U.S. patent application number 11/845680 was filed with the patent office on 2011-01-06 for self-sensing array of microcantilevers chemical detection.
Invention is credited to Jesse D. Adams.
Application Number | 20110003718 11/845680 |
Document ID | / |
Family ID | 36660250 |
Filed Date | 2011-01-06 |
United States Patent
Application |
20110003718 |
Kind Code |
A1 |
Adams; Jesse D. |
January 6, 2011 |
SELF-SENSING ARRAY OF MICROCANTILEVERS CHEMICAL DETECTION
Abstract
The invention provides a chemical detection system for detecting
at least one target chemical species, including a self-sensed
cantilevered probe array having a plurality of self-sensed
cantilevered probes, at least one chemical-sensitive coating
material applied to at least one cantilevered probe in the
cantilevered probe array, and an interface circuit that is coupled
to the cantilevered probe array. At least one cantilevered probe in
the cantilevered probe array exhibits a shifted cantilevered probe
response when the cantilevered probe array is exposed to the target
chemical species and the interface circuit actuates the
cantilevered probe. A handheld chemical detection system and a
method of operation are also disclosed.
Inventors: |
Adams; Jesse D.; (Reno,
NV) |
Correspondence
Address: |
UNR/DRI Technology Transfer Office
UNR-DRI Technology Transfer Office, Mail stop 321, 1664 N. Virginia St
Reno
NV
89557
US
|
Family ID: |
36660250 |
Appl. No.: |
11/845680 |
Filed: |
August 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10967748 |
Oct 15, 2004 |
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11845680 |
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60512504 |
Oct 17, 2003 |
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Current U.S.
Class: |
506/39 |
Current CPC
Class: |
G01Q 60/24 20130101;
G01N 29/022 20130101; G01N 33/54366 20130101; G01N 2291/0255
20130101; G01N 2291/0257 20130101; G01N 33/0009 20130101; G01N
2291/0256 20130101; G01N 2291/106 20130101; G01N 29/4418 20130101;
G01Q 10/045 20130101; G01N 33/54373 20130101; G01N 29/46 20130101;
G01N 29/036 20130101; G01N 2291/0427 20130101; G01N 2291/014
20130101; G01N 2291/018 20130101 |
Class at
Publication: |
506/39 |
International
Class: |
C40B 60/12 20060101
C40B060/12 |
Claims
1-68. (canceled)
69. A chemical detection system for detecting at least one target
chemical species, comprising: a frequency-differentiated
cantilevered probe array comprising a plurality of cantilevered
probes, each cantilevered probe comprising: a piezoelectric layer;
a treated section, wherein the treated sections of the plurality of
cantilevered probes are different from one another; a first
electrode electrically coupled to the piezoelectric layer; and a
second electrode electrically coupled to the piezoelectric layer; a
first electrical lead electrically coupled to a first electrode of
at least one of the plurality of cantilevered probes and in
electrical communication with the first electrode of each of the
plurality of cantilevered probes; a second electrical lead
electrically coupled to a second electrode of at least one of the
plurality of cantilevered probes and in electrical communication
with the second electrode of each of the plurality of cantilevered
probes; an interface circuit electrically coupled to the first and
second electrical leads and configured to actuate the cantilevered
probes; a sensing circuit electrically coupled to the first and
second electrical leads; and wherein the cantilevered probes are
actuated when, through the first and second leads, a drive voltage
is applied to the piezoelectric layer by the interface circuit thus
generating an electrical response transmitted to the sensing
circuit and at least one cantilevered probe in the array exhibits a
shifted electrical response when the cantilevered probe array is
exposed to the target chemical species and the at least one
cantilevered probe is actuated by the interface circuit as a result
of the exposure of the treated section to the target chemical
species.
70. The chemical detection system of claim 69 wherein the first and
second electrodes of the plurality of cantilevered probes are
electrically coupled to one another, the plurality of cantilevered
probes thus being connected in series to the first and second
leads.
71. The chemical detection system of claim 69 wherein the first
lead is electrically coupled to the first electrode of each of the
plurality of cantilevered probes and the second lead is
electrically coupled to the second electrode of each of the
plurality of cantilevered probes, the first and second leads thus
being connected in parallel to the plurality of cantilevered
probes.
72. The chemical detection system of claim 69 wherein the
cantilevered probe array comprises a network of series-connected
and parallel-connected cantilevered probes electrically connected
to a pair of cantilevered probe array drive pads.
73. The chemical detection system of claim 69 wherein the interface
circuit comprises an adjustable frequency generator that is scanned
through a predetermined frequency range.
74. The chemical detection system of claim 69 wherein the interface
circuit comprises an impedance analyzer that is scanned through a
resonant frequency of the at least one cantilevered probe in the
cantilevered probe array.
75. The chemical detection system of claim 69 wherein the interface
circuit comprises an oscillator circuit operating at a resonant
frequency of the at least one cantilevered probe in the
cantilevered probe array.
76. The chemical detection system of claim 69 wherein the interface
circuit comprises an oscillator circuit operating at a
predetermined frequency, wherein the predetermined frequency is
off-resonance with respect to the at least one cantilevered probe
in the cantilevered probe array.
77. The chemical detection system of claim 69 wherein the interface
circuit comprises an impulse circuit for applying an electrical
impulse to the cantilevered probe array.
78. The chemical detection system of claim 69 wherein the interface
circuit includes a fast Fourier transform generator to perform a
fast Fourier transform on the shifted cantilevered probe
response.
79. The chemical detection system of claim 69 wherein the interface
circuit detects a shifted electrical response from the at least one
actuated cantilevered probe.
80. The chemical detection system of claim 79 wherein the shifted
electrical response comprises one of a shifted resonant frequency,
a shifted Q factor, a shifted impedance, and a shifted deflection
amplitude.
81. The chemical detection system of claim 69 further comprising: a
controller in communication with the interface circuit; wherein the
controller receives a shifted electrical response from a set of
cantilevered probes in the cantilevered probe array, and wherein
the target chemical species is determined based on the shifted
electrical response.
82. The chemical detection system of claim 69 further comprising: a
controller in communication with the interface circuit; wherein the
controller receives a shifted electrical response from a set of
cantilevered probes in the cantilevered probe array, and wherein
the target chemical species is determined based on a comparison
between the shifted electrical response and a reference set of
electrical responses.
83. The chemical detection system of claim 82 wherein the reference
set of electrical responses comprises measured responses from known
exposure conditions.
84. The chemical detection system of claim 69 wherein the
chemical-sensitive coating material comprises a coating applied
through a mask disposed on a portion of the at least one
cantilevered probe.
85. The chemical detection system of claim 69 wherein the
chemical-sensitive coating material comprises a non-homogeneous
coating material applied to a set of cantilevered probes in the
cantilevered probe array.
86. The chemical detection system of claim 69 further comprising: a
reference cantilevered probe in the cantilevered probe array,
wherein the reference cantilevered probe provides a reference
electrical response when the cantilevered probe array is exposed to
the target chemical species.
87. The chemical detection system of claim 69 further comprising: a
species attraction electrode disposed on the at least one
cantilevered probe in the cantilevered probe array to allow
application of a species attraction potential.
88. The chemical detection system of claim 69, wherein a resistive
heater is coupled to at least one cantilevered probe in the
cantilevered probe array and the chemical detection system further
comprises a heater circuit electrically coupled to the resistive
heater.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This utility application claims the priority benefit of, and
hereby incorporates by reference in its entirety, the applicant's
prior U.S. Provisional Application No. 60/512,504, filed Oct. 17,
2004.
FIELD OF THE INVENTION
[0002] This invention relates generally to chemical-sensing
methods, and in particular, relates to a method and system for
sensing specific chemicals and biological materials using an array
of piezoelectrically driven cantilevered probes with selectively
disposed chemical sensitive coatings.
BACKGROUND OF THE INVENTION
[0003] Micromachined cantilevers are used in atomic force
microscopy (AFM) for surface scanning and for chemical, biological,
and other sensing applications. Micromachined cantilevers may
become the basis for specialized, ultraminiature, ultrasensitive
sensors for detection of specific target chemical species such as
chemical compounds, bioactive agents, or toxins. Miniaturized
chemical sensors hold promise for applications needing sensitive
chemical detection, quality control of materials processing, and
measurements of small or limited quantities of a chemical or
biological material. Resonance-based detection has been
demonstrated specifically for sensing mercury vapor, ultraviolet
radiation, relative humidity, magnetic susceptibility, and
sub-nanogram masses.
[0004] AFM is a method of measuring surface topography on a scale
typically from a few angstroms or less to a hundred micrometers or
more. The technique involves imaging a sample through the use of a
probe or tip suspended from one end of a microcantilever. A surface
is probed with the tip, and the interaction between the tip and
sample is measured. Physical topography, surface chemistry, charge
density, magnetic properties, local temperature and other surface
properties can be analyzed.
[0005] Lasers can be used for optical detection of cantilever
movement, though AFM systems using lasers require comparably high
power on the order of milliwatts, need alignment, have limited
resolution, and are prone to drift because of the size of the
optical path. Current systems typically require external lighting
for sample illumination and setup, and are not very compact because
of the long optical path, the need to have the photodetector at an
ample distance from the sample, and constrained viewing and
positioning systems for optical alignment. Sample testing in
liquids such as water or saline solution presents additional
difficulties for optical sensing due to aberrations and refraction
of the light beam traversing the fluid.
[0006] Lasers have been used to detect frequency changes of a
microcantilever that is oscillated by a piezoelectric transducer,
as taught in "Microbar Sensor," Wachter et al., U.S. Pat. No.
5,445,008 issued Aug. 29, 1995. Oscillation frequency changes are
detected by a center-crossing photodiode that responds to a laser
diode beam reflected from the microcantilever surface resulting in
an output frequency from the photodiode that is synchronous with
the microcantilever frequency.
[0007] AFM systems using microcantilevers and laser detection have
been used for analyzing explosive gas molecules adsorbed onto the
microcantilevers, as described in "Microcantilever Detector for
Explosives," Thundat, U.S. Pat. No. 5,918,263 issued Jun. 29, 1999.
Analysis can be made of the laser beam reflected by the
heat-induced deflection and transient resonant response of the
microcantilever.
[0008] Because power efficiency is important to the size, lifetime,
and utility of a cantilever sensor, alternative detection schemes
to those using lasers have been proposed. Notably, capacitive
systems are being developed to monitor cantilever deflection. While
a low-power option, capacitive cantilever sensing is most suitable
under vacuum conditions to avoid excessive air damping between the
two electrodes of the capacitor. Other limitations of capacitive
schemes include small tolerances for fabrication and coatings of a
cantilever, a reliance on a small sensing gap size, and
difficulties with sensing in liquid solutions.
[0009] In an alternative sensing scheme to optical detection or
capacitive sensing, AFM systems in a vibrating or tapping mode may
use actuated piezoresistive cantilevers. Piezoresistive sense
methods are more compact than optical systems, though they can
self-heat and cause drift. Furthermore, piezoresistive sensing
typically consumes large portions of available power when used in a
portable device. A typical piezoresistive cantilever, which also
can use milliwatts of power, is a
micro-electrical-mechanical-system (MEMS) device, micromachined
from bulk silicon with a piezoelectric film patterned along a
portion of the microcantilever. At the free end of the cantilever
is a tip with nanometer-scale radius, optimally shaped to probe the
sample surface. The microcantilever is displaced by voltage applied
to the piezoelectric actuator, resulting in a controlled vertical
movement of the tip. Control electronics drive the microcantilever
while simultaneously positioning it vertically to track the sample
topography and follow the surface features. A macro-scale position
actuator may be used to null the position of the cantilever,
following the topology of the sample as the probe is scanned over
the surface.
[0010] Chemicals can be sensed based on frequency shifts of
microcantilevers treated with a compound-selective substance, as
disclosed in "Microcantilever Sensor," Thundat et al., U.S. Pat.
No. 5,719,324 issued Feb. 17, 1998. A microsensor with a cantilever
attached to a piezoelectric transducer is capable of detecting
changes in the resonance frequency and the bending of the vibrated
cantilever in a monitored atmosphere. Upon insertion into a
monitored atmosphere, molecules of a targeted chemical to be sensed
attach to the treated regions of the microcantilever resulting in a
change in oscillating mass as well as a change in microcantilever
spring constant thereby influencing the resonant frequency of the
microcantilever oscillation.
[0011] Oscillating silicon nitride cantilevered beams coated with a
thin gold film have been used to detect mercury vapor in air due to
changes in cantilever resonant frequency and stress levels induced
in the gold overlayer as described by Thundat, et al., in
"Detection of Mercury Vapor Using Resonating Microcantilevers,"
Appl. Phys. Lett. 66 (13), 27 Mar. 1995, pp. 1695-1697. An uncoated
microcantilever can be used for chemical sensing by exciting charge
carriers into or out of surface states with discrete photon
wavelengths as disclosed by Thundat, et al., in "Uncoated
Microcantilevers as Chemical Sensors," U.S. Pat. No. 6,212,939,
issued Apr. 10, 2001. Attempts at DNA sequencing and detection
using an AFM is described by Allen in "Method and Apparatus for DNA
Sequencing Using a Local Sensitive Force Detector," U.S. Pat. No.
6,280,939, issued Aug. 28, 2001.
[0012] An exemplary cantilever with a piezoelectric drive and a
piezoresistive sense is disclosed in "Atomic Force Microscope for
High Speed Imaging Including Integral Actuator and Sensor," Minne
et al., U.S. Pat. No. 5,883,705 issued Mar. 16, 1999, and
"Cantilever for Scanning Probe Microscope Including Piezoelectric
Element and Method of Using the Same," Minne et al., U.S. Pat. No.
5,742,377 issued Apr. 21, 1998. When the scanning probe microscope
(SPM) operates in the constant force mode, the piezoelectric
element is used to control the tip-sample separation. Since the
resonant frequency of the piezoelectric element is substantially
higher than that of conventional piezoelectric tube scanners, much
higher scan rates can be achieved. When the SPM operates in the
dynamic or intermittent contact mode, a superimposed AC-DC signal
is applied to'the piezoelectric element, and the latter is used to
vibrate the cantilever as well as to control the tip-sample
spacing.
[0013] Piezoelectrically driven cantilevers have been proposed to
eliminate the need for external actuators. An exemplary
self-actuating cantilever is described in "Active Probe for an
Atomic Force Microscope and Method of Use Thereof," Adderton et
al., U.S. Pat. No. 6,530,266 issued Mar. 11, 2003 and "Atomic Force
Microscope for High Speed Imaging Including Integral Actuator and
Sensor," Adderton et al., U.S. Pat. No. 6,189,374 issued Feb. 20,
2001. This system includes a self-actuated cantilever having a
Z-positioning element integrated therewith and an oscillator that
oscillates the self-actuated cantilever at a frequency generally
equal to a resonant frequency of the self-actuated cantilever.
[0014] In response to the growing interest in using cantilevers for
chemical sensing, researchers are developing systems with multiple
cantilever sensors or modular sensor array systems to characterize
larger numbers of material samples more quickly. An example of an
system of multiple cantilevers in a substantially linear
configuration that uses individually-selectable cantilevers with a
different resonance frequency for each is disclosed in "Multiprobe
and Scanning Probe Microscope," Shimizu et al., U.S. Pat. No.
6,469,293 issued Oct. 22, 2002. A modular sensor array system has
been suggested for rapid deposition of sample chemicals on sensor
arrays in "Sensor Array-Based System and Method for Rapid Materials
Characterization," Mansky et al., U.S. Pat. No. 6,535,824, issued
Mar. 18, 2003 and "Sensor Array for Rapid Materials
Characterization," Mansky et al., U.S. Pat. No. 6,535,822, issued
Mar. 18, 2003. One intended goal is to eliminate the need for
multiple materials characterization machines and the need for
application-specific active circuitry within the sensor arrays
themselves.
[0015] In light of the discussion above, an improved system for
sensing chemicals is desirable that is more compact and
power-efficient than piezoresistively or optically sensed AFM
cantilevers, does not require off-chip actuation for frequency
measurements, does not require individual addressing of each
cantilever to determine the natural frequencies, is capable of
operating in liquid or gas, and generates less unwanted heat than
other AFM cantilever systems. Cantilevers need to be small and
light for rapid detection of minute concentrations of target
chemicals and biomaterials. Therefore, a desirable method and
system for chemical sensing incorporates these improvements and
overcomes the deficiencies described above.
SUMMARY OF THE INVENTION
[0016] One aspect of the invention provides a chemical detection
system for detecting at least one target chemical species. The
system includes a self-sensed cantilevered probe array with a
plurality of self-sensed cantilevered probes; one or more
chemical-sensitive coating materials applied to at least one
cantilevered probe in the cantilevered probe array; and an
interface circuit coupled to the cantilevered probe array. One or
more chemical-sensitive coated cantilevered probes in the
cantilevered probe array exhibit a shifted cantilevered probe
response when the cantilevered probe array is exposed to the target
chemical species and is actuated by the interface circuit.
[0017] Another aspect of the invention is a method of chemical
detection. A self-sensed cantilevered probe is exposed to a target
chemical species and the exposed cantilevered probe array is
actuated. A cantilevered probe response from at least one
self-sensed cantilevered probe in the cantilevered probe array is
detected, and the target chemical species is determined based on
the detected cantilevered probe response.
[0018] Another aspect of the invention is a handheld system for
sensing a target chemical species including an enclosure, a
self-sensed cantilevered probe array coupled to the enclosure, at
least one chemical-sensitive coating material applied to at least
one cantilevered probe in the cantilevered probe array, and an
interface circuit coupled to the cantilevered array. The enclosure
includes an inlet port for the ingression of the target chemical
species and an outlet port for the egression of the target chemical
species. The cantilevered probe array includes a plurality of
self-sensed cantilevered probes. At least one cantilevered probe in
the cantilevered probe array exhibits a shifted cantilevered probe
response when the cantilevered probe array is exposed to the target
chemical species and is actuated by the interface circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The current invention is illustrated by the accompanying
drawings of various embodiments and the detailed description given
below. The drawings should not be taken to limit the invention to
the specific embodiments, but are for explanation and
understanding. The detailed description and drawings are merely
illustrative of the invention rather than limiting, the scope of
the invention being defined by the appended claims and equivalents
thereof. The foregoing aspects and other attendant advantages of
the present invention will become more readily appreciated by the
detailed description taken in conjunction with the accompanying
drawings. Various embodiments of the present invention are
illustrated by the accompanying figures, wherein:
[0020] FIG. 1 illustrates a chemical detection system for detecting
at least one target chemical species, in accordance with one
embodiment of the current invention;
[0021] FIG. 2 illustrates a self-sensed cantilevered probe array,
in accordance with one embodiment of the current invention;
[0022] FIG. 3 is a schematic diagram of a cantilevered probe array
with series-connected cantilevered probes electrically connected to
a pair of cantilevered probe array drive pads, in accordance with
one embodiment of the current invention;
[0023] FIG. 4 is a schematic diagram of a cantilevered probe array
with parallel-connected cantilevered probes electrically connected
to a pair of cantilevered probe array drive pads, in accordance
with one embodiment of the current invention;
[0024] FIG. 5 is a schematic diagram of a cantilevered probe array
with a network of series-connected and parallel-connected
cantilevered probes electrically connected to a pair of
cantilevered probe array drive pads, in accordance with one
embodiment of the current invention;
[0025] FIG. 6a is a schematic diagram of a controller and an
interface circuit connected to a self-sensed cantilevered probe
array, in accordance with one embodiment of the current
invention;
[0026] FIG. 6b is a plot of cantilevered probe responses from a
self-sensed cantilevered probe array scanned through a
predetermined frequency range, in accordance with one embodiment of
the current invention;
[0027] FIG. 7 illustrates a method for applying a
chemical-sensitive coating material to a cantilevered probe array
with a mask, in accordance with one embodiment of the current
invention;
[0028] FIG. 8 illustrates a top view of a self-sensed cantilevered
probe including a selectively deposited coating, a heater, and a
species attraction electrode;
[0029] FIG. 9 illustrates a handheld system for sensing a target
chemical species, in accordance with one embodiment of the current
invention;
[0030] FIG. 10 is a flow chart of a method for chemical detection,
in accordance with one embodiment of the current invention; and
[0031] FIG. 11 is a flow chart of a method for chemical detection,
in accordance with another embodiment of the current invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] FIG. 1 illustrates a chemical detection system for detecting
at least one target chemical species, in accordance with one
embodiment of the present invention. The chemical detection system
10 includes a self-sensed cantilevered probe array 20 with a
plurality of self-sensed cantilevered probes 30. Self-sensed
cantilevered probes have suspended cantilevered elements with a
piezoelectric drive 32 comprised of a deposited layer of zinc oxide
(ZnO), lead zircanate titinate (PZT), or other piezoelectric
material that bends, deflects and vibrates the cantilevered element
when excited or actuated with an applied drive voltage. The
piezoelectric material generates a voltage as the cantilevered
probes bend or vibrate, and can be used to sense cantilevered probe
motions as well as drive cantilevered probes 30, referred to herein
as self-sensing. At least one chemical-sensitive coating material
34 is applied to one or more cantilevered probes 30 in cantilevered
probe array 20 to allow for chemical detection and specificity. One
or more cantilevered probes 30 in cantilevered probe array 20 is
coated or otherwise treated to detect target chemical species 12.
An interface circuit 40, which is coupled to cantilevered probe
array 20, actuates and senses motions of cantilevered probes 30.
When cantilevered probe array 20 is exposed to a target chemical
species 12 and is actuated by interface circuit 40, one or more
cantilevered probes 30 in cantilevered probe array 20 exhibit a
shifted cantilevered probe response.
[0033] Cantilevered probes 30 in cantilevered probe array 20 are
frequency-differentiated such that cantilevered probes 30 having
different masses or effective spring constants exhibit different
resonant frequencies. Cantilevered probes 30 can be manufactured,
for example, with small differences in cantilever lengths,
resulting in separations in resonant frequencies so that the
resonant frequency of each cantilevered probe 30 in an array is
able to be detected with as few as two wires connected to
cantilevered probe array 20. Thus, cantilevered probe arrays 20
with two or more cantilevered probes 30 can be packaged and
connected to interface circuit 40 with a minimal number of bond
pads, interconnection traces and bond wires to external interface
and control electronics. Parallel arrays of cantilevered probes 30
can be configured with elements that number from a few to massively
parallel arrays with a million or more cantilevered probes 30 on
one substrate or die. Groups of cantilevered probe arrays 20 may be
connected during on-chip trace definition, while wire-bonding to a
leadframe or package, or at the socket or board level.
[0034] Non-overlapping, independent and orthogonal chemical-sensing
effects on individual cantilevered probes 30 in cantilevered probe
array 20 may be desirable but not necessary when many cantilevered
probes 30 with various coatings and coating thicknesses are used
for detection. Signal processing and pattern recognition of the
resonance-frequency data from multiple cantilever probes 30 may be
employed to differentiate between various target chemical species
in varying concentrations having sometimes small and sometimes null
effects. Differentiation between similar chemical substances can be
made and their constituency and concentration can be determined in
a system where a variety of coatings are applied to multiple
cantilevered probes 30. Chemical detection system 10 can detect one
or more target chemical species 12 such as mercury, hydrogen, an
alcohol, water vapor, an explosive material, a chemical element, a
chemical compound, an organic material, an inorganic material, a
gaseous substance, a liquid, a biological material, a DNA strand, a
bioactive agent, a toxin, and a combination thereof. Chemical
species refers to any chemical or biological material.
[0035] One or more cantilevered probes 30 respond when exposed to
target chemical species 12. Cantilevered probes 30 may respond by
absorbing, adsorbing, or otherwise reacting to target chemical
species 12. When exposed to target chemical species 12,
cantilevered probes 30 may increase or decrease in mass, or become
more rigid or less rigid. In one example, cantilevered probe 30
comprises a patterned layer of gold. When exposed to mercury, the
two react to form an amalgam. The gold-mercury amalgam adds mass to
cantilevered probe 30 and therefore tends to decrease the resonant
frequency of cantilevered probe 30. Amalgam formation, however,
increases the mechanical stiffness of cantilevered probe 30 thereby
increasing its natural resonant frequency. The two effects tend to
cancel each other, though one effect can be made dominant by
careful selection and placement of chemical-sensitive coating
material 34 on cantilevered probe 30.
[0036] Target chemical species 12, which may be located in a liquid
or gas carrier 14 such as air or water, in a low-pressure gas, or a
plasma, are transported in a forced or free manner towards
cantilevered probes 30 where they contact surfaces of cantilevered
probes 30 and invoke shifts in resonant frequency, Q factor,
impedance, or deflection amplitudes.
[0037] Cantilevered probe array 20 is actuated with an excitation
voltage applied to piezoelectric drive 32 disposed on each
cantilevered probe 30 in cantilevered probe array 20. To reduce the
number of external connections, a group of cantilevered probes 30
may be connected in series and electrically connected to a pair of
cantilevered probe array drive pads 24, which in turn is
electrically connected to interface circuit 40. While this
configuration can increase the series resistance of the string,
differentiation of individual cantilevered probes 30 may be made
with detection of signals at or near the resonant frequency of
selected cantilevered probe 30. Alternatively, a group of
cantilevered probes 30 may be connected in parallel and
electrically connected to a pair of cantilevered probe array drive
pads 24, increasing the effective capacitance and decreasing the
effective resistance, while still allowing differentiation of
individual cantilevered probe responses based on frequency.
Alternatively, cantilevered probes 30 may be connected in a network
of series-connected and parallel-connected cantilevered probes with
frequency-identifiable addressable elements.
[0038] Interface circuit 40 provides excitation voltages for the
piezoelectric material on cantilevered probes 30 and senses
deflections and vibrations of cantilevered probes 30 with the same
piezoelectric material. In one example, interface circuit 40
includes an adjustable frequency generator that is scanned through
a predetermined frequency range to excite one or more cantilevered
probes 30 in cantilevered probe array 20. In another example,
interface circuit 40 includes an impedance analyzer that is scanned
through a resonant frequency of at least one cantilevered probe 30,
measuring the magnitude and phase from cantilevered probes 30 and
monitoring for any variations in the impedance as cantilevered
probes 30 are exposed to one or more target chemical species 12. In
another example, interface circuit 40 includes an oscillator
circuit operating at a resonant frequency of at least one
cantilevered probe 30 in cantilevered probe array 20. In another
example, interface circuit 40 includes an oscillator circuit
operating at a predetermined frequency that is near, yet
off-resonance with respect to one or more cantilevered probes 30 in
cantilevered probe array 20, so that as the resonant frequency of
the selected cantilevered probe 30 shifts, a large output signal
can be obtained as the resonant frequency shifts and moves towards
the predetermined frequency, resulting in higher amplitudes of
vibration and therefore higher output signals. The predetermined
frequency may be set, for example, slightly above or slightly below
the resonant frequency of one of cantilevered probes 30. In another
example, the amplitude of bending and vibration is monitored as
cantilevered probe 30 strikes against a fixed or adjustable
mechanical stop such as a piezoelectric slab or a piezotube. In
another example, interface circuit 40 includes an impulse circuit
for applying an electrical impulse to cantilevered probe array 20,
and ring-down of cantilever probes 30 is monitored. In another
example, noise such as pink noise or white noise is applied to
excite cantilevered probe array 20. In another example, interface
circuit 40 includes a network analyzer for detecting signals from
cantilevered probe array 20. Interface circuit 40 or controller 50
may include a fast Fourier transform generator to perform a fast
Fourier transform (FFT) on the shifted cantilevered probe response
and provide respective frequencies of cantilevered probes 30 in
cantilevered probe array 20 for correlation with previously
measured probe responses and determination of target chemical
species 12.
[0039] Interface circuit 40 detects shifted cantilevered probe
responses from one or more actuated cantilevered probes 30 in
cantilevered probe array 20. Shifted cantilevered probe responses
include, for example, a shift in a resonant frequency of one or
more cantilevered probes 30, a shift in a quality (Q) factor of one
or more cantilevered probes 30, a shift in impedance of one or more
cantilevered probes 30, a shift in deflection amplitude of one or
more cantilevered probes 30, or a combination thereof. With
exposure to target chemical species 12, one or more cantilevered
probes 30 in cantilevered probe array 20 can exhibit shifts.
Similarly, with exposure to more than one target chemical species
12, one or more cantilevered probes 30 in cantilevered probe array
20 may exhibit shifts from which multiple target chemical species
12 can be determined.
[0040] A controller 50 such as a central processing unit (CPU), a
digital signal processor (DSP), a microcontroller, or a
field-programmable gate array (FPGA) may be included in chemical
detection system 10 to execute programmed code and provide
monitoring, controlling and analyzing functions. Controller 50 is
in electrical communication with interface circuit 40 and may be
located, for example, on substrate 22 along with cantilevered probe
array 20, within enclosure 60 on the same circuit board or in the
same package as cantilevered probe array 20, or located remotely
with respect to enclosure 60. Controller 50 may internally contain
the functions and capabilities of interface circuit 40. Controller
50 receives shifted cantilevered probe responses from a set of one
or more cantilevered probes 30 in cantilevered probe array 20.
Target chemical species 12 may be determined based on the shifted
cantilevered probe response using, for example, an algebraic model
that relates shifts in cantilevered probe responses to target
chemical species and concentration. Alternatively, target chemical
species 12 may be determined based on a comparison between the
shifted cantilevered probe responses and a reference set of
cantilevered probe responses. Such reference sets can be obtained
by exposing cantilevered probes 30 to controlled environments with
known target chemical species and concentrations during calibration
at the factory or on site. Controller 50 can determine one or more
target chemical species 12 through pattern recognition techniques,
statistical processes, and fuzzy logic with comparison to the
reference set of cantilevered probe responses. The reference set of
cantilevered probe response comprises, for example, a learned set
obtained from shifts in cantilevered probe responses by
cantilevered probes 30 that are exposed to known target chemical
species and concentrations under controlled laboratory or factory
environments.
[0041] Chemical-sensitive coating material 34 is applied to at
least a portion of one or more cantilevered probes 30 of
cantilevered probe array 20. For example, chemical-sensitive
coating material 34 may be applied to the topside or bottom side of
one or more cantilevered probes 30 or to portions thereof.
Chemical-sensitive coating material 34 includes, for example, an
epoxy resin such as Novolac.TM., a fluoropolymer such as
FluoroPel.TM., a gold layer, a palladium layer, an
alcohol-absorbent polymer, a water-absorbent material, a
chemical-sensitive polymer, a chemical-sensitive layer, a
biosensitive material, a thiol, and combinations thereof.
[0042] Various application methods are used to deposit or apply
coating materials and to treat surfaces of cantilevered probes 30.
Chemical-sensitive coating materials 34 comprise, for example, a
dipped coating, a sprayed coating, or a dispensed coating disposed
on at least of portion of one or more cantilevered probes 30. An
exemplary chemical-sensitive coating material 34 includes a masked
coating disposed on a portion of one or more cantilevered probes
30. In an alternative application method, a non-homogeneous coating
material is applied to a set of cantilevered probes 30 in
cantilevered probe array 20, such that constituents of the
non-homogeneous coating material are deposited on cantilevered
probes 30 with suitable variations in composition, coverage, and
thickness.
[0043] In one embodiment of the present invention, chemical
detection system 10 includes one or more reference cantilevered
probes in the cantilevered probe array. The reference cantilevered
probe provides a reference cantilevered probe response when
cantilevered probe array 20 is exposed to target chemical species
12. Reference cantilevered probes are formed, for example, with no
coating materials disposed thereon to reduce or eliminate
sensitivity to target chemical species 12. Alternatively, reference
cantilevered probes have an inert coating disposed on the surface
to reduce or eliminate sensitivity to target chemical species 12.
Alternatively, one or more reference cantilevered probes are
mechanically isolated from exposure to target chemical species 12
while other portions of cantilevered probe array 20 are
exposed.
[0044] In cases where heating of select cantilevered probes 30
burns off, evaporates off, or otherwise cleans and resets
cantilevered probe 30 to a nascent condition, a resistive heater 36
may be coupled to at least one cantilevered probe 30 in the
cantilevered probe array 20. Resistive heater 36 may be formed with
a resistive layer disposed on the surface of or formed within
cantilevered probe 30. Exemplary resistive heaters 36, which may be
connected in series or parallel or individually connected are
formed on one, several, or all cantilevered probes 30 within
cantilevered probe array 20. Resistive heaters 36 also may be used
to react a target chemical species on cantilevered probe 30 by
heating the probe to a predetermined temperature where the reaction
can occur. Alternatively, resistive heaters 36 may be used to
ignite or deflagrate condensate of explosive vapors on cantilevered
probes 30.
[0045] Species attraction electrodes 38 disposed on cantilevered
probes 30 can be used to apply voltage to preferentially attract
target chemical species 12 or to allow the monitoring of
electrochemical reactions in the vicinity of cantilevered probes
30. Species attraction electrodes 38, which may be disposed on one
or more cantilevered probes 30 in cantilevered probe array 20,
allow the application of a species attraction potential.
[0046] Exemplary chemical detection system 10 contains one or more
cantilevered probe arrays 20 in an enclosure 60, which includes an
inlet port 62 and an outlet port 64 for transport of target
chemical species 12 and carriers 14. Target chemical species 12
enters enclosure 60 through inlet port 62 and is exposed to
cantilevered probe array 20. Target chemical species 12 or
by-products thereof exit through outlet port 64. Enclosure 60 may
include filters, scrubbers, and other media treatment elements to
aid in the detection of target chemical species 12.
[0047] A transport mechanism 66 such as a pump or a fan with
ductwork or piping may be included for transporting target chemical
species 12 to cantilevered probe array 20.
[0048] A concentrator 68 such as a pressurizing system or a
condenser and heater system may be included to concentrate target
chemical species 12 proximal to cantilevered probe array 20 for
detection of target chemical species 12.
[0049] Chemical detection system 10 may be connected to a local
area network (LAN), a wide area network (WAN), the Internet, or
other networked communication system via one or more wired or
wireless connections.
[0050] Chemical detection system 10 may be installed, for example,
into an air handling system of a building or airport that has many
inlets, into a standalone unit with a portal for chemical
detection, and into handheld units for portable use. Chemical
detection system 10 may be installed in shipping containers and
crates during storage and transit for chemical detection and
monitoring.
[0051] FIG. 2 illustrates a self-sensed cantilevered probe array,
in accordance with one embodiment of the present invention.
Self-sensed cantilevered probe array 20 includes a plurality of
cantilevered probes 30 on a substrate 22. At least one
chemical-sensitive coating material 34 is applied to one or more
cantilevered probes 30 in cantilevered probe array 20. Variations
in length or thickness of cantilevered probes 30 and variations in
the thickness and coverage of applied coatings allow frequency
differentiation between cantilevered probes within cantilevered
probe array 20.
[0052] Cantilevered probes 30 may have a rectangular shape, though
other shapes may be suitably used such as a pointed cantilever, a
V-shaped cantilever, a triangular-shaped cantilever, a dual-arm
cantilever, or a balanced cantilever. Cantilevered probes 30 may be
arranged and attached to substrate 22 in an array of cantilevered
beams, the cantilevers being all identical, all different, or some
combination thereof.
[0053] Cantilevered probe array 20 is actuated with an excitation
voltage applied to a piezoelectric drive 32 of piezoelectric
material disposed on each cantilevered probe 30. Cantilevered
probes 30 may be series-connected to a pair of cantilevered probe
array drive pads 24 on substrate 22. Alternatively, cantilevered
probes 30 may be parallel-connected to the pair of cantilevered
probe array drive pads 24. Alternatively, cantilevered probe array
20 may comprise a network of series-connected and
parallel-connected cantilevered probes electrically connected to
the pair of cantilevered probe array drive pads 24. More than one
group or array of cantilevered probes 30 may be included on
substrate 22. Substrate 22 may have through-wafer vias for backside
connection.
[0054] Substrate 22 includes a semiconductor substrate such as a
silicon wafer, a silicon-on-insulator (SOI) wafer, a glass
substrate, or other suitable substrate for forming cantilevered
probes 30 thereon. Cantilevered probes 30 comprise materials such
as silicon, polysilicon, silicon nitride, a metal film, a metal
sheet, a zinc oxide film, a PZT film, a polymeric layer, and
combinations thereof. For example, a zinc oxide film is deposited
on a layer of single-crystal silicon, patterned, and etched.
Conductive layers for top and bottom electrodes, interconnections,
and heater connections are deposited and etched accordingly.
Definition of cantilevered probes 30 with a photomask and
associated lithographic sequences along with deep reactive ion
etching (D-RIE) or anisotropic etching of the cantilevers and
substrate allows the formation and freeing of silicon cantilevers
with interconnected ZnO electrodes in series, parallel, and
series-parallel configurations. Excitation and detection of the
cantilevers occur with voltages applied to the piezoelectric
material and detection thereof.
[0055] Chemical-sensitive coating material 34 is applied to at
least a portion of one or more cantilevered probes 30. The
chemical-sensitive coating material includes, for example, an epoxy
resin, a fluoropolymer, a gold layer, a palladium layer, an
alcohol-absorbent polymer, a water-absorbent material, a
chemical-sensitive polymer, a chemical-sensitive layer, a
biosensitive material, a thiol, and a combination thereof.
Chemical-sensitive coating material 34 may be applied, for example,
with techniques such as dipping, spraying, or dispensing the
coating on at least a portion of one or more cantilevered probes.
The chemical-sensitive coating material may be applied onto a
portion of one or more cantilevered probes with the use of stencil
masks or photomasks and photolithographic patterning techniques.
Chemical-sensitive coating material 34 may be applied, for example,
using standard sputtering and other deposition techniques known in
the art.
[0056] Multiple masking sequences can be used to apply multiple
coating materials. Alternatively, multiple-component
chemical-sensitive coating materials 34 may comprise a
non-homogeneous coating material applied to a set of cantilevered
probes 30 in the cantilevered probe array 20, applied in such a way
that variations in coating thickness and composition occur when
they are deposited.
[0057] When exposed to target chemical species 12, one or more
cantilevered probes 30 in cantilevered probe array 20 may undergo
an electrical or a mechanical shift, such as a shifted resonant
frequency, a shifted Q factor, a shifted impedance, or a shifted
deflection amplitude.
[0058] Cantilevered probe array 20 may include one or more
reference cantilevered probes 30r to provide a reference
cantilevered probe response when cantilevered probe array 20 is
exposed to target chemical species 12. For example, reference
cantilevered probes may be uncoated, coated with an inert material,
or otherwise protected from exposure to target chemical species
12.
[0059] FIG. 3 is a schematic diagram of a cantilevered probe array
with series-connected cantilevered probes electrically connected to
a pair of cantilevered probe array drive pads, in accordance with
one embodiment of the present invention. Two or more cantilevered
probes 30 in a cantilevered probe array 20 are connected in series
to a pair of cantilevered probe array drive pads 24. Electrodes
above and below the piezoelectric material on each cantilevered
probe 30 are connected in series with electrodes above and below
the piezoelectric material on other cantilevered probes 30 in the
set. In the example illustrated, cantilevered probes 30a, 30b, . .
. 30n represent a plurality of series-connected cantilevered probes
with piezoelectric drives 32a, 32b, . . . 32n that are
frequency-differentiated with fundamental resonant frequencies f1,
f2, . . . fn, respectively. Each cantilevered probe 30a, 30b, . . .
30n may have one or more chemical-sensitive coating materials 34a,
34b, . . . 34n coated thereon. When activated, for example, with an
interface circuit (not shown) that scans through the resonant
frequencies of one or more cantilevered probes, each cantilevered
probe within the scanned frequency range is, in turn, excited and
oscillated by the interface circuit as the frequency of the
oscillator or frequency generator is scanned through its resonant
frequency. Multiple groups of series-connected cantilevered probes
30 may be further connected in series or in parallel to
cantilevered probe array drive pads 24 or to other sets of drive
pads.
[0060] FIG. 4 is a schematic diagram of a cantilevered probe array
with parallel-connected cantilevered probes electrically connected
to a pair of cantilevered probe array drive pads, in accordance
with one embodiment of the present invention. Two or more
cantilevered probes 30 are connected in parallel to a pair of
cantilevered probe array drive pads 24. Electrodes above and below
the piezoelectric material on each cantilevered probe 30 are
connected in parallel with electrodes above and below the
piezoelectric material on other cantilevered probes 30 in the set.
In the example illustrated, cantilevered probes 30a, 30b, . . . 30n
represent a plurality of parallel-connected cantilevered probes
with piezoelectric drives 32a, 32b, . . . 32n that are
frequency-differentiated with fundamental resonant frequencies f1,
f2, . . . fn, respectively. Each cantilevered probe 30a, 30b, . . .
30n may have one or more chemical-sensitive coating materials 34a,
34b, . . . 34n coated thereon. When activated, for example, with an
interface circuit (not shown) that scans through the resonant
frequencies of one or more cantilevered probes, each cantilevered
probe is, in turn, excited and oscillated by the interface circuit
as the frequency of the oscillator or frequency generator is
scanned through the resonant frequency. Multiple groups of
parallel-connected cantilevered probes 30 may be further connected
in series or in parallel to cantilevered probe array drive pads 24
or to other sets of drive pads.
[0061] FIG. 5 is a schematic diagram of a cantilevered probe array
with a network of series-connected and parallel-connected
cantilevered probes electrically connected to a pair of
cantilevered probe array drive pads, in accordance with one
embodiment of the present invention. A plurality of cantilevered
probes 30 is connected in a network of series and/or parallel sets
of cantilevered probes 30 to a pair of cantilevered probe array
drive pads 24. In the example illustrated, cantilevered probes 30a,
30b, . . . 30n represent series-connected and parallel-connected
cantilevered probes with piezoelectric drives 32a, 32b, . . . 32n
that are frequency-differentiated with fundamental resonant
frequencies f1, f2, . . . fn. Each cantilevered probe 30a, 30b, . .
. 30n may have one or more chemical-sensitive coating materials
34a, 34b, . . . 34n coated thereon. When activated, for example,
with an interface circuit (not shown) that scans through the
resonant frequencies of one or more cantilevered probes 30, each
cantilevered probe 30 is, in turn, excited and oscillated by the
interface circuit as the frequency of the oscillator or frequency
generator is scanned through the resonant frequency. Multiple
groups of networked cantilevered probe arrays 20 may be located on
the same substrate and connected to other pairs of drive pads.
[0062] FIG. 6a is a schematic diagram of a controller and an
interface circuit connected to a self-sensed cantilevered probe
array, in accordance with one embodiment of the present invention.
Controller 50 is connected to interface circuit 40 that drives and
senses a plurality of self-sensed cantilevered probes 30 in a
cantilevered probe array 20. It should be observed that
cantilevered probe array 20 may be electrically connected to
interface circuit 40 with as few as two cantilevered probe array
drive pads 24. At least one cantilevered probe 30 in cantilevered
probe array 20 exhibits a shifted cantilevered probe response when
cantilevered probe array 20 is exposed to target chemical species
12 and cantilevered probe array 20 is actuated by interface circuit
40.
[0063] Interface circuit 40 actuates cantilevered probe array 20
with an excitation voltage applied to a piezoelectric material
disposed on each cantilevered probe 30 in the cantilevered probe
array 20. In one example, interface circuit 40 includes an
adjustable frequency generator that is scanned through a
predetermined frequency range. In another example, interface
circuit 40 includes an impedance analyzer that is scanned through a
resonant frequency of one or more cantilevered probes 30 in
cantilevered probe array 20. In another example, interface circuit
40 includes an oscillator circuit operating at a resonant frequency
of at least one cantilevered probe in the cantilevered probe array.
In another example, interface circuit 40 includes an oscillator
circuit operating at a predetermined frequency that is set to be
off-resonance with respect to at least one cantilevered probe 30 in
cantilevered probe array 20. In another example, interface circuit
40 includes control circuitry to monitor the amplitude of bending
and vibration as cantilevered probe 30 strikes against a fixed or
adjustable mechanical stop. In another example, interface circuit
40 comprises an impulse circuit for applying an electrical impulse
to all cantilevered probes 30 in cantilevered probe array 20. In
another example, interface circuit 40 or controller 50 includes a
fast Fourier transform generator to perform a fast Fourier
transform on the shifted cantilevered probe response. Interface
circuit 40 detects a shifted cantilevered probe response from one
or more actuated cantilevered probes 30 such as a shifted resonant
frequency, a shifted Q factor, a shifted impedance, or a shifted
deflection amplitude.
[0064] Controller 50 receives a shifted cantilevered probe response
from a set of one or more cantilevered probes 30 in cantilevered
probe array 20. The target chemical species is determined based on
the shifted cantilevered probe response. For example, the target
chemical species may be determined based on a comparison between
the shifted cantilevered probe response and a reference set of
cantilevered probe responses. The reference set of cantilevered
probe responses comprises, for example, a learned set obtained
during the calibration of the chemical-sensing system or from a
statistical database of cantilevered probe responses.
[0065] To cancel out common mode effects such as temperature, one
of the cantilevered probes 30 in the cantilevered probe array 20
may be a reference cantilevered probe 30r, wherein the reference
cantilevered probe 30r provides a reference cantilevered probe
response when cantilevered probe array is exposed to target
chemical species 12.
[0066] FIG. 6b shows an illustrative plot of cantilevered probe
responses from a self-sensed cantilevered probe array scanned
through a predetermined frequency range, in accordance with one
embodiment of the present invention. When activated, for example,
with an interface circuit that scans through the resonant
frequencies of one or more cantilevered probes, each cantilevered
probe is, in turn, excited and oscillated by the interface circuit
as the frequency of the oscillator or frequency generator is
scanned through the resonant frequency. Depending on the type and
amount of a target chemical species and the coating on the
cantilevered probe, the cantilevered probes in the array may
exhibit shifted cantilevered probe responses such as a shifted
resonant frequency, a shifted Q factor, a shifted impedance, a
shifted deflection amplitude, or a combination thereof.
[0067] Output curve 90 shows exemplary output signals from an array
of cantilevered probes excited through a frequency range that
includes a resonant frequency of each of the cantilevered probes in
the array. Output curve 90 shows a baseline or reference set of
resonant peaks 90a, 90b, 90c, 90d, 90e, 90f, 90g and 90n
corresponding to a set of eight frequency-differentiated
cantilevered probes with nominally equal frequency separations
between the cantilevered probes. When the cantilevered probe array
is exposed to a target chemical species and is actuated by the
interface circuit, at least one cantilevered probe in the
cantilevered probe array exhibits a shifted cantilevered probe
response.
[0068] Exemplary output curve 92 shows resonant peaks 92a, 92b,
92c, 92d, 92e, 92f, 92g and 92n corresponding to the set of eight
frequency-differentiated cantilevered probes after exposure to one
or more target chemical species. In the example illustrated,
resonant peak 92a of the first cantilevered probe is shifted
downwards from resonant peak 90a after chemical exposure. Resonant
peak 92b of the second cantilevered probe is shifted higher than
resonant peak 90b. Resonant peak 92c of the third cantilevered
probe remains the same as resonant peak 90c. Resonant peak 92d of
the fourth cantilevered probe has a lower Q factor than resonant
peak 90d after chemical exposure. Resonant peak 92e of the fifth
cantilevered probe has a higher Q factor than resonant peak 90e
after chemical exposure. Resonant peak 92f has an amplitude less
than that of resonant peak 90f after chemical exposure, and
resonant peak 92g has an amplitude greater than that of resonant
peak 90g after chemical exposure. Resonant peak 92n exhibits a
combination of shifts in frequency, Q factor and amplitude after
chemical exposure.
[0069] An additional resonant peak 92r corresponding to a reference
cantilevered probe shows no change in cantilevered probe response
after exposure to the target chemical species compared to resonant
peak 90r corresponding to the reference cantilevered probe prior to
exposure.
[0070] FIG. 7 illustrates a chemical-sensitive coating material
applied to a cantilevered probe array with a mask, in accordance
with one embodiment of the present invention. A stencil mask 80
including at least one aperture 82 is positioned on or above a
surface of a self-sensed cantilevered probe array 20 having a
plurality of self-sensed cantilevered probes 30. A
chemical-sensitive coating material 34 is selectively applied to
cantilevered probe array 20 through apertures 82. In the example
shown, cantilevered probes 30a, 30b, . . . 30n are selectively
coated with chemical-sensitive coating material 34 by spraying the
material through stencil mask 80 and then drying chemical-sensitive
coating material 34a, 34b, . . . 34n on cantilevered probes 30a,
30b, . . . 30n, respectively. A reference cantilevered probe 30r is
shown with no coating, having been masked with stencil mask 80
during spraying.
[0071] In this example, cantilevered probes 30a, 30b, . . . 30n are
nominally the same size and thickness. Frequency differentiation
for this set of cantilevered probes is achieved by varying the area
of the cantilevered probes that is covered by the coating. An
angled aperture 82 in stencil mask 80 allows different amounts of
coating material to be disposed on each cantilevered probe, varying
the mass on each cantilevered probe and thereby changing the
resonant frequencies accordingly. Stencil mask 80 may be used to
cover cantilevered probe array drive pads 24 and other portions of
substrate 22 that need not be coated. Piezoelectric drives 32 on
cantilevered probes 30a, 30b, . . . 30n and 30r, respectively, may
be coated, partially coated, or uncoated with chemical-sensitive
coating materials 34.
[0072] FIG. 8 illustrates a top view of a self-sensed cantilevered
probe including a selectively deposited coating, a heater, and a
species attraction electrode. A resistive heater 36'is disposed on
or formed in cantilevered probe 30. Resistive heater 36 allows
cantilevered probe 30 to be heated, for example, to initialize
cantilevered probe 30 prior to exposing cantilevered probe array 20
to the target chemical species. In another role, resistive heater
36 may be used to burn off, deflagrate, or otherwise react a target
chemical species that deposits on a surface of cantilevered probe
30.
[0073] In another embodiment, a species attraction electrode 38 may
be disposed on cantilevered probe 30 of cantilevered probe array 20
to allow a species attraction potential to be applied. Species
attraction electrode 38 is positioned, for example, underneath or
adjacent to chemical-sensitive coating material 34. Electrical
connections to species attraction electrode 38 may be made with,
for example, one end of piezoelectric drive 32, one end of
resistive heater 36, or with a connection to an independent
electrical trace on substrate 22.
[0074] FIG. 9 illustrates a handheld system for sensing a target
chemical species, in accordance with one embodiment of the present
invention. Handheld system 70 includes an enclosure 60, a
self-sensed cantilevered probe array 20, at least one
chemical-sensitive coating material 34 applied to at least one
self-sensed cantilevered probe 30 in cantilevered probe array 20,
and an interface circuit 40 coupled to cantilevered probe array 20.
Enclosure 60 has an inlet port 62 to allow ingression of target
chemical species 12 into enclosure 60 and an outlet port 64 to
allow egression of target chemical species 12 or a by-product
thereof from enclosure 60. When cantilevered probe array 20 is
exposed to target chemical species 12 and cantilevered probe array
20 is actuated by interface circuit 40, one or more cantilevered
probes 30 in cantilevered probe array 20 exhibit a shifted
cantilevered probe response.
[0075] Cantilevered probe array 20 includes a plurality of
cantilevered probes 30 that are frequency-differentiated. The
plurality of cantilevered probes 30 in cantilevered probe array 20
is electrically connected to a pair of cantilevered probe array
drive pads, and one or more groups of cantilevered probes 30 may be
included within enclosure 60.
[0076] Handheld system 70 may include a controller 50 in
communication with interface circuit 40. Controller 50 receives a
shifted cantilevered probe response from a set of cantilevered
probes 30 in cantilevered probe array 20. The shifted cantilevered
probe responses are analyzed and the constituency and concentration
of target chemical species 12 may be determined based on the
shifted cantilevered probe response.
[0077] Cantilevered probe array 20 may include a reference
cantilevered probe 30r. The reference cantilevered probe 30r
provides a reference cantilevered probe response when cantilevered
probe array 20 is exposed to target chemical species 12.
[0078] One or more cantilevered probes 30 in cantilevered probe
array 20 may have resistive heaters 36 to locally heat selected
cantilevered probes 30. A species attraction electrode 38 may be
disposed on one or more cantilevered probes 30 in cantilevered
probe array 20 to allow application of a species attraction
potential.
[0079] Handheld system 70 may include a transport mechanism 66 such
as a pump, fan or blower and ductwork or piping for transporting
target chemical species 12 to cantilevered probe array 20. Handheld
system 70 may include a concentrator 68 such as a compressor or a
condenser to concentrate target chemical species 12 proximal to one
or more cantilevered probes 30 in cantilevered probe array 20.
[0080] Command and data entry input devices such as buttons,
keypads, or softkeys, allow the selection of the function and
operation of handheld system 70. Results of measurements are
displayed on an output device such as an LCD, or communicated to
another analysis system through a wired communication port such as
a universal serial bus (USB) port or through a wireless
communication protocol.
[0081] FIG. 10 is a flow chart of a method for chemical detection,
in accordance with one embodiment of the present invention. The
chemical detection method includes various steps to detect and
identify one or more target chemical species with a self-sensed
cantilevered probe array.
[0082] The cantilevered probes in the cantilevered probe array are
frequency-differentiated, separated in the frequency domain such
that any one of the cantilevered probes can be measured
independently of the others using, for example, a frequency
generator, a frequency synthesizer, a controlled oscillator, or an
impedance analyzer when the cantilevered probes are configured in
series or in parallel with other cantilevered probes. The
cantilevered probe array includes, for example, at least two-series
connected cantilevered probes electrically connected to a pair of
cantilevered probe array drive pads. Alternatively, the
cantilevered probe array includes at least two parallel-connected
cantilevered probes electrically connected to a pair of
cantilevered probe array drive pads. Alternatively, the
cantilevered probe array includes a network of series-connected and
parallel-connected cantilevered probes electrically connected to a
pair of cantilevered probe array drive pads. One or more groups of
cantilevered probes may be connected to the same set of
cantilevered probe array drive pads or to a different set of
cantilevered probe array drive pads on the same substrate for
external connection to an interface circuit.
[0083] After fabrication of the cantilevered probe array, a
chemical-sensitive coating material may be applied to one or more
cantilevered probes in the cantilevered probe array, as seen at
block 100. The chemical-sensitive coating material may include, for
example, an epoxy resin, a fluoropolymer, a gold layer, a palladium
layer, an alcohol-absorbent polymer, a water-absorbent material, a
chemical-sensitive polymer, a chemical-sensitive layer, a
biosensitive material, a thiol, and combinations thereof.
[0084] The coating material may be applied, for example, by
standard deposition techniques such as sputter depositions,
electron beam depositions, or plasma-enhanced chemical vapor
depositions, or by dipping, spraying or dispensing the coating
material onto at least a portion of one or more cantilevered
probes. The coating material may be applied, for example, with a
stencil mask and selective masking of one or more cantilevered
probes and applying the chemical-sensitive coating through the
mask. A single material may be applied through the mask.
[0085] A plurality of chemical-sensitive coating materials may be
applied to a set of cantilevered probes in the cantilevered probe
array. For example, multiple masks may be used for multiple
coatings with different coating materials on selected portions of
one or more cantilevered probes. Alternatively, coating with
multiple materials through a single mask may be accomplished by
spraying a non-homogenous coating material onto a set of
cantilevered probes in the cantilevered probe array such that
cantilevered probes in the array are coated with substantive
differences in coating constituency, thickness, or fraction of
coverage.
[0086] When a resistive heater is used, the resistive heater that
is coupled to at least one cantilevered probe is heated to
initialize the cantilevered probe prior to exposing the
cantilevered probe array to the target chemical species, as seen at
block 102. The resistive heater locally heats up the cantilevered
probe to an elevated temperature to evaporate, burn off, or
otherwise remove residual materials from the surfaces of the
cantilevered probe.
[0087] The array is initialized, as seen at block 104.
Initialization of the array is accomplished, for example, by
running a scan through the resonant frequencies of the cantilevered
probes in the cantilevered probe array to establish a baseline or
to ensure that all the cantilevered probes and the interface
electronics are functioning properly.
[0088] The target chemical species may be transported to the
cantilevered probe array, as seen at block 106. Fans, blowers, or
pumps may be used, for example, to force flow of the target
chemical species and a carrier gas or liquid onto the cantilevered
probe array. Convective processes or normal diffusive processes due
to concentration gradients may be used, for example, to transport
the target chemical species to the cantilevered probe array for
detection.
[0089] The target chemical species may be concentrated proximal to
the cantilevered probe array, as seen at block 108. Concentration
of the target chemical species may be accomplished, for example,
with a compressor and a valve system to increase the pressure in
the vicinity of the cantilevered probe array. A condenser and a
heater may be used, for example, to collect samples of the target
chemical species and then release it in proximity to the
cantilevered probe array.
[0090] Selective attraction of chemical and biological species may
be accomplished with, for example, a species attraction potential
applied to a species attraction electrode disposed on at least one
cantilevered probe in the cantilevered probe array.
[0091] The self-sensed cantilevered probe array is exposed to a
target chemical species, as seen at block 110. The target chemical
species may be in a liquid or a gas. A valve and associated piping
may be used to expose the cantilevered probe array to the target
chemical species and the carrier.
[0092] When embodied so, the resistive heater coupled to at least
one cantilevered probe may be heated to react the target chemical
species, as seen at block 112. Reaction of the target chemical
species may be result, for example, in a volatile material that is
desorbed from one or more cantilevered probes resulting in a shift
in the resonant frequency due to less mass on the beam.
Alternatively, reaction of the target chemical species may result
in a formation of a material on the surface of the cantilevered
probe that increases the vibrational stiffness of the cantilevered
probe and produces a frequency shift. Alternatively, reaction of
the target chemical species may result in a stressed film on the
surface of the cantilevered probe that causes a static deflection
of the cantilevered probe, which may be measured, for example, with
a tapping mode where the cantilevered beam is tapped against a
reference surface adjusted to be a fixed distance away from the
cantilevered beam or with a tapping mode where the beam is tapped
against an adjustable mechanical stop, adjusted to allow the
cantilevered probe to tap a consistent amount against the
mechanical stop.
[0093] The exposed cantilevered probe array is actuated, as seen at
block 114. The exposed cantilevered probes are actuated, for
example, by applying an excitation voltage to a piezoelectric
material disposed on each cantilevered probe in the cantilevered
probe array. In another example, the exposed cantilevered probe
array is actuated with a frequency generator by scanning the
cantilevered probes through a predetermined frequency range. In
another example, the exposed cantilevered probe array is actuated
by driving the exposed array at a resonant frequency of one
cantilevered probe in the cantilevered probe array, then switching
as desired to a resonant frequency of another cantilevered probe
for additional measurements. In another example, the exposed
cantilevered probe array is actuated by driving the exposed array
at a predetermined frequency, wherein the predetermined frequency
is off-resonance with respect to at least one cantilevered probe in
the cantilevered probe array. In another example, the amplitude of
vibration is controlled as the cantilevered probe strikes against a
fixed or adjustable mechanical stop. In another example, the
exposed cantilevered array is actuated with an electrical impulse
applied to the cantilevered probe array.
[0094] A cantilevered probe response is detected from at least one
self-sensed cantilevered probe in the cantilevered probe array, as
seen at block 116. Detecting the cantilevered probe response from
one or more actuated cantilevered probes comprises, for example,
measuring a shifted resonant frequency, a shifted Q factor, a
shifted impedance, a shifted deflection amplitude, and a
combination thereof. A fast Fourier transform (FFT) may be
performed on the cantilevered probe response from one or more
actuated cantilevered probes. The entire array of cantilevered
probes, a subset thereof, or an individual cantilevered probe may
be addressed by selective actuation and detection.
[0095] With the availability of a reference cantilevered probe, a
reference cantilevered probe response may be detected from one or
more reference cantilevered probes in the cantilevered probe
array.
[0096] The target chemical species is determined based on the
detected cantilevered probe response, as seen at block 118. A
controller or a software application running on a computer or
digital device may be used to analyze the cantilevered probe
responses and determine one or more components and their
concentration in the sample. The target chemical species may be
determined in part based on the detected reference cantilevered
probe response, for example, by common mode correcting for effects
such as temperature, pressure and viscosity of the sampled medium.
The detected target chemical species may include, for example,
mercury, hydrogen, an alcohol, water vapor, an explosive material,
a chemical element, a chemical compound, an organic material, an
inorganic material, a gaseous substance, a liquid, a biological
material, a DNA strand, a bioactive agent, a toxin, and
combinations thereof.
[0097] Using pattern recognition, modeling functions or signal
processing techniques such as fuzzy logic, the target chemical
species may be determined based on comparing a measured shift from
one or more actuated cantilevered probes to a reference set of
cantilevered probe response, and determining the target chemical
species based on the reference set of cantilevered probe responses.
The reference set of cantilevered probe responses may comprise, for
example, a learned set from calibration runs or from a statistical
database with expectation values for various target chemical
species.
[0098] FIG. 11 is a flow chart of a method for chemical detection,
in accordance with another embodiment of the present invention. The
chemical detection method includes various steps to detect and
identify one or more target chemical species with a self-sensed
cantilevered probe array.
[0099] A self-sensed cantilevered probe array is provided, as seen
at block 120. The cantilevered probes in the cantilevered probe
array are frequency-differentiated, and may include at least two
series-connected or parallel-connected cantilevered probes
electrically connected to a pair of cantilevered probe array drive
pads. Alternatively, the cantilevered probe array includes a
network of series-connected and parallel-connected cantilevered
probes electrically connected to a pair of cantilevered probe array
drive pads.
[0100] The array is initialized, as seen at block 122.
Initialization of the array is accomplished, for example, by
running a scan through the resonant frequencies of the cantilevered
probes in the cantilevered probe array to establish a baseline or
to ensure that all the cantilevered probes and the interface
electronics are functioning properly.
[0101] The self-sensed cantilevered probe array is exposed to a
target chemical species, as seen at block 124. The target chemical
species may be in a liquid or a gas. A valve and associated piping
may be used to expose the cantilevered probe array to the target
chemical species and the carrier.
[0102] The exposed cantilevered probe array is actuated, as seen at
block 126. The exposed cantilevered probes are actuated, for
example, by applying an excitation voltage to a piezoelectric
material disposed on each cantilevered probe in the cantilevered
probe array; by scanning the cantilevered probes through a
predetermined frequency range; by driving the exposed array at a
resonant frequency of at least one cantilevered probe in the
cantilevered probe array; by driving the exposed array at a
predetermined off-resonance frequency; by driving and controlling
the tapping of the cantilevered probes against a fixed or
adjustable mechanical stop; or by applying an electrical impulse to
the cantilevered probe array.
[0103] A cantilevered probe response is detected from at least one
self-sensed cantilevered probe in the cantilevered probe array and
the target chemical species is determined, as seen at block 128.
Detecting the cantilevered probe response from one or more actuated
cantilevered probes comprises, for example, measuring a shifted
resonant frequency, a shifted Q factor, a shifted impedance, a
shifted deflection amplitude, and a combination thereof. A fast
Fourier transform (FFT) may be performed on the cantilevered probe
response from one or more actuated cantilevered probes to detect
the target chemical species. The target chemical species is
determined based on the detected cantilevered probe response. The
target chemical species may be determined based on comparing a
measured shift from one or more actuated cantilevered probes to a
reference set of cantilevered probe responses, and determining the
target chemical species based on the reference set of cantilevered
probe responses.
[0104] While the embodiments of the invention disclosed herein are
presently considered to be preferred, various changes and
modifications can be made without departing from the spirit and
scope of the invention. The detailed description and drawings are
merely illustrative of the invention rather than limiting, the
scope of the invention being defined by the appended claims and
equivalents thereof, and all variations and embodiments that come
within the meaning and range of equivalents are embraced
herein.
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