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 (HfO2) gate insulators fabricated using atomic layer deposition (ALD) at two different temperatures (150 °C and 300 °C). To assess the influence of hydrogen doping, we fabricate a-GIZO TFTs with double-layer HfO2 gate insulators deposited at varying temperatures. The hydrogen concentration in the HfO2 thin film deposited at 150 °C is approximately 2.6 times higher than that in the film deposited at 300 °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 HfO2 gate insulator (300 °C–40 nm) is 3.41 cm2/
$\text{V}\cdot \text{s}$
, whereas the mobility of GIZO TFTs with a double HfO2 (150 °C–10 nm)/HfO2 (300 °C–30 nm) gate insulator structure is significantly higher at 14.9 cm2/
$\text{V}\cdot \text{s}$
. The corresponding threshold voltage (
${V}_{\text {TH}}$
) values are 0.82 and 0.89 V, respectively. These differences are attributed to variations in hydrogen intensity between the HfO2 gate insulator deposits at 150 °C and 300 °C, as confirmed by TOF-SIMS. However, a distinct negative
${V}_{\text {TH}}$
shift occurs under positive bias stress (PBS) conditions with increased hydrogen concentration. This anomaly results from excessive hydrogen doping within a single HfO2 gate insulator deposited at 150 °C, which negatively impacts reliability and mobility. This study not only verifies the enhanced electrical characteristics of GIZO TFT devices employing double HfO2 gate insulators with optimized film thicknesses deposited at both 150 °C and 300 °C, leveraging the hydrogen doping effect but also emphasizes the significance of controlled hydrogen concentration for optimal electrical performance and stability.