Sensors are needed convert real life quantities into signal variations and hence has a very high importance. Or-ganics semiconductors have their own advantages, which can be exploited to create sensors. One of the mostly used sensor based on organic materials is the Organic Field-Effect Transistor (OFET). The channel material made from the organic compound interacts with the analyte and in turn causes variations in the device parameters. The major applications of OFET sensors are as bio-sensors, chemical, and gas sensors. Bio-sensors helps in disease diagnostics by detecting DNA, proteins, enzymes etc. Chemical sensors are used to find out the presence of ions, humidity, and pH levels. To get more information, furthur discussion is about a single OFET sensor fabricated with P3HT and CuTPP used for detecting nitro-based explosive compounds. OFET sensors are very promising and could be used in real applications in near future.

1. OFET Sensors
Titto Thomas
133079015
M.Tech Seminar

2. Introduction
 Sensors
 Transducer
 Conversion into signals
 Applications
[2]
 Organic conducting polymers
 Discovery [1]
 Applications
 Organic Thin Film Transistor (OTFT)
[1] H. Shirakawa et al. , “Synthesis of electrically conducting organic polymers: halogen derivatives of
polyacetylene, (ch),”, 1977
[2] P. Lin and F. Yan, “Organic thin-film transistors for chemical and biological sensing,” 2012
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3. More about OTFTs
 Internal amplification and noise correction
 Compatibility with existing VLSI Technology
 Sensors could be
 Biodegradable
 Flexible
 Cost effective
 More information than any other sensor
OTFT
OFET Sensors : IIT Bombay
OECT
OFET
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4. Device Structure & Working
 OECT
 Source & Drain electrodes
 OSC channel
 Electrolytic layer on top
 OFET
 Similar to OECT
 Direct interaction with analyte
 Two configurations
[1]
[1] P. Lin and F. Yan, “Organic thin-film transistors for chemical and biological sensing,”, 2012
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5. OFETs in detail
 Two configurations
 Top contact
 Bottom contact
 Lower mobility in the channel
 Follows standard MOSFET equations
[1]
[1] H. Ma, et al., “Multifunctional phosphoric acid self-assembled monolayers on metal oxides as
dielectrics, interface modification layers and semiconductors for low-voltage high-performance organic
field-effect transistors,”, 2012
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6. OFET Sensors in detail
OFET Sensors
Bio-Sensors
DNA
Proteins
Glucose
Others
OFET Sensors : IIT Bombay
Gas Sensors
Chemical
Sensors
Ions
Humidity
Other sensors
X-ray
Others
pH
Others
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7. Bio-sensors : DNA
[2]
 Zhang et al. used pentacene as the OSC channel
 DNA adsorption  VT shift  Electron extraction by DNA
 Improvement suggestions
 Reducing film thickness or
current
 Increase substrate
temperature
[3]
 Yan et al. proposed another device using P3HT
[2]
[1]
[1]http://www.intechopen.com/books/biosensors/design-and-fabrication-of-nanowire-basedconductance-biosensor-using-spacer-patterning-techniq
[2] Q. Zhang and V. Subramanian, 2012
[3] F. Yan, S. M. Mok, J. Yu, H. L. Chan, and M. Yang, 2009
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8. Bio-sensors : Glucose & Others
[1]
 J.Liu et al. proposed PEDOT-PSS organic channel with GOx
entrapped
 GOx entrapped during polymerization
 Redox reaction channel and glucose with Gox
catalysis
[2]
 Sensor based on Ta2O5 and P3HT , by Bartic et al.
 GOx anchored on surface
 Cyanopropyltrichlorosilane treatment
[3]
 Roberts et al. OFET to detect glucose, cystein, and MPA by
 DDFTTF as the OSC channel
[1] J. Liu, M. Agarwal, and K. Varahramyan, “Glucose sensor based on organic thin film transistor using glucose
oxidase and conducting polymer,” , 2008
[2] C. Bartic, A. Campitelli, and S. Borghs, “Field-effect detection of chemical species with hybrid
organic/inorganic transistors,” , 2003
[3] M. E. Roberts, S. C. B. Mannsfeld, N. Queralt, C. Reese, J. Locklin, W. Knoll, and Z. Bao, “Water-stable organic
transistors and their application in chemical and biological sensors,”
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9. Bio-sensors : Overview
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10. Chemical Sensors : Ions & pH
[1]
 Ji et al. P3HT as the OSC, with Ta2O5 and valinomycin
subsequently deposited on top
+ +
 Detects K , H ions and pH levels
[2]
 Scarpa et al. used P3HT as channel
+ +
2+
 K , Na, Ca ions and pH levels even at 0.001%
[3]
 Maddalena et al. had a sulfate receptor with incorporated
thiol group, coupled polystyrene layer
 Detects sulphate ions with 1mM
[1] T. Ji, P. Rai, S. Jung, and V. K. Varadan, “In vitro evaluation of flexible ph and potassium ion-sensitive organic
field effect transistor sensors,” 2008
[2] G. Scarpa, A.-L. Idzko, A. Yadav, and S. Thalhammer, “Organic ISFET based on poly (3-hexylthiophene),” 2010
[3] F. Maddalena, M. J. Kuiper, B. Poolman, F. Brouwer, J. C. Hummelen, D. M. de Leeuw, B. De Boer, and
P. W. M. Blom, “Organic field-effect transistor-based biosensors functionalized with protein receptors,” , 2010
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11. Chemical Sensors : Ions & pH
[1]
 Bartic et al. reported a P3HT OSC OFET
 Indicates the pH values after in-situ amplification
 Coating with arachidic acid improves the sensitivity
[2]
 Pentacene OSC based OFET proposed by Loi et al.
 variations in charge at the gate-channel interface
 coating the floating gate with thioaminic groups
 Water stable OFET which can detect pH 3 to 11, using DFTTF
OSC channel by Roberts et al.[3]
[1] C. Bartic, A. Campitelli, and S. Borghs, “Field-effect detection of chemical species with hybrid
organic/inorganic transistors,” 2003
[2] A. Loi, I. Manunza, and A. Bonfiglio, “Flexible, organic, ion-sensitive field-effect transistor,” 2005
[3] M. E. Roberts, S. C. B. Mannsfeld, N. Queralt, C. Reese, J. Locklin, W. Knoll, and Z. Bao, “Water-stable organic
transistors and their application in chemical and biological sensors,” 2008
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12. Chemical sensors : Overview
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13. Gas Sensors
[1]
 Laurs et al. observed that oxygen, iodine and bromine could
vary the current through the OFET fabricated with
phthalocyanines (Pcs) as the OSC.
[2]
 Torsi et al. fabricated NTCDA
based OFET, and found four
characteristic parameters to
be varying.
[3]
[4]
 Someya et al. and Torsi et al.
Reported the dependancy of
sensitivity on grain size.
[1] H. Laurs and G. Heiland, “Electrical and optical properties of phthalocyanine films,” 1987
[2] L. Torsi, A. Dodabalapur, L. Sabbatini, and P. Zambonin, “Multi-parameter gas sensors based on organic thinfilm-transistors,” 2000
[3] T. Someya, A. Dodabalapur, A. Gelperin, H. E. Katz, and Z. Bao, “Integration and response of organic
electronics with aqueous microfluidics,” 2002
[4] L. Torsi, A. J. Lovinger, B. Crone, T. Someya, A. Dodabalapur, H. E.Katz, and A. Gelperin, “Correlation between
oligothiophene thin film transistor morphology and vapor responses,” 2002
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14. Gas sensors : overview
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15. Explosive vapor sensor
 A particular type of gas sensor
 OFETs as explosive sensors
 RDX
[1]
 TNT
 Materials proposed to be
used as OSC channel
 Poly 3-hexylthiophene
(P3HT)
[2]
II
 Cu tetraphenylpophyrin
(CuTPP)
[1] Ravishankar S. et al. “Explosive vapor sensor using poly 3-hexylthiophene and Cu tetraphenylporphyrin
composite based organic field effect transistors“ 2008
[2] http://www.aist.go.jp/aist_e/aist_laboratories/2information
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16. Device structure and fabrication
[1]
 SiO2 layer grown on n silicon wafer
 Au / Ti Source & Drains are patterned
 HMDS Surface enhancement
 CuTPP & P3HT dissolved in chloroform is spin coated
[1] Ravishankar S. et al. “Explosive vapor sensor using poly 3-hexylthiophene and Cu tetraphenylporphyrin
composite based organic field effect transistors“ 2008
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17. Device Characterization
 Significant rise in drain current & conductance in the presence
of nitro compounds
 Threshold voltage is found out by linear fit of Transfer Chara
 Behavior can be modeled by using existing equations
 Shift in FTIR peaks on sensor exposure to RDX
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18. OFET explosive vapor sensor :
Results & Conclusion
 Selectivity of
the sensor for
various vapors
 The OFET formed has high sensitivity to nitro based explosives
 ION & S parameters can be evaluated to check the presence
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19. Conclusions & Future Scope
 OFETs are effective sensors for detecting various types of
materials
 Many materials being tried out to be used in sensors have a
promising performance
 Also there is a need for new structures and modifications to
enhance the sensing abilities of sensors
 Sensitivity, selectivity, stability all have to be improved before
using them in real life applications
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20. Thank You
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