Optical properties of epitaxial plzt thin films

In the epitaxial (Pb_1?x , La _x )(Zr_1?y , Ti _y )_1?x/4O₃ [PLZT] films, the composition dependence of the refractive index and electric-optic (EO) coefficient near the morphotropic phase boundary (MPB) composition was investigated. A (100/001)-oriented PLZT 10/65/35 epitaxial film is found to have isotropic optical properties. Highly (100/001)-oriented epitaxial PLZT films with compositions near the MPB on Nb–SrTiO₃ substrates were fabricated using a sol–gel process. The value of birefringence from 4?×?10^?3 to 5?×?10^?4 in PLZT epitaxial film was smaller than that of lithium niobate single crystal. The refractive index decreases with increasing lanthanum content. The difference in the refractive index obtained depended upon the lanthanum content up to 2%. This value is adequate for fabrication of waveguide structures. The EO coefficient of PLZT 9/65/35 thin films was 45 pm/V, which is larger than that of lithium niobate single crystal. A very small polarization dependence of the EO coefficient was also observed.     

Crystalline and optical properties of PLZT films prepared by pulsed laser deposition

Abstract

The PLZT (3/66/34), PLZT (3/46/54), PLZT (9/65/35) and PLZT (28/0/100) thin films were deposited on MgO (100), Sapphire (0001) and fused silica substrates by using pulsed KrF excimer laser deposition technique. The conventional in-situ and 2-step heating processes were utilized to facilitate the synthesis of a large area of uniform PLZT thin film. Pure perovskite phase can be obtained only under very narrow process conditions, the highly textured PLZT films can be easily obtained by in-situ heating process. For PLZT (28/0/100) material, epitaxial films were successfully coated on MgO (100) substrates by 600°C in-situ and RTA 650°C 2-step heating processes. The latter was found to possess higher refractive index and lower extinction coefficient.     

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     

Optical properties of RF-sputtered Ba0.65Sr0.35TiO3 thin films

Ba_0.65Sr_0.35TiO₃ (BST) thin films have been prepared by radio frequency magnetron sputtering on fused quartz at different substrate temperatures. Optical constants (refractive index n, extinction coefficient k) were determined from the optical transmittance spectra using the envelope method. The dispersion relationship of the refractive index vs. substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at λ?=?650 nm) as deposited temperature increases from 560°C to 650°C. The extinction coefficient of as-deposited BST thin films increased with the increase of the oxygen-to-argon ratio, which was due to the change of the film stoichiometry, structure, and texture of BST thin films. The oxygen-to-argon ratio also affected the fluorescence spectra. The fluorescence peaks intensity was greatly increased, apparent frequency shift was detected, and the linewidth became narrow as the ratio of oxygen to argon increased from 1:4 to 1:1. The fluorescence spectra also indicated the band transition of BST thin films was an indirect gap transition.     

Chemical solution technique to prepare perovskite PZT and PLZT thin films and powders

Abstract

PbZr_0.65Ti_0.35O₃ and Pb_0.91La_0.09Zr_0.65Ti_0.35O₃ thin films with thickness of around 100 nm were prepared by the chemical solution deposition technique on Si (100) substrate. Complex metal alkoxide precursors were synthesized by alcoholisis and alcohol exchange reactions starting from metallorganics compounds. NMR spectroscopic techniques, ¹H and ¹³C, and FTIR analysis were used to study the arrangement of the metals and oxygen in the precursor molecules. The films were deposited on Si (100) by spin coating technique and thermal treated by Rapid Thermal Processing for film crystallization. The thermal evolution and structural characterization were performed by DTA-TG/FTIR and by glazing incidence XRD and XRD powder. A PLZT powder with a well-crystallized perovskite structure was obtained at 700°C free of pyrochlore phase whereas the PLZT film exhibits a distorted perovskite structure and residual pyrochlore. The PZT films were less crystallized. The silicon substrate affects the crystal structure of the film. The residual acetylacetonate groups in the precursor of PLZT, would reduce the clustering of Zirconium species.     

Temperature tunable photonic bandgap in PLZT inverse opals

Three-dimensional periodic microstructure of air spheres in (Pb,La)(Zr,Ti)O₃ (PLZT) matrix were synthesized by sol–gel process using synthetic opals as template. The micro-region optical reflection spectra of PLZT inverse opal photonic crystals have been on-line measured continuously with treating temperature increasing. It demonstrates that the bandgap blue-shifts with treating temperature increasing based on the diminishment of periodical size in sintering process. The tunable band gap in PLZT inverse opals should be of high interest in device application.     

Ferroelectric properties of plzt thin films prepared by mocvd

Abstract

Lanthanum-modified lead zirconate titanate (PLZT) thin films have been grown on Pt/SiO₂/Si substrate at 650[ddot]C by metalorganic chemical vapor deposition. The relative dielectric constant increased as the La content was increased up to about 5 atomic percent (at%). The remanent polarization and coercive field decreased from 30 to 20 μC/cm² and from 53 to 30 kV/cm, respectively, with increasing La content in the range of 0–13 at%. The leakage current of PLZT film was 3 × 10^?9 A/cm² at an applied voltage of 3 V. The degradation of switched charge density of PLZT film was not observed even at 2 × 10¹¹ cycles.     

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.     

MOCVD PBZRxti1−xo3 thin films on platinized silicon wafers and srtio3 crystals

Abstract

PbZr_xTi_1-xO₃ (PZT) thin films were grown on 6” platinized silicon substrates (Pt / Si) and SrTiO₃ (STO) crystals by Metal-Organic Chemical Vapor Deposition (MOCVD) as a function of the Zr / (Zr+Ti) ratio in the gas phase. Morphology, optical properties, and crystal structure were investigated by scanning electron microscopy, atomic force microscopy, ellipsometry, and X-ray diffraction. The morphology, structure, and optical properties of the polycrystalline and epitaxial films were compared. The determination of the refractive index by ellipsometry (from 550 nm to 2000 nm) was not sensible for the films grown on (Pt / Si) but successful for the films grown on SrTiO₃.     

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.     

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.     

Analysis of band gap of non-bravais lattice photonic crystal fiber

This article designs a novel type of non-bravais lattice photonic crystal fiber. To form the nesting complexperiod with positive and negative refractive index materials respectively, a cylinder with the same radius and negative refractive index is introduced into the center of each lattice unit cell in the traditional square lattice air-holes photonic crystal fiber. The photonic band-gap of the photonic crystal fiber is calculated numerically by the plane wave expansion method. The result shows that compared with the traditional square photonic band-gap fiber (PBGF), when R/Λ is 0.35, the refractive index of the substrate, airhole, and medium-column are 1.30, 1.0, and −1:0, respectively. This new PBGF can transmit signal by the photonic band-gap effect. When the lattice constant Λ varies from 1:5 μm to 3:0 μm, the range of the wavelength ranges from 880 nm to 2300 nm. __________ Translated from Optoelectronic Technology, 2007, 27(4): 257–260 [译自: 光电子技术]     

Improved transverse piezoelectric properties in {110}-oriented B-site acceptor doped PLZT (8/65/35) thin films

Superior piezoelectric properties of lead-based perovskite type solid solution systems such as PLZT, having compositions near morphotropic phase boundary (MPB) make them ideal candidates for MEMS. The dielectric and piezoelectric characteristics in such perovskite based thin films are related to their structure and texture. In this study, we report the influence of aliovalent B-site acceptor dopants (Fe³⁺, Cu²⁺ and Mn³⁺) on the structure, dielectric and piezoelectric properties of {110}- preferentially oriented PLZT (8/65/35) thin films. Thin films having a thickness of 2.0 µm were prepared on silicon substrates (111) Pt/Ti/SiO₂/Si by Sol-gel spin coating technique. The preferential crystallographic orientation and crystalline phase formation in the thin films were analysed by X-ray diffraction and Raman spectroscopy respectively. The improved transverse piezoelectric coefficient, e_31,f and electric field induced bipolar strain characteristics of the acceptor doped PLZT films have been correlated with their crystal structure. Mechanism for higher bipolar strain in Cu²⁺ and Mn³⁺ doped PLZT films have also been studied and are reported.     

PLZT films prepared by aerosol deposition and their birefringence evaluation

Pb_0.91La_0.09(Zr_0.65Ti_0.35)O₃ (PLZT) films were prepared by the aerosol deposition method (ADM) and their optical and electro‐optic (EO) properties investigated for application to hologram optical switch. We found that a higher transmittance of the films was obtained with smaller particles. The transmittance of the PLZT film deposited with particles of 0.2 µm average diameter, the smallest size in this experiment, was nearly 100%, showing that the PLZT film deposited by aerosol deposition can be applied to practical optical devices. We evaluated the birefringence shift of the film to make the EO performance clear. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Synthesis of fullerene-modified P(St-MMA-AA) colloids and optical performance in colloidal crystals

Abstract

By constantly trying to change the amount of sodium dodecyl benzene sulfonate (SDBS), monodispersed P(St-MMA-AA) colloids with diameters about 240?nm was synthesized successfully using emulsion polymerization. The polymer latex particles having an amino group on the surface are grafted with fullerene acetic acid to obtain fullerene-modified P(St-MMA-AA) microspheres by an amidation reaction. The corresponding colloidal crystals were fabricated and investigated. In view of the high refractive index of fullerenes, the refractive index of the fullerene-modified P(St-MMA-AA) microspheres is improved.     

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%.     

Comparison of sputtered SBTN and PLZT thin film capacitors for FRAM applications

Abstract

Thin films of the solid solution SrBi₂Ta₂O₉-SrBi₂Nb₂O₉ (SBTN) and Ca and Sr doped (Pb, La)(Zr, Ti)O₃ (PLZT) were prepared by conventional, single target, rf-magnetron sputtering. The films were deposited onto Pt coated substrates with a diameter of 6 inches. The electrical properties were characterized by hysteresis and pulsed field switching measurements. A ferroelectric performance comparison between two types of capacitors will be presented. The recent improvement in PLZT capacitor processing have greatly extended fatigue resistance beyond what is usually observed and reported for SBTN capacitors.     

LARGE AREA PIEZOELECTRIC ACTUATORS USING METAL FOIL SUBSTRATES WITH Pb(Zrx,Ti1 - x)O3 THIN FILMS

ABSTRACT

We report on the deposition of Pb(Zr_x,Ti_{1 - x})O₃ (PZT) thin films by chemical solution deposition (CSD) on stainless steel foils. The electrical characterization proves good ferroelectric properties with a remnant polarization of 38 μ C/cm². Since PZT is also piezoelectric the 35 μ m and 50 μ m thick metal foils are used to make piezoelectric actuated cantilever beams of several millimeter lengths. Actuated with 10–30 V a displacement up to 32 μ m was measured in quasi-static mode. In resonance mode the displacement increases several times at the same driving voltage.     

Fibonacci sequences quasiperiodic A5B6C7 ferroelectric based photonic crystal: FDTD analysis

In this study, we present an investigation of the optical properties and band structures for the conventional and Fibonacci photonic crystals (PCs) based on some A⁵B⁶C⁷ ferroelectrics (SbSBr and BiTeCl). Here, we use one dimensional SbSBr and BiTeCl based layers in air background. We have theoretically calculated the photonic band structure and transmission spectra of SbSBr and BiTeCl based PC superlattices. The position of minima in the transmission spectrum correlates with the gaps obtained in the calculation. The intensity of the transmission depths is more intense in the case of higher refractive index contrast between the layers. In our simulation, we employed the finite-difference time domain technique and the plane wave expansion method, which implies the solution of Maxwell equations with centered finite-difference expressions for the space and time derivatives.     

Photonic Crystal Fibers and Their Applications

Dramatic advances in research and development on photonic crystal fibers (PCF) have created new properties that had not been achievable using conventional fibers. PCFs have many fascinating features. The very high relative refractive index between the fiber core and air-hole cladding enables several prominent properties, notably endlessly single-mode (ESM) operation, high nonlinearity, wide-ranging dispersion management, and the ability to maintain high polarization. The processes involved in manufacturing PCFs are quite different from those used to manufacture conventional fibers, and this is largely because of the profusion of air holes in the silica glass that comprises PCFs. The authors have optimized the technology to manufacture photonic crystals with the required optical characteristics. This paper describes the properties and application of large-mode and ESM guidance, nonlinearity, and double cladding. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.