Optimization of high temperature energy storage properties of PEI-based composite dielectric based on rapid in-situ growth of inorganic functional layer

The serious deterioration of the energy density of polymer energy storage dielectrics in high temperature environment is the main reason to curb the in-depth application of dielectric film capacitors in the field of modern electrical and electronic engineering. Here, aiming at the problem of low dielectric constant of polymer dielectric, a simple, low-cost method is proposed to grow inorganic polar functional layer on surface of polymer film in situ, which effectively improves the polarization characteristics of polymer dielectric at high temperature. The in situ growth of Ti(OH)₄ inorganic polar functional layer on surface of polyetherimide (PEI) film noteworthy to improve the energy storage performance of dielectric film. The energy storage density of 4.59 J/cm² is obtained at 150°C and 600 MV/m, which is 1.18 times that of PEI film under the same condition. The significant enhancement of high temperature energy storage density can be attributed to introduction of functional layer, which effectively improves the dielectric properties and polarization intensity of dielectric film. Furthermore, the facile preparation method provided in this paper can be applied to various thin films under the premise of controllable cost, which is of great significance to improve the high temperature energy storage characteristics of polymer dielectric.     

Breakdown field enhancement and energy storage performance in four-layered Aurivillius films

In dielectric capacitors, ferroelectric thin films with slim polarisation electric (P-E) hysteresis loops, which are mainly characterised by small residual polarisation (P_r) and large saturation polarisation (P_s) are expected to obtain high recoverable energy density (U_r) and efficiency (η). However, a lower breakdown in ferroelectric thin films usually impedes this result. Here, through the co-doping of La³⁺ and Pr³⁺ ions, a larger U_r of 54.27 J/cm³ and high η of 85.6% were obtained in four-layered Aurivillius phase ferroelectric thin films capacitors due to the enhanced breakdown electric field. The doped films annealed at relatively low temperatures showed similar energy storage properties compared with those of the prototype and higher energy storage efficiency compared with that of higher annealing films. In addition, the obtained thin film shows excellent energy storage properties in a wide frequency range, fatigue durability and good thermal stability. These results indicated that four-layered Aurivillius films are promising candidate materials for dielectric energy storage capacitors. The co-doping of double ions was an effective way to improve energy storage performance.     

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.     

Thickness dependence of microstructure,dielectric and leakage properties of BaSn0.15Ti0.85O3 thin films

The BaSn_0.15Ti_0.85O₃ (BTS) thin films are prepared on Pt-Si substrates with thickness ranging from ~ 60?nm to ~ 380?nm by radio frequency magnetron sputtering. The effects of thickness on microstructure, surface morphologies and dielectric properties of thin films are investigated. The thickness dependence of dielectric constant is explained based on the series capacitor model that the BTS thin film is consisted by a BTS bulk layer and an interfacial layer (dead layer) between the BTS and bottom electrode. The thin films with thickness of 260?nm give the largest figure of merit of 76.9@100?kHz, while the tunability and leakage current density are 64.6% and 7.46?×?10^?7 A/cm² at 400?kV/cm, respectively.     

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.     

Reinforced via the insulative boric oxide in the BaTiO3 amorphous thin film with high energy storage capability and stability

Dielectric film capacitors are considered as a potential candidate for advanced power electronics technology due to their fast charging and discharging rate and stability. However, the further improvement of energy storage density is still a major challenge. Herein, a reasonable amorphous structure is applied to the preparation of dielectric film capacitors to improve the dielectric and energy storage properties. The high breakdown strength and energy storage density in the amorphous film are assigned by the disordered structure and intrinsic high insulative for B₂O₃. As a result, a high discharge energy storage density of 68.64 J cm^?3 and an efficiency of 85% can be achieved in the BaTiO₃-5wt%B₂O₃ amorphous thin film at 7.3 MV cm^?1, together with excellent thermal stability (20–200 °C) and cyclic stability (up to 10⁵ times) This work provides a paradigmatic method to achieve high energy storage density and stability.     

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.     

Realizing high-performance capacitive energy storage in lead-free relaxor ferroelectrics via synergistic effect design

Developing lead-free dielectric ceramics with outstanding energy storage properties has become urgent for dielectric capacitors. Herein, a synergistic effect design strategy has been proposed that combined the merits of relaxor ferroelectrics with high polarization/low remanent polarization and enhanced linear materials with relatively high polarization/ultrahigh dielectric breakdown strength. Hence, a novel lead-free 0.955Bi_0.5Na_0.5TiO₃-0.045Ba(Al_0.5Ta_0.5)O₃-based ceramics are engineered though introducing the enhanced linear dielectrics of 0.9CaTiO₃-0.1BiScO₃. A large recoverable energy density (W_rec～3.13 J/cm³) and high efficiency (η～88.4 %) as well as excellent power density (P_D～95.1 MW/cm³) and discharge speed (t_0.9～36 ns), along with superior stabilities, have been simultaneously realized. The piezoelectric force microscope measurements reveals that incorporating CT-BS generates more highly-dynamic polar nanoregions (PNRs), giving rise to rapid reversibility of PNRs with concurrently tailored energy storage performance. This study demonstrates synergistic effect design is a feasible and paradigmatic way to explore high-efficiency dielectrics for high-power energy storage applications.     

Effect of sputtering pressure on structural and dielectric tunable properties of BaSn0.15Ti0.85O3 thin films grown by magnetron sputtering

Lead?free ferroelectric BaSn_0.15Ti_0.85O₃ (BTS) thin films are grown on Pt-coated Si substrates by magnetron sputtering at 650?°C, the effect of sputtering pressure on the microstructural, surface morphological, dielectric properties and leakage characteristic is systematically investigated. XRD analysis shows the crystallinity of BTS thin films with perovskite structure can be improved by appropriate control of the sputtering pressure. The surface morphology analyses reveal that grain size and roughness can be affected by sputtering pressure. The BTS thin films prepared at sputtering pressure of 3.0?Pa exhibit a low dispersion parameter of 0.006, a medium dielectric constant of ~357, a high dielectric tunability of 65.7%@?400?kV/cm and a low loss tangent of 0.0084?@?400?kV/cm. Calculation of figure of merit (FOM) displays a high value of 84.1, and the measurement of leak current shows a very low value of 4.39?×?10^–7 A/cm² at 400?kV/cm. The results indicate that BTS thin film deposited sputtering pressure of 3.0?Pa is an excellent candidate for electrically steerable applications     

Optimized energy storage performances in morphotropic phase boundary (Na0.8K0.2)0.5Bi0.5TiO3-based lead-free ferroelectric thin films

As microelectronic devices move toward integration and miniaturization, the thin film capacitors with high energy density and charge/discharge efficiency have attracted immense interests in modern electrical energy storage systems. Despite morphotropic phase boundary (Na_0.8K_0.2)_0.5Bi_0.5TiO₃-based lead-free materials with outstanding ferroelectric and piezoelectric properties, while large ferroelectric hysteresis with high remanent polarization (P_r) hinder to improve energy storage capability. Here, novel lead-free relaxor-ferroelectric (RFE) thin film capacitors with high energy density are successfully prepared in (1-x) (Na_0.8K_0.2)_0.5Bi_0.5TiO₃-xBa_0.3Sr_0.7TiO₃ [(1-x)NKBT-xBST] systems. Introducing BST into the NKBT systems is expected to reduce remanent polarization (P_r) on account of coupling reestablishment of the polar nano-regions (PNRs) and improving the relaxation behavior. As a result, 0.6NKBT-0.4BST thin film exhibits high energy density (W_rec ～ 54.79 J/cm³) together with satisfactory efficiency (η ～ 76.42%) at 3846 kV/cm. The stable energy storage performances are achieved within the scope of operating temperatures (20–200 °C) and fatigue cycles (1-10⁷ cycles). This work furnishes a new technological way for the design of high energy-density thin film capacitors.     

Ba-based complex perovskite ceramics with superior energy storage characteristics

Linear dielectrics are widely used to create high power capacitors, where it is a big challenge to achieve high energy storage density in such dielectrics. Here, Ba-based complex perovskite ceramics with high dielectric strength, medium dielectric constant, and ultra-low dielectric loss are proposed as the candidates for high energy storage density dielectric materials, and the significant effects of 1:2 B-site ordering and ordering domain structure are systematically investigated. In Ba(Mg_1/3Nb_2/3)O₃ ceramics, high dielectric strength of 1452 kV cm⁻¹ combined with high energy storage density of 3.31 J cm⁻³ are achieved in the samples after post-densification annealing, and they are 28% and 57%, respectively, higher than those in the as-sintered samples. The significant enhancement of energy storage performance could be attributed to the increased B-site ordering degree, and the uniform ordering domain structure. Furthermore, amorphous alumina thin films are introduced as the charge blocking layers, which significantly enhance the energy storage density to 5.09 J cm⁻³. The present work provides a new approach to develop the dielectric ceramics with high energy storage density.     

Fast ferroelectric domain wall motion in BiAlO3

The ferroelectric domain wall motion was investigated in epitaxial PbTiO₃ and BiAlO₃ thin films on SrRuO₃/SrTiO₃ substrates. To determine the switching speeds of two ferroelectric capacitors consisting of PbTiO₃ and BiAlO₃ thin films, the switching currents of the two capacitors were measured as a function of time. The BiAlO₃ thin film showed faster switching behavior than the PbTiO₃ thin film. Data from a piezoelectric force microscope study indicated that the high domain wall motion of the BiAlO₃ thin film is due to its low activation energy.     

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.     

Dielectric tunable properties of BaTi1-xSnxO3 thin films derived from sol-gel soft chemistry

Dense and homogeneous BaTi_1-xSn_xO₃ (BTS, x = 0.1, 0.15, 0.2, 0.25, and 0.3) thin films are prepared by sol-gel and spin-coating soft chemistry, which is a simple, repeatable and quality-controlled method. The effects of Sn content on the structure and dielectric properties are systemically studied. The BTS thin film with 0.25 mol% Sn is found to exhibit a moderate dielectric constant of 225–398, a high tunability of 43.3% under a low bias electric field of 8 kV/mm, and a corresponding leakage current density of 6.2×10^?8 A/cm². These improvements are a result of the enhancement in relaxor characteristics, the good crystallization conditions leading to a denser and more uniform structure, as well as the inhibition of oxygen vacancies resulting from the suppression of electronic transition from Ti⁴⁺ to Ti³⁺. The findings reported in this work provide a simple and effective way to prepare excellent tunable thin films that show great potential for the development of electrically tunable components and devices.     

Seed layer mediated growth of high dielectric and low leakage BaTiO3 thin film using two-step sputtering process

In this study, we demonstrated the seed layer mediated growth of high-quality BaTiO₃ (BTO) thin films using a two-step radio frequency (RF) magnetron sputtering process. Since the as-grown BTO thin films obtained by RF magnetron sputtering at the deposition temperatures of 300–500 °C were amorphous with a low dielectric constant of 20, it is necessary to develop a fabrication process for obtaining crystalline high-k BTO thin films without sacrificing other film properties such as morphology and leakage current. First, it was revealed that ex-situ post-deposition annealing (PDA) at high temperatures in the 700–800 °C range led to the crystallization of BTO films and a high dielectric constant of 121. However, the film morphology deteriorated significantly during PDA, and consequently, a high leakage current was observed due to the rough and discontinuous surface containing voids and micro-cracks. To achieve an excellent leakage current characteristic as well as a high dielectric constant for a crystalline BTO thin film, in-situ crystallization was carried out through local epitaxial growth using a crystalline seed layer. The crystalline BTO seed layer was formed by annealing a 5-nm-thick amorphous BTO film at 700 °C on which the in-situ crystallized BTO main layer was deposited at 500 °C. The in-situ crystallization method resulted in a smooth and uniform surface and a high dielectric constant of 113. In addition, the in-situ crystallized BTO film exhibited a low leakage current density of 10⁻⁶ A/cm² (at 0.8 V) displaying an improvement by a factor of 10³ compared to the ex-situ crystallized BTO film.     

High energy storage efficiency of NBT-SBT lead-free ferroelectric ceramics

Ceramic-based dielectrics have been widely used in pulsed power capacitors owing to their good mechanical and thermal properties. Bi_0.5Na_0.5TiO₃-based (NBT-based) solid solutions exhibit relatively high polarization, which is considered as a promising dielectric energy storage material. However, the high remnant polarization and low energy efficiency limit their application in dielectric capacitors. Herein, a typical relaxor ferroelectric Sr_0·7Bi_0·2TiO₃ (SBT) was introduced into the NBT system to strengthen the overall relaxor behavior, resulting in reduced remnant polarization. We prepared (1-x)NBT-xSBT (x = 0.35, 0.45, 0.55, and 0.65) ceramics by the conventional solid-phase reaction method and further investigated their microstructures, dielectric and energy storage properties. With the increase of SBT content, the size of the grains and the maximum dielectric constant gradually decreased, simultaneously. Furthermore, the dielectric shoulder corresponding to the maximum dielectric constant shifted to a lower temperature, indicating that the enhancement of polarization dynamics was a consequence of the domain refinement. As a result, the optimum property was identified in the 0.45NBT-0.55SBT sample with a high recoverable energy density of 1.34 J/cm³ and an outstanding energy efficiency of 96% at a low electric field of 100 kV/cm.     

Superior energy storage performance of all-inorganic flexible antiferroelectric-insulator multilayer thin films

In this work, we develop an all-inorganic flexible capacitor films that by growing antiferroelectric Pb_0.94(Li_0.5Al_0.5)_0.06ZrO₃ (PLAZO) and insulating Al₂O₃ (AO) layer by layer on the flexible mica substrates. The results show that the low-annealing temperature below 600°C endows the PLAZO films to have low polarization loss and high breakdown strength, conversely, the high-annealing temperature above 650°C gives rise to large maximum polarization at the expense of breakdown strength. The insulating AO layers are introduced to reconcile the polarization and breakdown strength, achieving a remarkable improvement in the energy storage density of 41.78 J/cm³ with an efficiency of 91.2% in the AO/PLAZO/AO/PLAZO/AO (APAPA) multilayer films, which can be attributed to the significant improvement in breakdown strength and suppression of polarization loss by introducing AO insulator layer. Moreover, the energy storage performance of the APAPA flexible thin film capacitors possesses excellent frequency stability as well as bending cyclic endurance.     

High energy storage density achieved in Bi3+-Li+ co-doped SrTi0.99Mn0.01O3 thin film via ionic pair doping-engineering

The demand for lead-free dielectric capacitors with rapid charge-discharge ability and high energy storage density is increasing owing to the rapid development of electronic equipment. Lead-free Sr_1-x(Bi_0.5Li_0.5)_xTi_0.99Mn_0.01O₃ (x = 0.02, 0.025, 0.03, 0.035) thin films grown on Pt/Ti/SiO₂/Si substrates were prepared by sol-gel method. A huge enhancement in polarization was found in Bi³⁺-Li⁺ co-doped SrTiO₃ thin films. The large lattice distortion and local broken-symmetry due to formation of Bi³⁺-Li⁺ ionic pairs are responsible for ferroelectricity and high polarization. The maximum polarization (42.1 μC/cm²) and largest energy storage density of 47.7 J/cm³ at 3307 kV/cm were both achieved in Sr_0.975(Bi_0.5Li_0.5)_0.025Ti_0.99Mn_0.01O₃ thin film. Moreover, an excellent temperature-dependent stability was also obtained in Sr_0.975(Bi_0.5Li_0.5)_0.025Ti_0.99Mn_0.01O₃ thin film from 30 to 110 °C.     

High-performance La-doped BCZT thin film capacitors on LaNiO3/Pt composite bottom electrodes with ultra-high efficiency and high thermal stability

Dielectric capacitors possessing large energy storage density, high efficiency and high thermal stability simultaneously are very attractive in modern electronic devices to be operated in harsh environment. Here, it is demonstrated that large energy storage density (W?～?15.5?J/cm³), ultra-high efficiency (η ～93.7%) and high thermal stability (the variation of both W from 20?°C to 260?°C and η from 20?°C to 140?°C is less than 5%) have been simultaneously achieved in the La-doped (Ba_0.904Ca_0.096)_0.9775+xLa_0.015(Zr_0.136Ti_0.864)O₃ (x?=?0.0075) lead-free relaxor ferroelectric thin film capacitors deposited on LaNiO₃/Pt composite bottom electrodes by using a sol-gel method. The good energy storage property of the thin film capacitors at x?=?0.0075 is mainly ascribed to the diversity of the structure of the nano-clusters around the three-phases coexisting component point (Ba_0.904Ca_0.096)(Zr_0.136Ti_0.864)O₃ where cubic, tetragonal and rhombohedral phases coexisted, as well as the ultra-high quality of thin film due to the utilization of the LaNiO₃/Pt composite bottom electrode, making it a promising candidate for dielectric capacitors working in harsh environments.     

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.