Low-cost Printed Electronic Nose Gas Sensors for Distributed Environmental Monitoring Vivek Subramanian Department of Electrical Engineering and Computer Sciences University of California, Berkeley RD83089901
Distributed environmental monitoring Need for distributed monitoring - Identification of environmental hazards - Triggering of proactive action - Development of accurate environmental models Sensor Requirements - Ultra-low-cost - Ease of dispersal - Trainability / adaptability Our Approach: Arrayed organic FETs - Easily arrayed at low-cost via printing - Flexible for easy dispersal - Trainable via electronic nose architecture
Commercial E-noses ppbrae Plus $6215 - For homeland security - Detects toxic agents, mildew Cyranose $7995 - Can be trained to detect a wide range of odors: alcohols, chemicals, oil, food
Commercial Gas Sensors Vernier O 2 sensor $186 Minimax Pro H 2 sensor $199 Gas Alert Micro 3 H 2 S sensor $612
Arrayed Gas Sensors Molecule in ambient Map Responses Substrate A B C D Sensor Parameter Responses to different molecules Pixel Array Index Generate Chemical Signatures
Printing: a pathway to low-cost No lithography No vacuum processing (CVD, PVD, Etch) Reduced abatement costs Cheap substrate handling Reduced packaging costs
Organic Gas Sensors Gas sensing with OTFTs is a good match - Good sensitivity - Synthetic richness - Easy array integration - Low performance requirements - Short-term applications available The New York Times, April 4, 2002, illustration by Mary Ann Smith
OTFT Gas Sensing Absorbed through grain boundaries and reactive molecular sites Film expands Analyte changes hopping barrier height Source Odors + + Active + Material + T T Gate Dielectric Gate T Drain Analyte donates carriers or activates existing donors Analyte introduces traps and scattering sites
Low-cost Fabrication Inkjet deposition of organic material allows integration of sensor array Ultra-low cost requires integration of supporting circuitry
Printed Transistors Gate electrode is printed using gold nanocrystals Polymer dielectric is deposited via inkjet Low-temperature anneal forms S/D stripes and connections (in plane of page) Substrate Substrate Substrate Source / Drain contacts are printed using gold nanocrystals Various active layers are deposited via inkjet Low-temperature anneal forms gate stripe to edge of array (out of page) Substrate Substrate Substrate
Baseline sensor screening process The channel is exposed to the analyte, resulting in performance changes S G D Materials are characterized using a substrate-gated architecture (easy fabrication for rapid screening) A silicon substrate enables easy I/O via an edge connector
Sensor Characterization Switching between individual sensors is performed via a switch matrix PCB Agilent 4156 To ensure accuracy, measurements are performed with a calibrated precision semiconductor parameter analyzer.
Experimental Setup Valve Valve Agilent 4156 N 2 Mass Flow Controller Analyte Delivery Valve Sensor Chamber Mass Flow Meter Bubbler Exhaust Exhaust
Sensor Repeatability Id-Vd (Zoomed) -5.00E-09-1.00E-08 Id (Amps) -1.50E-08-2.00E-08-2.50E-08-3.00E-08-2.60E+01-2.10E+01-1.60E+01-1.10E+01-6.00E+00 Vd (Volts) Baseline Toluene Regen Multiple cycles can be performed with full regeneration
Multi-parameter sensing Transconductance Mobility baseline 60 sccm regen 100 sccm regen 1.00E-08 8.00E-09 6.00E-09 4.00E-09 2.00E-09 0.00E+00 gm (S) baseline 60 sccm regen 100 sccm regen 4.50E-04 4.00E-04 3.50E-04 3.00E-04 2.50E-04 2.00E-04 1.50E-04 1.00E-04 5.00E-05 0.00E+00 u (cm2/vs) Threshold Voltage Drain Current 0.00E+00-2.00E+00 0.00E+00-2.00E-08-4.00E-08-4.00E+00-6.00E+00 V (Volts) -6.00E-08-8.00E-08-1.00E-07 Id (Amps) baseline 60 sccm regen 100 sccm regen -8.00E+00-1.00E+01 baseline 60 sccm regen 100 sccm regen -1.20E-07-1.40E-07-1.60E-07
Sensor dynamics transient response Change in Drain Current Under Toluene Exposure -5.00E-10-1.00E-09-1.50E-09 Id (Amps) -2.00E-09-2.50E-09-3.00E-09-3.50E-09-4.00E-09-4.50E-09-5.00E-09 0 30 60 90 120 150 Time (Minutes) Sensor response can be very slow, due to slow analyte absorption. Speed can be increased by reducing film thickness
Interaction Mechanisms - Sensors show a wide range of interactions, complicating analysis. Interactions include: Polar group interactions Chain / bulk interactions Swelling Percent of Baseline value 120 100 80 I on Change in P3HT due to Acetic Acid 12 nm 40 nm 75nm 100 nm 12 nm 40 nm 75nm 100 nm 60 40 Baseline 20 0-1 4 9 14 19 24 Time (min) Percent of Baseline Value 120 100 80 60 40 Baseline 20 0 I on Change in P3HT due to Ethanol 12 nm 75 nm 100nm -1 1 3 5 7 9 Time (min)
Differential sensitivity pathway to an electronic nose? Nose Response to Water (Pentacene) Nose Response to Water (P3HT) Id (Amps) -1.00E-06-1.20E-06-1.40E-06-1.60E-06-1.80E-06-2.00E-06-2.20E-06 0 10 20 30 40 Time (Minutes) Id (Amps) -7.00E-08-8.00E-08-9.00E-08-1.00E-07-1.10E-07-1.20E-07-1.30E-07-1.40E-07-1.50E-07 0 10 20 30 40 Time (Minutes) Nose Response to Water (P3OT) -1.50E-08-2.00E-08 Id (Amps) -2.50E-08-3.00E-08-3.50E-08-4.00E-08-4.50E-08 0 10 20 30 40 Time (Minutes)
Demonstration of basic electronic nose functionality Nose Response to Water and Milk Percentage of Baseline Current 110 100 90 80 70 60 50 40 30 Milk Water 0 10 20 30 40 Pentacene P3OT P3HT Time (Minutes)
Organic Transistor Stability Mobility (cm 2 /Vs) 0.01 0.008 0.006 0.004 0.002 mu (sat) mu (lin) Ion (sat) -4.E-07-3.E-07-2.E-07-1.E-07 Drive Current (A) 0 7/14 7/15 7/16 7/17 Time (Date) 0.E+00 Implication: We must either improve dielectric interface or use V T -insensitive differential sensing method
Sensing Circuits Amplify sensor response Desensitize against operational drift Integration of encapsulated and unencapsulated OTFTs Integration of sensing OTFTs with supporting OTFT or silicon CMOS circuitry
Sensing Circuits Crone et al, J. Appl. Phys, vol 91, pp. 1014-10146, 2002
Conclusions & Future Work Organic FET-based sensors show promising responses, including transient behavior and cycle life Work remains to optimize structure and process flow, particularly in terms of stability and reliability Future Work: - Integration of latest sensing materials into printed device architecture - Deployment in testing of environmentally-relevant analytes - Enhancement of specificity through functionalization / doping