Improvements in the bending performance and bias stability of flexible InGaZnO thin film transistors and optimum barrier structures for plastic poly(ethylene naphthalate) substrates

Amorphous indium gallium zinc oxide thin-film transistors (TFTs) were fabricated and characterized on flexible poly(ethylene naphthalate) (PEN) substrates. A hybrid inorganic/organic double-layered barrier layer structure was proposed for enhancing the permeability and the surface roughness of the PEN substrates, which was composed of a 3 μm-thick spin-coated organic layer and a 50 nm-thick atomic-layer-deposited Al 2 O 3 inorganic layer. The saturation mobility, subthreshold swing, and on/off ratio of the TFTs on the PEN substrates with the proposed hybrid barrier structure were found to be approximately 15.5 cm 2 V −1 s −1 , 0.2 V dec −1 , and 2.2 × 10 8 , respectively. These good TFT performances were not degraded even under the mechanical bending situation at a curvature radius of 3.3 mm and after the repetitive bending cycles. Furthermore, the variations in turn-on voltage of the TFT were evaluated to be approximately as small as −0.1 and +1.6 V under the negative and positive-bias stress tests, respectively. Bending characteristics of flexible oxide thin-film transistors could be enhanced by optimizing the barrier layers on the polyethylene naphthalate substrate.