Organic crystal transistors and ion-implanted polymers

Our new organic device fabrication laboratory on the Lower Ground corridor of the Old Main Building

Plastics are generally considered to be poor conductors of electricity. However, polymers can be made conductive by engineering them to contain alternating single and double carbon bonds. Organic electronics is of growing interest because while they are appearing in commercial applications, much of the electronic properties of conductive organic materials are still poorly understood. Presently we have two projects in this area – the first studies the electronic properties of transistors based on organic molecular crystals and the second involves using ion-implantation to engineer the conductivity of plastic films.

An important challenge in developing organic transistors is to improve the electrical mobility (how easily current can flow through the device). One way to achieve this is to use organic molecules that form highly ordered crystals. The polyacenes, which consist of molecules containing up to 5 benzene rings fused together into a linear chain, have shown considerable promise. These molecules readily form flat hexagonal crystals up to 1cm in diameter and have the requisite alternating single-double bond structure that allows them to conduct electricity effectively.

We produced our first working organic crystal transistors (FETs) in late 2004, and in 2005 we further optimized these devices using a newly developed technique where a prefabricated flexible transistor structure is laminated against the crystal. This eliminates the need to perform damaging fabrication processes on the fragile organic crystals. By the end of 2005 we were able to routinely fabricate organic FETs with channel lengths up to a few mm and mobilities of order 10 cm2/Vs. Such high mobilities are state-of-the-art for organic FETs.

We have also continued our measurements on the electronic properties of ion-implanted plastics as part of an ongoing collaboration with the soft condensed matter group at the University of Queensland. We are currently measuring a new series of samples aimed at better understanding this new material system.

Finally, in 2005 we also completed our new laboratories. These labs included a wet chemistry lab (shared with Mike Gal) and a device fabrication cleanroom for fabricating organic crystal FETs, silicone rubber transistor stamps and ion-implanted polymer films. With support from UNSW facilities, the new device fabrication lab has been made one of the showcase research labs in the school.

Laurence Bell, Adam Micolich,
Alex Hamilton and Jack Cochrane




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