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Effects of mechanical stress on printed polymer-based TFTs on flexible display backplanes


Additively printed polymer thin-film transistors (TFTs) arrays on plastic substrates can enable low cost displays with new functionality and performance. Here, we discuss some of the challenges arising from the integration of ink-jet printing and polymeric semiconductors to fabricate display backplanes on flexible substrates. Specifically, we present the results of in-situ electrical performance of printed bottom-gate TFTs subjected to a known mechanical strain during both static, or sequential, and dynamic, or cyclical, loading. These TFTs were fabricated on flexible polyester substrates, with a polythiophene derivative PQT-12 as the semiconducting polymer. Transfer/output characteristics and carrier mobilities as a function of elastic strain for 12 separate TFT's with three different W/L ratios and dimensions are evaluated and compared with those of amorphous Si. Transistor performance during high- and low-cycle fatigue is compared to that during incremental static loading, and the effects of TFTs dimensions and orientation on their performance while mechanically deformed are also discussed. We found that for all deformation modes, the TFTs functioned in compression down to the radius of curvature of 4 mm, corresponding to 2% strain, with little degradation in performance, while in tension the transistors failed due to dielectric cracking at ~ 1% strain.


Greer, J. R. ; Wong, W. S. ; Lujan, R. A. ; Krusor, B. S. ; Street, R. A. Effects of mechanical stress on printed polymer-based TFTs on flexible display backplanes. Materials Research Society, 2007 Spring Meeting; 2007 April 9-13; San Francisco; CA; USA.