Organic Electrochemical Transistor, Understanding and Modifying for Sensing Applications

  • Author / Creator
    Salmani-Rezaie, Salva
  • The field of conducting polymers and mainly organic electrochemical transistors (OECT) have been investigated for bioelectronics applications. Advantages such as conformability, high quality electrical contact, ease of fabrication and biocompatibility made OECTs a great potential of future bio diagnostic tools. Also, PEDOT: PSS conjugate polymer have emerged as an attractive polymer for a various application in the last years. In this study the working mechanism of OECT based on PEDOT: PSS has been studied to obtain parameters for designing biosensors. OECTs based on flexible substrate have been fabricated with high ON/OFF current ratio (2×103). Using gate current transient as a response to gate voltage pulsing at different gate voltages, the total amount of charge and capacitance per unit area has been calculated. Preliminary result showed the specific capacitance value to be 57 F/cm3. Effect of channel geometry on device performance has been studied and it has been found that devices with high w/l ratio has higher transconductance. Channel thickness also has major role in OECTs transconductance. By decreasing channel thickness, transconductance decreases however it reaches its maximum at lower gate voltages, indicating lower operating voltages for higher sensitivity for biosensing. Previous studies demonstrated application of PEDOT: PSS as an active material of depletion mode organic electrochemical transistor (OECT). In this work, we used over oxidized PEDOT: PSS film as a channel material of OECT and observed accumulation behavior. We study the structure of over-oxidized PEDOT: PSS and notice PEDOT degradation during over-oxidation process, while PSS remains intact. As a result, throughout this reaction, the electronic conductivity of PEDOT chain decrease dramatically. However, the ionic conductivity occurs primarily in the excess PSS and is independent of the oxidation state of PEDOT. This initiates a device which switches from depletion mode to accumulation mode by a simple oxidation process of hypochlorite treatment. In summary this works contributes to the better understating of OECTs and channel structure on working principle of OECTs to design future less invasive neuro-probes.

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  • Degree
    Master of Science
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