Paper TF-ThP25
Electrical Properties of In₂O₃ Thin-film Transistors under Vacuum and Inert Environments

Thursday, October 24, 2019, 6:30 pm, Room Union Station B

Indium oxide (In₂O₃)-based thin-film transistor (TFT) have attractive much attention because high field-effect mobility (> 10 cm²/Vs) can be obtained even room temperature deposition. However, a high-temperature post-annealing is necessary for typical fabrication processes. This sacrifices the merit of In₂O₃-based TFTs that can be fabricated at low temperature. One reason for high-temperature treatment is that an In₂O₃ surface might be sensitive to ambient gases, thus, the electrical properties of the film is changed in various environmental conditions. In order to clarify such instability, we investigate the electrical properties of In₂O₃ TFT in ambient, vacuum and N₂ environments.

The In₂O₃ TFT was fabricated on a Si substrate with a thermally-grown oxide layer (SiO₂ thickness: 200 nm). Before deposition of In₂O₃ active channels, the substrate was ultrasonically cleaned in acetone and isopropyl alcohol, and was irradiated by an excimer lamp (wavelength: 172 nm) for 5 min to remove the organic residue. The In₂O₃ film was then deposited at room temperature by RF magnetron sputtering. The O₂/(Ar + O₂) ratio, RF power and total pressure during sputtering deposition were fixed at 25 %, 100 W and 0.24 Pa, respectively. The background pressure was below ~5 × 10⁻⁴ Pa. The thickness of the active channel formed through a stencil shadow mask was 20 nm by optimizing the deposition time. Source and drain electrodes (Cu: 100 nm) were then formed by an electron beam evaporation through a stencil shadow mask. The In₂O₃ TFT was characterized in a vacuum probe station with a semiconductor parameter analyzer (Agilent 4156A) at room temperature in the dark condition. The electrical measurement of the TFTs was performed in ambient at first, then the chamber was evacuated to ~4 × 10^‒2 Pa for vacuum measurement. A N₂ gas was subsequently introduced into the chamber to be N₂ environmental condition.

The In₂O₃ TFT properties were drastically changed between ambient and vacuum conditions. This might be caused by desorption of excess oxygen in the film. To investigate a measurement environmental sensitivity in In₂O₃ TFT, a sequential I-V measurement was performed. The result showed that the transfer characteristics between 1st and 2nd measurement is obviously different. The degradation of the sensitivity after the 2nd measurement might be due to N₂ molecule passivation. However, the sensitivity tended to slight recover with increasing the number of measurements. We will discuss the N₂ passivation effect, and the relationship between the sensitivity and number of measurements.