Organic thin film transistor (OTFT) has been studied for several years because of their advantages of cheap process, simple fabrication and mechanical flexibility. Although, OTFTs still have some problems owing to low mobility, short life-time and electrical hysteresis in voltage-current characteristics. To commercialize OTFT devices, the improvement of mobility should be followed. The mobility can be improved by a surface treatment with self assembly monolayer (SAM) enabling the organic molecules aligned. Because of the protruded structure of the source and drain electrodes, the flat active layer may be perturbed, reducing the carrier motilities. The flat active layer could be achieved by embedded electrodes, in SiO2 layer.
We made source-drain electrodes by E-beam lithography, reactive ion etching (RIE) was used to etch the SiO2 (~30nm) for the embedded structure. Au was deposited by 30nm on the SiO2 layer using electron beam evaporation after depositing 10nm titanium (Ti) layer to improve the metal adhesion. OTS (octadecyltrichlorosilane) layer was formed and the RR-P3HT was dissolved in chloroform at 0.7wt% and spin-coated on the substrate. HP 4140B pAmeter/DC Voltage Source was used for measuring I-V characteristics of the device.
With the conventional structure of OTFT, voltage-current characteristics were recorded from zero through positive maximum to zero voltage (forward voltage sweep), and from zero through negative maximum voltage to zero (backward direction). The current levels for sweeping-up direction were bigger than the case of sweeping down. These phenomena were attributed to the existence of traps in the gate side and the channel side. The capture or the release of the charges in traps can influence the effective electric field in the active channel by the screening process. Capacitance-voltage measurement, fitted to the trap model. The details of the conduction mechanism in the embedded structure will be discussed in the presentation.
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