Ferroelectric Properties Of Pb Research Articles

Ferroelectric properties of Pb(Zr,Ti)O 3 heterolayered thin films for FRAM applications

Ferroelectric PZT (20/80)/PZT (80/20) heterolayered thin films were fabricated by spin-coating method on a Pt/Ti/SiO 2/Si substrate alternately using PZT (20/80) and PZT (80/20) alkoxide solutions. All PZT heterolayered films show dense and homogeneous structure without the presence of the rosette microstructure. The relative dielectric constant and dielectric loss at 100 kHz of the PZT-6 film were about 355 and 0.016, respectively. As the number of coats increased, remanent polarization increased, the coercive field decreased and the values of the PZT-6 film were 16.14 μC/cm 2 and 97.1 kV/cm, respectively. Leakage current density of the PZT-6 heterolayered film was 2.5×10 −7 A/cm 2 at 5 V.

Ferroelectric Pb(Mg 1/3Nb 2/3)O 3 thin films by PLD at varying oxygen pressures

Oxygen deposition pressure exerts a strong impact on the structure and ferroelectric properties of Pb(Mg 1/3Nb 2/3)O 3 (PMN) thin films derived from pulsed laser ablation (PLD), when perovskite PMN films on (La 1/3Sr 2/3)MnO 3/LaAlO 3 substrates were deposited at 520 °C and oxygen pressure varied from 0.1 to 0.6 mbar. Instead of showing the cubic structure of bulk ceramic PMN, the films exhibit a tetragonal structure, as confirmed by the splitting of (002) diffraction peak into (002) and (200) peaks. The intensity ratio of (002) and (200) increases with decreasing oxygen partial pressure. Both the remnant polarization and dielectric constant of the PMN thin films increase with decreasing deposition oxygen pressure. This is attributed to the enhancement of c-domains, which exhibit a larger polarization than that of a-domains. Typical depressed semicircles were observed in Cole–Cole curves, suggesting the coexistence of polarization relaxation and space charge relaxation in the oxygen deficient PMN films.

Epitaxial Growth and Ferroelectric Properties of the 20-nm-Thick Pb(Zr, Ti)O3 Film on SrTiO3(100) with an Atomically Flat Surface by Metalorganic Chemical Vapor Deposition

We investigated the influences of the surface flatness of a substrate on the surface morphology and ferroelectric properties of Pb(Zr, Ti)O3 (PZT) ultrathin films by metalorganic chemical vapor deposition (MOCVD). When SrTiO3 (STO) (100) was etched in a buffered NH4F–HF solution and annealed, an atomically flat surface with steps corresponding to one unit cell height was obtained. SrRuO3 (SRO) deposited on the treated STO also showed a flat surface with steps. Epitaxial PZT films with thickness of 20–60 nm on SRO/treated STO were successfully obtained. The 20-nm-thick PZT ultrathin film showed remanent polarization of 30 µC/cm2 and coercive electric field of 730 kV/cm. On the other hand, when PZT films were grown on SRO/nontreated STO, PZT films with thicknesses of 20–32 nm showed no hysteresis loops due to high leakage current. These results suggest that surface flatness of STO and SRO plays a very important role in the growth of PZT ultrathin films.

Processing effects on the microstructure and ferroelectric properties of Pb(Zr,Ti)O 3 thin films prepared by sol–gel process

Lead zirconate titanate Pb(Zr 0.53Ti 0.47)O 3 (PZT) thin films grown on Pt(1 1 1)/Ti/SiO 2/Si(1 0 0) substrates by a simple sol–gel process use various thermally decompose temperatures from 320 to 400 °C. Then PZT films were annealed at various temperatures from 550 to 600 °C in oxygen atmosphere by a rapid thermal annealing process, and highly (1 1 1)-oriented PZT thin films have been obtained. The microstructure and surface morphologies, and root mean square (RMS) roughness of the thin films were studied by X-ray diffraction and atomic force microscopy (AFM). AFM images shown that the higher (1 1 1) orientation present in the PZT thin films, the smaller grain size, and the lower RMS roughness. PZT films on Pt/Ti/SiO 2/Si substrates were initially heated at 400 and 320 °C, then annealed at 550 °C, the remanent polarization ( P r) and coercive electric field ( E c) were 16.1 μC/cm 2 and 105 kV/cm, 32.2 μC/cm 2 and 79.9 kV/cm; at 100 kHz, the dielectric constant and dissipation factor were 331 and 0.045, 539 and 0.066, respectively. The highly (1 1 1) oriented PZT films, have smooth surface, good ferroelectric and dielectric properties.

Comparative analysis for the crystalline and ferroelectric properties of Pb(Zr,Ti)O 3 thin films deposited on metallic LaNiO 3 and Pt electrodes

The crystalline quality and ferroelectricity of the Pb(Zr,Ti)O 3 (PZT) films deposited on the metallic LaNiO 3 (LNO) and Pt electrodes were comparatively analyzed to investigate the possibility for their application to non-volatile memory devices. LNO thin films were successfully deposited on various substrates by using r.f. magnetron sputtering even at a low temperature ranging from 250 to 500 °C, and the ferroelectric PZT thin films were spin-coated onto the LNO and Pt bottom electrodes. Metallic LNO thin films exhibited [100] orientation irrespective of the substrate species and PZT films coated onto LNO films had highly a- and c-axis orientations, while those with Pt bottom electrode were polycrystalline. PZT films with LNO bottom electrode had smaller grain size and larger dielectric constant compared to those grown on the Pt electrode. The ferroelectric thin films fabricated on LNO bottom electrode displayed an asymmetric D–E hysteresis loop, which was explained by the defect effects formed at the interface. Especially, the LNO/PZT/LNO capacitor was found to significantly improve the polarization fatigue and the effects of the LNO electrodes to the fatigue were discussed.

Dielectric and ferroelectric properties of Pb(Ni 1/3Nb 2/3)O 3–PbTiO 3 ferroelectic ceramic near the morphotropic phase boundary

(1− x)Pb(Ni 1/3Nb 2/3)O 3– xPbTiO 3 ( x=0.28–0.42) system ferroelectric ceramics were synthesized by the columbite precursor method. The phase structure and dielecric, ferroelectric properties were investigated. X-ray diffraction (XRD) results demonstrate that the morphotrophic phase boundary (MPB) lies in the composition range x=0.34–0.38. Examination of the dielectric behavior indicates that the ceramics exhibited very high dielectric constant near the MPB composition. In addition, the ferroelectric properties of the ceramics were found also quite well around the MPB.

Improvement of electric fatigue properties in PLZT ferroelectric ceramics due to SrBi 2Ta 2O 9 incorporation

The influences of SrBi 2Ta 2O 9 (SBT) on dielectric and ferroelectric properties of Pb 0.94La 0.04(Zr 0.70Ti 0.30)O 3 ceramics were investigated systematically. X-ray diffraction (XRD) patterns of PLZT–SBT composite showed that there was no chemical reaction between PLZT and SBT. SEM pictures on fracture section reflected a main transgranular fracture mode. An abnormal and interesting increase of dielectric constant was observed after SBT incorporation. Hysteresis loops of PLZT–SBT composites turned to slimmer shape with the increase of SBT content. No apparent decrease of switchable polarization strength was found in PLZT–SBT composites after repeated polarization switching. HRTEM picture of SBT grain in PLZT–SBT composite revealed a transformation from order to disorder near the tip of grain boundary as well as low angle of grain boundary, which could release concentrated internal stress and served as improvement mechanism of electric fatigue endurance in PLZT–SBT composites.

Properties of Ferroelectric Pb(Zr,Ti)O 3 -SiO 2 -B 2 O 3 Glass-Ceramic Thin Films Derived by Sol-Gel Method

Ferroelectric PZT-(5,10,20)mol%SiO 2 -lmol%B 2 O 3 glass-ceramic thin films were fabricated by sol-gel method on Pt/Ti/SiO 2 /Si substrates. The perovskite PZT crystallites grew in the films and were preferentially oriented in the (111) direction. The Zr stoichiometry in PZT crystallites was found decreased with the increase in glass concentration. The lower dielectric constant and loss, remnant polarization, and leakage current were obtained for the 5 mol% SiO 2 contained films annealed from 650 to 700°C, and for the 10 mol% SiO 2 contained films annealed at 700°C. This indicates that the ferroelectric glass-ceramic thin film is a promising material used for the gate material of ferroelectric-gate FETs.

Ferroelectric Properties of Pb(Zr 1−x Ti x )O 3 Graded Thin Films

Pb(Zr 1 m x Ti x )O 3 , PZT, thin films, with the composition changes continuously throughout the thickness of the films, have been synthesized using pulsed laser deposition process. Graded-structured PZT films, with PZT(25/75) on top layer and PZT(52/48) on bottom layer, exhibit markedly superior ferroelectric properties, whereas the double layer structured PZT films show pronouncedly inferior ferroelectric properties to uniform-compositioned PZT (52/48) films. The modification on ferroelectric properties of these graded PZT films is presumably due to the presence of film-to-substrate interfacial stress or layer-to-layer internal stress.

Relaxor behavior of Pb[(Mg0.5W0.5)1-xTix]1-ySnyO3 ceramics

The dielectric and ferroelectric properties of Pb[(Mg0.5W0.5 )1 – xTi x ]1 – ySn y O3 (x = 0.4–0.5, y = 0–0.15) solid solutions are studied. The results are used to elucidate the origin of the relaxor state developing in a temperature range between the para- and ferroelectric phases.

Ferroelectric Properties of Pb(Zr 1−x Ti x )O 3 Graded Thin Films

Pb(Zr 1 m x Ti x )O 3 , PZT, thin films, with the composition changes continuously throughout the thickness of the films, have been synthesized using pulsed laser deposition process. Graded-structured PZT films, with PZT(25/75) on top layer and PZT(52/48) on bottom layer, exhibit markedly superior ferroelectric properties, whereas the double layer structured PZT films show pronouncedly inferior ferroelectric properties to uniform-compositioned PZT (52/48) films. The modification on ferroelectric properties of these graded PZT films is presumably due to the presence of film-to-substrate interfacial stress or layer-to-layer internal stress.

Properties of Ferroelectric Pb(Zr,Ti)O 3 -SiO 2 -B 2 O 3 Glass-Ceramic Thin Films Derived by Sol-Gel Method

Ferroelectric PZT-(5,10,20)mol%SiO 2 -lmol%B 2 O 3 glass-ceramic thin films were fabricated by sol-gel method on Pt/Ti/SiO 2 /Si substrates. The perovskite PZT crystallites grew in the films and were preferentially oriented in the (111) direction. The Zr stoichiometry in PZT crystallites was found decreased with the increase in glass concentration. The lower dielectric constant and loss, remnant polarization, and leakage current were obtained for the 5 mol% SiO 2 contained films annealed from 650 to 700°C, and for the 10 mol% SiO 2 contained films annealed at 700°C. This indicates that the ferroelectric glass-ceramic thin film is a promising material used for the gate material of ferroelectric-gate FETs.

Effects of Remanent Polarization State and Internal Field in Ferroelctric Film on the Hydrogen-Induced Degradation Characteristics in Pt/Pb(Zr,Ti)O3/Pt Capacitor

The ferroelectric properties of Pb(Zr,Ti)O<TEX>$_3$</TEX>[PZT] films degrade when the films with Pt top electrodes are annealed in hydrogen containing environment. This is due to the reduction activity of atomic hydrogen that is generated by the catalytic activity of the Pt top electrode. At the initial stage of hydrogen annealing, oxygen vacancies are formed by the reduction activity of hydrogen mainly at the vicinity of top Pt/PZT interface, resulting in a shift of P-E (polarization-electric field) hysteresis curve toward the negative electric field direction. As the hydrogen annealing time increases, oxygen vacancies are formed inside the PZT film by the inward diffusion of hydrogen ions, as a result, the polarization degrades significantly and the degree of P-E curve shift decreases gradually. The direction and the magnitude of the remnant polarization in the PZT film affect the motion of hydrogen ions which determines the degradation of polarization characteristics and the shift in the P-E hysteresis curve of the PZT capacitor during hydrogen annealing. When the remnant polarization is formed in the PZT film by applying a pre-poling voltage prior to hydrogen annealing, the direction of the P-E curve shift induced by hydrogen annealing is opposite to the polarity of the pre-poling voltage. The hydrogen-induced degradation behavior of the PZT capacitor is also affected by the internal field that has been generated in the PZT film by the charges located at the top interface prior to hydrogen annealing.

Influence of Sputtering and Annealing Conditions on the Structure and Ferroelectric Properties of Pb(Zr,Ti)O3 Thin Films Prepared by RF Magnetron Sputtering

Lead zirconate titanate (PZT) thin films were prepared on Pt/Ti/Corning 7059 glass substrates by RF magnetron sputtering using a Pb(Zr0.5,Ti0.5)O3 ceramic target. X-ray diffraction studies were performed on the films to optimize the sputtering pressure, O2/(Ar+O2) mixing ratio (OMR), annealing temperature and annealing time, to prepare the films in the perovskite phase. As-deposited amorphous film goes through an intermediate pyrochlore phase before crystallizing in the perovskite phase. Perovskite phase formation started at 625°C and annealing at 650°C for 2 h was found to be necessary for complete crystallization in the single perovskite phase. Perovskite phase formation was confirmed with the existence of a perovskite rosette structure by scanning electron micrograph (SEM). Energy dispersive X-ray (EDX) compositional analysis of as-deposited films showed Pb/(Zr+Ti) ≃ 1.1; a 10% deviation from the target stoichiometry. Ferroelectric and dielectric properties of the capacitor with thin platinum films as both electrodes were investigated in detail as functions of annealing temperature and annealing time. The marked improvement in the structural and electrical properties observed in the deposited film after annealing was mainly due to the crystal growth of small crystallites. The dielectric constant and loss tangent of the films annealed at 650°C for 2 h were 580 and 0.06, respectively. The films with 1.4 µm thickness that were annealed at 650°C showed a remanent polarization (Pr)=26 µC/cm2 and coercive field (Ec)=51 kV/cm.

Phase relations and ferroelectric properties of Pb(Zr, Sn, Ti)O3 ceramics

Dielectric and ferroelectric properties of ceramics Pb0.99[(Zr1−xSnx)1-yTiy]0.98Nb0.02O3 with x = 0.4 (y = 0.06–0.009) (I), x = 0.5 (y = 0.04–0.12) (II) and x = 0.6 (y = 0.08–0.2) (III) have been studied. T-x and E-T diagrams are proposed. It is confirmed that increase in content favors extension of temperature range of coexistence of ferroelectric and antiferroelectric phases and coexistence of the nonpolar phase between the antiferroelectic and paraelectric phases. The electrocaloric effect has been measured in ceramics III. A rather high Δ = 0.6 K has been obtained at E = 14 kV/cm.

Control of Crystal Structure and Ferroelectric Properties of Pb(ZrXTi1-X)O3 Films Formed by Pulsed Laser Deposition

Pb(ZrXTi1-X)O3 (PZT) thin films on Pt/SiO2/Si substrates formed by pulsed laser deposition (PLD) and subsequent rapid thermal annealing (RTA) have been investigated. X-ray diffraction (XRD) and atomic force microscopy showed that the crystalline structure and the crystallographic orientation of PZT films after RTA, sensitively depended on the microstructure of as-deposited films. The preferentially (100)-oriented perovskite PZT films forming a trigonal structure were obtained from the as-deposited films that had contained small grains having a pyrochlore structure. This type of perovskite structure was found to depend also on the oxygen pressure during PLD. Chemical composition analysis by X-ray photoelectron spectroscopy clearly revealed the characteristics of a Zr-rich composition which induced the trigonal phases in the films, which were consistent with the XRD results. The capacitors made from these films showed large remanent polarization.

Phase states and ferroelectric properties of Pb(Zr, Sn, Ti)O3 ceramic

The ferroelectric and dielectric properties of Pb0.99[(Zr1−x Snx)1−y Tiy]0.98Nb0.02O3 ceramic of composition (I) x=0.5, y=0.04–0.12 and (II) x=0.4, y=0.06–0.09 were studied, and the T-x and E-T diagrams were constructed. When zinc is substituted for tin, the range of coexistence of the ferroelectric and antiferroelectric phases extends. The range of the nonpolar phase shrinks when the titanium content is increased.

Effect of excess-PB and prenucleation layer on properties of Pb(ZryTi1-y)O3 thin films prepared by mod process

A modified metal-organic decomposition process, MOD has been successfully utilized to improve the ferroelectric properties of Pb(Zr0.52Ti0.48)O3, PZT, thin films. Multilayer PZT/Pt(Si) films, which contain 0.12 μm layer of spin coated PbO-excess (10 mol%) precursors on top of 0.12 μm layer of stoichiometric PZT precursors, exhibit superior ferroelectric properties (Pr=14.2 μC/cm2; Ec=62 kV/cm) to the single layer PZT/Pt(Si) films of the same thickness (0.24 μm), which are either stoichiometric or 10 mol% Pb-enriched. The ferroelectric properties are further improved when the PZT films were synthesized using a thin pulsed laser deposited (PLD) prenucleation layer (0.06 μm). The subsequently MOD-prepared PZT films posses high remanent polarization (Pr=23.2–26.6 μC/cm2) and low coercive field (Ec=62.9–69.0 kV/cm).

Ferroelectric Properties of Pb(Zi, Ti)O3 Capacitor with Thin SrRuO3 Films within Both Electrodes

Ferroelectric properties of a Pb(Zi, Ti)O3 (PZT) capacitor with thin SrRuO3(SRO) films within both electrodes were investigated in detail. Thin SRO films of 10 nm thickness markedly improve the electrical performance, such as switching charge (Qsw), saturation characteristics of the hysteresis curve and imprint performance even at an elevated temperature. It should also be noted that there was no Qsw degradation after 5×1010 read/write cycles at 5 V. No leakage current increase after the test was observed. The results of transmission electron microscope (TEM) and electron dispersive X-ray (EDX) analyses also showed that there is no diffusion of either Sr or Ru in the PZT film. The Qsw increase can be explained by the model in which excess oxygen ions existing in the SRO films drift into the PZT due to the external electric field where they fill the oxygen vacancies in the PZT near the interfaces. We confirmed that the proposed electrode structure was a key to realizing highly reliable ferroelectric random access memories (FRAMs).

Phase Diagram and Dielectric Properties of Pb[Zr1 – x (Fe0.5Nb0.5) x ]O3 (0 < x < 0.2) Solid Solutions

The structural, dielectric, and ferroelectric properties of Pb[Zr1 – x (Fe0.5Nb0.5) x ]O3 (0 < x < 0.2) solid solutions were investigated. The results were used to assess in detail the phase relations near the morphotropic boundary.