Structural and Electrical Characteristics of ZnO Thin Films on Polycrystalline AlN Substrates

Fostered by the increasing use of AlN in highly thermally conductive electronic packages, it is attempted to grow ZnO thin films on polycrystalline AlN in the present work. Effects of the polycrystalline substrate on the structural and electrical properties of the ZnO films are highlighted. The ZnO films are synthesized by low-cost spin-coating technique from a precursor solution containing zinc acetate, 2-methoxyethanol, and monoethanolamine. Structural analysis was performed using X-ray diffraction, which showed all the films to be polycrystalline of hexagonal phase with no preferred orientation, in sharp contrast to numerous reports of strong c -axis orientation on glass substrates. The films, which were heat-treated at 700°C followed by firing in nitrogen containing 5% hydrogen at 500°C, exhibited better crystallinity and dense microstructure among all the samples and had the lowest resistivity (1.36 × 10⁻¹Ω·cm). The minimum resistivity obtained in the present work is comparable to the values reported for the films grown using similar technique, thus indicating the negligible dependence of electrical properties on orientation of the films.     

Deposition of Pb(Zr,Ti)O3 Thin Films by Metal-Organic Chemical Vapor Deposition Using β-diketonate Precursors at Low Temperatures

Lead zirconate titanate (PZT) thin films were deposited by metal-organic chemical vapor deposition (MOCVD) using β-diketonate precursors and 0₂ at temperatures below 500°C on variously passivated Si substrates. PZT thin films could not be deposited on bare Si substrates, owing to a serious diffusion of Pb into the Si substrate during deposition. Pt/SiO₂/Si substrates could partially block the diffusion of Pb, but a direct deposition of PZT thin films on the Pt/SiO₂/Si substrates resulted in a very inhomogeneous deposition. A TiO₂ buffer layer deposited on Pt/SiO₂/Si substrates could partially suppress the diffusion of Pb and produce homogeneous thin films. However, the crystallinity of PZT thin films deposited on the TiO₂-buffered Pt/SiO₂/Si substrate was not good enough, and the films showed random growth direction. PZT thin films deposited on the PbTiO₃-buffered Pt/SiO₂/Si substrates had good crystallinity and a- and c-axis oriented growth direction. However, the PZT thin film deposited at 350°C showed fine amorphous phases at the grain boundaries, owing to the low chemical reactivities of the constituent elements at that temperature, but they could be crystallized by rapid thermal anneaiing (RTA) at 700°C. PZT thin film deposited on a 1000-å PbTiO₃,-thin-film-buffered Pt/SiO₂/Si substrate at 350°C and rapid thermally annealed at 700°C for 6 min showed a single-phase perovskite structure with a composition near the morphotropic boundary composition.     

The Effect of Deposition Temperature and Postanneal on the Bi3.63Pr0.3Ti3O12 thin Films Prepared by RF-Magnetron Sputtering Method

Praseodymium doped Bi₄Ti₃O₁₂ (BTO) thin films with composition Bi_3.63Pr_0.3Ti₃O₁₂ (BPT) were successfully prepared on Pt/Ti/SiO₂/Si substrates by RF-magnetron sputtering method at substrate temperatures ranging between 500° and 750°C. The structural phase and orientation of the deposited films were investigated in order to understand the effect of the deposition temperature on the properties of the BPT films. As the substrate temperature was increased to 700°C, the films started showing a tendency of assuming a c -axis preferred orientation. At lower temperatures, however, polycrystalline films were formed. The Pt/BPT/Pt capacitor showed an interesting dependence of the remnant polarization (2 P _r) as well as dc leakage current values on the growth temperature. The film deposited at 650°C showed the largest 2 P _r of 29.6 μC/cm². With the increase of deposited temperature, the leakage current densities of films decreased at the same applied field and the film deposited at 750°C exhibited the best leakage current characteristics. In addition, the ferroelectric fatigue and Raman measurements were carried out on the as-prepared, postannealed in air and postannealed in oxygen BPT films. It was revealed that the BPT film postannealed in air exhibited the weakest fatigue-resistance characteristics and highest frequency shifted Raman vibration modes, indicating the highest oxygen vacancy concentration in this film.     

Preparation of Ba2YCu3O7-δ Thin Films with Preferred Orientation through an Organometallic Route

Superconducting Ba₂YCu₃O_7-δ thin films were prepared through an organometallic route. Single-phase Ba₂YCu₃O_7-δ thin films with preferred orientation were successfully prepared on SrTiO₃ (100) single-crystal substrates at 800°C by a dip coating method using partially hydrolyzed Ba-Y-Cu organometallic solutions. Preferentially oriented Ba₂YCu₃-O_7-δ thin films were also prepared on MgO (100) substrates. By controlling the partial hydrolysis conditions, a coating solution for precursor thin films was kept accurately at the stoichiometric composition. The use of ozone gas during the pyrolysis of the precursor thin films was found to suppress the formation of BaCO₃. Ba₂YCu₃O_7-δ thin films with c -axis orientation perpendicular to a SrTiO₃ (100) substrate, which were heat-treated at 900°C for 15 min, exhibited a superconductivity transition with an onset of 90 K and an end of 75 K.     

Pb-Diffusion Barrier Layers for PbTiO3 Thin Films Deposited on Si Substrates by Metal Organic Chemical Vapor Deposition

The interfaces between metal organic chemical vapor deposited PbTiO₃ thin films and various diffusion barrier layers deposited on Si substrates were investigated by transmission electron microscopy. Several diffusion barrier thin films such as polycrystalline TiO₂, amorphous TiO₂, ZrO₂, and TiN were deposited between the PbTiO₃ thin film and Si substrate, because the deposition of PbTiO₃ thin films on bare Si substrates produced Pb silicate layers at the interface irrespective of the deposition conditions. The TiO₂ films were converted to PbTiO₃ by their reaction with diffused Pb and O ions during PbTiO₃ deposition at a gubstrate temperature of 410°C. Further diffusion of Pb and O induces formation of a Pb silicate layer at the interface. ZrO₂ did not seem to react with Pb and O during PbTiO₃ deposition at the same temperature, but the Pb and O ions that diffused through the ZrO₂ layer formed a Pb silicate layer between the ZrO₂ and Si substrate. The TiN films did not seem to react with Pb and O ions during the deposition of PbTiO₃ at 410°C, but reacted with PbTiO₃ to form a lead-deficient pyrochlore during postdeposition rapid thermal annealing at 700°C. However, TiN could effectively block the diffusion of Pb and O ions into the Si substrate and the formation of Pb silicate at the interface.     

Metal Propionate Synthesis of Magnetoresistive La1−x(Ca,Sr)xMnO3 Thin Films

A flexible chemical solution deposition (CSD) method for the preparation of magnetoresistive La_1−x (Ca,Sr)x MnO₃thin films based completely on metal propionates is pre-sented.A number of polycrystalline thin films with varying stoichiometries were deposited on different substrate ma-terials at temperatures between 550° and 850°C. The crys-tallization behavior on selected substrates was found to de-pend on the thin film stoichiometry. Magnetoresistivity and magnetization were measured as a function of temperature. For the selected samples, a magnetic Curie temperature TC, a metal–semiconductor transition, and magnetoresistive behavior were observed. These measurements demon-strated that La_1−x(Ca,Sr)x MnO₃ thin films with properties well known from films deposited by PLD or sputtering can be prepared by a simple, propionate-based CSD method.     

Liquid Precursor Route for Hetero-epitaxy of Zr(Y)O2 Thin Films on (001) Cubic Zirconia

ZrO₂–3 mol% Y₂O₃„single-crystal” thin films with multiple variants were epitaxially formed on (100) cubic zirconia substrates. The films were prepared by spin-coating an aqueous zirconium acetate/yttrium nitrate solution onto the cubic zirconia substrates and subsequently heat-treated at temperatures between 1100° and 1400°C. Electron diffraction and dark-field TEM observations showed that the film has tetragonal symmetry and consists of 50–100 nm variants with their c-axes aligned with one of the three substrate cube axes. Unrelaxed strain energy estimates indicate that the two variants with their c ₁-axis parallel to the substrate/thin film interface are energetically favorable.     

Synthesis of Lead Barium Niobate Powders and Thin Films by the Sol-Gel Method

Crack-free, dense, and transparent Pb_0.6Ba_0.4Nb₂O₆ (PBN60) thin films have been prepared by a sol-gel method with metal alkoxides and metal acetate. A homogeneous and stable precursor solution was obtained from Ba metal, Pb(CH₃COO)₂, and Nb(OEt)₅ in 2-methoxyethanol. PBN60 powder crystallized to the hexagonal phase at 600°C and then completely transformed to the orthorhombic phase of the tungsten bronze structure at 1250°C. The hexagonal phase was formed on SiO₂ glass, MgO(lOO), and sapphire(R) substrate at 600°C, while the orthorhombic phase was only on a sapphire(C) substrate. Orthorhombic PBN60 films with c -axis preferred orientation were successfully synthesized on sapphire(C) substrates at 600°C.     

Hydrothermal Processing of PbTiO3 and PbTiO3/Polymer Thin Films from Titanium Metallo-organic Precursors

PbTiO₃ and PbTiO₃/polymer thin films were synthesized from metallo-organic precursors on metallized quartz substrates. Titanium dimethoxy dineodecanoate (TDD) was spin-cast onto the substrates and converted to polycrystalline TiO₂ via hydrolysis in deionized water for 5 h at 80°C. Polycrystalline PbTiO₃ films were then formed by reacting the TiO₂ films for 4 h at 200°C in aqueous solutions of KOH and Pb(CH₃COO)₂·3H₂O. Low KOH concentrations suppressed film coarsening, thereby facilitating the formation of fine-grain continuous PbTiO₃ films. PbTiO₃/polymer thin films were processed as above after first dissolving TDD and a polystyrene/polybutadiene block copolymer in p -xylene. PbTiO₃ and PbTiO₃/polymer films had relative permittivities of ≈56 and 34 and dielectric strengths of ≈250 and 850 kV/cm, respectively.     

Synthesis and Preparation of Lanthanum Aluminate Target for Radio-Frequency Magnetron Sputtering

A polycrystalline LaAlO₃ target for the radio-frequency (rf) magnetron sputterings of LaAlO₃ thin films has been prepared. These films serve as a buffer layer for high- T _c YBa₂Cu₃O_{7– x} superconducting thin films on Si. Synthesis of lanthanum aluminate powder from a mixture of La₂O₃ and Al₂O₃ powders was performed by calcining from 1000° to 1600°C in air. Characterization of the calcined powders by X-ray diffraction indicates that full development of LaAlO₃ phase was evident in the sample calcined for 3 h at 1600°C in air. A polycrystalline LaAlO₃ target was prepared by heat treatment at 1500°C for 2 h in air after pressureless sintering at 1750°C for 3 h in Ar. Thin films of the LaAlO₃ on Si (100) were obtained by rf magnetron sputtering using the target and oxygen-annealing the as-deposited films.     

Excimer Laser Crystallized (Pb,La)(Zr,Ti)O3 Thin Films

A KrF pulsed excimer laser (248 nm) was utilized to crystallize sputtered La-modified Pb(Zr,Ti)O₃ (3:30:70) (PLZT) films on LaNiO₃-coated silicon substrates. The film surface was irradiated with defocused laser pulses in an oxygen ambient at various substrate temperatures. Polycrystalline, phase pure perovskite PLZT thin films were produced for substrate temperatures of 250°C and higher. The dielectric constant and loss tangent values of laser-assisted crystallized (10 min exposure at 10 Hz using a substrate temperature of 400°C) PLZT thin films at 10 kHz were 406 and 0.027; in comparison, rapid thermal annealed films (annealed at 700°C for 1 min) showed values of 400 and 0.021, respectively. Laser crystallized films exhibited a remanent polarization value of 14 μC/cm² with a coercive field |( E _+c+ E _−c)|/2 of 95 kV/cm.     

Epitaxial Thin Film Growth of Lanthanum and Neodymium Aluminate Films on Roll-Textured Nickel Using a Sol-Gel Method

As part of an effort to develop a new, non-vacuum-processed substrate for high current superconducting films, thin films of LaAlO₃ and NdAlO₃ were deposited on biaxially textured (100) nickel substrates using a solution deposition technique. On heating to 1150°C in Ar-4% H₂ for 1 h, epitaxial films were obtained. Out-of-plane alignment was confirmed by obtaining rocking curves of the (002) plane of the LaAlO₃ (full width at half-maximum (fwhm) = 7.2°) and the NdAlO₃ (fwhm = 5.8°) films. In-plane alignment was demonstrated by obtaining phi scans of the (110) plane of the LaAlO₃ (fwhm = 13.4°) and the NdAlO₃ (fwhm = 8.8°) films. Grain alignment in the films is approximately equivalent to the alignment of the Ni substrate. Analysis of pole figures indicated that in both films there are two in-plane orientations present, the major being (001)[100] and the minor (001)[110].     

Two-Layer Crystallization of Amorphous YMnO3 Thin Films on Si (100) Substrates

During a rapid thermal annealing process at 850°C in a N₂ ambient, an as-deposited amorphous YMnO₃ thin film on Si (100) substrates was crystallized with two distinct layers. High-resolution transmission electron microscopy showed a top layer of c -axis-oriented YMnO₃ and a bottom layer of polycrystalline YMnO₃ in the 100-nm-thick YMnO₃ thin film. The abrupt change of the crystalline orientation from the c -axis-preferred orientation to the random orientation is caused primarily by high stress induced by the c -axis-oriented YMnO₃ layer. High-resolution X-ray diffraction showed that the c -axis-oriented YMnO₃/polycrystalline YMnO₃ structure effectively relieved the stress.     

Growth of Single-Crystal and Polycrystalline Thin Films of MgAl2O4 and MgFe2O4

Single-crystal and polycrystalline films of Mg-Al₂O₄ and MgFe₂O₄ were formed by two methods on cleavage surfaces of MgO single crystals. In one procedure, aluminum was deposited on MgO by vacuum evaporation. Subsequent heating in air at about 510°C formed a polycrystalline γ-Al₂O₈ film. Above 540°C, the γ-Al₂O, and MgO reacted to form a single-crystal MgAl₂O₄ film with {001} MgAl₂O₄‖{001} MgO. Above 590°C, an additional layer of MgAl₂O₄, which is polycrystalline, formed between the γ-Al₂O₃ and the single-crystal spinel. Polycrystalline Mg-Al₂O₄ formed only when diffusion of Mg²⁺ ions proceeded into the polycrystalline γ-Al₂O₃ region. Corresponding results were obtained for Mg-Fe₂O₄. MgAl₂O₄ films were also formed on cleaved MgO single-crystal substrates by direct evaporation, using an Al₂O₃ crucible as a source. Very slow deposition rates were used with source temperatures of ∼1350°C and substrate temperatures of ∼800°C. Departures from single-crystal character in the films may arise through temperature gradients in the substrate.     

(100)-Orientation of Pseudocubic Perovskite-Type LaNiO3 Thin Films on Glass Substrates via the Sol–Gel Process

(100)-oriented, perovskite-type LaNiO₃ thin films were prepared on SiO₂ glass substrates by the sol–gel method. Effects of thermal processing on the orientation, surface morphology, and electrical properties of the films were investigated. The nearly complete (100)-orientation was achieved by drying the films at temperatures above 350°C before a final heat treatment at 700°C. It was the key to heat the substrate from the other side to obtain the oriented films. A possible mechanism of the orientation is proposed on the basis of surface energies of the films and the substrates and the interfacial energy between them.     

Structural Variation of the BaTi4O9 Thin Films Grown by RF Magnetron Sputtering

BaTi₄O₉ thin films were grown on a Pt/Ti/SiO₂/Si substrate using rf magnetron sputtering and the structure of the thin films were then investigated. For the films grown at low temperature (≤350°C), an amorphous phase was formed during the deposition, which then changed to the BaTi₅O₁₁ phase when the annealing was conducted below 950°C. However, when the annealing temperature was higher than 950°C, a BaTi₄O₉ phase was formed. On the contrary, for the films grown at high temperature (>450°C), small BaTi₄O₉ grains were formed during the deposition, which grew during the annealing. The homogeneous BaTi₄O₉ thin films were successfully grown on Pt/Ti/SiO₂/Si substrate when they were deposited at 550°C and subsequently rapid thermal annealed at 900°C for 3 min.     

Characterization of Photoluminescent (Y1–xEux)2O3 Thin Films Prepared by Metallorganic Chemical Vapor Deposition

The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium-doped Y₂O₃ (Y_{1– x} Eu _x )₂O₃ thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y_{1– x} Eu _x )₂O₃ thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6-tetramethyl–3,5-heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 × 10³ Pa)) and low substrate temperatures (500°–700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y₂O₃, grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y_{1– x} Eu _x )₂O₃ was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area-reduction effect.     

Synthesis of KTiOPO4 (KTP) Thin Films Using Metallo-organics

Crack-free and highly transparent KTiOPO₄ (KTP) thin films were synthesized by the sol-gel method using a homogeneous precursor solution prepared from ("BuO)₂-P(O)(OH), Ti(OEt)₄, and KOEt in EtOH. Precipitated powders from the solution crystallized directly to KTP above 550°C. Polycrystalline KTP thin films were obtained at 600°C on various substrates. On NdAlO₃(100) substrates, KTP films with (101) and (240) preferred orientations were formed at 600°C. KTP films on glass substrates showed a refractive index of 1.75 and an absorption edge of 350 nm. KTP films exhibited the second harmonic generation of the 532 nm light on irradiaton with 1064 nm light.     

Synthesis of Highly Oriented Lead Zirconate–Lead Titanate Film Using Metallo-organics

Crack-free Pb(Zr,Ti)O₃ (PZT) thin films with preferred orientation were prepared successfully on MgO (100), SrTiO₃ (100), and Pt/Ti/SiO₂/Si substrates from metal alkoxide solutions. Calcination of precursor films in a H₂O─-O₂ gas mixture was found to be effective not only for low-temperature crystallization of perovskite PZT, but also for obtaining the preferred orientation of PZT films. Single-phase PZT films with high preferred orientation were synthesized on MgO (100) and Pt/Ti/SiO₂/Si substrates at 550° and 600°C for 2 h, respectively. The PZT film on the Pt/Ti/SiO₂/Si substrate showed a permittivity of 520, tan δ of 0.03, a remanent polarization of 24 μC/cm², and a coercive field of 54 kV/cm.     

Phase Separation of Alkoxy-derived (Ti,Sn)O2 Oriented Thin Films

Oriented (Ti,Sn)O₂ thin films with modulated microstructure were successfully synthesized on sapphire substrates by using sol–gel processing combined with spinodal decomposition. The degree of orientation of (Ti_0.5Sn_0.5)O₂ thin films increased in the following order: sapphire (0001), (11     0), and (01     2). (Ti_0.5Sn_0.5)O₂ thin films underwent spinodal decomposition at 900°C by annealing. The variation of the 2theta value of the 202 reflection of (Ti_0.5Sn_0.5)O₂ films showed the typical behavior of spinodal decomposition. The rate of spinodal decomposition of the (Ti_0.5Sn_0.5)O₂ films on sapphire (11     0) was faster than that on sapphire (01     2) substrates. The characteristic modulated microstructure was observed for the spinodally decomposed (Ti_0.5Sn_0.5)O₂ films on sapphire (01     2) substrates by transmission electron microscopy. (Ti_0.3Sn_0.7)O₂ films on sapphire (01     2) substrates were binodally decomposed during annealing at 1300°C.