|Photograph of a Rubrene molecular crystal
(right) and an FET device based on this material (left).
||a) Resistance vs. temperature data demonstrating
superconductivity in our ion-implanted plastic material. b)
SEM image of the cross-section of the device showing the buried
Sn-C conducting layer, c) and d) Photographs of two of our measured
Plastics are generally considered to be poor conductors of electricity.
However, polymers can be made conductive by manipulating their chemical
structure so that they contain long chains of alternating single
and double carbon bonds. This has lead to the development of ‘plastic
electronics’, with a number of associated advantages including
mechanical flexibility, robustness, chemical versatility, low weight,
and most significantly low cost and ease of large scale production.
Organic electronics is also a growing area of basic research as
much of the electronic properties of organic semiconductors are
still poorly understood.
An important factor in developing field-effect transistors (FETs)
using organic materials is how to improve the electrical mobility
(i.e., how easily current can flow through the device) to a level
sufficient for practical applications. To do this you just need
to reduce the disorder in your conducting system by moving from
an amorphous structure (currently most conducting polymer materials
consist of a tangled spaghetti of very long molecules) to more ordered
structures, for example, crystals formed from small conducting molecules.
The most interesting and potentially useful molecular crystals for
FET applications are polyacene crystals, which consist of molecules
that contain up to 5 benzene rings fused together into a linear
We spent much of 2004 working on developing our first research-quality
organic crystal FETs for this new project. This included building
and optimizing furnaces for physical vapour growth of various organic
molecular crystals, and developing a capability to produce elastomer
transistor stamps for making the FETs. In late 2004, we produced
our first high-quality crystals and made our first working FET device
and in the year ahead we will begin exploring the electronic properties
of these molecular crystal FETs in more detail.
We have also continued our measurements on the electronic properties
of ion-implanted plastics as part of an ongoing collaboration with
Paul Meredith’s group at the University of Queensland. In
late 2003 we discovered both metallic conductivity and superconductivity
at very low temperatures in this new material. This discovery has
resulted in the filing of an Australian Preliminary Patent Application
Adam Micolich, Alex Hamilton,
Jack Cochrane and Ali Rashid