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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 solution processed materials such as printable metals and polymeric semiconductors used to fabricate display backplanes on flexible substrates. Inkjet printing of silver nanoparticles deposited from solution is utilized to form the conducting lines of the backplane. This deposition technique is fundamentally different from the well-understood CVD methods, driving the need for mechanical evaluation of these materials. We present results of stress measurements of the nanoparticle films and lines as well as their hardnesses and modul as a function of deposition and curing conditions. Another significant challenge arises from the "run-out" issue, which manifests itself as a misalignment error between the flexible substrate (polyethylenenaphthalate, or PEN) and the subsequently printed features. This error is generally caused by the substrate deformation in response to the imposed strain during fabrication. We present a preliminary predictive model for the run-out error as a function of strain, elastic properties of the substrate and the film stack. Finally, the electrical performance of printed bottom-gate TFTs subjected to a known mechanical strain was evaluated. These TFTs were fabricated on flexible PEN substrates, with a polythiophene derivative PQT-12 as the semiconducting polymer. Transfer/output characteristics and carrier mobilities were evaluated as a function of strain under both static and dynamic testing conditions.

 
citation

Greer, J. R. ; Endicott, F .; Lujan, R. A. ; Street, R. A. Effects of mechanical stress on printed polymer-based TFTs on flexible display backplanes. 2006 Gordon Research Conference (GRC) on Thin Films; 2006 July 30 - August 4; Waterville; ME; USA.