I was a post-doc in Bell Laboratories between 1990 and 1992. At the time, I was working on compound semiconductor optoelectronic devices. Because I was always looking for new, greener pastures, some new area of research, I proposed to the senior management at the laboratory that they start a program in organic semiconductor devices—in particular, light-emitting diodes and transistors. I was prompted to make the suggestion after reading a couple of then recent articles on polymer LEDs—a couple of reports from Europe and Japan that fascinated me. I was hired as a principle investigator at the laboratory in 1992, and I helped set up the organic transistor effort at Bell Labs, which has since been extremely successful. My first paper came out in 1994 (Dodabalapur A, et al., "Microcavity effects in organic semiconductors," Appl. Phys. Lett. 64[19]: 2486-8, 9 May 1994) and I’m still very active in that area. I’d say more than half of my work is on organic transistors.

“What we want and what we need is to be able to make both n-channel and p-channel semiconductors simply, by printing.”

This particular paper was the first report of high mobilities in a conjugated polymer semiconductor transistor. Up until then the mobilities people had achieved with polymers were quite modest. This represented an increase by a factor of 100.

The key was our recognition that regioregularity leads to increases in mobility. Zhenan Bao deserves much of the credit for this.

Not at all. In fact, based on that paper, I subsequently started a company to develop these circuits. I knew that was a big breakthrough. Circuits ultimately are what result in applications. I don’t mean to downplay materials and devices, but they are all part of a chain and when you reach the top of the chain, when the circuits behave well, then you can think of applications. There’s a big gap between having promising materials and circuits that function well. That Nature paper was bridging the gap.

In our case, the biggest challenge was that we really had to develop all the tools and techniques from scratch. We had to do everything ourselves.

The field has evolved since then in the sense that there are new materials coming out. Some of that is our work. We have some recent advances making solution-based CMOS, which means we can actually print n-channel and p-channel semiconductors for first time. That happened last year, in 2006.

We’re now at the stage that CMOS not only works but also can be fabricated by organic printing processes. We’ve done that with several collaborations over the past year, working mostly with other chemists. What we want and what we need is to be able to make both n-channel and p-channel semiconductors simply, by printing. If the production process is complicated, then the benefits—the ease of fabrication and the low cost—diminish greatly. For us to successfully realize those benefits we have to upgrade with solution-based materials. So this was like a decade-long experiment and, in a sense, it’s still going on. We’re still working to improve organic transistors and to simplify the production process.

We’re going to have electronic paper prototypes based on organic transistors. We’re probably going to have organic RFID tags, and we’re going to see the emergence of all these other new applications. We’re also going to see a further refinement in the materials available for organic transistors, with improvements in charge mobility, speed and stability.

In the area of organic transistors, we have about three main projects. The first is studying how fast these things work—how quickly they can switch and the closely related phenomenon of charge transport. How charges move in these organic semiconductors. The second continues to be the development of organic CMOS circuit technology. The third is the development of these organic transistor-based chemical and biological sensors. These are our three main areas of emphasis.

In fact, it has more or less kept pace with our early predictions. I have a stack of articles based on interviews I gave 10 to 12 years ago when I was saying that the time to applications would be 10 to 15 years. We’re now reaching the point that this is starting to happen. Prototypes are now available and we’re hoping very soon to have products. It’s just another example of how long it takes basic research to take the route to applications.

Within the domain of organic transistors, I would have to say there are three, all closely related: the first would have to be the development of organic CMOS. The second is the development of display backplanes and integrated transistors for display applications. And the third is our pioneering work on chemical and biosensors.

I would say that one thing that makes this field so unique and so rewarding is that it requires a combination of chemistry, physics, and engineering—electrical engineering—to make progress. It is truly interdisciplinary in nature. If you’re a chemist by training, you must know some electrical engineering and physics to succeed. If you’re an electrical engineer, you have to know the necessary chemistry and physics. And this interdisciplinary nature makes the work that more challenging and rewarding. As for applications, I would say we can start to look for them in the next few years. While nothing is available quite yet, they will start to roll out soon. There are many companies that are now very serious about this technology.

Ananth Dodabalapur, Ph.D.
Microelectronics Research Center
University of Texas at Austin
Austin, TX, USA