Enhanced Stability in Sn-Doped InGaZnO TFTs: The Critical Role of Channel Length and the Dual Effect of Lateral Field Revealed by eMSM Analysis

This work investigates the positive bias stress (PBS) instability in amorphous indium gallium zinc oxide (a-IGZO) and Sn-doped indium gallium zinc oxide (a-IGZTO) thin-film transistors (TFTs). Utilizing an extended Measure-Stress-Measure (eMSM) method, we capture the complete stress and relaxation dynamics within a single experiment. The observed positive threshold voltage (<inline-formula> <tex-math notation="LaTeX">$V_{TH}$ </tex-math></inline-formula>) shifts are well-described by a universal relaxation model, which also enables the extraction of recoverable component (<inline-formula> <tex-math notation="LaTeX">$R$ </tex-math></inline-formula>) and permanent component (<inline-formula> <tex-math notation="LaTeX">$P$ </tex-math></inline-formula>) for comparative analysis of the relaxation-phase characteristics between the two types of TFT. Under identical stress conditions (6–8 V applied across a 20-nm-thick gate dielectric), the IGZTO TFT exhibits a significant reduction in <inline-formula> <tex-math notation="LaTeX">$V_{TH}$ </tex-math></inline-formula> shift compared to its IGZO counterpart. Analysis indicates that the incorporation of Sn enhances PBS stability by mitigating the formation of oxygen vacancy-related defects while facilitating more recoverable charge trapping/de-trapping processes. Deeper investigations into IGZTO TFTs reveal a critical channel-length dependence, achieved through measurements across varied channel lengths and analysis of dynamic stress-relaxation cycles. Here, the lateral electric field in shorter channels accelerates both hot-carrier degradation during stress and field-assisted recovery during relaxation. These findings highlight the eMSM method’s efficacy in decoupling complex degradation dynamics for developing reliable oxide TFTs.