Organic electronics has its origins in materials science and concerns the development of electronic and opto-electronic devices that exploit the properties of organic materials, i.e those based on carbon rather than silicon. The most successful commercial product to date is the liquid crystal display, LCD. However, organic light-emitting devices (e.g. OLED TVs), organic solar cells, organic electronics circuitry and biochemical sensors are beginning to make their technological marks. The Nobel Prize in Chemistry for 2000 was awarded to three scientists working in the area of organic electronics: Alan Heeger, Alan MacDiarmid and Hideki Shirakawa, who have made significant contributions to the development of electrically conductive polymers. Much of the current industrially-oriented organic electronics work is being pursued under names such as plastic electronics or printable electronics, referring to the materials being exploited and the processing technology, respectively.
More challenging is molecular electronics. Here, the focus is on the behaviour of individual organic molecules or groups of molecules, and the precise three-dimensional positional control of individual atoms and molecules. Topics as diverse as molecular switching, DNA-electronics and molecular manufacturing have all been proposed. Much of the research activity is directed towards computational architectures that may, one day, rival silicon microelectronics. However, even the most optimistic researchers recognize that this is going to be some time away!
Molecular electronics also falls under the umbrella of nanotechnology. In particular, it exemplifies the ‘bottom-up’ theme of nanotechnology, which refers to making nanoscale structures by building organic and inorganic architectures atom-by-atom, or molecule-by-molecule. The physicist Richard Feynman was one of the first to predict a future for molecular-scale electronics. In a lecture in December 1959, at the annual meeting of the American Physical Society, entitled ‘There’s Plenty of Room at the Bottom,’ he described how the laws of physics do not limit our ability to manipulate single atoms and molecules. Instead, it was our lack of the appropriate methods for doing so. Feynman correctly predicted that the time would come in which atomically precise manipulation of matter would be possible.
My current research interests in organic electronics are focused in two main areas: evolvable electronics and electronic memories.
Computing with Carbon Nanotubes
Living systems are able to achieve incredible feats of computation with remarkable speed and efficiency. Many of these tasks have not yet been adequately solved using algorithms running on the most powerful computers. Natural evolution is a bottom-up design process. Living systems assemble themselves from molecules and are extremely energetically efficient when compared to man-made computational devices. The technological drive to produce ever-smaller devices is leading to the construction of machines at the molecular level. However, the basic computational paradigm is unchanged. A radically different approach is not to assemble piecemeal signal processing and memory elements but to produce systems that emulate the processing and memory devices found in nature. This is a rapidly emerging and vibrant research area that may have a significant impact on electronics as progress is made in the 21stCentury.
Conventional (Von Neumann) computer architecture
The rationale for developing organic memory devices is that some memory capability is essential if plastic/organic electronics is to become a fully integrated and significant technology.
Clearly, options for organic memory are to develop the organic equivalents of silicon DRAM, SRAM and flash, i.e. based around organic transistors. As organic electronics is not likely to compete directly, in terms of operational speed and device density, with inorganic-based technologies, the specifications for the memory elements can, to some extent, be relaxed. The polymer ferroelectric memory developed by the Xerox is very attractive. There are other simple concepts for memory devices, such as those based on resistive switching and ferroelectric tunnel junctions. However, the research on organic compounds has quite a long way to go – in terms of understanding the physics behind the device operation and developing arrays of reproducible memory cells that can be addressed in crossed-bar architectures – before the technology can find its way into the marketplace.
One category in which organic memories will excel is those devices exploiting individual molecules or small groups of molecules. This field presents formidable scientific and technological challenges. The problems of fabricating reproducible arrays of devices on a commercial scale should not be underestimated (remember IBM’s attempts to commercialise the Josephson junction in the 1970 s and 1980s?). However, the availability of memory elements on the molecular scale would revolutionise not only organic electronics but solve a potential ‘bottleneck’ Moore’s Law scaling issue for inorganic-based technologies.
A different approach to developing organic memories is not to assemble piecemeal signal processing and memory elements but to look beyond von Neumann architectures (diagram above) and, thereby, to produce systems that emulate the processing and memory devices found in nature (see section above on Evolvable Electronics).