microcantilever gas chemical sensors with multi-modal capability
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Carnegie Mellon
Microcantilever Gas Chemical Sensors with Multi-modal Capability
Sarah S. Bedair1
(sbedair@andrew.cmu.edu)
Advisor: Gary K. Fedder1,2
1Department of Electrical & Computer Engineering and 2The Robotics Institute
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Carnegie MellonMotivation
Application fields: environmental monitoring, fire safety, homeland security
Need for chemical detection system Portable, inexpensive relative to gas chromatograph
systems MicroElectroMechanical Systems (MEMS) – platform technology
for chemical detection Sensors integrated with CMOS circuitry to process and
multiplex output signals Arrays of sensors – for multi-modal detection
Enhanced selectivity Device scaling -> improved sensitivity
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Carnegie MellonChemical Sensor Implementation
Implementation: Chemically sensitive layer on a transducer
Transducer
Sensitive layer
Physico-chemical interaction
Interface Circuitry
Detection signal:Voltage, current, frequency, etc.
gas/analyte
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Carnegie MellonChemical Sensor Modalities
Sensing modes
Transducer
Sensitive layer
Physico-chemical interaction
Resistive
Calorimetric
Mass
Sensing Mode: Example Device Type:
Chemresistor
ThermistorPellistor
Surface Acoustic WaveCantilevers
Capacitive Chemocapacitorgas/analyte
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Carnegie MellonChemresistor Gas Sensor
Sensitive layer -> resistor Example conductive polymer -
regioregular polythiophene (Rick McCullough’s group)
With analyte -> resistance change
Silicon substrateInsulator
Sensitive layer
Electrodes
IntroduceAnalyte
Silicon substrateInsulator
I
R
R
R
SS
SS
n
R
R
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Carnegie MellonChemical Sensor Modalities
Sensing modes
Transducer
Sensitive layer
Physico-chemical interaction
Resistive
Calorimetric
Mass
Sensing Mode: Example Device Types:
Chemresistor
ThermistorPellistor
Surface Acoustic WaveCantilevers
Capacitive Chemocapacitorgas/analyte
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Carnegie Mellon
Sensitive polymer+
gas
Gravimetric/Mass Gas Sensors
Modeled as mass, spring, damper system
Sensitive polymer deposited on mass
Slower motion with absorbed analyte
IntroduceAnalyte
Sensitive polymer
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Carnegie MellonChemical Sensor Modalities
Sensing modes
Transducer
Sensitive layer
Physico-chemical interaction
Resistive
Calorimetric
Mass
Sensing Mode: Example Device Types:
Chemresistor
ThermistorPellistor
Surface Acoustic WaveCantilevers
Capacitive ChemocapacitorCombined these two modes in a multi-modal platform
gas/analyte
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Carnegie Mellon
Top metal electrode
Bottom electrode
Cross section
1 μm
2 μm
Al
AlSiO2
AlSiO2
Al
AlSiO2
AlSiO2
Multi-modal Platform; Gravimetric & Chemiresistive Sensing
Actuatorelectrodes
Sensingelectrodes
Sensitizedpolymer
Gravimetric Sensor: Imbedded Chemresistor Sensor:
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Carnegie MellonConclusions
MEMS – technology for chemical detection system Demonstration of multi-modal platform Future work
Characterization of multi-modal approach Exploring methods for device scaling -> improved
sensitivity
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