Current-voltage behaviour in Liquid-state organic field-effect transistors (LOFETs)

Abstract

<p> In this thesis, the current-voltage (I-V) behaviour of Liquid Organic Field-Effect Transistor (LOFET) was systematically studied with respect to the gate voltage, channel length and channel fluid. LOFETs in both internal and external gate modes were successfully fabricated in four-probe configuration. </p> <p> It was discovered that the effect of gate voltage on the source-to-drain current of LOFETs was significant. The drain current clearly increased when the gate voltage increased. This phenomenon was found in all LOFETs samples with different channel fluids and channel lengths. In addition, it was also proved that anions are the majority carriers in LOFETs. The concentration of anions inside the LOFET channel increased while applying a larger voltage to the gate, resulted in an increase of the drain current. This achievable gate modulation set up a solid foundation for further research on the manipulation of ionic and molecular species. </p> <p>It was also obtained that the drain current was changed with variable channel lengths. The current through the LOFET channel decreased while the channel length increased. At the same time, the difference between drain current in various channels evidently increased when the gate voltage increased from 0 to 5V. This was found to be due to the anion concentration change with varying gate voltages. </p> <p> The drain currents through LOFET channels filled with fluids of different polarities were also measured. It was observed that when the polarity of the molecule increased from that of 4,4'-Dihydroxybiphenyl to that of 2-Amino-4 Phenylphenol, the drain current increased significantly. At the same time, the difference between drain current in specific solutions was also more significant, when applying higher voltage to the gate. Combining these results with the gate modulation above, there is great potential of developing new sensing techniques and even logic operation in the future. </p> <p> This work represents a step towards a new group of cheap and effiecient electronic components of LOFETs. Guided by systemic observations from the effects of gate voltage, channel length and fluid structure, there is no doubt that LOFET will become a more attractive research topic because of its promising advantages, such as easy fabrication, low cost and its highly sensitive response. </p>