Excellent Polyimide Dielectrics Containing Conjugated ACAT for High-Temperature Polymer Film Capacitor

In order to meet the requirements of polymer dielectric materials for high thermal stability and excellent dielectric properties in the application of high-temperature film capacitors, a series of polyimide (PI) films are fabricated by introducing a self-synthesized aniline trimer (ACAT) with a conjugated structure in this work. Since the conjugated ACAT in the main chains of PI improves the electron polarization and carrier mobility of the PI molecular chains, the dielectric constant of the ACAT-PI films is greatly enhanced (4.4–7.4). Meanwhile, the dissipation factor does not increase apparently (0.002–0.013). The dielectric properties are stable even when the temperature is up to 200 °C, the thermal degradation temperature is as high as 450 °C, and the mechanical properties are also excellent (70–105 MPa). Among all the films, the PI film with 5 mol% ACAT exhibits the maximal energy density of 3.6 J cm⁻³ under the field of 426 kV mm⁻¹, the high tensile strength (90 MPa) and the excellent thermal stability (T_d5 = 515 °C). The work paves the way to prepare high-temperature polymer dielectric film materials with high energy storage density.     

High-temperature resistant polyimide-based sandwich-structured dielectric nanocomposite films with enhanced energy density and efficiency

Development of advanced dielectric materials with both high-electric energy density and high-temperature resistant attributes is highly desirable in modern electronics and electrical systems. Herein, a series of polyimide (PI)-based sandwich-structured dielectric nanocomposite films have been attempted to develop the advanced high-temperature resistant capacitor films, wherein the boron nitride nanosheets/PI nanocomposite acts as the outer layers and the zinc oxide (ZnO)/PI as the middle layer. Benefitting from the merits of both fillers and the unique structure, the resulting nanocomposite films can simultaneously achieve both high-dielectric constant and high-breakdown strength, as well as low-electrical conduction loss, thus leading to improved discharged energy densities (U_e) and charge/discharge efficiency (η) at elevated temperatures. It is found that the sandwich-structured nanocomposite film with 0.4 vol% ZnO (0.4ZnO/PI-S) can deliver a maximum U_e of 5.29 J cm⁻³ at 400 MV m⁻¹ and 150°C, which is about 1.9 times that of the pristine PI film. Moreover, outstanding dielectric stability over 10,000 charge/discharge cycles has been demonstrated in such PI-based sandwich-structured nanocomposite films at 150°C and 200 MV m⁻¹. This research may provide a new paradigm to explore polymer nanocomposites having excellent energy storage and efficiency at elevated temperatures.     

Dielectric properties and energy-storage performance of two-dimensional molybdenum disulfide nanosheets/polyimide composite films

Flexible dielectric materials with high electric energy density and high-temperature resistant characteristic are of great importance for modern electronics and electrical systems. Herein, two-dimensional molybdenum disulfide (MoS₂) nanosheets were efficiently produced via liquid-phase exfoliation and then incorporated into polyimide (PI) to prepare MoS₂/PI dielectric nanocomposites. Compared to the pristine PI, MoS₂/PI nanocomposite films exhibited much larger dielectric permittivity while their dielectric losses still maintained relatively low levels. On the other hand, the Weibull breakdown strength of these nanocomposite films initially increased and then decreased with the increase in the MoS₂ content and gave rise to a maximum value of 395 MV m⁻¹ at 1 vol % loading. Combination of the improved dielectric permittivity and breakdown strength makes the MoS₂/PI nanocomposite film with 1 vol % MoS₂ possess an elevated energy density of about 3.35 J cm⁻³. Moreover, good tensile and thermal properties of the nanocomposite films hold great promise for their applications in high-temperature and harsh conditions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47991.     

Electrical properties and energy-storage performance of (Pb0.92Ba0.05La0.02)(Zr0.68Sn0.27Ti0.05)O3 antiferroelectric thick films prepared by tape-casing method

The energy-storage performance and dielectric properties of tape-cast (Pb_0.92Ba_0.05La_0.02)(Zr_0.68Sn_0.27Ti_0.05)O₃ (PBLZST) antiferroelectric (AFE) thick films with different thicknesses were systematically studied. As the thickness of the thick films increased from 40 to 80 µm, the dielectric constant and saturation polarization (P_s) of the thick films were gradually increased, while their corresponding breakdown strength (BDS) was decreased. A maximum recoverable energy-storage density of 6.8 J/cm³, companied by an efficiency of 61.2%, was achieved in the PBLZST AFE thick film with a thickness of 40 µm at room temperature. Moreover, the energy density of the PBLZST AFE thick films also displayed good thermal stability over 25–200 °C. In addition, all the samples had a low leakage current density of ~10⁻⁶ A/cm² at room temperature. These findings demonstrated that the PBLZST thick films should be a promising candidate for applications in high energy-storage capacitors.     

Giant dielectric constant and tunable phase-transition characteristics of ZnF2/BaF2-modified BaTiO3 thick films

High performance capacitors have been investigated to meet higher integration density with optimized charge-storing capability. Here, we introduce nonconventional thick film dielectric compositions based on 95BaTiO₃–xZnF₂–(2−x)BaF₂–3glass (x = 0.5, 1.0, and 1.5) where the relative content of ZnF₂/BaF₂ is critical in controlling dielectric behavior. The thick films were prepared on Cu foils by regular screen-printing and then firing at 950°C in inert atmosphere. As an optimal example, thick film composition modified with 1.0ZnF₂/1.0BaF₂ exhibited a dielectric constant of ~1903 and a dielectric loss of ~0.04 at 1 MHz with dispersive dielectric relaxation behavior, which are far better than any reported corresponding values so far. Particularly, it was very interesting to observe that Curie temperature was tunable from −19 to +34°C, depending on the relative content of fluoride additives only within the 2 mol% range. Dependency of the relative contents of the fluorides is primarily investigated with regard to microstructure and dielectric properties.     

Large recoverable energy density with excellent thermal stability in Mn‐modified NaNbO3‐CaZrO3 lead‐free thin films

Effect of Mn dopant on energy storage properties in lead‐free NaNbO₃?0.04CaZrO₃ (NNCZ) thin films was investigated. The leakage current was largely suppressed, whereas dielectric constant, breakdown fields, and the difference between maximum polarization and remnant polarization were improved significantly by Mn doping, resulting in a large enhancement of energy storage performance. A large recoverable energy storage density of ~19.64 J/cm³ and an excellent thermal stability (from 30 to 160°C) were simultaneously achieved in the NNCZ thin film with 1 mol% Mn addition. Our results ascertain the great potential of NNCZ lead‐free thin films for the applications in energy storage devices over a wide temperature range.     

2D MoS2 Nanosheet-Based Polyimide Nanocomposite with High Energy Density for High Temperature Capacitor Applications

With the development of electrical vehicles and power electronics, the demand for high-temperature energy storage capacitors with high energy density has grown rapidly. In this investigation, 2D MoS₂ nanosheets are coated with a thin layer of poly(methyl methacrylate) and then mixed with polyimide (PI) solution to fabricate nanocomposites. The dielectric constant of MoS₂-g-PMMA/PI (MPP-3%) reaches 4.2, which is 20% higher than that of a pristine PI film. The energy density of the MPP-3% nanocomposite reaches 8.6 J cm⁻³, which is 40% higher than the highest energy density of a pristine PI film. In addition, the electric breakdown field of the MPP-3% composite is 50% higher than that of the MoS₂/PI nanocomposite without a surface coating. Furthermore, it is found that the highest energy density of MoS₂-g-PMMA/PI reaches 3.92 J cm⁻³, which is 47.9% higher than that of the PI film at 150 °C. The charge–discharge efficiency of the nanocomposite film reaches 61.7% at 150 °C. This result is much higher than the previously reported research results for high-temperature capacitor applications. The MoS₂-g-PMMA/PI-based nanocomposite shows great promise for use in high-temperature capacitor applications.     

Pyrochlore structure and dielectric properties of bismuth zinc niobate thin films prepared by RF sputtering

Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films with thickness from 60 nm to 200 nm were prepared by radio-frequency magnetron sputtering and post-annealed from 550 °C to 650 °C. The x-ray diffraction results indicated that the BZN thin films possessed a cubic pyrochlore phase. The BZN thin films exhibited thickness-independent dielectric properties with dielectric constant of ~180 and low loss tangent less than 1% at 10 kHz as the film thickness decreased to 60 nm. The BZN thin films with thickness of 200 nm and post-annealed at 650 °C had a tunability of 32.7% at a DC bias field of 1.5 MV/cm. The results suggest that the BZN thin films have promising applications on the embedded capacitors, tunable devices and energy storage devices.     

Interdependence of piezoelectric coefficient and film thickness in LiTaO3 cantilevers

Electromechanical energy demands on homogenous thick films of piezoceramics with sufficiently large piezoelectric constant and reproducible performance. Single-phase LiTaO₃ films deposited by sol-gel processing have been fabricated as cantilevers to investigate the interdependence of dielectric and piezoelectric properties as a function of film thickness. Phase pure LiTaO₃ films with varying thickness in the range of 2.07-4.37 µm on stainless steel substrates were obtained after calcination of samples at 650°C. The relative permittivity of optimized spin-coated films peaked at 479.73 (1 kHz), whereas the piezoelectric coefficient (d₃₃ mode) determined by piezoresponse force microscopy was in the range of 21-24 pm/V. The effect of poling was studied through the butterfly and phase curves. A figure of merit (FOM) up to 3.29 (10⁻¹⁸ m²/V²) was determined for cantilever devices, which were able to generate a peak-to-peak voltage of 0.046-0.15 V using a 1 MΩ resistor as an impedance load at a fixed acceleration of 1.5 m/s². While the power density was in the range of ~4-20 × 10⁻⁹ W/m³, which increased with the increasing film thickness. The leakage current density decreased in the range of 4 × 10⁻⁵-6 × 10⁻⁷ A/m² in the same direction. As both ferroelectric and piezoelectric properties of LiTaO₃ films are dependent on film thickness, an optimal energy conversion efficiency was obtained for a thickness of ~3 µm. Furthermore, these devices were tested up to a temperature of 150°C for voltage generation. Given the need for lead-free piezoelectric materials for environmental applications, these LiTaO₃ cantilevers are very promising for vibrational energy harvester (VEH) applications especially due to their cost effectiveness, small size, stability at higher temperatures, and repeatable properties, which makes them suitable for MEMS devices for industrial applications.     

Effect of (Zn,Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe_1-2xZn_xMn_xO₃ (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO₃ (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10^?6 A/cm²) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm² was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm². The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.     

High-energy storage density in NaNbO3-modified (Bi0.5Na0.5)TiO3-BiAlO3-based lead-free ceramics under low electric field

Ceramic-based dielectric capacitor are highly suitable for pulsed power applications due to their high power density and excellent reliability. However, the ultrahigh applied electric field limit their applications in integrated electronic devices. In this work, (1−x){0.96(Bi_0.5Na_0.5)(Ti_0.995Mn_0.005)O₃-0.04BiAlO₃}-xNaNbO₃ (BNT-BA-xNN, x = 0, 0.04, 0.08, 0.12, and 0.16) ternary ceramics were designed to achieve excellent energy storage properties. It was found that the introduction of NaNbO₃ (NN) effectively increase the difference (ΔP) between P_max and P_r, resulting in an obvious enhancement of the energy storage properties. High recoverable energy storage density, responsivity, and power density, that is, W_rec = 2.01 J/cm³, ξ = W_rec/E = 130.69 J/(kV⋅m²), and P_D = 25.59 MW/cm³, accompanied with superior temperature stability were realized at x = 0.14 composition. In addition, the thermal stable dielectric properties of the sample can be prominently improved with increasing NN content. The temperature coefficient of capacitance (TCC) of x = 0.16 composition is lower than 15% over the temperature range from 49°C to 340°C, with a high dielectric permittivity of 1647 and a low dielectric loss (0.0107) at 150°C. All these features show that the BNT-BA-xNN ceramics are promising materials for energy storage application.     

Effect of argon-oxygen ratio on dielectric and energy storage properties of Ba(Zr0.35Ti0.65)O3 thin films

Lead-free Ba(Zr_0.35Ti_0.65)O₃(short as BZT35) ferroelectric thin films are prepared by RF magnetron sputtering on Pt/Ti/SiO₂/Si substrates. Effects of argon-to-oxygen (short as Ar/O₂) ratios on phase transition, dielectric and energy storage properties are studied. The research found that all thin films are perovskite structures. With the decrease of Ar/O₂, the oxygen vacancies (OVs) in the film are effectively suppressed, which promotes the film to obtain a larger dielectric constant, smaller dielectric loss, and lower leakage current density. The BZT35 film prepared under Ar/O₂ = 40:10 has excellent energy storage density (48.03 J/cm³) and efficiency (87.7%) because of its elongated hysteresis loop, the largest polarization difference (ΔP = 22.91 μC/cm²), higher breakdown field strength (E_b = 4.50 MV/cm) and lower leakage current density (J = 2.3 × 10^?5 A/cm²) and high power density of 7.94 MW/cm³. In addition, the BZT35 film also has excellent frequency stability (500 Hz-20 kHz). These excellent properties show that BZT35 has very broad application prospects in energy storage.     

High energy storage efficiency and thermal stability of A-site-deficient and 110-textured BaTiO3–BiScO3 thin films

The development of thin film dielectrics having both high energy density and energy conversion efficiency, as well as good thermal stability, is necessary for practical application in high-temperature power electronics. In addition, there is a demand for the development of new Pb-free high-energy density dielectric materials due to environmental concerns. In this regard, thin films of weakly coupled relaxors based on solid solutions of BaTiO₃–BiMeO₃ have shown good promise, because they exhibit a remarkably large polarization over a wide temperature range. Nevertheless, the performance of Pb-free thin films has lagged behind that of their Pb-based counterparts in terms of thermal stability and energy conversion efficiency. Toward this end, most recent studies on BaTiO₃–BiMeO₃ systems have focused on the optimization of material composition, while relatively less attention has been paid to other aspects such as defect chemistry and crystallographic texture. In this study, we examine the effects of A-site vacancy and crystallographic texture on the energy storage performance of BaTiO₃–BiScO₃ thin films synthesized using pulsed laser deposition (PLD). It is shown that a high energy storage density (W_r) of ~28.8 J/cm³ and a high efficiency of η >90% are achieved through a combination of moderate A-site vacancy concentration and (110) crystallographic texture. Furthermore, W_r remains nearly temperature independent while a high efficiency of η >80% is maintained for temperatures up to 200°C, which constitutes one of the best performances for Pb-free ferroelectric films for high-temperature capacitor applications.     

Improvement of high-temperature energy storage properties of polyimide-based nanocomposites with sandwich structure

The demand for dielectric materials that have high energy and power density properties, and are operational at high temperature has increased with the advancement in new energy technology, high-end microelectronics, and other industries. Pure ceramic and polymer capacitors are not enough to meet the ever increasing energy requirements in a wide range of applications. In this article, we report a sandwich structure nanocomposite film based on polyimide (PI) with high breakdown strength SiO₂/PI as the outer layers and high dielectric constant strontium titanate (SrTiO₃)/PI as the sandwich layer. The results showed that the prepared composites can obtain high energy storage density and low dielectric loss at high temperatures. The composites achieved an energy storage density of 5.5 J cm⁻³ and a dielectric loss of 0.004 at a temperature of 150°C when the filling amount of SrTiO₃ was 0.5 vol% and the filling amount of SiO₂ was 3 vol%. This work shows that the composites are promising dielectrics for applications at high temperature and provides a new idea for high-temperature energy storage devices.     

Investigation of dielectric and piezoelectric properties in aliovalent Eu3+-modified Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics

Rare earth (Eu³⁺)-modified Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) polycrystalline ferroelectric ceramics were fabricated by high-temperature solid-state sintering, the phase structure, dielectric and piezoelectric properties were investigated. Eu³⁺ addition was found to significantly improve dielectric and piezoelectric properties of PMN-PT, where the optimized properties were achieved for the composition of 2.5 mol%Eu: 0.72PMN-0.28PT, with the piezoelectric d₃₃ = 1420 pC/N, dielectric ε_r = 12 200 and electromechanical k₃₃ = 0.78, respectively. All these results indicate that the Eu³⁺-doped PMN-PT ceramics are promising candidates for high-performance room-temperature piezoelectric devices.     

Energy storage and discharge performance for (1−x)BaSrTiO3−xBi(Zn1/2Ti1/2)O3 ceramics

Although lead-free dielectric ceramics have been widely studied to obtain excellent dielectric properties and good energy storage properties, the primary challenge of low energy storage density has not yet been resolved. Here, we introduce the concept of crossover relaxor ferroelectrics, which represent a state intermediate between normal ferroelectrics and relaxor ferroelectrics, as a solution to address the issue of low energy density. The (1−x)BaSrTiO₃−xBi(Zn_1/2Ti_1/2)O₃ (x = 0,.05, .1, .15, .2) ceramics were prepared by a solid-state method. Remarkably, 0.85BST–0.15BZT ceramics achieved a high recoverable energy density (W_rec) of 2.18 J/cm³ under an electric field of 240 kV/cm. BST–BZT materials exhibit substantial recoverable energy density, high breakdown strength, and superior energy efficiency, positioning them as a promising alternative to meet the diverse demands of high-power applications.     

Structure and microwave dielectric properties of Li(Al1-xLix)SiO4-x ceramics

Li(Al_1-xLi_x)SiO_4-x (x = 0.005, 0.01, 0.015, and 0.02) ceramics were synthesized via a traditional solid phase reaction method with different sintering temperatures. To determine the positions occupied by Li⁺ in the lattice, the defect formation energies and total energies of various sites of LiAlSiO₄ (LAS) occupied by Li⁺ were examined, and the energy of LAS systems were calculated using density functional theory of first-principle with the CASTEP module. The results demonstrated that the Al-sites occupied by Li⁺ had the lowest formation energies and total energy, so Li ⁺ should substitute Al³⁺. The impacts of replacing Al³⁺ with Li⁺ on the bulk density, sintering properties, phase composition, microstructure, and microwave dielectric properties of Li(Al_1-xLi_x)SiO_4-x (0 = x ≤ 0.02) ceramics were thoroughly studied. With Li⁺-doping, the sintering temperature decreased from 1300 °C (x = 0) to 1175 °C (x = 0.02), while the Q × f and τ_f values of LAS ceramics significantly increased. The Li(Al_0.99Li_0.01)SiO_3.99 ceramic was fully sintered at 1250 °C for 10 h to obtain excellent microwave dielectric properties: ε_r = 3.49, Q × f = 51,358 GHz, and τ_f = ?51.48 × 10^?6 °C^?1.     

Novel Temperature Stable Li2MnO3 Dielectric Ceramics with High Q for LTCC Applications

Novel microwave dielectric ceramics in the Li₂MnO₃ system with high Q prepared through a conventional solid‐state route had been investigated. All the specimens exhibited single phase ceramics sintered in the temperature range 1140°C–1230°C. The microwave dielectric properties of Li₂MnO₃ ceramics were strongly correlated with sintering temperature and density. The best microwave dielectric properties of ε_r = 13.6, Q × f = 97 000 (GHz), and τ_f = ?5.2 ppm/°C could be obtained as sintered at 1200°C for 4 h. BaCu(B₂O₅) (BCB) could effectively lower the sintering temperature from 1200°C to 930°C and slightly induced degradation of the microwave dielectric properties. The Li₂MnO₃ ceramics doped with 2 wt% BaCu(B₂O₅) had excellent dielectric properties of ε_r = 11.9, Q × f = 80 600 (GHz), and τ_f = 0 ppm/°C. With low sintering temperature and good dielectric properties, the BCB added Li₂MnO₃ ceramics are suitable candidates for LTCC applications in wireless communication system.     

Enhanced dielectric and energy-storage properties in BiFeO3-modified Bi0.5(Na0.8K0.2)0.5TiO3 thin films

Lead free Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ thin films doped with BiFeO₃ (abbreviated as BNKT-xBFO) (x = 0, 0.02, 0.04, 0.08, 0.10) were deposited on Pt(111)/Ti/SiO₂/Si substrates by sol-gel/spin coating technique and the effects of BiFeO₃ content on the crystal structure and electrical properties were investigated in detail. The results showed that all the BNKT-xBFO thin films exhibited a single perovskite phase structure and high-dense surface. Reduced leakage current density, enhanced dielectric and ferroelectric properties were achieved at the optimal composition of BNKT-0.10BFO thin films, with a leakage current density, dielectric constant, dielectric loss and maximum polarization of < 2 × 10⁻⁴ A/cm³, ~ 978^, ~ 0.028 and ~ 74.13 μC/cm² at room temperature, respectively. Moreover, the BNKT-0.10BFO thin films possessed superior energy storage properties due to their slim P-E loops and large maximum polarization, with an energy storage density of 22.12 J/cm³ and an energy conversion efficiency of 60.85% under a relatively low electric field of 1200 kV/cm. Furthermore, the first half period of the BNKT-0.10BFO thin film capacitor was about 0.15 μs, during which most charges and energy were released. The large recoverable energy density and the fast discharge process indicated the potential application of the BNKT-0.10BFO thin films in electrostatic capacitors and embedded devices.     

Sol‐gel derived TiNb2O7 dielectric thin films for transparent electronic applications

To reduce power consumption of transparent oxide‐semiconductor thin film transistors, a gate dielectric material with high dielectric constant and low leakage current density is favorable. According to previous study, the bulk TiNb₂O₇ with outstanding dielectric properties may have an interest in its thin‐film form. The optical, chemical states and surface morphology of sol‐gel derived TiNb₂O₇ (TNO) thin films are investigated the effect of postannealing temperature lower than 500°C, which is crucial to the glass transition temperature. All films possess a transmittance near 80% in the visible region. The existence of non‐lattice oxygen in the TNO film is proposed. The peak area ratio of non‐lattice oxygen plays an important role in the control of leakage current density of MIM capacitors. Also, the capacitance density and dissipation factor were affected by the indium tin oxide (ITO) sheet resistance at high frequencies. The sample after postannealing at 300°C and electrode‐annealing at 150°C possesses a high dielectric constant (>30 at 1 MHz) and a low leakage current density (<1 × 10^?6 A/cm² at 1 V), which makes it a very promising gate dielectric material for transparent oxide‐semiconductor thin film transistors.