Microcantilever Gas Chemical Sensors with Multi-modal Capability

1
Microcantilever Gas Chemical Sensors with
Multi-modal Capability

• Sarah S. Bedair1
• (sbedair_at_andrew.cmu.edu)
• Advisor Gary K. Fedder1,2
• 1Department of Electrical Computer Engineering
  and 2The Robotics Institute

2
Motivation

• 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 -gt improved sensitivity

3
Chemical Sensor Implementation

• Implementation
• Chemically sensitive layer on a transducer

gas/analyte
Physico-chemical interaction
Interface Circuitry
Detection signal Voltage, current, frequency,
etc.
4
Chemical Sensor Modalities
Sensing Mode
Example Device Type

• Sensing modes

Chemresistor
Resistive
gas/analyte
Chemocapacitor
Capacitive
Physico-chemical interaction
Thermistor Pellistor
Calorimetric
Surface Acoustic Wave Cantilevers
Mass
5
Chemresistor Gas Sensor
R

• Sensitive layer -gt resistor
• Example conductive polymer - regioregular
  polythiophene (Rick McCulloughs group)
• With analyte -gt resistance change

I
Electrodes
Sensitive layer
Introduce Analyte
Insulator
Insulator
Silicon substrate
Silicon substrate
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Chemical Sensor Modalities
Sensing Mode
Example Device Types

• Sensing modes

Chemresistor
Resistive
gas/analyte
Chemocapacitor
Capacitive
Physico-chemical interaction
Thermistor Pellistor
Calorimetric
Surface Acoustic Wave Cantilevers
Mass
7
Gravimetric/Mass Gas Sensors

• Modeled as mass, spring, damper system
• Sensitive polymer deposited on mass
• Slower motion with absorbed analyte

Introduce Analyte
Sensitive polymer gas
Sensitive polymer
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Chemical Sensor Modalities
Sensing Mode
Example Device Types

• Sensing modes

Chemresistor
Resistive
gas/analyte
Combined these two modes in a multi-modal platform
Chemocapacitor
Capacitive
Physico-chemical interaction
Thermistor Pellistor
Calorimetric
Surface Acoustic Wave Cantilevers
Mass
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Multi-modal Platform Gravimetric
Chemiresistive Sensing
Imbedded Chemresistor Sensor
Gravimetric Sensor
Bottom electrode
Top metal electrode
Sensitized polymer
Sensing electrodes
Actuator electrodes
Cross section
1 µm
2 µm
10
Conclusions

• MEMS technology for chemical detection system
• Demonstration of multi-modal platform
• Future work
• Characterization of multi-modal approach
• Exploring methods for device scaling -gt improved
  sensitivity