OFET sensors

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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.

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OFET sensors

  1. 1. OFET Sensors Titto Thomas 133079015 M.Tech Seminar
  2. 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 OFET Sensors : IIT Bombay 2
  3. 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 3
  4. 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 OFET Sensors : IIT Bombay 4
  5. 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 OFET Sensors : IIT Bombay 5
  6. 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 6
  7. 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 OFET Sensors : IIT Bombay 7
  8. 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,” OFET Sensors : IIT Bombay 8
  9. 9. Bio-sensors : Overview OFET Sensors : IIT Bombay 9
  10. 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 OFET Sensors : IIT Bombay 10
  11. 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 OFET Sensors : IIT Bombay 11
  12. 12. Chemical sensors : Overview OFET Sensors : IIT Bombay 12
  13. 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 OFET Sensors : IIT Bombay 13
  14. 14. Gas sensors : overview OFET Sensors : IIT Bombay 14
  15. 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 OFET Sensors : IIT Bombay 15
  16. 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 OFET Sensors : IIT Bombay 16
  17. 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 OFET Sensors : IIT Bombay 17
  18. 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 OFET Sensors : IIT Bombay 18
  19. 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 OFET Sensors : IIT Bombay 19
  20. 20. Thank You OFET Sensors : IIT Bombay 20

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