Effects of Laser Treatment of Terbium-Doped Indium Oxide Thin Films and Transistors

In this study, a KrF excimer laser with a high-absorption coefficient in metal oxide films and a wavelength of 248 nm was selected for the post-processing of a film and metal oxide thin film transistor (MOTFT). Due to the poor negative bias illumination stress (NBIS) stability of indium gallium zinc oxide thin film transistor (IGZO-TFT) devices, terbium-doped Tb:In₂O₃ material was selected as the target of this study. The XPS test revealed the presence of both Tb³⁺ and Tb⁴⁺ ions in the Tb:In₂O₃ film. It was hypothesized that the peak of the laser thermal effect was reduced and the action time was prolonged by the f-f jump of Tb³⁺ ions and the C-T jump of Tb⁴⁺ ions during the laser treatment. Studies related to the treatment of Tb:In₂O₃ films with different laser energy densities have been carried out. It is shown that as the laser energy density increases, the film density increases, the thickness decreases, the carrier concentration increases, and the optical band gap widens. Terbium has a low electronegativity (1.1 eV) and a high Tb-O dissociation energy (707 kJ/mol), which brings about a large lattice distortion. The Tb:In₂O₃ films did not show significant crystallization even under laser energy density treatment of up to 250 mJ/cm². Compared with pure In₂O₃-TFT, the doping of Tb ions effectively reduces the off-state current (1.16 × 10^-11 A vs. 1.66 × 10^-12 A), improves the switching current ratio (1.63 × 10⁶ vs. 1.34 × 10⁷) and improves the NBIS stability (ΔV_ON = -10.4 V vs. 6.4 V) and positive bias illumination stress (PBIS) stability (ΔV_ON = 8 V vs. 1.6 V).