Vapor phase deposition of organic semiconductors for field effect transistor applications

(eng) The coming of age of organic circuits requires the development of high-performance and cost-effective processing techniques. In this work, the Organic Vapor Phase Deposition (OVPD) of small-molecular-weight organic molecules is investigated for the production of thin semiconducting films used as the active layer of circuits. Two OVPD systems are designed and assembled: A Static OVPD system that is inspired from a chemical vapor phase deposition tool and an In-line OVPD system that accommodates a linearly moving substrate and that is roll-to-roll compatible. These two tools are optimized for the growth of pentacene and PTCDI-C13, two high-mobility organic semiconductors. With saturation mobilities of up to 1.5 cm²/Vs and reproducible well-behaved characteristics, high-quality p-type transistors based on OVPD-grown pentacene films are demonstrated. High-quality circuits are also produced using these pentacene layers grown on flexible substrates. The demonstration of high-mobility n-type transistors based on OVPD-deposited PTCDI-C13 film paves the way towards the production of complementary circuits. Analytical and numerical transport models are developed in order to understand and characterize the link between processing conditions, material use efficiency, film thickness uniformity and growth speeds. A material use efficiency of up to 65% and a thickness uniformity as low as 1.1% over 4’’ substrates are demonstrated in our systems. Moreover, high production throughput is investigated by maximizing film growth speeds. A deposition rate of 15 Å/s is obtained for PTCDI-C13 in the Static system and a record average deposition rate of 105 Å/s is achieved for pentacene in the In–line system. In addition, we show that, in this system, thin film electrical characteristics are conserved up to the highest growth speeds. Finally, sub-monolayer growth of pentacene is investigated. We show that growth by OVPD follows the same patterns as vacuum growth. However, the presence of the background gas delays nucleation and enhances growth kinetics. As a conclusion, this work shows that OVPD, especially in the in-line architecture, is a very promising candidate for the low-cost production of high-performance organic semiconducting thin films.