1

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

2

Carnegie Mellon

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 -> improved sensitivity

3

Carnegie Mellon

Chemical 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

4

Carnegie Mellon

Chemical 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

5

Carnegie Mellon

Chemresistor Gas Sensor

Sensitive layer -> resistor

Example conductive polymer - regioregular polythiophene (Rick McCullough’s group)

With analyte -> resistance change

Silicon substrateInsulator

Sensitive layer

Electrodes

Introduce

Analyte

Silicon substrateInsulator

I

R

R

R

S

SS

S

n

R

R

6

Carnegie Mellon

Chemical 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

7

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

Introduce

Analyte

Sensitive polymer

8

Carnegie Mellon

Chemical 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

9

Carnegie Mellon

Top metal electrode

Bottom electrode

Cross section

1 μm

2 μm

Al

Al

SiO2

AlSiO2

Al

Al

SiO2

AlSiO2

Multi-modal Platform; Gravimetric & Chemiresistive Sensing

Actuatorelectrodes

Sensingelectrodes

Sensitizedpolymer

Gravimetric Sensor:Imbedded Chemresistor

Sensor:

10

Carnegie Mellon

Conclusions

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