Electrical Properties of Nb-Doped PZT 65/35 Ceramics: Influence of Nb and Excess PbO

The effect of Nb and excess PbO on the structural and electrical properties of conventionally prepared Nb-doped PZT 65/35 ceramics has been studied in this work. It is found that, from excess PbO contents as high as 4 mol%, the solubility limit of Nb in PZT occurs below 4 mol%, while a secondary prevoskite-like phase develops in the dielectric system for a further increase of Nb content. The ferroelectric and piezoelectric properties (permittivity, ferro-paraelectric phase transition, polarization, electromechanical coefficients) of such materials are thus found to be strongly dependent on the degree of densification and structural phase development during sintering at high temperatures. In particular, the nature of the ferro- to para-electric phase transition is in these materials noted to better fit a generalized rather than Smolenskii-Isupov equation, the former being appropriate for the characterization of non-purely diffuse transitions. In nice agreement with the Bokov model, substitution of Nb^{5 +} for (Zr,Ti)^{4 +} is found to induce only poorly diffuse phase transition in these materials. The electrical properties reported in this work are in magnitude comparable to those exhibited by PZT-based materials.     

Device effects of various Zr/Ti ratios of PZT thin-films prepared by sol-gel method

Abstract

PZT, PbZr_xTI_1?xO₃, thin-films with various Zr/Ti ratios, 100/0 (lead zirconate) to 0/100 (lead titanate), were prepared by the sol-gel method. Basic electric properties, dielectric constant, tan σ, P-E hysteresis curve, switching properties were measured respectively as a function of composition. Dielectric constant indicated a specific peak value (～1100) around the morphotropic phase boundary between tetragonal and rhombohedral phase. Satisfactory low-voltage saturated hysteresis curves were observed for the compositions of PZT(90/10) through PZT(20/80). The remanent polarization and the coercive field increased as the titanium content decreased. The result of X-ray measurement showed that the lattice constants of thin-Film PZT are different from bulk ceramics for compatible compositionsS. The boundary, on which the c/a ratio must be 1 (rhombohedral phase), was slightly shifted to PbTiO₃ side. This distortion in crystal structure is considered to be due to the thin-film effect, which the lattice mismatch between the platinum substrate and the PZT layer, restricted the ions to position into proper cites.     

Microstructure and Properties of Solution Deposited, Nb-Doped PZT Thin Films

Nb doped PZT films with Nb concentrations of 0, 5, 8 and 12 mol% are being processed via chemical solution deposition on platinized Silicon substrates. An original processing route including seed layer and additional PbO coating is presented whereby homogeneous, pyrochlore free microstructures with 111/100 texture are obtained. The temperature dependence of the dielectric constant shows diffuse peaks corresponding to the paraelectric to ferroelectric transition. The transition temperature is found to decrease from 325°C to 220°C with increasing Nb content. Nb is however found to lead to a substantial increase in the dielectric constant in comparison to non-doped PZT. The dependence of the dielectric constant on DC bias field is also reported. Strong asymmetries towards positive values both in the values of the dielectric constant and coercive fields are obtained at room temperature, and become replenished at 100°C. This is interpreted in terms of space charge effects on the pinning of domain walls. Furthermore, the loss tangent shows a relaxation peak which shifts to higher frequencies with increasing Nb content, and suggests that Nb-doping affects the dielectric properties of the interfacial layer. Finally, Nb addition is found to lead to slant hysteresis loops with lower remnant polarization and coercive field.     

Studies of a PT/PZT/PT sandwich structure for feram applications using sol-gel processing

Abstract

A silicon-based PbTiO₃/Pb(Zr,Ti)O₃/PbTiO₃ (PT/PZT/PT) sandwich structure with Pt electrodes are prepared by a sol-gel method. Effects of the PT buffer layers to the phase formation of the PZT films are studies. Dielectric and ferroelectric properties of the sandwich structure are measured. Maximum dielectric constant of about 900 is obtained at the coercive field 20 kV/cm. The leakage current density is less than 5 × 10^?9 A/cm2 below 200 kV/cm, which is much lower than that of PZT/PT structure. And there is almost no fatigue even after 5 × 109 read/write cycles for the PT/PZT/PT sandwich structure.     

Investigation on the Dielectric and Polarization Behavior of Sol-Gel Derived Erbium Doped Pb(Zr 0.53 Ti 0.47 )O 3 Thin Films

We have studied the effect of Er 3+ doping on the dielectric and polarization hysteresis behavior of sol-gel derived Pb 1.05 (Zr 0.53 Ti 0.47 )O 3 thin films. Up to 1 at% Er doping, the dielectric constant of undoped PZT increases from 1245 to 1477 (measured at 50 kHz, 500 mV oscillation voltage), whereas the remnant polarization increases from 30 to 41 w C/cm 2 . Under the subswitching external field, the dielectric permittivities follow the Rayleigh law. The Rayleigh coefficient ( f ) was considered as a measure of the ease of domain wall motion. Up to 1 at% Er doping, the increase of f indicates minimal defect-domain wall interaction due to lower defect concentration. Under the switching field, the irreversible part of the switchable polarization was estimated from the C-V and hysteresis measurements. At the saturation field it was observed that up to 1 at% Er doping the irreversible component at switchable polarization increases and reversible component remains low. The improvements of dielectric and ferroelectric properties for up to 1 at% Er doping have been correlated to the relative site occupancy of Er 3+ as a function of Er content in PZT host lattice.     

Piezoelectric and dielectric aging in pb(zr,ti)o3 thin films and bulk ceramics

Abstract

Piezoelectric and dielectric aging was studied in Pb(Zr,Ti)O₃ (PZT) thin films and bulk ceramics. It was found that piezoelectric aging in thin films obeys the logarithmic time dependence with the relative aging rate much higher than that of the dielectric constant, while comparable aging rates of piezoelectric and dielectric constants were found in PZT ceramics. The origin of piezoelectric aging in PZT films was related to depolarization of the films rather than to suppression of the domain wall motion as was generally accepted for PZT ceramics.     

PZT-NiCuZn复合材料的电磁特性

首先用溶胶-凝胶法制得Pb(Zr0.52Ti0.48)O3纳米(简称PZT)粉料,然后采用固相反应法制备PZT-NiCuZn铁氧体复合材料.研究了PZT含量对复合材料的显微结构、物相组成、致密化过程以及电磁性能的影响.结果显示,PZT组分与铁氧体之间没有任何反应,复合材料的主晶相为尖晶石相.随着PZT含量的增加,起始磁导率逐渐减小,品质因数增大,同时介电常数增大.该材料具有高的介电常数和良好的高频性能,有望用于抗电磁干扰滤波器.     

Niobium doping effects and ferroelectric relaxor behavior of bismuth lantanium titanate

Ferroelectrics Bi_3.25La_0.75(Ti_3−x Nb_x)O₁₂ (BLTN, x = 0∼ 0.1) solid solution systems were prepared, and Nb doping effects and relaxor behaviors were investigated. The BLTN single phases were confirmed by XRD. The phase transition temperature decreased as the Nb content increased, and the corresponding dielectric constant maximum broadened. The temperature T _m of the dielectric maximum depended on frequency and increased, which indicate that the relaxor behavior was caused by Nb substitution. The substitution of Nb for Ti ions affected the degree of disorder and modified the dielectric properties from those of normal ferroelectrics to relaxor ferroelectrics.     

Preparation and properties of sol-gel derived PZT thin films for decoupling capacitor applications

Abstract

The use of ceramic thin films as decoupling capacitors offers the possibility of capacitor integration within the integrated circuit (IC) package, and potentially, directly onto the IC itself. Since these configurations minimize series inductance, higher operational speeds are possible. In the present study we have investigated the dielectric and leakage characteristics of sol-gel PZT films. For compositions near the morphotropic phase boundary, dielectric constants of 1000, and loss tangents of about 0.02, were observed. The current-voltage behavior of the capacitors was characterized by a non-linear response, and significant asymmetry in both the leakage and breakdown characteristics as a function of bias sign was observed. Breakdown fields for PZT 53/47 thin films were typically ～800 kV/cm at 25°C. We have also studied the effects of La and Nb dopant additions and alternate firing strategies on film leakage characteristics. Donor doping at 2–5 mol% lowered leakage currents by a factor of 10³ For films prepared by a multilayering approach, firing each layer to crystallization resulted in leakage currents that were a factor of 10² lower than films prepared by the standard process.     

Thick piezoelectric coatings via modified sol-gel technique

Abstract

A hybrid sol-gel approach is reported for the deposition of high-quality composite PZT films of the thickness  1 μm. In this approach, the metallo-organic sol-gel precursor solution is mixed with fine piezoelectric powders and dip-coated onto Pt/Ti/SiO₂/Si substrates. Different organic viscous additives and deposition strategies were tried in order to deposit dense films with the properties approaching to those of bulk PZT. Using commercial PZT powder (TRS600FG) and ultrasonic mixing during deposition process, composite films having dielectric permittivity of ～2500 and saturation polarization ～35 μC/cm² were obtained. These values are intermediate between bulk ceramics and conventional sol-gel PZT films and therefore are indicative of good piezoelectric properties.     

Effect of Calcium Doping on Dielectric and Pyroelectric Properties of PLZT

Effect of calcium doping on structural, dielectric and pyroelectric properties of Pb_0.92-xLa_0.08Cax(Zr0.65Ti0.35)_0.98O₃ (PLCZT) composition derived by the solid state reaction method was studied. Rhombohedral perovskite phase was confirmed in all the PLCZT samples. Calcium doping did not show any structural change in PLCZT (8/65/35) up to 2.5 % doping, however grain size and crystallite size was found to increase up to 1%, but no systematic variation of transition temperature was found with Ca doping. P-E hysteresis loop parameters (E_c and P_r) and pyroelectric properties were found to decrease with Ca doping up to 1% and there after increased.     

Effects of complex doping on microstructural and electrical properties of PZT ceramics

The influence of complex dopants including donor and acceptor ions on microstructure and electrical properties of PZT (Zr/Ti = 53/47) ceramics was investigated. The prepared PZT ceramics modified with complex soft dopants, La⁺³ and Nb⁺⁵, showed that the piezoelectric properties were enhanced and stable with the compositional variations, which made it possible to establish the higher reliability and reproducibility of the piezoelectric performances. For 1.0 mol% La and 1.2 mol% Nb doped composition, the maximum value, k _P = 0.66, was obtained. Unlike single element doping, the complex doping of both the donor and acceptor ions caused various compensation effects for the piezoelectric properties of the PZT ceramics. The improved piezoelectric properties, i.e., enhanced Q _m with remaining higher k _p , were obtained in the PZT composition complexly doped with La⁺³ and Fe⁺³. For 1.0 mol% La and 2.0 mol% Fe doped PZT composition, relatively high Q _m and k _p values of 580 and 0.53, respectively, were obtained. It was also shown that the PZT composition had the rather lowered dielectric constant, ε _r = 800, and considerably low loss, tanδ = 0.003. By changing the dopants compositions, the properties can also be tailored over wider range.     

Anomalous fatigue behavior in Zn doped PZT

Abstract

Doping lead zirconate titanate (PZT) has often been examined in order to investigate changes in the electrical behavior of thin film ferroelectric capacitors.¹ In this study, PZT has been doped with Hf, Nb, and Zn. After reviewing the results of the initial studies, Zn doping of PZT was further investigated. Physical and electrical studies of Zn doped PZT have been conducted. These studies include x-ray diffraction analysis, hysteresis, pulsed switching, fatigue and retention measurements. Endurance measurements indicate an anomalous fatigue behavior of some Zn doped PZT thin film capacitors.     

High throughput experimentation for the development of new piezoelectric ceramics

Piezoelectric ceramics based on the perovskite Pb(Zr,Ti)O₃ (PZT) system are widely used as sensors and actuators. The toxicity of lead has motivated research in the field of alternative environmentally friendly lead-free materials. Lead-free piezoelectric ceramics are numerous and in comparison to PZT poorly investigated. The performance of PZT cannot yet be achieved by any lead-free material. Thus High Throughput Experimentation (HTE) shall be applied to discover new lead-free piezoelectric ceramics. In the present study a parallel solid state synthesis method was established for bulk ceramics. Libraries consisting of chemically diverse oxides are produced via the mixed-oxide route. Subsequently, classical piezoelectric parameters such as ɛ, d₃₃ and Curie temperature are screened. The high throughput route, which allows the synthesis and characterisation of over one hundred samples per week, has to be validated with PZT samples. The morphotropic phase boundary was clearly identified and dielectric measurement shows excellent results. The method may be extended to lead-free materials.     

Thick film fabrication of ferroelectric phase shifter materials

Abstract

Various composites of BSTO combined with other nonelectrically active oxide ceramics have been formulated. In general, the composites have adjustable electronic properties which can be tailored for use in phased array antennas and other phase shifting devices. The dielectric constant and the loss tangents have been reduced to enhance the overall impedance matching and thereby lowering the insertion loss of the device. In addition, the overall tunability, the change in the dielectric constant with applied voltage, is maintained at a sufficiently high level. The thickness limitation of the bulk materials is around 3–4 mils which can be used up to approximately 15 GHz. In order to increase the operating frequencies of the phase shifters, thick films were fabricated using non-aqueous tape-casting. The tapes were electrically characterized and compared to bulk ceramics. Also, laminated stacks of high dielectric constant and low dielectric constant alternating layers were fabricated.     

Origin of voltage offset and built-in polarization in in-situ sputter deposited pzt thin films

Abstract

Voltage offset and built-in polarization were investigated in in-situ reactively sputter deposited PZT thin films on Pt, as a function of composition, doping and cooling conditions. The voltage offset increases with increasing Ti content. Hot-poling treatments show that the voltage offset originates from non-mobile defects. Cooling the samples at various O₂ partial pressures leads to a change in lattice parameters and orientation, showing a ‘bulk’ effect rather than a simple ‘surface’ effect. While doping with Nb does not change the status of the films, doping with Fe increases coercive fields but removes the asymmetrical behavior of the voltage offset after hot-poling at positive and negative voltages. Annealing/cooling cycles are reversible in the suppression/creation of voltage offset and built-in polarization, respectively, excluding the idea of oxygen and lead vacancy dipolar defects. Experimental data suggest that oxygen is lost and the vacancies diffuse during cooling without being compensated to equilibrate with surface or electrode band bending, resulting in the creation of an internal bias field.     

Drying temperature effects on the electro-optic coefficients of PZT thin films

Abstract

PZT thin films were fabricated on ITO/glass substrates using sol-gel method. The main processing variable was the drying temperature: 300, 350, 450 and 500°C. The microstructure and electric properties (polarization and dielectric constant) were investigated. The electric properties were dependent on the perovskite phase content and the grain size affected by the nucleation of perovskite phase. The two-beams polarization interferometer was used for the measurement of electro-optic coefficients of PZT thin films, and these values were analyzed by comparing the electric properties.     

Electrical properties of sol-gel derived La-doped PbTiO3-containing films

Abstract

A series of sol-gel derived La-doped PbTiO₃-containing films was prepared on platinized Si wafers. The compositions investigated include PLT (0-28 mole % La) and PLZT (e.g., 9/65/35 and 12/80/20) films. These films were fired at temperatures ranging from 500 to 750°C. While most of the films were single-phase perovskite when fired at 700°C, lower firing temperatures (～500°C) are sufficient to obtain crystalline PLT films, especially when the La content is more than 15 mole %. The paraelectric or ferroelectric character of the films as a function of La content is also addressed. In PLZT films, the Zr/Ti ratio affects the crystallization behavior and also the perovskite structure, i.e., either tetragonal or rhombohedral. Ferroelectric PLZT films exhibit high values of both dielectric constant (>700) and leakage current. The values of dielectric constant in the relaxor PLZT films are low, especially when compared to their bulk ceramic values (5000–10000). Paraelectric PLT films exhibit high values of dielectric constant (>500) and low leakage currents.     

Poling Conditions of Pre-Stressed Piezoelectric Actuators and Their Displacement

The poling procedure has always been the key issue in producing piezoelectric actuators with optimised performance. This is also true with the relatively new category of pre-stressed bender actuators, where mechanical bias achieved with a passive layer is introduced in the actuators during manufacturing. Due to these factors, the behaviour of the actuator under poling is different compared to its bulk counterparts. In this paper, two different thicknesses of commercial PZT 5A and PZT 5H materials were used in bulk actuators and pre-stressed benders realised by new method. Pre-stress was introduced by using a post-fired biasing layer utilising sintering shrinkage and difference in thermal expansion. The hysteresis loop of the actuators was measured under 0.5–7.0 MV/m electric fields at 25–125^∘C temperatures, providing information about their remnant polarisation and coercive field before poling. The results showed that high electric field and 25^∘C temperatures in poling provided higher remnant polarisation and coercive electric field than using 125^∘C temperature at poling. Difference was especially significant in coercive electric field values where up to 114.8% difference was obtained for PZT 5H bulk actuator and 65.9% for pre-stressed actuators. Higher coercive fields can be utilized as increased operating voltage range of piezoelectric devices. The differences in results obtained here and by others can be explained by the different pre-stress level, stronger clamping of the thicker passive layers of the RAINBOW and THUNDER actuators and passive ring area introducing high tensile stresses. The same conditions were used to pole the actuators, after which the displacement and dielectric constant of the actuators were measured. The displacement measurements showed that remnant polarisation has good correlation with displacement. This fact can be used in estimating pre-stressed actuator performance before actual poling. The dielectric constant measurements with a small signal after poling gave even better correlation than the remnant polarisation.     

Development of ferroelectric Pb(ZrxTi1−x)O3 thin films by metallo-organic decomposition process and rapid thermal annealing

Polycrystalline Pb(Zr_0.5Ti_0.5)O₃ thin films with good ferroelectric properties have been prepared by metallo-organic decomposition (MOD) process, using acetate-based precursors, and followed by two different kinds of annealing process, independently, including oven annealing and rapid thermal annealing (RTA). The experimental procedures were described for the films deposited on Pt-coated silicon substrates. There were distinct differences between oven annealing and RTA process, in terms of structures, morphologies, and electrical properties of the films. The films with RTA process showed denser and smoother surface, finer grain sizes, and much higher dielectric constant (1200–1400), remnant polarization of 30–35 μC/cm² and lower coercive field of 65–85 kv/cm in the entire annealing temperature range of this study. At an annealing temperature of 550°C, RTA processed films showed identical XRD patterns of perovskite phase and clear ferroelectricity; however, it was not possible to realize the perovskite structure and ferroelectricity in the films oven-annealed at that temperature. These acetate-derived PZT films with RTA process were reproducible, showed high quality in uniformity and homogeneity.