Low-temperature Co-fired Ceramic Technology Research Articles

Low-temperature sintering and ferrimagnetic properties of LiZnTiMn ferrites with Bi2O3-CuO eutectic mixture

The effects of Bi2O3-CuO mixture on the microstructural development and gyromagnetic properties of low-temperature sintered Li0.42Zn0.27Ti0.11Mn0.1Fe2.1O4 (LiZnTiMn) ferrites have been studied in order to adapt the development of low-temperature co-fired ceramics (LTCC) technology and produce gyromagnetic devices with a multilayer process. In this work, a pure spinel phase can be formed with a sintering temperature ranging from 880 °C to 900 °C, which allows them to be co-fired with silver internal electrodes. The addition of Bi2O3-CuO mixture in LiZnTiMn ferrites contributes significantly to the grain growth, densification and improving ferrimagnetic properties through a low-temperature sintering process. Their low-temperature sintering mechanism was proposed and discussed. The results show that the codoping of 0.21 wt% Bi2O3 and 0.29 wt% CuO cannot only double increase the saturation induction, but also drastically reduce the ferromagnetic resonance line width at 9.3 GHz, indicating that Bi2O3-CuO additive is a good candidate for reducing the sintering temperature of LiZnTiMn ferrites.

Two novel low-firing Na2AMg2V3O12(A=Nd, Sm) ceramics and their chemical compatibility with silver

Two novel microwave dielectric ceramics Na2AMg2V3O12 (A=Nd, Sm) with cubic garnet structure were obtained by the conventional solid-state reaction method. Both ceramics could be well densified at 850°C for 4h. The Na2NdMg2V3O12 (NNMV) ceramic exhibited good microwave dielectric properties with a permittivity εr of 12, a quality factor Qu×f value of 26,544GHz (at 10GHz) and a negative temperature coefficient of resonant frequency τf value of −63ppm/°C and the Na2SmMg2V3O12 (NSMV) ceramic had a εr of 12.1, a Qu×f value of 36,207GHz (at 9.8GHz) and a negative τf value of −69ppm/°C. The large negative τf values could be compensated by forming solid solution with LiCa2Mg2V3O12 and 0.7Na2AMg2V3O12 (A=Nd, Sm)–0.3LiCa2Mg2V3O12 sintered at 880°C for 4h exhibited a near zero τf ~−4.5ppm/°C and 5.5ppm/°C, respectively. Both ceramics were found to be chemically compatible with Ag electrode at 850°C for 4h. These merits make them promising candidates for low-temperature co-fired ceramic technology (LTCC).

A compact circularly‐polarized GPS antenna using LTCC technology

ABSTRACTA circularly‐polarized GPS antenna for L1 (1575 MHz) is designed and fabricated using low temperature cofired ceramic (LTCC) technology. A parallel patch and high dielectric constant composite ceramic with LTCC fabrication method are employed to design a compact structure. The electrical connected parallel patch interval and size are the main parameters for achieving resonance frequency at L1‐band to support modern GPS coding schemes. The proposed electrically connected upper and lower patches are connected together with vertical via pins and therefore did not have any connection with the ground plane. By embedding a truncated corner patch and rectangular slots to this design, the right‐hand circularly‐polarized (RHCP) field property is achieved. By using these features, a compact simple CP‐GPS antenna with 2.32 dBic gain at 1575 MHz is designed and fabricated. The proposed antenna has a total compact size of 15 × 15× 4 mm3and operates over the frequency band from 1570 to 1585 MHz for VSWR < 2. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2926–2930, 2016

A flat-gain LNA based on LTCC technology at UHF (300-500 MHz)

This paper presents a design of a low noise amplifiers (LNA) with all passives elements embedded on low temperature co-fired ceramic (LTCC) substrate. Simulation results reveal that the proposed LNA has a flat-gain of 23.34 dB from 300 to 500 MHz, a noise figure below 0.73 dB and a compact size of 16.7 mm x 8.5 mm.

A novel wireless gas sensor based on LTCC technology

This work presents the development of a highly selective wireless NO2 gas sensor based on a resonant antenna circuit using a low temperature co-fired ceramic (LTCC) technique. The wireless LTCC based gas sensor consists of a planar inductor-interdigital capacitor (LC) resonant antenna, which incorporates two dimensional (2D) SnS2 nanoflakes as a model NO2 gas selective material. The fabrication of the LTCC platform is fully described, a brief description on the characterization of the gas sensitive material is presented and eventually the operation of the system for the sensing of NO2 gas is investigated. The response of the LTCC template was associated to the changes of its resistance and capacitance due to the alterations in the properties of 2D SnS2 as a result of physical adsorption of NO2 gas molecules onto its surface. The wireless gas sensing performance under different operating temperatures and NO2 gas concentrations are presented. The obtained LC gas sensor is successfully used for the wireless sensing of NO2 in the background of atmospheric gas at concentrations lower than 0.6ppm. The developed technology has a great promise for establishing wireless gas sensors for harsh environments

Multilayer capacitors with bismuth copper tantalate dielectric fabricated in LTCC technology

Purpose The work was aimed at preparation of green tapes based on a new material Bi2/3CuTa4O12, to achieve spontaneously formation of an internal barrier layer capacitor (IBLC), fabrication of multilayer elements using low temperature cofired ceramics (LTCC) technology and their characterization. Design/methodology/approach The study focused on tape casting, lamination and co-sintering procedures and dielectric properties of Bi2/3CuTa4O12 multilayer capacitors. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies of the ceramic elements were performed. Impedance spectroscopy was used for characterization of dielectric properties in the frequency range of 0.1 Hz to −2 MHz and in the temperature range from −55 to 400°C. DC conductivity was investigated in the temperature range 20 to 740°C. Findings SEM observations revealed a good compatibility of the applied commercial Pt paste with the ceramic layers. The EDS microanalysis showed a higher content of oxygen at grain boundaries. The dominant dielectric response, which was recorded in the low frequency range and at temperatures above 0°C, was attributed to grain boundaries. The dielectric response at low temperatures and/or high frequencies was related to grains. The fabricated multilayer capacitors based on Bi2/3CuTa4O12 exhibited a high specific capacitance. Originality/value A new material Bi2/3CuTa4O12 was applied for preparation of green ceramic tapes and utilized for fabrication of multilayer ceramic capacitors using the LTCC technology. This material belongs to the group of high permittivity nonferroelectric compounds with a complex perovskite structure of CaCu3Ti4O12, that causes the spontaneously formation of IBLCs.

The utilization of LTCC-PDMS bonding technology for microfluidic system applications – a simple fluorescent sensor

Purpose This paper aims to present a research on utilization of an irreversible bonding between non-transparent low temperature co-fired ceramics (LTCC) and transparent poly(dimethylsiloxane) (PDMS). The research presented in this paper is focused on the technology and performance of the miniature microfluidic module for fluorescence measurement. Design/methodology/approach The chemical combination of both materials is achieved through surface modification using argon-oxygen dielectric barrier discharge (DBD) plasma. According to the performed spectroscopic analyses (X-ray photoelectron spectroscopy, XPS; attenuated total reflection-Fourier infrared spectroscopy, ATR-FTIR) and contact angle measurements, the LTCC and PDMS surfaces are oxidized during the process. The presented microfluidic module was fabricated using LTCC technology. The possibility for the fabrication of LTCC-PDMS microfluidic fluorescent sensor is studied. The performance of the sensor was examined experimentally. Findings As a result of DBD plasma oxidation, the LTCC and PDMS surfaces change in character from hydrophobic to hydrophilic and were permanently bonded. The presented LTCC-PDMS bonding technique was used to fabricate a microfluidic fluorescent sensor. The preliminary measurements of the sensor have proven that it is possible to observe the fluorescence of a liquid sample from a very small volume. Research limitations/implications The presented research is a preliminary work which is focused on the fabrication of the LTCC-PDMS fluorescent sensor. The microfluidic device was positively tested only for ethanolic fluorescein solutions. Therefore, fluorescence measurements should be performed for biological specimen (e.g. DNA). Practical implications The LTCC-PDMS bonding technology combines the advantages of both materials. One the one hand, transparent PDMS with precise, transparent three-dimensional structures can be fabricated using hot embossing, soft lithography or laser ablation. On the other hand, rigid LTCC substrate consisting of microfluidic structures, electric interconnections, heaters and optoelectronic components can be fabricated. The development of the LTCC-PDMS microfluidic modules provides opportunity for the construction of a lab-on-chip, or micro-total analysis systems-type system, for analytical chemistry and fast medical diagnoses. Originality/value This paper shows utilization of the PDMS-LTCC bonding technology for microfluidics. Moreover, the design, fabrication and performance of the PDMS-LTCC fluorescent sensor are presented.

A new approach to construction of extended kit for M-Sequence UWB sensor system based on LTCC

Purpose The purpose of this paper is to introduce modified in–phase and quadrature components (I–Q) demodulator based on low temperature co-fired ceramics (LTCC) dielectric substrate GreenTape 951PX for M-Sequence ultra-wide band (UWB) sensor system. Design/methodology/approach Microstrip low pass (LP) and band pass (BP) filters for UWB sensor systems with required properties (for both filters, minimum attenuation is −40dB in stopband, bandwidth of pass band is 6 to 8.5 GHz for BP filter and cutoff frequency is 2.5 GHz for LP filter) were designed, simulated, fabricated and measured using dielectric substrates Du Pont GreenTape 951 PX. The developed microstrip filters were integrated with all parts of I–Q demodulator on one multilayer structure based on LTCC substrate Du Pont GreenTape 951 PX. Findings Both type of microstrip filters integrated in the I– Q demodulator achieved better transmission characteristics in comparison with commercial available filters. It was shown that LTCC technology based on GreenTape 951PX proves good stability in gigahertz frequency and suitability for fabrication of I–Q demodulator with a multilayer approach. Originality/value The novelty of this work lies in substituting commercially available LP and BP filters used in I– Q demodulator by microstrip LP and BP filters with better performance and furthermore the I– Q demodulator is fabricated based on LTCC instead of previously used PCB.

Optical Biosensor for Permanent Monitoring of Phenol Derivatives in Water Solutions

Phenolics are part of a large group of pollutants, widely expanded throughout the medical, food and environmental matrices. They are main contaminants in ground and surface water. In view of their toxicity and persistence in the environment, the identification of phenolic compounds becomes an important matter. Enzymatic biosensors represent potential options to detect these species especially in case of in situ techniques. Particularly, biosensors based on polyphenol oxidase as well as tyrosinase or laccase have been developed for the determination of phenol derivatives. Due to the fact, here is reported a ceramic-based biosensing system fabricated through the immobilization of laccase in an electrochemically synthesized polymer - poly[2,7-bis(carbazole)-N-hexylacridone], based on low temperature co-fired ceramics technology (LTCC). This setup can be adequate for the permanent monitoring of aqueous solutions (i.e. presence of phenolics). The enzyme was immobilized on the surface of polymer film covering the microreaction chamber. The work of the biosensing system was estimated in the presence of ABTS (ammonium salt of 2,2'-azino- bis(3-ethylbenzthiazoline-6-sulphonic acid)), used as an enzymatic assay substrate. The setup revealed clear catalytic activity, and the analyte was optically determined. Due to the fact, the designed catalytic system showed sufficient efficiency, the obtained results suggest that, the phenoloxidase immobilization possesses potential to fabricate the bioelectronic devices.

MEMS Fabrication on LTCC Substrates for RF Applications: Challenges and Perspectives

Abstract Microelectromechanical Systems (MEMS) are often used in transceiver modules, especially for telecommunication and radar applications. In this paper, we present recent progress in the development on a MEMS-on-LTCC process. We focus on the Low Temperature Co-fired Ceramic (LTCC) substrate issues and we present a successful solution for overcoming the substrate challenges through surface pre-treatment using a chemical mechanical surface polishing (CMP) process which allows us to reach the required smoothness for the fabrication of MEMS devices. We discuss various process parameters such as slurry type, rotating pad and rotation speed, and show their impact on the final surface finish. With an optimized process, the maximum roughness was decreased from more than 10μm to less than 0.5 μm over a 640 × 640 μm2 LTCC sample. Also, we present the various MEMS process steps starting with the deposition and patterning of various layers to a prototype switch highlighting the validated steps and the challenges encountered. A brief discussion of the perspectives for the integration of MEMS and LTCC technologies is also presented.

A comparative study on four different transmission lines in LTCC for 60 GHz applications

Abstract The wireless telecommunication systems have an undeniable role in today's society. The rapid progress of wireless services and applications accelerates demands for high data-rate reliable systems. The 60 GHz band with its 5 GHz globally unlicensed available spectrum, provides a great opportunity for the next generation of high data-rate wireless communication. Despite this attractive bandwidth surrounding 60 GHz, there are still many challenges to be addressed such as the loss performance and the integration with other systems. Low Temperature Cofired Ceramic (LTCC) technology, with its unique and mature multilayer fabrication process, has excellent capability of realizing miniaturized 3D low loss structures to overcome these challenges. Since, one of the key components in any communication system for both interconnecting and designing components is Low loss transmission lines, in this article we overview the performances and challenges for four different most practical transmission lines at 60 GHz in LTCC: Microstrip, Stripline, Coplanar Waveguide (CPW), and LTCC Integrated Waveguide (LIW).

Solutions for thermally mismatched brazing operations for ceramic tokamak magnetic sensor

Abstract To monitor high-frequency fluctuations of the equilibrium magnetic field in tokamaks, a 3D magnetic sensor has been developed. The sensor, which is positioned inside the vacuum vessel behind the protective tiles of the tokamak and is exposed to potential temperatures up to 400°C, is based on thick-film and LTCC (low-temperature co-fired ceramic) technology. To connect the sensor to the cabling that runs inside the vacuum vessel, mineral-insulated cables have to be brazed to the sensor to ensure electrical connection together with mechanical robustness and sufficient thermal stability. As the brazing temperature is about 600°C, direct brazing to the alumina sensor substrate can cause failure by cracking induced by thermal stresses. It arises both by temperature gradients stemming from the localised heating and by the high thermal mismatch of alumina with the braze and wire materials. In previous work, high stresses from temperature gradients were efficiently decoupled by brazing indirectly to alumina beams attached to the main substrate, and local thermal stresses between alumina and braze/wire by using a porous metallisation. However, as the slender alumina beams protruding out of the substrate are somewhat cumbersome and fragile, three alternatives were studied in the present work: 1) testing shorter and more robust beams, 2) replacing the alumina beam by a silver wire, and 3) depositing a porous temperature- and stress-decoupling dielectric to enable direct brazing on the main alumina substrate. These solutions are characterised with respect to their mechanical robustness and of the degree of thermal decoupling with the substrate they provide.

Multilayered Coupled Interdigital Resonator Filters for General Chebyshev Filtering Functions

This paper presents compact multilayer interdigital filters for realizing general Chebyshev (i.e., quasi-elliptic) filtering functions. Several coupling elements are proposed for implementing a wide range of couplings between quarter-wavelength resonators, which are placed on a unique layer or stacked thanks to a multilayer technology. Several multipole filters are designed and fabricated using low-temperature co-fired ceramic (LTCC) technology. Designs and experimental results are detailed in order to appreciate the potential of the proposed technology. The multilayer interdigital filters proposed in this paper are designed especially for electronic warfare specifications from S- to Ku-band.

Compact THz LTCC Receiver Module for 300 GHz Wireless Communications

A compact, low-cost, fully-integrated package solution has been developed for 300 GHz short-range communication systems. Using low-temperature co-fired ceramic (LTCC) technology, an integrated reflector for the on-chip antenna and high-data-rate signal interconnections including a flip-chip and via transition are embedded in a package. A reduced-size silicon lens antenna is placed in a package cavity together with a flip-chip bonded receiver IC with an on-chip antenna. The overall size of the front-end receiver is only $10 \times 10 \times 4 {\rm mm}^{3}$ , including the 6 mm diameter silicon lens. This compact terahertz receiver, mounted on an evaluation board, demonstrated wireless links with data rates up to 27Gb/s.

Compact 60 GHz low‐temperature cofired ceramic filter with quasi‐elliptic bandpass response

This study presents a 60 GHz quasi-elliptic bandpass filter with a compact and planar structure. The proposed filter was constructed by stacking substrate integrated waveguide (SIW) cavities on the central transverse plane of a shielding SIW cavity. Jerusalem cross (JC) apertures and circular apertures were etched on the metal layers of the stacked SIW cavities to enable dual-mode operation and energy coupling. In the dual-mode cavities, the TM110 cavity mode and JC aperture mode can be excited simultaneously. Cross-mutual couplings exist among the resonant modes, resulting in two finite transmission zeros with each at either side of the passband. Multilayer low-temperature cofired ceramic technology was adopted to manufacture the experimental filter. The measured centre frequency was 60 GHz at a fractional bandwidth of 4.5% with two finite transmission zeros located at 53.7 and 65 GHz, thereby achieving high-frequency selectivity.

Composition, microstructures and ferrimagnetic properties of Bi-modified LiZnTiMn ferrites for LTCC application

The effects of Bi modification on the microstructural development and gyromagnetic properties of low-temperature sintered ferrites with composition of Li0.42Zn0.27Ti0.11Mn0.1Fe2.1−xBixO4 (x = 0.0-0.1) have been studied in order to adapt the development of low-temperature cofired ceramics technology (LTCC) and produce gyromagnetic devices with a multilayer process. In the present work, a pure spinel phase can be formed with a sintering temperature ranging from 880°C to 900°C, which allows them to be co-fired with silver. We found that Bi3+ ions could enter into the ferrite lattice, which enhanced the grain growth and densification during sintering due to the activation of the lattice. Results show that the modifying of x = 0.003 cannot only double saturation induction but also drastically reduce ferromagnetic resonance line width at 9.3 GHz, indicating that Bi modification is a good approach for lowing the sintering temperature of LiZnTiMn ferrites.

Novel 5MgO–3Li2O–4WO3 ceramic: preparation, phase evolution and its microwave dielectric properties

A new low-temperature firing microwave dielectric ceramic with the composition of 5MgO–3Li2O–4WO3 was synthesized by a solid-state reaction method. The ceramic was found to be a novel pure compound (Li2Mg2W2O9) when the sintering temperature was 720–760 °C, but transformed to mixed phases with Li2Mg2W2O9 and Li2WO4 when the sintering temperature was 820–840 °C. The ceramic sintered at ~820 °C exhibited good properties with relative permittivity of ~10.3, Q × f value about 20,537 GHz (at the frequency f ~ 11 GHz) and a negative temperature coefficient of resonant frequency of −76.9 ppm/°C. 5MgO–3Li2O–4WO3 ceramic had a promising application in low-temperature cofired ceramic technology.

Design, fabrication and characterization of LTCC-based electromagnetic microgenerators

Design, manufacturing process and properties of electromagnetic microgenerators fabricated in LTCC (Low Temperature Co-fired Ceramics) technology are presented in this paper. Electromagnetic microgenerators consist of planar coils spatially arranged on several layers of LTCC and of a multipole permanent magnet. Two different patterns of coils with 2-, 8-,10- and 12-layers and outer diameter of 50 mm were designed and fabricated. Silver-based pastes ESL 903-A or DuPont 6145 were used. In order to estimate the inductance of a single spatial coil the Greenhouse (self-inductance) and Hoer (mutual inductance) calculation methods were used. To verify the calculation results a single-layer coil was fabricated for each pattern and its inductance was measured using the precision RLC Meter. Fabricated LTCC microgenerators with embedded coils allow to generate voltage higher than ten volts and the electrical output power of approximately 600 mW at the rotor rotation speed of 12 thousands rpm. The self-made system was used for characterization of LTCC-based electromagnetic microgenerators.

Printable Planar Dielectric Antennas

Thick film screen-printing technology is employed to introduce planar dielectric antennas. The micron-size-thick film is made from high-permittivity dielectric paste, which is printed on a low-loss low-permittivity microwave substrate to operate as a magnetic wall boundary. A simplified theoretical model is developed to analyze the antenna structure. The accuracy of this model is evaluated by the results of a commercial three-dimensional (3-D) electromagnetic field solver. The model works well with less than 5% deviation from time-consuming simulations, providing the permittivity contrast between the film and substrate is kept high (e.g., > 30). The impact of dielectric loss of the film in antenna performance is significantly less than that of the substrate, allowing medium-loss films (e.g., ε"= 3) results in highly efficient antennas with over 95% radiation efficiency. A prototype was made using screen printing and experimentally characterized at Ku-band. The experimental results confirm the theoretical achievements. The measured -10 dB impedance bandwidth of the printable planar dielectric antenna having dimensions of 0.2 λ0× 0.2 λ0 is over 10% with a measured gain ranging from 4.5 to 5.5 dBi. Broadside radiation patterns with cross polarization levels of lower than -20 dB are achieved. This process is compatible with low-temperature cofired ceramic (LTCC) technology where similar idea can be applied to other passive microwave components.

Low temperature sintering behavior of La-Co substituted M-type strontium hexaferrites for use in microwave LTCC technology

The La-Co substituted Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites with appropriate Bi2O3 additive were prepared by conventional sintering method and microwave sintering method at low sintering temperatures compatible with LTCC (low temperature co-fired ceramics) systems, and their sintering behavior was chiefly investigated, including the crystal structure, saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC. Experiment results clearly showed that the pure M-type crystal phase was successfully obtained when the La-Co substitution amount x did not exceed 0.3. However, the single M-type phase structure transformed to multiphase structure with further increased x, where the M-type phase coexisted with the non-magnetic phase such as α-Fe2O3 phase, La2O3 phase, and LaCoO3 phase. Appropriate La-Co substitution improved the Ms (>62 emu/g), Ha (>1400 kA/m), and Hci (>320 kA/m) for the ferrites with x varying from 0.1 to 0.3, but the TC decreased with increasing substitution amount. Moreover, the microwave sintered ferrites could provide larger Hci and similar Ms compared with the conventional sintered ferrites.