Organic Thin Film Transistors: A Materials Science Perspective

In the last 20 years substantial progress has been made in the development of -conjugated organic semiconductors as an alternative to amorphous silicon for low cost, thin film electronics. The attractive properties of organic semiconductors, including low temperature processability and reasonable charge carrier mobilities, have led to widespread efforts to incorporate these materials into functional circuitry. In the late 1990s, organic semiconductors achieved sufficiently high levels of performance in thin film transistors (TFTs) that printed circuit applications could be envisioned. Increasing charge mobilities in order to increase transistor switching speeds remains an important goal, but other figures of merit, such as threshold voltage stability, are becoming vitally important. Better knowledge of structure-property relationships for organic semiconductors and for organic semiconductor/gate insulator interfaces will be important for further advancements in OTFTs.

This talk will begin with an overview of OTFT operation and historical development. We will then describe our efforts to understand structure-property relationships in pentacene TFTs, which have become the benchmark devices in organic electronics. We will also discuss the synthesis of new organic semiconductor materials, organic semiconductor film growth, structure characterization by X-ray diffraction and atomic force microscopy, and device current-voltage characteristics. If time permits, we will discuss some recent work on the use of very high capacitance gate insulators to achieve low voltage TFT operation. A recurrent theme is the effect of structure at all length scales- including molecular structure, crystal packing, and film morphology- on critical OTFT figures of merit such as the charge mobility, the threshold voltage for conduction, and the on-to-off current ratio.

References
[1] H. Klauk, T.N. Jackson, Sol. State Technol 43, 63 (2000).
[2] C.R. Newman, C.D. Frisbie, D.d.S. Filho, J.L. Bredas, P. Ewbank, K.R. Mann, "Introduction to Organic Thin Film Transistors", Chem. Mater. 16, 4436 (2004).
[3] Malliaras, G.G.; Friend, R.H. "An Organic Electronics Primer", Physics Today, 58, 53 (2005).
[4] Zaumseil, J.; Sirringhaus, H. "Electron and Ambipolar Transport in Organic Field Effect Transistors", Chem. Rev. 107, 1296 (2007).

For more information contact Dr. Jean-Luc Brédas (404-385-4986).