Apparatus, methods, and systems to detect an analyte based on changes in a resonant frequency of a spring element

• US 20050262943A1
• Filed: 05/27/2004
• Published: 12/01/2005
• Est. Priority Date: 05/27/2004
• Status: Abandoned Application

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Malenfant, Patrick R. L., Cicha, Walter V., Zribi, Anis, Tian, Wei-Cheng, Knobloch, Aaron, Claydon, Glenn, Goodwin, Stacey
• Application Number:
  US10/854,845
• Publication Number:
  US 20050262943A1
• Time in Patent Office: Days
• US Class Current: 73/579
• CPC Class Codes: G01N 2291/0215 Mixtures of three or more gases, e.g. air
• CPC Class Codes: G01N 2291/0255 (Bio)chemical reactions, e.g. on biosensors
• CPC Class Codes: G01N 2291/0256 Adsorption, desorption, surface mass change, e.g. on biosensors
• CPC Class Codes: G01N 29/022 Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices microdevices per se B81B
• CPC Class Codes: G01N 29/036 by measuring frequency or resonance of acoustic waves
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046

Abstract

According to some embodiments, a Microelectromechanical System (MEMS) sensor includes a sensing material on a spring element. The sensor may also include a detector adapted to determine a resonant frequency associated with the spring element, wherein the resonant frequency changes upon the exposure of the sensing material to an analyte.

Claims

1. A microelectromechanical system sensor, comprising:

a spring element;

a sensing material on the spring element; and

a detector adapted to determine a resonant frequency associated with the spring element, wherein the resonant frequency changes upon the exposure of the sensing material to an analyte.

2. The sensor of claim 1, wherein the detector includes:

a conducting path through which an alternating current is to flow; and

a magnet field source having a magnetic field substantially normal to direction of current flow through the conducting path.

3. The sensor of claim 2, further comprising:

a wafer substantially parallel to and supporting the spring element, wherein a Lorenz force moves the spring element in a direction substantially normal to the wafer.

4. The sensor of claim 3, wherein the detector further comprises:

an amplitude measuring device, wherein the amplitude of spring element movement is measured over a plurality of alternating current frequencies to determine the resonant frequency.

5. The sensor of claim 4, wherein the amplitude measuring device comprises:

a conducting plane proximate to the conducting path wherein the amplitude is associated with an amount of capacitance between the conducting plane and conducting path.

6. The sensor of claim 4, wherein the amplitude measuring device comprises at least one of:

(i) a direct current strain gauge, wherein the amplitude is associated with an amount of strain created by the movement of the spring element, and (ii) an alternating current stress gauge, wherein the amplitude is associated with an amount of stress created by movement of the spring element.

7. The sensor of claim 4, wherein the amplitude measuring device comprises:

an optical source; and

an optical detector, wherein the amplitude is associated with an optical characteristic of the spring element.

8. The sensor of claim 1, wherein the spring element comprises at least one of:

(i) a free standing membrane, (ii) a cantilever beam, and (iii) a bridge structure.

9. The sensor of claim 1, further comprising:

a reference spring element; and

a reference detector adapted to determine a reference resonant frequency associated with the reference spring element, wherein the reference resonant frequency does not change upon the exposure of the reference spring element to the analyte.

10. The sensor of claim 1, further comprising:

a second spring element;

a second sensing material on the second spring element; and

a second detector adapted to determine a second resonant frequency associated with the second spring element, wherein the second resonant frequency changes upon the exposure of the second sensing material to a second analyte.

11. The sensor of claim 1, further comprising:

a screen to help prevent contaminant particles from reaching the sensing material.

12. The sensor of claim 1, wherein the analyte is CO and the sensing material is a layer that includes at least one of:

(i) ZSM-5, and (ii) MFI.

13. The sensor of claim 1, wherein the analyte is CO₂ and the sensing material is a layer that includes at least one of:

(i) ZS500A, (ii) Zeochem Z10-02, (iii) SAP-34, and (iv) AFR.

14. The sensor of claim 1, wherein the analyte is O₂ and the sensing material is a layer that includes at least one of:

(i) A-type zeolites, (ii) SX6, and (iii) zeolite rho.

15. The sensor of claim 1, wherein the analyte is ammonia and the sensing material is a layer that includes at least one of:

(i) zeolite 4A, (ii) zeolite 5A, (iii) zeolite 13X, (iv) FAU, and (v) polyelectrolytes.

16. The sensor of claim 1, wherein the analyte is N₂ and the sensing material is a layer that includes at least one of:

(i) SX6, (ii) CaX, (iii) LTA, and (iv) zincophosphate.

17. The sensor of claim 1, wherein the analyte is H₂O and the sensing material is a layer that includes at least one of:

(i) polyelectrolytes, (ii) A-zeolite, and (iii) polystyrene sulfonic acid.

18. The sensor of claim 1, wherein the analyte is CH₄ and the sensing material is a layer that includes at least one of:

(i) LTA, and (ii) zincophosphate.

19. The sensor of claim 1, wherein the analyte is NOx and the sensing material is a layer that includes NA-Y.

20. The sensor of claim 1, wherein the analyte is aromatics and the sensing material is a layer that includes ZSM5.

21. The sensor of claim 1, wherein the analyte is hydro-fluorocarbons and the sensing material is a layer that includes NA-Y.

22. The sensor of claim 1, wherein the analyte is SO₂ and the sensing material is a layer that includes at least one of:

(i) zeolite X, (ii) zeolite Y, and (iii) Na-P1.

23. The sensor of claim 1, wherein the analyte is alcohol and the sensing material is a layer that includes H-ZSM 5.

24. The sensor of claim 1, wherein the sensing material is at least one of:

(i) a single carbon nanotube, and (ii) a plurality of carbon nanotubes.

25. The sensor of claim 24, wherein the analyte comprises CO₂.

26. The sensor of claim 25, wherein at least one carbon nanotube comprises at least one of:

(i) a single wall carbon nanotube, and (ii) a multi-wall carbon nanotube.

27. A method of producing a microelectromechanical system sensor, comprising:

forming a first insulating layer of a first side of a silicon wafer;

forming a second insulating layer on a second side of the silicon wafer, the second side being opposite the first side;

depositing and patterning of current carrying conductor on the first insulating layer on the first side of the silicon wafer;

etching away an area of the second insulating layer;

etching away a portion of the silicon wafer associated with the area to form a cavity substantially reaching the first insulating layer; and

forming a sensing layer on the first insulating layer proximate to the cavity, wherein the sensing layer is to change a resonant frequency of the first insulating layer proximate to the cavity upon exposure to an analyte; and

providing a sensing material for the sensing layer.

28. The method of claim 27, wherein the sensing material comprises at least one of:

(i) a single nanotube, and (ii) a plurality of nanotubes.

29. The method of claim 28, wherein at least one nanotube comprises at least one of:

(i) a single wall carbon nanotube, and (ii) a multi-wall carbon nanotube.

30. The method of claim 29, wherein said providing comprises:

adding at least one carbon nanotube via solution deposition of dispersed nanotubes in an appropriate solvent.

31. The method of claim 28, wherein the analyte comprises CO₂.

32. A microelectromechanical system sensor, comprising:

a spring element;

a sensing material on the spring element; and

a detector adapted to determine a resonant frequency associated with the spring element, wherein the resonant frequency changes upon the exposure of the sensing material to an analyte, and wherein the detector includes;

a conducting path through which an alternating current is to flow, and

a magnet having a magnetic field substantially normal to direction of current flow through the conducting path;

a reference spring element; and

a reference detector adapted to determine a reference resonant frequency associated with the reference spring element, wherein the reference resonant frequency does not change upon the exposure of the reference spring element to the analyte.

33. The sensor of claim 32, further comprising:

a wafer substantially parallel to and supporting the spring element, wherein a Lorenz force moves the spring element in a direction substantially normal to the wafer.

34. The sensor of claim 33, wherein the detector further comprises:

an amplitude measuring device, wherein the amplitude of spring element movement is measured over a plurality of alternating current frequencies to determine the resonant frequency.

35. The sensor of claim 34, wherein the amplitude measuring device comprises:

a conducting plane proximate to the conducting path wherein the amplitude is associated with an amount of capacitance between the conducting plane and conducting path.

36. The sensor of claim 34, wherein the amplitude measuring device comprises:

a strain gauge, wherein the amplitude is associated with an amount of strain created by the movement of the spring element.

37. The sensor of claim 34, wherein the amplitude measuring device comprises:

an optical source; and

an optical detector, wherein the amplitude is associated with an optical characteristic of the spring element.

38. The sensor of claim 32, wherein the spring element comprises a silicon nitride membrane.

39. A method of detecting an analyte, comprising:

determining a resonant frequency associated with a spring element having a sensing material; and

based on the resonant frequency, detecting the presence of the analyte.

40. The method of claim 39, wherein said determining comprises:

measuring amplitudes associated with each of a plurality of frequencies; and

selecting the frequency having the greatest amplitude as the resonant frequency.

41. A method of producing a microelectromechanical system sensor, comprising:

forming a first insulating layer of a first side of a silicon wafer;

forming a second insulating layer on a second side of the silicon wafer, the second side being opposite the first side;

depositing and patterning of current carrying conductor on the first insulating layer on the first side of the silicon wafer;

etching away an area of the second insulating layer;

etching away the silicon wafer associated with the area to form a cavity that reaches the first insulating layer; and

forming a sensing layer on the first insulating layer proximate to the cavity, wherein the sensing layer is to change a resonant frequency of the first insulating layer proximate to the cavity upon exposure to an analyte.

42. A system, comprising:

a microelectromechanical system sensor, including;

a spring element,

a sensing material on the spring element, and

a detector adapted to determine a resonant frequency associated with the spring element, wherein the resonant frequency changes upon the exposure of the sensing material to an analyte; and

a sensor dependent device.

43. The system of claim 42, wherein the sensor dependent device is associated with at least one of:

(i) a consumer device, (ii) an air quality device, (iii) an industrial process control device, (iv) a heating, ventilation, air conditioning device, (v) a breath analyzer, (vi) a blood alcohol measuring device, (vii) a blood glucose monitor device, (viii) an emissions management device, (ix) a leak detector, (x) a poison detector, (xi) a flammable material detector, (xii) a chemical weapon detector, (xiii) a toxic material detector, (xiv) an explosive material detector, (xv) a hydrogen economy detector, (xvi) a bioanalyte sensor, (xvii) a pharmaceutical process control device, and (xviii) an alarm.