Co-fired Ceramic Research Articles

Machine Learning-Assisted Materials Design and Discovery of Low-Melting-Point Inorganic Oxides for Low-Temperature Cofired Ceramic Applications

The fabrication of low-temperature cofired ceramics (LTCCs) densified at a low sintering temperature (<900 °C) is energy-saving and environmentally friendly. However, finding novel LTCC materials by the trial-and-error method is time-consuming and costly. The LTCC materials often have low melting points, so it is feasible to discover high-performance LTCC materials out of the low-melting-point ceramics. A two-stage machine learning framework was adopted to establish the melting-point prediction model for inorganic oxides. Chemical compositions were used as features in stage 1 modeling; while in stage 2, more features were integrated according to domain knowledge to optimize the prediction model. Stage 2 model built by an artificial neural network algorithm shows the best performances with R2 = 0.7968 and root-mean-square error = 247.4 (K). Three features, including formation energy per atom (fepa), theoretical density (d), and number of atoms (na), were extracted as the decisive characteristics of inorganic oxides. The melting point demonstrates positive correlations with the absolute value of fepa and d. The na acts as a “recessive gene” because its contribution is indirect but necessary. The physical relationships between features and the melting point were also discussed. Furthermore, the LTCC inorganic oxides often have melting points lower than 1400 °C statistically. This criterion was verified by the reported LTCC/ultra-LTCC materials. The melting points of materials in the prediction set consisting of ∼3600 inorganic oxides were calculated by the ML model, and thus, the underlying LTCC materials could be screened out efficiently.

Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb5+ ions substituted Ni0.29Cu0.18Zn0.53NbxFe2-xO4 (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb5+ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πMs = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb5+ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.

LTCC Strip Electrode Arrays for Gas Electron Multiplier Detectors.

The Low Temperature Cofired Ceramic (LTCC) technology has proven to be highly suitable for 3D microstructures manufacturing in electronic devices due to its excellent electrical and mechanical properties. In this paper, a novel idea of implementing the LTCC structures into high-energy particle detectors technology is proposed. It can be applied in High Energy Physics (HEP) laboratories, where such sophisticated sensors are constantly exposed to particles of the TeV energy range for many years. The most advanced applications of the concept are based on dedicated gas amplifier systems coupled with readout microstructures. Typically, the readout microstructures are made in the Printed Circuit Boards (PCB) technology and processed in a sophisticated and patent-protected way. This article presents the manufacturing process and parameters of the novel microstructures made in the LTCC technology. The structures were implemented into the high-energy particle detector, and the first results are presented.

Design and preparation of BaO–Al2O3–SiO2–B2O3/Quartz LTCC composites with tailored coefficient of thermal expansion

In this work, by focusing on widespread problem of thermal mismatch caused by different coefficients of thermal expansion (CTE) in electronic packaging materials, low-temperature co-fired ceramic (LTCC) materials with tunable CTE values were designed. By substituting Ba2+ with Sr2+ and replacing quartz with alumina and zirconia, respectively, BaO–Al2O3–SiO2–B2O3/quartz LTCC composites with CTE of 7.05–9.52 × 10−6/°C were developed. Results show that major crystalline phases of LTCC composite materials are quartz and hexacelsian. By replacing quartz with alumina or zirconia, sintering behavior and subsequently thermal expansion and dielectric properties were modulated. On the other hand, substituting Ba2+ with Sr2+ can be beneficial to the densification of composite materials. The introduction of Sr2+ triggered mixed alkali effect and hindered the crystallization of hexacelsian phase, which can further improve mechanical properties. Finally, sandwich structure module of BaO–Al2O3–SiO2–B2O3/quartz with gradient CTE values was obtained, which showed potential for electronic packaging with sustained thermal compatibility under cyclic temperatures.

Microwave dielectric properties of Li3A3Te2O12 (A = Y, Yb) garnets for low temperature cofired ceramic technologies

Te6+-containing microwave dielectric ceramics Li3A3Te2O12 (A = Y, Yb) with low firing temperatures were prepared using the solid-state reaction method. Li3Y3Te2O12 and Li3Yb3Te2O12 can be obtained as garnet single-phase ceramics with low sintering temperatures of 940 ℃ and 950 ℃, respectively. The cations, such as Li+, Te6+, and Y3+/Yb3+, fully occupied the tetrahedral, octahedral, and dodecahedral sites of garnet structure, respectively. Li3A3Te2O12 (A = Y, Yb) ceramics exhibit εr ∼ 7.83 ± 0.2 and 5.94 ± 0.2, Q × f ∼ 47,800 ± 500 GHz and 41,800 ± 500 GHz, and τf ∼ –47 ± 3.0 ppm/°C and –76 ± 3.0 ppm/°C, respectively. The full width at half-maximum (FWHM) values of the A1g Raman mode correlate negatively with the Q × f values. Moreover, Li3A3Te2O12(A = Y, Yb) ceramics possess good chemical compatibility with the Ag electrode, making them promising candidates for low-temperature cofired ceramics (LTCC) technologies.

Meshed Stacked LTCC Antenna for Space Application

Meshed conductors have been used to realize antenna systems. Previous studies have concentrated on single layer patch designs. In this paper, different mesh configurations of stacked meshed patch antennas are studied; when both patches are meshed, when only the top patch is meshed, when only the bottom patch is meshed and when both patches are continuous solid metal. In addition, the effect of conventional slot loading on stacked meshed patches is also investigated through parametric studies. The designs are fed by coaxial feed probe in the lower patch. The results showed that the stacked mesh performance in terms of the resonant frequency, return loss, gain and radiation efficiency can be comparable to that of a typical, continuous metal stacked design. Both patches are 20.86 mm <inline-formula> <tex-math notation="LaTeX">$\times21.46$ </tex-math></inline-formula> mm. The maximum absolute gain and radiation efficiency of the solid stacked patch were 5.05 dBi and 91.6&#x0025; while those of the meshed stacked patch were 5.22 dBi and 91.8&#x0025; respectively. The measurements of stacked meshed design showed that the antenna was resonant at 2.52 GHz with a reflection coefficient in dB of &#x2212;23.69 dB. It has a 40 MHz &#x2212;10 dB impedance bandwidth (1.5&#x0025;) from 2.50 GHz to 2.54 GHz. The antenna exhibited a maximum measured gain of &#x2212;0.12 dBi and cross polarization of 10 dB at boresight. An equivalent circuit model for the design was also proposed. The antenna was intended for space application, and therefore it was implemented using Low Temperature Co-fired Ceramic (LTCC) technology as the LTCC properties can withstand the harsh environment of space. Although the meshed lines increase the line impedance and therefore can result in increased losses, this can be mitigated by careful mesh selection. Lastly, the meshed design allows for better bonding between the LTCC tape layers.

Mm-Wave Complex Permittivity Extraction of LTCC Substrate Under the Influence of Surface Roughness

As many emerging technologies require the use of high-speed signals, the understanding of dielectric properties of materials used in manufacturing printed circuit boards (PCBs) is an essential aspect for accurate high-speed circuit designs, especially at millimeter-wave (mm-wave) frequencies. This work demonstrates a methodology for extracting complex relative permittivity of dielectric substrates covering mm-wave frequencies. For this purpose, low-temperature cofired ceramic (LTCC) substrate was measured up to 85 GHz and its complex relative permittivity was extracted. The approach used in this work is based on multiline thru–reflect–line (TRL) calibration for measuring the propagation constant and electromagnetic (EM) simulations to estimate the losses contributed by the conductor while accounting for surface roughness. An estimate of complex relative effective permittivity is obtained, from which the actual relative dielectric constant and the loss tangent of LTCC substrate are extracted. The estimated values for the relative dielectric constant and the loss tangent show an excellent agreement compared with the results obtained via split cavity resonator measurements.

A High Temperature SOI-CMOS Chipset Focusing Sensor Electronics for Operating Temperatures up to 300°C

Abstract Sensors are the key elements for capturing environmental properties and are increasingly important in the industry for the intelligent control of industrial processes. While in many everyday objects highly integrated sensor systems are already state of the art, the situation in an industrial environment is clearly different. Frequently, the use of sensor systems is impossible, because the extreme ambient conditions of industrial processes like high operating temperatures or strong mechanical load do not allow the reliable operation of sensitive electronic components. Fraunhofer is running the Lighthouse Project “eHarsh” to overcome this hurdle. In the course of the project, an integrated sensor readout electronic has been realized based on a set of three chips. A dedicated sensor fron-tend provides the analog sensor interface for resistive sensors typically arranged in a Wheatstone configuration. Furthermore, the chipset includes a 32-bit microcontroller for signal conditioning and sensor control. Finally, it comprises an interface chip including a bus transceiver and voltage regulators. The chipset has been realized in a high-temperature 0.35-micron SOI-CMOS technology focusing operating temperatures up to 300°C. The chipset is assembled on a multilayer ceramic low-temperature cofired ceramics (LTCC) board using flip chip technology. The ceramic board consists of four layers with a total thickness of approximately 0.9 mm. The internal wiring is based on silver paste while the external contacts were alternatively manufactured in silver (sintering/soldering) or in gold alloys (wire bonding). As an interconnection technology, silver sintering has been applied. It has already been shown that a significant increase in lifetime can be reached by using silver sintering for die attach applications. Using silver sintering for flip chip technology is a new and challenging approach. By adjusting the process parameter geared to the chipset design and the design of the ceramic board high-quality flip chip interconnects can be generated.

Delineation of Parametric Controls on LTCC-Based Eddy Current Sensor Exposed to High Temperature

The investigation is focused on the parametric evaluation of a micro-fabricated Multi-Layer Planar (MLP) coil exposed to high temperature (≥ 600 °C). It can potentially be used as eddy current (EC) sensor for in-situ structural health monitoring (SHM) of critical engineering components. A detailed analysis of various contributing factors that affects the performance of the MLP coil is discussed. The coil is micro-fabricated on a ceramic substrate (DuPont L951 green tape) using state-of-the-art Low-Temperature Co-Fired-Ceramic (LTCC) technique. The stacked layer configuration (30 layers) soars the performance of the coil in terms of sensitivity and robustness. Emphasis is given on the performance both for dynamic & prolonged static thermal exposure. Delineation of electrical parameters particularly the series inductance (LS) of the sensor is found to be stable (~ 130 μH ±3%) up to 600 °C beyond which up to 800 °C, there is a decreasing trend (~ 70 μH ±3%). Also, the sensor shows stable and consistent behaviour with a nominal deviation of ± 1 % during prolonged thermal exposure. These findings throw light on the application of the MLP coil for in-situ SHM of critical engineering components exposed to high temperature.

Development of Anti-Reduction Cao-Al2o3-Mgo-Sio2 Low-Temperature Co-Fired Ceramics for 5g Copper Antennas

Development of Anti-Reduction Cao-Al2o3-Mgo-Sio2 Low-Temperature Co-Fired Ceramics for 5g Copper Antennas

Оптимизация параметров источника опорной частоты с композитным резонатором-термостатом

A promising design of a thermostated quartz oscillator with a resonator-thermostat is considered. In order to study the effect of replacing the material of the microplate in the resonator-thermostat on the operation of the generator, the processes of establishing a stationary temperature regime after switching on are investigated. The material of the new microplate corresponds to the technology of lowtemperature co-fired ceramics. An unacceptable change in the nature of the establishment of a stationary regime has been detected. To solve the problem found, the design change is proposed.

Soft magnetic, gyromagnetic, and microstructural properties of BBSZ-Nb2O5 doped NiCuZn ferrites for LTCC applications

The development of 5G technology places higher performance requirements on low-temperature co-fired ceramic (LTCC) materials. Here, a solid phase method was used to prepare BBSZ-Nb2O5 doped Ni0.22Cu0.31Zn0.47Fe2O4 samples, and the effects of doping 0.3 wt% BBSZ and different contents of Nb2O5 (x = 0.1, 0.3, 0.5, 0.7, 0.9 and 1.1 wt%) on the microstructure as well as the soft magnetic and gyromagnetic properties of the resulting samples were studied. The doping with Nb2O5 promoted crystal lattice expansion and densification under low temperature sintering conditions. The sample containing an Nb2O5 content of x = 0.9 had the highest measured μ′ value of 212.6, which had increased by 15.9% relative to x = 0.1. Moreover, the measured Ms was the maximum value of 32.61 emu/g and ΔH reached the minimum value of 280 Oe for the x = 0.9 sample, which were 25.5% higher and 32.0% lower than those measured for the x = 0.1 sample, respectively. At x = 1.1, ε′ had the minimum value of 21.4, which was 21.6% lower, and Hc reached the maximum value of 30.8 Oe, which increased by 7.6%. This reduction in ΔH for the doped NiCuZn samples makes them promising materials for use in microwave gyromagnetic devices or as antenna substrates based on LTCC integration technology.

Low-Temperature Metallization and Laser Trimming Process for Microwave Dielectric Ceramic Filters.

This paper describes a low-temperature metallization and laser trimming process for microwave dielectric ceramic filters. The ceramic was metalized by electroless copper plating at a temperature lower than those of conventional low-temperature co-fired ceramic (LTCC) and direct bond copper (DBC) methods. Compared with filters made via traditional silver paste sintering, the metal in the holes of the microwave dielectric filters is uniform, smooth, and does not cause clogging nor become detached. Further, the batches of fabricated filters do not require individual inspection, reducing energy, labor, cost, and time requirements. A microwave dielectric filter was then manufactured from the prepared ceramic using a laser trimming machine with a line width and position error within ±50 μm; this demonstrates a more accurately controlled line width than that offered by screen printing. After using HFSS software simulations for preliminary experiments, the microwave dielectric filter was tuned to a target Wi-Fi band of 5.15–5.33 GHz; the return loss was <−10 dB, and the insertion loss was >−3 dB. To implement the real-world process, the laser parameters were optimized. Laser trimming has a higher success rate than traditional manual trimming, and the microwave dielectric filter manufactured here verified the feasibility of this process.

Low-temperature sintering of ZnAl2O4 ceramics with 4CuO-TiO2-2Nb2O5 composite oxide sintering aid

In this work, 4CuO-TiO2-2Nb2O5 (CTN) composite oxide was added to ZnAl2O4 as sintering aid. XRD analysis revealed that trace amount of new phases formed in the ceramic samples with CTN, which might promote the low temperature sintering of ZnAl2O4 ceramics. The sample with 2 wt% CTN addition sintered at 1125 °C can achieve the highest thermal conductivity of 8.6 W/m·K and the lowest microwave dielectric loss of 3.59 × 10−4. The sintering temperature and thermal conductivity of ZnAl2O4 ceramics decreased while the dielectric constant and loss increased with the increase of the CNT contents. ZnAl2O4 ceramics can be sintered at a low temperature of 950 °C with the CTN content increasing to 10 wt%, which make it a potential material for the low temperature co-fired ceramics (LTCC) application.

A 3D LTCC-Based Ceramic Microfluidic System with RF Dielectric Heating of Liquids.

The design, fabrication and functional evaluation of the radio-frequency dielectric heating of liquids in an LTCC-based ceramic microfluidic system are described and discussed. The device, which relies on the dielectric heating of liquids, was fabricated using a low temperature co-fired ceramic (LTCC) technology. A multilayered ceramic structure with integrated electrodes, buried channels and cavities in micro and millimetre scales was fabricated. The structure with the dimensions of 35 mm × 22 mm × 2.4 mm includes a buried cavity with a diameter of 17.3 mm and a volume of 0.3 mL. The top and bottom faces of the cavity consist of silver/palladium electrodes protected with 100 μm thick layers of LTCC. The power, used to heat a polar liquid (water) in the cavity with the volume of 0.3 mL, ranges from 5 to 40 W. This novel application of RF dielectric heating could enable the miniaturization of microfluidic systems in many applications. The working principle of such a device and its efficiency are demonstrated using water as the heated medium.

The origin of interfacial delamination in Au/ceramic cofired LTCC structure

The interfacial delamination of electrode/ceramic multilayer structure will seriously damage the reliability of low temperature co-fired ceramic (LTCC) module in practical applications. In this work, three kinds of glasses employed in Au electrode are designed and prepared to study the abnormal expansion and delamination process in the Au/ceramic LTCC multilayer structure. The interfacial delamination in the co-fired structure is found to be attributed to the abnormal expansion of glass in respect to Au electrode at high temperature, which is originated from the enlarged closed pores during the co-firing process. This conclusion is further confirmed by co-firing the sample in a low-pressure condition. The mechanism and elimination of interfacial delamination here provides a feasible solution for the design of novel glasses in Au electrode for LTCC applications.

Effects of 0.5B2O3–0.5CuO on the microwave dielectric properties of low-temperature sintered ZZNT ceramics

The effects of BCu (0.5B2O3–0.5CuO) additive on the microstructure and microwave dielectric properties of ZZNT (0.3ZnZrNb2O8-0.7TiO2) ceramics were investigated in the current study. The findings suggested that a small amount of BCu was capable of significantly reducing the sintering temperature from 1150 °C to 940 °C. Furthermore, only rutile-like ZnCuTiO4 and Zn0.17Nb0.33Ti0.5O2 secondary phases were detected and characterized. Based on the observations, the cooling mechanism was ascribed to the formation of low-melting-point liquid phases. Additionally, the specimen comprising 2 wt% BCu, which was sintered at 940 °C for 6h demonstrated excellent dielectric properties with εr, Q × f ∼, and τf values of 40.6, 28,800 GHz, and −4.1 ppm/°C, respectively. Moreover, the tape-casting low-temperature sintered ceramics demonstrated excellent chemical compatibility with the Ag electrode during the sintering process, establishing an extremely promising material for low temperature co-fired ceramics (LTCC) applications.

Lithium aluminosilicate (LAS) glass-ceramics: a review of recent progress

ABSTRACT The lithium aluminosilicate system (LAS) is being explored for almost seven decades due to its anomalous and attractive properties (especially low/negative thermal expansion and fast ion conduction) and its commercial significance in consumer as well as strategic sectors. This review introduces current commercial applications of LAS systems, necessary background science, structural features of different LAS crystal systems, including their polymorphs and solid-solutions, and the origin of unusual properties. Significant emphasis is provided on processing transparent, nanocrystalline, low thermal expansion glass-ceramic (LEGC), the role of chemical constituents and additives, the effect of heat-treatment, and microstructural evolution while processing LEGC. Detailed discussions are provided on the following areas: LAS matrix composites, chemical strengthening of glass and glass-ceramic, low temperature co-fired ceramics (LTCC) and associated joining technologies (hydrolysis catalysis bonding, anodic bonding, brazing, etc.) that would further extend the application portfolio of LAS system.

Sintering characteristics and microwave dielectric properties of 0.5(Ca0.7Nd0.2)TiO3–0.5(Li0.5Nd0.5)TiO3 ceramics with La2O3–B2O3–CaO–P2O5 additive

In this paper, the effects of glass-ceramics sintering aid, La2O3–B2O3–CaO–P2O5 (LBCP), on the sinterability, microstructure, and microwave dielectric properties of 0.5(Ca[Formula: see text]Nd[Formula: see text]TiO3–0.5(Li[Formula: see text]Nd[Formula: see text]TiO3 (CNT–LNT) ceramic have been investigated. The results indicated that LBCP glass-ceramics has good wettability to CNT–LNT (contact angle at 980[Formula: see text]C is 31.9[Formula: see text]), and it can be used as an effective sintering aid to reduce the sintering temperature of CNT–LNT ceramic from 1300[Formula: see text]C to 980[Formula: see text]C. LBCP glass-ceramics did not change the main crystal phase (perovskite structure) of the sample, but a small amount of LaBO3 and LaPO4 phases was precipitated. Since the LaBO3 and LaPO4 phases are low-loss phases, it is believed that the crystal phases can improve the dielectric properties of the sample, especially the dielectric loss. The samples with 10 wt.% of glass additive sintered for 4 h at 980[Formula: see text]C exhibit the optimized properties: a high dielectric constant of 80.8 and a [Formula: see text] value of 2031 GHz. The high [Formula: see text] and [Formula: see text] value, coupled with a relatively low sintering temperature, suggest that the optimized compositions have the potential to be used in microwave low-temperature co-fired ceramics applications.

Bismuth modified zinc ferrites for low-temperature ceramic co-firing technology

The present article is proposed to study the structural properties of bismuth-doped zinc ferrite (BixZnFe2-xO4) nanoparticles. The bismuth concentration x varies as 0.03, 0.06, 0.09 and 0.12. Bismuth doped zinc ferrite nanoparticles are synthesized by the hydrothermal method followed by microwave sintering at a relatively low temperature of 800 °C for 30 min. The X-ray diffraction (XRD) data substantiate the single-phase spinel structure of the ferrites. The morphology of the sintered ferrite surface is studied using scanning electron microscope (SEM) images. From the fourier transform infrared (FTIR) data the metal oxide vibrational bonds corresponding to octahedral and tetrahedral sites are confirmed. Using the vibrational bond data, the bond lengths and bond angles of cation-cation and cation-anion and elastic constants of the ferrites are estimated. From the UV–Visible spectroscopy, refractive index and dielectric behaviour of the ferrites at the optical frequencies are discussed.