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    Comparative investigation of electronic parameters of low voltage organic field-effect transistors with variable capacitance non-ionic gel gate dielectrics
    (Elsevier, 2019) Yardım, Tayfun; Yücedağ, İbrahim; Allı, Sema; Allı, Abdulkadir; Demir, Ahmet; Kösemen, Arif
    Non-ionic gel dielectrics (NIGDs) have high effective capacitances (C-EFF) which can be used to reduce the operating voltage of the organic field-effect transistors (OFETs). Limited work has been carried out about these kinds of dielectrics although they have advantages of low cost and easy production. Besides, by mixing propylene carbonate (PC) with various kinds of polymers in order to tune the C-EFF of the blend, electronic parameter performance of the OFETs can be improved. In this study, regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT) based OFETs were fabricated. Specifying the poly(methyl-acrylate) (PMA) as a reference dielectric and adjusting the soybean oil to methyl acrylate weight ratio in the polymerization process to form copolymers of PMA, totally three types of dielectrics were synthesized and transformed into a gel state to obtain the reduced C-EFF. Gel dielectrics were named according to the soybean oil to methyl acrylate weight ratio. Such that, %0 ratio stands for NIGDO, %8 ratio stands for NIGD1 and %11 ratio stands for NIGD2 and OFETs fabricated with these NIGDs were named with regard to these names (NIGOFET0, NIGOFET1, and NIGOFET2). After the electrical characterization, it was seen that mobility enhanced as the C-EFF decreased as predicted. It could be attributed to a formation of less self-localization of the charge carriers in the semiconductor-dielectric interface. Moreover, it was seen that NIGOFET1 had the lowest Subthreshold Swing (SS) and off-current (I-OFF) consequently the highest on-to-off current ratio (I-ON/I-OFF). It implied that it had better insulation property and semiconductor-dielectric interface compared to the other NIGOFETs.
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    Comparison of Electronic Parameters of Low Voltage Organic Field-Effect Transistors with Novel Gel Gate Insulators
    (Amer Scientific Publishers, 2019) Yardım, Tayfun; Demir, Ahmet; Allı, Sema; Allı, Abdulkadir; Kösemen, Arif; Yücedağ, İbrahim
    In this paper, regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT)-based low voltage organic field-effect transistors (OFETs) with three kinds of non-ionic gel gate insulators (NIGIs) were fabricated and compared in terms of their electronic properties. One of the NIGI was prepared by mixing solution-processed poly(methyl acrylate) (PMA) with propylene carbonate (PC) until it becoming a gel state and same procedure was applied to the solution-processed copolymers of PMA called as P18 and P28. As a result, it was seen that fabricated OFETs could be operated at low voltages which is very significant property in order to manipulate the devices in low power electronic applications. On the other hand, it was noted that mobilities of the transistors were enhanced by reducing the effective capacitance (EC) of the NIGIs. This could be attributed to less charge carrier self-localization formation between the insulator-semiconductor interface when the EC was decreased. Furthermore, devices showed similar on-to-off current (I-ON/I-OFF) ratio which was good for using them in inverter applications. Besides, subthreshold swing (SS) for the P18 non-ionic gel OFET (NIGOFET) was the highest probably due to the less water-repellent chemical structure of the P18 NIGI.
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    Organic field effect transistor with a novel poly(linoleic acid)-g-poly(methyl methacrylate)-g-poly(D,L-lactide) graft copolymer insulator using a PEDOT:PSS composite electrode
    (Springer, 2019) Demir, Ahmet; Allı, Sema; Allı, Abdulkadir; Kösemen, Arif
    This study presents a one-pot process used to synthesize novel poly(linoleic acid)-g-poly(methyl methacrylate)-g-poly(D,L-lactide) (PLina-g-PMMA-g-PLA (PLiMALA-3)) graft copolymers. The process was carried out by combining the free radical polymerization (FRP) of methyl methacrylate with the ring-opening polymerization (ROP) of D,L-lactide from polymeric linolenic acid having peroxide groups in the main chain. The characterization of the graft copolymers was performed using proton nuclear magnetic resonance, gel permeation chromatography, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques. Afterwards, an organic field effect transistor (OFET) was fabricated with the novel poly(linoleic acid)-g-poly(methyl methacrylate)-g-poly(D,L-lactide) graft copolymer (PLiMALA-3) as the insulator layer. Poly(3-hexylthiophene) (P3HT) was used as the active layer and pre-patterned OFET substrates were used as the source/drain electrodes. In order to measure capacitance, an ITO/(PLiMALA-3)/PEDOT:PSS structure was prepared using the same method. For electrical characterization of the OFET, the device was held in the dark at room temperature in ambient air in order to determine the characteristics of the output and transfer current-voltage (I-V). The main parameters of the device, which included the threshold voltage (V-Th), field effect mobility ((FET)) and current on/off ratio (I-on/I-off), were determined by measuring the capacitance-frequency (C-f) plot of the ITO/Polymer/PEDOT:PSS structure. Results showed that the fabricated OFET device exhibited good performance including low V-Th, comparable mobility and I-on/I-off.