Amorphous N-doped InSnZnO thin films deposited by RF sputtering for thin-film transistor application

N-doped InSnZnO (ITZO:N) thin films as the active layer of thin film transistors (TFTs) were prepared using radio frequency (RF) magnetron sputtering at room temperature. The influence of RF power on the microstructure and optical properties of films was investigated. The relationship between the active layer quality and the TFT's electrical properties was also studied. The results show that no evident impacts of RF power are observed on the optical transmittance in the visible range of amorphous ITZO:N thin films. Their optical band gaps increase from 3.44 to 3.54 eV. An appropriate RF power can enhance ITZO:N film's quality, and reduce the interface state density, which is beneficial to improving the carrier concentration of ITZO:N TFTs. Then, the device's performance is optimized. The threshold voltage of TFTs shows a negative shift as the RF power gradually increases. When the RF power is 60 W, the ITZO:N thin film is amorphous with a dense microstructure. The corresponding TFT device exhibits optimal electrical characteristics. Its field-effect mobility, on/off ratio and subthreshold swing are 14.66 cm2 V−1 s−1, >106 and 0.7 V dec−1, respectively.