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

ABSTRACT 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 (V TH ) 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 V TH 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.