Co-fired Ceramic Research Articles

A Generalized Design of On-Chip LTCC Balanced Filters Using Novel Hybrid Resonators with Intrinsic Ultra-Wideband Suppression for 5G Applications

In this paper, we examine an ultra-compact on-chip balanced filter based on novel hybrid resonators (NHRs) comprising short transmission line sections (STLSs) and series LC blocks using low-temperature co-fired ceramic (LTCC) technology. Based on a rigorous theoretical analysis, the proposed NHR demonstrates the potential for intrinsic ultra-wideband differential-mode (DM) and common-mode (CM) suppression without any additional suppressing structures. Furthermore, the resonance of NHRs was determined by four degrees of freedom, providing flexibility for miniaturization. Theoretical extensions of the Nth-order topology can be easily achieved by the simple coupling schemes that occur exclusively between STLSs. For verification, a balanced filter covering the 5G band n78 with an area of 0.065λg × 0.072λg was designed using the proposed optimization-based design procedure. An ultra-low insertion loss of 0.8 dB was obtained. The quasi-full CM stopband with a 20 dB rejection level ranged from 0 to 12.9 GHz. And the ultra-wide upper DM stopband with a 20 dB rejection level ranged from 4.4 to 11.5 GHz. Good agreement between the theoretical, simulated, and measured results indicate the validity of the proposed design principle.

Low-Temperature Sintering and Microwave Dielectric Properties of CuxZn1-xTi0.2Zr0.8Nb2O8 Ceramics with the Aid of LiF.

M2+N4+Nb2O8-type ceramics (where M = Mg, Ca, Mn, Co, Ni, Zn and N = Ti, Zr) are essential for satellite communication and mobile base stations due to their medium relative permittivity (εr) and high quality factor (Q × f). Although ZnTi0.2Zr0.8Nb2O8 ceramic exhibits impressive microwave dielectric properties, including an εr of 29.75, a Q × f of 107,303 GHz, and a τf of -24.41 ppm/°C, its sintering temperature of 1150 °C remains a significant barrier for integration into low-temperature co-fired ceramic (LTCC) technologies. To overcome this limitation, a strategy involving the partial substitution of Zn2+ with Cu2+ and the addition of LiF as a sintering aid was devised for ZnTi0.2Zr0.8Nb2O8. The dual impact of Cu2+ partial substitution and LiF as a sintering enhancer facilitated the successful sintering of Cu0.3Zn0.7Ti0.2Zr0.8Nb2O8 ceramics at a reduced temperature of 950 °C using the conventional solid-state reaction method. These ceramics exhibited excellent microwave dielectric properties. Notably, Cu0.3Zn0.7Ti0.2Zr0.8Nb2O8 ceramic with 40 mol% LiF addition demonstrated optimal microwave dielectric properties without any reaction with a silver electrode at a sintering temperature of 950 °C, yielding εr = 32, Q × f = 45,543 GHz, and τf = -43.5 ppm/°C.

A D-Band Dual-Polarized High-Gain LTCC-Based Reflectarray Antenna Using SIW Magnetoelectric-Dipole Elements.

This paper presents a D-band dual linear-polarized wideband high-gain reflectarray (RA) antenna using low-temperature co-fired-ceramic (LTCC) technology. The proposed element comprises a dual-polarized magnetoelectric (ME) dipole and a multilayer slot-coupling substrate-integrated waveguide (SIW) phase-delay structure, which are organized in accordance with the receiving/reradiating (R/R) principle. The coverage of phase shifts for both orthogonal polarizations is set to be greater than 360 degrees by varying the length of the phase-delay structure. For verification, a D-band 1296-element RA prototype using the proposed unit cell is fabricated and measured in a THz chamber. The measured results show that the proposed RA achieves a peak gain of 32.25 and 33.03 dBi for the two orthogonal polarizations. The measured 3 dB gain bandwidths for the two orthogonal polarizations are 122-149 GHz (20%) and 123-149 GHz (19.3%), respectively.

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.

Rational optimizations of high K microwave dielectric ceramic Bi2(Li0.5Ta1.5)O7 toward LTCC applications

AbstractMicrowave dielectric ceramics have drawn intensive interests in recent years due to the advanced development in communication area. High‐permittivity dielectric ceramics have thus become the highlight owing to dielectric ceramics with high permittivity could meet the demand of electronic components in both stabilization and miniaturization features. Bi2(Li0.5Ta1.5)O7 shows its great potential among various high‐permittivity dielectric ceramics with a suitable permittivity and a considerable quality factor. Based on previous studies, a series of rational optimizations were conducted on Bi2(Li0.5Ta1.5)O7 to manipulate the temperature coefficient of resonant frequency (TCF) and the sintering temperature for potential Low Temperature Co‐fired Ceramic (LTCC) applications. Two distinguished ceramics were obtained, Bi2(Li0.5Ta1.5)O7–0.03Bi2O3 (sintering temperature of 850°C, εr ∼ 64.1, Qf ∼ 8510 GHz, TCF—25.3 ppm/°C) and Bi2[(Li0.5Ta1.5)0.975Ti0.05]O7–0.015Bi2O3 (sintering temperature of 980°C, εr ∼ 66.2, Qf ∼ 10 950 GHz, TCF—8.5 ppm/°C). Dielectric resonator antenna (DRA) simulation was subsequently conducted and proved the ceramics holding excellent potential for microwave applications.

Mo site nonstoichiometry engineering: An effective strategy to enhance microwave dielectric properties of Al2Mo3+xO12 ceramic

Al2Mo3O12 materials exhibit remarkable potential in Low-Temperature Co-fired Ceramics devices due to their low relative permittivity and favorable low-temperature sintering properties; nevertheless, its Q×f value is not satisfactory. In this study, non-stoichiometric modification engineering of Mo site ions was designed, to investigate the effects of non-stoichiometric design on structural evolution and microwave dielectric responses of Al2Mo3+xO12 ceramic. The results demonstrate that the excessive contents of Mo6+ cations within the range of x = 0.02 to 0.06 leads to the formation of a monoclinic Al2Mo3O12 solid solution ceramic, different shrinkage of the unit cell cause structural distortion, which can be confirmed by the normalized variations of chemical bonds and Raman spectra. Both the structural evolution and sintering conditions contribute to the enhancement of microwave dielectric properties. Specifically, based on dielectric theory of chemical bonds, the average bond ionicity primarily affects the high frequency micro-polarizability of Al2Mo3+xO12 ceramic; the inherent dielectric loss is affected by the lattice stability, as indicated by the variation of total lattice energy. Also, the outer factors including bulk density and average crystallite size cannot be ignored. Through the inherent dielectric response analysis method of Al2Mo3.04O12 ceramic, the specific influence of each phonon mode to the inherent dielectric response were calculated, revealing that the phonon mode at 159.84 cm-1 provides significant contributions to the dielectric properties. It is found that non-stoichiometry design on Mo site effectively improves the Q×f value of Al2Mo3+xO12 material. Typically, the microwave dielectric properties of Al2Mo3+xO12 (x = 0.04) ceramic are: εr = 6.19, Q×f = 63216 GHz (@13.87 GHz), when sintered at 800 oC.

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.

Alumina densification at low temperatures using CaV2O6 for LTCC application

AbstractLow‐temperature densification of alumina using calcium vanadate (CaV2O6, CV) having a similar dielectric constant as a liquid‐forming additive has been studied. The alumina‒CV composites containing 20‒40 vol.% CV achieve ∼94% of theoretical density at low temperatures of 1100°C‒900°C by liquid‐phase sintering. A reduction in the average size of grains from .87 to .42 µm with a surge in CV amount from 20 to 40 vol.% is observed. The permittivity decreases from 9.2 to 8.90, and the dielectric loss increases from 2.154 × 10‒3 to 4.761 × 10‒3 when the amount of CV in the alumina‒CV composite rises from 20 to 40 vol.%. The temperature coefficient of resonance frequency, thermal expansion coefficient, and thermal conductivity of the alumina‒CV composites are observed in the ranges of ‒54 to ‒72 ppm °C‒1, 6.94‒7.32 ppm °C‒1, and 13.78‒8.02 W m‒1 K‒1, respectively. The compatibility of the composites with Ag for low‐temperature co‐fired ceramics (LTCC) application is established through co‐sintering and energy‐Dispersive X‐ray spectroscopy line spectra analysis. The low‐temperature densification, acceptable range of dielectric and thermal properties, and silver compatibility make the alumina‒CV composite a candidate for LTCC application.

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.