Ferroelectric Properties Of PZT Films Research Articles

Structural, Morphologic, and Ferroelectric Properties of PZT Films Deposited through Layer-by-Layer Reactive DC Magnetron Sputtering

Lead zirconate titanate (PZT) is a widely used material with applications ranging from piezoelectric sensors to developing non-volatile memory devices. Pb(ZrxTi1−x)O3 films were deposited by DC reactive magnetron sputtering at a temperature range of (500–600) °C. X-ray diffraction (XRD) indicated the perovskite phase formation in samples synthesized at 550 °C, which agrees with Raman data analysis. Scanning electron microscopy (SEM) measurements supplemented XRD data and showed the formation of dense PZT microstructures. Further X-ray photoelectron spectroscopy (XPS) analysis confirmed that the Zr/Ti ratio corresponds to the Pb(Zr0.58Ti0.42)O3 content. Dielectric measurement of the same sample indicated dielectric permittivity to be around 150 at room temperature, possibly due to the defects in the structure. P-E measurements show ferroelectric behavior at a temperature range of (50–180) °C. It was found that the remnant polarization increased with temperature, and at the same time, coercive field values decreased. Such behavior can be attributed to energetically deep defects.

Influence of substrate stress on in-plane and out-of-plane ferroelectric properties of PZT films

Solution-deposited ferroelectric films often are under mechanical stress due to the difference in thermal expansion coefficients between films and substrate materials. Knowledge of how stress changes the ferroelectric response under different actuation conditions is essential when selecting a substrate for film deposition. Here, a comparative study of the ferroelectric properties of lead zirconate titanate thin films on transparent fused silica glass and sapphire substrates is presented. Sapphire exerts a compressive in-plane stress on the film, favoring an out-of-plane domain orientation, while fused silica causes tensile in-plane stress and a predominantly in-plane domain configuration. As expected, the out-of-plane polarization is high under in-plane compressive stress but reduced by a factor of nearly 4 by in-plane tensile stress. In contrast, the in-plane polarization shows an unexpectedly weak stress dependence. It is larger by only about 10% under tensile stress compared to compressive stress. Permittivity increases when the major domain orientation does not coincide with the electric field. The observations are explained based on a model taking into account the crystallographic structure of the film.

Preparation and Ferroelectric Properties of PZT Multilayer Film

The PZT multilayer films were prepared by sol-gel method. The effects of formamide content, crystallization temperature and number of layers on the microstructure and ferroelectric properties of PZT films were investigated by optical microscopy, XRD, AFM and SEM. When the content of formamide in the PZT precursor solution is 0.34% by weight, the surface morphology is flat, and the film formation and crystallization are highest when the crystallization temperature is 690 °C. The surface of the four-layer film has low undulation, less impurities, and uniform particle size and particle distribution on the surface of the film. The maximum undulation of the film is 10 nm, the average undulation is 6 nm, and the ferroelectric domain is dominated by 20° domain and 200° domain. When the polarization inversion voltage is 8.0V, the loaded pattern is polarized and flipped, and the flip angle is about 180°. The inverted ferroelectric domain is very stable.

Effect of the lead oxide content on the microstructure and properties of PZT films obtained by RF magnetron sputtering

Experimental studies of the influence of lead oxide as well as temperature and time of heat treatment on the microstructure and ferroelectric properties of PZT films obtained by the high-frequency magnetron sputtering method were carried out. It is shown that the change in the ferroelectric properties of polycrystalline PZT films can be explained by their heterophase structure with inclusions of lead oxide. It was found that the presence of a sublayer of lead oxide leads to a self-polarization of the film of the PZT. During the formation of the perovskite structure, the diffusion of lead oxide to the surface of the film occurs more intensively than after its formation.

Influence of oxygen partial pressure on the properties of PZT thin film deposited by RF magnetron sputtering

In magnetron sputtering systems, lead-zirconium-titanium oxide (PbZr1−xTixO3 or PZT) thin films were prepared in a mixture atmosphere of Ar and O2 with various oxygen partial pressures (0, 0.5, 1, 1.5 and 2% oxygen). About 600 nm PZT ferroelectric thin films were deposited on substrates, and then annealed at 600°C for 35 s. The structural, electrical and ferroelectric properties of PZT films were studied. As the oxygen partial pressure increased, the remanent polarisation rose first and went down later, and the leakage current density decreased first and then increased. At the oxygen partial pressure of 0.5%, we obtained the largest remanent polarisation and the minimum leakage current density. The XRD diffraction spectrum of all films displayed predominant (111) preferred orientation, and there was a weak XRD diffraction peak of pyrochlore phase in the PZT films deposited in pure Ar.

Fabrication and Characterization of PZT/CuO Thin Film

Pb(Zr0.52Ti0.48)O3 or PZT thin films embedded with CuO nano-particles were successfully prepared by a hybrid sol-gel process. In this process, CuO (0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1wt%) nanopowder was suspended in an organometallic solution of PZT, and then coated on platinised silicon substrates using a spin-coating technique. X-ray diffraction patterns showed a perovskite phase in all the films. The CuO particles were not detected in the film, but the small amount of second phase was present when CuO concentration was above 0.4 wt%. The addition of CuO nano-particles also affected the orientation of PZT films. The CuO nano-particles were generally found to reduce both dielectric and ferroelectric properties of PZT films. However, at 0.2 wt% CuO concentration, the film exhibited good ferroelectric properties which were comparable to those of pure PZT thin films.

Synthesis and Characterization of PZT Thin Films Embedded with WO3 Nanoparticles by a Hybrid Chemical Solution Route

PZT thin films embedded with WO3 nanoparticles were prepared by a hybrid chemical solution process. WO3 at 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 1 wt% nanopowders were suspended in an organometallic precursor solution of PZT, and then coated on platinized silicon substrate using spin-coating technique. The increase of WO3 resulted in a reduction of densification of the films. However, at 1 wt% WO3 concentration, the reaction between PZT and WO3 occurred during heat-treatment process at 600°C and seemed to improve the film's density. The WO3 nanoparticles were also found to affect both dielectric and ferroelectric properties of PZT films. Moreover, the addition of WO3 nanoparticles was found to improve a fatigue phenomenon in ferroelectric PZT thin films.

Preparation and Characterization of Pb(Zr,Ti)O3 films prepared by a modified sol-gel route

ABSTRACTPb(Zr0.53Ti0.47)O3 (PZT) films have been fabricated on stainless steel substrates by a Polyvinylpirrolidone (PVP) modified sol-gel route. The single layer of about 0.26 μm was achieved by using the PVP-modified PZT sol, and Crack-free PZT films with thickness of up to 2.37 μm were fabricated by repeating the deposition process. The variations in crystallite orientation, microstructure, dielectric and ferroelectric properties of PZT films were investigated as a function of film thickness. Our results indicate that PZT films prepared on stainless steel substrates maintain good dielectric and ferroelectric properties.

Sol–gel derived PZT films doped with vanadium pentoxide

The present research investigated the sol–gel preparation, dielectric and ferroelectric properties of PZT films doped with 5 mol% vanadium oxide. Stable PZTV sols can be readily formed, and homogeneous, micrometer thick and pinhole-free PZTV films were obtained by using spin coating followed with rapid annealing. The X-ray diffraction patterns revealed that no parasitic or secondary phases were formed in the sol–gel PZT films with the addition of vanadium oxide. The material doped with vanadium pentoxide showed enhanced dielectric constant and remanent polarization with reduced loss tangent and coercive field.

Fabrication and Characterization of Direct-patternable PZT Film Prepared by Photochemical Metal-organic Deposition

The ferroelectric properties of UV irradiated and non-irradiated PZT films prepared via photochemical metal-organic deposition using photosensitive precursors were characterized. Fourier transform infrared spectroscopy showed that complete removal of organic groups was possible through UV exposure of the spin-coated PZT precursor films at room temperature. The measured remnant polarization values of UV- irradiated and non-irradiated PZT films after annealing at 650 C were 29 and 23 µC/cm , respectively. The UV irradiation was found to be effective for the enhancement of the growth orientation and ferroelectric property of PZT film and in the direct patterning in the fabrication of micro-patterned systems without dry etching.

Investigation of PbZr0.4Ti0.6O3 capacitors with room temperature as-grown LaNiO3 electrodes

LaNiO3 (LNO) film grown at room temperature (RT) by RF magnetron sputtering is used as the electrode for integrating LaNiO3/PbZr0.4Ti0.6O3/LaNiO3 (LNO/PZT/LNO) capacitor on SrTiO3 (STO) substrate. For comparison, LNO film grown at 250 °C is also used as the electrode of PZT capacitor. Reflection high energy electron diffraction (RHEED) technique is used to characterize the LNO film, it is found that LNO film prepared at 250 °C is epitaxial although no diffraction pattern is found for RT as-grown LNO. Ferroelectric properties of PZT films strongly depend on the LNO bottom electrodes. The remanent polarization (P r) and coercive voltage (V c), measured at 5 V, for the capacitors with LNO bottom electrodes prepared at RT and 250 °C, are 20 and 37 μC/cm2, 1.67 and 1.95 V, respectively. No obvious degradation of polarization for PZT capacitors with RT as-grown LNO electrodes can be found. Room temperature as-grown LNO as both bottom and top electrodes to fabricate ferroelectric capacitors can save 2/3 thermal budgets, which may pay a way to decrease the potential challenges of devices resulting from the oxidation, interdiffusion or reactions during integrating ferroelectric capacitors with Si technologies.

Effect of Pb Content on the Fatigue Properties of D.C. Reactive Sputtering-Derived PZT Thin Films

Lead zirconate titanate (Pb(Zr0.48Ti0.52)O3 or PZT) films were grown on platinized silicon wafers (Pt/SiO2/Si) by d.c. reactive sputtering method with multi targets. The Pb content of PZT films has been widely recognized as affecting not only the phase formation and microstructure but also the dielectric and ferroelectric properties. Pb content of PZT films was controlled by the variation of Pb target current. The relation between Pb content and Pb target current was expressed as y=0.89x-11.09. The x and y are Pb target current and Pb content, respectively. The pyrochlore phase was transformed to perovskite phase as Pb content was increased. This phase transformation improved the ferroelectric properties of PZT films. In PZT films with perovskite phase, fatigue properties were not improved with excess Pb content. Fatigue properties of PZT films began to be fatigued after 106 switching cycles and coincided with the typical PZT fatigue behavior. Excess Pb content (Pb vacancy) did not affect the fatigue properties of PZT films.

Combined annealing temperature and thickness effects on properties of PbZr 0.53Ti 0.47O 3 films on LaNiO 3/Si substrate by sol–gel process

PbZr 0.53Ti 0.47O 3 (PZT) films with different thickness were deposited on LaNiO 3-coated Si substrate by modified sol–gel process. The thickness effect on structure and properties of PZT films annealed at different temperature have been investigated. Single perovskite-phase PZT films with preferred [1 0 0] orientation and denser columnar structure were obtained, when annealed at a lower temperature of 600 °C, whereas a higher annealing temperature of 700 °C resulted in [1 1 0] preferred orientation and porous structure. The dielectric and ferroelectric properties of PZT films annealed at different temperature were evaluated systemically as a function of thickness, and the dielectric and ferroelectric properties of PZT films were found to greatly depend on both thickness and annealing temperature.

Crystallization behavior and domain structure in textured Pb(Zr 0.52Ti 0.48)O 3 thin films by different annealing processes

Amorphous Pb(Zr 0.52Ti 0.48)O 3 (PZT) thin films were prepared on the Pt/Ti/SiO 2/Si substrates by radio-frequency magnetron sputtering at room temperature. After rapid thermal annealing (RTA) and conventional furnace annealing (CFA) at different temperatures, the films were transformed into polycrystalline PZT thin films with (111) and (100) orientation, respectively. The phase formation and ferroelectric domains correlated with different orientation were systematically investigated by X-ray diffraction and piezoresponse force microscopy. The results showed that the perovskite PZT crystal with [111] orientation hetero-nucleated preferentially on top of the PtPb intermetallic phase at the PZT/Pt interface during RTA process. It is of interest to find that the domain self-organized into a structure with rounded shape at the early stage of crystallization. While the nucleation of the films treated by CFA dominantly homo-nucleated, thus the (100) orientation grains with minimum surface energy were easy to grow. The texture effects on ferroelectric properties of PZT films were also discussed in relation to the domain structure.

PRECURSOR-MONOMER METHOD OF SOL-GEL FOR FABRICATION PT/PZT/PT FERROELECTRIC FILMS

ABSTRACT Lead zirconate titanate Pb(Zr0.52Ti0.48)O3 (PZT) thin films was successfully deposited on Pt(111)/Ti/SiO2/Si(100) substrates by a new modified sol-gel technique: precursor-monomer method. In this process three separated Pb2 +, Zr4 +, Ti4 + precursor-monomers and metal chelating agents were mixed together to prepare PZT sol-solution (precursor). The precursor-monomer method has several advantages over conventional sol-gel methods, including easy change the atomic ratio of Pb2 +/Zr4 +/Ti4 + and doping metallic ions, rapid PZT precursor synthesis, low processing temperature, without dry condition and distillation, long storage period, simplicity and low cost, etc. The paper investigated the effects of hydrolysis degree on the stability of PZT precursor, and it was found that the sample with 12.5% (v/v) adding water had the longest storage time. The inference of lead titanate (PbTiO3, PT) seeding layers on the microstructures, surface morphologies and ferroelectric properties of PZT films has also been systematically examined. We found that PZT films with PT/PZT/PT structure had lower perovskite phase crystallization temperature, larger grain size, better microstructure and ferroelectric properties as compared with no PT seeding layers films.

Effect of Pb2Ru2O7-x (PRO) conductive interfacial layers on ferroelectric properties of Pt/Pb(Zr0.35Ti0.65)O3/Pt capacitors for nonvolatile memory applications

A conductive material, Pb2Ru2O7-x (PRO), containing Pb in a cubic structure was introduced into a Pt/PZT interface in an attempt to improve the ferroelectric properties of PZT films. PRO and PZT films were prepared by rf magnetron sputtering and chemical solution deposition, respectively. The resistivity of PRO thin films in a hybrid-type electrode (PRO/Pt) structure was approximately 35–45 μΩ·cm and the surface roughness remained constant with increasing annealing temperature. The PRO interlayers suppressed the loss of Pb in PZT layers by diffusion to the Pt/PZT interface. The increase in remanent polarization was largely dependent on the PRO interlayers inserted at the bottom-Pt/PZT interface rather than at the top-Pt/PZT interface. In addition, the leakage-current behavior of PZT films in a sandwich structure was improved substantially compared to the case of PRO interlayers only at the bottom-Pt/PZT interface. Thus, the PRO interlayers play an important role in improving the ferroelectric properties of PZT thin films for use in nonvolatile memory device applications.

Enhancement of Polarization Property of PZT Film by Ion-Substitution Using Rare-Earth Elements

Rare-earth-substituted lead zirconate titanate thin films were synthesized to improve the ferroelectric properties of lead zirconate titanate through the enhancement of its crystal anisotropy. Thin films of Pb1.00-(3x/2)REx(Zr0.40Ti0.60)O3 [RE-PZT(A)] and Pb1.00REx(Zr0.40Ti0.60)1-(3x/4)O3 [RE-PZT(B)] with RE=La or Dy were deposited on (111)Pt/Ti/SiO2/(100)Si substrates by chemical solution deposition (CSD). Rare-earth-substitution did not affect the crystal orientation of the PZT-based films where the PZT(111) plane was oriented along the surface-normal direction. Dy3+ substitution based on Dy-PZT(B) up to x=0.02 enhanced the crystal anisotropy (c/a) and remanent polarization (Pr) of PZT films simultaneously, while both c/a and Pr values of Dy-PZT(A) decreased as x increased continuously. On the other hand, La3+ substitution degraded the ferroelectric properties gradually in both the case of La-PZT(A) and (B). The Dy3+ ion could be substituted for a B-site in a PZT crystal preferentially, and that promoted the crystal anisotropy and the ferroelectric properties of PZT films.

A slim type microvalve driven by PZT films

A slim type microvalve actuated by PZT films was developed. Three different sizes of microvalves having a thickness of 528 μm were designed. Each one has 120 cantilevers arrayed circularly. In designing them, tip deflections of PZT cantilevers were calculated, and compared with those obtained by FEM simulations. Leakage and flow rate were calculated. Fabrication process and the PZT film deposition process are explained. The microvalve structure with PZT films was fabricated on a SiO 2 layer over a supporting silicon on insulator (SOI) wafer. The ferroelectric properties of PZT films were studied with polarization–voltage ( P– V) and dielectric constant, dielectric loss-voltage measurement. Tip deflections were measured on the fabricated array, applied with different voltages. Tip displacement of 12 μm ( Φ = 10 mm-type) was obtained with the applied voltage of 5 V. When the microvalve was closed, the air leakage was 15 μl/s. The air-flow rate of 122 μl/s ( Φ = 10 mm-type) was measured with the pressure difference of 1000 Pa in the opened position at 15 V.

Ferroelectric properties of PZT films on LaNiO 3 bottom electrode deposited under different oxygen partial pressure

LaNiO 3 (LNO) films were deposited on by RF magnetron sputtering of Ni metal target and La metal chips on top of it under Ar and O 2 atmosphere at different oxygen partial pressures (20, 25, 30, 35, and 40% oxygen). The resistivity of the LNO films increased with the increasing oxygen partial pressure. This is attributed to the reduction of oxygen vacancy concentration. About 150 nm thick Pb(Zr 0.35Ti 0.65)O 3 (PZT) ferroelectric thin films were spin coated on the LNO films with subsequent post annealing. To find out the relationship, the electrical properties of the PZT/LNO thin film capacitors and the oxygen partial pressure, the P– E curve, X-ray diffraction, microstructure, leakage current density, and fatigue property were investigated as a function of oxygen partial pressure. An optimal remanent polarization and lowest leakage current density of the PZT capacitor has been obtained when its LNO thin film bottom electrode was deposited at 30% oxygen partial pressure. The microstructure of the LNO film deposited at 30% oxygen partial pressure had columnar structure, while the ones deposited under other conditions had granular structure. The ferroelectric properties of the PZT/LNO capacitor are critically affected by the structure of LNO bottom electrode, and they are excellent when optimally processed as discussed above.

Effect of annealing ambient on structure and ferroelectric properties of Pb(Zr 0.4Ti 0.6)O 3 thin films on LaNiO 3 coated Si substrates

Pb(Zr 0.4Ti 0.6)O 3 [PZT(40/60)] thin films were deposited onto LaNiO 3 (LNO) coated Si substrates by sol–gel technique. Three kinds of gases, air, O 2 and N 2, were used as the annealing ambient. The effect of the annealing ambient on their structure and ferroelectric properties was investigated. The results showed that both the films annealed in air and O 2 were the complete perovskite phase with (1 0 0) preferential orientation, while those annealed in N 2 were random orientation including some pyrochlore phases. As compared with the air ambient, either too much O 2 or too much N 2 was detrimental to the ferroelectric properties of PZT films. The difference in structure and ferroelectric properties was mainly associated with the intermediate phases and the concentration of domain pinning centers in the films.