**4. Conclusions**

The GZO/Ag/GZO multilayer structures were deposited sequentially by using DC mode only in the magnetron sputtering for both oxide and metal components of the multilayer structure in pure Ar medium and without any purposeful substrate heating. We investigated the structural, electrical, and optical properties of multilayer structures deposited in various combinations of thicknesses of the Ag interlayer and GZO layers. Comparison between XRD, SEM, and electro-optical performance data with each other, as well as with the data from other authors, allows us to draw the following conclusions:


The highest FOM value was 5.15 <sup>×</sup> 10−<sup>2</sup> <sup>Ω</sup>−<sup>1</sup> for the symmetric GZO/Ag/GZO multilayer with GZO and Ag thicknesses of 40 and 10 nm, respectively, and was achieved when optimizing the geometry of the multilayered structure. This multilayer structure has an average visible transmittance of above 81% and resistivity of 2.2 <sup>×</sup> <sup>10</sup>−<sup>5</sup> <sup>Ω</sup>·cm, values that were unchanged after 500 days storage in a normal environment. In conclusion, using only DC mode in magnetron sputtering and the absence of substrate heating during sample preparation in the context of this work makes our results very promising in terms of further industrial compatibility.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-6412/10/3/269/s1, Figure S1: Cross-sectional SEM images of the GAG-3 (a) and GAG-4 (b) trilayer structures, Figure S2: AFM images (2×<sup>2</sup> <sup>μ</sup>m2) prepared in semi-contact mode for GAG-0 (a), GAG-1 (b), GAG-3 (c), GAG-4 (d), GAG-5 (e), and GAG-6 (f), Figure S3: GAG-3 XRD plot in comparison with XRD spectra of pure bulk Ag and pure bulk ZnO materials.

**Author Contributions:** A.K.A. and A.Sh.A. carried out most of the deposition and testing experiments. A.K.A., A.E.M. and A.Sh.A. performed the investigations of samples properties. A.Sh.A., A.Kh.A. and V.M.K. analyzed the data. Writing—original draft preparation, A.K.A. and A.Sh.A. Writing—review and editing, A.Sh.A. In this study, A.Kh.A. and V.M.K. provided the financial and technical support for designing and conducting the research, as well as supervised the whole research process. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was performed in the frame of state assignments of Ministry of Science and Higher Education of the Russian Federation for Dagestan Federal Research Center of Russian Academy of Sciences (Dagestan FRC of RAS) and Federal Scientific Research Center "Crystallography and Photonics" of Russian Academy of Sciences (FSRC "Crystallography and Photonics" RAS) and partially funded by Russian Foundation for Basic Research (research project no. 18-29-12099 and no. 19-07-00537). Access to the equipment of the Shared Research Center of FSRC "Crystallography and Photonics" RAS was supported by the Ministry of Science and Higher Education of the Russian Federation (project RFMEFI62119X0035).

**Acknowledgments:** The authors are grateful for additional technical support from the Shared Research Centers of Dagestan FRC of RAS. The authors acknowledge Alessandro Chiolerio for useful discussions and good recommendations during performing and preparation of the presented work.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
