Circular Structure for High Mechanical Bending Stability of a-IGZO TFTs

We employ a circular (Corbino) thin-film transistor (TFT) structure, in which the outer-ring is the drain and the inner-ring is the source, to improve the stability of amorphous-indium-gallium- zinc-oxide TFTs under tensile bending strain. We attribute the stability improvement to a more uniform electric field distribution across the circular channel, as it is isolated from local electric field crowding at sharp corners or channel edges. In addition, the effect of strain-induced increase in channel charge concentration is small in Corbino TFTs, owing to the larger outer-ring electrode, which depletes more electrons than the drain of rectangular TFTs. Furthermore, the circular shape results in bending direction independence, which is very important in multi-TFT circuits, where TFT orientation varies with position.