## 4 Conclusions  
In summary, MIM and TFT devices based on solution-processed AlOx dielectrics were fabricated, and the effect of mobile ions on the frequency-dependent capacitance of the solution-processed AlOx dielectrics is studied. It is found that the capacitance of the AlOx dielectrics annealed at 250 or 300 \({}^{\circ}\)C depends on the frequency greatly, while the AlOx film annealed at 350 \({}^{\circ}\)C is almost independent of the frequency (<100 kHz); and the water treatment causes more seriously frequency-dependent capacitance. The strong frequency-dependent capacitance of the AlOx annealed at 250 or 300 \({}^{\circ}\)C is attributed to relaxation polarization of the weakly bound ions in the incompletely decomposed AlOx films. The water treatment introduces a large number of protons (H\({}^{+}\)) that would migrate  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Water Treatment** & _C/1_kHz** & _C/QS_ & _Vth_ & \(\mu\) & \(\SS\) \\ \cline{2-6}  & **(nF/cm\({}^{2}\))** & **(nF/cm\({}^{2}\))** & **(V)** & **(cm\({}^{2}\) V\({}^{-1}\)s\({}^{-1}\))** & **(V dec\({}^{-1}\))** \\ \hline With & 387.9 & 647.0 & 0.61 & 6.72 (forward) & 0.113 \\  & & & & 5.02 (reverse) & 0.187 \\ Without & 148.1 & 152.8 & 0.92 & 6.75 (forward) & 0.187 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Electrical properties of the InScOx/AlOx TFTs with or without water treatment.  
Figure 5: Transfer curves for InScOx TFTs with AlOx gate dielectrics (**a**) without and (**b**) with water treatment; the AlOx gate dielectrics were annealed at 350 \({}^{\circ}\)C for 1 h.  
to the ITO/AlO\({}_{\rm x}\) interface under a certain electric field and form an electric double layer (EDL) that has ultrahigh capacitance at low frequency. The oxide TFTs based on water treated AlOx\({}_{\rm x}\) dielectrics exhibit anticlockwise hysteresis in the transfer curves that confirm existence of mobile ions in the AlOx films. The calculated mobilities for forward- and reversed-sweep curves of the TFTs without water treatment is 6.75 and 9.71 cm\({}^{2}\) V\({}^{-1}\)s\({}^{-1}\), respectively, while those for forward- and reversed-sweep curves of water-treated ones are 6.72 and 5.02 cm\({}^{2}\) V\({}^{-1}\)s\({}^{-1}\), respectively. Although the TFT with water treatment is high on-current, the mobility is lower than that of the TFT without water treatment. The results confirm that the mobility of the water-treated TFTs is overestimated if using the same capacitance (\(C_{i}\)) of the untreated TFTs for calculating mobility.  
Conceptualization, L.L., Y.W. and P.H.; formal analysis, Y.W. and Y.L.; investigation, C.D., S.C. and J.P.; writing--original draft, Y.W.; writing--review editing, L.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (Grant Nos. 62022034, 51673068, 62074059), the Guangdong Natural Science Foundation (Grant No. 2017A030306007), the Guangdong Project of R&D Plan in Key Areas (Grant Nos. 2020B010180001, and 2019B010934001), the Guangdong Major Project of Basic and Applied Basic Research (No. 2019B030302007), and the Key Project of Guangzhou Science and Technology Plan (Grant No. 201904020034).  
Not applicable.  
Authors would like to extend thanks to [PERSON] for his support in capacitance test and data analysis.  
The authors declare no conflict of interest.