Nanoscale phenomenon in relaxor ferroelectric thin films
Accordo di cooperazione CNR/CNPq (Brasile)
Funded by: Consiglio Nazionale delle Ricerche (CNR)
Calls: Accordo bilaterale CNR/CNPq
Start date: 2012-01-01 End date: 2013-12-31
Total Budget: EUR 13.000,00 INO share of the total budget: EUR 13.000,00
Scientific manager: Dinelli Franco and for INO is: Dinelli Franco
Organization/Institution/Company main assignee: CNR – Istituto Nazionale di Ottica (INO)
Calls: Accordo bilaterale CNR/CNPq
Start date: 2012-01-01 End date: 2013-12-31
Total Budget: EUR 13.000,00 INO share of the total budget: EUR 13.000,00
Scientific manager: Dinelli Franco and for INO is: Dinelli Franco
Organization/Institution/Company main assignee: CNR – Istituto Nazionale di Ottica (INO)
other Organization/Institution/Company involved:
Raicol Crystal Ltd. (Israel)
Abstract: Ferroelectric materials have offered an exciting potential for applications since the discovery of ferroelectric perovskites more than 50 years ago. The properties of ferroelectrics – materials having a spontaneous electric polarization that can be reversed by an applied electric field – have been extensively studied during the past decade.
Nowadays, there are two main reasons for studying ferroelectric materials: scientific and technologic. Several important devices, such as Ferroelectric Random Access Memories (FeRAMs) and Dynamic Random Access Memory (DRAM), are manufactured based on ferroelectrics thin films. With the crescent and continuous demand for portability in consumer electronics, it is becoming increasingly important to understand the effects of miniaturization on the properties of ferroelectrics in electronic devices. Although continued improvements in conventional semiconductor designs are verified, the basic physics in such a reduced size, however, is poorly understood. The consideration of an alternative paradigm, the investigation of size effects on ferroelectric thin films, is the main motivation to propose this research project.
It is well known that the crystallite/particle size plays an important role in tailoring ferroelectrics properties. In such materials a decrease in particle size causes a reduction in the ferroelectric distortion of the lattice, and makes the diffuse ferroelectric phase transition. In some cases, typical antiferroelectric materials become ferroelectrics due to small particle size, particularly in thin films. Also, the variation of size led to an increase in the coercive field (Ec), and a decrease in the remanent polarization (Pr). For that reason, it is believed that ferroelectricity can be suppressed by fabrication of fine particles and very thin films. However, recent experiments identified ferroelectric ground states in PbZr0.2Ti0.8O3 films with thicknesses ranging from 80 to 4 nm. A stable ferroelectric phase was also observed for PbTiO3 with thicknesses down to 3 unit cells (1,2 nm). Though some work has already been reported in the recent past, detailed and systematic studies on ultrathin films remain an attractive/fascinating subject to study the size effects of ferroelectric, as we will describe in the next sections.
Despite the size effects above described for normal ferroelectrics, these effects on properties of relaxors materials also have been intensively studied. The nature of the polar nanoclusters is the central problem in the physics of relaxors, since it is believed to be responsible for the multi-scale dynamics, spatial inhomogeneity and many other physical properties of these materials such as giant piezo-electricity and electrostriction. Relaxors such as Pb1-xLax(Zr1-yTiy)1-x/4O3 (PLZT) and strontium barium niobate, Sr1-xBaxNb2O6 (SBN) has received great attention as a ferroelectric material due to its large pyroelectric coefficient, piezoelectric and electro-optic properties. Both PLZT and SBN are solid solutions. While PLZT has a perovskite structure has a tetragonal tungsten bronze structure for x = 0.25-0.75. At room temperature the Curie temperature of SBN can be altered in the range 60-250°C, depending of the Sr/Ba ratio. The size effects on relaxor properties of these materials have been little studied in recent years. Thus, it is the main purpose and motivation for this proposal.
Nowadays, there are two main reasons for studying ferroelectric materials: scientific and technologic. Several important devices, such as Ferroelectric Random Access Memories (FeRAMs) and Dynamic Random Access Memory (DRAM), are manufactured based on ferroelectrics thin films. With the crescent and continuous demand for portability in consumer electronics, it is becoming increasingly important to understand the effects of miniaturization on the properties of ferroelectrics in electronic devices. Although continued improvements in conventional semiconductor designs are verified, the basic physics in such a reduced size, however, is poorly understood. The consideration of an alternative paradigm, the investigation of size effects on ferroelectric thin films, is the main motivation to propose this research project.
It is well known that the crystallite/particle size plays an important role in tailoring ferroelectrics properties. In such materials a decrease in particle size causes a reduction in the ferroelectric distortion of the lattice, and makes the diffuse ferroelectric phase transition. In some cases, typical antiferroelectric materials become ferroelectrics due to small particle size, particularly in thin films. Also, the variation of size led to an increase in the coercive field (Ec), and a decrease in the remanent polarization (Pr). For that reason, it is believed that ferroelectricity can be suppressed by fabrication of fine particles and very thin films. However, recent experiments identified ferroelectric ground states in PbZr0.2Ti0.8O3 films with thicknesses ranging from 80 to 4 nm. A stable ferroelectric phase was also observed for PbTiO3 with thicknesses down to 3 unit cells (1,2 nm). Though some work has already been reported in the recent past, detailed and systematic studies on ultrathin films remain an attractive/fascinating subject to study the size effects of ferroelectric, as we will describe in the next sections.
Despite the size effects above described for normal ferroelectrics, these effects on properties of relaxors materials also have been intensively studied. The nature of the polar nanoclusters is the central problem in the physics of relaxors, since it is believed to be responsible for the multi-scale dynamics, spatial inhomogeneity and many other physical properties of these materials such as giant piezo-electricity and electrostriction. Relaxors such as Pb1-xLax(Zr1-yTiy)1-x/4O3 (PLZT) and strontium barium niobate, Sr1-xBaxNb2O6 (SBN) has received great attention as a ferroelectric material due to its large pyroelectric coefficient, piezoelectric and electro-optic properties. Both PLZT and SBN are solid solutions. While PLZT has a perovskite structure has a tetragonal tungsten bronze structure for x = 0.25-0.75. At room temperature the Curie temperature of SBN can be altered in the range 60-250°C, depending of the Sr/Ba ratio. The size effects on relaxor properties of these materials have been little studied in recent years. Thus, it is the main purpose and motivation for this proposal.
INO’s Experiments/Theoretical Study correlated:
Thin Film Properties on the Nanoscale: from Oligomers to Polymer, from 2D Materials to Ferroelectrics
Ultrasonic Force Microscopy (UFM): Nanomechanics and Subsurface Detection