## 3 Results and Discussion
Figure 9 shows the top view and polarizing graphs of the MIM structure. In order to compare the electrical homogeneity of the insulating films mentioned above, we select nine feature points on the insulating film to measure the leakage current density, as shown in Figure 9. Figure 10 shows the leakage current density of each feature point. Table 3 shows the statistics of electrical properties of each feature point. It can be seen that the ZrO\({}_{2}\) film achieved by spin-coating with 0.3 M precursor for six times had better electrical uniformity. Figure 11 is the AFM diagram of ZrO\({}_{2}\) films fabricated by spin-coating with 0.6 M precursor for three times and 0.3 M precursor for six times. Both of them had low roughness, and the root mean square of ZrO\({}_{2}\) films in devices A and B were 0.16 nm and 0.18 nm, respectively. After the precursor was spin-coated, a wet film was formed containing a large number of ions. The high-concentration  
Figure 10: The leakage current density of each feature point on the ZrO\({}_{2}\) film. (**a**) 0.3 M precursor spin-coating 6 times. (**b**) 0.6 M precursor spin-coating 3 times. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**ZrO\({}_{2}\) Films**} & \multicolumn{4}{c}{**Leakage Current Density (A/cm\({}^{2}\)) (10 V)**} \\ \cline{2-5}  & **Average Value** & **Maximum Value** & **Minimum Value** & **Standard Deviation** \\ \hline
0.6 M precursor spin-coating 3 times & \(6.9\times 10^{-6}\) & \(2.1\times 10^{-5}\) & \(5.1\times 10^{-7}\) & \(7.8\times 10^{-6}\) \\ \hline
0.3 M precursor spin-coating 6 times & \(1.6\times 10^{-6}\) & \(3.4\times 10^{-6}\) & \(4.0\times 10^{-7}\) & \(9.39\times 10^{-7}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The statistics of electrical properties of each feature point. Figure 9: The overlook view of the MIM structure. (**a**) Overlook view. (**b**) Polarizing photograph. precursor (0.6 M) might lead to high surface roughness due to the irregular arrangement of atoms during the annealing process, during which Zr and O elements moved and recombined to form Zr-O bonding. From the results above, the ZrO\({}_{2}\) films in device A showed smoother surface, lower leakage current density and better electrical uniformity. A smooth surface morphology may result in the alleviation of electron trapping at the channel-insulator interface, which is a great contribution to improve the electrical properties and bias stability of TFTs [28; 29; 30]. From the XRR fitting results, the densities of ZrO\({}_{2}\) films fabricated by spin-coating with 0.3 M precursor for six times and 0.6 M precursor for three times were 4.77 and 4.70 g/cm\({}^{3}\), respectively. The relative porosity volume can be calculated from the densities of ZrO\({}_{2}\) films using the following equation:  
\[\mathrm{q}=\frac{\rho_{1}-\rho}{\rho_{1}-\rho_{2}},\]  
where q, \(\rho\), \(\rho\)1 and \(\rho\)2 represent the relative porosity volume, film density, bulk ZrO\({}_{2}\) density (5.68 g/cm\({}^{3}\)) and void density (air), respectively. The calculated relative porosity volume of 0.3 M ZrO\({}_{2}\) dielectric layer and 0.6 M ZrO\({}_{2}\) dielectric layer were 16.02% and 17.26%, respectively. Figure 12 shows a schematic diagram describing the internal defects of ZrO\({}_{2}\) films. The solution-processed films may have many pores and impurities, which were possibly formed during vaporization, decomposition and condensation processes [31]. The advantage of multilayered stacks of ZrO\({}_{2}\) films is that the pinholes and pore regions of the sub layers may be filled by the subsequent solution process. Another advantage is that the multilayer structure can make the direct penetration of each layer more random, and it is not easy to form a direct penetration channel that runs through all layers. Furthermore, the wet film obtained by low-concentration precursor is thinner during each spin-coating.