Fatigue-free Characteristics Research Articles

Enhanced energy storage properties and excellent fatigue resistance of Pb-free Bi0.47Na0.376K0.094Ba0.06Nb0.024Ti0.97−x(Ta0.24Sn0.7)xO3 relaxor ceramics

Pb-free Bi0.47Na0.376K0.094Ba0.06Nb0.024Ti0.97−x(Ta0.24Sn0.7)xO3 perovskite ceramics were prepared using a mixed-oxide reaction technique, and their structural, dielectric, ferroelectric, and energy storage properties were systematically investigated. All the compositions exhibited a pseudo-cubic perovskite crystal structure with a highly dense morphology. The doping of complex ions (Ta0.24Sn0.7)4+ disturbed the long-range ordering, which reduced the ferroelectric-to-relaxor phase transition temperature to room temperature. Hence, the modified ceramics exhibited relaxor behavior in their polarization and current density versus applied field plots. Owing to the excellent field-induced ferroelectricity and facile reversibility of ferroelectric-relaxor phase transition of polar nanoregions (PNRs), a high recoverable energy density of 1.65 J/cm3 with a good efficiency of 77.69% was achieved under 125 kV/cm at x = 0.03. In addition, the ceramic with x = 0.03 showed a high recoverable energy density of 1.01 J/cm3 with a high conversion efficiency of 84.22% at 70 °C under 80 kV/cm and fatigue-free characteristics during 105 cycles, demonstrating the highly dynamic and very stable nature of PNRs and very few ionic defects in the grains. Therefore, such ceramics (x = 0.03) are expected to be suitable for high-energy-density materials in electronic industries.

Integration of multiferroic BiFeO3 on Y2O3/Si(100) for metal-ferroelectric-insulator-field-effect-transistors based ferroelectric memories

We report the investigation of BiFeO3 and Y2O3 gate stack for the metal-ferroelectric-insulator-field-effect-transistors (MFIS-FET) for nonvolatile memory applications deposited by sputtering. X-Ray diffraction and electrical characterization have been carried out to investigate the structural and ferroelectric characteristics respectively of the deposited individual films and their stack. Structural investigation reveals the crystallized BiFeO3 film with pervoskite phase upon annealing. Memory improvement with the introduction of dielectric layer from 3.8 V in the metal-ferroelectric-silicon structure to 7.97 V in the MFIS structure with 8 nm buffer layer has been observed. The MFIS structure shows fatigue free characteristics with high data retention time.

Controllable Ferroelastic Switching in Epitaxial Self-Assembled Aurivillius Nanobricks.

Layered perovskites with Aurivillius phase have drawn tremendous attention recently, owing to their high ferroelectric Curie temperatures, large spontaneous polarization, and fatigue-free and environment-friendly characteristics. Bi2WO6 is one of the simplest members in the Aurivillius family with superior ferroelastic and photo-electrochemical behaviors. The self-assembly fabrication of its nanoarchitectures and strategic modulation of their ferroelastic switching are crucial toward highly efficient nanoscale applications. In this work, Bi2WO6 nanobrick arrays were epitaxially grown along the orthorhombic direction in a self-assembled way. Such a nanoscale topology supports out-of-plane and in-plane vectors of ferroelectric polarizations, enabling a perpendicular voltage manipulation of these emerging ferroelectric/elastic domains. Combining the scanning probe technique and transmission electron microscopy, we confirmed the in-plane polarization vectors of 78.6 and 101.4° within the crystallographic axes of the nanobricks with respect to the (110) plane of the substrate. Thus, this work provides new opportunities for ferroelectric/elastic engineering in Bi2WO6 nanostructures for a wide range of applications, such as sensing, actuating, and catalysis.

Structural, ferroelectric and leakage current properties of Bi3.96Pr0.04Ti2.95Nb0.05O12 thin films

Praseodymium and niobium-substituted bismuth titanate (Bi3.96Pr0.04Ti2.95Nb0.05O12, BPTNO) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by a sol–gel technology. The effects of annealing temperature (500~800°C) on microstructure and electric properties of thin films were investigated. X-ray diffraction analysis shows that the BPTNO thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The intensities of (117) peak increases with increasing annealing temperature. With the increase of annealing temperature from 500°C to 800°C, the grain size of BPTNO thin films increases. The highly (117)-oriented BPTNO thin films exhibits a high remnant polarization (2Pr) of 48μC/cm2 and a low coercive field (2Ec) of 110kV/cm, fatigue free characteristics up to >108 switching cycles. A small leakage current density (J) was 6.23×10−8A/cm2 at 200kV/cm. The leakage current mechanisms were controlled by Poole–Frenkel emission in the low electric field region and by Schottky emission in the high field region.

Enhanced electrical properties in bilayered ferroelectric thin films

Sr2Bi4Ti5O18 (SBTi) single layered and Sr2Bi4Ti5O18/Pb(Zr0.53Ti0.47)O3 (SBTi/PZT) bilayered thin films have been prepared on Pt/TiO2/SiO2/Si substrates by pulsed-laser deposition (PLD). The related structural characterizations and electrical properties have been comparatively investigated. X-ray diffraction reveals that both films have crystallized into perovskite phases and scanning electron microscopy shows the sharp interfaces. Both films show well-saturated ferroelectric hysteresis loops, however, compared with the single layered SBTi films, the SBTi/PZT bilayered films have significantly increased remnant polarization (Pr) and decreased coercive field (Ec), with the applied field of 260 kV/cm. The measured Pr and Ec of SBTi and SBTi/PZT films were 7.9 μC/cm2, 88.1 kV/cm and 13.0 μC/cm2, 51.2 kV/cm, respectively. In addition, both films showed good fatigue-free characteristics, the switchable polarization decreased by 9% and 11% of the initial values after 2.2×109 switching cycles for the SBTi single layered films and the SBTi/PZT bilayered films, respectively. Our results may provide some guidelines for further optimization of multilayered ferroelectric thin films.

The microstructure and ferroelectric properties of Sm and Ta-doped bismuth titanate ferroelectric thin films

Sm–Ta co-doped Bi4Ti3O12 (Bi3.96Sm0.04Ti2.92Ta0.08O12, BSTTO) thin films were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by sol–gel technology, and the microstructure, dielectric, ferroelectric and leakage current properties of the thin films were investigated. BSTTO thin film exhibits a high remanent polarization (2Pr) of 46.2μC/cm2 and a low coercive field (2Ec) of 102kV/cm, fatigue-free characteristics up to ≧108 switching cycles. The 2Pr of the BSTTO thin film is larger than that of the Bi4Ti3O12 thin film (2Pr=26μC/cm2). In addition, the leakage current density of Sm–Ta co-doped Bi4Ti3O12 thin film is 2.56×10−8A/cm2, which is lower than that of the Bi4Ti3O12 thin film (1.0×10−5A/cm2). These improvements in the ferroelectric and leakage current properties can be attributed to the enhanced stability of the oxygen in the Ti–O octahedron layer by the substitution with Sm and Ta for Bi3+ and Ti4+ in A-site and B-site of the BTO thin film, respectively.

Effects of tantalum doping on microstructure and ferroelectric properties of Bi 4Ti 3O 12 thin films prepared by a sol–gel method

Tantalum-substituted Bi 4Ti 3O 12 (Bi 4Ti 3- x/5 Ta x/5 O 12, BTTO) thin films were fabricated on Pt(111)/Ti/SiO 2/Si(100) substrates by sol–gel technology. The effects of various processing parameters, including Ta content ( x=0∼0.08) and annealing temperature (500∼800 °C), on the growth and properties of thin films were investigated. X-ray diffraction analysis shows that the BTTO thin films have a bismuth-layered perovskite structure with preferred (117) orientation. With the increase of Ta content, the grain size of film decreased slightly, and highly (117)-oriented BTTO films were obtained in the composition of x=0.06. Ta doping on the B-site of Bi 4Ti 3O 12 could induce the distortion of oxygen octahedral and decrease the oxygen vacancy concentration by a compensating effect. The highly (117)-oriented BTTO thin films with x=0.06 exhibits the maximum remanent polarization (2 P r) of 50 μC/cm 2 and a low coercive field (2 E c) of 104 kV/cm, fatigue free characteristics up to ≧ 10 8 switching cycles.

Ferroelectric and dielectric properties of Bi4-xNdxTi3O12 thin films prepared by sol–gel method

Bi4-xNdxTi3O12 (BNT-x, x = 0, 0.25, 0.50, 0.75 and 1.0) thin films were prepared on Pt/Ti/SiO2/Si substrates by a sol–gel method. The microstructure, ferroelectric and dielectric properties of BNT-x thin films were investigated. The single-phase BNT-x thin films were obtained. With increasing Nd content, the preferred orientation changed from random to (117) and surface morphologies changed from the mixture of rod- and plate-like grains to rod-like grains. The Nd substitution improved the ferroelectric and dielectric properties of BTO films. BNT-x films showed better electrical properties at x = 0.50—1.0. BNT-0.75 film exhibited the best electrical properties with remanent polarization (2Pr) of 26.6 μC/cm2, dielectric constant (er) of 366 (at 1 MHz), dielectric loss (tanδ) of 0.034 (at 1 MHz), leakage current density (J) of ±3.0 × 10−6 A/cm2 (at ± 5 V) and fatigue-free characteristics.

Effects of ion-doping at different sites on multiferroic properties of BiFeO3 thin films

A-site Ce and B-site Zr codoped Bi1−x Ce x Fe1−y Zr y O3 (BCFZ) thin films with different compositions were successfully prepared on the Pt/Ti/SiO2/Si substrates by chemical solution deposition. The influence of the A-site Ce and B-site Zr codoping on the structure, surface morphology, electrical and magnetic properties of BFO films were investigated, respectively. The comparative study suggested that the A-site Ce doping with various contents have notable influences on the electrical properties of the BFO films, while the B-site Zr doping with different contents affect mainly the magnetic properties of the BFO films. Compared with the other BCFZ films studied here, the Bi0.97Ce0.03Fe0.97Zr0.03O3 film showed the lowest dielectric loss and leakage current density, a well-squared P–E loop and fatigue-free characteristics as well as the strong magnetization.

Polarization fatigue in Pb(In 0.5Nb 0.5)O 3–Pb(Mg 1/3Nb 2/3)O 3–PbTiO 3 single crystals

Electric fatigue tests have been conducted on pure and manganese-modified Pb(In 0.5Nb 0.5)O 3–Pb(Mg 1/3Nb 2/3)O 3–PbTiO 3 (PIN–PMN–PT) single crystals along different crystallographic directions. Polarization degradation was observed to suddenly occur above 50–100 bipolar cycles in 〈1 1 0〉 oriented samples, while 〈0 0 1〉 oriented samples exhibited almost fatigue free characteristics. The fatigue behavior was investigated as a function of orientation, magnitude of the electric field and manganese dopant. It was found that 〈0 0 1〉 oriented PIN–PMN–PT crystals were fatigue free, due to its small domain size, being on the order of 1 μm. The 〈1 1 0〉 direction exhibited a strong electrical fatigue behavior due to mechanical degradation. Micro/macro cracks developed in fatigued 〈1 1 0〉 oriented single crystals. Fatigue and cracks were the result of strong anisotropic piezoelectric stress and non-180° domain switching, which completely locked the non-180° domains. Furthermore, manganese-modified PIN–PMN–PT crystals were found to show improved fatigue behavior due to an enhanced coercive field.

Electrical Properties with Annealing Temperature of SBN Thin Film

The thin films were deposited on Si substrate using RF magnetron sputtering method. And the SBN thin films were annealed at 650~800]. The surface rougness showed about 0.42[nm] in annealed thin film at ]. The dielectric constant(150) of SBN thin film was obtained by annealing temperature above ]. The voltage dependence of dielectric loss showed a value within 0.02 in voltage ranges of -10~＋10[V]. The dielectric constant characteristics showed a stable value with the increase of frequency. Also, the SBN thin films annealed at ] showed a fatigue-free characteristics up to cycles.

Preparation and Ferroelectric Properties of Ho3+/Mo6+ Cosubstituted Bi4Ti3O12 Thin Films by Sol–Gel Method

We have prepared Ho3+/Mo6+ cosubstituted bismuth titanate [(Bi3.6Ho0.4)3.99- Ti2.985Mo0.015O12, BHTM] thin films on Pt/Ti/SiO2/Si substrates using the sol–gel method. The crystal structure and morphology of the BHTM films were characterized. The BHTM samples show a single phase of Bi-layered Aurivillius structure and a dense microstructure. The dielectric constant and dielectric loss of the BHTM films were about 359 and 0.043, respectively, at a frequency of 1 MHz. The films exhibit 2Pr of 57.7 μC/cm2 and 2Ec of 290.0 kV/cm at an applied field of 470 kV/cm, and have fatigue-free characteristics. They also showed good insulating behavior according to leakage current testing.

Effects of annealing atmosphere on microstructure and ferroelectric properties of praseodymium-doped Bi 4Ti 3O 12 thin films prepared by sol–gel method

Praseodymium-substituted bismuth titanate (Bi 3.2Pr 0.8Ti 3O 12, BPTO) thin films were successfully deposited on Pt(111)/Ti/SiO 2/Si(100) substrates by spin coating with a sol–gel technology and rapid thermal annealing. The effects of annealing atmospheres (vacuum, ambient atmosphere and oxygen) on the growth and properties of thin films were investigated. The results show that the intensity of the (117) diffraction peak of Bi 3.2Pr 0.8Ti 3O 12 film annealed in oxygen is stronger than those annealed in ambient atmosphere and vacuum. The XRD spectra demonstrated that a highly (117) orientation could be obtained when the Bi 3.2Pr 0.8Ti 3O 12 thin film was annealed in an oxygen-sufficient environment. The BPTO thin films annealed in oxygen atmosphere exhibits the maximum remanent polarization (2 P r) of 49 μC/cm 2 and a low coercive field (2 E c) of 130 kV/cm, fatigue free characteristics up to ≧ 10 11 switching cycles. These results indicate that the BPTO thin film is useful in nonvolatile ferroelectric random access memory applications.

Improved ferroelectric polarization of KSrBi 2Ta 3O 12 thin films

KSrBi 2Ta 3O 12 (KSBT, in which there should be three TaO 6 octahedra between neighboring (Bi 2O 2) 2+ layers), was designed to improve ferroelectric polarization of SrBi 2Ta 2O 9 (SBT). Thin films of SBT and KSBT were fabricated on Pt/TiO 2/SiO 2/Si substrates by pulsed laser deposition for comparison study. No x-ray diffraction peaks of KTaO 3 could be detected in the XRD patterns of the KSBT films, indicating a single phase of KSBT was obtained. The measured remnant polarization ( 2 P r ) values of SBT and KSBT films were 3.6 μC/cm 2 and 15.6 μC/cm 2, respectively. The possible microstructural background responsible for the 4-times improved polarization was discussed. Furthermore, excellent ferroelectric fatigue-free property, retention property, and dielectric property of the KSBT films were exhibited experimentally. These results indicate that other than conventional site engineering such as substitution, adjusting the octahedra number between neighboring (Bi 2O 2) 2+ layers is an alternative way to improve polarization of SBT while keeping its fatigue-free characteristics.

Effect of seed layer on the ferroelectric properties and leakage current characteristics of sol–gel derived vanadium doped PbZr0.53Ti0.47O3 films

In this paper, we report the ferroelectric properties and leakage current characteristics of vanadium-doped PbZr0.53Ti0.47O3 (PZTV) films grown on various seed layers prepared by a sol–gel process. The PZTV multilayered film of ~250-nm-thick showed excellent ferroelectric properties, with a large remnant polarization (P r) of ~30 μC/cm2 (E c ~ 90 kV/cm), a high saturation polarization (P s) of ~85 μC/cm2 for an applied field of 1,000 kV/cm, fatigue-free characteristics of up to ≥ 1010 switching cycles, and a low leakage current density of 7 × 10−8 A/cm2 at 100 kV/cm. X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) investigations indicated that PZTV films grown on PbZr0.53Ti0.47O3/PbLa0.05TiO3 (PZT/PLT) seed layers exhibited a dense, well-crystallized microstructure with random orientations and a rather smooth surface morphology.

Effect of yttrium doping on microstructure and ferroelectric properties of Bi 4Ti 3O 12 thin film

Bi 4 − x Y x Ti 3O 12 thin films were successfully deposited on Pt(111)/Ti/SiO2/Si(100) substrates by sol–gel method and rapid thermal annealing. The effects of yttrium-substitution and annealing temperature (500–800 °C) on the microstructure and electrical properties of bismuth titanate thin films were investigated. X-ray diffraction analysis reveals that the degree of (117) orientation increases as the yttrium content increased. The improved ferroelectric properties can be attributed to the enhanced degree of (117) orientation of Bi 4 − x Y x Ti 3O 12 thin films. The highly (117)-oriented Bi 3.2Y 0.8Ti 3O 12 thin films exhibit high remanent polarization (2P r) of 58 μC/cm 2 and low coercive field (2E c) of 116 kV/cm, with fatigue-free characteristics up to > 10 8 switching cycles. The corresponding results show that the obtained Bi 3.2Y 0.8Ti 3O 12 thin film exhibited excellent ferroelectric properties and, thus, was suitable for application to non-volatile ferroelectric random access memory applications.

Microstructure and ferroelectric properties of Bi 3.2Y 0.8Ti 3O 12 thin films prepared by sol–gel method

Yttrium-substituted bismuth titanate (Bi 3.2Y 0.8Ti 3O 12, BYT) thin films were successfully deposited on Pt(1 1 1)/Ti/SiO 2/Si(1 0 0) substrates by spin coating with a sol–gel technology and rapid thermal annealing. The effects of annealing temperature (500–800 °C) on microstructure and electrical properties of thin films were investigated. X-ray diffraction analysis shows that the BYT thin films have a bismuth-layered perovskite structure with preferred (1 1 7) orientation. The intensities of (1 1 7) peaks increases with increasing annealing temperature. With the increase of annealing temperature from 500 to 800 °C, the grain size of BYT thin films increases. The highly (1 1 7)-oriented BYT thin films exhibit a high-remnant polarization (2 P r) of 58 μC/cm 2 and a low-coercive field (2 E c) of 116 kV/cm, fatigue free characteristics up to >10 8 switching cycles. The leakage current density ( J) were 4.38×10 −8 A/cm 2 at 200 kV/cm. These results indicate that the highly (1 1 7)-oriented BYT thin film is useful in nonvolatile ferroelectric random access memory applications.

Effect of the microwave oven on structural, morphological and electrical properties of SrBi 4Ti 4O 15 thin films grown on Pt/Ti/SiO 2/Si substrates by a soft chemical method

Thin films of SrBi 4Ti 4O 15 (SBTi), a prototype of the Bi-layered-ferroelectric oxide family, were obtained by a soft chemical method and crystallized in a domestic microwave oven. For comparison, films were also crystallized in a conventional method at 700 °C for 2 h. Structural and morphological characterization of the SBTi thin films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Using platinum coated silicon substrates, the ferroelectric properties of the films were determined. Remanent polarization P r and a coercive field E c values of 5.1 μC/cm 2 and 135 kV/cm for the film thermally treated in the microwave oven and 5.4 μC/cm 2 and 85 kV/cm for the film thermally treated in conventional furnace were found. The films thermally treated in the conventional furnace exhibited excellent fatigue-free characteristics up to 10 10 switching cycles indicating that SBTi thin films are a promising material for use in non-volatile memories.

Oriented growth of Bi3.25La0.75Ti3O12 thin films on RuO2/SiO2/Si substrates by using the polymeric precursor method: Structural, microstructural and electrical properties

c-axis oriented Bi3.25La0.75Ti3O12 (BLT) thin films were grown on a RuO2 top electrode deposited on a (100) SiO2/Si substrate by the polymeric precursor method. X-ray diffraction and atomic force microscope investigations indicate that the films exhibit a dense, well crystallized microstructure having random orientations with a rather smooth surface morphology. The electrical properties of preferred oriented Bi3.25La0.75Ti3O12 (BLT) thin films deposited on RuO2 bottom electrode leaded to a large remnant polarization (P r ) of 17.2 μC/cm2 and (V c ) of 1.8 V, fatigue free characteristics up to 1010 switching cycles and a current density of 2.2 μA/cm2 at 5 V. We found that the polarization loss is insignificant with nine write/read voltages at a waiting time of 10,000 s. Independently of the applied electric field the retained switchable polarization approached a nearly steady-state value after a retention time of 10 s.

Electrical properties of V-doped Bi3.15Nd0.85Ti3O12 thin films with different contents

Thin films of Nd3+-∕V5+-cosubstituted bismuth titanate, (Bi3.15Nd0.85)(Ti3−xVx)O12 (BNTV), were fabricated by chemical solution deposition technique. For different vanadium contents (x=0.03, 0.06, and 0.09), the crystallized phase and electrical properties of the films were investigated using x-ray diffraction, polarization hysteresis loops, leakage current-voltage, and capacitance butterfly loops. The authors found that increasing vanadium content leads to the decrease of coercive field and the increase of capacitance. The film of vanadium content x=0.09 exhibits fatigue-free and excellent leakage current characteristics with I=5.99×10−9A at applied voltage of 3V, which is much lower than that of Bi3.15Nd0.85Ti3O12 thin film [X. S. Gao and J. Wang, Thin Solid Films 515, 1683 (2006)]. The frequency dependence of the remanent polarization for the BNTV thin film was discussed.