Effect of hfo₂-based multi-dielectrics on electrical properties of amorphous in-ga-zn-o thin film transistors

We report the fabrication of bottom gate a-IGZO TFTs based on HfO₂ stacked dielectrics with decent electrical characteristics and bias stability. The microscopic, electrical, and optical properties of room temperature deposited a-IGZO film with varied oxygen content were explored. In order to suppress the bulk defects in the HfO₂ thin film and hence maximize the quality, surface modification of the SiN_x film was investigated so as to achieve a more uniform layer. The root mean square (RMS) roughness of SiN_x/HfO₂/SiN_x (SHS) stacked dielectrics was only 0.66 nm, which was reduced by 35% compared with HfO₂ single film (1.04 nm). The basic electrical characteristics of SHS-based a-IGZO TFT were as follows: V_th is 2.4 V, µ_sat is 21.1 cm² V⁻¹ s⁻¹, I_on/I_off of 3.3 × 10⁷, I_off is 10⁻¹¹ A, and SS is 0.22 V/dec. Zr-doped HfO₂ could form a more stable surface, which will decrease the bulk defect states so that the stability of device can be improved. It was found that the electrical characteristics were improved after Zr doping, with a V_th of 1.4 V, I_on/I_off of 10⁸, µ_sat of 19.5 cm² V⁻¹ s⁻¹, I_off of 10⁻¹² A, SS of 0.18 V/dec. After positive gate bias stress of 10⁴ s, the ∆V_th was decreased from 0.43 V (without Zr doping) to 0.09 V (with Zr doping), the ∆SS was decreased from 0.19 V/dec to 0.057 V/dec, respectively, which shows a meaningful impact to realize the long-term working stability of TFT devices.