Enhancing AC stress stability in amorphous indium gallium zinc oxide thin-film transistors via controlled hydrogen diffusion

Abstract

Amorphous oxide semiconductors (AOS) offer significant benefits in electronics, such as high electron mobility, optical transparency, low off-current, and low-temperature fabrication, making them particularly suitable for flexible and transparent displays. Despite these benefits, the widespread adoption of AOS is hindered by reliability issues such as instability under illumination, radiation, and bias stress. This study investigates the impact of AC stress on AOS-based devices, focusing on the degradation mechanisms associated with hot carrier effects (HCE). A novel approach employing hydrogen doping using hafnium oxide (HfO₂) as a passivation layer was explored. The HfO₂ layer was deposited via atomic layer deposition (ALD) using tetrakis(ethylmethylamino)hafnium (TEMAhf) and H₂O, with the latter facilitating hydrogen diffusion into the oxide semiconductor layer during deposition. Post-deposition annealing was employed to optimize hydrogen concentration in the amorphous indium–gallium–zinc oxide (a-IGZO) layer. Our results show that a 5 nm HfO₂ passivation layer significantly enhances the AC stress stability of a-IGZO TFTs, with the optimal performance achieved at an annealing temperature of 360 °C, resulting in an I_on degradation rate of 9% and a threshold voltage shift of 0.2 V. Secondary ion mass spectroscopy (SIMS) confirmed the hydrogen distribution, while atomic force microscopy (AFM), X-ray diffraction (XRD), and contact angle measurements validated the film morphology. This study underscores the potential of advanced passivation techniques in improving the durability and operational stability of AOS-based electronic devices.