Heterolayered PZT thin films of different thicknesses and stacking sequence

The effects of stacking sequence and thickness toward the texture and electrical properties of heterolayered PbZr _x Ti_1−x O₃ (PZT) films, consisting of alternating PbZr_0.7Ti_0.3O₃ and PbZr_0.3Ti_0.7O₃ layers, have been studied. Thickness dependence is observed in the ferroelectric and dielectric behavior of the heterolayered PZT films whereby the remanent polarization (P _r) and relative permittivity (ε) increase with thickness, while coercive field (E _c) decreases. When baked at 500 °C and thermally annealed at 650 °C, the heterolayered PZT films regardless of their stacking sequence exhibit perovskite phase with (001)/(100) preferred orientation. Interestingly, the stacking sequence of the heterolayered PZT films dictates the morphology of the films which eventually affects the ferroelectric and dielectric performance. The heterolayered PZT film with PbZr_0.7Ti_0.3O₃ as the first layer (heterolayered PZ₇₀T₃₀ film) exhibits a large grain size in the range of 1–3 μm and shows superior properties as compared to the heterolayered PZT films with PbZr_0.3Ti_0.7O₃ as the first layer (heterolayered PZ₃₀T₇₀ film), which exhibits a much smaller grain size. From the sub-switching field measurement according to the Rayleigh law, there appears a lower concentration or mobility of domain walls in the small-grained heterolayered PZ₃₀T₇₀ films.     

Impact of Zr/Ti ratio in the PZT on the photoreduction of silver nanoparticles

Silver nanoparticle deposition from an aqueous solution of silver nitrate onto the surface of PZT thin films of stoichiometric compositions PbZr_0.3Ti_0.7O₃ and PbZr_0.52Ti_0.48O₃ has been investigated. The impact of Zr/Ti ratio on the photochemical properties of PZT is shown by the preferential growth of silver nanoparticles onto the surface. Photoreduction of silver occurs on both c⁺ and c⁻ domains on PbZr_0.52Ti_0.48O₃ whereas it occurs only on c⁺ domains on a PbZr_0.3Ti_0.7O₃ surface. The difference in deposition pattern is attributed to difference in magnitude of spontaneous polarization, effective hole concentration and band gap of the two samples which impacts shape and width of space charge layer in the two samples resulting in a change in band bending at the surface.     

Effect of excess Pb in PbTiO<Subscript>3</Subscript> precursors on ferroelectric and fatigue property of sol–gel derived PbTiO<Subscript>3</Subscript>/PbZr<Subscript>0.3</Subscript>Ti<Subscript>0.7</Subscript>O<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> thin films

A series of Pb_(1+x)TiO₃/PbZr_0.3Ti_0.7O₃/Pb_(1+x)TiO₃ (PTO/PZT/PTO) and PbZr_0.3Ti_0.7O₃ (PZT) thin films were prepared by a sol–gel method. Different excess Pb content (x) (x = 0, 0.05, 0.10, 0.15, 0.20) were added to the PbTiO₃ (PTO) precursors to investigate their effect on ferroelectric and fatigue properties of the PTO/PZT/PTO thin films. X-ray diffraction results show that the crystallization behavior of the PTO/PZT/PTO thin films is greatly affected by the excess Pb content (x) in PTO precursors. Topographic images show that the PTO/PZT/PTO thin films with excess Pb content x = 0.10 appears the densest and the most uniform grain size surface morphology. The ferroelectric and fatigue properties of the films correlate straightforwardly to the crystallization behaviors and excess Pb content (x) in the PTO precursors. The excess Pb content (x) in the PTO layers which acts as a nucleation site or seeding layer for PZT films affects the crystallization of the PTO layer and ultimately affects the perovskite phase formation of the PZT films. With the proper excess Pb content (x = 0.10–0.15) in the PTO precursors, the pure perovskite structure PTO/PZT/PTO thin films, with dense, void-free, and uniform fine grain size are obtained, and a well-saturated hysteresis loop with higher remnant polarization is achieved. Using an appropriate Pb content, the fatigue has been avoided by controlling the inter-diffusion and surface volatilization.     

Thickness-dependent electrical properties of sol–gel derived Pb(Zr0.52Ti0.48)O3 thick films using PbTiO3 buffer layers

Pb(Zr_0.52Ti_0.48)O₃ (PZT) thick films, with thickness up to 4 μm, using PbTiO₃ (PT) buffer layers were successfully prepared on silicon-based substrates by a sol–gel method. Thermal analysis (thermogravimetric–differential thermal analysis) of PT and PZT sols were used to determine the pyrolysis and annealing temperatures. X-ray diffraction results show that the PZT/PT composite thick films possess perovskite structure and the dominant crystalline orientation changes from (100) to (110) with increasing the film thickness. Furthermore, the composite thick films exhibit thickness-dependent ferroelectric and dielectric properties, i.e., the coercive field decreases while dielectric constant increases as the thickness increases. Theoretical analysis shows that the thickness-dependent electrical properties are mainly attributed to the low dielectric constant of PT buffer layer and the relaxation of internal stress in PZT films.     

Microstructure and texture development in single layered and heterolayered PZT thin films

Single-layered Pb(Zr_0.7Ti_0.3)O₃ and Pb(Zr_0.3Ti_0.7)O₃ thin films and heterolayered Pb(Zr_1−x Ti _x )O₃ thin films consisting of alternating Pb(Zr_0.7Ti_0.3)O₃ and Pb(Zr_0.3Ti_0.7)O₃ layers were studied for their microstructure and texture development. The texture in the single-layered PZT films is affected by the Zr/Ti ratio as they have different crystallization behavior depending on the Zr/Ti ratio. With increasing film thickness, the average grain size of Pb(Zr_1−x Ti _x )O₃ increases. An unusually large grain size of 1–3 μm together with a strong (001)/(100) preferred orientation were observed for the heterolayered PZ₇₀T₃₀, whereby Pb(Zr_0.7Ti_0.3)O₃ was used as the seeding layer, for film as thin as 150 nm. The film microstructure is refined drastically when the stacking sequence is changed, i.e., when Pb(Zr_0.3Ti_0.7)O₃ is employed as the seeding layer. Thermal treatment of the PZ₇₀T₃₀ seeding layer also plays an important function in the microstructure development of the heterolayered PZ₇₀T₃₀ film. The formation of the large-grained film is correlated to the lowered nucleation energy of crystallizing Pb(Zr_0.7Ti_0.3)O₃ by the top Pb(Zr_0.3Ti_0.7)O₃. The Pb(Zr_0.3Ti_0.7)O₃ layer facilitated the nucleation and crystallization of the Pb(Zr_0.7Ti_0.3)O₃ amorphous seeding layer, whereby the overall microstructure of the heterolayered thin film was dictated by the Pb(Zr_0.7Ti_0.3)O₃ seeding layer leading to the growth of larger PZT grains.     

Preparation of high (100) oriented PST thin films deposited on PT/Tb inducing layer by rf-sputtering method

Tb doped PbTiO₃ (PT) thin films with (001)/(100) preferred orientation are prepared by sol-gel method. High (100) oriented Pb_0.4Sr_0.6(Ti_0.97Mg_0.03)O_2.97(PST) thin films are then deposited on the Tb doped PbTiO₃ inducing layer by rf-sputtering technique. The crystalline phase structure and orientation of the thin film are determined by X-ray diffraction. The dielectric properties of the thin films are measured by an Impedance Analyzer. Results show that the Tb doped PT films exhibit preferred orientation. The PST thin films deposited on substrate with and without PT inducing layer show (100) orientation and random orientation respectively. Higher (100) orientation appears in the PST thin films deposited on thinner inducing PT layer (one layer compare to more layers). A dielectric tunability of 39% is obtained in the PST thin film deposited on thinner PT inducing layer. It is a little higher than that deposited on thicker inducing layer.     

Enhanced ferroelectric properties of epitaxial Pb(Zr,Ti)O3 film with LaAlO3 buffer

PbZr_0.52Ti_0.48O₃ films (PZT) have been grown epitaxially on SrRuO₃/LaAlO₃ (SRO/LAO) substrates using pulse laser deposition. In order to improve the ferroelectric properties of the PZT, one LAO buffer was introduced into the interface of PZT/SRO. The dependence of the electrical properties of the PZT films on the buffer thickness was studied. When a 10-nm-thick buffer was used, the remnant polarization (Pr) of the PZT film reached 58 ± 5 μC/cm², 2 times larger than the sample without any buffer layer. The leakage current was reduced 1-2 orders of magnitude. Besides, the PZT film with 10-nm-thick LAO buffer also exhibited good fatigue endurance after 10⁹ switching cycles. These results could propose one effective way to improve the properties of ferroelectric films deposited on oxide electrodes.     

Asymmetric switching behavior of Ni/Pb1.1(Zr0.3Ti0.7)O3/Pt thin films

An asymmetric behavior of P–E response was observed in Ni/Pb_1.1(Zr_0.3Ti_0.7)O₃/Pt multilayer thin films where Ni was used as top electrode. This interesting phenomenon was investigated by comparative analysis of the hysteresis loops and dynamic pyroelectric responses. The PZT thin films were prepared under the same conditions but different Ni and Pt top electrodes were used in the hysteresis loop measurement, and the Pt was used as the common bottom electrode. It is believed that this asymmetric behavior in hysteresis loop is originated from the strong domain pinning near the top Ni electrode. Dynamic pyroelectric response to 633 nm radiation of the Ni/Pb_1.1(Zr_0.3Ti_0.7)O₃/Pt thin films with polarization up and down was carried out. Higher dynamic pyroelectric response was observed in the positively poled film, in which the direction of the polarization was from the top to bottom electrode. It provides further evidence that the domain pinning near the top electrode dominates the asymmetric switching behavior.     

Damping property of epoxy-based composite embedded with sol–gel-derived Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin film

The Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on Pt/Ti/SiO₂/Si substrate by sol–gel method. The effect of the annealing holding time on microstructure, ferroelectric and dielectric properties was investigated. The single-phase PZT films were obtained with different annealing holding time. PZT films annealed for 30–90 min had better dielectric and ferroelectric properties. The epoxy/PZT film/epoxy sandwich composites were prepared, and the annealing holding time of PZT films influenced the damping property of the composites. The epoxy-based composites embedded with PZT films annealed for 90 min had largest damping loss factor of 0.906.     

Synthesis of PbZr0.7Ti0.3O3 nanoparticles in a new tetragonal crystal structure with a polymer precursor

Nanoparticles (16- to 25-nm diameter) of PbZr_0.7Ti_0.3O₃, lead zirconate titanate (PZT), are synthesized by a controlled reconstructive thermal decomposition and crystallization from an amorphous polymer precursor with polyvinyl alcohol (PVA) and sucrose at 400 to 700 °C in air. When adding through a mixed acidic solution (with stirring) the ingredients of Pb²⁺ (nitrate) and Zr⁴⁺/Ti⁴⁺ (oxyhydroxides) cations mix-up with PVA-sucrose polymer molecules (dissolved in water) and reorganize in a dispersed structure of precursor. A dispersed structure of the cations through the polymer molecules retain on evaporating (at 50 to 80 °C in air) the excess water in a solid polymer precursor. It is found that a single phase compound of PbZr_0.7Ti_0.3O₃ forms on heating it at 400 to 700 °C temperature in air. It has a new tetragonal crystal structure in comparison to the rhombohedral bulk structure in the Zr-rich or the tetragonal structure in the Ti-rich PZTs. The PbZr_0.7Ti_0.3O₃ nanoparticles calcined under selected conditions in this polymorph are characterized by X-ray diffraction and microstructure in correlation with thermal analysis of the polymer precursor.     

Large electrocaloric effect of highly (100)-oriented 0.68PbMg1/3Nb2/3O3-0.32PbTiO3 thin films with a Pb(Zr0.3Ti0.7)O3/PbOx buffer layer

0.68PbMg_1/3Nb_2/3O₃-0.32PbTiO₃ (PMN-PT) thin films with a lead zirconate titanate Pb(Zr_0.3Ti_0.7)O₃ (PZT)/PbO_x buffer layer were deposited on Pt/TiO₂/SiO₂/Si substrates by radio frequency magnetron sputtering technique, and pure perovskite crystalline phase with highly (100)-preferred orientation was formed in the ferroelectric films. We found that the highly (100)-oriented thin films possess not only excellent dielectric and ferroelectric properties but also a large electrocaloric effect (13.4 K at 15 V, i.e., 0.89 K/V) which is attributed to the large electric field-induced polarization and entropy change during the ferroelectric-paraelectric phase transition. The experimental results indicate that the use of PZT/PbO_x buffer layer can induce the crystal orientation and phase purity of the PMN-PT thin films, and consequently enhance their electrical properties.     

Damping properties of epoxy-based composite embedded with sol–gel-derived Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin film annealed at different temperatures

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on Pt/Ti/SiO₂/Si substrate by sol–gel method. The effect of annealing temperature on microstructure, ferroelectric and dielectric properties of PZT films was investigated. When the films were annealed at 550–850 °C, the single-phase PZT films were obtained. PZT films annealed at 650–750 °C had better dielectric and ferroelectric properties. The sandwich composites with epoxy resin/PZT film with substrate/epoxy resin were prepared. The annealing temperature of PZT films influenced their damping properties, and the epoxy-based composites embedded with PZT film annealed at 700 °C had the largest damping loss factor of 0.923.     

Synthesis and electrical properties of Pb(Zr0.52Ti0.48)O3 thick films embedded with ZnO nanoneedles prepared by the hybrid sol–gel method

Pb(Zr_0.52Ti_0.48)O₃ thick films embedded with ZnO nanoneedles (PZT–ZnO_n) were successfully prepared on Pt/Cr/SiO₂/Si substrates by the hybrid sol–gel method via spin-coating ZnO_n suspension and lead zirconate titanate (PZT) sol. To control the orientation of the films, a PbTiO₃ (PT) layer was first deposited as a seed layer. Effects of annealing method and ZnO_n contents on the corresponding orientation and crystallization of PZT–ZnO_n films were investigated by XRD and SEM. The results show that all the PZT–ZnO_n composite thick films have pure perovskite structure and high-quality film surface. The dielectric and ferroelectric properties of the PZT–ZnO_n films are close to the PZT films, and have a little decrease with the increasing of the ZnO_n contents.     

Effect of seed layer on the ferroelectric properties and leakage current characteristics of sol–gel derived vanadium doped PbZr0.53Ti0.47O3 films

In this paper, we report the ferroelectric properties and leakage current characteristics of vanadium-doped PbZr_0.53Ti_0.47O₃ (PZTV) films grown on various seed layers prepared by a sol–gel process. The PZTV multilayered film of ~250-nm-thick showed excellent ferroelectric properties, with a large remnant polarization (P _r) of ~30 μC/cm² (E _c ~ 90 kV/cm), a high saturation polarization (P _s) of ~85 μC/cm² for an applied field of 1,000 kV/cm, fatigue-free characteristics of up to ≥ 10¹⁰ switching cycles, and a low leakage current density of 7 × 10⁻⁸ A/cm² at 100 kV/cm. X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) investigations indicated that PZTV films grown on PbZr_0.53Ti_0.47O₃/PbLa_0.05TiO₃ (PZT/PLT) seed layers exhibited a dense, well-crystallized microstructure with random orientations and a rather smooth surface morphology.     

Pb(Zr0.52Ti0.48)O3/TiNi multilayered heterostructures on Si substrates for smart systems

Ferroelectric/shape memory alloy thin film multilayered heterostructures possess both sensing and actuating functions and are considered to be smart. In this article, Pb(Zr_0.52Ti_0.48)O₃ (PZT) ferroelectric thin films and Ti-riched TiNi shape memory alloy thin films have been deposited on Si and SiO₂/Si substrates in the 400-600 °C temperature range by pulsed laser deposition technique. Deposition processing, microstructure and surface morphology of these films are described. The TiNi films deposited at 500 °C had an austenitic B2 structure with preferred (110) orientation. The surfaces of the films were very smooth with the root-mean-square roughness on a unit cell level. The structure of the TiNi films had a significant influence on that of the subsequently deposited PZT films. The single B2 austenite phase of the TiNi favored the growth of perovskite PZT films. The PZT/TiNi heterostructures with the PZT and TiNi films respectively deposited at 600 and 500 °C exhibited a polarization-electric field hysteresis behavior with a leakage current of about 2 × 10^− 6 A/cm².     

Comparison of Pb(Zr,Ti)O3 capacitors sandwiched with conductive La0.5Sr0.5CoO3 and non-conductive Bi3.25La0.75Ti3O12 layers

Ferroelectric capacitors of Bi_3.25La_0.75Ti₃O₁₂/PbZr_0.4Ti_0.6O₃/Bi_3.25La_0.75Ti₃O₁₂ (BLT/PZT/BLT) and La_0.5Sr_0.5CoO₃/PbZr_0.4Ti_0.6O₃/La_0.5Sr_0.5CoO₃ (LSCO/PZT/LSCO) are fabricated, respectively, on Si substrates in order to study the properties of PZT film sandwiched by conductive oxide and non-conductive oxide layers. It is found that the crystallinity of PZT film grown on LSCO electrode is much better than that on BLT film although the growth temperature of BLT/PZT/BLT is 100 °C higher than that of LSCO/PZT/LSCO. Remanent polarization of LSCO/PZT/LSCO capacitors measured at 10 V is 31.1 μC/cm², which is much higher than the value of 19.8 μC/cm² for BLT/PZT/BLT. Both kinds of the capacitors are fatigue-free up to 10¹⁰ switching cycles. The leakage current density measured at 5 V is about 4.7 × 10^− 6 A/cm² and 1.9 × 10^− 5 A/cm² for BLT/PZT/BLT and LSCO/PZT/LSCO, respectively. The differences for the two kinds of capacitors are discussed in the article.     

Dielectric enhancement of the trilayered Bi3.15Eu0.85Ti3O12/Bi3.15Nd0.85Ti3O12/Bi3.15Eu0.85Ti3O12 thin film deposited on Pt/Ti/SiO2/Si substrate

The trilayered Bi_3.15Eu_0.85Ti₃O₁₂/Bi_3.15Nd_0.85Ti₃O₁₂/Bi_3.15Eu_0.85Ti₃O₁₂ (BET/BNT/BET) thin film was deposited on Pt/Ti/SiO₂/Si(100) substrates by metal organic decomposition at annealing temperature of 650 °C, and the microstructure, chemical composition, leakage current, dielectric and ferroelectric properties were investigated by field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, semiconductor characterization system, impedance analyzer and ferroelectric tester. The trilayered thin film is of crack-free and dense surface with some discrete cluster distribution, and typical Bi-layered perovskite polycrystalline phase. The dielectric constant ε _r and dissipation factor tanδ are 1,233 and 0.0215 at 100 kHz for the trilayered thin film. Comparing with the pure BET and BNT thin films, the dielectric constant of trilayered thin film is enhanced, which is due to the space charge and the intermediate superlattice. The trilayered thin film shows excellent dielectric properties and can be promisingly used for the high dielectric layer of silicon-based embedded capacitors in package substrate.     

Structural evaluation of sol-gel derived lead strontium titanate diffusion barrier for integration in lead zirconate titanate transducer design

Sol-gel derived Pb₄₀Sr₆₀TiO₃ (PST) thin film has been investigated as a diffusion barrier for integrating in PbZr₃₀Ti₇₀O₃ (PZT) device structures on Si substrates. PST film was deposited on SiO₂/Si substrate and annealed at a relatively low temperature range of 550-600 °C producing a crack-free, smooth and textured surface. Following deposition on PST/SiO₂/Si template PZT thin film was crystallised exhibiting random grain orientations and an insertion of the bottom Pt/Ti electrode forming PZT/Pt/Ti/PST/SiO₂/Si stacks promoted the preferred PZT (111) perovskite phase. PZT (111) peak intensity gradually decreased along with slight increase of the PZT (110) peak with increasing annealing temperature of the buffer PST film. The dielectric and ferroelectric properties of the PZT with barrier PST deposited at 550 °C were assessed. The dielectric constant and loss factor were estimated as 390 and 0.034 at 100 kHz respectively and the remnant polarisation was 28 µC/cm² at 19 V. The performance of the PZT/PST device structures was compared to similar PZT transducer stacks having widely used barrier TiO₂ layer.     

The thickness effect of Bi3.25La0.75Ti3O12 buffer layer in PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 (PZT/BLT) multilayered ferroelectric thin films

A series of PbZr_0.58Ti_0.42O₃ (PZT) thin films with various Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer thicknesses were deposited on Pt/TiO₂/SiO₂/p-Si(100) substrates by RF magnetron sputtering. The X-ray diffraction measurements of PZT film and PZT/BLT multilayered films illustrate that the pure PZT film shows (111) preferential orientation, and the PZT/BLT films show (110) preferential orientation with increasing thickness of the BLT layer. There are no obvious diffraction peaks for the BLT buffer layer in the multilayered films, for interaction effect between the bottom BLT and top PZT films during annealing at the same time. From the surface images of field-emission scanning electron microscope, there are the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples. The growth direction and grain size have significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics of PZT and PZT/BLT films suggest that 30-nm-thick BLT is just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results with that of PZT/Pt/TiO₂/SiO₂/p-Si(100) basic structured film suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

Mechanism of grain growth and excellent polarization,dielectric relaxtion of La<Superscript>3+</Superscript>, Nd<Superscript>3+</Superscript> modified PZT nano-films prepared by sol–gel technique

Ferroelectric PbZr_0.52Ti_0.48O₃ film and its partial substitutions by rare earth ions La³⁺ and Nd³⁺ Pb_0.9(La/Nd)_0.1Zr_0.52Ti_0.48O₃, grown on Pt(111)/Ti/SiO₂/Si(100) substrates, were prepared via sol–gel and rapid thermal processes. Structural characterization by X-ray diffraction and scanning electron microscopy showed that Pb(Zr_0.52Ti_0.48)O₃ and Pb_0.9La_0.1(Zr_0.52Ti_0.48)O₃ films are of (111) preferred orientation but Pb_0.9Nd_0.1(Zr_0.52Ti_0.48)O₃ is more inclined to (100) reflection though both are of tetragonal perovskite structure. The results indicate that the piezoelectric properties of PZT thin films can be improved by doping La³⁺ and Nd³⁺ substituted A-site. The d₃₃ can be dramatically improved by doping La³⁺. Moreover, Pr of Pb(Zr_0.52Ti_0.48)O₃ films reaches up to 120.53 µC/cm², while the doping samples present relatively inferior ferroelectric hysteresis loops (Pr_La?=?64.32, Pr_Nd?=?53.17 µC/cm²), greater dielectric constants, higher dielectric loss and lower leakage current than the undoped Pb(Zr_0.52Ti_0.48)O₃ sample. And meanwhile, the samples showed a typical non-Debye dielectric spectroscopy of multiple quantum relaxation time distribution observing from the Cole–Cole plot at room temperature.