Preparation And Electrical Properties Optimization Of Indium Based Thin Film Transistors By Solution Process

With the rapid development of the display industry,thin-film transistors（TFTs）have attracted considerable attention as central devices for flat panel displays.In recent years,metal oxide thin-film transistors（MOTFTs）have been widely used in flat panel display technology due to their high mobility,high transparency,high stability,and uniformity in large-area preparation.With the continuous development of technology and the improvement of people’s quality of life,display devices are required to be able to achieve higher resolution,enriched colors,lower energy consumption,smaller size,and large area displays,which leads to TFTs being required to have a variety of properties such as miniaturization,low driving voltage,high response speed,and low preparation costs,etc.Although conventional vacuum preparation methods are favored for the fabrication of high-quality films and devices,they suffer from time inefficiency,expensive expenditure,and difficulty in achieving large-area preparation.In recent years,the solution process has attracted much attention because of its simple preparation process,low cost,easy controllability of chemical stoichiometry,and amenability to mass production.In this work,high-performance indium-based TFTs were fabricated through structural design and material selection using the solution method,with the following specific results:（1）Single-layer In₂O₃ and In₂O₃:Gd（In Gd O）TFTs and bilayer In₂O₃:Gd/In₂O₃（In Gd O/In₂O₃）TFTs were fabricated using the solution process with the SiO₂ as the dielectric layer.Firstly,the effect of Gd doping on the electrical properties of In₂O₃ films and In₂O₃ TFTs was first investigated,and it was found that the Gd-doped In Gd O TFT exhibited a large current switching ratio(I_on/I_off)of 1.30×10⁷,a smaller subthreshold swing（SS）of 1.75 V/dec and a better bias stability(ΔV_th)of 0.85 V.Then,the bilayer In Gd O/In₂O₃ TFT was constructed and compared with single-layer In₂O₃ and In Gd O TFTs to verify the advantages of the bilayer structure.Next,we optimized the electrical properties of the In Gd O/In₂O₃ TFTs by varying the Gd doping concentration.It was found that the device exhibited the best electrical properties at a 7%Gd doping concentration,with a high mobility（μ）of 4.34 cm²V^-1s^-1,a near-zero threshold voltage(V_th),a low off-state current(I_off)of 1.24×10^-9 A,an I_on/I_off as high as 3.18×10⁵,a small SS and good bias stability.Finally,the devices were age tested after three months and were found to have good switching ratios and mobilities,which indicates the good environmental stability of the devices.（2）Low driving voltage In GdO TFTs were prepared with high permittivity（high-k）ZrO₂ as the dielectric layers using the solution process.Firstly,the effect of different annealing temperatures on the structure and morphology of ZrO₂ films was investigated,and it was found that films that had higher annealing temperatures exhibited increasing crystallinity and larger roughness.Then,Al/ZrO₂/n⁺⁺Si metal–insulator–semiconductor（MIS）capacitor structures were prepared to investigate the effect of annealing temperature on the leakage current-voltage（I-V）characteristics and capacitance-frequency（C-f）characteristics of ZrO₂ films.To verify the applicability of ZrO₂ films in TFTs,we fabricated In Gd O/ZrO₂TFTs with different annealing temperatures of ZrO₂ as the dielectric layers and investigated the effect of annealing temperature on the electrical properties of TFTs.It was found that In Gd O/ZrO₂ TFT had the best electrical properties when the annealing temperature was 500℃,with an operating voltage as low as 2 V,a near-zero threshold voltage of 0.299 V,a large switching ratio of 7.06×10⁵,a small subthreshold swing of0.135 V/dec,a smaller current hysteresis of 0.260 V and a good bias stability of 0.047 V.（3）Virtually current hysteresis-free,low driving voltage In Gd O TFTs were fabricated with anionic F-doped ZrO₂ as the dielectric layer using the solution process.Firstly,based on ZrO₂ thin films annealed at500℃,the effect of F doping concentration on the structure and morphology of ZrO₂ thin films was investigated,and it was found that the films all were smooth and homogeneous.Then,Al/F:ZrO₂/n⁺⁺Si MIS capacitor structures were prepared to investigate the effect of F doping concentration on the I-V and C-f characteristics of ZrO₂ thin films.It was found that when the F doping concentration was 10%,the ZrO₂thin film had the lowest leakage current density of 6.75×10^-9 A/cm² and a capacitance density of280.162 n F/cm2（at a frequency of 10 k Hz）,which fully met the requirements of the dielectric layers for TFTs.Finally,In Gd O/F:ZrO₂ TFTs with different F-doping concentrations of F:ZrO₂ as the dielectric layers were prepared and investigate.It was found that In Gd O/F:ZrO₂TFT exhibited the optimal performance at a 10%F doping concentration,with a low driving voltage of 2 V,high mobility of12.05±0.5 cm²V^-1s^-1 over a wide frequency range,almost negligible current hysteresis of 0.017 V,high switching ratio of 1.25×10⁴ and improved bias stability of 0.045 V.