Fabrication and Electrical Characterization of Organic Neuromorphic Memory Devices.

The organic polymer has gained considerable interest in the field of bioelectronics during the last few decades. Organic materials based devices have several unique characteristics; low-cost and low thermal budget fabrication processes, tunable properties through chemical synthesis, flexibility and biocompatibility. Those entire features make organic materials suitable for new functionalities in comparison to their inorganic counterparts. Moreover, the attributes mentioned earlier give an additional degree of freedom to use organic materials in neuromorphic devices whose functions have the potential to induce biological realism in brain-inspired information processing. Nowadays, neuromorphic devices have attracted the interest in research and industry. The use of organic materials might lead to a new class of neuromorphic devices that has several applications in areas that range from brain-computer interfaces to circuits for local data processing in energy restricted environments. However, flexibility and biocompatibility helps to optimize the mechanical mismatch between electronics and biological substances that might be a new way of signal processing at the interface with biology.

In this thesis project, three-terminal organic polymer-based Organic Electrochemical Transistors (OECTs) have fabricated in cleanroom-based fabrication process. PEDOT:PSS and p(g2T-TT) thin-film polymers were used as active channel materials in OECTs. Ions inject from the liquid electrolytes by using a specific gate bias. The migrated ions modulate the entire bulk-volume conductivity of the organic polymer channel due to the strong coupling between ionic and electronic charges within the channel. Several electrical characterizations of OECTs were investigated in the presence of liquid electrolytes. The memory phenomena of PEDOT:PSS and p(g2T-TT) polymer-based OECTs were systematically studied in this work. It was observed that PEDOT:PSS organic polymer shows no memory properties/negligible memory, and p(g2T-TT) polymer exhibits memory phenomena due to its unique polymer structure. It also seen that the memory process in p(g2T-TT) polymer is a reversible process that can be return to its initial state by applying opposite gate bias. Beside it, the polymer's behavior also was investigated in contact with and without aqueous solutions. Additionally, it observed that p(g2T-TT) polymer is less hydrophilic compared to PEDOT:PSS due to its intrinsic properties. Multiple memory devices were fabricated at different times and reproducible memory phenomenon was observed in OECTs.