Small Remanent Polarization Research Articles

Growth and ferroelectric properties of sol–gel derived Bi(Mg1/2Zr1/2)O3–PbTiO3 thin films

The electrical properties included temperature-dependent polarization of (1−x)Bi(Mg1/2Zr1/2)O3–xPbTiO3 (BMZ–xPT) new ferroelectric films were investigated. The films with 220nm thickness grown on Pt(111)/Ti/SiO2/Si substrates via sol–gel method were well crystallized with a phase-pure perovskite structure and homogeneous microstructure. Saturated polarization hysteresis loops are observed for all BMZ–xPT compounds, and BMZ–0.85PT films with high (100) orientation show a small leakage and remanent polarization of 36.1μCcm−2, which is comparable to the (100)-oriented BiScO3–PbTiO3 thin films. The present films have high dielectric constants about 544-833. Furthermore, the polarization with elevated temperature slightly decreases, exhibiting stable ferroelectric properties and potentials for memory applications above room temperature such as non-volatile ferroelectric random access memories.

Relaxor ferroelectric properties of 85PZN–15BT transparent ceramic at low temperatures

Dielectric, hysteresis (P–E) loops and TSDC properties of transparent 85PZN–15BT ceramic over -150–150°C were investigated. The sample was found to exhibit a strong relaxor behavior and a relatively small remanent polarization. TSDC studies showed that there existed an electric field-dependent peak in the p versus T. Such interesting features were attributed to the electric field-induced transition and coexistence of polar nanoregion, long-range ordered polar region and nonpolarizable BZN-rich region.

Ferroelectric properties of ultrathin films of Nylon 11

Ferroelectric properties of ultrathin films of Nylon 11 were investigated. The thickness was in the range of 25 to 55 nm. Ferroelectric response was largely affected by thermal annealing and following cooling conditions. Thermal annealing at higher temperature followed by quenching in liquid nitrogen gave larger remanent polarization and smoother surface, whereas cooling down in an ambient atmosphere caused smaller remanent polarization and rough surface. Surface roughness strongly affected the polarization reversal and remanent polarization. Hydrogen bonding in crystal was also significantly related to the polarization reversal and thus remanent polarization.

Effects of annealing process and Mn substitution on structure and ferroelectric properties of BiFeO 3 films

The BiFe 1 − x Mn x O 3 (BFMO) ( x = 0.03, 0.05 and 0.07) thin films were deposited on indium tin oxide/glass substrates using a metal organic decomposition method. X-ray diffraction analysis reveals that the structure of BiFeO 3 films is distorted somewhat by Mn substitution. The leakage measurements indicate that Mn doping content is a dominant factor affecting the leakage current of BFMO films. Due to the poor crystallinity, a small remanent polarization ( P r) is observed in the BFMO x = 0.05 thin film annealed using the conventional method. The P r values for the sequential-layer annealed BFMO films are found to be related to the intensity of (012) peak and the content of defect complexes between the oxygen vacancies and acceptors.

Phase transition in Bi8Fe6Ti3O27 multiferroic ceramics

Abstract The polycrystalline Bi8Fe6Ti3O27 compound was prepared by a high-temperature solid-state reaction technique. Preliminary structural analysis by X-ray diffraction (XRD) confirms the formation of a single-phase compound in an orthorhombic crystal system at room temperature. The elemental content of the compound was analyzed by EDAX microanalysis. Microstructural analysis by scanning electron microscopy (SEM) shows that the compound has well defined grains, which are distributed uniformly throughout the surface of the pellet sample. Detailed studies of temperature-dependent dielectric response at various frequencies show dielectric anomalies at 380, 389 and 403°C for 10 kHz, 100 kHz, and 1 MHz respectively. The hysteresis loop observed by applying an electric field of 12 kV/cm on the poled sample with smaller remanent polarization supports the existence of ferroelectricity in this material. The value of d33 of the compound was found to be 19 pC/N.

Fabrication and electrical properties of Pb(Co1/3Nb2/3)O3 ceramics

Abstract Pb(Co 1/3 Nb 2/3 )O 3 (PCN) ceramics have been produced by sintering PCN powders synthesized from lead oxide (PbO) and cobalt niobate (CoNb 2 O 6 ) with an effective method developed for minimizing the level of PbO loss during sintering. Attention has been focused on relationships between sintering conditions, phase formation, density, microstructural development, dielectric and ferroelectric properties of the sintered ceramics. From X-ray diffraction analysis, the optimum sintering temperature for the high purity PCN phase was found at approximately 1050 and 1100 °C. The densities of sintered PCN ceramics increased with increasing sintering temperature. However, it is also observed that at very high temperature the density began to decrease. PCN ceramic sintered at 1050 °C has small grain size with variation in grain shape. There is insignificant change of dielectric properties with sintering temperature. The P – E hysteresis loops observed at −70 °C are of slim-loop type with small remanent polarization values, which confirmed relaxor ferroelectric behavior of PCN ceramics.

Electrical characteristics of (0 0 1)- and random-oriented Bi3.15Nd0.85Ti3O12 thin films: a comparative study

Highly (0 0 1)-oriented Bi3.15Nd0.85Ti3O12 (BNdT) films were deposited directly on single-crystalline Nb-doped SrTiO3 (STON) conductive substrates by chemical solution deposition. The electrical characteristics of BNdT films were studied and compared with random-oriented BNdT films on Pt/TiO2/SiO2/Si substrates. BNdT films on STON substrates show much smaller remanent polarization and ϵr values. This indicates that dominant polarization of BNdT is not along the (0 0 1)-axis. However, (0 0 1)-oriented BNdT films exhibit better retention characteristics, which can be ascribed to the better film/electrode interface between BNdT and STON.

High-oxygen-pressure crystal growth of ferroelectric Bi4Ti3O12 single crystals

We have investigated the effects of high-oxygen-pressure crystal growth of ferroelectric Bi4Ti3O12 on the polarization properties along the a(b) axis. Domain observations by piezoresponse force microscope demonstrate that a small remanent polarization (Pr) for the crystals grown at 0.02MPa is attributed to the clamping of 90° domain walls by oxygen vacancies. The vacancy formation of Bi and O during crystal growth at high temperatures is suppressed at a higher oxygen pressure, leading to a larger Pr of 47μC∕cm2 for the crystals grown at 1MPa oxygen. High-oxygen-pressure sintering is proposed to be effective for obtaining Bi4Ti3O12-based devices with enhanced polarization properties.

Orientation dependent ferroelectric properties in samarium doped bismuth titanate thin films grown by the pulsed-laser-ablation method

Samarium doped bismuth titanate thin films with the composition of Bi3.25Sm0.75Ti3O12 and with strong preferred orientations along the c axis and the (117) direction were fabricated on Pt∕TiO2∕SiO2∕Si substrate by pulsed laser ablation. Measurements on Pt∕BSmT∕Pt capacitors showed that the c-axis oriented film had a small remanent polarization (2Pr) of 5μC∕cm2, while the highly (117) oriented film showed a 2Pr value of 54μC∕cm2 at an electrical field of 268kV∕cm and a coercive field Ec of 89kV∕cm. This is different from the sol-gel derived c-axis oriented Bi3.15Sm0.85Ti3O12 film showing a 2Pr value of 49μC∕cm2.

Thermal, Structural and Ferroelectric Properties of Amorphous Phases in Quenched Nylon 6 Film

Three types of amorphous phases (ferroelectric metastable phase A with large remanent polarization, ferroelectric metastable phase B with small remanent polarization and paraelectric stable phase C) are identified in as-quenched and/or annealed nylon 6 films on the basis of the thermal data obtained by light-modulated differential scanning calorimetry (LMDSC) as well as X-ray data, which show different glass transition temperatures and d -spacings. The irreversible exothermic anomaly at 328 K observed through heating process in the conventional DSC is attributed to transition from phases A and/or B to nematic phase. The transition from phase A to phase B is considered to complete after 15 min annealing at 320 K on the basis of the LMDSC data, which corresponds to abrupt diminution of the remanent polarization by the correspondent annealing condition. Such results suggest that ferroelectricity of nylon 6 film is mainly attributed to phase A (frozen state of the melt) formed in the quenched nylon 6 thin film.

Recrystallization Study of High-Energy Electron-Irradiated P(VDF−TrFE) 65/35 Copolymer

Electron-irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer exhibits a very high electromechanical performance that is attractive for many applications. A study of recrystallization of irradiated P(VDF-TrFE) 65/35 mol % copolymer is reported in this paper. The structure and morphology of the recrystallized samples were determined using DSC and X-ray diffraction, and the polarization behavior of the recrystallized samples was studied. The nonpolar phase content of the recrystallized samples was much lower than that of the irradiated samples. For irradiated samples that exhibited the best electromechanical performance, the corresponding recrystallized material had a high polar phase content, with a correspondingly high remanent polarization. For samples irradiated with higher doses, although the polarization level was low immediately after irradiation, after recrystallization the material exhibited a much higher polarization level with a very small remanent polarization, an attractive combination for many electromechanical applications.

Characteristics of SrBi 2 Ta 2 O 9 ferroelectric films on GaAs with a TiO 2 buffer layer

Mainly [115]-oriented SrBi2Ta2O9 (SBT) films were prepared on GaAs(100) substrates with TiO2 buffer layers. Both the SBT films and the TiO2 buffer layers were deposited by pulsed laser deposition (PLD) using a KrF excimer laser. The depth profile of the constituent elements observed by Auger electron spectrometry (AES) shows no remarkable diffusion at both the interfaces between SBT and TiO2 and between TiO2 and the GaAs substrate. The electrical characteristics of the Pt/SBT/TiO2/GaAs(100) structures show a ferroelectric hysteresis loop with a small remanent polarization (∼0.5 μC/cm2).

Preparation and Characterization of Sol-Gel Derived (Sr,Ba)Bi 2 (Ta,Nb) 2 O 9 Thin Films for Ferroelectric-Gate FET Applications

We have fabricated (Sr,Ba) 0.8 Bi 2.2 (Ta,Nb) 2 O 9 (SBBTN) thin films by the sol-gel technique to obtain a small remanent polarization and a large coercive field for ferroelectric-gate FET applications. Ba and Ta compositions are varied from 0 to 0.2 and from 0 to 0.5, respectively. It is demonstrated that the coercive field becomes large by the partial replacement of Ta with Nb atoms and that the Ba doping results in slight decrease of the remanent polarization. A remanent polarization as small as 5 w C/cm 2 and a coercive field as large as 100 kV/cm can be obtained for Sr 0.6 Ba 0.2 Bi 2.2 Ta 1.5 Nb 0.5 O 9 thin films, which were crystallized at 850°C.

Sm Doping Effects on Electrical Properties of Sol-Gel Derived SrBi2Ta2O9 Films

ABSTRACTWe have characterized (Sr,Sm)Bi2Ta2O9 (SSBT) films fabricated by the sol-gel technique on Pt/Ti/SiO2/Si substrates. For ferroelectric-gate FET applications, a ferroelectric film which has a small remanent polarization and a relatively large coercive field is required. It is demonstrated that Sm doping in ferroelectric SBT films is effective to reduce the remanent polarization and enhance the coercive field. Sr0.5Sm0.2Bi2.2Ta2O9 films (150nm) crystallized at 850°C exhibits good electrical properties with a remanent polarization of 1.7 μC/cm2 and a coercive fields of 85 kV/cm. These values are suitable for ferroelectric-gate FET applications.

Sm Doping Effects on Electrical Properties of Sol-Gel Derived SrBi2Ta 2O9 Films

ABSTRACTWe have characterized (Sr,Sm)Bi2Ta 2O9 (SSBT) films fabricated by the sol-gel technique on Pt/Ti/SiO2/Si substrates. For ferroelectric-gate FET applications, a ferroelectric film which has a small remanent polarization and a relatively large coercive field is required. It is demonstrated that Sm doping in ferroelectric SBT films is effective to reduce the remanent polarization and enhance the coercive field. Sr0.5Sm0.2Bi2.2Ta2O9 films (150nm) crystallized at 850°C exhibits good electrical properties with a remanent polarization of 1.7 μC/cm2 and a coercive fields of 85 kV/cm. These values are suitable for ferroelectric-gate FET applications.

Characterization of Highly Preferred Pb(Zr,Ti)O3 Thin Films on La0.5Sr0.5CoO3 and LaNi0.6Co0.4O3 Electrodes Prepared at Low Temperature

La0.5Sr0.5CoO3 (LSCO) and LaNi0.6Co0.4O3 (LNCO) thin films were deposited on Pt/Ti/SiO2/Si substrates by DC reactive sputtering at 450°C and were annealed at temperatures ranging from 550°C to 750°C for 30 min in an O2 ambient to improve the crystallinity of the films and to reduce their resistivity. LSCO and LNCO thin films were successfully prepared at temperatures as low as 450°C. Pb(Zr0.48Ti0.52)O3 (PZT) thin films of 150 nm thickness were deposited on the LSCO and LNCO electrodes by DC reactive sputtering at a substrate temperature of 550°C. PZT films grown on LSCO and LNCO electrodes showed a (001) preferred orientation and had a uniform matrix of densely packed round grains. The leakage current density remained on the order of 10-7–10-9 A/cm2 at an applied voltage below 5 V. PZT thin films grown on LSCO/Pt showed a remanent polarization (2Pr) of about 46–52 µC/cm2, and a coercive voltage of about 1 V. PZT thin films grown on LNCO/Pt electrodes showed a lower coercive voltage (<0.6 V) and a smaller remanent polarization (2Pr) of about 28.8 µC/cm2 than those of PZT films grown on LSCO/Pt. LSCO/Pt and LNCO/Pt electrodes were essential for lowering the crystallization temperature as well as for obtaining good electrical properties of PZT capacitors.

Fabrication and Characterization of Pt/(Bi, La)4Ti3O12/Si3N4/Si Metal Ferroelectric Insulator Semiconductor Structure for FET-Type Ferroelectric Memory Applications

For field effect transistor (FET)-type ferroelectric memories, c-axis oriented (Bi, La)4Ti3O12 films with small remanent polarization Pr of 4 µC/cm2 were investigated. Bi3.25La0.75Ti3O12 films were prepared by the sol-gel method on amorphous Si3N4 layers formed on Si substrates using atomic nitrogen radicals. It was found that the films formed using stoichiometric sol-gel solution did not crystallize even after annealing at 800°C in O2 ambient. Therefore, 2.5 to 7.5% excess-Bi solutions were used and such parameters as pre annealing and crystallization temperatures, film thickness and crystallization ambient were optimized. As a result, the well c-axis-oriented Bi3.25La0.75Ti3O12 films with good crystallinity and good surface morphology were obtained at temperatures higher than 600°C. It was also found in a Pt/100 nm-Bi3.25La0.75Ti3O12/3 nm-Si3N4/Si (metal/ferroelectric/insulator/semiconductor) structure that C–V characteristics showed a hysteresis loop with a memory window of about 1 V and both high and low capacitance values kept at zero bias voltage did not change for more than 3 h.

Effects of annealing on the structure and switching characteristics of VDF/TrFE copolymers

Structure-property relationship has been investigated in concern with the ferroelectric switching characteristics of a VDF(78)/TrFE(22) copolymer. Unoriented and oriented film samples prepared by melt-quenching and melt-extrusion, respectively, were subjected to annealing and resulting structural changes were characterized by SEM, X-ray, density and DSC measurements. It was found that annealing just above the Curie point (120–130°C) caused a marked increase in crystallinity, whereas annealing in the paraelectric state (130–145°C) induced a crystal growth into thick lamellae. Such structural changes resulted in the ferroelectric switching characteristics with larger remanent polarization and shorter switching time. The unoriented sample yielded a smaller remanent polarization than the oriented sample by a factor of π/4, which substantiated that polarization reversal occurred as a result of rotation of molecules rotation about their chain axis. The melt-extruded and well-annealed sample consisted of regularly stacked large lamellae, thus providing information on the switching process occurring in constituent crystallites. Analysis of the observed switching transient has shown that polarization reversal progresses through a conventional nucleation-growth mechanism with a large waiting time.

Structural and Dielectric Properties of Ba(Ti1-xSnx)O3 Thin Films

Close correlation between the dielectric constant and the degree of preferential (111) orientation is found for Ba(Ti0.85Sn0.15)O3 ( BTS15) solid-solution thin films deposited on a Pt/Ti/SiO2/Si(100) substrate by pulsed laser deposition. It is shown that substrate temperature is the principal factor which determines orientation and crystalline quality of the films. Substrate temperatures higher than 700° C are required to achieve (111) orientation with good crystalline quality. BTS15 films with strong (111) orientation have large dielectric constant which reaches 2500 at 22° C. These films exhibit a D-E hysteresis loop, but small remanent polarization of 0.89 µ C/cm2 and coercive field of 3.2 kV/cm are obtained at 18° C. Films having the composition with lower Sn ratio exhibit larger remanent polarization. Causal relationships among the dominant film orientation, crystalline quality and dielectric constant are discussed.

Ferroelectric behavior in vinylidene fluoride-tetrafluoroethylene copolymers

Abstract Ferroelectric properties have been studied for copolymers of vinylidene fluoride (VDF) and tetrafluoroethylene (TeFE) with different TeFE content of 17 to 30 mol%. The Curie transition in the copolymers was considerably influenced by annealing as well as poling in preparation of specimens. The polarization reversal and the ferroelectric hysteresis were observed using 10 mHz high voltage triangular wave. A large remanent polarization above 80 mCm−2 was exhibited by melt crystallized samples of copolymers with 20–25 mol% TeFE, while the coercive field scarcely depended on the comonomer content. Drawn films of the copolymer showed a rather small remanent polarization which contrasted strikingly with the case of the copolymer of trifluoroethylene. The pyroelectric coefficient was highest for 20–25 mol% TeFE copolymer, exhibiting a linear relationship with the remanent polarization. The coercive field and the remanent polarization were slightly increased by hydrostatic pressure in a pressure range of ...