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A multi-layered MoS 2 film was formed on a SiO 2 film by high-temperature sputtering, which is one of the alternative methods of Si LSI technology. It was found that the carrier density of a sputter-deposited MoS 2 film is 1000 times smaller than that of an exfoliated one. By sputtering, two different orientations, namely a layer lateral to a SiO 2 /Si substrate and a layer perpendicular to the substrate, were formed. The lateral layer showed a lower carrier density than the perpendicular layer because of the decrease in the number of sulfur vacancies, as commonly discussed in several research studies. However, the vacancies are not sufficient for describing this significant reduction in carrier density. It is considered that a sodium ion functioning as an interface trapped charge is one of the main origins of carriers. Sputtering, which enables us to determine the sodium contamination level, can be seen as appropriate for reducing the carrier density; hence, this method is considered to be efficient in realizing enhancement-mode MoS 2 MOSFETs. In addition, sputtering also enable us to form large-scale MoS 2 films up to a wafer size. Therefore, a sputterdeposited MoS 2 film is a promising material for post-silicon devices.

The effect of crystallized ZrO2 (ZrO2-seed), amorphous Hf0.43Zr0.57O2 (HZO; HZO-seed), and amorphous Al2O3 (Al2O3-seed) seed layers on the ferroelectricity of HZO films was investigated. The remanent polarization () of a TiN-electroded capacitor with a ZrO2-seed layer was much larger than that of capacitors with a HZO-seed, Al2O3-seed, or no seed layer. Furthermore, the maximum 2Pr was exhibited when the thickness of the ZrO2-seed layer was 2 nm. Large grain growth was observed, which satisfied the same lattice pattern between ZrO2 and HZO films, and indicates that the ZrO2 seed layer plays an important role in the nucleation of the HZO film.

A ferroelectric HfxZr1−xO2 (HZO) thin film crystallized with nanocrystalline top- and bottom-ZrO2 nucleation layers (D-ZrO2) exhibited superior remanent polarization (2Pr = Pr+ − Pr− = 29 μC/cm2) compared to that of similar thin films (12 μC/cm2) crystallized without a ZrO2 nucleation layer (w/o) when the HZO film thickness was 10 nm. Epitaxial-like grain growth of the HZO film was observed on the surfaces of both the top- and bottom-ZrO2 layers, while there was almost no significant difference in the crystal grain size of the HZO film in all samples, as determined by cross-sectional transmission electron microscopy images. Consequently, the ferroelectric orthorhombic, tetragonal, and cubic (O/T/C) phase ratio of the HZO film was significantly increased by using the ZrO2 nucleation layers. It was furthermore confirmed that the 2Pr values were strongly correlated with the O/T/C phase ratio of the HZO film. Therefore, it is clear that the top- and bottom-ZrO2 nucleation layers play an important role in the formation of the ferroelectric HZO film. These results suggest that the HZO film fabrication technique using a nanocrystalline ZrO2 nucleation layer is a promising candidate for next-generation device applications.

The change in the interplanar spacing (d-spacing) including the ferroelectric orthorhombic (O) phase in the low-temperature fabricated HfxZr1−xO2 (HZO) films was studied using synchrotron grazing-incidence wide-angle x-ray scattering analysis. The 10-nm-thick HZO films were fabricated by thermal and plasma-enhanced atomic layer deposition (TH- and PE-ALD) methods using H2O gas and O2 plasma as oxidants, respectively, and a post-metallization annealing (PMA) was performed at 300–400 °C. The d-spacing of the mixture of (111)-, (101)-, and (111)-planes of O, tetragonal (T), and cubic (C) phases, respectively, for the TH- and PE-ALD HZO films increased up to 2.99 Å with an increase in PMA temperature, while the d-spacing estimated by conventional x-ray diffraction was 2.92 Å regardless of the PMA temperature. The remanent polarization (2Pr = Pr+ − Pr−) of the HZO films increased as the PMA temperature increased. It is clear that the 2Pr value satisfied a linear relationship as a function of the d-spacing of O(111)/T(101)/C(111) phases. Furthermore, the wake-up effect was found to depend on the ferroelectric O phase formation. The wake-up effect was significantly reduced in both the TH- and PE-ALD HZO films after the PMA at 400 °C due to the increase in the ferroelectric O phase formation. The leakage current density (J)–electric field properties of the PE-ALD HZO film with the lowest d-spacing were divided into three steps, such as low, middle, and large J values, in the wake-up (103 cycles), pristine (100 cycle), and fatigue (107 cycles) states, respectively. Therefore, an analysis of the ferroelectric O phase is very important for understanding the ferroelectricity including endurance.