Degradation Mechanisms Of Low Temperature Poly-Si Thin-Film Transistors Under Circuit Applications

Device reliability of low temperature poly-Si (LTPS) thin-film transistors (TFTs) under circuit application is a key issue to be addressed for integration of TFT-based driver circuits. In this paper, degradation mechanisms of LTPS TFTs under various electrical biases are reviewed, including both DC and AC conditions. For n-type TFTs under DC stresses, either hot carrier (HC) or self-heating (SH) can be the controlling degradation mechanism. While for p-type TFTs biased in the ON or OFF-state, negative or positive bias temperature instability (NBTI or PBTI) dominates the device degradation. Under AC operation by V-g switching only, dynamic HC effect is the controlling degradation mechanism for n-type TFTs, while both NBTI and the dynamic HC mechanisms are effective for p-type TFTs. Under AC operation by V-d switching only, another dynamic HC mechanism due to non-equilibrium drain junction causes HC degradation in both n- and p- type TFTs. Under AC operation by synchronized Vg and Vd switching, device degradation is dominated by SH at low-frequencies whereas by dynamic HC at high-frequencies in n-type TFTs.