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Epitaxial rhombohedral Pb(Zr0.65Ti0.35)O3films with (100) and (110)/(10-1) and (111)/(11-1) orientations were grown on various kinds of singlecrystal substrates having different thermal expansion coefficient. Volume fractions of (110) and (111) orientations in respective (110)/(10-1) and (111)/(11-1)-oriented films were almost linearly increased with increasing thermal strain, εthermal, applied to the films that wasgenerated under the cooling process after the deposition from the growth temperature to the Curie temperature.Observed saturationpolarization (Psat)was changed linearly with the volume fractions of (110) and (111) orientations, in the same manner asthe volume fractions of (001) and (101) orientations in (001)/(100) and (101)/(110) oriented tetragonal Pb(Zr,Ti)O3 filmsreported previously. These results showed that the volume fraction of the non-180o domains Pb(Zr,Ti)O3films of both tetragonal and rhombohedral symmetriescan be manipulated by εthermal, which brings possibly to control the Psat value.
Crystal structure change with an applied electric field was investigated by Raman spectroscopy and X-ray diffraction (XRD) for the 1 μm-thick (100)/(001) one-axis oriented tetragonal Pb(Zr0.3Ti0.7)O3 films prepared on Pt-covered (100) Si substrates by chemical solution deposition technique. As-deposited films were under the strained condition in good agreement with the estimation from the thermal strain applied under the cooling process after the deposition from the Curie temperature to the room temperature. This strain was ascertained to be relaxed by an applied electric field in accompanying with the dramatic increase of the volume fraction of (001) orientation. These results demonstrate the importance of the crystal structure measurement not only as-deposited films, but also after applied electric field, such as after poling.
La-Ni-O films were deposited at deposition temperature ranging from 250 to 540°C by rf magnetron sputter deposition. The effects of deposition temperature and the following heat-treatment condition on the constituent phases and characteristics of LaNiO3 films were investigated. LaNiO3 phase was obtained at the deposition temperature of 250 and 360°C, while La-rich phase of La2NiO4 was appeared above 540°C. Crystalline phases of resultant films after the following heat-treatment strongly depended on the partial pressure of oxygen gas in ambience, i.e., in case of the heat-treatment at 800°C, diffraction peaks originated from LaNiO3 phase disappeared on XRD patterns in pure nitrogen gas ambience, while impurity peaks of NiO appeared in oxygen-excess (>50%) ambience. As a result, LaNiO3 films with high crystallinity and the same lattice parameter as the bulk one were obtained in the deposition at 360°C followed by the heat-treatment at 700°C in air.
Pb(ZrxTi1-x)O3 (PZT) thin films with the various Zr/(Zr+Ti) ratios and the film thickness of 50 and 250 nm were epitaxiallly grown on (100)cSrRuO3//(100)SrTiO3 substrates by metalorganic chemical vapor deposition at 540 °C. 50 nm-thick tetragonal PZT films consistd of 100% c-axis-orientation for the Zr/(Zr+Ti) ratio ranging from 0.13 to 0.56, while 250 nm-thick tetragonal ones consistd of about 70% c-axis-orientation for the range from 0.19 to 0.45. On the other hand, 50 and 250 nm-thick films composed rhombohedral single phase for the Zr/(Zr+Ti) ratio above 0.56 and 0.60, respectively. Mixture region of tetragonal and rhombohedral phases was observed from 0.45 to 0.60 for 250 nm-thick films, but was not for 50 nm-thick ones. Remanent polarization monotonously decreased with increasing the Zr/(Zr+Ti) ratio for 50 nm-thick films in tetragonal PZT films. These results show that Ti rich tetragonal PZT thin films have large spontaneous polarization with good square-shape hysteresis loops and are applicable for the high-density capacitor-type ferroelectric random access memories.
200-nm-thick Pb(Zrx,Ti1-x)O3 (PZT) thin films with zirconium composition in the range from 0% to 65% were epitaxially grown on (001)c SrRuO3 (SRO)//SrTiO3 (STO) single crystal substrates by pulsed metalorganic chemical vapor deposition (pulsed MOCVD). Constituent crystallographic phases were characterized by high-resolution X-ray diffraction reciprocal space mapping. It was found that PZT thin films having zirconium composition from 45% to 60% show mixed tetragonal and pseudocubic phases and their lattice parameters remained constant in this composition range.
Pb(Zr,Ti)O3 (PZT) is one of the most promising materials for ferroelectric random access memory (FeRAM) application. Among the various preparation methods, metalorganic chemical vapor deposition (MOCVD) has been recognized as a most important one to realize high density FeRAM because of its potential of high-step-coverage and large-area-uniformity of the film quality.
In the present study, pulsed-MOCVD was developed in which a mixture of the source gases was pulsed introduced into reaction chamber with interval. By using this deposition technique, simultaneous improvements of the crystallinity, surface smoothness, and electrical property of the film have been reached by comparing to the conventional continuous gas-supplied MOCVD. Moreover, this film had larger remanent polarization (Pr) and lower leakage current density. This is owing to reevaporation of excess Pb element from the film and increase of migration on the surface of substrate during the interval time.
This process is also very effective to decrease the deposition temperature of the film having high quality. In fact, the Pr and the leakage current density of polycrystalline Pb(Zr0.35Ti0.65)O3 film deposited at 415 °C were 41.4 μC/cm2 and on the order of 10−7 A/cm2 at 200 kV/cm. This Pr value was almost the same as that of the epitaxially grown film deposited at 415 °C with the same composition corrected for the orientation difference. This suggests that the polycrystalline PZT film prepared by pulsed-MOCVD had the epitaxial-grade ferroelectric properties even through the deposition temperature was as low as 415 °C. Moreover, large “process window” comparable to the process window at 580 °C, above 150 °C higher temperature and was widely used condition, was achieved even at 395°C by the optimization of the deposition condition.
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