La doped PZT 60/40 films by MOD technology

Abstract

Ferroelectric La doped PZT 60/40 thin films with uniform composition have been synthesized using metallo-organic precursor solutions. These metallo-organic precursors have been stored for more than four years and are very stable in ambient conditions, compared to the sol-gel solutions. The structural properties of these films have been studied using X-ray diffraction and atomic force microscopy. The excellent ferroelectric properties of the films, such as less than 10% polarization loss after 10¹¹ cycles, low leakage current of 3·06×10^?12 A at 2 V, and small separation of polarization peaks in a voltage loop by the small-signal measurement, are attributed to the high quality of the metalloorganic solutions used in this study, which have been carefully home-synthesized. The oxygen vacancy in the films was reduced by optimizing the annealing conditions, and to minimize the blocking oxygen vacancy at the interface by Pt electrodes a suitable amount of La ions was doped. We suggest that greater attention should be paid to the elimination/minimization of the oxygen vacancy in the ferroelectric PZT films instead of using oxide electrodes, which allow a relatively larger leakage current flowing through the films and the electrodes.     

The dependence of ferroelectric and fatigue behaviors of PZT films on microstructure and orientation

Microstructure of PbZr_0.53Ti_0.47O₃ films about 0.2 μm thick was studied as a function of annealing temperature and time using TEM and SEM. The films were heat treated in the temperature range 550–650°C for times from 10 minutes to 4 hours. The features characterized were crystal structure of individual PZT particles, PZT grain size and shape, porosity, and grain boundaries. The films were prepared by the metallo-organic decomposition (MOD) process which produced films amorphous to x-rays after pyrolysis. A growth mechanism of PZT particles from the amorphous film is discussed. It was found that at mild annealing conditions (i.e., low temperature and short annealing times), agglomerates of microcrystallites of perovskite, and probably pyrochlore, were formed. As the temperature was increased, the microcrystallites grew into porous submicron perovskite single crystals. With excessive heating, intraparticle pores were found to migrate and became pinned at the grain boundaries, causing widening of boundaries which probably was responsible for the degradation in ferroelectric properties observed in such films. The dependence of ferroelectric and fatigue behaviors on grain orientation was also investigated. It was found that PZT films oriented in the [111] direction demonstrated better fatigue behavior but not necessarily higher polarizations.     

Difference in microstructure between PZT thin films on Pt/Ti and those on Pt

Abstract

PZT thin films were synthesized by sol-gel on a Pt/Ti double layer bottom electrode or on a Pt single layer bottom electrode to investigate the bottom electrode dependence of PZT film structure. On Pt/Ti, <111> oriented perovskite grains with 50–100 nm lateral size were densely packed. On Pt, large perovskite grains (2?3 μm) were surrounded by fine pyrochlore grains (about 5 nm), and no certain orientation was observed. TEM and EDX analyses suggested that a fraction of Ti in the Pt/Ti layer diffused along Pt grain boundaries up to the Pt surface and was oxidized during the PZT annealing process. A model for the crystallization of sol-gel derived PZT was proposed, in which TiOx particles at the Pt surface act as nucleation sites for PZT crystallization. This model well explained the experimental results.     

Mechanical and electric fatigue of PZT(53/47) films on metallic substrates

Abstract

We have investigated the fatigue of electromechanical and dielectric properties of sol-gel derived PZT(53/47) thin films deposited on metallic substrates by means of electric and mechanical cycling. For the mechanical cycling a two point bending method was used to apply transversal stress to the samples. During mechanical cycling the piezoelectric coefficient d₃₁ remained constant up to about 10⁵ cycles, for a higher number of cycles a strong decrease was observed. During electric cycling no significant changes in the ferroelectric and electromechanical hysteresis loops could be found up to about 3×10⁵ cycles. Above this number the coercive field increases, the maximum strain and the remanent polarization decrease.

Obviously each electric cycling of the investigated films is accompanied by a mechanical cycling. It is assumed, that microcracks induced by mechanical stress are the main reason for the deterioration of the physical properties films during electric and mechanical cycling both.     

Effect of Gd doping on crystalline orientation,structural and electric properties of PZT thin films prepared by Sol-Gel methods

Gadolinium (Gd)-doped lead zirconium titanate (PGZT) thin films have been prepared by Sol-Gel methods to investigate the effects of Gd doping on crystalline orientation, structural and electric properties of lead zirconium titanate (PZT) films according to doping concentration from 0% to 5%. Conventional heat process and appropriate doping concentration, without introducing a single crystal seed layer, were used for obtaining (100)-oriented PGZT thin films with dense columnar structures. The maximum dielectric constant (1310.35 at 100 Hz) and the optimum ferroelectric properties were obtained for 2% Gd-doped film. 1% Gd-doped PZT film exhibited excellent piezoelectric properties.     

Structural and Dielectric Properties of Sol-Gel Derived PLZT (x/60/40)

Polycrystalline samples of (Pb_1-zLa_z)(Zr_0.60Ti_0.40)_1-z/4O₃ (where z = 0.00, 0.05, 0.09, 0.12, 0.14 mol %) (abbreviated as PLZT) were synthesized through acetate-alkoxide sol-gel route. The formation and existence of different crystallographic phases as a function of z was checked through X-ray, TEM, SEM and dielectric studies. The diffuse phase transition (DPT) was observed in PLZT with higher concentration of La (i.e., for z = 0.00 to 0.12), but for z = 0.14, the compound did not show any phase transition.     

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.     

Effect of ion damage on the crystallization of PZT thin films

Abstract

Effects of Ar ion damage prior to the phase transformation from pyrochlore to perovskite structure of PZT thin films have been investigated. As the degree of damage increased by increasing the acceleration voltage in the ion mass doping system, the phase transformation temperature decreased such that the temperature could be lowered down to 550°C when the film was damaged at 15kV for 5 minutes. When the films were damaged prior to the heat treatment, the final grain size of the perovskite thin films became less than 300Å. The microstructure showed the granular type rather than columnar structure after ion damage treatment and annealing. It turned out that relatively high value of the remanent polarization (about 30 μC/cm²) as well as improvement of the fatigue characteristics to a large extent are closely related to the fine grain size of thus obtained PZT films.     

Effect of Nb doping on structural and electric properties of PZT (65/35) ceramic

The aim of this study is to determine the effect of Nb⁵⁺ doping on PZT (65/35) based bulk materials in their structure, micro structure and electrical properties. The Nb content was chosen 0-9 mole%. These materials were prepared by conventional mixed oxide method. X ray diffraction studies suggest the compound to be of rhombohedral perovskite phase. Excess addition of Nb result in pyrochlore and fluorite phase develops in PZT (65/35) sample. Detailed studies of dielectric constant as a function of temperature (40degC to 500degC) and frequency (100 Hz to 1 MHz) suggest that the compounds undergo diffuse type of phase transition. Maximum dielectric constant and resistivity were found to be strongly dependent on doping and measuring frequencies. Using complex impedance analysis micro structural parameters such as bulk and grain boundary resistance, bulk charge carrier concentration and relaxation time were determined     

An aqueous,low temperature process for synthesizing PZT(53,47) thin films

Abstract

The Deposition by Aqueous Acetate Solution (DAAS) technique has been developed for the preparation of thin films of Pb(Zr_0.53Ti_0.47)O₃[PZT(53,47)] perovskites. This process, which employs titanium acetate, tends to establish a chemically bound network in the pre-annealed phase and facilitates the crystallization of ferroelectric lead perovskites at a relatively low temperature. The addition of surface wetting reagents and oxidants and the action of ultrasonic waves were shown to affect the crystallinity and film quality of PZT(53, 47) perovskites on Pt<111>/Ti/SiO₂/Si<100> substrates. The band structure analysis of the FTIR spectrum is illustrated to be a simple way of monitoring the crystallization of PZT(53, 47) perovskites. Physical and electrical characterization of the resultant thin films were performed. The advantages of the DAAS process for fabricating thin ferroelectric films are examined.     

Preparation and characterization of PZT thin films deposited on PZT buffer layer with different lead content

Lead zirconate titanate (PZT) thin films deposited on Pt electrode and Pb_1+x(Zr_0.52,Ti_0.48)O₃ (x = 0.10, 0.15, 0.25, 0.30) buffer layer have been prepared by sol-gel methods to investigate the effects of lead content in the buffer layer on crystalline orientation, electric and fatigue properties of PZT films. XRD and SEM showed that all films exhibited dense perovskite structure with (100) preferential orientation. The maximum dielectric constant (1571 at 100 Hz) was obtained in the PZT film with buffer layer containing 25% excess lead, which increased by 42.5% compared with the film without buffer layer. Fatigue resistance was improved by introducing buffer layer.     

Preparation and Characterization of PZT films Fabricated on Si Substrate

Lead zirconium titanate (PZT) films (Zr/Ti=45:55) with a high dielectric constant are prepared successfully on the low-resistance Si substrate in sol–gel dip-coating process with PT film used as the buffer layer. The dielectric and ferroelectric properties of the films as well as the relationship between crystallization and preparing condition are studied. It is shown that the PZT ferroelectric thin films with a (110) preferred orientation and a well-crystallized perovskite structure could be obtained after annealing at 800°C for 15 min. The particle size of the sample is about 14–25 nm. The P–E hysteresis loops are measured by means of the Sawyer-Tower test system with a compensation resistor at room temperature. The remanent polarization (P _r) and coercive electric field (E _c) of the measured PZT thin films are 47.7 μC/cm² and 18 kV/cm, respectively. The relative dielectric constant ε _r and the dissipation factor tgδ of the PZT thin films were measured with an LCR meter and were found to be 158 and 0.04–0.005, respectively. Translated from “Preparation and Characterization of PZT Films Fabricated on Si Substrates” published in Chinese Journal of Semiconductors, 2004, 25(4): 404–409 (in Chinese)     

Raman,X-ray and electrical properties of MOD PZT/PLZT thin films

Abstract

Ferroelectric PZT/PLZT thin films have been fabricated using the metallo-organic precursor compounds. The structural development, spectroscopic and dielectric properties of these films have been investigated using atomic force microscopy (AFM), X-ray diffraction, Raman scattering and dielectric measurements. Experimental results show that Raman spectroscopy is an effective tool of monitoring the structural development of the small sized PZT films in the tetragonal phase field. Dielectric characteristics have been improved by the rapid thermal processing approach. A rosette growth model is proposed to explain the observation of the tri-intersection of the perovskite phase in PZT films.     

Preparation of thick PZT films on stainless steel substrates

Abstract

Lead zirconate titanate (PZT, PbZr_0.52Ti_0.48O₃) films of thickness 22 μm have been deposited on stainless steel substrates by spin-coating a PZT solution containing PZT powder. The solution had a concentration of 1.2 M and was dispersed with PZT powder in a 1:1 powder/solution molar ratio. The films were rapidly heated to 400°C and annealed for 15 min, and then they were further annealed in an oven at 650°C for 30 min. The results of X-ray diffraction studies show that the films have a pure perovskite phase. The inter-diffusion of ions at the PZT/stainless steel interface was prevented by using a ZrO₂ barrier layer. The films were found to have good ferroelectric and piezoelectric properties.     

Fabrication and characteristics of PZT thick films on Pt/Ti foil substrates for piezoelectric vibrators

Crack free perovskite PbZr_0.53Ti_0.47O₃ (PZT (53/47)) thick films up to 30 μm were prepared on flexible platinum-coated titanium foil substrates (Pt/Ti) by a metal organic decomposition (MOD) process. The dielectric, ferroelectric and piezoelectric properties of the films were examined and discussed. A well-saturated hysteresis loop of the thick film was present in almost rectangular shape (Pr?=?35 μC/cm²; Ec?=?32 kV/cm). The efficient piezoelectric coefficient d _{33, f} of the thick film is about 448 (1 kHz). PZT piezoelectric vibrators were made in bimorph mode. The displacements of the vibrators were investigated as the functions of the applied electric field and the substrate thickness. Under the same condition, the vibrator made from the thinnest Pt/Ti substrate gives the largest displacement.     

Terfenol-D/PZT/Terfenol-D层状复合磁电传感器磁电效应

采用树脂粘结法制作了L-T型(磁致伸缩层的磁化方向与压电层的极化方向相互垂直)Terfenol-D/PZT/Terfenol-D层状复合磁电传感器。采用等效电路法对磁电系数进行了详细推导,得到磁电系数方程。磁电系数方程显示磁电系数决定于Terfenol-D与PZT的性能参数和磁电传感器中两种材料的体积比。为此从理论和实验上分析了偏置磁场、传感器中两种材料所占的体积比以及驱动磁场频率对磁电系数的影响规律。结果表明偏置磁场、传感器中两种材料所占的体积比和驱动磁场频率对磁电传感器磁电系数的影响都很明显,并且磁电系数的计算结果与实验结果一致,对于所制作的复合磁电传感器,相同条件下磁电系数的计算值与实验值的相对差值小于6%。     

Simulation and Characterization of Piezoelectric Micromachined Ultrasonic Transducers (PMUT's) Based on PZT/SOI Membranes

Piezoelectric micromachined ultrasonic transducers for airborne and immersed applications working in the frequency range from 20 kHz in liquid to 750 kHz in air have been fabricated and characterized, as well as simulated by finite element modelling. The basic element consisted of a oxidized and platinized silicon membrane coated with a 2 μm thick (100)-textured Pb(Zr,Ti)O₃ (PZT) thin film deposited by sol-gel techniques. SOI wafers have been applied to obtain a good definition of the silicon part of the membrane. The unclamping of the silicon membrane at the border increases drastically the coupling factor. For unclamped structures the membranes completely covered with top electrode show the highest coupling coefficient (k² = 5.6%). Immersed (in Fluorinert?) membranes show 7 times smaller quality factor, while the coupling factor k² remains the same. The obtained structures were enough sensitive to detect acoustic waves in air and in liquid emitted from the same type of elements at a distance of 20 and 2 cm, respectively. Good agreement between the experimental results (membrane deflection, admittance in air and in liquid) and FEA simulations has been obtained.     

Growth Stages of Sol-Gel Derived PZT(30/70) on Pt/Ti/SiO 2 as Shown by SPM (PFM and Topography)

The integration of PZT into devices based on silicon is of great interest for the further miniaturisation of sensors and actuators and their integration into MEMS devices. PZT is the material of choice for these applications due to it's good piezoelectric properties. When PZT is produced by sol-gel the material undergoes a series of transformations. After the initial drying stage the sol transforms into the non-ferroelectric pyrochlore phase. Upon further heat treatment the ferroelectric perovskite phase is formed. A single layer (ca. 70nm thick) film of PZT has been deposited onto highly [111] orientated Pt. The degree of transformation from the pyrochlore phase to the perovskite phase has been recorded using XRD and a variety of scanning probe techniques, including Piezoresponse force microscopic (PFM) and contact mode topographic analysis. A map of the surface topography and the PFM image show variations in both topography and distribution of piezoelectric regions as the perovskite/pyrochlore ratio changes. The method by which the changes occur can be explained by the nucleation of perovskite phase from the pyrochlore phase. The range of temperatures examined were 400 to 530, the sample being left at each temperature for 5 minutes. It was found that fully transformed perovskite PZT was produced at 530C. The XRD pattern for the sample shows that it is [111] orientated.     

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.     

Pyroelectric properties of sol-gel derived PZT thin films with various Zr/Ti ratios

Abstract

Integrated pyroelectric arrays are receiving serious attention for the next generation of room temperature uncooled IR cameras. Such pyroelectric arrays are based on monolithic ferroelectric(FE) thin films. FE films with large values of reported pyroelectric coefficients include PbTiO₃, Ca-doped PbTiO₃, La-doped PbTiO₃, PZT 53/47 and Pb(Sc_0.5Ta_0.5)O₃. The present paper reports a systematic study of the compositional dependence of PZT thin films on their pyroelectric properties. A series of sol-gel derived PZT (lead zirconate titanate) thin films with various Zr/Ti ratios, namely, PbTiO₃, PZT 20/80, PZT 35/65, PZT 53/47, PZT 65/35, PZT 92/8 and PbZrO₃, were prepared on platinized Si substrates. The films were fired to 650 – 700°C to crystallize them into single-phase perovskite. The degree of preferred orientation, grain size and firing temperature affect the pyroelectric responses. Pyroelectric coefficients as large as 2.5 × 10^?8 C/cm²-K were obtained, making such PZT thin films attractive in pyroelectric arrays.