The effects of post-annealing on the performance of ZnO thin film transistors

In this study, we investigated the effects of a post-annealing process on the performance and stability of zinc oxide thin film transistors fabricated by atomic layer deposition. After the post-annealing process in ambient air at 250 °C for 2 h, the value of the saturation mobility increased from 1.2 to 1.8 cm/Vs, the subthreshold swing decreased from 0.53 to 0.34 V/decade, and the I_on/I_off ratio increased from 3.1 × 10⁶ to 1.7 × 10⁷. The positive bias stability was also enhanced after post-annealing. These results are related to the formation of another phase in which the difference of enthalpy between the semiconductor material and contact metal electrode causes the carrier concentration at the metal/semiconductor interface to increase, leading to decreased contact resistivity. Additionally, internal modification of the semiconductor/dielectric interface and/or improving the semiconductor structure, which is related to a change in the oxidation state of Zn through the incorporation of oxygen and/or hydroxide, can result in improved device performance.