Oriented Lead Zirconate Titanate Research Articles

Highly (111) oriented lead zirconate titanate thin films deposited using a non-polymeric route

This paper presents a simple non-polymeric solution route and its process conditions for depositing reproducible very highly (111) oriented lead zirconate titanate Pb(Zr 0.53, Ti 0.47)O 3 (abbreviated PZT) thin films, with an excellent combination of electrical properties, on Pt(111)/Ti/SiO 2/Si wafers. Unlike sol–gel derived routes, non-polymeric methods do not rely on polymerisation in solution of metal precursors, so that the viscosity of the starting sol remains constant, which is important for good reproducibility in the commercialisation of ‘micro electro mechanical systems’ (MEMS). The route presented uses Pb 2-ethylhexanoate, Ti (diisopropoxide) bis (2,4-pentanedionate), and Zr n-butoxide, mixed in the solvent xylene. Sol preparation is performed in an open atmosphere, without the need for refluxing. Crystallisation was carried out both by conventional furnace annealing and rapid thermal annealing (RTA). With furnace annealing, precursor solutions with 30% excess Pb produced films with satisfactory ferroelectric properties; whilst by reaching the onset of perovskite crystallisation rapidly with RTA, starting solutions with only 10% Pb excess produced perovskite PZT films with excellent electrical properties (relative permittivity ε r∼1700, remnant polarisation P r∼20 μC/cm 2 and coercive field E c∼55 kV/cm), with a high degree of (111) orientation. Both (111)/(100) and (111)/(110) X-ray diffraction peak intensity ratios were above 100. The films were 1 μm thick.

Preparation and Characterization of Epitaxial Lead Zirconate Titanate Films on Pt/(Ti, Al)N/TiN/Si Substrates by Metalorganic Chemical Vapor Deposition

[001]-Oriented lead zirconate titanate (PZT) thin films were epitaxially grown on Pt/titanium-aluminum-nitride (TAN)/titanium-nitride (TiN)/Si substrates by metalorganic chemical vapor deposition (MOCVD). Epitaxial thin films of TAN were formed as buffer layers on the Si substrates by pulsed-laser deposition (PLD) using TiN seed layers. Oxidation of the TAN was prevented by a sufficiently thick epitaxial Pt layer between the PZT and the TAN, thereby improving the crystallinity and electrical properties of the PZT films. The epitaxial PZT films had a dielectric constant of 697 and a remanent polarization of 38 µC/cm2.

Domain switching characteristics of preferentially oriented lead zirconate titanate thin films

Domain switching characteristics of preferentially oriented lead zirconate titanate thin films

Orientation control in PZT/Pt/TiN multilayers with various Si and SiO2 underlayers for high performance ferroelectric memories

To suppress fluctuation in capacitor characteristics, highly oriented lead zirconate titanate (or PbZrxTi1−xO3 (PZT) films are required in ultralarge scale ferroelectric memories whose capacitor size is comparable to PZT grain size. The (111) orientation, which is closely related to spontaneous polarization, is achieved when PZT film is grown on highly (111) oriented platinum film. The degree of Pt(111) orientation is dependent on the crystallinity of the underlying TiN barrier metal. Furthermore, the crystallinity of the TiN is strongly dependent on the type of underlying material. The crystallinity of the TiN film grown on amorphous Si is much better than the crystallinity achieved on thermally oxidized Si. The surface energy difference between the TiN and underlayer may affect the growth mode of the TiN films. The crystallinity of the TiN film on rougher Si surfaces, such as in situ crystallized poly-Si, is inferior to the crystallinity observed on amorphous Si. Therefore, a smooth Si buffer layer is required underneath the capacitor to improve performance of the PZT/Pt/TiN capacitor. The modified planarized stacked structure presented in this article uses a postannealed crystalline Si as a buffer layer underneath the capacitor.

Growth of highly oriented Pb(Zr, Ti)O3 films on MgO-buffered oxidized Si substrates and its application to ferroelectric nonvolatile memory field-effect transistors

We have grown highly oriented lead zirconate titanate [Pb(Zr, Ti)O3 or PZT] films on oxidized silicon substrates using a thin MgO buffer layer (7–70 nm thick). Ferroelectric nonvolatile memory field-effect transistors (FETs) were successfully fabricated using the metal/PZT/MgO/SiO2/Si structure in conjunction with radio-frequency sputter deposition of PZT and MgO films. The fabricated devices show excellent performance in ferroelectric polarization switching and memory retention. The results indicate that a thin MgO buffer serves well not only as a template layer for the growth of oriented PZT films on amorphous substrates, but also as a diffusion barrier between a ferroelectric and a substrate during device fabrication, protecting the SiO2/Si interface and the FET channel region.

Lattice disorder and recovery in Pb implanted PZT thin films

Epitaxial 〈0 0 1〉 oriented lead–zirconate–titanate (PZT) thin films (Pb 0.98Zr 0.54Ti 0.46O 3) were prepared by sputtering onto (1 0 0) SrTiO 3 and (1 0 0) MgO substrates at 570 ∘C. Rutherford backscattering (RBS) analysis of the as-deposited thin films revealed that the Pb content increased with increasing O 2 partial pressure in the Ar–O 2 sputter gas and reached a value of Pb 0.98 under optimized conditions. Channeling measurements (RBS-C) resulted minimum yield values of 7%. The dechanneling component was attributed to stacking faults as determined from energy-dependent dechanneling measurements. Implantation of 260 keV Pb ions at room temperature at a dose of 5×10 13 Pb +/ cm 2 amorphized the thin films. Solid phase epitaxial regrowth occurred in the temperature region between 400 ∘C and 500 ∘C. At temperatures above 500 ∘C the recovery is retarded while at the same time a disturbed interface appeared. Besides the amorphous region in the range of the implanted layer, ion implantation produces enhanced dechanneling throughout the total film thickness, which is attributed to dislocations.

Preparation and Pyroelectric Characteristics of Pb(Zr, Ti)O3 Thin Films Grown by Metalorganic Chemical Vapor Deposition

Highly (001), (110) and (111)-oriented lead zirconate titanate (PZT) thin films with a thickness of 2 µ m were grown on Pt(100)/MgO(100), RuO2(110)/MgO(100) and Pt(111)/SiO2/Si(100) substrates, respectively, by metalorganic chemical vapor deposition. The pyroelectric properties of these films were investigated in relation to application to infrared sensors. Pyroelectric currents were detected on three differently oriented films without poling treatment. Pyroelectric coefficients of (001), (110) and (111)-oriented films were 3.0, 1.0 and 0.5×10-8 C/cm2· K, respectively, due to strong dependence on their crystalline orientations. With poling treatment, these values were increased and attained values 3 times as large as those of as-grown films for (111)-oriented films.

Kinetic energy distributions of ions ejected during laser ablation of lead zirconate titanate and their correlation to deposition of ferroelectric thin films

Highly oriented lead zirconate titanate (PZT) has been deposited on MgO(100) by pulsed laser deposition, using Nd:YAG (532 nm, 4 ns) laser radiation, followed by subsequent annealing at 570°C. An estimatedPbZr + Ti ratio of 0.86, obtained from an as-deposited calibration curve, showed the formation of a lead depleted PZT thin film. The full-width half-maximum (FWHM) of the PZT(001) peak decreased sharply as a function of increasing laser fluence indicated good crystallinity at 12 J/cm2 (FWHM 0.17°). The effect of extended laser irradiation on the durability of the target, the plume constituents and the stoichiometry of the PZT thin films was investigated by electron probe microanalysis and energy-dispersive mass spectrometry: The laser plasma contained excess quantities of Pb+ ions at low fluences (1.67 J/cm2) whilst congruent transfer was observed under high fluence (> 6 J/cm2) conditions. High laser fluenceand the presence of oxygen serves to stabilise the PZT stoichiometry at temperatures (i.e. 570°C) which promote perovskite phase formation.Kinetic energy (KE) and mass spectrometric measurements were also used to characterise ionic species generated in the ablation plume. Pb+, Ti+, TiO+, Zr+, ZrO+ and O+ ions were detected and showed a trimodal KE distribution with the lowest energy peak constant between 10–40 eV. ZrO+ ions were also found to be particularly stable within the laser ablation plasma with respect to TiO+ species. At moderate laser fluences (< 10 J/cm2) mean kinetic energies of up to 180 eV of the ions were detected. The average KE increased linearly with laser fluence, with ion acceleration by electron-ion space charge interaction the most likely mechanism.

Growth of [111]-Oriented Lead Zirconate Titanate Thin Film with Smooth Surface to Improve Electrical Properties

[111]-Oriented lead zirconate titanate (PZT) films with smooth surfaces were successfully grown on (111)-oriented polycrystalline Pt substrates after in-situ Ar-plasma cleaning by low-temperature reactive sputtering and rapid thermal annealing. The Pb composition was stoichiometrically controlled not only for total composition but also in the depth direction by low-temperature reactive sputtering. A (111)-oriented perovskite-phase PZT film with a very smooth surface was then obtained by rapid thermal annealing. The leakage current of quasi-epitaxial PZT films was markedly reduced to 10-7 A/cm2 and the equivalent SiO2 layer thickness of around 0.4 nm was obtained for the fatigue-free PZT films thinner than 100 nm.

Oriented Lead Zirconate Titanate thin Films: Characterization of Film Crystallization

AbstractThrough systematic variation of film processing temperature and time, we have characterized the pyrochlore to perovskite crystallization process of solution-derived PZT 20/80 thin films. The ≈3000 Å thick films were prepared by spin deposition using &lt;100&gt; single crystal MgO as the film substrate. By controlled rapid thermal processing, films at different stages in the perovskite crystallization process were prepared with the tetragonal PZT 20/80 phase being &lt;100&gt;/&lt;001&gt; oriented relative to the MgO surface. An activation energy for the conversion process of 326 kJ/mole was determined by use of an Arrhenius expression using rate constants found by application of the method of Avrami. The activation energy for formation of the PZT 20/80 perovskite phase of the solution-derived films compared favorably with that calculated from data by Kwok and Desu [1] for sputter-deposited 3500 Å thick PZT 55/45 films. The similarity in activation energies indicates that the energetics of the conversion process is not strongly dependent on the method used for film deposition.

Preparation and electrical properties of MOCVD-deposited PZT thin films

Strongly [001] oriented lead zirconate-titanate [Pb(ZrxTi1−x)O3] thin films with tetragonal structure (0&amp;lt;x&amp;lt;0.52) have been successfully grown on (100)Pt/(100)MgO substrates by using metalorganic chemical vapor deposition (MOCVD). The metalorganic precursors were Pb(C2H5)4, Zr(DPM)4 and Ti(i-OC3H7)4. Scanning electron micrographs showed dense and noncolumnar growth with good surface morphology. The relative dielectric constants at room temperature were 200–350, and appeared to have less dependence on composition x than for PZT bulk ceramics. Typical D-E hysteresis loops which occur with PZT bulk ceramics were observed. Remanent polarizations were 30–40 μC/cm2. The coercive field decreased from 65 to 40 kV/cm with increases in Zr content. The pyroelectric coefficients without poling treatment were about 3×10−8 C/cm2 K, showing almost the same value as that of poled PZT bulk ceramics.