The Effects of Mechanical Bending and Illumination on the Performance of Flexible IGZO TFTs

Amorphous indium-gallium-zinc-oxide (a-IGZO) is an interesting semiconducting material for use in flexible thin-film-transistor (TFT) fabrication due to the high carrier mobility and low deposition temperatures. To use these TFTs in flexible applications, their behavior under applied mechanical strain and changing illumination, as well as the influence of bending on reflattened TFTs, needs to be understood. We have fabricated a-IGZO TFTs on flexible substrates and measured their behavior under tensile and compressive strains down to bending radii < 10 mm. Bending tests were applied in the dark, as well as under 90-lx illumination. Without illumination, the tensile and compressive strains caused a little change in the TFT performance, but the influence of the tensile strain combined with illumination causes changes in the TFT mobility of 15% and changes in threshold voltage of -0.11 V. By comparison, the performance of illuminated TFTs under the applied compressive strain changes little compared with measurements in the dark. The impact of repeated tensile bending and reflattening shows a similar picture; bending tests carried out in the dark resulted in a nearly constant threshold voltage, but with illumination, we observed a shift of -0.1 V after 40 min of repeated bending.