Environmental stability of polymeric thin-film transistors
Relatively little is known about the stability of the electrical performance of polymeric thin film transistors. Organic polymers are known to absorb significant quantities of impurities from vapor relative to the carrier concentration in operating devices. These properties have been used to form sensors with organic TFTs, but have not been extensively studied from the standpoint of operational lifetime and stability. We will discuss the effects of humidity and oxygen on the device characteristics of TFTs made with poly[5,5'-bis(3-dodecyl-2-thienyl)-2,2'-bithiophene] PQT-12, and poly(3-hexylthiophene), P3HT. In PQT-12, water was found to increase the rate of hole trapping in the semiconducting layer with a lesser effect on the carrier mobility. The effects of self-assembled monolayers (SAMs) formed on inorganic dielectrics on device stability will also be discussed. Exposure to oxygen was found to have little effect on the device characteristics of PQT-12 and P3HT over long time periods (months), but shorter term (hours) exposure to the ambient environment causes a reduction in the on-to-off current ratio. Simple polymeric encapsulation layers were found to mitigate these effects in devices left in the ambient environment.
Chabinyc, M. ; Endicott, F .; Vogt, B. D.; Delongchamp, D. M.; Lin, E. K.; Liu, P.; Wu, Y.; Ong, B. S. Environmental stability of polymeric thin-film transistors. SPIE Optics and Photonics; 2006 August 13-17; San Digeo; CA; USA.