Low-temperature Co-fired Ceramic Technology Research Articles

Low temperature sintered Ca1-x(Li0.5Bi0.5)xWO4 ceramics with enhanced microwave dielectric properties for LTCC applications

This research explored microwave dielectric properties of Ca1-x(Li0.5Bi0.5)xWO4 (x = 0–0.15) ceramics obtained by traditional solid-phase reaction method. Effects of replacing Ca2+ with (Li0.5Bi0.5)2+ on crystal structure, phase composition, grain size, and dielectric characteristics were investigated via X-ray diffraction (XRD), Rietveld refinement analysis, scanning electron microscopy, and Raman spectroscopy. According to results, the substitution of Ca2+ with (Li0.5Bi0.5)2+ caused samples to form only single phase and also reduced optimal sintering temperature of CaWO4 from 1150 °C to 900 °C. Q × f value under low temperature sintering was optimized from 27,624 to 46,049 GHz. In addition, τf value changed from −53 to −36 ppm/°C, indicating that temperature stability improved to some extent. Ca0.97(Li0.5Bi0.5)0.03WO4 sample sintered at 900 °C exhibited satisfactory dielectric characteristics with εr = 10.2, Q × f = 46,049 GHz, and τf = −36 ppm/°C. Therefore, Ca1-x(Li0.5Bi0.5)xWO4 composite ceramics are potential materials for low-temperature co-fired ceramics technology.

Effect of BaCu(B2O5) additives on the sintering behavior and microwave dielectric properties of LiNb0.6Ti0.5O3 ceramics for LTCC application

Herein, Li1.0Nb0.6Ti0.5O3 + x wt% BaCu(B2O5) (0 ≤ x ≤ 0.8) ceramics were synthesized via the traditional solid-state reaction method. The sintering behavior, phase, Raman spectra, microwave dielectric characteristics, and chemical compatibility with Ag of the Li1.0Nb0.6Ti0.5O3 + x wt% BaCu(B2O5) samples were comprehensively analyzed. The results show that doping the Li1.0Nb0.6Ti0.5O3 ceramics with BaCu(B2O5) can not only reduce the sintering temperature from 1100 °C to 950 °C but also effectively improve the density and quality factor (Q×f) of the Li1.0Nb0.6Ti0.5O3 samples. Additionally, Li1.0Nb0.6Ti0.5O3 + 0.4 wt% BaCu(B2O5) samples, which were sintered at 950 °C for 4 h, exhibit excellent microwave dielectric properties (εr= 61.4, Q×f = 6423 GHz, and τf= 27.5 ppm/°C) and excellent chemical compatibility with Ag, which makes these ceramics potential candidate materials in the low-temperature co-fired ceramic technology.

Influence of Photo-initiator concentration on photoactivation of composites prepared with LTCC and silver powders for DLP based 3D printing and their characterization

DLP (Digital Light Processing) based 3D (three dimensional) printing had been a widely used additive manufacturing technique with its broad aspects in rapid prototyping, packaging, biomedical applications, PCB etc due to its high resolution and reliability. Since, drive for miniaturization in electronic industry had been increasing; the need of additive manufacturing becomes better and reliable solution for fabrication of electronic device. In this study, we attempt to adopt LTCC (Low Temperature co-fired ceramic) technology with DLP based additive manufacturing machine to reduce lead time, running cost and investment cost while increasing production volume to levels suited for SMEs. This work reports our 3D Printing trials with composites using LTCC/dielectric and silver powder. Initial trials using the commercially available resins showed residue after firing the package which indicates its unsuitability for electronic packaging applications. Hence, the new resin was formulated by varying the Photo-initiator 2,4,6 -trimethyl benzoyl diphenyl phosphine oxide (TPO) Concentration. Photoresist was prepared by mixing the Photo-initiator (1 to 3wt %), Surfactant (2.5wt %) and diacrylate based monomer (96.5 -94.5wt%) in planetary mixer and the composition was optimised. Curing parameters for the unloaded resin such as exposure time, Intensity etc were varied accordingly and optimised. The photoresist and the printed samples were analysed for their viscosity, optical inspection, NMR, FTIR. Printing trials were done by preparing composites with Dielectric (LTCC) and conducting material (Silver) using above prepared photopolymer in 50:50 ratio. Effect of variation in the exposure time and intensity on the loading of functional material for curing has also been studied. Printed patterns were then sintered at about 875°C with standard LTCC firing cycle. No residue was observed after the sintering cycle. Trials using composites with different material were also tried. Characterisation of these composites and printed packages are reported. For 50% loading of functional material shrinkage of about 29% was observed. Effect of solid loading on shrinkage of sintered sample were also studied and reported.

Fluorescence Imaging Characterization of the Separation Process in a Monolithic Microfluidic Free-Flow Electrophoresis Device Fabricated Using Low-Temperature Co-Fired Ceramics.

A monolithic microfluidic free-flow electrophoresis device, fabricated using low-temperature co-fired ceramic technology, is presented. The device integrates gold electrodes and a 20 µm thick transparent ceramic optical window, suitable for fluorescence imaging, into a multilevel microfluidic chamber design. The microfluidic chamber consists of a 60 µm deep separation chamber and two, 50 µm deep electrode chambers separated by 10 µm deep side channel arrays. Fluorescence imaging was used for in-chip, spatial-temporal characterization of local pH variations in separation conditions as well as to characterize the separation process. The device allowed baseline resolution separation of a sample mixture of Fluorescein, Rhodamine 6G, and 4-Methylumbelliferone at pH 7.0, in only 6 s, using 378 V.s/cm. The results demonstrate the possibility of studying a chemical process using fluorescence imaging within the traditional fields of low-temperature co-fired ceramics technology, such as high-electrical-field applications, while using a simple fabrication procedure suitable for low-cost mass production.

Structural characteristics and microwave dielectric properties of Zn1−xBixVxW1−xO4-based ceramics for LTCC applications

Herein, the improvement of the microwave dielectric properties and sintering characteristics of Zn1−xBixVxW1−xO4(x = 0–0.15)-based ceramics is reported. The results showed that an appropriate amount of doping could not only reduce the optimum sintering temperature from 1100° to 900°C, but also enhance the densification of the microstructures and increase the Q×f value from 5351 to 42525 GHz. Additionally, various structural parameters including the phase composition, crystal structure, vibrational and chemical bond characteristics that are correlated with the dielectric properties were systematically investigated. By considering the chemical bond characteristics, the first-principles calculations and the acquired Raman spectra, the interaction between W-O is stronger than Zn-O in the ZnWO4 structure, while the interaction between V-O is stronger than Bi-O in BiVO4. Interestingly, when the Zn0.97Bi0.03V0.03W0.97O4-based ceramics were sintered at 900 °C, improved microwave dielectric properties were acquired (εr =18.32, Q×f=42525 GHz, τf=−67.51 ppm/°C), which provides a promising candidate in low-temperature co-fired ceramics technology.

Matching correlation study of titanium-based ceramics with glass based on dissolution characteristics

Glass-ceramics are ideal candidates in Low-temperature Cofired Ceramic (LTCC) technology. The “dissolution-precipitation” mechanism ensures the sintering compactness of glass-ceramics at low temperatures. The ceramics must be dissolved and precipitated in the liquid phase with the assistance of glass additives. In this case, the characterization of dissolution behaviors that should be highly valued has rarely been emphasized. This study puts forward a simple, repeatable, and efficient design for characterizing the dissolution behaviors of several titanium-based ceramics in glass frits under variable temperature conditions. Interestingly, a glass frit with good wettability does not ensure the low-temperature sintering process of a ceramic matrix. In contrast, the dissolution characteristics of ceramics in the glass should be seriously considered. Hopefully, the study of dissolution behaviors could strengthen the fundamental understanding of the low-temperature sintering of ceramics and offer a glass-ceramic design strategy for developing high-performance.

Low sintering temperature, temperature-stable scheelite structured Bi[V1−x (Fe1/3W 2/3)x]O4 microwave dielectric ceramics

Low sintering temperature Bi[V1−x(Fe1/3W2/3)x]O4 (BVFWx) (0.02 ≤ x ≤ 0.08) ceramics have been prepared by solid-state reaction. Compositions with 0.02 ≤ x ≤ 0.08 were scheelite-structure, but distortion of [BO4] tetrahedra decreased with increase in x. Although the crystal class remained monoclinic, the phase transition temperature (TC) decreased from 255 ℃ (BV) to 51 ℃ (BVFW0.08), suggesting that higher concentrations of (Fe1/3W2/3) would result in the stabilization of tetragonal scheelite at room temperature. The decrease in the [BO4] distortion additionally resulted in a large reduction in the magnitude of the temperature coefficient of resonant frequency (TCF) with near-zero values obtained by sintering BVFW0.08:2BVFW0.06 at 780 °C to give TCF ≈ −5.9 ppm / °C, relative permittivity εr ≈ 77.4, and microwave quality factor, Q × f ≈ 8100 GHz (@ ~ 4.3 GHz). These promising microwave dielectric properties coupled with the low sintering temperature suggest that BVFWx ceramics are of interest in low-temperature cofired ceramic (LTCC) technology, and for monolithic resonator and filter applications.

Low loss and good chemical compatibility with silver electrodes of Cu2+-substituted Ba3Ti4Nb4O21 ceramics realizing low temperature co-fired ceramics technology: Crystal structure, vibration modes and chemical bonds studies

New low loss and low-sintering temperature co-fired Ba3-xCuxTi4Nb4O21 (BCTN, 0 ≤ x ≤ 0.12) ceramics with 0.60 wt% Li2O-B2O3-SiO2-CaO-Al2O3 (LBSCA) glass were prepared by solid-state reaction methodology. This work showed that CuO and LBSCA were effective sintering aid, which improved the densification and decreased sintering temperature. Thus, the excellent microwave dielectric properties of BCTN ceramics (x = 0.08) were obtained after sintering at 925 ℃ with εr ~ 44.18, Q×f ~ 17,860 GHz (@ 5.6 GHz) and τf ~ 94.76 ppm/℃. Q×f value was increased nearly 3-fold compared to pure BTN ceramics (~ 6090 GHz). Based on the P-V-L bond theory, the Ti-O and Nb-O bonds together contributed greatly to εr. The Nb-O bonds was the main factor affecting the internal loss on Q×f. The τf closely related to the oxygen octahedron [Ti1/Nb1O6]. The BCTN ceramics would not react with Ag electrodes, and had great potential to be used in LTCC microwave devices.

Layered MXene heterostructured with In2O3 nanoparticles for ammonia sensors at room temperature

The MXene/In2O3 heterostructure was formed through a facile hybridization process which enables the In2O3 nanoparticles to be coated dispersively on the surface and also partly intercalated into the interlayers of the layered MXene. The MXene/In2O3 hybrids based chemiresistive-type gas sensor exhibited good sensitivity and selectivity toward NH3 at room temperature. The response of the MXene/In2O3 hybrids based sensors to 20 ppm ammonia increased remarkably from 3.6% to 100.7% at room temperature in comparison to the pristine MXene-based one. Moreover, it was found that the gas response of the MXene/In2O3 based sensors to ammonia increased with the increase of relative humidity in the gas mixture. Furthermore, the wireless-type response of the MXene/In2O3 based sensors coupled with a LC antenna fabricated by a LTCC (low temperature co-fired ceramic) technology has also been examined. The wireless-type sensors displayed an excellent sensing performance with a significantly improved response/recovery time less than 2 s and a long-term stability toward ammonia. The in-situ infrared spectroscopy of MXene/In2O3 exposed to NH3 indicated the production of gaseous nitric oxides during the sensing process. The a.c. impedance spectroscopy shows that the bulk resistance of MXene/In2O3 heterostructured particles was mainly responsible for the generation of the sensor signals.

A novel high-frequency planar converter with heterogeneous ferrites based on the matching co-firing technology

The converter is an important component of integrated circuits. A novel planar converter was designed with heterogeneous ferrites (different permeability). The permeability of the ferrite distributed in the middle part and both ends of the planar converter is 70 and 500, respectively. Compared with the traditional converter, the designed one has a smaller size (4 mm × 4 mm × 0.55 mm), higher working frequency (3 MHz) and higher efficiency (91%). Co0.01Ni0.39Zn0.43Cu0.17Fe1.98O4 (F70, permeability of 70) and Co0.01Ni0.26Zn0.56Cu0.17Fe1.98O4 (F500, permeability of 500) ferrites were synthesised in our laboratory to fabricate such a heterogeneous planar converter. Bi2O3 was used to modify the sintering mechanical properties of F70 and F500 ferrites and realise matching co-firing of these two materials. Bi2O3 can coexist with both ferrites. A heterogeneous model was built based on the F70 + 0.8 wt%Bi2O3 and F500 + 0.4 wt%Bi2O3 ferrites, and the variations in geometry and stress were researched through finite element simulation. Simulation results indicate that matching co-firing of these two ferrites was achieved. The designed planar converter with a heterogeneous layer was fabricated with the F70 + 0.8 wt%Bi2O3 and F500 + 0.4 wt%Bi2O3 ferrites through the low-temperature co-fired ceramic technology. No crack and curving were observed at the heterogeneous interface, and the performance of the fabricated planar converter was consistent with that of the designed one. The quantification and simulation of sintering mechanical properties are promising methods to realise the matching co-firing of heterogeneous layers, which could promote the development of passive integration.

Enhanced electromagnetic properties of low-temperature sintered NiCuZn ferrites by doping with Bi2O3

NiCuZn ferrite is a material suitable for low-temperature co-fired ceramic (LTCC) technology due to its high permeability and relatively low sintering temperature. The main research questions regarding NiCuZn ferrites are focused on reducing the sintering temperature of the NiCuZn ferrites to achieve compatibility with the Ag electrodes and improve their electromagnetic properties. In this study, the electromagnetic properties of NiCuZn (Ni0.29Cu0.14Zn0.60Fe1.94O3.94) ferrites were enhanced by doping with Bi2O3, resulting in a reduction of the sintering temperature to 925 °C. The findings show that a suitable concentration of Bi2O3 doping could promote the growth of grains and result in NiCuZn ferrites with denser microstructures sintered at a low temperature. Furthermore, adding 0.30 wt% Bi2O3 to NiCuZn ferrite enhances its electromagnetic properties, such as a high real part of permeability (∼937.6 @ 1 MHz), high saturation magnetization (∼60.353 emu/g), low coercivity (∼0.265 kA/m), and excellent dielectric constant (∼14.71 @ 1 MHz). In addition, the chemically compatible Ag electrodes suggest that the NiCuZn +0.30 wt% Bi2O3 ceramics may be acceptable for LTCC technology.

LTCC-Based Antenna-in-Package Array for 5G User Equipment With Dual-Polarized Endfire Radiations at Millimeter-Wave Frequencies

An antenna-in-package (AiP) of endfire and dual-polarization at 28 GHz is presented. It is formed by four periodic antennas of broad bandwidth and high-isolation, fabricated by the low-temperature cofired ceramics technology. The dual-polarizations are realized by integrating a horizontal metal stripline-coupled dipole with a vertical magneto-electric monopole, incorporated into a multilayer architecture for compactness. The AiP skillfully implements vertical vias and horizontal strip lines in the cavities between antennas to improve isolation and polarization purity. This AiP has numerically been examined for endfire high gain and beam steering in user equipment (UE) applications. The prototype was measured to show good isolation lower than −25 dB from 26.5 to 29.5 GHz and agree with full-wave simulations. The antenna array is finally integrated with 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 boresight radiation microstrip antennas to form a complete UE AiP.

LTCC Bandpass Filter Chips With Controllable Transmission Zeros and Bandwidths Using Stepped-Impedance Stubs

A novel bandpass filter (BPF) chip using stepped-impedance stubs (SISs) embedded in coupled lines (CLs) based on the low-temperature cofired ceramic (LTCC) technology is proposed in this brief. The controllable bandwidth (BW) is mainly realized by the wide range of variable coupling strength of the broadside CLs, and the controllable transmission zeros (TZs) can be generated by SISs to obtain high selectivity. Furthermore, in order to obtain a general design method for the proposed BPF with different BWs, the analytical (closed-form) process based on the even- and odd- mode analysis method is presented. For verification, a prototype for the proposed BPF operating at 3.5 GHz with the 3-dB fractional bandwidth (FBW) of 32.0% is designed, simulated, fabricated, and measured, respectively. Finally, the measured results that are in good agreement with the simulation show good performance of the proposed circuit.

The Second Source Harmonic Optimization in Continuous Class-GF Power Amplifiers

In this letter, the second source harmonic in continuous-mode class GF (CCGF) is optimized to flatten the power amplifier’s (PA) frequency response over a wideband. A new design space is explored by considering the effects of controlling the input nonlinearity of the gate–source capacitance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\mathrm {gs}}$ </tex-math></inline-formula> ) on the drain current waveforms under continuous-mode drain voltage waveforms. A wideband CCGF PA is designed and fabricated using a commercial 10-W gallium nitride (GaN) device and low-temperature co-fired ceramic (LTCC) technology. Results of the measurement show a flat frequency response from 3.3 to 4.3 GHz with variations less than ±0.4 dB for 40 dBm output power, and 17 dB large signal gain at 3-dB compression point. A drain efficiency of 66 ± 2% is achieved over the entire bandwidth.

A sintering strategy for lithium zinc ferrite with a high saturation magnetization and low ferromagnetic resonance line-width

Based on the activation energy and diffusion kinetics theory of grain growth, Li0.42Zn0.28Ti0.1Fe2.2O4 ceramics with a low ferromagnetic resonance line-width (ΔH) and high saturation magnetization (Ms) were synthesized by adopting LTCC (low-temperature cofired ceramics) technology. The critical sintering temperature of ferrite synthesis was reduced to 925 °C due to activation energy reduction and the liquid phase sintering mechanism of Bi2O3. The sintering agent B2O3 further improved the grain size, homogeneity, density and properties. EDS and XRD refinement showed that Bi3+ and B3+ ions did not enter lattices, but Ti4+ ions entered lattices and replaced part of the Fe3+ ions, leading to the lattice expansion. Finally, homogeneous and compact Li0.42Zn0.28Ti0.1Fe2.2O4 ferrite with Ms up to 354.6 kA/m and ΔH as low as 184.2 Oe was synthesized at temperatures as low as 925 °C by adding an appropriate content of Bi2O3 and B2O3. In the present study, the exploration and practice of reducing the sintering temperature and improving the material properties based on sintering agents is a beneficial supplement and improvement to the wider application of the LTCC technique.

Design, Fabrication and Characterization of Inter-Layer Microheaters Using LTCC Technology

This paper presents design, fabrication and characterization of novel inter-layer microheaters based on low temperature co-fired ceramics (LTCC) technology. LTCC microheater structures (S1 to S3) with three different heater configurations has been presented. Microheater structure S1 has a heater pattern generated only on the top LTCC layer while S2 and S3 structures have inter-layer heater patterns. These structures have been simulated using COMSOL software to depict the temperature distribution over the active area. LTCC being a multilayer technology, heater patterns are generated in two different layers of LTCC tapes and connected through vias (3D interconnections) to fabricate inter-layer microheaters. By distributing the heater pattern of S1 equally in two LTCC tape layers (as in S3), this method allows possibility to develop miniature LTCC microheaters using conventional screen-printing process. The developed microheaters are characterized and the results are compared. At an input power of ∼1 W, structure S3 reaches a peak temperature of 316 °C as compared to 272 °C achieved with S1 configuration. Thermal imaging results shows better temperature uniformity in the active area for inter-layer microheaters as compared to microheater having heater pattern only on the top LTCC layer.

Design of On-Chip Dual-Band Bandpass Filter Using Lumped Elements in LTCC Technology

In this brief, a novel on-chip dual-band bandpass filter (D-BPF) with two independently controllable transmission zeros (TZs) is proposed. Based on resonators transformation, the schematic and design procedure of the filter are presented. Using even-/odd-mode analysis, analytical equations are used for demonstration of the theory. As an example, a 3.32/5.17-GHz D-BPF with 3-dB fractional bandwidth (3-dB FBW) of 25.45&#x0025;/14.20&#x0025; for 5G applications is designed, fabricated, and measured. The size of the filter in low-temperature cofired ceramic (LTCC) is only 11.4 mm &#x002A; 6 mm &#x002A; 0.94 mm. The filter has been successfully measured with the minimum insertion loss of 1.38/1.53-dB and high return loss of 28/23-dB at the center frequency.

Preparation and characterization of doped LiZn0.92Cu0.08PO4 ceramic for microwave and millimeter-wave substrates

PurposeThis paper aims to report on fabrication procedure and presents microstructure and dielectric behaviour of LiZn0.92Cu0.08PO4 ceramic material with Li2CO3 as a sintering aid.Design/methodology/approachSubstrates based on LiZn0.92Cu0.08PO4 with Li2CO3 addition were prepared via solid-state synthesis, doping, milling, pressing and sintering. Characterization of the composition, microstructure and dielectric properties was performed using X-ray diffractometry, energy dispersive spectroscopy, scanning electron microscopy, impedance spectroscopy in the 100 Hz to 2 MHz range and time-domain spectroscopy in the 0.1–3 THz range.FindingsDoped LiZnPO4 ceramic, which exhibits a low dielectric constant of 5.9 at 1 THz and low sintering temperature of 800 °C, suitable for low temperature co-fired ceramics (LTCC) technology, was successfully prepared. However, further studies are needed to lower dielectric losses by optimising the doping level, synthesis and sintering conditions.Originality/valueSearch for new low dielectric constant materials applicable in LTCC technology and optimization of processing are essential tasks for developing modern microwave circuits. The dielectric characterization of doped LiZnPO4 ceramic in the terahertz range, which was performed for the first time, is crucial for potential millimetre-wave applications of this substrate material.

The Modeling of Magnetic Fields in Electromagnetic Microgenerators Using the Finite Element Method

The purpose of this paper is to analyze the magnetic field distribution over a disc with magnets. This disk is part of an electromagnetic microgenerator that allows the generation of electricity as a result of changes in the magnetic field. The other part of the microgenerator is the structure of the coils. In the previous work of the authors, a complete microgenerator system was presented where the coils were made using thick-film and low-temperature co-fired ceramic (LTCC) technology. Several studies related to the influence of the shape and number of coils on the generated power were carried out, as well as the realization of complete electromagnetic microgenerators with voltage rectifying circuits. Until now, a disc with 28 neodymium magnets of size 10 × 3 × 1.5 mm3 was used for testing. In order to optimize the structure of the microgenerator with respect to the disc with magnets and thus increase the generated power, it was decided to perform appropriate tests to analyze the magnetic field distribution for several configurations of the disc varying in the shape and the dimensions of the magnets. Simulations were performed in COMSOL Multiphysics using the finite element method.

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.