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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