To investigate the impact of mechanical stress on their ferroelectric properties, polycrystalline (Hf0.5Zr0.5)O2 thin films were deposited on (111)Pt-coated SiO2, Si, and CaF2 substrates with thermal expansion coefficients of 0.47, 4.5, and 22 × 10−6/ °C, respectively. In-plane X-ray diffraction measurements revealed that the (Hf0.5Zr0.5)O2 thin films deposited on SiO2 and Si substrates were under in-plane tensile strain and that their volume fraction of monoclinic phase decreased as this strain increased. In contrast, films deposited on CaF2 substrates were under in-plane compressive strain, and their volume fraction of monoclinic phase was the largest among the three kinds of substrates. The maximum remanent polarization of 9.3 μC/cm2 was observed for Pt/(Hf0.5Zr0.5)O2/Pt/TiO2/SiO2, while ferroelectricity was barely observable for Pt/(Hf0.5Zr0.5)O2/Pt/TiO2/SiO2/CaF2. This result suggests that the in-plane tensile strain effectively enhanced the ferroelectricity of the (Hf0.5Zr0.5)O2 thin films.

The exclusive b → + − decay is analysed in the model III version of the two Higgs doublet model. We especially studied the branching ratio and the forward-backward asymmetry of this process and investigated the sensitivity of these physical observables to the model parameters. We have found that they are highly sensitive to new physics and hence provide powerful probe of the SM.

The composition dependence and orientation anisotropy of the dielectric and ferroelectric properties of epitaxial Pb(ZrxTi1−x)O3 (PZT) thin films grown using metalorganic chemical vapor deposition were investigated. {100}-, {110}-, and {111}-oriented PZT films were ascertained to have been grown on (100)c, (110)c, and (111)cSrRuO3//SrTiO3 substrates, respectively. The relative dielectric constant reached a maximum near x=0.5, around the morphotropic phase boundary (MPB) composition, irrespective of film orientation, with the {111}-oriented film showing the largest value. Well-saturated hysteresis loops were observed for all films, and abrupt saturation of the remanent polarization (Pr) and coercive field (Ec) values were observed when the value of x was small, irrespective of film orientation. The Ec value reached a minimum around the composition for {110}- and {111}-oriented films but not for {100}-oriented ones. The saturated polarization (Psat) and Pr values for the {111}-oriented film reached a maximum around the MPB composition, while attaining a minimum for films with other orientations. The ratio of Pr to Psat decreased near the MPB composition regardless of film orientation. These results suggest that the electrical properties of epitaxial PZT thin films strongly depend on both of the composition and orientation of the films.

Epitaxial Pb(Zr,Ti)O3 (PZT) films 50 and 250nm thick with the Zr∕(Zr+Ti) ratio from 0.13 to 0.65 were grown on (100)cSrRuO3∕∕(100)SrTiO3 substrates at 540°C by pulsed-metalorganic chemical vapor deposition. The crystal orientation, lattice parameter, axial angle, and relative volume fraction of constituent domains were determined by high-resolution x-ray diffraction reciprocal space mapping. We grew (100) and∕or (001)-oriented epitaxial PZT films for the whole Zr∕(Zr+Ti) ratio. A tetragonal single phase was obtained for the Zr∕(Zr+Ti) ratio ranging from 0.13 to 0.54 and 0.19 to 0.45 with the 50 and 250nm thick films, respectively, while mixed phases of a tetragonal and rhombohedral from 0.45 to 0.60 for the 250nm thick films was obtained. For the films consisting of a tetragonal single phase, lattice parameters of a- and c-axes and their ratio (c∕a) were almost the same as the reported data for the PZT powder, suggesting a small amount of residual strain in them. In addition, perfectly polar-axis (c-axis)-oriented tetragonal films were obtained for the 50nm thick films, while an ∼70% c-axis-orientation for the 250nm thick ones was obtained. Polarization–electric-field hysteresis loops with a good square shape were observed for all films. Also, spontaneous polarization (Ps) values that were directly measured for the 50nm thick films and estimated for the 250nm thick films taking into account the volume fraction of the polar-axis-orientated domain were closely in line with the Zr∕(Zr+Ti) ratio, and they decreased as the ratio increased. The square of the estimated Ps was found to be proportional to the crystal distortion, c∕a−1. These results are essential not only for understanding the origin of the large Ps of PZT but for the property design of the ferroelectric devices using PZT.

100% polar-axis (c-axis)-oriented epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) thin films were grown and their large remanent polarization (Pr) was directly measured. Perfectly c-axis-oriented epitaxial PZT thin films were obtained on (100)cSrRuO3//(100)SrTiO3 substrates when the deposition temperature increased to 540 °C together with a decrease in the film thickness down to 50 nm. Polarization–electric-field hysteresis loops were well saturated and had a square shape. The Pr of a 50 nm thick film saturated at 0.9 V, and its value was over 90 μC/cm2; almost independent of the measurement frequency within the range from 20 Hz to 1 kHz. This value was in good agreement with the estimated one from the a- and c-axes mixture-oriented epitaxial PZT film having the same composition taking into account the fact that only the c-axis-oriented domain contributed to the polarization. On the other hand, the coercive field value of a perfectly c-axis-oriented film was 140 kV/cm and almost the same as that of the mixture-oriented one having the same film thickness. These results show that PZT has a large Pr applicable for high-density ferroelectric random access memory.

The ferroelectric properties of the (Hf0.5Zr0.5)O2 films on Pt/Ti/SiO2/Si substrate are investigated. It is found that the films crystallized by annealing in O2 and N2 atmospheres have similar crystal structures as well as remanent polarization and coercive fields. Weak temperature and frequency dependences of the ferroelectric properties indicate that the hysteretic behavior in HfO2-based films originates not from the mobile defects but rather from the lattice ionic displacement, as is the case of the typical ferroelectric materials.

No abstract

Remanent polarizations (Pr) of 200-nm-thick epitaxial Pb(Zr0.35,Ti0.65)O3 (PZT) thin films deposited on (001), (110), and (111) SrTiO3 (STO) substrates coated with SrRuO3 (SRO) were compared to the domain configurations that were precisely and quantitatively characterized by high-resolution x-ray diffraction reciprocal space mapping (HRXRD-RSM). (001)/(100), (101)/(110), and (111) oriented domains were obtained for films grown on (001), (110), and (111) STO substrates coated with SRO, respectively. HRXRD-RSM showed that the films grown on (001) and (110) STO substrates mainly consisted of (001) and (101) domains, although they also included about 32% and 25% of (100) and (110) domain, respectively. Tilt growths in the domains were found except for the (001) domain. The tilt growths in the (100), (101), and (110) domains were attributed to the geometrically induced tilt by the 90° domain that had {101} domain walls. On the other hand, the tilt in the (111) domain was attributed to the misfit strain relaxation by introducing tilt growth in the domain but not due to the 90° domain. The Pr ratios of films having different domain configurations were well explained by the estimated Pr ratios from the volume fractions of the domains, based on the assumption that the 90° domain was not reoriented by the externally applied electrical field and did not contribute to the measured Pr values. This indicates that the 90° domain is strongly pinned in epitaxial 200-nm-thick PZT films and the 180° domain switching is the dominant contribution to the total remanent polarization.