Study on Residual Image in Low-Temperature Poly-Si Oxide TFT-Based OLED Display on Polyimide Substrate

We study the reduction in residual image in low-temperature poly-Si oxide (LTPO) thin-film transistor (TFT)-based flexible organic light-emitting diode (OLED) displays on polyimide (PI) substrate. Conventional voltage compensation circuit (seven TFTs plus one capacitor) is used with modification of driving and some switching TFTs. The measurement results on the threshold-voltage ( ${V}_{\text{TH}}$ ) shift and SPICE simulation data on the pixel circuits indicate that the residual image is due to the PI charging effect when a single-gate coplanar poly-Si TFT is used as driving one. It is shown here that adding a bottom electrode to the coplanar poly-Si driving TFT (D-TFT) eliminates the residual image by shielding the poly-Si active layer from the PI charging effect.