ABSTRACT
High-k Y2O3 thin films were investigated as the gate dielectric for amorphous indium zinc tin oxide (IZTO) thin-film transistors (TFTs). Y2O3 gate dielectric was deposited by radio frequency magnetron sputtering (RF-MS) under various working pressures and annealing conditions. Amorphous IZTO TFTs with SiO2 as the gate dielectric showed a high field-effect mobility (µFE) of 19.6 cm²/Vs, threshold voltage (Vth) of 0.75 V, on/off current ratio (Ion/Ioff) of 2.0×106, and subthreshold swing (SS) value of 1.01 V/dec. The IZTO TFT sample device fabricated with the Y2O3 gate dielectric showed an improved subthreshold swing value compared to that of the IZTO TFT device with SiO2 gate dielectric. The IZTO TFT device using the Y2O3 gate dielectric deposited at a working pressure of 5 mtorr and annealed at 400 °C in 6 sccm O2 for 1 hour showed a high µFE of 51.8 cm²/Vs, Vth of -0.26 V, Ion/Ioff of 6.0×10³, and SS value of 0.19 V/dec. With the application of a Y2O3 gate dielectric, the Vth shift improved under a positive bias stress (PBS) but was relatively unaffected by negative bias stress (NBS). These shifts were attributed to charge traps within the gate dielectric and/or interfaces between the channel and gate dielectric layer.
ABSTRACT
Ternary oxide thin films in the In2O3-ZnO-SnO2 system were studied for potential applications in oxide semiconductor thin film transistors (TFTs). An amorphous In-Zn-Sn-O (a-IZTO) active channel layer was deposited by RF magnetron sputtering at room temperature on an n++ Si substrate. Films from a sintered ceramic target with a nominal chemical composition of In:Zn:Sn = 40:50:10 at.% were prepared with thicknesses ranging from 15 nm to 150 nm, which was followed by annealing at 350 °C for 30 minutes in air. Subsequently, a bilayer Cu/Ti metal contact was deposited as the source/drain electrodes on the top surface through a shadow mask using an e-beam evaporator. The thickness of the active channel layer greatly influenced the characteristics of the oxide thin film transistors. The best transistor characteristics were observed from the test device with a channel thickness of 30 nm and a high on/off current ratio of approximately 108, high field effect mobility of 25 cm²/Vs, low threshold voltage of -0.1 V, and very small subthreshold swing of 0.14 V/dec.
ABSTRACT
IZTO20 (In0.6Zn0.2Sn0.2O1.5) ceramic target was prepared from oxide mixture of In2O3, ZnO, and SnO2 powders. IZTO20 thin films were then deposited onto glass substrate at 400 °C by DC magnetron sputtering. The average optical transmittance determined by ultraviolet-visible spectroscopy was higher than 85% for all films. The minimum resistivity of the annealed IZTO20 thin film was approximately 6.1×10-4 Ω·cm, which tended to increase with decreasing indium content. Substrate heating and annealing were found to be important parameters affecting the electrical and optical properties. An organic photovoltaic (OPV) cell was fabricated using the IZTO20 film deposited under the optimized condition as an anode electrode and the efficiency of up to 80% compared to that of a similar OPV cell using ITO film was observed. Reduction of surface roughness and electrical resistivity through annealing treatment was found to contribute to the improved efficiency of the OPV cell.
ABSTRACT
Top-contact bottom-gate thin film transistors (TFTs) with zinc-rich indium zinc tin oxide (IZTO) active layer were prepared at room temperature by radio frequency magnetron sputtering. Sintered ceramic target was prepared and used for deposition from oxide powder mixture having the molar ratio of In2O3:ZnO:SnO2 = 2:5:1. Annealing treatment was carried out for as-deposited films at various temperatures to investigate its effect on TFT performances. It was found that annealing treatment at 350 °C for 30 min in air atmosphere yielded the best result, with the high field effect mobility value of 34 cm2/Vs and the minimum subthreshold swing value of 0.12 V/dec. All IZTO thin films were amorphous, even after annealing treatment of up to 350 °C.
