Characterization of DC-Stress-Induced Degradation in Bridged-Grain Polycrystalline Silicon Thin-Film Transistors

In this paper, dc-stress-induced degradation in bridged-grain (BG) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) is systemically characterized and investigated. Compared with normal poly-Si TFTs, BG poly-Si TFTs exhibit better hot-carrier (HC) reliability, better self-heating (SH) reliability, and better negative bias temperature (NBT) instability. Resulting from the heavily doped BG lines inside the active channel, lateral electric field reduction at the drain side, Joule heat diffusion enhancement at the channel length direction, and boron-hydrogen bond formation at interface/grain boundaries are, respectively, responsible for the improved HC reliability, SH reliability, and NBT reliability in BG poly-Si TFTs. In addition, stress V_g-dependent HC degradation with fixed stress Vd, stress power density-dependent SH degradation, and vertical electrical field-dependent NBT degradation are also examined in both normal poly-Si TFTs and BG poly-Si TFTs. All test results indicate that such high-performance and highly reliable BG poly-Si TFT has a great potential for system-on-panel application.