Surface Energy Characterized Self-Assembled Monolayer for Improving Electrical Stability of IGZO Thin Film Transistor

Abstract

The surface energy characterized self-assembled monolayer (SAM) for improving the electrical stability of Indium gallium zinc oxide (IGZO) semiconductor is proposed. In order to compare properly, the head group and body group were fixed with silane and alkyl chains, respectively, and only the functional group was changed, NH2, CH3, CF3 respectively. The surface energies of NH2, CH3 and CF3 functional group SAMs were measured as 50 mJ/m2, 29 mJ/m2 and 24 mJ/m2, respectively by Owens-Wendt model with the contact angle values. The SAM treatment for IGZO TFT backchannel passivation amazingly improves the positive bias stability (PBS) and clockwise hysteresis stability to the very similar tendency by making oxygen-related molecules difficult to be adsorbed onto IGZO backchannel depending on the surface energies of SAMs. In case of NH2 SAM treated IGZO TFT, the PBS improvement ratio by the treatment was 78.7 % (from 11.6 V to 2.5 V) and the clockwise hysteresis improvement ratio was 70.5 % (from 0.8 V to 0.2 V). Furthermore, it was confirmed that the better result was obtained at a lower surface energy functional group. The IGZO TFT PBS further improved 87.0 % after the lowest surface energy with CF3 SAM treatment (from 2.5 V to 0.3 V), and the IGZO TFT clockwise hysteresis was also further enhanced 52.2 % (from 0.2 V to 0.1 V) without any deterioration of TFT characteristics. The field-effect mobility and sub-threshold swing of the IGZO reference TFT with non-SAM treated were 11.2 cm2 / Vs and 0.2 V / decade, respectively. NH2, CH3, and CF3 functional group SAM treated IGZO TFTs show the field-effect mobility of 13.5 cm2 / Vs, 13.0 cm2 / Vs, 13.1 cm2 / Vs, and sub-threshold swing of 0.18 V / decade, 0.20 V / decade, 0.18 V / decade, respectively. As a result, the simple and economical SAM treatment with lower surface energy functional group surface at same head and body group can be a better way in passivating and protecting the IGZO backchannel region from oxygen molecules in the atmosphere in order to enhance the electrical stability of IGZO TFT. Figure 1