## 3 Results and Discussion
With the discharge power of ZrO\({}_{2}\) target increasing from 15 W to 45 W, the mean peak and D value respectively decrease from 139.3 mV to 80.9 mV and from 1.54 to  
Figure 1:0 The XRR images of Zr-AZTO films: (**a**) Sample A; (**b**) Sample B; (**c**) Sample C; (**d**) Sample D; (**e**) Sample E.  
Figure 1:1 The XRD image of Zr-AZTO films of different power combinations annealed at 350 \({}^{\circ}\)C.  
0.77. As for the influence of the change of mean peak and D value, we will discuss these variables below after the electrical properties of devices are exhibited. Figure 9 shows the output and transfer characteristics of Zr-AZTO TFTs of different power combinations. The electrical properties were measured by the semiconductor parameter analyzer (Agilent 4155C). As shown in Figure 9a-e, after a 350 \({}^{\circ}\)C annealing treatment, the devices of Sample A and Sample B have a similar on-state current while the devices of Sample C and Sample D have a similar but lower one. For the devices of Sample E, the on-state current is the lowest. For the transfer characteristics, Figure 9f shows that when the Zr content increases, the curves shift to positive direction. Because of the low standard electrode potential of Zr (\(-\)1.45 V), Zr can suppress the carrier concentration [5]. This result also reached a consensus with the XPS measurement. It is known that the oxygen vacancy can represent the carrier concentration [23]. When combined in Figure 3, the films of Sample A and Sample B have a similar carrier concentration, so their on-state current and V\({}_{\text{on}}\) are similar. The films of Sample C and Sample D have a lower oxygen vacancy concentration, which means they have a lower carrier concentration. As a result, their on-state current is lower and the transfer curves shift to a positive direction. Table 4 shows the electrical parameters of Zr-AZTO TFT devices. The \(\mu_{sat}\) means the carriers mobility in a saturation regime, and it can be calculated by the following equation:  
Figure 1:2  
where \(I_{DS}\) is the drain-source current, \(C_{i}\) is the gate capacitance per unit area, \(\frac{W}{L}\) is the channel width/length, \(V_{GS}\) is the gate voltage, and \(V_{th}\) is the threshold voltage. The SS is defined as the inverse of the maximum slope of the transfer curve:  
Figure 1:3  
For an oxide semiconductor, there are two recombination processes: shallow localized states and deep localized states. The shallow localized states can be evaluated by the D value and the deep localized states can be evaluated by the mean peak. The high peak level and the high D value respectively represent the low density of deep localized states and the low density of shallow localized states [24; 25]. It is known that the localized states could impose restrictions on the mobility of the semiconductor. Therefore, the low density of localized states can be conducive to the high mobility. Combining Table 3 with Table 4, it is found that the devices of Sample B can get the highest mean peak and D value, which means the density of deep localized states and shallow localized states reaches the lowest level at the same time. Correspondingly, the saturation mobility of Sample B is the highest level available. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Sample A** & **Sample B** & **Sample C** & **Sample D** & **Sample E** \\ \hline Density by XRR (g/cm\({}^{3}\)) & 5.97 \(\pm\) 0.02 & 5.85 \(\pm\) 0.12 & 5.84 \(\pm\) 0.15 & 5.88 \(\pm\) 0.09 & 5.90 \(\pm\) 0.10 \\ Thickness by XRR (nm) & 20.2 \(\pm\) 0.1 & 20.6 \(\pm\) 0.1 & 20.6 \(\pm\) 0.1 & 20.7 \(\pm\) 0.1 & 20.8 \(\pm\) 0.1 \\ Roughness by XRR(nm) & 0.96 \(\pm\) 0.04 & 1.12 \(\pm\) 0.03 & 1.16 \(\pm\) 0.12 & 1.10 \(\pm\) 0.10 & 1.09 \(\pm\) 0.04 \\ Zr content (at.\%) & 0.34 \(\pm\) 0.01 & 0.63 \(\pm\) 0.01 & 1.00 \(\pm\) 0.01 & 1.78 \(\pm\) 0.01 & 2.79 \(\pm\) 0.01 \\ Sc\({}_{\textAs seen through comprehensive consideration, Sample B has a better electrical performance than other samples. Thus Sample B was chosen to measure the bias stress.