_M.

32. The method of claim 31, wherein said substrate pattern includes resistors disposed on top of electrodes, and wherein the resistors are aligned to the electrodes by a self-aligned process.

33. The method of claim 31, wherein said bonding comprises roller-mill bonding, whereby roll-level fabrication is provided.

34. A method of making an imaging pressure sensor for providing an image of a textured surface, the method comprising:

a) providing a flexible substrate capable of being affixed to a flexible surface without breaking;

b) processing the substrate to form a substrate pattern;

c) providing a flexible membrane conformable to the textured surface;

d) processing the membrane to form a membrane pattern;

e) bonding the membrane and the substrate together such that the substrate pattern faces the membrane pattern;

wherein the membrane and substrate patterns define at least two pressure sensor elements each having an electrical resistance greater than 25 kΩ

responsive to a separation between a part of the membrane and a corresponding part of the substrate;

wherein each of the separations has a corresponding non-zero nominal value determined in part by a spacer formed by the membrane and substrate patterns;

wherein said spacer comprises a local standoff corresponding to each of said pressure sensor elements, and wherein each local standoff comprises a pressure sensitive resistor.

35. The method of claim 34, wherein said substrate pattern includes resistors disposed on top of electrodes, and wherein the resistors are aligned to the electrodes by a self-aligned process.

36. The method of claim 34, wherein said bonding comprises roller-mill bonding, whereby roll-level fabrication is provided.

37. A method for sensing a textured surface, the method comprising:

a) providing a flexible membrane conformable to the textured surface;

b) providing a flexible substrate capable of being affixed to a flexible surface without breaking;

c) providing at least two pressure sensor elements, wherein each pressure sensor element has an electrical resistance greater than 25 kΩ

responsive to a separation between a part of the membrane and a corresponding part of the substrate; and

d) providing a spacer disposed between and connected to the membrane and the substrate wherein each of the separations has a corresponding non-zero nominal value determined in part by the spacer;

e) providing an output signal responsive to one or more signals from one or more of the pressure sensor elements;

wherein said substrate has a flexural rigidity D_S and said membrane has a flexural rigidity D_M, and wherein D_M<

D_S<

10⁶ D_M.

38. The method of claim 37, wherein said output signal comprises a textured surface image or a binary touch signal.

39. The method of claim 38, wherein said output signal is a fingerprint image.

40. The method of claim 39, wherein said fingerprint image is employed in a system selected from the group consisting of identification systems, security systems, motion sensing systems, and cursor control systems.

41. The method of claim 40, wherein said system is a cursor control system and further comprising comparing said fingerprint images taken at different times to estimate a motion of said textured surface, wherein the estimate of the motion is employed for control of a pointing device.

42. The method of claim 38, wherein said output signal is a binary touch signal, and wherein the binary touch signal is employed in a system selected from the group consisting of power switch systems, menu selection systems, pointer activation systems, and standby/wakeup systems.