1 Carnegie Mellon Microcantilever Gas Chemical Sensors with Multi-modal Capability Sarah S. Bedair 1 Advisor: Gary K. Fedder 1,2 1 Department of Electrical & Computer Engineering and 2 The 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 Thermistor Pellistor Surface Acoustic Wave Cantilevers Capacitive Chemocapacitor gas/analyte

5 Carnegie Mellon Chemresistor Gas Sensor Sensitive layer -> resistor Example conductive polymer - regioregular polythiophene (Rick McCullough’s group) With analyte -> resistance change Silicon substrate Insulator Sensitive layer Electrodes Introduce Analyte Silicon substrate Insulator I R

6 Carnegie Mellon Chemical Sensor Modalities Sensing modes Transducer Sensitive layer Physico-chemical interaction Resistive Calorimetric Mass Sensing Mode: Example Device Types: Chemresistor Thermistor Pellistor Surface Acoustic Wave Cantilevers Capacitive Chemocapacitor gas/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 Thermistor Pellistor Surface Acoustic Wave Cantilevers Capacitive Chemocapacitor Combined 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 SiO 2 Al SiO 2 Al SiO 2 Al SiO 2 Multi-modal Platform; Gravimetric & Chemiresistive Sensing Actuator electrodes Sensing electrodes Sensitized polymer 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