Method using photo-induced and thermal bending of MEMS sensors

Details Method using photo-induced and thermal bending of MEMS sensors Method using photo-induced and thermal bending of MEMS sensors

1999-03-30

2001-11-06

Snay, Jeffrey (Department: 1743)

Chemistry: analytical and immunological testing

Measurement includes temperature change of the material...

C436S164000

Reexamination Certificate

active

06312959

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an instrument and a method for the detection of chemical analytes and physical forces in trace amounts using a coated surface of a microcantilever and measurement after imposing a photo-induced stress on the device.
2. Description of the Prior Art
Microeletromechanical structures are ultra-sensitive fabricated polycrystalline or single crystal devices useful for the measurement of physical forces and chemical interactions.
Vibrating quartz sensors have been used to measure antigen-antibody reactions as described in U.S. Pat. No. 4,236,893 to Rice. The detection of specific chemicals using chemical coatings over quartz crystals to obtain a bulk acoustical wave or surface acoustical wave resonator matrix detector is disclosed by Balato, U.S. Pat. No. 4,596,697. The measurement of ambient gas concentrations with a coated quartz piezoelectric crystal was disclosed by Minten et al., U.S. Pat. No. 4,637,987.
Improved sensors for immunoassays using surface acoustic waves on piezoelectric crystals are disclosed in U.S. Pat. No. 4,735,906 to Bastiaans, U.S. Pat. No. 4,847,193 to Richards et al., U.S. Pat. No. 5,501,986 to Ward et al., U.S. Patent No. 5,595,908 to Fawcett et al., U.S. Pat. No. 5,658,732 to Ebersole et al. and U.S. Pat. No. 5,705,399 to Larue. All of the above acoustical wave detectors are limited to exposure of a single reactive surface.
MEMS devices offer the potential of faster response, alternative methods of measurement of the observed changes, and smaller size.
Binnig et al.,
Phys. Rev. Lett.
56, 930 (1986) reported the use of a microfabricated beam as a mechanical stylus, which became the basis for atomic force microscopes. Detection with a split-segment photodetector allows measurement of very small movements at the cantilever tip. In 1992, Hoh et al. [
J. Am. Chem. Soc.,
114, 4917 (1992)] reported the resolution of hydrogen bonds at a force of 1×10
−11
N using v-shaped cantilevers of Si
3
N
4
.
Vibrating quartz crystal detectors in the shape of a tuning fork are disclosed for the detection of antibodies and other binding pairs in U.S. Pat. No. 5,179,028 to Vali et al. A refinement of the Vali et al. patent may be found in U.S. Pat. No. 5,323,636 which employs the tuning fork concept using GaAs for the substrate.
Gimzewski et al. reported the use of a coated Si cantilever as a micro-calorimeter using reflected light to measure the degree of bending of a cantilever as the result of a chemical reaction. [
Chem. Phys. Lett.,
217, 589 (1994)]. U.S. Pat. No. 5,411,709 to Furuki et al. discloses a method for gas detection using a vibrating microcantilever coated with a thin film of a dye which fluoresces or phosphoresces in the presence of an oxidizing or reducing gas.
Wachter et al., U.S. Pat. No. 5,445,008 describes a chemical vapor detector using a piezoelectric vibrated cantilever coated with a compound-selective surface having substantially exclusive affinity for the targeted compound. Upon attachment of the targeted compound to the surface coating, the resonance frequency of the vibrating cantilever changes in a concentration-dependant way as measured by the reflected beam from a laser diode received by a photodiode detector.
Properly coated microcantilevers can be used for sophisticated detection taking advantage of both the change in resonance frequency but also stress-induced bending of the sensor, as described and claimed in U.S. Pat. No. 5,719,324 to Thundat et al. A summary of uses for microcantilever sensors may be found in Thundat et al.,
Microscale Thermophysical Enoineering
1, 185 (1997).
The methods described above are subject to variations in coatings and require many different devices for any spectrum of detection. In addition, accurate quantitation of the result over a range of concentrations becomes more difficult because of the need to be able to measure absolute values of deflection when resonance methods are not used.
BRIEF SUMMARY OF THE INVENTION
It is an object of this invention to provide a MEMS detector for chemical species and physical forces having a high degree of accuracy and reproducability over a greater dynamic range.
It is an object of this invention to provide a tunable MEMS detector having a greater dynamic range.
It is an object of this invention to provide a less expensive MEMS detection method by simplifying the fabrication process.
It is an object of this invention to provide a MEMS chemical sensor that can be made to become highly stressed before exposure to analytes. It is well known that the more stressed a surface is the more efficiently it can adsorb analytes or interact with analytes preset. The highly stressed state of the MEMS device can be accomplished using a photo-induced (electronic) stress or just thermal stress. This can apply equally to the coating or the substrate.
It is an object of this invention to provide a MEMS chemical sensor that can be made to become more selective by introducing electronic states in the surface using for example photon irradiation. In effect this would accomplish the same task as if different coatings were used. The specificity of a chemically selective layer can be tuned or even altered by the presence of electronic states. This applies to the coating, substrate, or adsorbed analytes themselves.
These and other objectives can be achieved by using the band gap of a semiconductor from which a MEMS device is fabricated to adjust the stress-induced bending of the microcantilever in the presence of chemical analytes and physical forces acting on the device.


REFERENCES:
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patent: 5372930 (1994-12-01), Colton et al.
patent: 5411709 (1995-05-01), Furuki et al.
patent: 5445008 (1995-08-01), Wachter et al.
patent: 5464977 (1995-11-01), Nakagiri et al.
patent: 5479024 (1995-12-01), Hillner et al.
patent: 5719324 (1998-02-01), Thundat et al.
patent: 5737086 (1998-04-01), Gerber et al.
patent: 5770856 (1998-06-01), Fillard et al.
patent: 5918263 (1999-06-01), Thundat
patent: 5977544 (1999-11-01), Datskos et al.
patent: 6096559 (2000-08-01), Thundat et al.
patent: 2 169 418 A (1985-01-01), None
patent: WO 97/26556 (1997-07-01), None
Lang, H. P. et al., “The Nanomechanical NOSE” Technical Digest; pp. 9-13, 1999.
MEMS Sensos and WirelessTelemetry for Distributed Systems, by C.L. Britton, Jr., et al., Presented at SPIE 5th International Symposium on Smart Materials and Structures, Mar. 2, 1998, San Diego, CA (8 pages total).
Measuring Intermolecular Binding Forces With the Atomic-Force Microscope: The Magnetic Jump Method, by Jan H. Hoh et al.,Proceedings, 52nd Annual Meeting o Microscopy Society of America, Jul. 31-Aug. 5, 1994, pp. 1054-1055.
Microcantilever Sensors, by T. Thundat, et al.,Microscale Thermophysical Engineering, 1:185-199, 1997.

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