Superior ultra-high temperature multilayer ceramic capacitors based on polar nanoregion engineered lead-free relaxor

The assembly of high-temperature electronic equipment places great demands on ultra-high temperature multilayer ceramic capacitors (UHT-MLCCs). However, the relatively low dielectric constant and inferior reliability associated with the protruding ferroelectric phase transition for existing dielectric materials have hindered the development of UHT-MLCCs. Here, these concerns have been addressed by the strategy of composition modulation of different types of polar nanoregions (PNRs) in bismuth-based perovskite relaxor. A new lead-free dielectric system (1-x)(0.8Na_0.5Bi_0.5TiO₃-0.2K_0.5Bi_0.5TiO₃)-xBi(Mg_2/3Nb_1/3)O₃ (NBT-KBT-xBMN) dominated by P4bm PNRs has been built and the corresponding UHT-MLCCs with 70Ag/30Pd inner electrodes are fabricated by tape casting and cofiring processes. A record-high dielectric constant (ε_r = 1800 ± 15%) together with low dielectric loss (tanδ ≤ 0.025) is achieved over a wide range of 100 °C–440 °C for NBT-KBT-0.2BMN MLCC, which consists of nine dielectric layers with the single-layer thickness of 70 μm. The excellent results suggest that NBT-KBT-0.2BMN MLCC can provide realistic solutions for next-generation UHT-MLCC applications and the material design strategy can be generalized for the construction of more high performance capacitor dielectrics.     

Highly-reliable dielectric capacitors with excellent comprehensive energy-storage properties using Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics

The development of capacitors with high reliability and good comprehensive performances is of great significance for practical applications. In this work, lead-free relaxor ferroelectric (FE) ceramics of (1-x)(0.5(Bi_0.5Na_0.5)TiO₃-0.5SrTiO₃)-xBi(Mg_2/3Nb_1/3)O₃ ((1-x)(BNT-ST)-xBMN) were prepared by a conventional solid-state reaction method. The introduction of BMN was found to enhance local structure disorder, leading to the significantly reduced size of FE nanodomains, which is responsible for the slim polarization-electric field hysteresis loops. A giant energy-storage density of 6.62 J/cm³ and a high efficiency of 82 % can be achieved simultaneously under a moderate electric field of 34 kV/mm at x = 0.08. It also exhibits high discharge density ～ 2.74 J/cm³, large power density ～ 248 MW/cm³ and ultrafast discharge rate ～ 28 ns at 20 kV/mm in addition to excellent temperature (10–130 °C) and frequency (1–100 Hz) stabilities. These results demonstrate that the (1-x)(BNT-ST)-xBMN ceramic system is a promising lead-free candidate for advanced pulsed power capacitor applications.     

Localization of dielectric breakdown defects in multilayer ceramic capacitors using 3D X-ray imaging

In this article, a non-destructive method using 3D X-ray imaging to find dielectric breakdown defects in multilayer ceramic capacitors (MLCCs) aged by high temperature and high voltage in an accelerated test is presented. In total, 64 aged samples were investigated using 2D X-ray imaging and half of them were further analysed with 3D X-ray imaging. Miniscule dielectric breakdown defects located in the MLCC active region are extremely difficult to identify solely using cross-section analysis or 2D X-ray imaging. In this study, the information provided by the 3D X-ray analysis was used to localize the defects for cross-section analysis. Cross-section analysis was performed to verify the dielectric breakdowns and their locations. 3D X-ray imaging is an effective method for detecting dielectric breakdown defects in MLCCs due to its short analysis time and high accuracy. This further facilitates failure analysis processes by providing the required grinding depth in cross-section analysis procedures.     

Synthesis of fine-grain Ba0.96La0.04TiO3 dielectric ceramics by different routes for multilayer ceramic capacitors

Spherical Ba_0.96La_0.04TiO₃ powders were synthesized by a wet chemical method-based on a precipitation process, able of controlling uniformity and particle size. After sintering, fine-grain Ba_0.96La_0.04TiO₃ ceramics with good dielectric properties were obtained. Different synthesis routes of Ba_0.96La_0.04TiO₃ ceramics were used, and their effects on microstructure and dielectric properties were examined. Results showed that the ceramics samples prepared by La³⁺ and Ba²⁺ added together (abbreviated as, BLT-T) resulted in a mixture of large and small grains, sharp permittivity peaks, and high dielectrics loss. By comparison, another ceramics samples prepared by La³⁺ and Ba²⁺ added separately (BLT-S) exhibited uniform grain size and broadened/flattened permittivity peaks. The high value of ε_r (3255) and low tan δ (0.01) at room temperature and negligible temperature coefficient of capacitance from − 35 to 85 °C suggested the suitability of the above materials for multilayer capacitor applications.     

Simultaneous enhancement of dielectric properties and temperature stability in BaTiO3-based ceramics enabling X8R multilayer ceramic capacitor

Modified BaTiO₃ ceramics that possess high dielectric permittivity and acceptable temperature stability have been widely utilized as multilayer ceramic capacitors (MLCCs) for high-frequency bypass and power filtering in automotive applications. However, since the increasing demand for high-capacity and small-size, high-permittivity materials that can serve as dielectric layers in MLCCs are urgently required. In this work, we design and fabricate a special BaTiO₃-0.03Mg-0.02Y-0.02CaZrO₃ ceramic with a high dielectric permittivity of 3000 and the dielectric variation below ±13% in the temperature range of -55–150°C, fulfilling the requirements of X8R capacitors. To achieve these results, we employed grain size engineering and cation doping, using BaTiO₃ precursors with a particle size of 240 nm to prepare the BaTiO₃-based ceramics with fine grains, while Mg and Y co-doping was used for improving the temperature stability due to dielectric dispersion. Utilizing these high-permittivity BaTiO₃-based materials, we fabricated MLCCs that satisfy the X8R criterion, possessing a high dielectric constant of 2950 and a high breakdown field (410 kV/cm).     

Prototyping Na0.5Bi0.5TiO3-based multilayer ceramic capacitors for high-temperature and power electronics

Currently, research on capacitor materials for high-temperature and power electronics focuses on achieving new record-breaking limits for dielectric properties or energy storage densities, with little regard for the stability of key parameters during operation or component reliability. While environmental conditions usually do not exceed 300 °C, the voltage ratings of capacitors are still unclear. Within this work, multilayer ceramic capacitors based on lead-free sodium bismuth titanate with AgPd inner electrodes have exhibited exceptional stability of properties and capacitance at high temperatures and voltages during operation. Despite the lack of precise requirements and limits specified by manufacturers and industry, these prototype MLCCs can help to open up the field of high-temperature and power electronics. Their extensive stability of dielectric properties allows for a rather universal application.     

Effect of layered structure on dielectric properties and energy storage density in xBa0.7Sr0.3TiO3-SrTiO3 multilayer ceramics

xBa_0.7Sr_0.3TiO₃-SrTiO₃ (BST-ST) multilayer ceramics with different BST layers (x=1, 3, 5) were designed and fabricated by lamination of Ba_0.7Sr_0.3TiO₃ (BST) and SrTiO₃ (ST) tapes. Dielectric and energy storage properties of the multilayer ceramics were investigated. BST-ST multilayer ceramics exhibited enhanced temperature- and frequency-stability of dielectric properties, accompanying high permittivity (~2000) and low dielectric loss (<0.005) at room temperature. P-E loops revealed that BST-ST multilayer ceramics displayed low remnant polarization and favorable maximum polarization. The optimal energy storage performance was obtained in the composition of x=5 with dielectric breakdown strength of 220 kV/cm and energy storage density of 2.3 J/cm³. These results indicate that BST-ST multilayer ceramics can be a favorable candidate for dielectric capacitor applications.     

High temperature dielectric properties of calcium zirconate

The electrical properties of dense, high purity CaZrO₃ discs, sintered at 1380°C with and without added ZrO₂, were investigated up to 950°C. Dielectric constant, loss tangent, and electrical conductivity were measured from 25 to 725°C, and the real and imaginary impedances were measured between 800 and 950°C by impedance spectroscopy techniques. Dielectric constant increased by 8% above 300°C and loss tangent increased from .1% at 25°C to ∼2% above 300°C. Activation energy of electrical conductivity determined between 300°C and 950°C by alternative current (AC) and direct current (DC) measurements. These results indicate that CaZrO₃ could be a useful dielectric material for capacitor applications up to 500°C. A reported decrease in conductivity due to addition of excess ZrO₂ into stoichiometric CaZrO₃ could not be confirmed.     

Low‐temperature sintering and thermal stability of Li2GeO3‐based microwave dielectric ceramics with low permittivity

A low‐permittivity dielectric ceramic Li₂GeO₃ was prepared by the solid‐state reaction route. Single‐phase Li₂GeO₃ crystallized in an orthorhombic structure. Dense ceramics with high relative density and homogeneous microstructure were obtained as sintered at 1000‐1100°C. The optimum microwave dielectric properties were achieved in the sample sintered at 1080°C with a high relative density ~ 96%, a relative permittivity ε_r ~ 6.36, a quality factor Q × f ~ 29 000 GHz (at 14.5 GHz), and a temperature coefficient of resonance frequency τ_f ~ ?72 ppm/^°C. The sintering temperature of Li₂GeO₃ was successfully lowered via the appropriate addition of B₂O₃. Only 2 wt.% B₂O₃ addition contributed to a 21.2% decrease in sintering temperature to 850°C without deteriorating the dielectric properties. The temperature dependence of the resonance frequency was successfully suppressed by the addition of TiO₂ to form Li₂TiO₃ with a positive τ_f value. These results demonstrate potential applications of Li₂GeO₃ in low‐temperature cofiring ceramics technology.     

A novel BaMg1.98Zn0.02V2O8 ceramic with low dielectric loss and good temperature stability for low temperature co-fired ceramic technology

In this paper, a series of BaMg_2-xZn_xV₂O₈ (0.02 ≤ x ≤ 0.08) ceramic has been obtained by ionic substitution at the Mg-site of BaMg₂V₂O₈ ceramics through the conventional solid-state reaction method. The relationship between the surface morphology and the microwave properties of ceramic samples was analyzed intensively. The results showed that the substitution of Mg²⁺ by an appropriate amount of Zn²⁺ can promote their densification, lower their sintering temperature, and reduce the dielectric loss of BaMg₂V₂O₈ ceramics significantly. The BaMg_1.98Zn_0.02V₂O₈ ceramic exhibits microwave dielectric properties as ε_r ～13.4, Q × f ～ 178,760 GHz, τ_f ～ -14.9 ppm/°C at the optimum sintering temperature (940 °C). This indicates that the ceramic prepared in this work, which combines low dielectric loss, good temperature stability, and low-temperature sintering ability, can be an ideal microwave dielectric material for low-temperature co-firing technology.     

Crystal structure and performance modification of a novel triclinic CaMgP2O7 microwave dielectric ceramic with low sintering temperature

In this study, crystal structure and microwave dielectric properties of phosphate CaMgP₂O₇ were comprehensively investigated. As a novel microwave dielectric ceramic, CaMgP₂O₇ consists of highly dense structure with optimal microwave dielectric properties (ε_r = 7.8 ± 0.124, Q×f = 13,165 ± 836 GHz, and τ_f = −85.04 ± 1.205 ppm/℃) at a low sintering temperature (950 ℃). The Rietveld refinement of XRD patterns revealed that CaMgP₂O₇ belongs to a triclinic system with P-1 symmetry type. Moreover, the substitution of Zn²⁺ for Mg²⁺ in CaMgP₂O₇ can further reduce the sintering temperature, effectively promote the densification process, and improve the Q×f value. The effects of porosity (or density) and chemical bond characteristics on the performance of CaMg_1-xZn_xP₂O₇ ceramics were carefully analyzed as well. Outstanding performance (ε_r = 8.05 ± 0.12, Q×f = 20,670 ± 923 GHz, and τ_f = −87.59 ± 3.24 ppm/℃) can be achieved for the CaMg_0.84Zn_0.16P₂O₇ ceramic sintered at 875 ℃ for 3 h.     

Low temperature sintered Li6MgTiNb1-xVxO8F microwave dielectric ceramics with high-quality factor

Li₆MgTiNb_1?xV_xO₈F (0 ≤ x ≤ 0.08) ceramics were prepared using a solid-state reaction. The correlations between their sintering characteristics and the microwave dielectric performance as functions of V⁵⁺ substitution and sintering temperature were investigated systematically. Rietveld refinements of the X-ray diffraction data showed that all the samples had a cubic rock-salt structure. The Li₆MgTiNbO₈F ceramic sintered at 1175 °C exhibited an attractive Q × f value of 105,700 ± 1600 GHz. The substitution of V⁵⁺ for Nb⁵⁺ decreased the sintering temperature while improving the relative density and relative permittivity. The V-beared Li₆MgTiNb_0.98V_0.02O₈F ceramic sintered at 850 °C showed outstanding dielectric properties of ε_r = 18.14 ± 0.05, Q × f = 58,300 ± 1300 GHz, and τ_f = ?42.66 ± 0.33 ppm/°C. Good chemical compatibility with Ag electrodes highlighted the potential of the ceramic in low-temperature co-fired ceramic applications.     

Effects of SnCl2 concentration and Ti source on the phase composition,sinterability, and microwave dielectric properties of Zr0.8Sn0.2TiO4 ceramics by choline chloride-malonic acid deep eutectic solvent

Zr_0.8Sn_0.2TiO₄ (ZST) ceramics were prepared by choline chloride-malonic acid deep eutectic solvent (Cm-DES) route using analytical-grade raw materials such as Zr(CH₃COO)₄, SnCl₂·2H₂O, titanium isopropoxide, and so on. The effects of SnCl₂ concentration and Ti source on phase composition, sinterability, and microwave dielectric properties of ZST ceramics processed by Cm-DES routes were investigated. Single-phase ZST powders were processed by Cm-DES routes calcined at 450 °C, and no second phase was detected in all the ceramics. The sintering temperature of ZST ceramics processed by Cm-DES routes was seriously decreased to 1350 °C. Excellent dielectric properties (ε_r = 38.0, Q×f = 44,500 GHz, and τ_f = 1.9 ppm/°C) were obtained when 0.6 mol/L SnCl₂ and titanium isopropanol were employed. These results give the underlying enlightenments needed for cost-saving and low energy consumption fabrication of microwave dielectric ceramics.     

Effect of nano aluminum nitride filler on mechanical,thermal, and dielectric properties of the glass/mullite composites for low-temperature co-fired ceramic applications

Mullite/glass/nano aluminum nitride (AlN) filler (1–10 wt% AlN) composites were successfully fabricated for the low-temperature co-fired ceramics applications that require densification temperatures lower than 950°C, high thermal conductivity to dissipate heat and thermal expansion coefficient matched to Si for reliability, and low dielectric constant for high signal transmission speed. Densification temperatures were ≤825°C for all composites due to the viscous sintering of the glass matrix. X-ray diffraction proved that AlN neither chemically reacted with other phases nor decomposed with temperature. The number of closed pores increased with the AlN content, which limited the property improvement expected. A dense mullite/glass/AlN (10 wt%) composite had a thermal expansion coefficient of 4.44 ppm/°C between 25 and 300°C, thermal conductivity of 1.76 W/m.K at 25°C, dielectric constant (loss) of 6.42 (0.0017) at 5 MHz, flexural strength of 88 MPa and elastic modulus of 82 GPa, that are comparable to the commercial low temperature co-fired ceramics products.     

Effects of Zn2+/Mg2+ ratio on dielectric properties of BaTiO3-based ceramics with excellent temperature stability: Experiments and the first-principle calculations

To satisfy the development of MLCC devices, the dielectric properties and temperature stability of ceramic materials urgently needs to be improved. In our work, the 0.9BaTiO₃-0.1Bi(Zn_xMg_0.5-xY_0.5)O_2.75 ceramics with x=0.0–0.5 are successfully prepared based on a traditional solid-state method. Meanwhile, the ceramic sample (core-shell structure) with x = 0.1 exhibits excellent dielectric properties and temperature stability (ε_r: 1207, tanδ: 0.009 and ε_r/ε₂₅ ≤±15% within ?80 to 200 °C), which satisfies the Electronic Industries Association (EIA) X9R (-55–150 °C, Δε_r/ε₂₅ ≤±15%) specification. In addition, the physical mechanism behind dielectric properties and temperature stability is systematic investigated based on experimental characterization and the first-principle calculations. The interface polarization is regarded as the primary cause affecting the dielectric properties, and has a close relationship with shell structure of ceramic samples. The lattice deformation of shell structure is caused by the introduction of heterovalent ions and non-equivalent substitution. Dielectric constant may be advance as content of Zn²⁺ ions increases due to the electronic enrichment around the zinc site in distorted lattice matrix. However, the weaken force between atom and electron results in the poor temperature stability.     

The role of Pb and annealing temperature on the structural,magnetic, optical and dielectric properties of W-type hexaferrite nanostructures

In this paper, W-type Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructures were synthesized by auto-combustion sol-gel method. Then, the effects of annealing temperature and Pb contents on the structural, magnetic, optical, and dielectric properties of Sr_1-xPb_xCo₂Fe₁₆O₂₇ nanostructure were investigated. First, a gel of metal nitrates with a specific molar ratio with x different was prepared and then the gel was annealed at different temperatures for 4?h. To determine the annealing temperature of the samples, the prepared gel was examined by thermogravimetric analysis and differential thermal analysis. The morphology and crystal structure of the prepared samples were characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction pattern (XRD). The results of XRD patterns indicated that the annealing temperature of synthesized Sr_1-xPb_xCo₂Fe₁₆O₂₇ was reduced by increasing Pb contents. In addition, FESEM images showed that the microstructure of the samples was homogeneous and uniform, but since the samples have a magnetic property, the particles were aggregated. Fourier transform infrared analysis (FT-IR) was used to confirm the phase formation. The FT-IR results of the samples indicated that the tetrahedral and octahedral sites, which are the important attributes of hexaferrites, were formed. The magnetic properties of the samples were measured by vibrating sample magnetometer (VSM). The VSM results of the samples showed that because of increasing Pb content, the amount of saturation magnetization and that of magnetic coercivity decreased from 81.29 to 10.23?emu/g and 2285–477?Oe, respectively. The optical properties of the samples were investigated by ultraviolet–visible spectroscopy, which revealed that the energy gap decreases and the absorption peaks move towards longer wavelengths by increasing Pb content. The dielectric properties of the samples were investigated by the LCR meter. It was found that by increasing frequency, the dielectric constant (ε^′) and the dielectric loss (?) of the samples were decreased.     

Ultra‐low temperature sintering microwave dielectric ceramics based on Ag2O–MoO3 binary system

The Ag₂Mo₂O₇ and Ag₆Mo₁₀O₃₃ ceramics for ultra‐low temperature co‐fired ceramic application were prepared by the solid‐state reaction route. The optimized densification temperatures of Ag₂Mo₂O₇ and Ag₆Mo₁₀O₃₃ are 460°C and 500°C, respectively. The phase structures and microstructures of these ceramics were systematically studied. The Ag₂Mo₂O₇ ceramic sintered at 460°C/4 h exhibits excellent microwave dielectric properties with ε_r=13.3, Q×f=25 300 GHz and τ_f=?142 ppm/°C at 9.25 GHz. The Ag₆Mo₁₀O₃₃ ceramic sintered at 500°C/4 h shows the microwave dielectric properties with ε_r=14.0, Q×f=8500 GHz and τ_f=?50 ppm/°C at 9.00 GHz. Moreover, when Ag₂Mo₂O₇ samples are sintered at ultra‐low sintering temperatures of 420°C‐490°C, the Q×f values of them are all above 20 000 GHz. Besides, the Ag₂Mo₂O₇ ceramic does not react with silver powder or aluminum powder. The variation of relative permittivity, resonant frequency, and Q×f values as a function of operating temperature has been also studied. All the results indicate that the Ag₂Mo₂O₇ ceramic is a good candidate for ultra‐low temperature co‐fired microwave devices.     

Enhanced Na+-substituted Li2Mg2Mo3O12 ceramic substrate based on ultra-low temperature co-fired ceramic technology for microwave and terahertz polarization-selective functions

A novel Li₂Mg_2-xNa_2xMo₃O₁₂ (x = 0.09) ceramic with ultra-low sintering temperature is prepared by the solid-state reaction method. This ceramic (625 °C) exhibits excellent microwave dielectric properties (ε_r = 7.9, Q×f = 43844 GHz, τ_f = ?48.3 ppm/°C), terahertz transmission properties (ε_r¹ = 7.4, tan σ¹ = 0.0158, T_coefficient = 0.598), and chemical compatibility with Ag. For the first time, two polarization selective devices are designed in the microwave and terahertz regions by using this ceramic substrate, respectively. The transmission amplitudes of the right- and left-handed circularly polarized waves of the microwave device at 9.7 GHz are 0.895 and 0.019, respectively. The transmission coefficients of the y- and x-polarized waves of the terahertz device at 0.45 THz are 0.598 and 0.075, respectively. Both functions are verified by the overall far-field radiation pattern. This work promotes the application of dielectric ceramics and ULTCC technology in the microwave and terahertz regions.     

Fabrication and performance of dielectric tape based on CaO-B2O3-SiO2 glass/Al2O3 for LTCC applications

A non-aqueous tape-casting process for fabricating CaO-B₂O₃-SiO₂ glass/Al₂O₃ dielectric tape for LTCC applications was investigated. An isopropanol/ethanol/xylene ternary solvent-based slurry was developed by using castor oil, poly(vinyl butyral), and dibutyl phthalate as dispersant, binder, and plasticizer, respectively. The effects of dispersant concentration, binder content, plasticizer/binder ratio, and solid loading, on the properties of the casting slurry and resultant tape were systematically investigated. The results showed that the optimal values for the dispersant and binder contents, plasticizer/binder ratio, and solid loading were 2.0 wt%, 7.5 wt%, 0.6, and 62 wt%, respectively. The resultant flexible and uniform, 120-μm-thick CaO-B₂O₃-SiO₂ glass/Al₂O₃ tape had a density of 1.90 g/cm^?3, tensile strength of 1.66 MPa, and average surface roughness of 310 nm. Laminated tapes sintered at 875 °C for 15 min exhibited excellent properties: relative density of 97.3%, ε_r of 7.98, tan δ of 1.3 × 10^?3 (10 MHz), flexural strength of 205 MPa, and thermal expansion coefficient of 5.47 ppm/°C. The material demonstrated good chemical compatibility with Ag electrodes, indicating a significant potential in LTCC applications.