Influence of the Lead Source Materials on the Microstructure and Ferroelectric Properties of PZT Films Sputter-Deposited Using Lead and Lead Oxide

In this investigation, PZT films were sputter-deposited on Si/SiO₂/Ti/Pt substrates using a dual-target system. The dual targets Pb/PZT(PbZr_0.54Ti_0.46O₃) and PbO/PZT(PbZr_0.54Ti_0.46O₃) were used to reveal the effects of various lead compensation source materials on the microstructure and ferroelectric properties of the films. The structures of the films were characterized by X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM). The chemical binding state was determined using X-ray photoelectron spectrometry (XPS). Ferroelectric polarizability was measured using a Radiant Technology RT66A tester. The influence of deposition temperatures on the microstructure and ferroelectric properties of the films was studied. Perovskite PZT films were successfully deposited using the Pb/PZT and the PbO/PZT dual target sputtering systems at a substrate temperature of between 500 and 580C. Structural change was elucidated as a function of deposition temperatures and the lead sources were correlated with the ferroelectric properties of the film. The ferroelectric characteristics of the PZT films deposited using the PbO/PZT dual target were better than those of films deposited using the Pb/PZT dual target, because the former films had a higher bonding energy.     

Pyroelectric Properties of PZT/PMNZTU Composite Thick Films

Lead zirconate titanate/uranium doped lead magnesium niobate—lead zirconate titanate (PZT/PMNZTU) composite thick films have been fabricated on silicon substrates at 710°C using a composite sol gel technique. A slurry, made up of PMNZTU powder and PZT sol, was spun onto a silicon substrate and fired to yield a porous skeletal ceramic structure. Subsequent sol infiltration and pyrolysis was used to modify the density of the films prior to final sintering at 710°C.Pyroelectric and dielectric properties have been measured as a function of sol infiltration. The pyroelectric coefficients (p _max = 2.41 × 10^–4 Cm^–2 K^–1) of the composite thick films were found to be comparable to the tape cast and monolithic ceramics of similar composition (2.8 and 3.0 × 10^–4 Cm^–2 K^–1 respectively).Maximum figures of merit (F _V = 2.23 × 10^–2 m² C^–1, F _D = 0.89 × 10^–5 Pa^–1/2), calculated using the electrical properties of the thick films, can be compared with those of screen printed thick films (F _V = 2.7–3.9 × 10^–2 m² C^–1, F _D = 0.8–1.1 × 10^–5 Pa^–1/2) processed at temperatures of ca 1100°C. The ability to directly integrate thick pyroelectric films onto substrates at temperatures as low as 710°C, while maintaining competitive figures-of-merit is of considerable interest for future device applications.     

Dielectric and Pyroelectric Properties of Lead Zirconate Titanate Composite Films

A new sol-gel approach has been established to prepare dense and crack-free lead zirconate titanate (PZT)/PZT composite films. This new process combines the modified sol-gel method for preparing ceramic/ceramic composite films and the infiltration technique. In the modified sol-gel method, sintered PZT powder is dispersed in a PZT precursor solution to form a slurry which is then spin-coated on a substrate. However, the resulting composite film usually contains a considerable amount of pores, and thus resulting in serious degradation of the mechanical, ferroelectric and piezoelectric properties of the films. In the present work, an additional step, infiltration, has been included in the method. A diluted PZT precursor solution is deposited on the composite film to infiltrate and fill-up the pores, and hence a dense composite film is obtained. The dielectric, ferroelectric and pyroelectric properties of the resulting PZT/PZT composite film are comparable to those of a sol-gel derived PZT film; showing the values of 1200, 0.04, 21 μC/cm² and 180 μC/m² K for relative permittivity, dielectric loss, remanent polarization and pyroelectric coefficient, respectively.     

Effects of Sintering Temperature on the Dielectric and Piezoelectric Properties of Nb-Doped PZT Ceramics and Their Applications

The PZT-based ceramics with a composition of Pb_{1 ? 0.5x} (Zr_0.52Ti_0.48)_{1 ? x} Nb _x O₃; x = 0.04–0.06 were prepared by conventional mixed-oxide method, with sintering temperature at 1200°–1300° for 2 hours. Microstructural and compositional analyses of the PZT-based ceramics have been carried out using XRD and SEM. The dielectric constant measured at 1 kHz is about 1500 and the loss factor is small than 2%. The maximum planar electromechanical coupling coefficient, k _p , is 0.59. It showed that the Nb additives were helpful improve both of the dielectric and piezoelectric properties. Surface acoustic wave (SAW) filters were fabricated and the property, phase velocity, were measured.     

稀土掺杂对BaTiO3陶瓷结构和性能的影响

综合了国内外稀土改性BaTiO3陶瓷的相关研究报导,着重阐述了稀土掺杂对BaTiO3陶瓷电阻率和介电性能的影响规律,并分析了其作用机理。稀土元素作为BaTiO3陶瓷常见的添加剂,可以降低陶瓷电阻率,开发BaTiO3陶瓷半导体领域的应用;可以提高介电常数和改善电容量温度特性,使Ba-TiO3陶瓷满足X7R或X8R特性,可以应用于高压高介电陶瓷电容器中。     

Effect of Buffer Layer on the Properties of Laser Ablated PZT Thin Films

Lead zirconate titanate (PbZr _x Ti_1?x O₃) or PZT ceramics are a class of piezoelectric materials that are currently experiencing widespread use in industry as electromechanical devices. PtSi/ZnO/PZT thin films were deposited by pulsed laser deposition at relatively low substrate temperature. The PZT thin films on PtSi substrates and on ZnO buffer layer were deposited at substrate temperature 300°C. The composition analysis shows that the film deposited at low temperature is stoichiometric. The films exhibit ferroelectric nature with coercive field of 19.6 kV/cm for 800 nm thick film. The leakage current density of the films shows a good insulating behavior.     

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.     

The Effect of Sintering Processes on the Properties of Mn-F Doped PZT Ceramics

Fluoridated PZT ceramics were produced by solid-state and liquid-phase sintering methods, according to the formula Pb(Zr_0.52Ti_0.48)_1-xMn_xO_3-yF_y, where 0 < x < 0.015 and 0 < y < 0.1. The effects of sintering processes on the phase development and microstructure of Mn-F doped PZT ceramics have been investigated using XRD and FEGSEM. In solid-state sintering, the fluoride additive enhanced the densification of PZT ceramics, enabling densification to >95% relative density at a temperature as low as 1000°C. However, fluoride loss at high temperatures was found to be a significant problem. Alternatively, ceramics with a density >92% were prepared by sintering at a temperature of 850°C by incorporating a eutectic mixture of PbO and V₂O₅ as sintering aid. Problems associated with volatilization of fluoride compounds during sintering could be alleviated using this approach. EPMA was employed to analyze the distribution of the additives in the calcined powders and sintered ceramics. The nonlinear dielectric properties were determined by measuring P-E loops, using an AC electric field in the range 0.1 to 2.0 kV mm^?1.     

Phase Formation,Dielectric, Ferroelectric and Magnetic Properties of Cr2O3 Doped (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

Abstract

In this paper, we studied the effect of Cr₂O₃ doping (0–0.8?wt%) on the phase formation, dielectric, ferroelectric and magnetic properties of (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ (BCTZ) ceramics prepared by the solid state combustion method. All samples were prepared with a calcined and sintered temperature of 1050?°C and 1450?°C, respectively, for 2?h. The results of the XRD patterns showed the coexistence between the tetragonal (T) and orthorhombic (O) phases for all samples, and the tetragonal phase increased with increasing amounts of Cr₂O₃. The dielectric constant decreased when Cr₂O₃ increased. The P-E hysteresis loops of the BCTZ ceramics doped with Cr₂O₃ between 0 and 0.2?wt% showed slim and saturated loops. By increasing Cr₂O₃ doping from 0.4 to 0.8?wt%, the P-E loops were unsaturated and a leakage current was produced. The undoped BCTZ ceramics exhibited diamagnetic behavior. The sample with 0.2?wt% Cr₂O₃ showed ferromagnetic behavior. Increasing Cr₂O₃ doping from 0.4 to 0.8?wt%, caused the ceramics to exhibit paramagnetic behavior. Doping with Cr₂O₃ led to improper ratios between the tetragonal and orthorhombic phases, decreased density and increased porosity which caused a decrease in the electric properties.     

Piezoelectric and Pyroelectric Properties of Pb(Zr,Ti)O3 Films for Micro-Sensors and Actuators

The piezoelectric and the pyroelectric properties of PZT films are systematically investigated for tetragonal (Zr/Ti = 30/70), morphotropic (52/48), and rhombohedral (70/30) compositions. The magnitude of the effective longitudinal piezoelectric coefficient (d₃₃) and pyroelectric coefficient (p) of these films is measured by atomic force microscopy and Byer-Roundy method, respectively. All films are consistently highly textured (111) orientation and have dense microstructures. Slightly less degree of texture in higher Zr-rich composition is observed due to the lattice mismatch between PZT and Pt bottom electrode and higher activation energy for nucleation. Squareness of polarization hysteresis loops is optimized in tetragonal composition, which indicates the tetragonal PZT is closer to the ideal hysteresis behavior than other compositions. It is shown that the piezoelectric coefficient and the pyroelectric figure of merit are dependent on the dielectric properties of the films. The morphotropic PZT films with high dielectric constant and low pyroelectric figure of merit show the largest piezoelectric coefficient values, while the tetragonal PZT films with low dielectric constant and high remanent polarization values show the largest pyroelectric figure of merit compared to other compositions, which indicate the suitability for PIR sensor devices.     

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.     

Characterization of Ferroelectric Properties of PZT Grains Utilizing KFM Measurements

Ferroelectric properties of PbZr_0.4Ti_0.6O₃ (PZT) grains were examined by monitoring the surface potential. Hysteretic and time dependent behaviors of small grain were compared with those of large grain. The smaller grain yields smaller value of the surface potential. However, the normalize voltage versus surface potential behavior indicates the earlier saturation with respect to writing voltages. On the other hand, the surface potential hysteresis loop obtained from the smaller grain shows a similar shape that might be obtained from Zr rich PZT film, whereas hysteresis loop of the larger grain looks like that obtained from Ti-rich film. In addition, the time dependent behaviors of the smaller grains also reveal the better response than those of the larger grains. The overall ferroelectric property of smaller grain seems to be better than that of larger grain. At present, it is not sure about the whether the difference is due to the difference in the stoichiometry or not. In this study, the Ti/Zr ratio of PZT film was 60/40.     

Non-Linear Imprint Behavior of PZT Thin Films

Ferroelectric thin film capacitors are promising candidates for non-volatile ferroelectric Random Access Memories (FeRAM's) as they exhibit a switchable polarization. There are three important failure-mechanisms influencing the performance of these capacitors and disturbing the long-term stability and reliability under operation conditions fatigue, retention, and imprint. The imprint effect of lead zirconate titanate (PZT) thin films was investigated in this paper. Establishing and maintaining a polarization state leads to a shift of the hysteresis loop on the voltage axis and also to a loss of polarization. The voltage shift as well as the loss of polarization can cause a failure of the ferroelectric memory cell (read and write failure). The experimental results obtained on PZT films are discussed in view of the predictions of imprint models proposed in the literature.     

Peculiarities of Variation of the Dielectric Permittivity and the Pyroelectric Coefficient with Temperature in PZT-Based Ferrosoft Ceramics Modified with Different Additives of PbGeO3

ABSTRACT

The temperature dependencies of the dielectric permittivity ?(T) the dynamic pyroelectric coefficient γ_d(T) and the quasi-static pyroelectric coefficient γ_st(T) of prepoled samples of the low-coercive materials belonging to the PZT-based multicomponent system modified with 0.5%; 1% and 2% PbGeO₃ and having the Curie temperaturesT _c = 207, 215 and 206°C, respectively, were studied. Polarization of the samples was performed under three different conditions. It was been established that in the ?(T) curve one can observe a step-like variation of ?(T) or a slope variation at temperatures below the temperature maximum by 40–50°C. The additional low- and high-temperature maxima are observed in the γ_d(T) and γ_st(T) curves.     

Processing Effects on the Microstructure and Dielectric Properties of Barium Strontium Titanate (BST) Ceramics

Barium Strontium Titanate (BST) ferroelectric thick films have been investigated as potential candidates for use in frequency agile microwave circuit devices. Powder processing techniques such as screen-printing have been used to make BST thick films. However, due to the interactions between the BST and substrates such as alumina, the sintering temperatures for the BST thick films are limited and the resultant films are difficult to achieve full densification. In this paper, the effects of different powder processing conditions (calcination, sintering temperature and time) on the sintering behaviour and dielectric properties of the BST ceramics have been investigated. The dielectric behaviour of the ceramics has been correlated with composition and microstructural features such as chemical homogeneity, grain size and domain wall movements.     

Pyroelectric properties and X-ray photoelectron spectroscopic study of R.F. magnetron-sputtering-derived PZT thin films deposited on various interlayers

PZT thin films and interlayers were fabricated by the radio frequency (r.f.) Magnetron-sputtering from the Pb_1.1Zr_0.53Ti_0.47O₃, PbO and TiO₂ target. As a result of the XPS depth profile analysis, we can confirm that the substrate temperature affects the oxidation condition of each element of interlayers and the PZT film. Compared to the PZT/Pt structure, the dielectric and pyroelectric properties of PZT thin films inserted by interlayers were measured to a relatively high value. In particular, the PZT/PbO structure had the highest pyroelectric properties (P = 189.4 μC/cm²K; F _D = 12.7×10⁻⁶ Pa^−1/2; F _V = 0.018 m²/C).     

Effect of Solution Processing on PZT Thin Films Prepared by a Hybrid MOD Solution Deposition Route

Lead zirconate titanate, Pb(Zr_0.53Ti_0.47)O₃ (PZT), thin films were prepared by a hybrid metalorganic decomposition (MOD) solution deposition route; the effects of processing conditions on the film structure and properties were investigated. Solutions were synthesized by mixing and reacting Zr acetylacetonate and Pb acetate trihydrate with a solution prepared from Ti isopropoxide, acetic acid and water. Chemical changes in the solution during preparation and solution storage (i.e., aging) were investigated by visual observation and FTIR, and were evidenced by changes in phase content and properties of the final PZT films. Results suggest that Zr acetylacetonate and Pb acetate trihydrate react with a Ti oxoacetate-based precursor, and that this reaction continues during aging at room temperature. The PZT film quality and properties improved with aging time of the solution before deposition. To achieve good properties and design a convenient processing route, an accelerated aging scheme, including a brief aging at 60°C and freezing to prevent further reaction, was developed. PZT films prepared from these solutions had average dielectric constants of 1040, loss tangents of 0.05, remnant polarizations of 26 C/cm², and coercive fields of 39 kV/cm.     

Influence of Stress on the Performance of PZT Thin Films for Microphone Application

ABSTRACT

A series of microphone cells based on integrated PZT thin films were fabricated by typical MEMS process. The thickness of back silicon as a load of the vibrating diaphragm was controlled by changing ICP (Inductive Coupling Plasma) etching time and power. Concaved diaphragms with different radius were formed due to the balanced tensile stress among the multi-layer films structure. The remnent and saturated polarization strength of microphone cells decreased with the increased deformation of diaphragm. The phenomenon was explained as the weakening of mechanical-electrical coupling in piezoelectric thin films in stressed state.     

Grain-Boundary Effect on the Curie-Weiss Law of Ferroelectric Ceramics and Polycrystalline Thin Films: Calculation by the Method of Effective Medium

The influence of grain boundaries on the dielectric properties of ferroelectric ceramics and polycrystalline thin films is described theoretically by the method of effective medium. Grain boundaries are modeled by low-permittivity (dead) layers, which do not exhibit ferroelectric instability. The effective permittivity of a polycrystalline material is calculated in the paraelectric regime above the transition temperature. The calculations are based on the solution of electrostatic problem for a spherical dielectric inclusion separated from the surrounding dissimilar matrix by a low-permittivity interface layer. For isotropic bulk ceramics, an analytic expression is derived for the effective permittivity as a function of the grain size, dead-layer thickness, and its permittivity. Temperature dependence of the aggregate dielectric response is calculated for BaTiO₃ (BT) ceramics of different grain sizes and found to be in good agreement with measurements. It is shown that grain boundaries not only renormalize the Curie-Weiss temperature and constant, but may also cause deviations from the Curie-Weiss law. For BT polycrystalline thin films grown on dissimilar substrates, numerical calculations of the effective dielectric constants are performed, taking into account both the grain-boundary and substrate effects on the film anisotropic dielectric response. Theoretical predictions are compared with the grain size dependence of the permittivity of BT films grown on Pt-coated Si.     

The dependence of ferroelectric and fatigue behaviors of PZT films on annealing conditions

Films of PZT about 0.2 μm thick with the composition PbZr_0.53Ti_0.47O₃ were prepared using the metalloorganic decomposition (MOD) process. The amorphous films produced by pyrolysis at 350°C were annealed at 550, 575, 600 and 650°C for 10 minutes, 1 hour or 4 hours. Films annealed at temperatures below 550°C showed no ferroelectric behavior while others annealed above 650°C showed signs of loss of ferroelectric behavior. Most films demonstrated satisfactory ferroelectric properties such as low switching voltage and high polarization values. Some PZT films also demonstrated fatigue life-time of more than 10⁹ switching reversals. The performance of the films was dependent on the annealing time and temperature. It was found that films with better initial polarization values did not necessarily demonstrate better fatigue behavior. The causes of film degradation as a result of switching based on the pinning of domains at grain boundaries triggered by the migration of pores is discussed.