Conducting polymers have been the focus of massive international research effort during the last few decades, to the point where the first conducting polymer displays have begun appearing in commercial products such as digital cameras. However, conducting polymer devices don't come without problems including lifetime issues under exposure to oxygen, moisture and light, difficulties in fabrication and their high molecular disorder, which leads to a low charge carrier mobility, and poor electrical characteristics compared to commonly used inorganic materials such as silicon. Research at UNSW is ongoing in two areas: a) developing new electronic devices using ion-implantation of polymer films and b) developing high-mobility organic field-effect transistor devices using flexible elastomer transistor stamps laminated against organic molecular crystals.

We are studying ion-implanted plastics as part of an ongoing collaboration with Paul Meredith’s group at the University of Queensland. Our discovery of superconductivity in ion mixed Sb-PEEK films has attracted significant international interest.

In parallel with developing better electrical interconnects, we are also working on making better transistors. An important challenge in developing transistors using organic materials is to improve the electrical mobility (how easily current can flow through the device). Organic molecules that form highly ordered crystals instead of disordered polymer films allow very high mobilities – as high as polycrystalline silicon. However these crystals can easily be damaged while being made into transistors. Our Nanotechnology Honours students have been working with Dr. Adam Micolich to develop a simplified process for making the transistor structure and electrical connections on a sheet of PDMS (silicone), which is then gently pressed against a single rubrene crystal to make a complete working transistor. Using this process we have built organic transistors with mobilities as high as 10 cm²/Vs – comparable to the best in the world.

Two new Honours students have extended the work on these organic transistors in 2006: Julia Sokolova has been developing a more complex processing method to further increase the mobility using ‘air-gap’ techniques, and Jason Chen has been investigating the properties of PDMS based transistors at low temperatures.

Fig. 1: Photograph of a single crystal organic transitor	Fig. 2: Electrical characteristics of a rubrene transistor

Jason Chen, Julia Sokolova, Adam Micolich, Alex Hamilton, Jack Cochrane