Effect of Ru and LaNiO3 barrier layers on lead zirconate titanate films grown on nickel-based metal foils by sol–gel process

Lead zirconate titanate [Pb(Zr_0.52, Ti_0.48)O₃ (PZT)] films were grown by sol–gel process on nickel and hastelloy foils. PZT perovskite phase was obtained at 650 °C annealing condition and surface topography showed uniform and dense microstructure. The characterization on dielectric properties indicates that diffusion of foil elements into the PZT and the formation of low capacitance interfacial layer occur during process. In order to reduce the diffusion effect of foil element and/or interfacial layer, barrier layers such as Ru(RuO₂) and LaNiO₃ layers were utilized on foil substrates. The increase of grain size was observed in PZT films grown on barrier layers. Dielectric properties are greatly improved without degrading ultimate dielectric breakdown strength.     

Oxygen plasma-assisted ultra-low temperature sol-gel-preparation of the PZT thin films

PbTi_1-xZr_xO₃ (PZT) thin films prepared by sol-gel method have paid much attention due to the excellent performances in piezoelectric, dielectric, ferroelectric and electro-optical. However, the high crystallization temperature of the PZT thin films restricts the compatibility with modern COMS technology. In this work, PbZr_0.52Ti_0.48O₃ (PZT) ferroelectric thin films were successfully prepared by sol-gel method at an ultra-low temperature (～450 °C) in an oxygen plasma-assisted environment. A large spontaneous polarization ～30 μC/cm² and a large dielectric breakdown ～2,900 kV/cm were obtained in the sample annealed at 450 °C for 25 h. We believe that the oxygen plasma-assisted ultra-low temperature (OPAULT) annealing process is a promising way for the sol-gel technology applied in the modern COMS devices.     

Achieving high breakdown strength and figure of merit of Ba0.6Sr0.4TiO3 films through coating a Y3Fe5O12 layer

Low tunability and figure of merit significantly limited the application of Ba_0.6Sr_0.4TiO₃ (BST) ferroelectric film, which originates from the low electric breakdown strength and high dielectric loss of BST layer. Garnet structured Y₃Fe₅O₁₂ (YIG) exhibits the merits of good microwave dielectric property and a much high resistivity, which are helpful for enhancing the breakdown strength and suppressing the dielectric loss. In this work, Y₃Fe₅O₁₂/Ba_0.6Sr_0.4TiO₃ (YIG/BST) composite films were fabricated via chemical solution deposition method. The composite films exhibited a low dielectric loss (0.006) and an almost frequency independent dielectric constant in a frequency range from 10 kHz to 1 MHz. The electric breakdown strength was significantly enhanced from less than 400 kV/cm to around 800 kV/cm through coating a YIG layer, causing an excellent tunability of 72.84% and an ultra-high figure of merit (FOM=118) at 800 kV/cm in YIG/BST film. It is physically clarified that the conduction loss plays an important role in BST film while the intrinsic loss is the dominate factor for the YIG/BST composite films.     

Control of ferroelectric and linear piezoelectric response of PZT films through texture

The high and low field ferroelectric response of freestanding PbZr_0.52Ti_0.48O₃ (PZT) films, with texture varying from 100% (001) to 100% (111) was investigated via 500 nm thick PZT unimorphs deposited on the same substrate. It is shown that the ferroelectric and piezoelectric properties depend strongly on texture, and the effective transverse strain and stress coefficients vary linearly with %(001) and %(111) texture factors. PZT films with 100% (001) orientation displayed 150%, 140%, and 80% larger linear piezoelectric strain coefficient, saturated strain coefficient, and saturated stress coefficient, respectively, compared to films with 100% (111) orientation. As a result, pure (001) textured PZT films with 20% higher dielectric constant have 50% higher figure of merit in sensing than films with pure (111) texture. The piezoelectric and ferroelectric properties of all but one combinations of (001) and (111) texture were shown for the first time to be bounded by the values for 100% (001) and 100% (111) texture. A notable exception was PZT films comprised of 73% (001) and 27% (111) texture which showed stable piezoelectric coefficients at all electric fields, with major technological implication to low power microdevices. Finally, the coercive field was shown to decrease with (001) texture factor and excess‐Pb in the PZT and the PbTiO₃ seed layer.     

Effects of annealing temperatures on energy storage performance of sol-gel derived (Ba0.95, Sr0.05) (Zr0.2, Ti0.8) O3 thin films

Dielectric polarization and breakdown strength of dielectrics generally show directly and inversely dependent upon their crystallization, respectively. Therefore, achieving the maximum energy storage density should be expected by controlling the crystallization. A serial of ferroelectric (Ba_0.95, Sr_0.05)(Zr_0.2, Ti_0.8)O₃ (BSZT) thin films were prepared by the sol-gel method. Effects of annealing temperatures on the microstructure, dielectric and energy storage performance of the films were investigated. The results indicate that BSZT thin films annealed at 600 °C for 30 min demonstrate the highest recoverable energy density and efficiency (50.5 J/cm³ and 91.9%). Such superior energy storage performance is attributed to an ultrahigh electric breakdown strength (6.65 MV/cm) induced by the dense amorphous-nanocrystalline microstructure. This work creates a new way for optimizing the energy storage performance of dielectric thin films via balancing their dielectric polarization and breakdown strength at appropriate heating processing temperature.     

MnO2 Thin Film Electrodes for Enhanced Reliability of Thin Glass Capacitors

Many dielectric thin films for energy storage capacitors fail by thermal breakdown events under high‐field drive conditions. The lifetime of the device can be improved under conditions where the current path within the defect regions in dielectrics is eliminated. Self‐healing electrodes were developed by depositing a manganese dioxide (MnO₂) thin film between the glass substrate and an aluminum film. For this purpose, thin films of MnO₂ on boroaluminosilicate glass were fabricated via chemical solution deposition and heat‐treated at temperatures in the range 500°C–900°C. The α‐MnO₂ structure was stabilized by Ba²⁺ insertion to form the hollandite structure. The phase transition temperature of α‐MnO₂ to Mn₂O₃ is strongly dependent on the Ba concentration, with transition temperatures of 600°C and 675°C with Ba concentrations of [Ba]/[Mn] = 0.04 and 0.1, respectively. The electrical resistivity increased from 4.5 Ω·cm for MnO₂ to 10⁵ Ω·cm for Mn₂O₃. Both dielectric breakdown strength and the associated cleared aluminum electrode area increased with an MnO₂ interlayer between Al electrodes and the borosilicate glass. The enhancement in dielectric strength was related with self‐healing. The associated redox reaction between MnO₂ and Mn₂O₃ was also proved by RAMAN spectroscopy following dielectric breakdown.     

Micro-patterning of PZT thick film by lift-off using ZnO as a sacrificial layer

Micro-pattern of 8.2-μm-thick PZT films was prepared on Pt/Ti/SiO₂/Si (1 0 0) substrate wafer by combining composite sol–gel and a novel lift-off using ZnO as a sacrificial layer. The processes include ZnO sacrificial layer deposition and patterning, PZT film preparation, and final lift-off. The results reveal the micro-pattern was better than that formed by wet etching, the PZT thick films patterned by lift-off possessed similar dielectric characters, better ferroelectric properties, and higher breakdown voltage than those of films patterned by wet etching. The lift-off is suitable for micro-patterning of PZT thick films.     

Interfacial polarization and layer thickness effect on electrical insulation in multilayered polysulfone/poly(vinylidene fluoride) films

In this study, we report layer thickness effect on the electrical insulation property of polysulfone (PSF)/poly(vinylidene fluoride) (PVDF) multilayer films having a fixed composition of PSF/PVDF = 30/70 (vol./vol.). Breakdown strength, dielectric lifetime, and electrical conductivity were studied for 32- and 256-layer films having various total film thicknesses. Among these films, those having thinner PVDF and PSF layers exhibited lower breakdown strength, shorter lifetime, and higher electrical conductivity than those having thicker layers. These experimental results were explained by Maxwell–Wagner–Sillars interfacial polarization due to contrasts in dielectric constant and electronic conductivity for PVDF and PSF, respectively. When both PVDF and PSF layers were thick (ca. > 100–200 nm), more space charges were available in PVDF and no electronic conduction was allowed for PSF. These accumulated interfacial charges could serve as effective traps for injected electrons from metal electrodes under high electric fields. As a result, reduced electrical conductivity and enhanced breakdown strength/dielectric lifetime properties were obtained. When both layers were thin (ca. < 100 nm), fewer space charges were available in PVDF and significant electronic conduction through PSF resulted in low interfacial polarization. Consequently, higher electrical conductivity, lower breakdown strength, and shorter lifetime were observed. These results provide us insights into potential physics to enhance electrical insulation property of polymer films using a multilayered structure having large dielectric constant contrast.     

Enhanced ferroelectric properties of 0.95Pb(Sc0.5Ta0.5)O3–0.05PbTiO3 thin films with Pb(Zr0.52,Ti0.48)O3 seed layer

0.95Pb(Sc_0.5Ta_0.5)O₃–0.05%PbTiO₃ (PSTT5) thin films with and without a Pb(Zr_0.52,Ti_0.48)O₃ (PZT52/48) seed layer were deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering. X-ray diffraction patterns indicate that the PSTT5 film with a PZT52/48 seed layer exhibited nearly pure perovskite crystalline phase with highly (4 0 0)-preferred orientation. Piezoresponse force microscopy observations reveal that a large out-of-plane spontaneous polarization exists in the highly (4 0 0)-oriented PSTT5 thin film. The PSTT5/PZT(52/48) possesses good ferroelectric properties with large remnant polarization P_r (12 μC/cm²) and low coercive field E_c (110 kV/cm). Moreover, The perfect butterfly-shaped capacitance–voltage characteristic curve and the relative dielectric constant as high as 733 is obtained in this PSTT5 thin film at 100 kHz.     

Ultrahigh breakdown strength and energy storage properties of xBiMg0.5Zr0.5O3-(1-x)BaZr0.25Ti0.75O3 thin films

The development of miniaturized and lightweight electronic equipment requires the improvement of the dielectric breakdown strength and energy storage performance of dielectric capacitors. Therefore, in this study, a method for obtaining an amorphous phase by reducing the annealing temperature of a material is proposed to considerably improve the electrical breakdown, and a high-polarized substance is introduced to compensate for the polarization of the material. Lead-free xBiMg_0.5Zr_0.5O₃-(1-x)BaZr_0.25Ti_0.75O₃ (abbreviated as xBMZ-(1-x)BZT, x = 0.01, 0.02, 0.03, 0.04, and 0.05) thin films were prepared on Pt/Ti/SiO₂/Si substrates by using the sol-gel spin-coating method. The microstructure with coexisting nanocrystalline and amorphous phases was successfully controlled by reducing the annealing temperature and employing a rapid annealing process. All the films with this microstructure exhibited extremely high breakdown strength, and the effectiveness of this method was verified. When x = 0.04, the ultra-high breakdown strength of 6640 kV/cm, high energy storage density of 81.6 J/cm³ and high energy storage efficiency of 87% were achieved. Moreover, the dielectric and energy storage performance were excellent under temperatures from 20 °C to 200 °C. This study presents a feasible approach for designing new high-performance dielectric capacitors for energy storage devices in the future.     

Dielectric Breakdown of Polycrystalline Alumina: A Weakest‐Link Failure Analysis

The effects of varying electrode geometry (ball and ring) and size (radius), dielectric liquid (castor oil and Diala^® oil), and specimen thickness on the dielectric breakdown of a commercial‐grade alumina were investigated. The breakdown strength was expressed in terms of the maximum electric field in the ceramic calculated by finite element analysis (FEA) at the breakdown voltage. The breakdown strength decreased systematically with increasing electrode radius and specimen thickness, and the strength was higher in the Diala^® oil (dielectric constant, ε_r = 2.3 ± 0.06) as compared to the castor oil (ε_r = 4.6 ± 0.13). These effects of the electrode geometry, specimen thickness, and of the dielectric liquid on the breakdown strength of the alumina were analyzed with a weakest‐link failure model employing Laplace and Weibull distributions for a population of defects in the material. The measured size or scaling effects of the electrodes, specimen thickness, and of the dielectric liquid on breakdown strength were in better agreement with the Laplace distribution for a population of surface defects. The dielectric breakdown is likely initiated at surface pits produced by grain pullout. The measured area concentration of surface pits agreed with the defect density analyzed from the weakest‐link failure theory. FEA of specimens containing surface and subsurface cavities revealed that electric field concentrations were always greater for surface pits as compared to subsurface cavities. There is, in fact, no electric field concentration at a subsurface cavity located more than about 100–800 μm below the surface depending on the top electrode size.     

CaTiO3 linear dielectric ceramics with greatly enhanced dielectric strength and energy storage density

CaTiO₃ is a typical linear dielectric material with high dielectric constant, low dielectric loss, and high resistivity, which is expected as a promising candidate for the high energy storage density applications. In the previous work, an energy density of 1.5 J/cm³ was obtained in CaTiO₃ ceramics, where the dielectric strength was only 435 kV/cm. In fact, the intrinsic dielectric strength of CaTiO₃ is predicted as high as 4.2 MV/cm. Therefore, it should be a challenge issue to enhance the dielectric strength and energy storage density of CaTiO₃ ceramics by optimizing the microstructures. In the present work, dense CaTiO₃ ceramics with fine and uniform microstructures are prepared by spark plasma sintering, and the greatly enhanced dielectric strength (910 kV/cm) and energy storage density (6.9 J/cm³) are obtained. This can be ascribed to the improved resistivity and thermal conductivity, associated with the fine and uniform microstructures. The different post‐breakdown features of CaTiO₃ ceramics prepared by different process well interpret why the enhanced dielectric strength is achieved in the SPS sample. The energy storage density can be further improved to 11.8 J/cm³ by introducing the amorphous alumina thin films as the charge blocking layer, where the dielectric strength is 1188 kV/cm.     

Growth of thin film ferroelectric PZT,PHT, and antiferroelectric PHO from atomic layer deposition precursors

We present a conformal method of growing ferroelectric lead hafnate-titanate (PbHf_xTi_1−xO₃, PHT) and lead zirconate-titanate (PbZr_xTi_1−xO₃, PZT) using atomic layer deposition (ALD) precursors. The 4+ cation precursors consist of tetrakis dimethylamino titanium (TDMAT), tetrakis dimethylamino zirconium (TDMAZ) and tetrakis dimethyl amino hafnium (TDMAH) for Ti, Zr, and Hf, respectively. The Pb (2+) precursor was Lead bis(3-N,N-dimethyl-2-methyl-2-propanoxide) [Pb(DMAMP)₂]. PZT was limited to lead titanate (PTO)-rich compositions, where x <0.25 for PbZr_xTi_1−xO₃, and exhibited a remnant polarization of 26-27 µC/cm² with a coercive field between 150 and 170 kV/cm. The 3D-structure coating capability of PZT was demonstrated by deposition on micromachined trench sidewalls 45 µm deep. We fabricated Microelectromechanical systems (MEMS) cantilever arrays with PZT thin films grown using the present method and demonstrated piezoelectric actuation. Alternatively, PHT was deposited with Ti and Hf compositions within ±1 at.% of the morphotropic phase boundary (MPB). The PHT exhibited a remanent polarization of 7.0-8.7 µC/cm² with a coercive field between 84-100 kV/cm. We applied the same Pb and Hf precursors from the PHT process to grow antiferroelectric lead-hafnate (PHO), which showed the characteristic electric field-induced ferroelectric phase transition at approximately ±280 kV/cm and a maximum polarization of approximately ±32.8 µC/cm².     

Lead zirconium titanate thin films prepared by thermal annealing of multilayer structures composed of PbO,ZrO2 and TiO2

Lead zirconium titanate [Pb(Zr_xTi_1?x)O₃ or PZT] thin films were prepared by the thermal annealing of multilayer films composed of binary oxide layers of PbO, ZrO₂ and TiO₂. The binary oxides were deposited by metal organic chemical vapor deposition. An interdiffusion reaction for perovskite PZT thin films was initiated at approximately 550 °C and nearly completed at 750 °C for 1 h under O₂ annealing atmosphere. The composition of Pb/Zr/Ti in perovskite PZT could be controlled by the thickness ratio of PbO/ZrO₂/TiO₂ where the contribution of each binary oxide at the same thickness was 1:0.55:0.94. The electrical properties of PZT (Zr/Ti = 40/60, 300 nm) prepared on a Pt-coated substrate included a dielectric constant ?_r of 475, a coercive field E_c of 320 kV/cm, and remnant polarization P_r of 11 μC/cm² at an applied voltage of 18 V.     

Cubic Pyrochlore Bismuth Zinc Niobate Thin Films for High‐Temperature Dielectric Energy Storage

Thin films of cubic pyrochlore bismuth zinc niobate, a lead‐free dielectric, were fabricated using a solution chemistry based upon the Pechini method. Scanning electron microscopy confirmed that the films are smooth and mostly dense. The films exhibit a dielectric constant of 145 ± 5, a low dielectric loss of 0.00065 ± 0.0001, and a room temperature, 1 kHz maximum field of approximately 4.7 MV/cm. At frequencies of 100 Hz and 10 kHz, the maximum field sustained by the material increased to 5.0 MV/cm and 5.1 MV/cm, although the dielectric loss increased to 0.0065 ± 0.001. At a measurement frequency of 10 kHz, the maximum energy storage density was ~60.8 ± 2.0 J/cm³, while at a measurement frequency of 100 Hz, the maximum energy storage was ~46.7 ± 1.7 J/cm³. As the temperature was increased to 200°C, the breakdown strength of the films decreased, while the loss tangent remained modest. At 200°C and a measurement frequency of 100 Hz, the maximum energy storage density was ~23.1 ± 0.8 J/cm³, and at 10 kHz, the maximum energy storage density was ~27.3 ± 1.0 J/cm³.     

Effect of excess lead on the structural and electrical characteristics of sol-gel synthesized RuO2/Pb(ZrxTi1−x)O3/RuO2

In this study, we investigated the effect of excess lead on the structural and electrical characteristics of lead zirconate titanate [Pb(Zr_xTi_1−x)O₃, PZT] thin films using the sol-gel spin coating method. X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy were used to study the structural, morphological, chemical, and microstructural features, respectively, of these films as functions of the growth conditions (excess lead concentrations of 10, 20, and 25 mol%). The PZT thin film prepared at the 20 mol% condition exhibited the best electrical characteristics including a lower leakage current of 6×10⁻⁷ A/cm² at an electric field of 50 kV/cm, a larger capacitance value of 1.92 μF/cm² at a frequency of 1 kHz, and a higher remanent polarization of 20.1 μC/cm² at a frequency of 5 kHz. We attribute this behavior to the optimal amount of excess lead in this PZT film forming a perovskite structure and suppressing the reaction of PZT film with RuO₂ electrode.     

Structural and electrical properties of Pb(Zr0.53Ti0.47)O3 films prepared on La0.5Sr0.5CoO3 coated Si substrates

PbZr_0.53Ti_0.47O₃ (PZT) thin films with thickness of 0.9 μm were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates. Both PZT and LSCO were prepared by the sol–gel method. The concentration of LSCO sol was varied from 0.3 to 0.1 mol/L, which could modify the preferential orientation of PZT thin films and consequently affect the dielectric and ferroelectric properties. The LSCO electrode layers derived from lower sol concentration of 0.1 mol/L have much more densified structure, which facilitates the formation of (1 0 0) textured PZT films with smooth and compact columnar grains. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.     

Preparation of ferroelectric Pb(Zr0.52 Ti0.48)O3 thin films by sol-gel processing

Ferroelectric Pb(Zr_0.52 Ti_0.48)O₃ thin films were prepared by sol-gel processing on the Pt/Ti/SiO₂/Si(100) substrates. Effects of the concentration (0.2–0.8 M) of the starting solution (Pb/Zr/Ti= 1.1/0.52/0.48) and the sintering temperature (500–700 ‡C) on crystallinity, microstructure and electrical properties of PZT thin films were investigated. For the thin film prepared at 0.4 M starting solution, the highest crystallinity appeared at a sintering temperature of 650 ‡C. The average grain size of the PZT thin films was about 0.17 Μm. The film thickness was about 0.2 Μm. The relative dielectric constant and the dissipation factor of the film measured at 1 kHz were about 750 and 4.3%, respectively. The remnant polarization (Pr) and coercive field (Ec) of the film measured at the applied voltage of 5 V were about 49 ΜC/cm² and 134 kV/cm, respectively.     

Reduced leakage current and improved multiferroic properties of 0.5((1−x)BLPFO-xPZT)-0.5PVDF composite films

0.5((1−x)Bi_0.8La_0.1Pr_0.2FeO₃ (BLPFO)-xPb(Zr_0.52Ti_0.48)O₃ (PZT))-0.5Polyvinylidene difluoride (PVDF) composite films with x variations 0.25, 0.40 and 0.50 were synthesized using two step mixing, followed by hot pressing. The structural, microstructural, dielectric, magnetic, ferroelectric and magnetodielectric properties of composite films have been systematically investigated. The measurement of the dielectric properties at 1 kHz shows that the dielectric loss (tan δ) decreases with increasing the volume fraction of PZT. The value of maximum room temperature ε_r ~78 and low tan δ ~0.061 for 0.5((1−x)BLPFO-xPZT)-0.5PVDF composite film with x=0.50 suggests its usefulness for capacitor applications. For predictions of effective dielectric constant of composite films experimental data were fitted with Lichtenecker model. Among all the composite films, the film with x=0.50 was found to exhibit smallest leakage current density ~7×10⁻⁸ A/cm² and hence improved electrical resistivity. The variation of magnetization with temperature indicates the presence of spin glass behavior along with the ferromagnetic component at 5 K. The value of remnant polarization (2P_r) is found to increase with increase of PZT content in composite films. In the present composite films a significant dependence of dielectric constant on magnetic field has been observed, and highest value of magnetodielectric response of 2.85% is observed for composite film with x=0.50.     

Ferroelectric properties of PZT/BFO multilayer thin films prepared using the sol-gel method

In this study, Pb(Zr_0.52Ti_0.48)O₃/BiFeO₃ [PZT/BFO] multilayer thin films were fabricated using the spin-coating method on a Pt(200 nm)/Ti(10 nm)/SiO₂(100 nm)/p-Si(100) substrate alternately using BFO and PZT metal alkoxide solutions. The coating-and-heating procedure was repeated several times to form the multilayer thin films. All PZT/BFO multilayer thin films show a void-free, uniform grain structure without the presence of rosette structures. The relative dielectric constant and dielectric loss of the six-coated PZT/BFO [PZT/BFO-6] thin film were approximately 405 and 0.03%, respectively. As the number of coatings increased, the remanent polarization and coercive field increased. The values for the BFO-6 multilayer thin film were 41.3 C/cm² and 15.1 MV/cm, respectively. The leakage current density of the BFO-6 multilayer thin film at 5 V was 2.52 × 10^-7 A/cm².