Effects of Hydrogen Doping on a-GIZO Thin-Film Transistors With Hafnium Dioxide Gate Insulators Formed by Atomic Layer Deposition at Different Temperatures

초록

This study investigates the impact of hydrogen doping on amorphous gallium-indium-zincoxide (a-GIZO) thin-film transistors (TFTs) with hafniumdioxide (HfO2) gate insulators fabricated using atomiclayer deposition (ALD) at two different temperatures(150 degrees C and 300 degrees 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 degrees C is approximately 2.6 times higher than that in the film deposited at 300 degrees 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 degrees C-40 nm) is 3.41 cm(2)/V.s, whereas the mobility of GIZO TFTs with a double HfO2 (150 degrees C-10 nm)/HfO2 (300 degrees C-30 nm) gate insulator structure is significantly higher at 14.9 cm(2)/V.s. The corresponding threshold voltage (VTH) values are 0.82 and 0.89 V, respectively. These differences are attributed to variations in hydrogenintensity between the HfO(2)gate insulator deposits at 150 degrees Cand 300 degrees C, as confirmed by TOF-SIMS. However, a distinctnegative VTH shift occurs under positive bias stress (PBS)conditions with increased hydrogen concentration. This anomaly results from excessive hydrogen doping withina single HfO2 gate insulator deposited at 150 degrees C, which negatively impacts reliability and mobility. This study notonly verifies the enhanced electrical characteristics ofGIZO TFT devices employing double HfO2 gate insulatorswith optimized film thicknesses deposited at both 150 degrees C and 300 degrees C, leveraging the hydrogen doping effect but alsoemphasizes the significance of controlled hydrogen con-centration for optimal electrical performance and stability.

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