Characterization of hetero-epitaxial PZT capacitor

Abstract

A hetero-epitaxial Au/PbZr_0.48Ti_0.52O₃(PZT)/SrRuO₃(SRO) capacitor was fabricated on a single crystal SrTiO₃ (STO) substrate by pulsed laser deposition. An SRO buffer layer (a nucleation layer) was formed at the SRO/STO interface to ensure the highly epitaxial growth of the PZT and SRO films. An X-ray diffraction measurement revealed that the (00l) planes of the PZT and SRO grew parallel to the substrate surface. A transition layer of ～ 5 nm thickness was observed at the SRO/STO interface by high-resolution transmission electron microscopy (HR-TEM). This transition layer corresponds to the nucleation layer intentionally grown at the interface. Remanent polarization of the capacitor was 32.1 μC/cm² due to the good epitaxial growth of the films.     

Growth and characterization of epitaxial SrBi2Ta2O9 films on (110) SrTiO3 substrates

Abstract

SrBi₂Ta₂O₉ (SBT) is an attractive material for nonvolatile ferroelectric memory applications. In this paper we report on the deposition of highly epitaxial and smooth SrBi₂Ta₂O₉ films on (110) SrTiO₃substrates. The films were grown by pulsed laser deposition at temperatures ranging from 600 to 800°C and at various laser fluences from a Bi-excess SBT target. The background oxygen pressure was maintained at 28 Pa during the film deposition. Structural characterization of the films was performed by x-ray diffraction. Atomic force microscopy was used to investigate morphology and growth of the films. The films grew with preferred (115) or (116) orientation. The roughness was of the order of unit cell height. The films display a growth pattern resulting in corrugated film morphology.     

Influence of the growth temperature on the epitaxial quality of PbTiO3 films deposited in-situ by sputtering

Abstract

Thin films of lead titanate were prepared in-situ on SrTiO₃ substrates using radio-frequency magnetron sputter deposition. The epitaxial quality of the films has been studied as a function of the substrate temperature. Stoichiometric films have been obtained in the temperature range [550°C, 600°C]. The films deposited in the equilibrium zone have a high degree of c-axis oriented epitaxial crystalline structure as shown by X-ray diffraction in the 2θ/θ, θ, and ? scans configuration as well as by electron channeling pattern. The optimum conditions for growing epitaxial PbTiO₃ layers were determined. The crystallinity of films deposited at 550°C is suprior to those deposited at 600°C. The PbTiO₃ films grown at 550°C have a rocking curve full width at half maximum (FWHM) of 0.2°; Normaski optical and atomic force microscopy show that the surface is apparently free of grain boundaries and very smooth. The refractive index of these films has been evaluated from transmission spectra; it is very close to the bulk material value.     

Epitaxial ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 thin films on La0.7Sr0.3MnO3 bottom electrode

Epitaxial (001)-oriented 0.7Pb(Mg_0.33Nb_0.67)O₃-0.3PbTiO₃ (PMN-PT) thin films were deposited by pulsed laser deposition on vicinal SrTiO₃ (001) substrates using La_0.7Sr_0.3MnO₃ as bottom electrode. Detailed microstructural investigations of these films were carried out using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Polarization-field hysteresis curves were measured at room temperature. Spontaneous polarization P _s , remnant polarization P _r and coercive voltage V _c were found to be 25 μC/cm², 15 μC/cm² and 0.81 V, respectively. Field dependent dielectric constant measurements exhibited butterfly shaped curves, indicating the true ferroelectric nature of these films at room temperature. The dielectric constant and the dielectric loss at 100 kHz were found to be 238 and 0.14, respectively. The local piezoelectric properties of PMN-PT films were investigated by piezoelectric force microscopy and were found to exhibit a local piezoelectric coefficient of 7.8 pm/V.     

X-RAY DIFFRACTION OF FERROELECTRIC NANODOMAINS IN PBTIO3 THIN FILMS

ABSTRACT

X-ray diffraction constitutes a powerful technique with which to characterise ferroelectric domains. Here we describe the principles of ferroelectric nanodomain diffraction and present some results for PbTiO₃ thin films grown under tensile strain on two different substrates, with thicknesses below and above the critical thickness for strain relaxation. The combination of conventional and grazing incidence diffraction and the analysis of the scattering between Bragg peaks allowed the identification of a new polar symmetry in ultra-thin films with only anti-parallel 180° domains. Thick films showed tetragonal 90° ferroelectric/ferroelastic domains instead, with a depressed TC and a domain periodicity largely independent of temperature.     

Microstructure and epitaxial characteristics of PbTiO3 ferroelectric thin film on NaCI by mocvd

Abstract

Ferroelectric PbTiO₃ thin films have been epitaxially grown on (100) NaCl cleavage surface by MOCVD using tetraethyllead and titanium isopropoxide as precursors. The microstructures and epitaxial characteristics of as-grown thin films were investigated by means of transmission electron microscopy. TEM studies have shown that the epitaxial thin film was highly (001) oriented and even near single-crystal epitaxy if without a small volume of 45° rotated grains, the average grain size is around 1000 A. Lowangle grain boundary formed universally when islands coalesced during the early stage of epitaxial growth. A possible growth mechanism has been given to explain this epitaxial phenomenon by consideration of two-dimensional coincidence superlattice. 90° ferroelectric domains were also observed both in the large matrix grains and small 45° rotated grains.     

Epitaxial structure SrBi2Ta2O9<116> /SrTiO3<011> /Ce0.12Zr0.88O2<001> /Si<001> for ferroelectric-gate FET memory

Abstract

Epitaxial thin film growth of SrBi₂Ta₂O₉/SrTiO₃/Ce_0.12Zr_0.88O₂ on Si was studied, and this epitaxial layer structure was applied to fabrication of ferroelectric-gate field effect transistors (FETs). The films were prepared by a pulsed laser deposition technique and epitaxial growth was identified by x-ray diffraction. The devices exhibited excellent electrical performances: Capacitance-voltage characteristic of a metal-ferroelectric-insulator-semiconductor (MFIS) diode showed a retention longer than 10 days and I_d-V_g characteristic of an MFIS-FET showed 1 day retention. It is proved that the crystalline quality of ferroelectric thin films is of great importance to develop integrated devices with high performance.     

Epitaxial growth of multilayered (Bi,La)4Ti3O12/Pb(Zr,Ti)O3 ferroelectric thin films with different orientations

Epitaxial (Bi,La)₄Ti₃O₁₂ (BLT) thin films, epitaxial Pb(Zr,Ti)O₃ (PZT) thin films, and epitaxial multilayered BLT/PZT ferroelectric thin films with different orientations were prepared on SrTiO₃ (STO) single crystal substrates by pulsed laser deposition. From X-ray pole-figures and electron diffraction patterns, the epitaxial orientation relationships between BLT layers, PZT layers, and STO substrates were identified to be (1) BLT(001)//PZT(001)//STO(001), and BLT[110]//PZT[100]//STO[100] for the multilayered thin films on (001)-oriented STO substrates, and (2) BLT(118)//PZT(011)//STO(011), and $ {\text{BLT}}{\left[ {\overline{1} \overline{1} 0} \right]}//{\text{PZT}}{\left[ {100} \right]}//{\text{SrTiO}}_{3} {\left[ {100} \right]} $ for the multilayered films on (011)-oriented STO substrates. Tri-layered films of the same compositions showed well-defined hysteresis loops as well as a high fatigue resistance up to 1?×?10¹⁰ switching cycles.     

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.     

Structure and Properties of Preferential (110) Orientation BiFeO3 Thin Films by Sol-Gel Method

Abstract

Multiferroic materials, coexisting of ferroelectric, ferromagnetic and ferroelastic properties, possess potential applications in functional devices. BiFeO₃ (BFO) is a unique room temperature multiferroic material with high ferroelectric Curie temperature and Neel temperature. The BFO thin films were prepared on Si (111) substrate by sol-gel method in this paper. XRD analyses show that the thin films exhibit pure phase and preferred (100) orientation when annealing temperature is 500?°C. Field emission scanning electron microscopy shows that the crystallization degree of the films is getting better with the increase of annealing temperature. The thickness of the sample is about 400?nm. The hysteresis loop of BFO films annealing at 500?°C show 1.93?µC/cm² remnant polarizations. However, the hysteresis loop is not perfect, which may be caused by a large leakage current. The magnetic hysteresis loop of BFO films is tested as well, indicating that the BFO film is antiferromagnetic and the residual magnetization (Mr) and coercive field (Hc) of the BFO films were 0.054?emu/g and 1026.4?Oe, respectively.     

Deposition and characterization of low-loss epitaxial non-linear dielectric thin films for microwave devices

Abstract

Oxide ferroelectric thin films for frequency-tunable microwave devices, in which the dielectric constant of the non-linear dielectric is varied by application of electric fields, have been deposited using PLD. We have fabricated single phase epitaxial Ba_0.6Sr_0.4TiO₃ and KTaO₃ thin film capacitors for applications at 300K and 77K, respectively. Single phase KTaO₃ films were obtained only with excess potassium source in the target along with KTaO₃ perovskite phase. The films have been characterized for structure and morphology by X-ray diffraction and AFM. The dielectric properties were measured in the low frequency range from 100 kHz to 10 MHz, using interdigitated capacitors. Low loss tangents (0.002 at 300K) were observed for highly oriented Ba_0.6Sr_0.4TiO₃ films. The importance of low losses for various devices is discussed and the dielectric constants, loss tangents and tunability of these films are reported in this paper.     

SYNTHESIS AND CHARACTERIZATION OF NICKEL FERRITE-BARIUM TITANATE CERAMIC COMPOSITES

ABSTRACT

Magnetoelectric composites were synthesized from piezoelectric BaTiO₃ and ferrimagnetic NiFe₂O₄. These two phases are mixed, mechanically milled and heat treated. A characterization is made by means of electronic microscopy and x-ray diffraction. The results of the magnetic, electric, ferroelectric and piezoelectrical response of two different compositions are obtained. The composites are superparamagnetic in all the measured temperature range. It was observe a magnetic change induced by a structural transition of the ferroelectric phase. The composites behaves as an acceptable mechanical resonator when the content of the ferroelectric phase is equal or greater than 60 wt.%.     

Epitaxial behavior and interface structures of BSTO thin films

Abstract

Ferroelectric Ba_(1-x)Sr_xTiO₃ (x = 0.5 and 0.25) thin films were grown on (001) LaAlO₃ by using pulsed laser ablation. Extensive x-ray diffraction and selected area electron diffraction reveal that the as-grown films were (001) oriented with a good in plane relationship of <100>_BSTO // <100>_LAO. Rutherford Backscattering Spectroscopy ion-channeling studies suggested that the films had excellent epitaxial quality and crystallinity with an ion beam minimum yield χ_min of only 2.6%. Atomically sharp interfaces were seen by cross-sectional high-resolution electron microscopy, indicated that the density of misfit dislocations was consistent with the lattice mismatch from the theoretical calculation.     

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).     

Preparation of hafnium oxide thin films by sol–gel method

Hafnium oxide (HfO₂) films were grown on SiO₂/Si substrates by a sol–gel method, and their crystalline structure, microstructure and electrical properties were investigated. X-ray diffraction analysis indicated that the monoclinic HfO₂ films could be obtained by annealing at 500 °C. A transmission electron microscopy (TEM) image showed that the films were grown as a spherulite grain structure with a mean grain size of approximately 15 nm. The dielectric constant of the HfO₂ films of 300 nm was approximately 21.6, and the current–voltage measurements showed that the leakage current density of the HfO₂ films was approximately 1.14?×?10^?5 A/cm² at an applied electric field of 100 kV/cm. The sol–gel method-fabricated HfO₂ films are concluded to be feasible for MEMS applications, such as capacitive-type MEMS switches.     

EFFECT OF ANNEALING ON THE ELECTRICAL PROPERTIES OF SrTiO3 THIN FILMS PRODUCED BY ION BEAM SPUTTERING

ABSTRACT

Thin film capacitors with SrTiO₃ (STO) as dielectric and Pt as electrode material have been prepared by ion beam sputtering. The as-deposited film is amorphous and exhibits a crystallization temperature around 321°C as proved by X-ray diffraction. The effect of post annealing on the crystalline quality of the films was systematically studied by x-ray diffraction and Atomic Force microscopy (AFM). The temperature and frequency dependent dielectric properties were measured from 30°C to 200°C and 0.01 Hz to 10⁵ Hz, respectively. The influence of the microstructure of SrTiO₃ thin films on their electrical properties was investigated through an extensive characterization. The electrical properties of SrTiO₃ films appear to be strongly depending on the annealing temperatures. The capacitance voltage (C-V) characteristics reveal an improvement of capacitance density with increasing the annealing temperature.     

Piezo- and pyroelectric properties of lead scandium tantalate thin films

Abstract

This paper discusses the piezo- and pyroelectric properties of lead scandium tantalate thin films prepared by modified sol-gel technology. Films were deposited on Pt/Ti/SiO₂/Si-sub-strates at 530–630 °C. The quality of the thin films was optimized by design of both the deposition conditions and the solution chemistry. These approaches include spin coating speed, drying plus crystallization temperature and time, drying atmosphere, the use of rapid thermal annealing, PST sol composition, Pb-excess concentration and mixing method. The finished thin films were characterized by optical microscopy, X-ray diffraction, atomic force microscopy, and pyroelectric measurements at 30°C under a DC-bias. Piezo-response AFM was conducted on PST to monitor various piezoelectric responses, which depend on the micro-structure of the film. The maximum pyroelectric figure-of-merit F_D was 3.85×10^?5 Pa^?1/2 at 30°C and 1 kHz under a 35 V DC-bias.     

Microstructural Properties of Ba0.6Sr0.4TiO3/RuO2 Multi-Layers Grown on MgO and YSZ by Pulsed-Laser Deposition

The microstructure of Ba_0.6Sr_0.4TiO₃ (BST)/RuO₂ multi-layers grown on (100) MgO and (100) YSZ substrates, respectively, by pulsed-laser deposition (PLD) has been studied by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The RuO₂ films deposited at 700°C adopt epitaxial relationships with both substrates. The epitaxial films on (100) MgO consist of two variants with an orientation relationship given by (110) RuO₂//(100) MgO and [001] RuO₂//[011] MgO. The epitaxial films on (100) YSZ contain four variants with an orientation relationship given by (200) RuO₂//(100) YSZ and [011] RuO₂//[001] YSZ. The BST films deposited on the RuO₂ electrode are epitaxial on the (200) RuO₂ films deposited on YSZ, and non-epitaxial on the (110) RuO₂ films deposited on MgO. The epitaxial relationship between the BST and (200) RuO₂ films can be described as (111) BST//(200) RuO₂ and [1&1macr;0] BST//[011] RuO₂. The BST films contain at least four variants. The growth and microstructural properties of the multi-layer structures can be understood based on geometrical consideration of the crystal structures.     

ELECTRON BACKSCATTER DIFFRACTION AND PIEZORESPONSE FORCE MICROSCOPY STUDY OF BULK AND THIN FILM PZT SAMPLES

ABSTRACT

In this work, bulk and PZT thin films have been investigated with electron backscatter diffraction (EBSD) and piezoresponse force microscopy (PFM). After depositing a thin carbon layer to negate the effects of charging, EBSD was able to map the grain and domain orientations across the ferroelectric materials, showing features smaller than 100 nm. In addition, PFM was also performed in order to obtain quantifiable maps of the ferroelectric response. Both techniques indicated the presence of random grain and domain orientation in PZT(30/70) films deposited onto ITO/glass substrates. For these films, both single and multi domain grains were observed.     

Tin Oxide Thin Films Grown on the (1012) Sapphire Substrate

Tin oxide thin films were deposited on the R-cut sapphire substrate by the electron-beam evaporation of a ceramic SnO₂ source. X-ray diffraction and transmission electron microscopy studies revealed that the films deposited at lower temperatures were amorphous while those grown at temperatures above 350°C consisted of the -SnO phase with the PbO type structure. Epitaxial -SnO films on the R-cut sapphire substrate were obtained when deposited at 600°C. Atomic force microscopy studies showed that films deposited at low temperature have a smooth surface, while epitaxial SnO films deposited at high temperatures (above 600°C) have a relatively rough surface. The atomic mobilities in the films at the various deposition temperatures and the lattice mismatch between the films and the substrates ultimately determine the microstructure and surface mophology. X-ray photoelectron spectroscopy analysis shows that the Sn/O ratios are 52.7/47.6 for the amorphous film deposited at the ambient temperature (30°C), 48.8/51.2 for the films deposited at 350°C, and 49.2/50.8 for the epitaxial film deposited at 600°C. Electrical properties were determined by four point probe measurements.