Low-temperature Co-fired Ceramic Technology Research Articles

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.

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.

Preparation of high-performance multilayer circuits by controlling the diffusion of Ag in borosilicate glass-ceramics through the addition of SiO2

Due to its superior reliability and performance, thick film technology is extensively employed in various applications, including automotive electronics, consumer electronics, communication engineering, and aerospace. However, a challenge arises from the mutual diffusion during the electronic paste production process, which leads to a decline in insulation performance and hinders the production of three-dimensional equipment. Inspired by the principles of low-temperature co-fired ceramic technology, a multi-layered ceramic structure has been successfully bonded using thick film technology by introducing a borosilicate glass-ceramics layer. To further enhance the properties of this multi-layered ceramic structure, approximately 8 wt% SiO2 was incorporated into the borosilicate glass-ceramics. This addition effectively inhibits silver diffusion and reduces the diffusion depth within the glass-ceramic film. The key mechanisms behind this improvement are the increased activation energy for crystallization, resulting in a slower crystallization rate due to the addition of SiO2. Moreover, the multi-layered ceramic with a sandwich structure exhibits remarkable properties. Notably, the dielectric strength of this system has been significantly enhanced to 13.9 kV/mm, accompanied by a high adhesion strength of 790 N. These enhanced properties of the optimized system indicate promising characteristics for multi-layer circuit applications.

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.

Preparation of high-performance Bi-YG ferrite based on LTCC technology and theoretical analysis of its sintering mechanism

In the preparation process of Microwave Multi-Chip Module (MMCM), it is necessary to simultaneously sinter both microwave medium (ferrite) and silver electrodes. Hence, this necessitates keeping the sintering temperature below the melting point of silver (961 °C). An excessively low sintering temperature would significantly impair the electromagnetic properties of the ferrite material. To address this concern, this study synthesizes Bi-YIG (Y3-xBixFe5O12, x = 0–1.0) ferrites with optimized characteristics, including low ferromagnetic resonance line-width (ΔH) and high saturation magnetization (Ms), at 945 °C using Low Temperature Co-fired Ceramic (LTCC) technology. The mechanism of low-temperature liquid phase sintering, facilitated by a fluxing agent, was investigated using a theoretical model. The addition of Bi2O3 fluxing agent was found to reduce the reaction activation energy, disrupt the chemical reaction equilibrium, and promote low-temperature liquid phase sintering, thus lowering the critical sintering temperature below the melting point of silver. Furthermore, optimal bismuth content was identified to regulate the dynamic balance between grain growth and boundary diffusion, suppressing abnormal grain growth and enhancing the electromagnetic properties of the ferrite. This exploration, leveraging LTCC technology, may offer valuable insights for enhancing the overall performance of MMCMs.

Millimeter‐wave end‐fire dual‐polarized frequency scanning antenna using LTCC technology

AbstractThis letter proposes a millimeter‐wave dual‐polarized (DP) end‐fire frequency scanning antenna utilizing low temperature co‐fired ceramic (LTCC) technology. The antenna features DP radiating elements, each comprising a quasi‐Yagi antenna for horizontal polarization (H‐pol) and a pyramidal horn antenna for vertical polarization (V‐pol). These elements are excited via a mode‐composited transmission line (MCTL), integrating substrate integrated coaxial line (TEM mode) with substrate integrated waveguide (TE10 mode). To mitigate phase imbalances between polarizations during beam scanning, a delay line is embedded in each quasi‐Yagi element, ensuring consistent scanning ranges for the two polarizations. Furthermore, the implementation of amplitude weighting in the feeding networks contributes to the enhancement of antenna efficiency. A 1 × 8‐element prototype was fabricated and its performance is assessed. The results show closely matched beam scanning ranges for the two polarizations (±28° for H‐pol and −30° to +34° for V‐pol) across the 26–29 GHz frequency band, with a measured maximum peak gain exceeding 9.2 dBi for both polarizations. The proposed design emerges as a promising candidate for compact mmW frequency scanning front‐end antenna systems.

Structure evolution and τf influence mechanism of Bi1–xHoxVO4 microwave dielectric ceramics for LTCC applications

Bi1–xHoxVO4 (0.1 ≤ x ≤ 0.9) ceramics were prepared via a solid-state reaction method, and all the ceramics could be well densified in the 920–980 °C range. The ceramics with 0.1 ≤ x < 0.4 were composed of both monoclinic scheelite (M) and tetragonal zircon (T) phases, and a single M phase could be obtained in the range of x ≥ 0.4. The measured εr decreased from 58.9 (x = 0.1) to 14.7 (x = 0.9), so do the calculated values (εr(C−M) = 34.3–12.1), and the main reason for εr > εr(C−M) was the rattling of Ho3+ in the dodecahedron. Two points with zero τf appeared in Bi1–xHoxVO4 (0 ≤ x ≤ 1) ceramics, and the best microwave dielectric properties with εr = 16.6, Q × f = 18,400 GHz (f = 10.69 GHz), and τf = +3.29 ppm/°C were obtained in the Bi0.2Ho0.8VO4 ceramic. The change in temperature coefficient of ionic polarizability (ταm) caused by the rattling effect of cations is the physical essence that affects τf. Therefore, the rattling effect can be used as an effective mechanism to regulate τf in low-εr materials. Furthermore, there was no chemical reaction between Bi1–xHoxVO4 and Ag electrode, which indicates potential applications in low-temperature co-fired ceramic (LTCC) technology.

Development of LTCC IR-Emitter and Its Packaging

In this paper, thick film-based IR source is fabricated using multilayer Low Temperature Co-fired Ceramic (LTCC) Technology. The proposed emitter is developed using screen printing of platinum material on LTCC substrates. The highly uniform meander shaped structure is fabricated with the size of 3.5 mm × 3.5 mm. Electrical, optical and thermal characterization of the fabricated device are carried out. Device temperature reaches 600 °C at 6.5 V. Optical characterization of the developed device shows the spectral range in the mid-IR region with power consumption of ∼3 W. In-house indigenised package is developed using glass-metal seal technique for packaging of developed IR source. Different windows viz., quartz, LiF and CaF2 are used for packaging. Developed IR source demonstrate the potential to meet the performance, size and cost requirements for various applications. The developed LTCC based IR source has planar and simple structure with high temperature stable lead-free interconnects.

Sintering behaviors and microwave dielectric properties of Ba3P4O13 ceramics

In this study, a Ba3P4O13 ceramic was synthesized adopting a conventional solid-state ceramic method. Optimal microwave dielectric properties were obtained in ceramic samples sintered at 840 °C for 4 h with a εr (permittivity) = 7.9, a Q × f (Q = 1/dielectric loss, f = resonant frequency) = 14,200 GHz (at 11.18 GHz), and a τf (TCF, temperature coefficient of resonant frequency) = + 48 ppm/°C. τf value shifted from + 45 ppm/°C to ‒ 31.5 ppm/°C with sintering temperature rising from 860 °C to 900 °C, and this decrease in τf value was mainly caused by the decomposition of Ba3P4O13 into BaP2O6 and Ba2P2O7. Furthermore, a ceramic sample sintered at 890 °C achieved a near zero τf (− 1.3 ppm/°C), together with a εr = 7.7 and a Q × f = 13,000 GHz (at 11.44 GHz). Ba3P4O13 ceramic has demonstrated potential as a material suitable for low-temperature co-fired ceramic technology (LTCC).

A Miniaturized Bandpass Filter with Wideband and High Stopband Rejection Using LTCC Technology

This paper designs an L-band wide stopband bandpass filter by applying low-temperature cofired ceramic (LTCC) technology to the global positioning system (GPS) frequency band. Taking the Chebyshev filter as a prototype, an equivalent collector element (capacitive and inductor) structure is adopted to fully use the three-dimensional package structure of LTCC to reduce the filter size. The filter is integrated into an eight-layer LTCC dielectric, and the series–parallel connection of the collector elements in the resonance unit is utilized to produce out-of-band transmission zeros, while the input and output ports’ capacitance is adjusted to control the bandwidth. Harmonic suppression is achieved by cascading two new compact stopband filters, while the size increase is insignificant due to LTCC technology. The simulation results are as follows: the center frequency is 1.575 GHz, 1 dB relative bandwidth is 6.3%, insertion loss in the passband is as slight as 1.6 dB, return loss is better than 30 dB, rejection bandwidth up to 16 GHz is more than 44 dB, and the volume of the whole filter is 6.2 × 3.7 × 0.78 mm3.

INFLUENCE OF THE ADDITIVE OF EUTECTIC COMPOSITION IN THE Li2O–B2O3 SYSTEM ON THE SINTERING PROCESS AND PROPERTIES OF CERAMICS BASED ON Li2MgTi3O8

The influence of the eutectic additive of the Li2O–B2O3 system on the sintering process and dielectric properties of ceramics based on Li2MgTi3O8 has been investigated. It was determined that the introduction of an additive in the amount of 10.0 – 15.0 % contributes to the sintering of ceramics by a liquid-phase mechanism. Li2MgTi3O8 ceramics, containing a sintering additive in an amount of 15.0 % and obtained at a firing temperature of 900 ?С, demonstrates the following level of properties ?av = 3.04 g/cm3, Po = 5.7 %, ?r = 19.0 and tg? = 0.028. The lowered sintering temperature of ceramic will allow the production of various electronic components based on it using low-temperature cofiring ceramic (LTCC) technology, and the specified level of dielectric properties will allow to miniaturize the devices.

Low-Permittivity and Low-Temperature Cofired BaSO4-BaF2 Microwave Dielectric Ceramics for High-Reliability Packaged Electronics.

In developing low-temperature cofired ceramic (LTCC) technology for high-density packaging or advanced packaged electronics, matching the coefficient of thermal expansion (CTE) among the packaged components is a critical challenge to improve reliability. The CTEs of solders and organic laminates are usually larger than 16.0 ppm of °C1-, while most low-permittivity (εr) dielectric ceramics have CTEs of less than 10.0 ppm °C1-. Therefore, a good CTE match between organic laminates and dielectric ceramics is required for further LTCC applications. In this paper, we propose a high-CTE BaSO4-BaF2 LTCC as a potential solution for high-reliability packaged electronics. The BaSO4-BaF2 ceramics have the advantages of a wide low-temperature sintering range (650-850 °C), low loss, temperature stability, and Ag compatibility, ensuring excellent performance in LTCC technology. The 95 wt %BaSO4-5 wt %BaF2 ceramic has a εr of 9.1, a Q × f of 40,100 GHz @11.03 GHz (Q = 1/tan δ), a temperature coefficient of the resonant frequency of -11.2 ppm °C1-, a CTE of +21.8 ppm °C1-, and a thermal conductivity of 1.3 W mK-1 when sintered at 750 °C. Furthermore, a dielectric resonant antenna using BaSO4-BaF2 ceramics, a typically packaged component of LTCC and laminate, was designed and used to verify the excellent performance by a gain of 6.0 dBi at a central frequency of 8.97 GHz and a high radiation efficiency of 90% over a bandwidth of 760 MHz. Good match and low thermal stress were found in the packaged components of BaSO4-BaF2 ceramics, organic laminates, and Sn-based solders by finite element analysis, proving the potential of this LTCC for high-reliability packaged electronics.

Sintering Behavior, Microstructure and Microwave Dielectric Properties of Li2TiO3-Based Solid Solution Ceramics with Lithium Fluoride Addition for Low-Temperature Co-Fired Ceramic Applications

Nowadays, low-temperature co-fired ceramic (LTCC) technology has become one of the main forms of manufacturing electronic devices. However, a majority of microwave dielectric ceramics are not suitable as LTCC materials due to their high sintering temperatures. Developing novel LTCC materials with good microwave dielectric properties is extremely urgent. In this paper, an LiF sintering aid was added to Li2Ti0.8(Co1/3Nb2/3)0.2O3 (LTCN) ceramics to explore new LTCC materials. The sintering behavior, microstructure and microwave dielectric properties of LTCN + x wt% LiF ceramics were investigated in detail. The results indicated that the addition of LiF increased the degree of disorder in the LTCN matrix, transforming it from a monoclinic to a cubic crystal system. The ceramics exhibited relatively dense and homogeneous microstructures at the sintering temperature of 950 °C as the LiF doping amount was not less than 2 wt%. By LiF doping, the quality factor (Q × f) value was significantly enhanced due to the improved microstructure. Meanwhile, the temperature coefficient of resonant frequency (τf) of LTCN ceramics was successfully regulated to the near zero value owing to the negative τf characteristic of LiF. Excellent microwave dielectric properties of dielectric constant (εr) = 19.01, Q × f = 144,890 GHz, τf = −1.52 ppm/°C were obtained when the sample doped 3 wt% LiF was sintered at 950 °C for 3 h. Furthermore, the good chemical compatibility of the LTCN-3 wt% LiF ceramic with silver electrodes suggested that the ceramic was a potential material for LTCC applications.

Enhanced properties of Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 ferrites co-fired with Bi2O3–B2O3 additive at low sintering temperatures

In this study, Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 ferrites were co-fired with Bi2O3–B2O3 (BB) additive at low sintering temperatures (∼920 °C), and the effects of BB additive on various properties of Li–Zn ferrites were systematically investigated. First of all, the existence of BB additive would not pollute the spinel phases of Li–Zn ferrites, in contrast, it could make the ferrites well-ripened at low temperatures. The micro-morphology results revealed that the introduction of BB additive could significantly promote the grain growth, where the average diameter of grain size increased from 0.81 μm (0.0 wt % BB) to 8.12 μm (0.5 wt % BB), leading to a higher densification degree and density. Owing to the liquid phase formed in the sintering process, magnetic properties of the Li–Zn ferrites were improved with the assistance of BB additive. The saturation flux density (Bs) and saturation magnetization could reach a maximum value of 319.3 mT and 74.2 emu/g, respectively. The coercivity (Hc) and ferromagnetic resonance (FMR) linewidths (ΔH) could reach a minimum value of 176.3 A/m and 243.2 Oe, respectively. Finally, it is noted that the optimal values of these parameters are obtained under the condition of 0.5 wt % BB additive doped, and most magnetic properties would be deteriorated when exceeding the above content. Thus, BB additive is considered as a promising sintering aid for synthesizing Li–Zn ferrites at low temperatures, which will play a vital role in the development of low-temperature co-fired ceramics (LTCC) technology.

Low-temperature sintering and microwave dielectric properties of CaMoO4 ceramics for LTCC and ULTCC applications

Low-temperature co-fired ceramic (LTCC) technology can meet the requirements of device miniaturization and integration. In this work, a novel series of CaMoO4 + x wt.% Li2MoO4 (CMO+ xLMO, x = 0.0–2.5) microwave dielectric ceramics were prepared. The sintering temperature of CMO ceramic significantly declines from 1050 °C to 600 °C by adding a small amount of LMO. A dissolution-precipitation process at the grain boundary has been demonstrated to be the mechanism for low-temperature sintering through transmission electron microscopy analysis. The low-temperature sintered CMO ceramics present excellent microwave dielectric properties, e.g. CMO+ 1.0 wt.% LMO ceramics sintered at 600 °C, εr ∼ 14.4, Q×f ∼ 13,060 GHz, τƒ ∼ − 41.0 ppm/°C; CMO+ 2.5 wt.% LMO ceramics sintered at 700 °C, εr ∼ 15.1, Q×f ∼ 16,122 GHz, τƒ ∼ − 43.8 ppm/°C, which show great potentials in both LTCC and ULTCC applications.

Low-temperature sintering vanadium-substituted ZnNb2O6 microwave dielectric ceramics for LTCC applications

The ZnNb2-xVx/2O6-1.25x (0.1 ≤ x ≤ 0.6) dielectric ceramics were synthesized through conventional solid-state technique and sintered at 925 °C–975 °C for 6 h. The specimens with the substitution of V5+ for Nb5+ could be sintered at a lower temperature than pure ZnNb2O6 ceramic, densifying the microstructure more densely and improving the quality factor. Density analysis proves that the dielectric constant is related to the relative density. In addition, the [NbO6] octahedral distortion, the bond valence and the average bond energy of the Nb–O bond also change, leading to a nonlinear variation for the temperature coefficient of the resonance frequency from x = 0.1 to 0.6. The ZnNb2-xVx/2O6-1.25x (x = 0.2) ceramics sintered at 950 °C exhibited the superior characteristic while taking into account the applications of low temperature co-fired ceramics technology. Not only did it possesses outstanding dielectric performances of εr = 22.25, Q×f = 51,701 GHz, and τf = −67.02 ppm/°C, but also has excellent chemical compatibility with the widely used Ag electrode.

On-Ground Small LTCC Chip Antenna and its Placement on IoT Devices

A low-profile on-ground chip antenna is presented to be installed in size-limited devices for 868 MHz IoT applications. The antenna presents a size of 0.064 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times 0.045\times 0.007\lambda _{0}^{3}$</tex-math></inline-formula> , has been fabricated in low-temperature cofired ceramic (LTCC) technology and is meant to be placed on a ground plane without a clearance area required. A study regarding matching and total efficiency is performed by analyzing the antenna in different positions of a variable-size ground plane with the use of characteristic modes analysis (CMA) and the correlation between modal and total radiated fields. The analysis demonstrates through the correlation which are the excited modes of the ground plane and, consequently, which is the best position for the antenna. Results show frequency stability and a total efficiency difference of up to 8.8 dB between different positions.

LTCC glass-ceramics based on diopside/cordierite/Al2O3 for ultra-high frequency applications

In this work, three glass-ceramic composites based on a commercial SiO2-B2O3-Al2O3-CaO-MgO glass and cordierite, diopside or Al2O3 were used for preparation of green tapes and low temperature cofired ceramics (LTCC) substrates. The thermal behavior, phase composition, microstructure and dielectric properties of the fabricated glass-ceramics were characterized using a heating microscope, thermal analysis, X-ray diffraction, scanning electron microscopy and time domain spectroscopy. The applicability of the developed materials for LTCC technology was demonstrated by the preparation of test multilayer substrates. The glass-ceramic substrates exhibit advantageous properties for ultra-high frequency LTCC applications, including low sintering temperatures of 900-980°C, good compatibility with commercial Ag and AgPd conductive pastes and a low dielectric permittivity of 3.5-7 at 1 THz.