Epitaxially grown ferroelectric thin films for memory applications (ferroelectric random access memories)

Abstract

Tetragonal Pb(Zr, Ti)O 3 films were epitaxially grown on SrRuO 3 -coated SrTiO 3 substrates by metal organic chemical vapor deposition. Perfect polar-axisoriented 50 nm thick tetragonal films were successfully grown on (100)SrRuO 3 // (100)SrTiO 3 substrates. The single phase of the tetragonal symmetry region was expanded to a Zr/(Zr þ Ti) ratio of around 0.6 for these films but was reduced to around 0.4 when (100)/(001)-mixture oriented 250 nm thick films were obtained. The dependence of spontaneous polarization (Ps) on the lattice parameter of c-axis to a-axis (c/a ratio) was demonstrated using perfectly polar-axis-oriented films with various Zr/(Zr þ Ti) ratios. The 250 nm thick (100)/(001), (110)/(101), and (111)-oriented tetragonal films were grown on (100), (110), and (111)-oriented substrates. The domain structure was analyzed in detail, and it was found that the observed saturation polarization (P sat ) value can be explained by the Ps value and the 90 domain contribution. These data clearly demonstrate the importance of epitaxial film research for actual ferroelectric random access memories applications.

New modalities of strain-control of ferroelectric thin films

“…Most research on epitaxial strain control of ferroelectricity in literature has been dominated by ferroelectric thin film heterostructures and devices grown on (00l )-oriented perovskite substrates. Nevertheless, there is increasing interest in the possibility of applying biaxial strain along other crystallographic planes to manipulate the nature of the ferroelectric phase and also engineer complex domain morphologies that are inaccessible in (001)-oriented films [345,346]. In particular, it has been known that complex domain structures with highly-enhanced dielectric and piezoelectric susceptibilities can be engineered by electrically poling bulk single-crystal ferroelectrics along non-polar directions that form equivalent angles with at least two possible directions of spontaneous polarization (sometimes referred to as frustrated poling) [97,[347][348][349][350].…”

Orientation-dependent structural phase diagrams and dielectric properties ofPbZr1−xTixO3polydomai

“…1,2 Recent experimental work has demonstrated that the control of film orientation is one promising and effective approach to manipulate ferroelectric domain structure and properties. 3,4 In studies of thin-film materials, such as the model ferroelectrics PbZr 1−x Ti x O 3 and BiFeO 3 , it has been noted that the variation of film orientation could result in exotic crystal and domain structures and give rise to enhanced ferroelectric susceptibilities. [5][6][7][8] In particular, recent work on (111)-oriented, tetragonal PbZr 0.2 Ti 0.8 O 3 films highlighted how domain-wall contributions to dielectric susceptibilities and ferroelectric switching characteristics can be dramatically tuned with film orientations.…”

Phase transitionsand ferroelectrics: revival and the future in the field

“…Over the past two decades, a significant amount of progress has been achieved in epitaxial growth of thin films and heterostructures of various complex oxides, including ferroelectrics (see e.g. [228][229][230][231][232][233][234][235][236][237]). The literature on strain engineering in ferroelectrics is indeed overwhelming and has led in the recent history, for instance, to the discovery of room-temperature ferroelectricity in strained SrTiO 3 [238].…”