Microelectro-mechanical chemical sensor

• US 20050276726A1
• Filed: 05/25/2005
• Published: 12/15/2005
• Est. Priority Date: 05/25/2004
• Status: Active Grant

• Current Assignee: The Government Of The United States Of America, As Represented By The Secretary Of The Navy, the united states of america as represented by the secretary of the navy
• Original Assignee: The Government Of The United States Of America, As Represented By The Secretary Of The Navy
• Inventors: McGill, Robert Andrew, Fedder, Gary K., Voiculescu, Ioana
• Granted Patent: US 7,556,775 B2
• Time in Patent Office: Days
• US Class Current: 422/96
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 2291/0257 with a layer containing at least one organic compound
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves

Abstract

A microelectro-mechanical chemical sensor includes an active cantilever beam having a chemically selective material layer disposed thereon and at least one, preferably two, resistors with the resistance corresponding to the cantilever beam deflection. The sensor also has at least two, and preferably four, auxiliary cantilever beams adjacent to the active cantilever and attached to the same substrate, each having a piezoresistor disposed thereon. The piezoresistors are elements of a Wheatstone bridge, and the Wheatstone bridge output indicates the amount of a predetermined target chemical sorbed by the chemically selective material layer. The sensor is electrostatically actuated in order to monitor the resonant frequency.

Claims

1. A microelectronics based chemical sensor comprising:

a first beam having at least one end attached to a structure;

excitation means for causing the beam to deflect;

a first resistor disposed on the first beam, the first resistor having a resistance that changes responsive to a deflection of the first beam;

at least one cantilevered beam on opposite sides of the first beam, each of the cantilevered beams having an end attached to the structure, each of the cantilevered beams having a resistor disposed thereon;

the first resistor on the first beam and the resistors on the cantilevered beams being elements of a Wheatstone bridge; and

a chemically selective material layer disposed on the first beam, wherein an output of the Wheatstone bridge corresponds to an amount of a chemical sorbed by the material layer, and the chemical is nerve agent simulant dimethylmethylphosphonate or a nerve agent.

2. A sensor according to claim 1, wherein the first beam is a cantilevered beam.

3. The sensor according to claim 1, wherein the first resistor and the resistors on the cantilevered beams are piezoresistors.

4. A sensor according to claim 1, further comprising a second resistor on the first beam, the second resistor having a resistance corresponding to a deflection of the first beam, the second resistor being an element of the Wheatstone bridge.

5. A sensor according to claim 1 comprising two cantilevered beams disposed on each side of the first beam, each of the cantilevered beams having a resistor disposed thereon, the resistors on the cantilevered beams being elements of the Wheatstone bridge.

6. The sensor according to claim 5, wherein a first of the arms of the Wheatstone bridge includes two of the resistors disposed on the cantilevered beams, and a second of the arms of the Wheatstone bridge includes a different two of the resistors disposed on the cantilevered beams.

7. The sensor according to claim 1, wherein the resistors on the first beam and on the cantilevered beams comprise polysilicon.

8. A sensor according to claim 1, wherein the Wheatstone bridge measures a resonance frequency of the first beam.

11. The sensor according to claim 19, wherein the chemically sensitive material comprises HCSA2.

12. The sensor according to claim 19, wherein the chemically sensitive material comprises a hexafluoroisopropanol-siloxane polymer.

14. The sensor according to claim 1, wherein the excitation means includes electrical conductors disposed on the first beam that carry an electrical charge for electrostatic actuation of the first beam.

15. The sensor according to claim 1, wherein the excitation means includes a plurality of electrically conductive protrusions on the first beam interdigitated with protrusions on the structure, the protrusions on the first beam and the protrusions on the structure carrying electrical charges for electrostatic actuation of the first beam.

16. The sensor according to claim 1, wherein at least two edges of the first beam have a plurality of electrically conductive protrusions interdigitated with electrically conductive protrusions on the structure extending from the structure toward the beam.

17. The sensor according to claim 1, wherein the resistors comprise polysilicon.

18. The sensor according to claim 1, wherein the structure is a CMOS device.

19. The device according to claim 2, wherein the cantilever has a length of between about 50 micrometers and about 300 micrometers and a width of between about 50 micrometers and about 150 micrometers.

9-10. -10. (canceled)

13. (canceled)

20. A microelectronics based chemical sensor comprising:

an electrostatically actuated first cantilever beam attached at one end to a structure, the first beam having a chemically selective material layer disposed thereon;

at least a first resistor disposed on the first beam, the first resistor having a resistance corresponding to a deflection of the first beam, a second cantilevered beam having a resistor disposed thereon, the second cantilevered beam attached at an end to the structure;

a third cantilevered beam having a resistor disposed thereon, the third cantilevered beam attached at an end to the structure;

the first, second, and third resistors being elements of a Wheatstone bridge,

the output of the Wheatstone bridge corresponding to the amount of an analyte sorbed by or a nerve agent.

23. The sensor according to claim 20, further comprising at least a fourth resistor disposed on the first beam, the fourth resistor having a resistance corresponding to a deflection of the first beam, the fourth resistor being an element of the Wheatstone bridge.

24. The sensor according to claim 20, the Wheatstone bridge having an output that corresponds to the resonance frequency of the first cantilever.

25. The sensor according to claim 20, wherein the first cantilevered beam is arranged between the second and the third cantilevered beams.

26. The sensor according to claim 20, further comprising:

a fourth cantilevered beam having a fourth resistor disposed thereon; and

a fifth cantilevered beam having a fifth resistor disposed thereon, the fourth and fifth cantilevers being arranged either side of the first cantilever, the fourth and the fifth resistors being elements of the Wheatstone bridge.

27. The device according to claim 20, wherein the structure is a CMOS chip.

28. The device according to claim 20, further comprising conductive protrusions on at least one edge of the cantilever interdigitated with conductive protrusions on the structure, the conductive protrusions carrying electrical charges for electrostatic actuation of the cantilever.

29. The device according to claim 20, wherein the nerve agent simulant is dimethylmethylphosphonate.

21-22. -22. (canceled)