Effective encapsulation of ZnO thin film transistors controlled by thermal energy

Abstract

Passivation still remains a challenging issue for the oxide-based thin film transistors because it requires thermal treatments at elevated temperatures to recover the original transistor characteristics. Particularly, the threshold voltage encounters a strong reduction due to the extraction of oxygen from the channel layers. This work demonstrates an effective way to reduce the reaction between the metal-organic precursor and the oxygen from the channel layers based on the bond-energy of the Al-O (569 kJ/mol) that is higher than Zn-O (250 kJ/mol). Reducing the growth temperatures of the passivation layers (PVLs) in the conventional process of thermal atomic layer deposition (ALD) leaves the performance of the thin film transistors (TFTs) only slightly varied but within an acceptable range. Among all devices, the TFTs with Al2O3 PVLs deposited at 100 °C by using H2O as oxidant remain a high mobility of 31.2 ± 0.4 cm2 V−1 s−1, a proper threshold voltage of 1.05 ± 0.04 V, a low subthreshold swing 0.17 ± 0.03 V/dec as well as an excellent stability with a small threshold voltage shift of 0.19, −0.03 and −0.12 V under positive bias stress, illumination bias stress and positive bias illumination stress, respectively. This improved stabilities are attributed to the presence of the high-quality PVLs that protect the channels from environmental effects.