Structure and properties of sol-gel processed (Pb,La)TiO3 ferroelectric thin films

Abstract

The influence of heat treatment and substrate materials on PLT thin films by sol-gel processing has been researched. Epitaxial growth PLT thin films with perovskite-type structure on sapphire, SrTiO₃ and MgO single crystal substrates have been prepared. The epitaxial relations are (100)PLT28/(100)SrTiO₃, (111)PLT28//(0001)sapphire and (100)PLT14//(100)MgO. The PLT polycrystal thin films with perovskite-type structure on Si single crystal and quartz glass substrates have been prepared. The remanent polarization Pr and the coercive field Ec of PLT15 ceramic thin films are 7.7 μc/cm² and 34 kv/cm at 4 KHz respectively. The optical transmittance of PLT28 ceramic thin films within the wavelength range of λ = 500–1000 nm is approximately 80%.     

Ferroelectric ceramics and thin films for pyroelectric applications

Abstract

The extensive work carried out at Caswell in recent years on ferroelectric ceramics for pyroelectric applications is reviewed briefly. With the ultimate aim of fully CMOS compatible integrated thermal detectors and imagers, pure and lanthanum doped lead titanate thin films have been deposited using the emerging PVD technique of dual ion beam sputtering (DIBS). The DIBS process produces high quality orientated perovskite films. Films have been formed at 500–600°C onto sapphire, MgO and silicon substrates by sputtering from an adjustable composite PLZT ceramic/Ti and Pb metallic target. Some substrates were coated with platinum/titanium prior to deposition to allow longitudinal electrical measurements to be made on the films. On silicon, the platinum/titanium electrodes were found to blister during the PLZT thin film deposition process. Pure and 7% lanthanum doped lead titanate films have shown pyroelectric effects with coefficients in the range 0.5–4.0 × 10^?4 Cm^?2 K^?1 and a figure of merit of 2.6 × 10^?5 Pa^?0.5 These results are encouraging with respect to the goal of integrated pyroelectric IR detector arrays on silicon. Further improvements should be possible since the process and substrate/electrode preparation have not yet been fully optimised.     

Fundamental characteristics of DRAM capacitor application of PLZT ultrathin films prepared by MOCVD

Lanthanum-modified lead zirconate titanate (PLZT) thin films (50 nm to 200 nm) were deposited on Pt/SiO₂/Si substrate by metal-organic chemical vapor deposition (MOCVD). The electrical properties of the films were investigated as a function of the La content or the substrate temperature. Ferroelectric PZT(0/50/50) films were obtained at substrate temperatures as low as 500 °C; their electrical characteristics improved with increasing substrate temperature. La exhibited adequate solid solution in the PZT above 650 °C. PLZT(15/45/55) films with a thickness of 100 nm were found to have good properties for application to the capacitors of dynamic random access memory (DRAM), namely, an effective charge density of 80 fF/μm², a permittivity of 1000, an SiO₂ equivalent thickness of 0.4 nm, and a leakage current density of 5 × 10⁻⁸ A/cm. Addition of La to PZT was effective in reducing the leakage current with an increase in the registration rate. RuO₂ and/or IrO₂ bottom electrodes for ferroelectric PLZT films were also investigated. The RuO₂ films were found effective as diffusion barriers for PLZT and MgO. Significant interdiffusion at RuO₂/Si and RuO₂/SiO₂ interfaces occurred during the deposition of PLZT films. Annealing of the RuO₂ film considerably depressed interface reactions. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 25–36, 1998     

Chemical solution processing and properties of tungsten bronze (ba,la)nb2o6 thin films

Abstract

Highly oriented (Ba,La)Nb₂O₆ thin films have been synthesized by a chemical solution deposition method. A homogeneous and stable (Ba_0.75La_0.167)Nb₂O₆ (BLN) precursor solution was prepared by controlling the reaction of metal alkoxides. BLN precursor films crystallized in the tetragonal tungsten bronze phase at 700°C. BLN thin films on MgO(100) and Pt(100)/MgO(100) substrates showed the prominent c-axis preferred orientation. BLN thin films on Pt(100)/MgO(100) exhibited the diffuse phase transition depending upon the frequency.     

Filament-assisted pulsed laser deposition of epitaxial PbZrxTi1−xO3 films: Morphological and electrical characterization

Abstract

A modification of the conventional pulsed laser deposition technique was employed, whereby a low energy electron emitting filament was placed between the target and the substrate (-20 V filament/substrate bias) in order to produce reactive species (O_2- and O_?) during deposition. Using this modification, epitaxial thin films of PbZr_xTi_1?xO3 (PZT, 0 ≤ × ≤ 0.6) were prepared in situ on virgin (100) MgO and (100) Pt/(100) MgO substrates at a substrate temperature of 550°C and in an oxygen ambient (0.3 Torr). The topography of films prepared without a filament on virgin MgO were porous and composed of grains of about 1000 Å in diameter. As the emission current was increased from 0 to 400 μA, the grain size decreased to less than 100 Å with a concomitant decrease in the porosity. The nucleation of crystallites of other orientations was observed at emission currents greater than about 500 μA. Trilayer structures (Pt/PZT/Pt/<100>MgO) were fabricated for electrical measurements. Non-filament-assisted PZT cells usually failed because of a high probability of conductive paths through the PZT layer. Filament-assisted films were much less prone to this problem. Typical remanent polarizations and coercive fields were 15–20 μC/cm² and 30–50 kV/cm, respectively.     

Preparation of BaPbO3 Electrode Thin Films by RF Magnetron Sputtering

For electrode materials of Pb(Zr,Ti)O₃ (PZT) thin films in ferroelectric random access memory (FeRAM), various materials have been studied. As new electrode material with which the polarization and fatigue properties are improved, we take notice of barium metaplumbate BaPbO₃ (BPO). Because the BPO contained lead (Pb) and oxygen is conductor that adopted same perovskite structure as PZT. BPO thin films were prepared by rf magnetron sputtering on various substrates. (SiO₂/Si, MgO, Al₂O₃ and Pt-coated substrates), and influence of growth conditions (sputtering gas, rf power, the substrate-heating temperature and post anneals) on crystallization and conductivity were investigated. In case of post anneal after sputtering at room temperature, perovskite single phase was obtained above 400°C. In case of substrate heating while sputtering, without post anneal, perovskite single phase was obtained at 350–500°C on SiO₂/Si substrates (110) preferred orientation BPO films obtained at low temperature, and resistivity of the films decreased at decreasing sputtering temperature. Resistivity of the film at substrate temperature 350°C was 3 × 10^?3 Ω cm. In the case of single crystal substrate, the BPO films were epitaxially grown. Orientation of the films was varied with the sputtering condition. The epitaxial PZT thin films were also grown on the BPO, revealing that PZT(111)[011] //BPO(111)[011] //Pt(100)[011] //MgO(100)[011] and PZT(111)[011] //BPO(111)[011] //Pt(111)[011] //Al₂O₃(001)[100] structures were obtained, and their ferroelectric properties were also evaluated.     

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.     

Epitaxial La0.5Sr0.5CoO3 electrode films for ferroelectric device applications

Abstract

We have grown high quality La_0.5Sr_0.5CoO₃ thin films by Pulsed Laser Deposition. This material is a electrically conducting perovskite which can be used as structurally compatible electrodes for devices using ferroelectric materials such as Pb-La-Zr-Ti-O (PLZT). Oxygen stability was investigated under various annealing conditions. LSCO/PLZT/LSCO heterostructures were grown epitaxially on SrTiO₃ (STO) and MgO substrates. P-E hysteresis loop was observed with P_r = 20 μC/cm² and E_c = 24 kV/cm. Direct observation of the piezoelectric effect in PLZT was made by measuring the PLZT c-axis lattice constant under various electric fields. LSCO/STO superlattice was also grown by PLD. The superlattice showed excellent crystallinity with a Rutherford Backscattering (RBS) channeling minimum yield of only 3.6%.     

Structure and Dielectric Properties of Heteroepitaxial PMNT Thin Films

Thin films of PbMg_1/3 Nb_2/3O₃(PMN) and (1 ? x)PbMg_1/3Nb_2/3O₃-xPbTiO₃ (PMNT) with x = 0.1 to 0.3 were epitaxially grown on (100) MgO and (100) SrTiO₃ (ST) substrates by magnetron sputtering. Typical film thickness was 300 to 900 nm. Pyrochlore free (001) PMN and (001) PMNT thin films were grown on the ST and MgO substrates at narrow temperature window of 500 ± 20°C. The cross-sectional TEM image showed that the sputtered PMN and PMNT thin films comprised high density and continuous structure. These sputtered films showed 3-dimensional epitaxy. The dielectric response of the sputtered thin films showed frequency dispersion similar to bulk relaxor-like behavior with a broad temperature anomaly. PMN-23PT (x = 0.23) thin films showed the temperature of maximum, Tm, at 80°C. The Tm coincided with that of corresponding bulk materials. However, the obtained maximum dielectric permittivity, ?_m, ?_m = 900 to 1000, was considerably smaller than that in the bulk. The relatively low dielectric permittivity was probably due to the presence of strained hetero-epitaxial layer having temperature independent dielectric properties.     

Preparation and properties of Lanthanum lead zirconate titanate thin films by hydrothermal method

Abstract

Ferroelectric polycrystalline Lanthanum lead zirconate titanate (abbreviated to PLZT) thin films with perovskite structure were prepared by hydrothermal method. Ferroelectric polycrystalline PLZT thin films with perovskite structure on titanium substrate were obtained at 180°C for 5 hr. The film thickness was easily controlled by repeating hydrothermal method. The densities of the PLZT thin films measured by Archimedes’ method were lower than those of ceramics. We fabricated bimorph-type bending actuators using these thin films and analyzed the displacement induced by the electric field. The actuators were bent by applied voltage without poling, because the polar axis in the as-deposited these thin films were aligned in the direction from the thin films surface to the substrate. The dielectric constant of these films were about 600 at room temperature for 1 kHz.     

Thin films of CCVD Ba0.5Sr0.5TiO3 and SrTiO3 for electrically tunable coupled microstripline phase shifters

Abstract

Epitaxial barium strontium titanate and strontium titanate thin films were deposited on (100) MgO single-crystal substrates, utilizing Combustion Chemical Vapor Deposition. The as-deposited films were patterned with gold electrodes to form interdigitated structure to function as electrically tunable devices, namely, coupled microstripline phase shifters (CMPS). Microwave dielectric properties were characterized at 11–20 GHz with an applied electric field up to ±35 V/μm. A maximum figure of merit of 53°/dB at 20 GHz and 23°C was measured. The demonstrated high degree of tunability and relatively low loss showed great potential of these films for the targeted frequency agile device applications. Characterization, using SEM, EDS, and XRD, is presented in addition to microwave performance as a function of dc bias and frequency.     

Structural and Electrical Properties of Ba(ZrxTi1-x)O3 Films Prepared by RF-magnetron Sputtering Using Metal Targets

Ba(Zr_xTi_1-x)O₃ (BZT) thin films with different Zr contents were deposited on (100)MgO and (100)Pt/(100)MgO substrates by RF-magnetron sputtering using metal targets. The BZT thin films had a single perovskite phase with only (001)/(100) orientation. In all cases, the ratio of Ba/Ti was stoichiometry and BZT films possess a dense microstructure. The grain size was decreased and BZT thin films showed ferroelectric-to-paraelectric properties with increasing Zr content. At room temperature, the tunability of nearly 30% was achieved at 1 MHz; meanwhile, a relatively low dielectric loss was obtained. These results indicated that we succeeded in depositing high-quality and potential tunable ferroelectrics.     

Microstructures and pyroelectric properties of (Pb,La)TiO3 thin films grown on MgO and ON Pt/MgO

Abstract

Comparison has been made between the microstructures and electrical properties of Pb_0·95La_0·05TiO₃ (PLT) thin films deposited on bare (100)MgO and on Pt/(100)MgO. Nearly perfect epitaxial PLT was grown on (100)MgO. (100)-oriented Pt film was obtained via coalescence of Pt islands formed on MgO. Highly c-axis oriented PLT thin film was successfully grown on the Pt bottom electrode with an electrically conductive network structure. High detectivity of 3·5 × 10⁸ and 2·6 × 10⁸ cm√Hz/W was obtained at 30 Hz without any poling treatments from the PLT/MgO- and PLT/Pt/MgO-based infrared detectors, respectively.     

Pulsed Laser Deposition of Ba0.6Sr0.4TiO3 Thin Films and Their Optical Properties

ABSTRACT

Barium strontium titanate [Ba_0.6Sr_0.4TiO₃ or BST (60/40)] thin films were deposited on MgO (100) substrates using pulsed laser deposition. X-ray diffraction (XRD) measurements revealed that the BST thin films had epitaxially grown on the MgO (100) substrates. The surface morphology of the thin films was observed using an atomic force microscope and the grain size was found to be about 100–150 nm. The surface roughness was around 4.9 nm for a 250 nm thick film. The optical transmittance of the BST thin film was measured using a transmission mode ellipsometer. The BST/MgO configuration was highly transparent in the visible region. The optical band gap energy of the BST film, calculated by applying the Tauc relation, was 3.56 eV. Optical waveguide characteristics of the BST (60/40) thin film were determined using a prism coupler. The electro-optic (E-O) properties were measured at 632.8 nm wavelength using a phase modulation detection method. The BST film exhibited a predominately quadratic E-O behavior and the quadratic E-O coefficient was found to be 0.58 × 10^{? 17} m²/V².     

Fabrication and Characterization of Ba(Ti,Zr)O3 Thin Films Through the Chemical Solution Deposition Process

Lead- and bismuth-free Ba(Ti_{1 ? x} Zr _x )O₃ (BTZ) thin films were fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates by the chemical solution deposition (CSD) process. The single phase BTZ thin films were obtained at 650°C by conventional process and the control of lattice parameter a was possible by Zr substitution. As the D-E hysteresis loops and J-V characteristics depended on the precipitates on film surface, the fabrication process was reexamined by 2-step sintering process. Consequently the decreasing of first sintering time was able to prevent the precipitates, and the larger grain of about 40–50 nm were obtained by additional sintering for 2 hour.     

Physical Properties of (Pb,La)(Zr,Ti)O 3 Films Crystallized by One-Step Postdeposition Annealing Using Nucleus-Insertion Method

Physical properties of two PLZT films using a initial PLZT nucleus (i-PLZT) layer deposited by sputtering on the respective Pt(100)/MgO and Pt(111)/SiO 2 /Si(100) substrates were investigated. Postannealed PLZT films formed on Pt/MgO and Pt/SiO 2 /Si substrates showed preferential (001)- and (111)-orientation, respectively. The results of energy dispersive X-ray analysis suggest the possibility that a part of Zr moved from the seeding layer upward to crystallized layer, while a part of Ti moved from the crystallized layer downward to the seeding layer by the interdiffusion between the above two layers during postannealing.     

Phase formations and ferroelectric properties of PLT thin films by MOCVD

Abstract

La-modified lead titanate, Pb_1-x La _x TiO₃(PLT), thin films were prepared on Si[100] and Pt/SiO₂/Si substrates by the low-pressure metalorganic chemical vapor deposition (LP-MOCVD) method with the hot-wall type. The PLT films were deposited at 500°C with the low-pressure of 0.1 Torr, and then annealed at 650°C with an oxygen ambient for 10 minutes. Irrespective of substrate properties and La molar fractions, the films revealed the [100] preferred-orientation. With increasing the La mole %(up to 34%) in the films, the surface morphology improved, and the ferroelectricity and the leakage current density decreased. On the other hand, up to the La 22 mole%, the relative dielectric constant increased from 900 to 1200.     

Structural and dielectric properties of epitaxial Ba0.6Sr0.4TiO3 thin films grown on Si substrates with thin SrO buffer layers

(100) epitaxial Ba_0.6Sr_0.4TiO₃ (BST) thin films were grown on Si substrates using a 9 nm thick SrO buffer layer. The phase shifter fabricated on BST films grown on a SrO buffered Si substrate showed a larger figure of merit (FOM) of 24.7°/dB as a result of improving the phase tuning while retaining an appropriate insertion loss compared to that (15.3°/dB) for the BST/MgO structure. This work demonstrates that a thin SrO buffer layer plays an important role in the successful integration of BST-based microwave tunable devices onto Si wafers.     

Texturing and electrical characteristics of sol-gel derived ferroelectric thin films

Abstract

Highly oriented PZT, PLZT and PMN thin films were fabricated on various substrates using sol-gel method. The thin films having different orientation were fabricated by different drying conditions for pyrolysis. The preferred orientations of the PZT, PLZT and PMN thin films were observed using XRD(X-ray diffraction). The hysteresis loops, capacitance-voltage, and fatigue characteristics of the films were investigated using an RT66A standardized ferroelectric test system. The dielectric constant and current-voltage characteristics of the films were investigated using impedance analyzer and pA meter, respectively. The films oriented in particular direction showed better electrical characteristics to the randomly oriented films.     

Electrical and optical properties of microwave dielectric thin films prepared by pulsed laser deposition

Abstract

Bi₂(Zn_1/3Nb_2/3)₂O₇, BiZN, materials possess high dielectric constant and low loss factor in microwave frequency region. They have good potential for device application, especially in the form of thin films. However, the microwave dielectric properties of a thin film are very difficult to be accurately measured. Evaluation on the dielectric behavior of the films through the performance of the microstrip line devices made of these films involves metallic conduction and stray field losses. A novel measuring technique, which can directly evaluate the microwave dielectric properties of a thin film is thus urgently needed.

In this paper, BiZN thin films were grown on [100] MgO single crystal substrates using pulsed laser deposition process. The high-frequency dielectric properties of thus obtained thin films were determined using optical transmission spectroscopy (OTS). The [100] preferentially oriented films with pyrochlore structure can be obtained for the thin films deposited at 400–600°C substrate temperature under 0.1 mbar oxygen pressure. OTS measurements reveal that the index of refraction (n=1.95–2.35) and absorption coefficient (k=0.28x10^?4-2.25 × 10^?4 nm^?1) of the films vary insignificantly with the crystallinity of the BiZN films.