Reliability Enhancement of Oxide Thin-Film Transistors via Suppression of a-IGZO Protrusions for Improved Image Quality in LTPO AMOLED Displays

초록

We identify a new origin of oxide thin-film transistor (TFT) instability and propose a process-level approach to effectively overcome reliability-induced degradation in low-temperature polycrystalline silicon and oxide (LTPO) backplanes. Multi-buffer protrusions originate from non-uniform LTPS processes, including excimer laser annealing and subsequent active-layer dry etching. These protrusions are transferred into the subsequently formed oxide TFT stack, inducing protrusion variations in the amorphous indium-gallium-zinc-oxide (a-IGZO) channel. Microscopic structural analyses, along with electrical characterization, demonstrate that these a-IGZO channel protrusion variations lead to threshold-voltage (VTH) variation and mobility degradation in oxide TFTs. To mitigate this issue, the active layer dry-etch process is optimized to enhance the etch selectivity between the polycrystalline silicon and multi-buffer layers. The optimized process reduces multi-buffer protrusion heights from 5.1 to 1.6 nm and improves a-IGZO channel protrusion uniformity within a single panel, thereby decreasing VTH variation after reliability testing from 0.92 to 0.15 V across the panel. This study reveals the root cause of oxide TFT instability and proposes effective process solutions for LTPO active-matrix organic light-emitting diode (AMOLED) displays.