Indium-Gallium-Zinc-Oxide (a-IGZO) is an amorphous oxide semiconductor that has been attracting increasing attention for use in flat panel display and optoelectronic applications. This is largely due to IGZO’s high mobility at low processing temperatures. In this thesis, IGZO films were successfully grown on polyethylene naphthalate (PEN) substrates by RF magnetron sputtering at room temperature. These films were flexible, transparent and had a good Hall mobility (5-12 cm2/Vs). High quality metal oxide Schottky contacts were fabricated on these as-grown IGZO/PEN films with on-off rectification ratios of up to 108. These were then used as the gate contacts in transparent metal semiconductor field effect transistors (MESFETs). The performance and device stability of these IGZO/PEN MESFETs were investigated via a series of stress tests in both dark conditions and under illumination at different wavelengths in the visible spectrum. During constant voltage stress testing under illumination, the threshold voltage shifted by -0.54 V and 0.38 V for negative and positive gate biasing, respectively. These shifts proved reversible when devices were left in dark conditions for extended periods of time. The effect of persistent photoconductivity after exposure to different illumination sources was examined, with three potential passivation coatings to reduce this unwanted effect explored. Transparent IGZO/PEN MESFETs with an absolute transmission of up to 75% were achieved with the use of ITO ohmic contacts. These devices survived mechanical bending down to a radius of 7 mm with negligible variation in on-current and threshold voltage. This allows for the possibility of incorporating their use in future applications such as flexible transparent electronics.

Conducting polymer is a rapidly developing area of research due to its potential in combining the physical properties of polymers with electrical properties previously found only in inorganic systems. These conducting polymers owe their unique properties to a conjugated polymer backbone and become conducting upon oxidation or reduction. Melanin, a biopolymer, possess a conjugated backbone required of a conducting polymer, and has shown properties of an amorphous semiconductor. However, there has not been much study done in this area despite its potential, and this is partially due to the lack of processing methods as melanin is generally synthesised as an intractable powder. Thus, a better synthetic method was required, and a possible solution is the use of electrochemical synthesis. In our previous study we have shown that melanin can be synthesised electrochemically as a free-standing film, which was the first step towards the use of melanin as a bulk material. This project aims to continue from this preliminary work, investigating the various synthetic parameters and possible modifications as well as investigating possible applications for the electrochemically synthesised melanin film.

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