Effects of Hydrogen Doping on A-Gizo Thin-Film Transistors with Hafnium Dioxide Gate Insulators Formed by Atomic Layer Deposition at Different Temperatures

This study investigates the impact of hydrogen doping on amorphous gallium-indium-zinc oxide (a-GIZO) thin-film transistors (TFTs) with hafnium dioxide (HfO $_{\text{2}}$ ) gate insulators fabricated using atomic layer deposition (ALD) at two different temperatures (150 $^{\circ}$ C and 300 $^{\circ}$ C). To assess the influence of hydrogen doping, we fabricate a-GIZO TFTs with double-layer HfO $_{\text{2}}$ gate insulators deposited at varying temperatures. The hydrogen concentration in the HfO $_{\text{2}}$ thin film deposited at 150 $^{\circ}$ C is approximately 2.6 times higher than that in the film deposited at 300 $^{\circ}$ C, as determined by the measurements of hydrogen intensity using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The mobility of GIZO TFTs with a single HfO $_{\text{2}}$ gate insulator (300 $^{\circ}$ C–40 nm) is 3.41 cm $^{\text{2}}$ /V $\cdot$ s, whereas the mobility of GIZO TFTs with a double HfO $_{\text{2}}$ (150 $^{\circ}$ C–10 nm)/HfO $_{\text{2}}$ (300 $^{\circ}$ C–30 nm) gate insulator structure is significantly higher at 14.9 cm $^{\text{2}}$ /V $\cdot$ s. The corresponding threshold voltage ( $\textit{V}_{\text{TH}}$ ) values are 0.82 and 0.89 V, respectively. These differences are attributed to variations in hydrogen intensity between the HfO $_{\text{2}}$ gate insulator deposits at 150 $^{\circ}$ C and 300 $^{\circ}$ C, as confirmed by TOF-SIMS. However, a distinct negative $\textit{V}_{\text{TH}}$ shift occurs under positive bias stress (PBS) conditions with increased hydrogen concentration. This anomaly results from excessive hydrogen doping within a single HfO $_{\text{2}}$ gate insulator deposited at 150 $^{\circ}$ C, which negatively impacts reliability and mobility. This study not only verifies the enhanced electrical characteristics of GIZO TFT devices employing double HfO $_{\text{2}}$ gate insulators with optimized film thicknesses deposited at both 150 $^{\circ}$ C and 300 $^{\circ}$ C, leveraging the hydrogen doping effect but also emphasizes the significance of controlled hydrogen concentration for optimal electrical performance and stability.