## 3 Results and Discussion  
In our experiment, we spun the 0.3 M zirconia precursor on glass substrates one, two, three, four, five and six times. It was found that the thickness of ZrO\({}_{2}\) films increased almost linearly with increasing spin-coating times. Figure 1 is the XRR fitting results of the ZrO\({}_{2}\) films with varying thicknesses. From the fitting results, the thickness of the single-spin-coating film was about 22 nm, and a 130 nm ZrO\({}_{2}\) film can be obtained by six-times spin-coating. Obviously, a thicker film would render a smaller leakage current density. Also, the 0.6 M ZrO\({}_{2}\) precursor was swirled for one, two and three times. The thickness of the ZrO\({}_{2}\) film obtained by using the 0.6 M precursor is about two-fold thicker than that of the ZrO\({}_{2}\) film obtained by using 0.3 M precursor. Additional details are listed in Table 1.  
The crystalline phase of the ZrO\({}_{2}\) films with dissimilar thicknesses (67 nm, 130 nm) annealed at different temperatures was investigated by XRD. Figure 2 is the XRD spectra of the ZrO\({}_{2}\) films. The 67-nm-thick film annealed at 400 \({}^{\circ}\)C had a clear crystal peak, while the 130-nm-film was still amorphous. We presumed that the thicker film may inhibit the transfer of heat and the crystallization of ZrO\({}_{2}\) film in the post-annealing processing. To increase the thickness of ZrO\({}_{2}\) film, increasing the concentration of precursor or spin-coating times is an effective method. From the XRR fitting results, the ZrO\({}_{2}\) films obtained by spin-coating 0.6 M precursor for three times, and 0.3 M precursor for three and six times, show a corresponding thickness of 132 nm, 67 nm and 130 nm, respectively. Figure 3 shows the leakage current density of the above ZrO\({}_{2}\) films. The ZrO\({}_{2}\) film with 67 nm thickness demonstrated the largest leakage current density. For ZrO\({}_{2}\) films with 132 nm and 130 nm thicknesses, they exhibited comparable leakage current density despite the difference in the precursor concentration and times. A thick ZrO\({}_{2}\) film may inhibit the crystallization of the film that led to the reduction in leakage current density. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Concentration** & **Layer** & **Density (g/cm\({}^{3}\))** & **Thickness (nm)** & **Roughness (nm)** \\ \hline
0.3 M & 1 & 4.86 & 19.98 & 0.46 \\
0.3 M & 2 & 4.70 & 43.53 & 0.46 \\
0.3 M & 3 & 4.83 & 66.98 & 0.26 \\
0.3 M & 4 & 4.78 & 91.61 & 0.49 \\
0.3 M & 5 & 4.76 & 118.89 & 0.55 \\
0.3 M & 6 & 4.77 & 129.29 & 0.41 \\
0.6 M & 3 & 4.70 & 132.62 & 0.43 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The density, thickness and roughness of 0.3 M precursor-based ZrO\({}_{2}\) films of different coating times. The roughness for glass substrate is 0.79 \(\pm\) 0.32 nm. Figure 1: X-ray reflectivity measurements of 0.3 M precursor-based ZrO\({}_{2}\) films of different coating times. Figure 4 shows the device architecture of IGZO-TFTs. IGZO-TFTs were prepared based on the dielectric films obtained by spin-coating with 0.6 M precursor for three times and 0.3 M precursor for six times. The corresponding bias stability is illustrated in Figures 5 and 6. The field effect mobility in the saturation region (\(V_{\text{ds}}\geq V_{\text{gs}}-V_{\text{th}}\)) and subthreshold swing (SS) were separately obtained by using the following equations:  
\[I_{\text{ds}}=\frac{1}{2}\frac{W}{L}\mu C_{\text{i}}\left(V_{\text{gs}}-V_{ \text{th}}\right)^{2}, \tag{1}\]  
\[\text{SS}=\frac{dV_{\text{gs}}}{d\log I_{\text{ds}}}. \tag{2}\]  
Figure 3: The leakage current density of the ZrO\({}_{2}\) films with altering thicknesses. Figure 2: XRD spectra of ZrO\({}_{2}\) films with different post-annealing temperatures. ZrO\({}_{2}\) film of (**a**) 67 nm and (**b**) 130 nm.