Low-temperature synthesis in vacuum of c-axis oriented ferroelectric YMnO3 thin films using alkoxy-derived precursors

Abstract

Hexagonal YMnO₃ thin films were prepared on Pt(111)/TiO_x/SiO₂/Si and Pt(111)/Al₂O₃(0001) substrates using alkoxy-derived precursor solutions. The films were prepared by spin coating the YMnO₃ precursor solutions and then, the films were calcined and crystallized via rapid thermal annealing in oxygen or vacuum ambient. The annealing conditions and substrates were critical for crystallization of ferroelectric YMnO₃ films. When annealed in vacuum, the films both on Pt(111)/TiO_x/SiO₂/Si and Pt(111)/Al₂O₃(0001) substrates crystallized to hexagonal YMnO₃ and the orientation depended on the substrates. The film on Pt(111)/Al₂O₃(0001) had c-axis orientation and the film on Pt(111)/TiO_x/SiO₂/Si had no preferred orientation. In addition, it was found that crystallization behavior, orientation and morphology of YMnO₃ films on Pt(111)/TiO_x/SiO₂/Si substrates depended on the annealing condition. The heat-treatment in vacuum at initial stage for crystallization affected the restraint of perovskite phase and formation of hexagonal phase. The following heat-treatment in oxygen promoted the c-axis orientation and grain growth. The optimum annealing procedure for crystallization of the c-axis oriented YMnO₃ films on Pt(111)/TiO_x/SiO₂/Si was addressed.     

Growth and electrical properties of (211) BaTiO3 thin films on Pt-coated Si(100) substrates

Abstract

Barium titanate (BaTiO₃) thin films with high (211) orientation have been prepared on Pt(111)/Si(100) substrates by R. F. magnetron sputtering at a substrate temperature between 550°C and 580°C in an Ar/O₂ atmosphere. The I-V curve of a thin film capacitor (Ag-BaTiO_3-Pt) has been measured and the C-V curves are obtained for frequencies between 100Hz and 1MHz. Neither the I-V curve nor the C-V curves are symmetrical and a very large change in the slope of all curves is found to occur at ～+0.5v.     

Synthesis, Microstructure and Electrical Properties of Hydrothermally Prepared Ferroelectric BaTiO3 Thin Films

Thin films of polycrystalline, tetragonal BaTiO₃ on oxidized Ti metal substrates were synthesized at 240°C under hydrothermal conditions. Microstructure and electrical properties of the films generated over a four week period of synthesis formed the focus of this study. The films displayed a smooth and shiny surface with a relatively dense structure and no observable cracks. Film thickness reached 0.5 m after two weeks of synthesis and thereafter remained constant. Diameters of the grains on the film surface were in the range of 12 m. It is proposed that initial formation of the BaTiO₃ film occurs by reaction of Ba²⁺ with solubilized titanium oxide on the Ti metal surface followed at later stages by an in-situ growth via reaction of TiO_x with Ba²⁺ diffusing through the BaTiO₃ film. X-ray diffraction and Raman spectroscopy indicated that the BaTiO₃ films are tetragonal, and the films exhibited typical ferroelectric hysteresis loops at room temperature. However, no evidence of the dielectric anomaly (Curie transition) between 30 and 200°C was observed. Dielectric constant of the films at 1 kHz at room temperature was between 400–500. Both dielectric constant and tan exhibited low dispersion as a function of frequency at temperatures below 150°C, and the dispersion increased with temperature.     

Improvement of the electrical properties of PZT thin films using TiO2 buffer layer

Abstract

Thin TiO₂ layers were sputter-deposited on Pt/Ti/SiO₂/Si wafers, as buffer layers for PZT thin film capacitors. It was found that TiO2 buffers of less than 4-nm-thickness could assist in obtaining highly uniform PZT thin films with no second phase. The leakage current behaviors of the PZT based capacitor are improved, while retaining the ferroelectric properties of PZT thin films such as remanent polarization and coercive field. In addition, the uniform distribution of oxygen in PZT on TiO₂/Pt indicates that the TiO₂ buffer layer act as a barrier for lead-platinum reaction, as well as for oxygen diffusion.     

Growth and characterization of non-c-axis-oriented SrBi2Ta2O9 epitaxial thin films on Si(100) substrates with SrRuO3 bottom electrodes

Abstract

We have successfully grown non-c-axis-oriented epitaxial ferroelectric SrBi₂Ta₂O₉ (SBT) films with (116) and (103) orientations on Si(100) substrates using epitaxial (110)- and (111)-oriented SrRuO₃ (SRO) bottom electrodes, respectively. The SRO orientations have been induced by coating the Si(100) substrates with epitaxial YSZ(100) and MgO(111)/ YSZ(100) buffer layers, respectively. All films were sequentially grown by pulsed laser deposition. Specific in-plane orientations of the epitaxial SBT films were found, which are in turn determined by specific in-plane orientations of the epitaxial SRO bottom electrodes. These include a diagonal rectangle-on-cube epitaxy of SRO(110) on YSZ(100) and a triangle-on-triangle epitaxy of SRO(111) on MgO(111).     

Chemical vapor deposition of Pb1−xLaxTiO3

Abstract

We report chemical vapor deposition (CVD) of PbLaTiO₃ films for integrated pyroelectric devices. Pb(thd)₂, La(thd)₃ and Ti(O-Pr)₂(thd)₂ were introduced to the reactor via a single liquid precursor solution that is vaporized. Substrate temperatures were approximately 535°C and post deposition annealing was not used. Films were deposited on fused silica and Pt metallized Si substrates. The liquid delivery technique permitted excellent composition control and films on fused silica were predominantly [100] oriented with trace amounts of [110] and [111] present. Pyroelectricity for 0.7μm thick films deposited on Pt metallized Si was measured using a modified Byer-Roundi technique and pyroelectric coefficients as high as 90 nC/cm²·K were observed. The high crystalline quality and pyroelectric properties are attributed to the excellent composition control afforded by the liquid delivery CVD technique.     

Growth of MgTiO3 thin films by pulsed laser deposition and their electrical properties

Abstract

MgTiO₃ thin films have been grown on various substrates by pulsed laser deposition (PLD) to investigate the application for microwave dielectrics and optical devices. Highly oriented MgTiO₃ thin films were obtained on sapphire (c-plane Al₂O₃). MgTiO₃ thin films deposited on SiO₂/Si and platinized silicon (Pt/Ti/SiO₂/Si) substrates were polycrystalline nature. MgTiO₃thin films grown on sapphire were transparent in the visible and had a sharp absorption edge at 280 nm. These MgTiO₃ thin films had extremely fine feature of surface morphology, i.e., rms roughness of 0.87 nm. Dielectric constant and loss of MgTiO₃ thin films deposited by PLD were about 24 and 1.5% at 1MHz, respectively. These MgTiO₃ thin films also exhibited little dielectric dispersion.     

Improvement of Capacitive Behavior on Gradient-Free PZT Thin Films

PbZr_0,52Ti_0,48O₃ thin films were synthetized by sol-gel techniques on large scale Pt(111)/TiO_x/SiO₂/Si substrates (200 mm in diameter). The Zr/Ti ratio gradient – that appears through the thickness of the layer with standard processing – can be reduced using an optimized “gradient-compensated” approach. Capacitance measurements revealed an augmentation of the effective permittivity from 5 to 15% using “gradient-free” PZT (reaching 1700 for 2μm). Large scale breakdown voltage analysis revealed an increase of 20% for the breakdown field for low thicknesses (1.25MV/cm for 240 nm-thick layer) suitable for capacitor integration.     

PREPARATION AND PROPERTIES OF LITHIUM-DOPED K0.5Na0.5NbO3 THIN FILMS BY CHEMICAL SOLUTION DEPOSITION

ABSTRACT

Lithium-doped K_0.5Na_0.5NbO₃ (KLNN) films were fabricated by chemical solution deposition on Pt/TiO₂/SiO₂/Si substrates. Homogeneous and stable precursor solutions were prepared by controlling the reaction of starting metal alkoxides. Perovskite KLNN single-phase thin films were successfully synthesized on Pt/TiO _x /SiO₂/Si substrates. The 0.75-μ m-thick KLNN film annealed at 650°C exhibited ferroelectric polarization hysteresis loops at ?250°C. The loop at room temperature was round, indicating the film contained leakage components. The dielectric constant under zero bias was 490 at room temperature. A typical upside-down butterfly DC bias-capacitance curve was obtained in the KLNN film capacitors at room temperature, indicating that polarization reversal occurred in the obtained KLNN films.     

Structural and dielectric properties of BaTiO3SrTiO3-multilayers deposited by PLD

Abstract

Dielectric superlattices are characterized by the structural variability of the film periodicity additional to the stochiometry. They have interesting dielectric properties different from the solid solutions of the same overall composition.

In this paper the structural and dielectric properties of BaTiO₃/SrTiO₃-superlattices prepared by pulsed laser deposition on single crystalline substrates are characterized in comparison to a (Ba_0.5Sr_0.5)TiO₃ solid solution. The films were characterized using X-ray diffraction, SEM and dielectric measurements.

The BaTiO₃/SrTiO₃-superlattices have a different frequency and a weaker bias and temperature dependence of the dielectric properties than the solid solution. The mechanical stresses caused by the lattice mismatch between the different layers could be one reason for this behaviour.     

STRUCTURAL AND ELECTRICAL PROPERTIES OF (BaxSr1-x)TiO3 THIN FILMS PREPARED BY A SOL-GEL METHOD

ABSTRACT

Ba_xSr_1-xTiO₃(BST) thin films with x = 0.5, 0.6, 0.7 and 0.8 were fabricated on p-type Si(100) substrates by a sol-gel spin coating method. All samples show the perovskite polycrystalline structures without the pyrochlore phase and have dense surface texture and crack-free uniform microstructures. The C-V characteristics of the BST thin film/p-type Si(100) capacitors exhibit clockwise hysteresis loops and also clearly show regions of accumulation, depletion and inversion corresponding to those of metal-ferroelectric-semiconductor structures. Furthermore, a constant memory window has been observed through the entire frequency ranges from 1 kHz to 10 MHz.     

Film Thickness Dependence of Electrical Properties for Pb(Zr,Ti)O3 Thin Films Prepared on (111)Ir/TiO2/SiO2/Si and (111)Pt/TiO2/SiO2/Si Substrates by Pulsed-Metalorganic Chemical Vapor Deposition

Polycrystalline Pb(Zr,Ti)O₃ (PZT) films with various film thicknesses were deposited on (111)Ir/TiO₂/SiO₂/Si and (111)Pt/TiO₂/SiO₂/Si substrates at 540°C by source-gas-pulsed metalorganic chemical vapor deposition (pulsed-MOCVD). PZT films deposited on (111)Ir/TiO₂/SiO₂/Si substrates showed good surface flatness and lower leakage current density. The rate of the decrease of remanent polarization (P _r ) and the rate of increase of coercive field (E _c ) for the films with decreasing the film thickness smaller on (111)Ir/TiO₂/SiO₂/Si substrates than those of (111)Pt/TiO₂/SiO₂/Si substrates. In addition, P _r and E _c values saturated at low voltage when the film thickness was the same. As a result, good ferroelectricity with P _r and E _c values of 40 μC/cm² and 140 kV/cm were obtained for 35 nm-thick films prepared on (111)Ir/TiO₂/SiO₂/Si substrates by pulsed-MOCVD.     

Glycolate tantalum based solutions for the sol-gel spin-coating deposition of SrBi2Ta2O9 thin films

Abstract

The reaction of tantalum ethoxide with a glycol solvent produces the interchange of the ethoxide groups with the glycol. As a result, a polymeric derivative is formed with a high resistance towards hydrolysis. Compounds of Sr(II) and Bi(II) can be added to this Ta-glycol sol, leading to strontium bismuth tantalate (SBT) precursor solutions stable in air. These solutions were spin-coated onto two substrates: Pt/TiO₂/SiO₂/(100)Si and Ti/Pt/Ti/SiO₂/(100)Si. Crystallisation of the SBT phase was carried out by a first formation of a fluorite phase that evolves to the layered perovskite at temperatures over 600°C. During crystallisation, a larger tendency to the formation of a substrate/film interface was observed in the films deposited onto Ti/Pt/Ti/SiO₂/(100)Si than onto Pt/TiO₂/SiO₂/(100)Si. A remanent polarisation of P_r5 μC/cm² and a coercive field of E_c <100 kV/cm were measured in the films on Pt/TiO₂/SiO₂/(100)Si. These films retain its remanent polarisation, P_r, up to 10⁵seconds and are fatigue-free up to 10⁹ cycles.     

A 11×6 element pyroelectric detector array utilizing self-polarized pzt thin films grown by sputtering

Abstract

A planar multi target sputtering approach was used to deposit PbTiO₃ (PT) and Pb(Zr, Ti)O₃ (PZT) films on TiO₂/Pt bottom electrodes for the use in thin film pyroelectric IR detector arrays. PZT films with a Zr content of 28 at% (PZ28T) exhibited the best pyroelectric coefficient of typically 2×10^?4 Cm^?2K^?1. The PZ28T films have been used for fabricating a two dimensional 11×6 pixel pyroelectric detector array on Si wafers. The array pixels with a sensitive area of 280 ×280 μm² have a noise lequivalent power NEP of less than 0.7 nW at 1 Hz. It is planned to use the detector array in systems for motion detection.     

Effects of Heating Process on Crystalline Orientation and Electrical Properties of (Bi,La)4Ti3O12 Thin Films Derived by Chemical Solution Deposition Method

(Bi,La)₄Ti₃O₁₂ (BLT) thin films were prepared on Pt-coated Si (Pt/Ti/SiO₂/Si(100)) substrates by chemical solution deposition method. The effect of heating process on structural and electrical properties of BLT thin films was investigated. The c-axis preferentially oriented films were obtained by lower drying temperature with heating from bottom by a hot plate or IR lamp heater. On the other hand, randomly oriented films were obtained by higher drying temperature with heating from top of films by IR lamp heater or with heating substrate all around by tube type furnace. The orientation of BLT thin films deposited on Pt-coated substrates can be controlled by heating process.     

Self-Organized (100)-/(001)-Preferred Orientation in Pb(Zr,Ti)O3 Films Grown on Polycrystalline Substrates by Metalorganic Chemical Vapor Deposition

Lead zirconate titanate [Pb(Zr _x Ti_{1 ? x} )O₃, PZT] films were grown on (100), (110) and (111)SrRuO₃//SrTiO₃ substrates at 600°C by metalorganic chemical vapor deposition (MOCVD). The crystal orientation dependence of the growth rate was investigated for these films. The growth rate of (100)-/(001)-oriented epitaxial films was approximately 1.7 and 2.0 times higher than that of (110)-/(101)- and (111)-/(11&1macr;)-oriented epitaxial films, respectively. On the other hand, the growth rate of (100)-/(001)-preferred oriented PZT films grown on (111)Pt/TiO₂/SiO₂/(100)Si substrates was almost the same with that of (100)-/(001)-oriented epitaxial films. The deposition rate of these films was approximately 1.5 μm/h. High growth rate of (100)-/(001)-oriented PZT grains makes (100)-/(001)-preferred orientation on (111)Pt/TiO₂/SiO₂/(100)Si substrate. From transmission electron microscopy observation, (100)-/(001)-oriented grains were found to be directly grown on (111)-oriented Pt grains without obvious another oriented grains. As a result, orientation-controlled PZT films were successfully grown on (100)Si substrates having (111)-oriented Pt bottom electrodes.     

The Effect of La-Doped Bi4Ti3O12 Buffer Layer on Crystallinity and Ferroelectric Properties of PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 Multilayered Thin Films

PbZr_0.58Ti_0.42O₃ (PZT) ferroelectric thin films with Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer of various thickness were fabricated on Pt/TiO₂/SiO₂/p-Si(100) substrates by rf-magnetron sputtering method. The pure PZT film showed (111) preferential orientation in the XRD patterns, and the PZT/BLT films showed (110) preferential orientation with increasing thickness of the BLT layer. There were no obvious diffraction peaks for the BLT buffer layer, for its thin thickness in PZT/BLT multilayered films. There were the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples from the surface images of FESEM. The growth direction and grain size had significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics suggested that 30-nm-thick BLT was just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

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.     

The influence of microstructure on the electronic properties of thin films of barium strontium titanium oxide composites

Abstract

Microstructural and electrical properties were investigated for barium strontium titanium oxide (BSTO) magnesium oxide doped (0 to 10 wt.%) thin films deposited by the pulsed laser deposition (PLD) method on Pt/TiO_x/SiO₂/Si substrates. The dielectric properties were found to be strongly dependent on composition and microstructure. In cross-section, all films exhibited a columnar polycrystalline microstructure with vertical orientation deviations dictated by the surface roughness of the Pt electrode. A uniform granular microstructure was observed for all films in plan view. The dielectric constant, loss tangent and grain size decreased with increasing MgO concentration.     

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%.