Co-fired Ceramic Research Articles

Reflectionless Filtering Power Divider with Wide Passband Using LTCC Technology

Abstract This paper presents a reflectionless filtering power divider (FPD) in low-temperature co-fired ceramic (LTCC) technology. The proposed FPD consists of a pair of parallel-coupled lines (PCLs), an absorptive bandstop filtering (ABSF) section and a Wilkinson power divider section, which are distributed in different LTCC layers. A controllable wide passband is realized by quarter-wavelength PCLs and reflectionless performance at the out-of-band is achieved by employing a lossy resistor loaded in the ABSF section. For demonstration, a prototype of the proposed FPD operating at 6.5 GHz with a 3-dB fractional bandwidth of 60% is designed and fabricated using LTCC. The measured results are in good agreement with the simulated ones, which validates the theoretical prediction and design idea.

Temperature stable (1-x)BaAl2Si2O8-xBa3V2O8 (0.2 ≤ x ≤ 0.5) microwave dielectric composite ceramics for LTCC applications

BaAl2Si2O8 microwave dielectric ceramics possess dielectric properties of low permittivity (εr) and low loss, coupled with low synthesis cost, making them promising for commercialization. However, the hexagonal structure undergoes high-temperature phase transitions that deteriorate thermal shock resistance and durability, hindering its practical use. In this work, we report temperature-stable BaAl2Si2O8-Ba3V2O8 low temperature co-fired ceramics (LTCC). The combination of Ba3V2O8 and G9 glass achieved a near-zero τf and a thermal expansion coefficient of ∼ 8.5 ppm/℃, significantly enhancing the temperature stability of BaAl2Si2O8 ceramics. By employing ion substitution and enhancing lattice disorder, the components of G9 glass were strategically designed to successfully induce hexagonal-to-monoclinic transformation of BaAl2Si2O8 phase. The dielectric properties of 0.5BaAl2Si2O8-0.5Ba3V2O8-9 wt% G9 sintered at 900 ℃ were εr ∼9, Q×f ∼22,000 GHz and τf ∼ +1.9 ppm/℃. Good chemical compatibility with silver powders was confirmed by further investigation of the co-firing behavior. This work provides attractive candidate for BaAl2Si2O8-based LTCCs and an available approach for modifying BaAl2Si2O8 ceramics.

Dielectric properties of low-temperature co-fired capacitor ceramics and MLCC devices with Ag inner electrodes

Low-temperature sintered 0.99((1−x)Bi0.5Na0.5TiO3-xNaNbO3)-0.01Sr0.8Na0.4Nb2O6 (100xNN, x = 0.25 and 0.30) ceramics and MLCC were successfully prepared, and the dielectric properties were systematically investigated. The dielectric permittivity at 25 °C (ε′25 °C) of 25NN ceramic is 1088, and the dielectric variation is small between −88 °C and 400 °C (|△ε′/ε′25 °C| ≤ 15%, △ε′=ε′-ε′25 °C). The dielectric loss tangent (tanδ) of 25NN ceramic is less than 0.02 between -65 °C and 358 °C. The MLCC with 25NN ceramic dielectrics and Ag inner electrode also has excellent dielectric stability, of which |△ε′/ε′25 °C| is less than 15 % between −100 °C and 400 °C, and the dielectric loss is less than 0.02 between −88 °C and 373 °C. All these results indicate that the low-temperature sintered MLCC with Ag inner electrodes is a promising capacitor in automobile engines and aerospace fields, where the usage temperature is often above 300 °C.

A Novel Microwave Dielectric Ceramic LiSrVO4 for LTCC

Abstract LiSrVO4 (LSV) ceramics were prepared using the solid-state synthesis method, and their phase structure, morphology, sintering characteristics, and microwave dielectric properties were investigated. The LSV ceramics could be densified by sintering at 875–925 °C for 4 hours. XRD indicated that LSV ceramics sintered at 875–925 °C for 4 hours were singlephase ceramics with a monoclinic structure. With the increase in sintering temperature, the dielectric constant and quality factor of LSV ceramics first increased and then decreased, while the temperature coefficient of the resonant frequency gradually decreased. LSV ceramics sintered at 900 °C for 4 hours exhibited a εr of 10.92, a Q×f value of 21115 GHz, and a τf of -4 ppm/°C. LSV ceramics demonstrated good chemical compatibility with silver, showing promising potential in the field of Low-Temperature Co-fired Ceramics.

High-entropy processed high quality and low-temperature cofired LiMgPO4-based dielectric ceramics for low-loss packaged millimeter-wave filters

In this work, we successfully integrated the high-entropy concept into LiMgPO4-based ceramics by strategically substituting Mg2+ with various divalent ions. Through a low-temperature solid-phase reaction method, a series of high-entropy LiMg0.9R0.1PO4 (R = Ni, NiCo, NiCoZn, NiCoZnCu, NiCoZnCuMn) ceramics were prepared successfully, and their MW dielectric properties were found to be heavily influenced by the ionic character, lattice energy, bond energy, entropy, ion radius disorder, and electronegativity of chemical bonds. Remarkably, LiMg0.9(Ni0.2Co0.2Zn0.2Cu0.2Mn0.2)0.1PO4 (LM5RP) ceramics exhibited exceptional MW dielectric properties (εr = 7.43, τf = − 27.6 ppm/°C, and Q × f = 83,216 GHz@13 GHz and 105,889 GHz@28 GHz) when sintered at an extraordinarily low temperature of 900 °C for 2 h. To demonstrate the real-world applicability of the LM5RP high-entropy ceramic, we designed and fabricated a state-of-the-art millimeter-wave (mmWave) filter, operating at 28 GHz, using low-temperature co-fired ceramic (LTCC) packaging technology. The filter exhibited unparalleled performance, featuring a low insertion loss (0.9 dB) and wide stopband suppression (> 17 dB @ 2.14 f0). These groundbreaking findings underscore the immense potential of high-entropy ceramics in revolutionizing advanced MW applications, particularly in the domain of B5G/6 G mmWave communication systems.

Impacts of P-site non-stoichiometry on the structure and properties of BaZnP2O7 ceramics

In this work, a series of P5+-enriched BaZnP2+xO7 ceramics were synthesized using the solid-state method at temperatures ranging from 825°C to 925°C. All ceramics exhibited a single triclinic phase. A suitable excess of P5+ promoted grain growth and densification, which also affected εr and Q×f. Subsequently, the relationship between total lattice energy and Q×f was explored, as well as the connection between total bond energy and τf. At 850°C, the BaZnP2.01O7 ceramics achieved a relative density of 97.7 % and demonstrated optimal properties: εr∼8.78, Q×f∼149,008 GHz, τf∼-28.92 ppm/°C. These ceramics present an outstanding combination of low εr, high Q×f and low sintering temperature, indicating their potential for application in Low-Temperature Co-fired Ceramics (LTCC) technology.

2D Computational Fluid Dynamics Simulation Analysis of the Assembly of Low‐Temperature Cofired Ceramics/Low‐Temperature Cofired Ceramics and Si/Si Sandwiches by Reactive Bonding

Numerical computational fluid dynamics simulations have been performed on 2D sandwich models to compare the performance of low‐temperature cofired ceramics (LTCC)/LTCC and Si/Si sandwiches used in reactive bonding. In the sandwich model layers of solder, silver and a reactive multilayer used to bond the substrates are modeled. Additional to this, the surrounding air environment is also modeled. For simulating the heat released by the multilayer system, a user‐defined function in the form of a square wave is written for the heat source with a defined width, corresponding to the reaction width, and this propagates at a fixed speed. Two sandwiches, one with LTCC/LTCC, and the other with Si/Si, are simulated and their response analyzed in terms of the solidification/melting of the solder and their respective time–temperature histories.

Microstrip dielectric patch antenna fabrication and characterization using ultra low permittivity and low temperature Co-fired LiAlSiO4 ceramics

LiBxAl1-xSiO4 (x = 0.02–0.1) ceramics were prepared by conventional solid-state method with a reduction in sintering temperature by up to 250–475 °C. The relative permittivity was significantly decreased by εr = 3.3–3.7, one of the lowest ever reported values among crystalline ceramics, while maintaining exceptional quality factors (Q×f = 25,000–28,000 GHz) and low temperature coefficients of resonance frequency (τf = −23 ∼ −16 ppm/°C). Furthermore, these LiBxAl1-xSiO4 ceramics possess a low density (∼2.3 g/cm3), making them highly promising for lightweight microwave devices. The potential application of LiB0.1Al0.9SiO4 ceramics in LTCC was assessed based on their ability to achieve low densification temperature and exhibit chemical compatibility with silver electrodes. A microstrip patch antenna with an operating frequency of 6.68 GHz, featuring high efficiency (91.88 %) and wide bandwidth (400 MHz), has been designed and fabricated from LiB0.1Al0.9SiO4 ceramics substrate, which provides a good application prospect for advanced wireless systems. The development of these ultra-low permittivity dielectric ceramics opens new potential to revolutionize the field of microwave dielectric ceramics.

Structure/property dynamics of low-temperature sintering pure and Mg-modified Zn3V2O8 ceramics

The pure and Mg-modified Zn3V2O8 ceramics were successfully synthesized using the solid-state reaction. Zn3V2O8 is well crystallized as the orthorhombic phase with a space group of Cmca. The Zn site of Zn3V2O8 ceramic can be partially substituted by Mg to form a continuous solid solution. Appropriate substitution can tremendously enhance the dielectric chartcteristics of the samples. P-V-L bond theory was also employed to investigate the structural and chemical bond effects on the microwave dielectric properties of the specimens. Raman spectrum was sensitive to crystallinity, and can highly reflect the dielectric loss of the ceramics. The Zn3V2O8 ceramic sintered at 690°C reveals a high Q×f =59,000 GHz, along with an εr =13.8, and τf =–120 ppm/°C.Remarkably, the Zn2.99Mg0.01V2O8 specimen demonstrates outstanding properties, with εr =14.7, Q×f =86,000 GHz and τf =–82 ppm/°C. This signifies an approximately 46 % improvement in Q×f compared to pure Zn3V2O8, indicating the ceramic's great promise for low-temperature co-fired ceramic (LTCC) applications, especially in high-frequency regions where low dielectric loss is essential.

Low-loss and low-temperature sintering of SrNb2V2O11 with a large positive τf value as an effective temperature compensator

Novel SrNb2V2O11 microwave dielectric was synthesized and proposed as a temperature compensator for Low-temperature cofired ceramics (LTCC)/Ultra-low-temperature cofired ceramics (ULTCC) applications. The X-ray diffractometer (XRD) patterns matched well with the SrNb2V2O11 phase, exhibiting a monoclinic structure and Cc space group over the entire experiment. The presence of the Nb-rich second phase at 850 °C was attributed to the melting of the samples. The microwave dielectric properties were highly correlated with the chemical bond parameters, which were intensively investigated using the P-V-L theory. The specimen sintered at 820 °C reveals dielectric properties, combining an εr of 74.5, Q × f of 13,000 GHz, and τf of 517 ppm/°C. The large positive τf can make the ceramic an effective temperature compensator for LTCC applications. Moreover, the medium-high εr value can also act as a practical material for dielectric resonators used in the base stations, where a stable environment and limited temperature changes are crucial.

Co-sintering of a ceramic-metal bilayer: Coupled experimental, analytical and numerical approaches

The co-sintering behavior of a ceramic-metal bilayer is carefully investigated. This bilayer is composed of a gold film deposited by screen-printing on a silica-based low-temperature cofired ceramic (LTCC) layer. First, behaviors of both materials in free sintering are finely characterized. LTCC exhibits a viscous flow sintering mechanism, whereas the densification mechanism of gold is controlled by grain boundary diffusion (with an identified apparent activation energy of 101 ± 15 kJ mol−1). Free sintering of gold is also marked by a two-step densification process due to its large bimodal particle size distribution. A methodology is proposed to estimate gold viscosity at high temperatures directly from raw experimental data in free sintering, without performing dedicated mechanical characterizations. Based on the constitutive laws identified for LTCC and gold materials, analytical and numerical models of the bilayer co-sintering process are built. During co-sintering, stresses generated by densification kinetic mismatch between gold and LTCC are progressively relaxed by camber phenomenon. Calculated evolutions of camber in co-sintering are compared to curvature monitoring by ombroscopy. Finite element simulation in 3D fits well with the experimental data, whereas the analytical solution strongly underestimates camber rates. This shows that the simplified numerical approach suggested here leads to a robust numerical model, faithfully describing thermomechanical interactions occurring in co-sintering within the ceramic-metal bilayer.

Characteristics of low-temperature plasma for activation of plastic-degrading microorganisms

Plastic pollution is a problem that threatens the future of humanity, and various methods are being researched to solve it. Plastic biodegradation using microorganisms is one of these methods, and a recent study reported that plastic-degrading microorganisms activated by plasma increase the plastic decomposition rate. In contrast to microbial sterilization using low-temperature plasma, microbial activation requires a stable plasma discharge with a low electrode temperature suitable for biological samples and precise control over a narrow operating range. In this study, various plasma characteristics were evaluated using SDBD (Surface Dielectric Barrier Discharge) to establish the optimal conditions of plasma that can activate plastic-degrading microorganisms. The SDBD electrode was manufactured using low-temperature co-fired ceramic (LTCC) technology to ensure chemical resistance, minimize impurities, improve heat conduction, and consider freedom in designing the electrode metal part. Plasma stability, which is important for microbial activation, was investigated by changing the frequency and pulse width of the voltage applied to the electrode, and the degree of activation of plastic-degrading microorganisms was evaluated under each condition. The results of this study are expected to be used as basic data for research on the activation of useful microorganisms using low-temperature plasma.

A novel Li3Mg4(Nb1-xVx)O8 ceramic with high Q×f value and good temperature stability with low sintering temperature

A series of low-loss Li3Mg4(Nb1-xVx)O8 (0.02 ≤ x ≤ 0.08) ceramics has been synthesized in this work, with the optimal sintering temperature lowered to 950°C due to the incorporation of V5+ ions. Moreover, the effects of substituting V5+ for Nb5+ on the sintering, composition, structure and properties of the ceramics have been systematically analyzed. It has been discovered that the permittivity (εr) and quality factor (Q×f) of Li3Mg4(Nb1-xVx)O8 ceramics exhibit a correlation with the relative density, which is influenced by the variation in grain size distribution resulting from the substitution of V5+ ions. Additionally, the total lattice energy of Li3Mg4(Nb1-xVx)O8 ceramics is also affected by the bond characteristics within the Nb-O octahedra, thus influencing the Q×f value. The resonant frequency temperature coefficient (τf) fluctuates within a small range. The Li3Mg4(Nb0.98V0.02)O8 ceramics exhibit excellent microwave dielectric properties at 950°C: εr∼14.03, Q×f∼93,425 GHz, τf∼-6.12 ppm/°C, with a relative density reaching 98.3 %. Compared to unsubstituted Li3Mg4NbO8 ceramics, the sintering temperature is reduced by 200°C without forming impurity phases. While adjusting the τf value to nearly zero, it maintains a high Q×f value, indicating promising applications in Low-Temperature Co-fired Ceramics (LTCC).

Relationship between chemical bond characteristics and microwave dielectric properties of low temperature sintering CoO-V2O5 ceramics

The two most fundamental compositions within the CoO-V2O5 family, namely CoV2O6 and Co2V2O7 ceramics, were synthesized using the traditional solid-state method. The microwave dielectric properties of both ceramics were investigated for the first time. The P-V-L bond theory was used to analyze the correlation between their microwave dielectric properties and chemical bond characteristics. The CoV2O6 ceramic exhibits a γ phase (εr = 11.6, Q×f = 39,177 GHz, and τf = −15 ppm/°C) when sintered at 660 °C. However, it experiences a phase transformation from the γ phase to the α phase at 690 °C, which causes the dielectric properties to degrade. The Co2V2O7 ceramic demonstrates excellent dielectric characteristics (εr = 9.4, Q×f = 88,645 GHz, and τf = −37 ppm/°C) at 720 °C. Importantly, its sintering temperature can be lowered to 660 °C while still maintaining a good combination of microwave dielectric properties (εr = 7.7, Q×f = 75,887 GHz, and τf = −58 ppm/°C). It is found that Co2V2O7 exhibits a low dielectric loss due to relatively high lattice energy resulting from the contribution of Co–O bonds. CoV2O6, on the other hand, shows a lower sintering temperature because it contains more V2O5, which acts as an effective sintering aid. These two ceramics both exhibit good chemical compatibility with aluminum and are promising candidates for applications in low-temperature and ultra-low-temperature co-fired ceramics (LTCCs and ULTCCs) that operate in the microwave frequency range or higher.

Characterization and degradation of β-Sn particles in thermal aged Pb-rich solder joint for low-temperature co-fired ceramic (LTCC) applications

Characterization and degradation of β-Sn particles in thermal aged Pb-rich solder joint for low-temperature co-fired ceramic (LTCC) applications

Enhancing microwave dielectric properties of Li4NbO4F for LTCC applications through tantalum ion doping

The atomic scale variation of tantalum ion doped Li4NbO4F ceramics is initially predicted through first principle calculations. Subsequently, Li4Nb(1-x)TaxO4F (0.00 ≤ x ≤ 0.10) ceramics are prepared using the solid phase reaction method. After sintering at 875 °C for 4 h, the Li4Nb0.96Ta0.04O4F ceramics exhibit optimum dielectric properties: εr = 14.73 ± 0.19, Q × f = 83,439 ± 2810 GHz (@9.31 GHz, improved by 41 %), τf = - 28.33 ± 1.36 ppm/°C. Both the increase in relative density from 95.9 ± 0.32 % to 96.2 ± 0.34 % and the increase in grain size from 14.9 μm to 15.6 μm are non-intrinsic factors that contribute to the optimization of the dielectric properties. Instead, the internal factors suggest that the primary cause of the gradual decrease in εr is the redshift of the Raman wave number. The reduction in dielectric loss is attributable to the weakening of damping behavior, as well as the increase in lattice energy and electron cloud density. Finally, promising potential of Li4Nb0.96Ta0.04O4F ceramics for low-temperature co-fired ceramic (LTCC) applications is indicated by their favourable chemical compatibility with Ag electrodes.

Research on material jetting fabrication and dielectric constant calculation of LTCC based on silica-borosilicate glass

Several material systems are available for low-temperature co-fired ceramics, and to achieve more efficient designs and applications using additive manufacturing (AM) techniques such as material jetting, the predictability of the dielectric constant of the sintered structure will significantly reduce the consumption of material development. In this work, the LTCC part was fabricated by 3D material jetting using silica-borosilicate glass LTCC ink and densified at 850°C. The borosilicate glass composition was derived from nanopowders prepared by radio frequency plasma spheronisation and configured as surface-grafted glass sols. Scanning electron microscopy results showed that silica particles were embedded in the glass matrix by a liquid phase sintering mechanism accompanied by several confined pores that were difficult to remove. A dielectric constant of around 3.78 was tested from room temperature to 100°C. Molecular dynamics sintering simulation was used to create sintered structures that matched the experimental values. The dipole moment fluctuation of the silica/glass bulk was counted to obtain an accurate value of the dielectric constant, and then the Bruggeman model based on the effective medium theory predicted the dielectric constant of the sintered body, with a prediction of 3.65, which is within 4 % difference from the measured value (3.78). The dielectric constant was predicted for different ceramic/glass compositions and sintering temperatures and found that 35 wt% and 60 wt% should be the upper and lower bounds for borosilicate glass additions to satisfy a stable structure with a relatively low dielectric constant range (3.38–4.42). In conclusion, an effective molecular dynamics approach to predict the dielectric constant of sintered bodies was developed to assist material design in LTCC AM fabrication.

Low temperature sintering and improvement of temperature Stability of Ba3P4O13 microwave dielectric ceramics by BCB additions

In our previous study, Ba3P4O13 ceramic was found to exhibit good microwave dielectric performance with a low permittivity (εr), a high Q × f (Q = 1/dielectric loss, f = resonant frequency) value but a large positive τf value (TCF, temperature coefficient of resonant frequency), which limits its application in low-temperature co-fired ceramic (LTCC) technology. BaCu(B2O5) (BCB) additions were selected in this study to adjust τf value of Ba3P4O13 ceramic samples. It was found that as BCB contents increased, sintering temperatures decreased from 840 °C (without BCB addition) to 820 °C (with 2 wt. % BCB), meanwhile τf values of ceramic samples were reduced from + 48 ppm/ °C to − 2 ppm/ °C. Moreover, BCB added Ba3P4O13 ceramic showed a good chemical compatibility with Cu electrode. These results indicate that BCB added Ba3P4O13 ceramics are promising candidate for LTCC applications.

Low-permittivity BaCuSi4O10-based dielectric Ceramics: An available solution to connect low temperature cofired ceramic technology and millimeter-wave communications

Low temperature cofired ceramic (LTCC) technology can serve for next-generation millimeter-wave electronic products to bring the advantages of integration, miniaturization and excellent high-frequency performance. However, challenges such as the performance of LTCC powders, quality of green tapes and Ag co-firing compatibility still need to be addressed for the application of LTCC technology. In this work, a systematic investigation from powder modification, LTCC process to filter design were carried out based on novel BaCuSi4O10-based dielectric ceramics. Multiple effects in terms of suitable sintering temperature (840 ℃ suit for Ag co-firing), low-permittivity (εr ∼ 5.7) and good thermal stability (temperature coefficient of resonant frequency ∼ − 27 ppm/℃, thermal expansion coefficient ∼3.9 ppm/℃) were achieved by introducing Li-B-Si glass and LiF composite additive. The origin of dielectric response of this LTCC system were discussed using the FIR reflectivity spectrum and THz-TDS. After optimizing the tape casting process for the LTCC powder, green tapes with uniform thickness, smooth surface and no cracking were obtained. Furthermore, the bandpass and lowpass filters exhibited a high level of filtering performance own to excellent dielectric properties and low surface roughness of the LTCC. Consequently, the BaCuSi4O10-based dielectric ceramic is an attractive candidate as LTCC technology expands into millimeter-wave communications.

Nano-borosilicate glass-silica ceramic material jetting technology for additive manufacturing of multilayer LTCC substrates

Although one of the simplest methods, various must be resolved before industrializing material jetting technology to fabricate low-temperature co-fired ceramics (LTCC). This research examines related glass-ceramic ink configurations and multi-material jet-sintering. Firstly, we present a method for obtaining a nanoscale borosilicate glass powder via radio frequency plasma spheronization, and its surface is grafted with acrylate molecules to create a jettable nanosol. By fusing this configured glass nanosol with silica nanosol in the typical glass-ceramic LTCC combination (4:6) and adding suitable photosensitizing elements, it can be configured into light-curable LTCC inks. 3D printing of multilayer structures using a multi-material jetting device provides a three-layer structure of ceramic layer - conductive layer - ceramic layer, with the ceramic layer cured by ultraviolet light and the conductor pattern scanned and surface-dried by a laser to obtain high-precision delivery of the green part. The sintering effect between different materials is intact and synchronized shrinkage is achieved. Conductivity tests during the sintering stage yielded high conductivity values up to 1.43 × 107 S/m, which further provides the microscopic morphology of the two embedded wires, and the complete and continuous results demonstrate the effectiveness of multilayer wire fabrication. The nanopowder, sol-gel configuration and material jetting under multiple energy loading proposed in this paper significantly support the LTCC additive manufacturing route.