**4. Conclusions**

In this study, the characteristics and electrical properties of ferroelectric HZO thin films obtained by PEALD were evaluated according to the deposition temperature and annealing temperature. Further, we developed and applied various processes to improve these characteristics and electrical properties. First, since the growth per cycle (GPC) according to the deposition temperature of HfO2 and ZrO2 was constant, it was possible to deposit HZO thin films with similar deposition rates at all temperatures. The thickness of the deposited HZO thin films, o-phase crystalline structure, and elemental composition profiles were examined through cross-sectional TEM images and EDS analysis. The X-ray intensity of the o-phase of the thin film deposited at the substrate temperature of 180 ◦C was the highest, and mixed secondary phases such as the m-phase were observed in the thin film deposited at 280 ◦C. Density analysis of the thin films showed that the HZO thin film deposited at 180 ◦C had the highest density and a decrease in density was observed in the thin films deposited at temperatures lower and higher than 180 ◦C. To investigate the density change according to annealing temperature, the thin film samples were annealed in the temperature range of 500–700 ◦C, and a post-annealing temperature of 600 ◦C yielded the highest thin film density. The 2Pr value of the thin film fabricated with the deposition

temperature of 180 ◦C and post-annealing at 600 ◦C was the highest, 38.2 μC/cm2, and the fatigue endurance was also the highest under these conditions, 1.6 × 107 cycles. Three methods were proposed to enhance the density of the low-temperature-deposited thin films. For the low-temperature-deposited thin films with an increased RF plasma discharge time, the enhanced maximum density and an excellent fatigue endurance of 2.5 × <sup>10</sup><sup>7</sup> cycles were obtained.

**Author Contributions:** Conceptualization, H.-G.K. and H.-C.L.; methodology, H.-G.K.; software, J.-H.Y.; validation, H.-G.K. and H.-C.L.; formal analysis, D.-H.H.; investigation, H.-G.K.; resources, H.-C.L.; data curation, J.-H.Y.; writing—original draft preparation, H.-G.K.; writing—review and editing, H.-C.L.; visualization, D.-H.H. and J.-H.Y.; supervision, H.-C.L.; project administration, H.-C.L.; funding acquisition, H.-C.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by the Industrial Technology Innovation Program (Grant No. 20006408) funded by the Ministry of Trade, Industry, and Energy (MOTIE) and the Priority Research Centers Program (2017R1A6A1A03015562) through the National Research Foundation (NRF) funded by the Ministry of Education.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are contained within the article.

**Conflicts of Interest:** The authors declare no conflict of interest.
