Please tell us a little about your research and educational background.

My formal educational background is in materials science and engineering. Throughout my professional career, however, my work was focused in the space between materials science and electrical engineering, with frequent excursions into relevant areas of chemistry and physics. For my Ph.D. thesis I studied polymeric electronic materials, specifically vacuum deposited polyimide dielectrics. This gave me the opportunity to move into the field of organic semiconductors during my two-year post-doctoral fellowship at Philips Research (1993-1995), at a time when the field was preparing to change gears and move into center stage in the decade that followed.

“This is the beauty of organic semiconductors: the possibilities are only limited by the availability of organic synthesis resources.”

One of the key results of my work during that period was the first comprehensive study on vacuum-deposited pentacene thin film transistors (TFTs), which was published in 1996 (Dimitrakopoulos CD, Brown AR, Pomp A, "Molecular beam deposited thin films of pentacene for organic field effect transistor applications," J. Appl. Phys. 80[4]: 2501-8, 15 August 1996—incidentally, the paper missed the Special Topics analysis cut-off date by one year). This paper is important because it showed that pentacene, which is now the dominant channel material in organic TFTs, could compete on equal terms with the best organic TFT channel materials at the time, i.e., thiophene oligomers. As more and more people began using pentacene in TFTs, great progress was made in improving charge mobility and other aspects of organic TFT performance, which have brought the field closer to commercial applications.

After joining IBM Research in late 1995, I initiated research work on organic transistors there, a project that lasted for about eight years. With a small team of researchers that later joined the project, we developed technologies and understanding that in the future may help enable the fabrication of high-performance, low-cost, flexible, active matrix flat-panel displays and other organic electronic devices. Some of that work has been published in papers highlighted in the Special Topics analysis of the field.

  What interested you in working in this field?

Initially, it was the potential of the unique properties of organic semiconductors to enable the fabrication of electronic devices that could not be made otherwise. But the more I was immersed in the field, the more I realize that the major reason for its existence and its success was the almost unlimited choice of organic semiconducting materials available to the scientist or engineer: both from the pool of already synthesized molecules and from molecules designed to address specific application needs in a tailor-made fashion. This is the beauty of organic semiconductors: the possibilities are only limited by the availability of organic synthesis resources.

This paper, which I wrote with P. R. L. Malenfant (then a post-doc at IBM Research, now at GE), was both a review of my team’s work—mostly published, but some unpublished work was also included—and a quite extensive, but not exhaustive, review of the field of organic transistors. The latter chronologically concentrated mainly on the decade that preceded this paper, but included a few older papers that we considered very important in the formation of the field as a whole. We tried to avoid a mere listing of papers and, whenever possible, we analyzed, compared, and commented on the importance of the data presented, and gave our vision for the future of the field.

I am happy to mention that this paper is cited quite often by authors outside the field of organic semiconductors, which indicates an underlying broader impact. Most importantly, colleagues from universities have informed me that they use this paper as standard reading material for their graduate students in the field of organic transistors, and this is quite gratifying for me.

  How has the field advanced since the 2002 review?

There have been important developments on several fronts. Organic transistor performance has been increased and understanding of the physics has been improved. Most importantly, a lot of energy is being spent on studies of processing and fabrication issues in much detail, and this is a very important and unavoidable phase for eventually achieving the goals set out for this field. As it was always the case in organic electronics, contributions from several disciplines of engineering and science have been required and used in the pursuit of performance and processing advances.

  What practical applications for organic thin-film transistors have come into being or are expected to do so?

As far as I know, there have been several applications in the development stage worldwide, both in the high-end space of organic transistors and the low end. In the high end, where cost is not the most important determining factor, one could mention backplanes for active matrix flat panel displays. For example, with the mobility of pentacene TFTs being two to three times higher than the mobility of the entrenched technology (a:Si-H TFTs), new applications have come within reach. If one considers this in combination with the recent development of highly efficient emissive pixels based on phosphorescent organic light-emitting diodes, one could clearly see a path to the holy grail of this field, i.e. the fabrication of high-performance, low-cost, flexible, active matrix, emissive flat-panel displays with organic TFT backplanes. This requires large investment and focused work, and I see such work taking place both in industry and academia.

In the low end, where cost is everything and high performance is not an obligatory requirement, the field’s expectation is that printable organic electronics will find their initial niche soon. In this space, too, there is a lot going on and the future seems quite bright.

And when we are talking about applications, I should not fail to mention the potential of organic semiconductors for bio-related applications such as sensors for biological molecules. Initial reports show a lot of promise.

I expect the future of organic TFTs to be bright, as I mentioned before. However, the entrenched technologies at various levels progress too, and as we all know, it is extremely difficult to dethrone mature technologies, even if a new technology has some performance advantage. This is why I expect organic TFTs to first complement the traditional types of TFTs, until a manufacturing base and vendor support is created. Of course, my hope, and I am sure everyone else’s in the field, is that there will be a new step in performance improvement, following the past trend that we had described in our review paper in 2002, i.e., the mobility will increase by one more order of magnitude. This would put organic TFTs in direct competition with poly-Si.

Christos Dimitrakopoulos, Ph.D.
IBM Research Division
Thomas J. Watson Research Center
Yorktown Heights, NY, USA